Evacuated tube solar hot water heaters
Saw an advertisement in the ATA magazine for the latest evacuated tube solar hot water heaters. Supposedly these are 70% more efficient. Can anyone give us a rundown if they have purchased and installed a system like that? What is the real gain, and is there a concern because they are fragile? Are they fragile?
On the web they seem to be available from Apricus, Endless Solar and SunPlus CPC. I would love those guys to join this discussion and give us an update on how these things perform. If there are any customers willing to share their experiences, please post here.
It does sound like a fantastic idea. I am in the market for a SHW system, and would like to talk to anyone about this.
June 22nd, 20076:05 pm at
Hi there
we installed a Sunplus CPC solar hot water system in April 2005. We opted for the Sunplus with the parabolic reflector because we are 40deg South latitude and we felt we needed all the efficiency gains we could get. We opted for split system (tank on ground) because I felt nervous about having a large weight of water on the roof of our old timber cottage. As far as comparative efficiencies go, I can’t say a lot because it’s the first solar water system we’ve owned and I don’t know anyone locally who has a flat panel job. What I can tell you is that we have had boosting switched off about 90% of the time in the last 9 months. We’ve only really had boosting on when the really grim winter weather set in. We have an 18 tube system raised 40% off horizontal, facing slightly east of north, a 315L tank, and two people in the house. Even on cloudy days the water is hot enough for a shower if you don’t turn the cold tap on. We’ve had hail and frost and it’s had no problems. We’ve had no broken tubes yet. Hope this helps. Good luck.
June 22nd, 20077:22 pm at
sorry that should read ‘raised 40deg off horizontal’ and the system was installed in April 2006.
June 25th, 20078:26 am at
Hi Bev
Thanks for this informative run-down. Can you tell us a little more about the booster and how this is turned on/off?
What was your experience getting a plumber to do this work, and were there any concerns expressed?
October 27th, 20077:32 pm at
I have just installed, or rather had installed, a Rinnai low line system with two “Excelsior” collecting panels and 315lL tank. On the first day of significant sun we have had boiling. The system is plumbed with 10 dia tubing ( the installer said that work done by Adelaide Uni showed this to be better than15 dia for heat collection. The idea being that a lower flow results in a higher temperature rise.) Have had a good look around and can’t see any reasons for flow restriction ( kinked pipes for example) Has any one had a similar experience and if so could you suggest a fix? As things are at the moment I am considering opening up the orifice in the 17W pump delivery line, or putting a tap controlled by pass of the orifice.
October 28th, 200710:53 am at
Two collecting panels. Are they plumbed in series, or in parallel? If in series, then this might be the problem. Perhaps you could make do with just one panel, or if you need both panels in parallel then ensure you have matched flows through both.
October 29th, 20078:57 pm at
In relation to Derek Louey comments
The advantage with the evacuated tube system that we are very familiar with, is that the loss of vacuum from tubes (while not as yet experienced or seen) is easily seen when the bottom of the tube turns from a chrome type appearance to a white colour and identifying a loss of vacuum – tube only needs to be replaced and lack of efficiency identified unlike flat plates, conversely no water is lost from the system at all
Evacuated tube systems are frost protected with the ability of liquid to expand when frozen where as flat plate systems require an additive or closed system for protection such as glycol. this system should be replaced (glycol) every 3 – 4 years not unsimilar to running coolant in your car & for better protection also replaced increasing running costs.
Most flat plate manufacturers in Australia that also have systems for Europe funnily enough use evacuated tubes for their solar collection (Rheem) due to their better performance in overcast conditions & colder climate as previously mentioned regarding frost & winter solar collection
I guess like anything in life there is evidence for & against but currently there is a debate on how much efficient they are, numbers to date say from 20% – 40% but i am sure that could & would be disputed maybe the CSRIO has some data on it for Australian conditions
October 30th, 20076:38 pm at
In relation to the questions about to whether evacuated tubes are effective in Australia I imagine the answer should be yes they are. The technology was developed by Dr. David Mills at the University of Sydney about 20 years ago [1]. There was little interest in the technology in Australia but Chinese firms took it up and manufactured under license to the University of Sydney. One would think than an Australian developed technology should be effective here.
[1] http://www.physics.usyd.edu.au/~mills/cv.pdf
October 31st, 200711:42 pm at
My Beasley collector has either a crack or a leak and is now turned off by the plumber so the tank is heated by the booster. It was leaking a lot. Just broke 2 days ago.
As I live in Brisbane I initially wanted to get evacuated tubes to be used in a thermosyhen set up. Is this possible or must I have a pump and a controller.
I am currently not in Brisbane but my thinking is if there is a crack in the panel it must be an insurance claim as glass doesn’t break without a reason……..just like a window needs an impact to break……it doesn’t occur spontaneously… to my knowledge..any views?
With half a flat plate collector and half evacuated tubes is this sensible for Brisbane
What would you replace the broken collector with. The other collector appears fine.
The booster is used about 60 to 80 hours a year on a 315 litre marine grade steel tank.
What process seals the glass tube. i believe this is critical to ensure the vacuum is maintained. eg on a hils Evacuated tube ET
What yearly cost to run the pump for an ETand would it last for the period of the tank life ………20 years!!!
What is the life of a tube and replacement cost.
I am sorry to ask these questions but i am stuck abroad and my emails by companies seem to get ignored!!!!!!!!!!!!!!!!!!!
The collectors is a 1995 vintage . How much better are the new collectors.it seems I should get a flat plate collector from the links that were posted at the start of this discussion.
I keep swinging from flat panel to evacuated tubes depending on the article I read.
Damage to a collector was something I never considered but at perhaps around a 1000 dollars to replace maybe an ET is better. I am awaiting quotes.
November 1st, 20078:28 am at
Redsquash,
You didn’t quite provide enough detail on your setup. It appears you have two flat panel collectors, one leaking. Are both of them thermosyphon with a roof-mounted tank? Where do the booster and the stainless tank come in?
You want to know whether you can replace just the leaking collector with an ET collector and run it in series with the other flat panel.
I don’t know the answer to that but I can’t see a problem with it either. I would urge you to try it and tell us the results. However if the flat panel collector (the good one) is a thermosyphon collector, then I am not sure it will work unless you bypass that tank and purely send the mains-pressure water through that tank. Are the flat panel systems designed to accept mains pressure water? I don’t know. If not, don’t do it. Your manufacturer would be able to tell you.
A thermosyphon setup requires the tank to be adjacent to the collector. I think this looks ugly on a roof anyway. If you want to hide your tank away, then you need a pump and this goes for ET as well as flat plate. I personally know a booster pump which has been operating intermittently for over 20 years without failure.
The crack in the glass may have been caused by thermal stress, and this may then be a warranty claim. Your insurance assessor’s opinion on this would carry some weight with the manufacturer.
As for the glass-to-metal seal, suggest you google the term “housekeeper’s seal” which takes you to a page which explains how this is done, but it is a technique which has been perfected in consumer items like fluorescent tubes. I am confident it can be done reliably and the MTBF accurately calculated.
Warranties aside, I believe a manufacturer would not be able to successfully launch such a product without extensive testing of the vacuum seal. As far as I know this is done, and the hail test to 30mm is also done.
The main advantage of an ET collector seems to be that with the higher efficiency in poor conditions, it affords greater flexibility in the placement of the collector.
You could give greater consideration to security or aesthetics, or your hot water usage patterns.
Alex
November 1st, 20072:44 pm at
The unit is a closed system with tank sitting on the roof
booster is in tank….
Its a thermosypehn system. Mains pressure system.
Beasley have an amcro coating and a Tinox coating…….spelling is probably incorrect.
How do these 2 surfaces differ in terms of % efficiency.
I think Brisbane is better with Non ET according to th tests results I read from earler posts in the US testing regime.
November 2nd, 200710:13 pm at
re: Tinox coating
The Rinnai rep provided me some info on this. Collector efficiency was up to 35% higher than a standard one – which translates to an improved solar energy yield of 15%. However, this was also dependent on the outside temperature. He openly admitted that much of the efficiency gains could be negated by other system losses. Apparently, there is a computer modelling program that can predict the overall system efficiency based on a number of parameters.
See http://www.orer.gov.au for more information.
November 3rd, 200712:17 am at
For a variety of reasons it may be just as economical for me to buy 2 flat panel collectors as it is to install a completely new system. lets assume that is true.
Selling the old tank which probably has 10 to 15 years left but probably longer isn an optionat the moment
Can I then have 2 tanks connected instead of one.?
It would seem to me ,that a few T junctions and some extra piping , perhaps with some insulation might be all that is needed.
Has anyone done this?
With a Brisbane climate I am guessing 2 tanks could be adequately heated most of the time adequately to service a family
November 4th, 20079:52 am at
This is an interesting discussion. I hope this blog is still going and is the appropriate place to ask questions re evacuated tube collector.
I was considering this type of collector because of perceived advantages regarding frosts and hail and possible better efficiency in cloudy conditions.
Can any one advise without fear or favour on the correct sizing of collector for our conditions?
We live in an east coast escarpment area west of Wollongong NSW and at elevation 750m which is subject to sitting in the cloud especially in moist summers. Depending on conditions, during rainy weather we will still be in cloud when 1 km away is sunny! We get winter frosts and every few years a snowfall or two.
It is therefore hard to get accurate average insolation figures as available long term measurements taken are for nearby areas that do not have the same conditions.
Our roof faces magnetic north and has a pitch of 18 degrees. We currently have a 250L off peak hot water tank for 4 people and have never recently run out of hot water. As we use 300-400L total water per day [not much outside] I don’t know what proportion is hot water, but it takes 8-10 kwh per day to heat with off -peak depending on the season.
I thought that because of some features of the roof and its facing the street [although set well back] it would be aesthetically preferable to have the collector at the roof pitch.
Taking the 18deg pitch into account and the extra cloudy conditions [mainly in summer], plus the lower cold water starting temperatures [esp in winter], would we need extra tubes [eg 30 instead of 22] to compensate?
Would the volume of hot water that we use being possibly much less than 250L/day warrant the extra? I was told that you can remove tubes if you when you find you don’t need them but I don’t fancy getting up on the roof too often to do this.
Thanks if anyone can help.
November 5th, 20078:30 am at
Hi Rob in Woolongong.
This blog is definitely still going. You seem to have done your homework. One thing is for sure, if you’re on electric hot you are a prime candidate for solar hot water. Given your elevation and obvious cold spells and frosts, an ET system seems appropriate.
It sounds like you want to keep your panels parallel to the roof instead of pitching them on a frame. Hmmm. I realise it will look nicer, but with 18deg you will have too much performance in summer, and not enough in winter. Having more pipes will probably only make this worse, unless you detune (shade) the pipes in the summer months.
You might even be better off vertically mounting the panel on a side wall of the house. If that’s possible.
If not I would definitely go the mounting frame to pitch the panel at 40N or so.
November 6th, 200710:35 am at
Hi Rob,
I think the general rule of thumb is to not over-engineer your collector size beyond being able to obtain 100% of your hot water from solar during summer. Summer insolation levels are around 2.5x winter levels – possibly less so in your micro-climate. If you size for minimal insolation levels – you will have anywhere up to 70% collector redundancy during summer.
This is from a commercial size but here is some info on insolation levels around the world and ET collector sizing:
http://www.apricus.com/html/insolation_levels_asiap.htm
http://www.apricus.com/html/solar_collector_size.htm
November 7th, 20079:47 pm at
Hi derek ,
your links in your intial post were excellent and I encourage all to read them and the links that they contain, particularly comparing ET to Falt Panels.
Re Tinox coating.
I have since found out the Rinnai Excelsior units only have tinox . They are 30% better because they have 10 risers instead of the 7 risers in the standard model.
If the rep said said 35% then 5 % would account for the coating.
The rinnai rep I spoke to, said 5% improvement, with a Tinox coating over an amcro coating, but only after I prodded and and cajoled her into putting her words into a percentage.
I have yet to see any independent data on the Beasly /rinai units. In fact I have seen not any graphs at all on these units.
I find this weird given they have been in the market decades.
The solar market must be strong in Brisbane.
I have been waiting 2 weeks, a few failed phone calls and several emails later for a price on a 20 or 30 unit ET system.
Can I get a ball park figure on price and a typical figure for installation.
Also thanks to shepard plumbing for private emails and advice . his approach was very helpful and very professional.
November 8th, 20075:32 pm at
Hi guys – I am back after pondering things for a while & more research when i have some time?
Just some clarifications – Our ET systems come in banks of the following configuration 10, 22 & 30 tube manifolds
It is preferable to mount the systems to maximize winter sun collection & on average that would be around 45+ Deg give or take but a lot of factors will determain that – there is however a specific formular to calculate this & sure Derek would know it
Redsquash – as you note from emails i have forward you inquiries on to a company in Brissy & just tonight they where after you details & have given it to them – by the way it is SHEFFIELD PLUMBING & subsidiary company is Enviro plus plumbing but thanks for the vote of confidence
I assume that reps & sale people do not wish to hand out technical data for fear of it being picked to pieces, annalized & handed to oppersition companies – so sorry for the self protection but scientist do the research & post their theory’s
As for Rob in Wollongong – your choices are a closed solar hot water system using glycol or ET and as posted previously by others for those conditions ET is probably better but a pitching frame would be preferable – that frame would negate summer efficiency (detuning) & increase winter efficiency – even Derek’s USA testing links advocate them in those environments
Also redsquash – as previously said with your pictures of system supplied you would be much better off replacing your flat plate with flat plate
November 11th, 200711:29 am at
You can roughly work out heating requirements by first principles:
Energy input (kWh) = Insolation (kWh/m2/day) x Absorber area (m2) x % collector efficiency
40-70% depending on how cold it is outside compared to the hot water temperature (see links for efficiency curves)
Convert Energy input (kwh) to joules: 1kWh = 3600000 joules
Temp rise possible (Celsius) = Energy input (Joules) x Tank capacity (L) / Specific heat of water (joules/L/Celsius)
This ignores other things like pipe heat losses, storage tank losses.
November 11th, 20071:51 pm at
PS Specific heat of water = 4000 J/kg/Kelvin
I assume 1kg = 1L of water and substituted Celsius for Kelvin.
For example a collector with a 2.5m2 absorber area (standard flat plate dimension) operating at 100% efficiency (always impossible even with ET) during winter can bring (at the most) 110L of water from 15 degrees to 60 degrees. (this ignores pipe/tank heat loss)
November 12th, 20078:02 pm at
That’s great – what about the calculation / formula on optimum pitching angle for the winter sun
I also believe that you need to have apples for apples not with oranges to compare systems – a standard two panel system comparison in m2 would equate to 40 tubes for your calculation
Your starting to sound like our tech guy – he lost me at hello to, but all jokes aside its handy information to know if it is required
Yes 1Ltr = 1Kg – well that’s what i was taught
November 12th, 20078:07 pm at
Derek is that 110 litres an hour?
As an aside once a tank has been heated additional water added to the system would mean instead of being heated from say 15 degrees, it would be heated from some higher temperature as it is mixed with left over hot water from the previous day…….plucking a figure from the air ..lets say average tank temp is 30 degrees
The time requirement to reach 60 degrees would not therefore be as long.
Several cloudy days of normal use may mean the required time to heat a tank would start again from scratch.
November 13th, 20078:17 am at
I would pitch my panels perpendicular to the sun at noon during the winter solstice. This should give the best winter performance, and maximum detuning in the summer.
So for Adelaide (35 South, 138.5 East) I get:
90 – 23.43 – 35 = 31.57
(23.43 is the Earth’s axial tilt).
I would pitch it about 32 degrees from the horizontal, pointing due north.
Is it really just as simple as that or am I totally on the wrong track?
November 14th, 200712:49 pm at
Redsquash
Good point about the cumulative energy gains over several days. This also assumes that there are minimal tank losses overnight.
November 14th, 200712:54 pm at
Admin,
Someone has probably done those calcs before. It probably is that simple but remember solar gains begin when the sun is low on the horizon (albeit weakly) which then reaches a maximum at noon. Do you pitch for noon day sun or the average angle over the area of gain?
November 14th, 20073:41 pm at
Derek,
You’re absolutely right. Suppose in midwinter you have 9 hours of daylight, but shade for the first 3 hours, then you should aim the panel to where the sun points at 1:30pm, not noon.
However in practice most people in domestic situations are forced to follow their roofline somewhat. So if they have a north-facing roof, then north it is, and size the collector accordingly. Otherwise it begins to look ugly, for probably minimal gain. Commercial, ground-mounted installations should probably consider it, but then they don’t typically have the same constraints in terms of obstruction.
November 14th, 20073:54 pm at
So Derek,
You realise you and I are both flying in the face of advice from apricus on their website? Namely that you should engineer your system for providing 90% of your summer needs.
Or would you say that their advice perhaps applies to collector size, not where to point it?
November 14th, 20078:02 pm at
Flat collectors are never gong to boil the water so detuning ie 90% of summer demandi, s a non issue from my experience. ie water overflowing because of internal pressure.
Aprt fro w2 months in Brisbane my SHW system provided suficent Hot water for 4 or 5 adults and a dishwasher
With ET I cant comment .on detuning
Admin are you going down the ET path? I am surprised, unless you can get a comparable price
November 15th, 20077:18 am at
RedSquash,
I will definitely be going down the ET path. It’s more that as creator of this site, I sort of have an obligation to go with something a little sexy than the run of the mill. That’s if solar hot water systems can ever be called sexy. (What has become of me?) Whether it’s actually more cost-effective than the mature technology is another matter. I have to believe that the economies of scale will take care of it in coming years. I like the fact that it has better winter performance. I like that there is no glycol to leak. It just seems, I don’t know, more advanced.
November 15th, 20071:32 pm at
I believe all the data on collectors is misleading, so please correct me if/where I am wrong
The efficiency of Flat Collectors FC, and Evacuated Tubes ET both increase when the inlet temperature of the water and the temperature of the collector are greatest.
In particular ET are more efficient at the higher temperature differences than FC
However all these measurements are taken with the thermometer in the shade.
Imagine, If you park a car in 30 degree heat you will soon notice inside an enclosed car the temperature will rise dramatically. The temperature could easily reach 50 + degrees
The collectors are steadily increasing in temperature through out the day.FC may be around 75 degrees and ET may be near 100 degrees
My point is , shouldn’t the temperature being measured be the exposed collector temp in the sun, which is getting hotter , and not the temperature measured in the shade which would be constant
Thus all the calculations will be incorrect because the temperature differences will be very large.
In particular ET will be given a lower score mathematically.
Additionally
Admin, you need to seriously assess your values when you start talking about Hot water services in terms of sex appeal! You need to get out more. ET do not work more efficiently until you start to get to locations such as thredbo or Canada. For OZ I think you will find that argument falls down. Dereks 2 links at the start of the thread show this. However if you have a link which shows the contrary , please supply.
In summary the formulas used don’t seem to take into account the heating up of the collectors throughout the day. Only the ambient temperature is being measured.
The ambient temp and collector temp could be vastly different.
Ok , where did I go wrong?
November 15th, 20071:50 pm at
Hi redsquash,
LOL. It’s true that I need to get out more!
You’re right that measuring the difference between inlet water and ambient “shade” temperature is not perfect. I can only imagine they thought taht the shade temperature is a reasonable proxy for insolation levels. In most of Australia, it probably lags the insolation levels by several hours. That implies that at noon, the temperature difference will be understated. This means that ET might be expected to outperform the flatties for lower levels of temperature differences, i.e. earlier.
So aren’t you actually defeating your own argument?
November 15th, 20072:29 pm at
I have been following the discussion with great interest. Now I seek some advice. Our locaL green group (SEE-Change Jamison – Canberra) is arranging a bulk buy of ET solar water heaters. We are very keen to get in touch with any other groups in Oz who have done, or are doing, anything similar to learn from them. I would be most grateful for any contacts, advice etc. Bill
November 15th, 20078:40 pm at
The impact of ambient/collector temperature is best explained by the link:
http://www.builditsolar.com/References/Measurements/CollectorPerformance.htm
Efficiency is predominantly related to the difference in temperature between the heated water within the collector and the outside ambient temperature. This follows Newton’s law of cooling which states that the rate of cooling is proportional to the difference in temperature between a body and its surroundings.
heat losses are large (and efficiencies are degraded) if the water is very hot or if the outside temperature is very cold.
No collector can prevent this happening to some degree.
However, the rate of cooling can be retarded by insulating the body. Pool collectors are only covered in polytube, flat plates have glass with an air gap, ETs utilise a vacuum.
Therefore ET is the most resistant to major differences between collector and ambient temperature
Its just simple thermodynamics.
November 15th, 20078:50 pm at
Shefplumb said:
“a standard two panel system comparison in m2 would equate to 40 tubes for your calculation”
I’ll take your word for this.
So in winter
Mythical perfect collector: 110L hot water per day
40 tube ET: ~ 80L hot water per day
2.5m2 flat plate ~44L hot water per day
Equivalent ET system give you 35L of extra free water per day during winter.
Can you quote me a 2.5m2 Flat plate vs 40 tube ET?
November 15th, 20078:55 pm at
Hi admin,
yes i am defeating my own argument. I have sent off an email to an expert in the field who I expect will tear down my argument shortly.
S as an example
at midday the temp might be 30 the FC might be 50 and the ET might be 100 so the inlet and collector diff in temps are huge
I too was keen on ET but the facts from my research shows that ET are not the way to go.
One very important note that has not been really stressed is my example .
I have 2 damaged FC collectors due to storm damage . If I had have had ET then perhaps a few tubes would have needed to be replaced ……not so expensive compared to 2 FC
seechange ….checkout ebay , there is a guy selling ET similar to Apricos, however when pushed for brand he wasn’t forth coming. Also Check out the Malaysian
http://www.microsolarsystem.com/
They will send you a container load and have a heap of data , but apparently no distribution network here
November 15th, 20079:04 pm at
Admin said:
“sort of have an obligation to go with something a little sexy than the run of the mill.
Whether it’s actually more cost-effective than the mature technology is another matter.
economies of scale will take care of it in coming years.
It just seems more advanced.”
The technology is well established for the climates in which it has been specifically designed – and its been even proven to work even in Antarctica! Australia’s market is peanuts – manufacturing costs will mainly come down from other markets who have a greater demand (and need) for this type of collector. Don’t forget there are other innovations (heat mirrors, spectrally selective surfaces) which may have good yields and don’t have to rely on fiddly vacuums.
Did you know that there are hot water systems that work like re-fridgerative air-conditioners and are even more energy efficient than solar collectors.
http://www.enviro-friendly.com/quantum-heat-pump-water-heater.shtml
November 15th, 200710:07 pm at
As far as detuning an ET, wouldn’t the easiest way be to cover part of the collector with a composite insulation material combining reflective foil and bulk insulation e.g. protherm. etherm, aircell.
November 16th, 200710:13 am at
Derek
I believe the best way to detune the collector is with the angle it makes with the sun. The apparent surface area of the collector varies with the cosine of the angle of incidence. Therefore if you position the collector perpendicular to the sun in midwinter, then in midsummer the angle of incidence is 90 – 46 = 44 degrees. This means that in summer, the apparent surface area of your collector is almost exactly half of what it is in winter.
Given that daylight hours are longer, and ambient temps are higher, this sounds like it should be about perfect.
If anyone has any practical experience to back this up (I don’t) then let’s hear it please.
November 16th, 200710:20 am at
Admin said
“Therefore if you position the collector perpendicular to the sun in midwinter, then in midsummer the angle of incidence is 90 – 46 = 44 degrees. This means that in summer, the apparent surface area of your collector is almost exactly half of what it is in winter.”
I’ll will try to do the math but you have to remember the sun is at a higher altitude for a given azimuth throughout all times of the day i.e. you already get more useful solar radiation the moment the sun hits the collector in the morning.
November 16th, 20077:07 pm at
A heat pump isnt more efficient than a solar collector , until you switch on the heat boosting element of the solar HWS.
It will then depend what part of Australia you are living in to determine the truth of the statement.
For Brisbane I can tel you a heat pump will cost you at least double that of solar.
November 16th, 20077:23 pm at
Admin ,
before you detune/vary the angle of application , wouldn’t it be necessary to know by how much hot water you require in the non winter months.
Is it possible you wont achieve much in winter because there isnt that much sun to capture. anyway.
It could well be in summer that you don’t meet your household requirements depending on your house hold use. and the reduced angle the sun hits the ET
You could also easily drain off excess hot water by running the washing machine on a warm or hot cycle or running the dishwasher at a different time
Where is your location?
November 16th, 20078:49 pm at
Red Squash,
“Heat pump will cost you at least double that of solar”.
That sounds quite plausible. The efficiency of a heat pump is given by the temperature difference you can achieve between intake and radiator. This is why a heat pump won’t necessarily perform that well in a hot climate. This is also why a geothermal plant in Iceland will always outperform a geothermal in the Australian desert. They have 5C feedwater and 120C steam, whereas the average condenser in Innamincka will be operating at 15C if you’re lucky. But I digress.
As for detuning by varying the angle. I don’t want to vary the angle – I don’t want to change anything. What I am saying is this and I think it’s quite simple:
An appropriately sized ET collector operating here in Adelaide promises to deliver 60C water even in midwinter, if it is mounted to maximise surface area, i.e. pointing to 32 degrees or pitched at 58 degrees from the horizontal.
The same collector, left at that angle will receive sunlight at around 45 degrees in the middle of summer, and thus present about half the collector area (being the cosine of 45) to the sun. Given that inherent insolation in summer is supposed to be 2.5 what it is in winter (from the apricus website), this means I should be producing about the same amount of heating, or slightly more. I should be able to meet my needs winter and summer, without boil-over and without risking life and limb getting on my roof in November and April. That’s all I’m saying.
I take your point that the usage patterns might throw a spanner in the works. I think though, that my summer demand will be less, because as I’ve said the feedwater will be warmer. All things being equal, I am convinced that this acute mounting angle is the way to go with ET. I have no proof, I am just throwing it out there by way of provocation. Yes I do intend to test this hypothesis at my house. Watch this space.
November 16th, 200710:10 pm at
Admin said:
“The apparent surface area of the collector varies with the cosine of the angle of incidence.”
This is true but remember the angle of incidence occurs in two dimensions – altitude and azimuth to the plane of the horizon (or more correctly in relation to the collector’s pitch). You should take the greater of the two.
November 16th, 200710:16 pm at
The government website simply recommends pitching the collector at 5-10 degrees more than the latitude of the location. Up to 15 degrees to improve gain in winter. However, this may be less aesthetic. They reckon +/-45 degrees change in aspect won’t make much difference to efficiency.
http://www.greenhouse.gov.au/yourhome/technical/fs43.htm
November 16th, 200710:18 pm at
Admin
What a brush fire we have now & all due respect as previously mentioned its all about choices that you make
If we spent as much time talking about it instead of installing the system maybe the energy saved would have off set the energy used in this forum
I agree totally with your comments about pitching angle when i said detune i did not necessarily mean removal of tubes just a option as the increased suns angle on collection area will be less affective in the summer months as opposed to the winter months – usage or demand also has a bearing
With the ET system the controller activates pump & has a shut down temperature of 74 C & will allow for minimal thermosyphon action & reduce discharge of water from storage unit
Conversely if FP is so affective would it not be reasonable to assume that in the summer months you would have more hot water discharge from storage cylinder?
While we talk about differences in efficiency we have not considered other factor into the equation such as our most precious resource – just a thought – unquantified
November 17th, 20077:27 pm at
Note – all good information to assist in choice of system suitable to ones needs
November 19th, 200711:20 pm at
Hi derek,
I am unaware of any discharge from my FP collector in Brisbane in summer.
has anyone actually had this happen.
The FP C will never reach 100 degrees to cause overflow from my experience . If this happened what brand and model was it?
Is the controller you talk of able to alter th 74 degree cutoff or is it built in?
November 20th, 20078:17 am at
The over temperature cut off is built in the controller – also note on detuning rather than say removal of tubes or covering we are also able to increase the flow rate of water through the manifold as another way of detuning the system if required dependant on your usage & situation
The 74C cut off is due to the fact you will get a heat differential between water stored in the lower part of tank (where sensor probe located) and the upper part of the tank to which the heat rises – thus preventing the unit from excessive water discharge & protection
November 21st, 20078:12 am at
Shefplumb said’:
‘ET system the controller activates pump & has a shut down temperature of 74 C & will allow for minimal thermosyphon action & reduce discharge of water from storage unit
increase the flow rate of water through the manifold as another way of detuning the system”
What do you do when the storage tank is full of hot water? What do you do with the excess water? Can you just switch off the intake? Would it damage the collector if it ran ‘dry’?
November 21st, 200710:12 am at
There are really two things going on here.
Firstly the tank has an overpressure release valve which vents water when the water exceeds 95C or so. This means it is designed to operate at a safe pressure should even when the collector starts to supply steam.
Secondly the collector when they manifold boils dry. This is an entirely reasonable scenario for a number of reasons, power failure, mains water cutoff, or pump failure. The manifold would boil dry possibly within minutes. I suppose the inner tubes would equilibriate at up to 200C, but remember that the inside of the inner tubes are filled with glycol or water at a partial vacuum. Even at 200C I don’t expect much stress on the copper welds. I am confident in saying the inner tube would be ok. As for the borosilicate glass, well i don’t really know except I have heard it’s pretty tough. I can only assume that manufacturers routinely do a boil-dry test as part of their product validation.
The
November 25th, 20077:53 pm at
Yes your exactly right
We also have what is called a calleicy valve which allows for excess air & pressure to vent off – in the likely hood of system boiling dry this will allow for heated air in system to vent off & valve will stay open to allow for this to happen as it requires water pressure behind it to close the valve – yet another protection of the system
No glycol at all
Due to its cylindrical shape & materials used ie borosilicate glass it will withstand up to 25mm + hail stones, also if they are damaged no water loss from system & individual tubes replaced with minimal fuss & cost
November 28th, 200712:49 am at
Whats the approximate cost of 1 tube replacement.
Is this almost the same as changing a light bulb?
There is a stress test on youtube with Aprcos tubes. From memory the breaking point was 135kg, but don’t quote me.
December 3rd, 200710:12 pm at
Around the $60.00 mark for individual tube
Yes its a rather primitive test on the tube using the boxes – personally i wouldn’t like to test it that way in an uncontrolled environment
December 9th, 20078:07 am at
just letting every body know that I recently purcased a Hills 22 tube evacuated tube system and installed it myself (sparky) and my brother (plumber). I purchased it through the internet from a company in NSW, (I am in Qld) . Every thing went really well witout a hitch. The company was really helpfull and cheaper than any one in Qld
I was impressed with the quality of the unit and the fittings supplied with it and the very detailed installation manual made it easy for us fist timers to install it
Ive had it operating for about 2 months now with the electricity supply turned off and we havnt run out of hot water yet. Now waiting for the cheques of approx $1800 worth of rebates. I couldnt be happier with the unit.
Im now shopping around for a solar system to power my lights and fridge. When this is up and working (I have a gas stove) the predicted increases in electricity prices and longer blackouts from more sever thunder storms will be less of a concern for us.
December 9th, 20077:00 pm at
If you look at the following ET design there are actually two ‘evacuated systems’. The glass tube and a copper pipe heat exchanger.
http://www.apricus.com/html/solar_collector_heat_pipe.htm
Some systems have the heating exchanger directly welded into the tube (glass-metal) or the water circulating through the tube.
Here the ET is just an blind-ending elongated glass sleeve (glass-glass) which clips around and insulates a evacuated copper pipe heat exchanger. The heat exchanger itself inserts into a manifold through which it transfers heat to the incoming water.
The advantage of a glass-glass tube is less of likelihood of vacuum loss (unlike glass-metal where the dissimilar materials may separate).
I would be interested to know if how frequently the copper heat exchanger welds will fail under the daily heating cycle and how much these would cost to replace.
December 9th, 20077:24 pm at
This is a report by the SRCC (Solar Rating and Certification Corporation), the key solar collector certifying body for the US and Canada. It is a shame that Australia doesn’t have something like this.
http://www.solar-rating.org/ratings/OG100DIRECTORIES/OG100DIRFULL.pdf
A collector will only be certified and rated if it passes a very rigorous durability/reliability test.
see page 16
December 12th, 20078:49 am at
I had a closer look at the Apricus website. They have an add-on system to ‘detune’ the set-up in summer. Essentially they have a temp controlled bypass valve that causes the water to recirculate pass a heat sink (essentially a metal fin) and dump all of the heat – very clever.
Of course, this adds a bit more to the complexity and cost of the system.
December 16th, 200712:49 pm at
Hi russell,
In your post ,did you mean you did not have the electric heating element turned on in the tank. Is that right?
Would there be much advantage if a non tradesman put everything together , up to the point where a plumber or sparky would then take over?
What time would be saved ?
What additional amount of time would a sparky or plumber require to complete from where a home owner had assembled whatever?.
Derek wrote………
The advantage of a glass-glass tube is less of likelihood of vacuum loss (unlike glass-metal where the dissimilar materials may separate)…….
Is the hills glas /glass tube.
With 22 tubes how many adults plus dishwasher is that?
Can you add , say 8 additional tubes on at a later date if your household requirements change.?
I think the real test will come in winter as most solar hws dont seem to easily run out of water in the warmer months.
My beasley solar HWS in Brisbane runs on boost for about 2 hours an evening for 6 to 7 weeks only in winter.
Where are you Russell.
December 16th, 20072:34 pm at
http://www.solar-rating.org/ratings/OG100DIRECTORIES/OG100DIRFULL.pdf
Hi Derek,
a very informative link.
I did calcs on Catagory C see page 71and see page 137.
I worked out that the megajoules per day ,per square metre ,for clear day
the AP30 apricos is 9.7496 mjoules
and
the rheem/ beasley RS21 collector with the titanium oxide coating is is 12.834 mjoules.
For a cloudy day, per sq mertre
the AP30 apricos is 4.480 mjoules
the rheem/ beasley RS21 is 4.812 mjoules.
The results mean the rheem is producing at least TWICE as
much energy as the Apricos becuase the Rheem units come with 2 collectors
Net area for the rheem for 2 collectors is 3.770 sq m
Apricos 30 tubes is 3.795 sq m
December 17th, 20077:05 pm at
Russell Miers – Glad to hear your vote of confidence in the ET system & ease of installation – i assume from your comments that you bought the system from Plumen in Sydney
It is also true the quality of the products that we use to complement the system & strive for the longevity of the system so that you maximize the benefits for years to come
Congratulations on doing your part for the environment & your hip pocket
December 25th, 200710:20 am at
Redsquash wrote:
“The results mean the rheem is producing at least TWICE as
much energy as the Apricos becuase the Rheem units come with 2 collectors
Net area for the rheem for 2 collectors is 3.770 sq m
Apricos 30 tubes is 3.795 sq m”
And how much is a flat-plate Rheeum unit versus ET Apricus 30?
Note that this also collector area, not absorber area. The Apricus has double efficiency if you consider that it is only working on half the absorber area as a Rheem. It’s you just get four times as much absorber area with a Rheem for less money.
January 5th, 20087:21 pm at
I don’t follow you Derek.
How is a collector area different from an absorber area?Aren’t they the same thing under a different name?
The space occupied by tubes or collector to work properly is what needs to be compared.
So both systems occupy the same collector or absorber area
I think you might be referring to the space between each tube. However if there’s no space between tubes then the tubes don’t work , do they?. In that case the space around the tube just cant be ignored, but needsto be included in the calculations.
If that is not your point then I have missed completely what you have written.
The energy output per sq metre per dollar should be an accurate and fair comparison
Price is something shefplumb would probably have a more accurate idea. The Evacuated Tubes are more pricey .I just paid a total of $2438 for 2 BEASLEY frost tolerant tinox collectors to be installed and the old ones disposed of.
Shefplumb earlier wrote a replacement tube cost $60, so once you add the labour to attach and fiddle with 30 collectors I can see the price jumping significantly.
January 7th, 200810:13 am at
Redsquash,
Before the advent of ETs, flat plates were described in collector area (the physical dimensions of the array) which is almost the same as absorber area (area over which solar gain is converted into heating energy).
With ET the absorber area only occupies about 50% of the collector array.
When the first measurements were performed by the SRCC, they derived various efficiency curves for the two types of collectors and worked out $cost savings based on collector area (see the references at the top of the page from my first post)
Efficiency is measured as the percentage of solar energy that can be converted into useful water heating. This runs between 40-70% for flat plate depending on climate. Efficiency is compromised by heat losses from the system.
The calculation assumed the whole ET collector was receiving solar gain and this affected its apparent ‘efficiency’. The reality is that for a given absorber area, ET is generally remains more efficient than Flat plate at all operating temperatures – but the difference is not that great in the usual range of domestic applications.
This does not change the fact that the $cost/absorber area is higher for ET is far higher than Flat plate.
Furthermore in a temperate to tropical climate – the cost savings obtained per absorber area is only marginally better for ET.
The equation becomes much more favourable for ET at cold temperate/alpine conditions. Whilst the capital cost remains high, the efficiency advantages of ET make it signficantly more cost effective.
January 7th, 200810:36 pm at
Redsquash,
I realised I did not answer your question directly. From the point of view of the consumer – collector area/absorber area is not so important (unless you have trouble fitting it on your roof). The discussion is more important for technical calculations.
As a consumer all I care is:
* How much does the unit cost?
* How much water can it heat?
* What percentage of my energy heating needs will it supply over the ENTIRE YEAR (not just for cold, bleak days or bright, sunny ones)
* What are maintenance issues? Ongoing costs?
* What is the durability? Frosts? Hot weather/boil over? What is the warranty? Who will fix it and how easily it can be done.
The RECS figure gives a good indication of the efficiency of the system – but you need to compare it for similarly sized systems (e.g. 3,4,5 or 6 person household) working in the same climatic zone.
http://www.orer.gov.au/publications/pubs/register-swh-models-less-700l-v2-1207.xls
January 8th, 200810:20 am at
Good post derek
With ET the absorber area only occupies about 50% of the collector array.
How do you work that out?
Just so I can sleep at night, are you counting the area or not counting the area either side of the ETubes
January 8th, 200810:11 pm at
Actually the figure probably is about 2/3 of the collector area.
I have lost the direct quote but you work it by inference from this site:
http://www.builditsolar.com/References/Measurements/CollectorPerformance.htm#Efficiency
Based on collector area – peak efficiency of ET = 52%
Based on absorber area – peak efficiency of ET = 80% (which is not much more than high quality flat plates)
52 divided by 80 is about two thirds.
You don’t count the gaps just the the tubes. Its that section that receives useful solar energy and transmits that to the water. You can’t jam the tubes together because you would like the bits on the sides to receive angled sun.
The ET advocates claim that this geometry improves efficiency but this is not the real reason (the vaccum is the thing that is important). At any particular sun angle, only a tiny arc of the tube is perpendicular to the rays. The other rays strike the rest of the curve at an angle – part of which is reflected off – thus reducing the useful solar gain.
I am still interested in whether anyone has tried desigining a flat plate collector and encase the whole thing in a highly insulated container with a cover of double or triple glazing.
January 9th, 200810:19 am at
I was just shown the easy REC calculator here:
http://www.solarhome.com.au/?page_id=104
which gives you REC number for all the solar hot water heater models available.
This supports my point that ET and FP are almost level pegging until you reach a cold temperate climate.
The REC system works on 4 climactic zones. In order of which area gets most insolation: Zone 2 > 1> 3> 4.
The REC number is generated from a complex formula which determines how much water heating energy the system saves over the course of a year.
Choose any system that gets the same REC for Zone 2 (optimal efficiency) and see how it drops in performance depending on climate.
The biggest fall is usually from Zone 3 to Zone 4. This is when ET significantly outscores FP.
January 12th, 200810:56 pm at
RECS are only an indication and can be slightly misleading at times
eg
If you have a 6 person household you very well may be using the electric booster everyday for several hours in winter to get adequate hot water.
With a 4 person house hold there may be sufficient hot water left over form the previous day combined with some sun , to avoid the electric booster daily or use it briefly.
Going onto a night tariff for electric boosting isn’t worth it in Brisbane as there is /was a minimum monthly charge last time I looked,so the general tariff though more expensive ……………….is actually cheaper when calculated for the year.
For my small household the cost of electric boosting is roughly $40 a year less than what various government publications tell me it should be for Brisbane.
Thus the RECS ,in my case ,are telling me, at first glance the system is less effecint than reality is telling me.
January 14th, 20088:40 pm at
Without looking into the formulas, I can’t comment for sure. However, I make the assumption that the calculation assume you are not using the system beyond its quoted specification e.g. six people using a 5 person system. It a way of making comparisons rather than giving an absolute figure. The relative savings presumably based on equal load on the system within the same climatic zone.
We should also discriminate between energy saved versus cost saved. The latter is dependent on the cost per unit of energy. The cost savings will inevitably increase with time (as prices go up) but the energy saved will remain stable (if not slightly worsen with aging)
February 3rd, 20086:25 am at
Hi,
This has been great.
I live in Hobart about 42 degrees south of the equator. I am looking at the sytems to install at the moment it is difficult to find an installer who can convince me of the horizontal angle reason.
My limtited and I thought common sense approach is to pitch at 42 degrees if you want all year performance increase the angle for winter and decrease the angle if you want better summer performance. So most are telling me just go at about 20 degrees that will be fine. I have a big family and want maximum bang for my buck therefore I am thinking about 50 something degrees would be ideal. I have a flat roof so as long as a manufacture makes this sort of frame I’m in business.
Can anyone confirm or argue this point. It seems we have a lot of experts so someone must have an idea.
Also I went to a website to investigate how many tubes I would need to give me hot water in winter, calculating 6 in the family shower 10 litres a minute 5 minutes a shower (if I am lucky) a bit of hot water for washing up etc…I throw in 300 litres insolation level of 2 and come up with needing something like 100 tubes!!! Can any one help me with a better sizing method as surely this can not be correct…
Also I see mention of a company in Sydney who sent a kit to Queensland can any one give me this website? Plumen was mentioned however I can not find an associated company?
I hope people have some views look forward to hearing them, if any one has good contacts in Hobart who is actually interested please let me know…
February 4th, 20088:31 am at
Hi Terry.
Within certain limits, the performance of the system is not very sensitive to the collector orientation. For maximum heating over the whole year, you are going to point due north, with an inclination of 42. That is clear. However if you are 30 deg north-west or north-east, your yield will be down a mere 5%. The same goes for the inclination although here the tolerance is somewhat smaller. Mount it at 52deg or at 32deg, either way you won’t lose more than 5%. Mount at 20 deg only if you are sizing the system so it supplies 100% of your needs in the summer, and you are happy to boost all winter. My own preference is to size it for 100% contribution in winter, and detune it for the summer.
Far more important is well-sealing insulation, a well-insulated tank, correct controller settings, sensors and the like. Ensure your tank is tall and slim to ensure maximum stratification.
Your sizing calculation is incorrect in that you are not factoring in a storage tank. Obviously if you need to heat all the water you need at any given point in time, you will need 100 tubes. All SHW systems need a tank, so the water can be heated slowly and stored throughout the day.
If you get 1.5m2 of collector area and a 300l tank, you will not be self-sufficient but will take a large chunk out of your hot water bill.
February 4th, 20081:26 pm at
Don’t pay more than 1000$ (delivered) for a 30 tube collector We are now taking orders for the North American market and can supply them from 300 to 750 $ depending on type and quantity. This price does not include shipping, but we will be expanding so that pickup is available for more people. If you are interested, email me at solarisfree@gmail.com
February 5th, 20085:46 pm at
Hi Terry,
If they all have a shower at night you will have no hot water for early morning,
Have you factored in showers evening and morning or ,even later adding a dishwasher?
I am guessing that an instantaneous gas booster will be require to supplement your needs for the lowest cost.
Which week is summer in Tassie
I suggest getting a bigger tank since not all the tank will be producing hot water. Also with a large tank,a good sunny day will hopefully be enough to cover a few cloudy days……………not a very scientific comment but just going on personal experience in qld
February 6th, 20087:38 am at
I agree the instantaneous gas booster certainly seems the best choice for ET in Oz, no matter what your usage patterns.
I have some questions for the audience, and some of the vendors that may be reading:
Does anyone have anything to share on circulation pumps? I have heard it mentioned that the efficiencies can vary widely, and it’s best to be careful about selecting the right one. It obviously has to be slow-flow with a high head.
February 6th, 20089:07 pm at
Terry
With the colder climate in Tasmania i think with its extreme temperature differences & more so its colder climate that evacuated tubes would be the better way to go for maximizing the efficiency. As far as the pitching angle of the solar collector while possible to obtain optimal performance angle one needs to explain that there is an Australian standard that must be adhered to and that is with all solar collectors irrespective of their construction – that is +- 20Deg of latitude
If Adelaide is at 35Deg then the maximum angle is 55 & the minimum is 15 – you are better off pitching it at the highest angle to maximize winter performance
Gas boosted solar is by far the most energy efficient form of providing hot water
As far as your tube configuration you could group up a 30 tube manifold & add an additional 10 tube manifold making it a 40 tube system coupled up with a 315Lt Gas boosted tank – Hence giving you the ability of not running out of hot water & coping with your needs, also allowing solar energy to reduce your energy usage significantly
If you require further assistance or further information then you can send me a personal email C/O shefplumb@adam.com.au
While there are some imports coming onto the market they are all not meeting the approval criteria so i would suggest decide carefully on the product, its backing, warranty & quality of materials used more so if your talking about bang for your bucks – all will primarily do it its just a case of how well? & How long?
Sorry i haven’t been on for a while but found it in parts quite argumentative & not productive from my point of view
February 10th, 20086:03 pm at
Terry,
In answer to your questions:
a) The relationship between efficiency of the system and angle to the sun – either bearing or inclination is related to the Lambert cosine rule:
http://en.wikipedia.org/wiki/Lambert%27s_cosine_law
e.g.
+/- 20 deg (6% loss of efficiency)
+/- 40 deg (25% loss of efficiency)
More information can be found at:
http://www.greenhouse.gov.au/yourhome/technical/fs43.htm
for optimal angle
b) The difference between winter and summer insolation varies over fourfold in Hobart
http://www.gaisma.com/en/location/hobart.html
Hence if you size a system for winter you will have over 75% in redundancy in Summer.
It is essential to angle for the lowest insolation levels of the year and expect better efficiency as you approach summer
c) A sizing calculator for ET can be found at:
http://www.apricus.com/html/solar_collector_size.htm
The sizing should be based on winter insolation levels. It is not specifically related to system efficiency or the system configuration. I have to disagree with Alex that the primary calculations are related to whether or not you use a split system. However there are practical advantages with a vertical tank
d) A good comparison of both boosting energy requirements and greenhouse emissions can be found at:
http://www.sustainability.vic.gov.au/resources/documents/Estimated_Household_Water_Heater_Energy_Use_Running_Costs_and_Emissions_Victoria.pdf
It is related to Victorian climates but it gives a good relative comparison
February 11th, 20081:06 pm at
After reading all I am more confuse than ever. I live on the Gold Coast in Advancetown. We are subject to hail and frost and need a system that can take bore water. Also I have been told the temperature of the water must be maintain to avoid contamination (cant remember the name of the bacteria. All this considering is one system better then the other?
February 13th, 200812:02 am at
Your climate zone is 3 which suggests you have good solar insolation.
This is supported by data from the Mt. Tambourine weather station which is about 10km away.
http://www.bom.gov.au/climate/averages/tables/cw_040197_All.shtml
This suggests that you don’t need a very high efficiency collector like an ET. Frost protected can be obtained with a glycol heat exchanger rather than water.
Some heaters have bore water tolerant tanks i.e. ceramic line or plastic moulded.
All hot water heaters needs to be kept at 60deg to prevent bacteria multiplying. It is should be either cold or hot – never in between.
Apart from this it is personal preference about configuration (thermosiphon or split) or energy source (gas or electric) for boosting.
February 13th, 20089:21 pm at
Basically for frost protection you have two options: closed loop or open loop. the closed loop system circulates a water+glycol mix between collector and a heat exchanger within the storage tank. Most of the flat plate systems are like that.
An ET system can also run closed-loop like this, or can be run as an open loop system. The open loop system circulates water directly between the tank and the collector. If freezing conditions are detected, the pump is turned on and circulates a small quantity of water from the (hot) tank to the collector to prevent freezing.
My personal preference is for an open-loop system. I also don’t favour the unattractive thermosyphon tank on the roof.
The booster should ideally be a continuous hot water heater. The gas ones are common but electric models are also available.
February 13th, 20089:27 pm at
Hi Be,
The bacteria of concern is legionella.
Derek
What you’re saying suggests the tank must be maintained at 60C. Are you sure? As far as I knew, it was enough to heat the (potentially lukewarm) water to >60C as it came out of the tank, and just prior to mixing and use…
Not that it would ever probably be lukewarm if using enough ET collectors (heh!)…
February 13th, 20089:46 pm at
Be – considering the use of bore water i would suggest a glass lined steel cylinder as this would be better if the Ph of the water falls outside of 6.5 – 8.5 as the water would be high in calcium carbonate or zinc. This is where particular stainless steal tanks lack in longevity, however you could couple the ET manifold to this tank to handle frost conditions as they also meet hail testing standards.
As for glycol flat plate systems I assume you also have rain water & potentially do not wish to contaminate the water source should the flat plate be damaged & allow the glycol into the system – personally split systems are the way to go so that there is not to much weight on your existing roof structure
You may even like to consider a heat pump as an alternative & a really good one on the market & a little better on running costs & efficiency (reflected by its REC points) is the Stieble Eltron system – cheaper on the installation costs & system, maybe not as good as solar but an adequate alternative – visit http://www.stieble.com.au
Bacteria is call – Legionella which would be the main one mainly prevalent in stagnant water supply & survives in ambient water – will start to be killed off at 58 Deg hence thermostat settings over 60 Deg – it will still survive but only for a brief part of time
One better than the other – It depends on who you speak too & what your criteria is – I think one is better than the other but happy to provide an alternative to suit & all have an advantage in some form
February 14th, 20089:03 am at
re ET collector array and heating capacity
Using the Apricus solar collector calculator:
http://www.apricus.com/html/solar_collector_size.htm
Hobart winter insolation (1.32 kWh/m2/day)
Tank capacity 250L
30 ET tubes
gives 7 degree temp
or looking it another way
30 ET tubes can give a 45 temp rise (to get to 60 deg) to about 39L of water
February 14th, 20089:12 am at
re Legionella
There are theoretical concerns about keeping water temps below 50C for prolonged periods.
Here is a table relating temperature to Legionella growth.
http://www.relianceworldwide.com/site/fs_legionella.htm
The question is how long you can leave temps between 20-50 before the bacterial load becomes concerning. Once temp reaches 60C it still takes about 1/2 hr to kill the bacteria.
If water is flash heated to 70-80 deg then it can instantaneously kill the bug.
February 16th, 200810:26 pm at
with the large variations between angling the collector during winter versus summer, you would think the manufacturers would change the frame design so it was easy to ‘wind up’ or ‘wind down’ the angle at which it faces, so users could easily optimise the unit for each season!
February 22nd, 20088:41 am at
Hey i was just reading your post, in most cases the evacuated tubes are not more efficent then a “flat panel” collector.
As you can see via the RECS which tests the efficeny of each solar hot water system, and its done by a stand alone government department ORER. Whilst a 22 tube 315 litre, Hills (which is one of the better brands i think) only obtains 23 RECS, whilst a Solahart 302KF gets 32 RECS. Now if they were more efficent shouldnt they be getting more RECS??
Also having a look at purchase prices, there isnt that much difference between the two, as a matter of fact, the solahart is about $200 cheaper after RECS.
I would be reccommend ing a Solahart to anybody as they are a true and tested brand of solar hot water heating, i know this because my mum and dad have had theirs for around 25 years.
February 22nd, 20088:49 pm at
If you get a Marine Grade steel Tank 316, then you will probably be dead before the tank fails and you wont be replacing anodes every 5 years or so
February 25th, 20082:55 pm at
I have installed a 30 tube Evacuated Tube chinese made solar Hot Water System 300 litre Tank, the type where the water is in the tube and found it boiled every day so have put 70% shade cloth over the tubes and find I am getting plenty of very hot water, haveing had flat plat solar’s over last 30 years this system is far more efficient, I am extreamly happy with it.
I am located in Perth outer Metro Area.
February 26th, 200811:43 am at
Hi Ross
That’s amazing performance. What brand is it and what did you pay? Are you saying the water circulates through the collector tube, instead of just the manifold? I take it this is not a frost-proof arrangement. Is it designed to circulate water if you encounter frost conditions? What make and model pump have you got?
Here’s an experiment for you: I would like to see you angle your collectors at say 22 degrees (i.e. quite steep) and see how it performs. You may be able to dispense with the shadecloth AND get better performance in winter.
Alex
February 26th, 20089:49 pm at
Admin – reference Ross
The system in question I believe is one purchased via eBay & is a thermosyphon system, not approved for REC’s or any other state rebate & potentially Federal rebates.
In referance to Solahart system yes a proven unit no question however there are maintenance requirements such as sacraficial anodes, PTR valve & elements
REC’s to my understanding has very little bearing on efficiency but is to do with the demands on the infrastructure it requires.
Two different animals one is a thermosyphon system & other a split requiring circulation pump be it only an additional 23w pump – 22 tubes is somewhat undersized for the 315Ltr tank as compared to the total surface area of the two flat plates on the Solahart system – a closer comparison may be a 315Ltr 30 tube system attracting 28 REC’s still 4 short but in the long run would outlast with minimal maintenance especially with the stainless steel system.
Having said that they both reduce impact on the environment which in my opinion is a good thing
22 Deg is flatter & 90 Deg is steeper is the way that we assess pitching angles for solar systems – the steeper the angle the better the winter performance but the standard is no more than +- 20 of latitude ie Adelaide is at 34 so no less than 14 & not greater than 54 outside of that is up to you
February 27th, 20088:15 am at
Hi Wayne,
You’re right about the angle – sorry about that. So what I meant was an angle of 90 – 22 = 68 deg. I agree it’s a pretty steep but if boiling is a problem, you’d be mad not to at least try it. The winter performance would definitely be pretty good.
Do you have any good recommendations on pumps? I hear there is a big difference in performance between the best and the worst pumps, and it’s worth getting a pump which is optimised for this type of use.
Readers note, there is enough hearsay evidence now to state categorically that it’s worth spending extra to get a stainless steel tank.
This is doubly true in South Australia, where the water is more saline and chlorinated than elsewhere.
February 28th, 20089:19 pm at
OK – I don’t have bore water, but my water is non-potable, River Murray water from a large, lengthy (and sometimes smelly) pipeline. I am considering et’s with a split system – so I can flush the tank when necessary. Also, our summer temperatures here are often in the mid to high forties.
I currently have no hws, and find that I use less water because it is cold. That is good for the environment. With winter coming on, I am looking for warmer water.
If I breed up some Legionella, how will it make me sick, ie. breathing it in, drinking it?
Can anyone offer any advice?
February 28th, 200810:22 pm at
Pumps – as far as i know the Salmon pump is what we use for the system & to date only had 2 fail – most of the solar units of any note seem to be using this one for the circulation of water from tank to collector
Stainless steel tanks are good so long as your water quality stays within some specifics to have the manufacturers warranty the unit
Ph value should be between 6.5 – 8.5
specific mention should be made on total dissolved solids, calcium carbonates & magnesium levels – these are only critical if using bore water & spring water, if the levels are high it is worth going to a steel glassed lined cylinder with sacrificial anode in them to get the longevity from the tank.
If the levels are within specifics then no question that stainless steel with give you the longer lasting & maintenance free situation
If worried about water quality please check with the manufacturer of the tank for clarification or your solar expert
February 29th, 20089:22 am at
Can anyone advise on the following? I have a NNE facing rock cliff about 3 metres behind my house. I have noticed how warm this surface becomes during the day. My house has a steel (Colorbond Light Green) roof. Would it be beter to mount my ET array on the roof or on the rockface?
February 29th, 200812:03 pm at
Mazza – one thing you shouldn’t do is get direct-flow ET pipes, where the water flows directly through the pipes. You should ensure that the water only flows through the manifold. Otherwise you might have problems of scale and corrosion. I believe that if you’re having showers with legionella-contaminated water, there is still a risk that you will inhale the organism. Best to ensure the water is heated above 70C after storage and before use. It’s probably even more important if your water is untreated.
Wayne – thanks for the tip. Sounds like Mazza needs to take special care selecting his tank. Have you got any suggestions for him?
Conrad – I don’t think there’s much in it. Green colorbond vs. dark rock. I would make the selection based on aesthetics.
March 1st, 20082:42 pm at
Alex – happy to put forward my view & personal recommendations from information posted previously – however I feel more information is required before a definite / informed recommendation being made without prejudice.
Conrad – Rock wall is it vertical as ET should not exceed 88 Deg, conversely I think that in the winter months & rock wall only 3m away from house you may get some shading issues as the winter sun is at a lower angle. How does one get the flow & return lines from collector to tank without major heat loss? – I would think roof mounted would be best option ? subject to further inspection or information
Mazza – concerned no HWS & non potable water ?
Personally I would have the water quality checked if you are considering a split system – most manufacturers will void warranty on standard tank if the total dissolved solids exceed 600 parts per million & in that case I would be asking for or installing a blue tipped anode in tank – further consultations with tank manufacturers would be preferable, without knowing full water quality I would be going for a steel glass lined cylinder or heat pump with a anode upgrade on both – efficiency wise & longer warranty a heat pump may be the preferred option – have one specific in mind
NB* this is a personal opinion & further information required prior to a professional opinion being made
March 5th, 20086:50 am at
Thanks for all the comments. I think that they have helped to increase my knowlege about ET if not make a decision. When placing the tank is there any efficiency gain/loss by placing the tank inside the house as opposed to outside? Also does anyone know of anyone/company that will supply/install around Geelong – I’m having trouble finding someone.
March 5th, 20087:44 am at
Hi Carol
If the pipe length is about the same, I would place the tank outside the house. My reasoning is that you don’t want all that extra heat in the house in the middle of summer, when the collector is working its hardest. I know the tank is insulated but it always does lose heat over time. Your best bet for ensuring efficiency is using quality insulation, applied neatly and correctly without any gaps. Also don’t take the controller for granted. If the thermostat is not accurate then it will take its toll.
Assuming you are choosing ET with an open loop tank, ensure that your storage tank is tall rather than squat. This allows for better stratification of the hot water.
March 5th, 20088:47 pm at
Carol -If you send me a private email I will forward the appropriate details to you – Don’t think I should list them here without expressed permission ?
Tank I think best positioned externally for many reasons & similar to Alex post – reasonably intuitive (could almost get you a part time job in sales – ha ha)
Alex – could you clarify for me or any one stratification of hot water – been a plumber for some 20+ years and all though familiar with term it escapes me at the moment – as always curious to re learn & learn as well as your idea with relation to hot water
You learn something every day if you don’t your probably under ground
March 6th, 20087:21 am at
Wayne,
Stratification refers to the fact that in a column of water like in a storage tank, water can remain in strata, i.e. hot water of the top, graduating to cooler water at the bottom of the tank. Once it’s mixed, it stays mixed, but if you carefully pour hot water in the top, it will stay at the top.
In an open loop SHW system, mains-pressure water is recirculated from the tank straight through the collector.
The cooler water is taken from the bottom of the tank, circulated through the collector, and returned to the top of the tank. No point heating water which is already hot…
The recommendation from the Solar Energy Society is that a tall tank has better “stratification” i.e. separation between warmer and cooler layers, than a squat tank of the same volume.
Other measures, like inflow baffles, are also apparently used to prevent mixing of the water when it flows back into the tank.
I am not sure whether or how this is affected by having an electric booster element within the tank. I personally favour an instant gas element downstream from the tank but I realise this is not a solution for everyone. I suspect any in-tank booster element would still have to sit at the bottom for best efficiency.
March 6th, 20089:10 pm at
Thanks for that – I have a clearer understanding of my original thought’ probably a good reason for our system to have the return loop from collector enter back into the bottom of the tank as opposed to other systems on the market that have the return line higher up on the tank
Thanks Alex – Information should be a win win situation for everyone
March 7th, 20087:37 am at
Hmm hang on is that right? The return loop enters the bottom of the tank? I think the opposite should be the case. Are we still talking about an open-loop system?
Surely the idea here is to prevent mixing the hot and cold water within the tank? If so, then the hot water should be very gently returned to the very top of the tank.
I am sure that in a closed loop system (i.e. heat exchanger loop running inside the tank) it doesn’t matter much, in fact there you’d want the loop at the bottom, but I gather we’re not talking about such a system…
March 7th, 20088:55 am at
http://www.wbdg.org/images/solarwaterheating_4.gif
Here is a graph showing which type of system is best under different conditions.
Aesthetics,susceptibility to damage,storage location,maintenance and running costs are the other decisions an individual needs to consider.
March 8th, 20087:24 am at
Alex – yes I think we are getting our wires crossed
Open loop system – close coupled thermosyphon system where collector is attached to tank or gravity feed storage tank to collectors runs the naturally circulated hot water back into tank at the top of storage unit tank with draw off to outlets in house also at the top of unit
Closed loop – split system with the storage tank on the ground & water circulated via a pump up to collectors & returned back to storage tank. Return lines enter back into bottom of tank & mix with the colder water & naturally rises to top of tank. It is the mixing of the water both hot & cold that reduces the need for electrically boosting of the stored water as the thermostat will measure the temperature of the water at the lower level of the tank & determines the need for boosting.
The other understanding of closed loop & open loop system in reference to solar is one of – closed loop the use of glycol in the system for frost protection. That is my understanding but stand corrected
I am happy to send you some pictures of the two types that we have done through private email (however that is done) but we only do the split system with the ET now – we use to do the thermosyphon system
March 11th, 20083:56 pm at
Thanks for the response re the ET array on a rock face. My house faces North East and is sunny in the morning but quite shaded during the late afternoon. Would it be better to mount my ET array on a NE facing roof surface with longer sun exposure OR on a NW facing roof surface with shorter sun exposure? Are there any ET power calculators with angle / orientation / lat / long etc?
March 11th, 20089:08 pm at
Conrad
I have here a 2d graph (which I probably shouldn’t reprint) from the solar energy society. It is for central Europe, but I believe the results are usable. It shows a hotspot of maximum solar irradiance extending from -10deg to 10deg due North, with an irradiance value of 1050. Not sure what the units are but it’s not relevant. Outside that is another area extending from -60deg to 50deg with a value of 1000. In other words, you will lose only 5% of the maximum if you stay roughly within that margin.
In other words, it probably does not much matter. Other factors come into play. The length of the pipe run, the quality of the insulation. The amount of dirt and dust on the collector. I think as I said before, you should probably let aesthetics guide your choice.
March 19th, 200810:05 pm at
Hi Terry from Hobart
Don’t know if you are still watching this thread, but I know of someone in Hobart who has organised bulk orders of ET systems(over 100 so far). Are you still interested?
March 20th, 20087:54 am at
Solar Lord Manager
Jared O’Meara
I have been working closely with our engineers with our evacuated tubes for a few years now and we have a dual system that supplies solar hydronic heating and domestic hot water which qualifys for government rebates. We use our award winning evacuated U-Tube collector for commercial and hydronic applications.
If anyone would like any help or a quotation I would be happy to help them out. Our engineers from Australia and overseas have alot of expierence if you want the right answers.
Best regards,
Jared
Contact
jared@solarlord.com.au
http://www.solarlord.com.au
March 20th, 20088:25 am at
Hi Jared
Thanks for dropping by. Could you tell us a little more about the U-tube design? Is this the design which is described here? Because that doesn’t look U-shaped, so I’m confused.
Nice site you’ve got, by the way. Wishing you every success.
Alex Fiedler
http://www.solarhome.com.au
March 22nd, 20089:48 am at
Hi.
Great and interesting discussion here!
Our situation is in Adelaide near hills. We face Glenelg from above the end of Cross Road if you know the city layout.
I’ve been putting off dealing with our electric offpeak HWS because replacing it is problematical. The existing unit is in the basement of our 3 level home, and it’s a long way to the roof. Additionally, we have a gable roof over 20 degrees, but it faces west and east. Family of 4, with 2 teenagers. Current offpeak use is 1000-1200kwh per 90 days ($80-90)
No town gas. We have a couple of bottles used for cooking. Not liking the idea of gas boost, cylinder gas is expensive.
We’ve provided ourselves with rainwater, and once the whole system is finally hooked up, we expect to be at least 70% self reliant for water.
Added complication: We have a geothermal heatpump AC system. It has a water circuit that takes excess heat ‘de-superheater’ and puts it into the HWS. Due to the stratification issues, I don’t think we get good value out of it currently (it basically mixes the tank)
For aesthetics, we’d like to put the collector on the west (no-one will see it except the spacemen
We could cant it up a bit to improve winter efficiency with no problem, I think.
So, the questions:
What do we do about the extreme distance between collector and tank? in a straight line, the distance must be over 15, maybe 20 metres! That must cause some losses?
Is ET best for this application?
Could the Geothermal be integrated successfully into a solar system?
What is the norm for these systems in terms of pressure. Do they run on mains pressure or use gravity and/or pressure pump to supply water to the taps?
That’s it for now
Mike.
March 25th, 20088:43 am at
Hi Mike,
So you are around Mt Osmond or thereabouts. I think a western orientation would definitely benefit you. It would heat your tank later in the day ready for the morning shower.
The majority of systems run on mains pressure. This applies both to closed loop and open loop systems. The tank is pressurised by the mains.
A 20 meter run can cause losses, and obviously the quality of the insulation is very important. Is it not possible to put your tank under the roof?
If you don’t like gas boosting, is it possible for you to use instant electric boosting? There are some german and swiss models available apparently. They are very compact, and economical. Alternately overspec your ET collectors.
March 25th, 20084:42 pm at
Hi Alex,
Yes, that’s the spot.
Thanks for the reply.
So, the system remains at mains pressure, and we use transfer pumps or convection to move water around within that system?
I think it would take a crane to install a tank in the roof, and I have this image if water raining down throughout the house when it leaks…
I’m wondering if overspec ET will cause any other issues. What about hot days in summer? If I overspec the solar, and leave out the booster, how game am I being? Will I face cold water on heavy cloud days in the middle of winter?
Mike
March 26th, 20086:59 am at
Mike – sounds like you are reasonably focused on various issues (I like it)
No great issue on the circulation from storage tank to ET collector its a case of using a larger pump to get the water there & use of better insulation on flow & returns . West facing would be fine with minimal loss. Not to sure on overspec ET collector with the advent of the geothermal intake – from all accounts of what you have mentioned I would suggest a site inspection to determine the feasibility & configuration of a system
If you wish send me a pm to see if we can assist you
July 7th, 20086:19 pm at
TITLE: Compare the cost savings in Winter (Adelaide) between a twin-collector flat plate collector and a 30 tube Evacuated tube collector
ASSUMPTIONS
* 300 L tank
* Insolation (Adelaide – June): 2.23 kWh/day
* Ground water temperature: 13 C
* Off-peak electricity cost: $0.131238
Solahart 302 J Flatplate
* Aperture area (2 collectors): 3.72 m2
* Collector efficiency (winter): 45%
Hills 30 tube Evacuated tube (315L)
* Aperture area: 2.844 m2
* Collector efficiency (winter): 80%
RESULTS
No solar heater
* Energy consumed: 16.4 kWh/day
* Electricity consumption: $1.18/day
Solahart 302 J Flatplate
* Hot water potentially heated: 68L/day
* Energy offset: 3.7 kWh/day
* Electricity consumption: $0.91/day
* Purchase price of collecotr $2305 (after rebate and RECS not install)
Hills 30 tube Evacuated tube
* Hot water potentially heated: 99L/day
* Energy offset: 5.1 kWh/day
* Electricity consumption: $0.81/day
* Purchase price of collecotr $2688 (after rebate and RECS not install)
CONCLUSION
Daily savings of 30 tube ET over Double collector FP (middle of winter in Adelaide) is about 1.4kWh or 10 cents per day. Initial outlay for ET is $383 more than FP.
NB annual energy offset is about 250 kWhr or $32 per year. Therefore ET will take 10 more years to payback cost than FP.
July 31st, 20087:10 pm at
Hi Derek,
So am I reading your calcs correctly?
If we install a Solahart 302J it will make 68L of hot water per day in winter.
The Hills ET 30 tube will make 99L per day in Winter?
That would mean we would definitely be on boost every day in winter…
The electricity calcs look wrong. ‘No solar’ consumes 16.4kWh/day for $1.18/day whilst the solar systems use $0.81 and $0.91/day Doesn’t make sense…
For the conclusion to be worthwhile, wouldn’t we also have to take into account the cost of boosting during winter?
Mike
August 1st, 20081:01 pm at
Taking Derek’s winter scenario and solar collector data as is, I don’t quite get his calculations. This is how I calculate it.
A non solar boosted 300L o/p HWS uses 16.4 kWh/d @ 0.131238 c/kWh, therefore costs $2.15/d
The Solahart flatplate contributes 3.7 kWh/d heat. Therefore (16.4 – 3.7) kwH of o/p electricity is needed to heat the balance of a 300 L tank. 12.7 kWh @ 0.131238 c/kWh = $1.67/d
The ET collector contributes 5.1 kWh/d heat. Therefore (16.4 – 5.1) kWh of o/p electricity is needed to heat the balance of a 315 L tank (won’t worry about small tank volume difference). 11.3 kWh @ 0.131238 c/ kWh = $1.48 /d
Therefore in winter FP costs $0.19 per day more than ET to heat a 300/315 L tank.
But why compare them just in winter? Surely an all seasons annual comparison is more relevant?
I don’t get the conclusion that the ET will take 10 more years to get payback than FP.
Over a ten year period the total cost = purchase plus installation price + running costs over 10 years.
If the ET is initially $383 more than the FP, but per annum less boosting is required, over 10 years wouldn’t it be about the same total costs for both?
August 1st, 20083:59 pm at
Hi Rob,
Here’s the thing:
Our OffPeak electric HWS has used less than $1 a day based on historical data over the last couple of years bills. It’s a 420L job.
Any solar system costs thousands of dollars to buy and install. Even after all the rebates.
With no boost or other running costs, our payback is something more than 2.5 years per $1000 invested. Any boost required is going to blow that out of the water.
Now we have had a back of the envelope estimate for an ET system on our roof (it’s high) at about $12,000.00 plus. No guarantee of winter sufficiency, and Derek’s and your calculations support that. Based on our payback, and assuming we get $4k back on rebates we are looking at 20 years and we are still out of pocket for the winter boost.
Based on these realities, we have gone ahead and installed a Siddons Solastream heatpump unit. It’s early days yet, but we’re expecting the HWS to consume around 1/3 the power of the old unit. This should put it at less than 33c/day consumption. Payback time is around half the solar unit, and within expected lifetime of the hardware. And, no surprises or low efficiency boost in winter.
If we wish, we can still hook up a solar panel in the future, but I get the impression it would have to be a backyard job to make it financially worthwhile.
Michael
August 2nd, 20088:46 pm at
Sorry for the confusion
It should read off-peak electricity is 7c per day. Otherwise the calculations stand. The cost savings for ET doesn’t begin until 10 years later. This obviously will change proportionately as energy costs rise. e.g. twice the cost, half the payback period. I have used winter figures because this is when ET has maximal advantage over FP. As the insolation improves over the course of the year, the difference narrows and hence the energy or cost savings. In other words, worse case scenario is 10 cents/day difference becoming less as it gets warmer. By summer, they both are able to provide 100% solar hot water needs. Mike’s real world figures suggest the difference is even less because he probably is not needing to use his entire tank each day (a little left over for the following morning).
August 2nd, 200810:36 pm at
Derek,
So the ET system will save 10c per day over the FP in winter.
I wonder how many days the system will run boost per year? At a price difference of $383, ET will need to make that saving on 3830 days before it catches up with FP!
In any event, what these calculations show is that unless power prices escalate radically, there is very little dollar saving in these technologies on an individual case basis. No argument that they make a collective impact for the whole community in terms of fossil fuel consumption.
Interesting that both these systems consume power in winter at roughly the same rate as our old electric storage unit. If they run boost for 1/3 the year, they will have an annual consumption close to our heatpump system which has cost about half of a standard solar install. That seems like a pointless investment. We haven’t even talked about the environmental opportunity cost of the investment in solar (and the energy consumed in their manufacture) compared to installing better insulation in the home etc.
I wonder if $8000 spent on improving the energy efficiency of a home might be better spent on technologies other than solar hot water.
August 3rd, 20085:30 pm at
Firstly, unless you completely over-spec your system then boosting will always be required in the colder months. Even once you system has paid for itself – there will always be a cost (albeit lower) for generating hot water. An over-spec system is not only expensive but you have to wonder if having the system constantly boiling over in Summer can be good for it in the long run.
Though my calculations stand I should have looked at it another way (which makes the extra premium of ET not as bad as I thought). I should have considered the net savings per year ($205-222) rather than the marginal savings per year ($17) ………
Gas instantaneous system ~ $1200: Annual water heating bill $380
Flat plate system ~ $2300: Annual water heating bill $175 (save $205)
ET system ~ $2700: Annual water heating bill $158 (save $222)
(Cost of gas taken to be: $0.063/kWh = $17.5/MJ)
Therefore for a FP:
After ~5 years – you will recover costs from the additional premium over that of a cheaper instant gas system.
After ~11 years – the FP unit would have paid itself off in energy savings (but not the cost of installing it)
After ~17 years – the full cost of installation would be paid off in energy savings
For ET, add about another year to those respective figures
If the government rebate is not available to you (shame on them for means testing), add about 3.5 years to all those figures
Mike does make an interesting point about the energy cost of manufacturing the units. ET is a more complicated system and some suggest (but no figures given) that the embodied energy for making ET is higher. I cannot comment on whether this difference should be a major consideration.
Mike’s $12000 ET system sounds a trifle expensive. It probably would give him 100% hot water needs in Winter (but as mentioned this is a law of diminishing returns).
If I had an extra $8000 in Adelaide I could achieve more by draught-sealing, increasing insulation/radiant barriers, install heavier curtains with pelments, maximising north facing glazing and adding appropriate external shading devices in Summer.
What bothers me sometimes about sections of the eco-movement is the focus on expensive gadgets or active systems or such as PV cells when the first step is to reduce energy consumption by good passive design.
August 3rd, 20087:41 pm at
The $12k was for a standard spec. Extra costs were attributed to a particularly difficult installation site. I share your concerns about overspec systems boiling over in summer. Maybe the manufacturers will come up with a solution to that in time.
You are correct about the means test. We can get RECs but not the rebate.
Looking at the water heater as a simple financial problem, I suspect most people would be better off leaving the money on term deposit and applying the interest to their hot water bill. By the time their current HWS dies, there might be some better solutions about than those on the table today. Of course, this approach doesn’t help the environment but it might take the ‘heat off’ the HWS issue and allow the homeowner to focus on things that might make a lot more difference than half their hot water bill.
August 3rd, 200811:02 pm at
Mike,
No doubt that heat pumps are another viable option. The difference in cost and efficiency that you state for heat pump vs solar seems different from other figures that I have been quoted. Your solar quote is very pricey even for ET. Most quotes I see in Adelaide still make solar an economically viable choice. Follow this link for a comparison table based on operation in North Queensland.
http://www.envirotalk.com.au/forum/uploads/1204534816/gallery_3068_42_9121.jpg
August 3rd, 200811:46 pm at
Derek,
Like I said, we have a particularly difficult installation…
In Nth Qld, I have no doubt that solar is very viable, but even the cheapest unit there ($2440) is 6.42 years to break even against net cost. Take that system down to Adelaide and the payback blows out to 17 years by your reckoning.
Basically, I think that if you have a well situated, unshaded north facing roof, town gas, and an easy install, then you are in a position to throw a bit of money away on solar in Adelaide, knowing that even though the decision is uneconomic, you’re doing the right thing for the environment. If you don’t have these things, you should first look elsewhere for energy savings.
Heatpump efficiency has moved forward since Siddons designed the unit that Quantum still sells. http://www.siddonssolarstream.com/
Mike.
August 4th, 200812:55 am at
Mike,
You may have misinterpreted me.
For an FP unit without the value of the govt rebate ($700) but including RECS.
5+3.5 = 8.5 years to recover cost compared to buying an instant gas system
11 + 3.5 = 14.5 year to pay for the cost of the unit ($3000)
17+ 3.5 = 20.5 years to completely pay for the unit and installation ($3000+1200)
The critical issue is the first line. You will always have to buy some kind of HWS and there will be an installation cost associated with any of them. Everything will have a limited lifespan. Ideally you want to ensure that the solar lasts at least long enough to pay the difference with a standard HWS. With good insolation and orientation in Adelaide, that should not be a problem. If it keeps chugging along and pays for itself +/- installation then even better. In the meantime you will still save 3300kWh of energy per year.
If your solar access is poor then heat pump will definitely be the way to go.
August 21st, 20088:10 pm at
Mike or others .
Did you compare quantum Heat pumps to a sidddoins.
Are they related but different heat pumps. Your link suggest a similarity.
I am tossing between a Heat pump and thermosyphen.
I have $2919 for a 340 litre with the standard Recs.
The additional plumbing to relocate is perhaps going to ramp up my cost significantly.
The opportunity cost with the extra funds is something everyone seems to ignore.
eg a $1000 extra spent on solar over 5 years produces a savings of $ 469 at 8% if paying off your Mortgage
August 21st, 20088:50 pm at
Over 10 years its $1159 or you could invest in some quality shares
August 21st, 200810:18 pm at
redsquash,
I did look at Quantum, and I found some differences that effected the efficiency of the unit. The most obvious of which was the use of a resistance de-icing heater in the condensor of the Quantum. Siddons employs some sort of heat feedback system which does not use resistance heating.
The Siddons comes only as a split unit which suits my installation exactly, as does the provision for a mid-tank water connection.
Ease of install goes to the Quantum, because of it’s integrated nature. Just plonk the unit down and hook up the power and water. It does have to be outside however.
And yes, the costs of these units do not really justify the savings they make. You have to spend a lot of money to save a few hundred dollars a year. Paybacks past 10 years are really a bit beyond the pale for most people.
Mike.
August 24th, 20081:13 am at
Is a de-icing heater in the condenser irrelevant if temperatures never approach freezing?
Why is the quantum method inferior to the siddons.
The big plus with siddons is the Marine grade steel tank, but I don know the cost of these units. Any idea?
The heat pumps are marginally more expensive for Brisbane than thermosyphen in terms of running costs for my particular situation.
I did some calcs years ago, where the payback was just over 7 years . i think though costs have risen the figures arent so different since conventional HWS heaters have also risen in price.
However payback and being financially ahead are 2 different things , if you can get both govt rebates .
In that case you would be better off in 2 or 3 years at the most, depeding on you hot water consumption.
Your figure of 10 years seems a little on the high side
May 1st, 200910:57 pm at
Just dropping in to update on running costs of the heat pump system we installed.
Previously, we had a 420L electric storage heater on off-peak power. Hot water bills averaged out at $1 per day. We have no town gas. After considering an electric boosted solar system and rejecting it due to installation cost and extended payback scenario, and general mistrust of the general attitude that if it’s solar then it must be good, even though these things use significant power for boost in southern states (and therefore undo some of the good they do by using that power in the most inefficient way possible)
The power consumed by the Siddons heat pump has been averaging $12 per 90 day bill – $0.13 per day.
May 4th, 20091:46 pm at
Hi Mike,
Thanks for the data on your heat pump system. It’s great you have been able to achieve such a huge saving on your energy bill – well done. Heat pump systems really are are fantastic and I would recommend them for many domestic situations where no tank is desired and especially where the usage is low or infrequent.
There are still many situations where the return on investment on solar is higher. A typical one would be where a storage tank is already necessary because of a requirement for a flow return line. Also where daily consumption is high or spread evenly throughout the day. Thirdly, where the temperature of the required water must exceed 45C. Generally speaking I believe that the advantages of solar are higher the larger the system.
May 14th, 200912:12 am at
Hi admin.
Not sure what you are getting at. Do you know what a heat pump HWS is?
Heat pump HWS have tanks. They are storage hot water systems that use a heatpump instead of an inefficient electrical element. We are a family of 4 and we have teenagers on board, so our usage is not low or infrequent.
Our water temp exceeds 45C every day???
Solar is a good deal in areas of Australia where there is high insolation – regardless of system size or demand. Of course, the system must be designed and sized to cope with the household hot water demand.
As soon as the system starts using significant electrical energy to make up hot water via an element (as it would in southern states during winter, definitely Melb, Adelaide, Tas) I have issues with them as previously stated. They are not a global panacea, and we should not be globally suggesting they be installed regardless of location.
Mike.
May 20th, 200910:01 am at
Fair cop Michael, for some reason when I wrote the email I thought heat pumps don’t have storage tanks. Of course they do and I did know that. Really I did…
It’s true that the electrical resistance element is horribly inefficient. It should be a last resort in any situation. Imagine taking all that thermal energy from a coal fired power plant, turning roughly a third of it into electrical energy, the most versatile, clean, transportable form of energy ever, then transmitting it with losses to the home, then squandering it by turning it back into heat. Crazy.
Heat pumps, even with a high COP, still always consume a considerable amount of electricity when they are running. There are two situations where they are not suitable. Where ambient temperatures are very low, they required additional resistance heating, or underground intakes. Where water temperatures required are very high, such as in process heat for industry, again they are not the obvious choice.
About the 45C water. What i meant was that the hot water required within a home for showering and washing, is usually comfortable at 42-45 degrees. In order to prevent legionella, the water in a storage tank must be heated to 60C by law at least periodically. Perhaps I should have said 60C.
Thanks for continuing to take an interest.
August 31st, 200912:35 pm at
Hi Admin,
Re HeatPump tanks, Fair enough.
Heat Pumps with High COP will operate efficiently anywhere in Australia except perhaps alpine areas. Hobart for instance is fine, and no resistive element is required – I have first hand info from an associate who lives there. I would suggest that if a supplier is specifying a resistive boost on a HeatPump, the unit is underspec or perhaps poorly designed – find an alternate supplier!
On the other hand, Solar in these marginal areas remains a problem due to boost energy requirements in Winter.
When connected to the electricity grid in marginal areas of insolation during winter, of course, both these systems will use electricity, but the heat pump will use it far, far more efficiently.
To answer a previous question from redsquash regarding the resistive de-icing of the condenser, I have seen our system operate de-icing and our ambient temperature was not near zero – the point of the heat pump is that the condenser operates below ambient, and during winter it is possible for the condenser to ice up on occasion. Once again, resistive de-icing is a wasteful use of power on an otherwise efficient appliance and should not be accepted by the energy conscious consumer.
I think in marginal areas the preference list should go something like this:
1) Gas boosted Solar
2) Heatpump boosted Solar
3) Heatpump (preferably with non-resistive de-icer)
4) Resistive boosted Solar
Mike.
August 31st, 20093:42 pm at
Welcome back Mike,
I would love to hear more about heat pump assisted solar. I always wondered whether anyone had a RECS approved system which had an ET collector, tank and heat pump. I haven’t been able to find one but haven’t looked very hard.
September 2nd, 20097:30 am at
Hi admin,
I haven’t seen one available commercially. The Siddons people mentioned the possibility of adding one to their system, but it would be a owner modification to an existing RECS installation.
I might do it one day.
Ours is a difficult installation for solar collectors as the roof is very high and it faces east/west. We do have a north facing wall though…
Mike
September 2nd, 20093:10 pm at
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