Peterws
Member
I am trying to come up with a simple cost effective Solar Hydronic heating system for my house.
I have read the article in Renew No95 which came up with a system that costed $19,000 which is a little hard to justify.
I don't pretend to know all the issues but I am interested in exploring the collective wisdom out there.
This basic sketch shows my intentions
Peter - I'm interested but inexperienced in the same topic but have a couple of suggestions that may be of some use:
The network you've drawn shows potable water coming off the same circuit as the hydronic heating water. I think this means they may be the same temperature (and probably limited by legislation). If too low a temperature was used I would be concerned that the hydronic panels might not heat up enough for them to work effectively.
Having the hydronic and potable water circuits combined also requires that the hydronic circuit be built to potable water standards. I don't know for sure but this might involve additional cost and difficulty.
I also suspect that you will need a larger collector than 30 tubes though this depends on how much you aim to use the gas booster. The solar fraction will always be better when a larger collector area is used.
In terms of system layouts I learnt a lot from the demo software version of Polysun. It has all sorts of system configurations and the full licence can provide simulations of various configurations. Just the demo version has plenty in it for me to learn from also.
Good Luck!
Benny
Member
You'll find several other threads in here discussing exactly this topic Peter - have you had a look through those ? One thing you should be aware of before you start is that if you are hoping to get a lot of heating from the system - and it looks like you are with 4 radiators - then the solar contribution will be limited. I don't want to dissuade you, but just be aware of how much heat it will contribute, esp in winter when you need it. The max thermal output from a ET system will be 1kw/sqm and thats at 100% efficiency and at perpendicular insolation. Others have quoted having gas etc fired systems with ratings of 10-30kW and some calculations show this how much power is needed to heat up typical homes.
As Munter says you'll probably need a bigger collector to get an appreciable fraction from solar.
Peterws
Member
Thanks for your responses
Munter- I was thinking of running the system at 70 degrees which I imagine to be suitable for DHW and radiators (just increases the size a fraction), I do need to calculate the size of the system etc and I will fine tune that part.
I would like at least 60% solar contribution, I intend to have a reverse brick vaneer construction and I was thinking that I would run the heating thru the day to heat the thermal mass and thereby reduce the heating load in the evenings - I will checkout the software you speak about - I am in the process of modelling the building with DesignBuilder
Benny,
I have read the other treads
I do intend to to detailed load calcs and solar calcs....as I said above the building will be thermally massive with large north windows which will reduce my heating requirements,I am more concerned with the system schematic and if it works technically as the calcs are relatively easy.
thanks
Peter
ghostgum
Member
My gut feeling is that it would be better to spend the money on double glazing the north windows and using well insulated window frames, than on solar hydronic. If you get the windows, thermal mass and insulation right, then there won't be much need for solar hydronic. On the days when it would run, you would already get ample heat through the windows. 10 square metres of window may be cheaper than 10 square metres of evacuated tubes.
The problem then becomes moving the heat from the north side of the house to the south side, which could be done with some low power fans.
Peterws
Member
ghostgum,
I suspect your gut feeling is right, although the windows and the general fabic will be "right" (windows U=2.1 walls U=0.25 and roof U=0.2)
We still have a significant heating load/requirement in Canberra.
My thinking has been - we need a domestic hot water system and we also need some space heating then why not try and use the one heat source? - however it just doesn't seem feasible at this stage, what with heat exchanges, multiple pumps and dual circuits and mixing valves its all a bit complicated, no wonder there isn't much on the market.
Munter - Ive downloaded Polysun demo which as you say is very impressive its a shame that it won't let you use the correct weather data
peter
Peter - Don't get disheartened - there is unquestionably potential in the concept but it is a case of getting the design and components right. Passive solar gain might be more effective but it also has limitations when retrofitting and moving heat to other parts of the house.
With solar thermal, I think that Chinese manufacture in evacuated tubes is growing strongly (anecdotally) and the prices for this equipment will fall further. There are several people importing equipment directly from China who may be able to provide you with equipment at a price that makes the system feasible. I am hoping to go down this path with a system at my house.
Physical constraints are harder. It is inevitable that a large collector area will be required if a high solar fraction is to be delivered. A large storage tank will also be necessary to give sufficient storage. At a guess I would assume that at least 100 evacuated tubes and over 1000L of storage would be required to have a system capable of providing reasonably heat output. Both these things will take considerable space. I am looking to use the northern wall of our house to mount collectors rather than putting everything up on the roof.
I am also having a look at T*Sol which is similar to Polysun but seems a little less aestheticly pleasing. The demo version is similarly constrained to doing calculations for a single location in Switzerland - lucky them!
Peterws
Member
I am somewhat disheartened - there is so much available in Europe/China etc but not here - I guess we still have cheap energy and its a small market.
I was speaking with a colleague that works in the field of Energy Consevation and he said that his approach was to focus on the building envelope and use a few electric panel heaters and buy green power.
Maybe thats the best way to go, with a really good solar passive design the heating requirements will be fairly low, and by using electric heaters you have a very flexible system as you can run any one panel in one room compared to the hydronic system were you need to run the whole system.
food for thought!!
peter
ghostgum
Member
With hydronic, you can have valves on each panel. These can be manual, or thermostatic valves (temperature sensitive). With a gas boiler (although it only heats to 70C not 100C) you can't run just one panel because the boiler won't be able to modulate the heat that low. With only one panel running, the panel won't use enough of the heat, and so hot water will return to the boiler, causing the boiler to shut down.
If you are using a solar hydronic system, then so long as you can make the pump run, I think you should be able to run it with only one radiator panel. The problem is that the pump is usually triggered by a wall thermostat,and this doesn't work correctly if you have a running a single radiator panel in different room.
Greenozi
Member
Dear Munter, I am afraid that prices for vaccum glass tubes systems hit the bottom already. The reason that you can not see it happen is new regulation and $20.000 instant fine for sales solar heaters without permission. I have been in the business of selling those complete systems inc electronic controller and electromagnetic valve at 700-$900. That is not longer possible. Now regulators may decide how much solar heatr muct cost to keep the price high. Even if Chinese give this system completely free you will still be paying exactly this same. Regards Peter
Samo
Member
Hi PeterWS,
I've recently obtained most of the parts (60 ev tubes, tank, controller) for my hydronic heating experiment for Canberra. Next month or so I will have all the other equipment ready. I understand you are in Canberra and maybe you are interested to assist? Previously I have successfully installed a solar air based space heater in my previous house in Canberra with very good results. So now for this house I want to try hydronic.
This is retro fit hydronic heating on existing house that I've been greening.
Have just insulated the brick cavity. Double glazing windows. R5 ordered for ceiling (thanks Kev). Will renovate North aspect for solar gain. Plan is to limit amount of additional heating actually required. Solar Hydronic with natural gas backup is preference.
contact me jwsamin@mrx.com.au
Samo
norbert
Member
We had our hydronic heating (no solar) commissioned two weeks ago and I am very happy with it.We have done a lot of research in regards to solar hydronic including advice from the ATA.
I came to the conclusion that when you need heating most (winter) the solar contribution will be minimal.This seems to be confirmed as we also have 30 tube apricus SWH to heat our domestic water and at current cold and cloudy days the temperature in the tank does hardly go above 30 degree celsius.Our hydronic consist of 7 radiators and a Baxi instentanious and cost us a total of $ 10500.Our daily gas consumption at current is 6.2 m3
I don't want to be neagative but I believe that solar hydronic systems don't make much sense as they require a huge amount of glass tubes and enormous tank which makes the whole thing very expensive for minimum result.
Peterws
Member
norbert, thanks for your input.
and I understand your logic, it is sound
however,
you have two independent systems doing the same time I.E. heating water, I think combining them is the way to go, the solar contibution will not be great however if the required heat load is minimised then maybe the system becomes more worthwhile??
peter
ghostgum
Member
Norbert,
My impression is that in the middle of winter, solar hydronic may not give much boost. But at this time of year (almost 2 months after the winter solstice), we are still using gas to partly warm the house in the morning, while during the day the sun heats it up further quite nicely. Solar hydronic might allow you to use heat from the previous day to heat the house in the morning (or more likely keep it warm overnight), without using gas. While our house is 5 star (pre 2008 stars), it doesn't have significant thermal mass and so cools down overnight. A solar hydronic system could provide the thermal mass.
It also sounds like 100 evacuated tubes and 1000-2000 litres of water may be an appropriate size, and is considerably more expensive than a gas water heater for hydronic. In the cities, gas is cheap enough that this doesn't make economic sense. If you were heating with bottled gas, and north of the divide where there is more sun, then the sums may be different.
Samo
Member
We get a lot of clear days in Canberra, not today it was quite foggy. 
My solar air heater (polyester cloth based) of 2sq meters lifted our lounge+Kitchen by 5-7 degrees C last winter - closed cct arrangement. 160 cf/m fan forced air output at 40 deg C +. It was so nice to stand under... During the winter days it produced lots of nice warm air, and surprisingly even when it seemed overcast... Anyway this exercise convinced me that there is enough heat in winter to make this a worthwhile heat source in canberra.
My plan is 60 Ev + 300l tank, small tank so it gets hot (75-80), and thermo switch will dump excess heat into the house, with a reserve in the tank for morning. I've boiled water with these tubes as a test in winter. As long as it's clear, the heat is good. I've stacks of internal thermal mass, I've just got to get heat into it in a controlled way.
I suppose time will tell. I don't think you can justify solar hydronic on price alone... If it works as seemlessly as the air heater, then as part of the overall green investment, the house will appreciate more than those around me. Thats where the real payback will be.
Samo
IanHill
Member
A few readers wanted more on our system, and some thoughts on items in this forum so far.
OK. Reading all of the above I may not have much to contribute as:
1. This home already has a high thermal mass (solid brick external and internal double brick, heavily insulated roof system, heavy slab floors, some double glazing done)
2. We already have the hydronic tubing in the slab, plus pumps,manifolds, we run on our own rainwater (215,000l avail) with plenty of hydronic circuits to bring in and turn off for adjusting our needs to the performance
3. its a large house with a big roof surface within 15 degrees of e-west alignment
4. we already have 2 slow combustion wood heaters in 2 living areas, plus a gas one for instant heat, and unlimited excellent wood on the farm,
so we have many of the decisions done, we know the building's thermal performance - that it takes only 2 days to heat it and about 3 for it to noticeably cool much, we are semi-retired with no debts so the cost was not the highest priority.
Our priorities were long-term cheapness to run, PLUS a top energy footprint and so our only decision was really what combination of energy sources should we install, how many panels do we need, and how much water to store.
Having said that, 36 tubes of the most efficient tubes I could find was the budget limit for now, our plumber advised a 1,000l tank with 75mm insulation, and gas instantaneous for back-up. Gas has about 30% of electrc energy's carbon footprint, and electricity prices are set to rocket, wheras my income from cattle, a little consulting and the super fund is not.
As an aside, if we wanted to have unlimited water stored hot, the very cheapest option is a 5,000gal common water tank inside another, with as much insulation sides, top and bottom, as this is really cheap to do because the temps ar not high. Unfortunatley we didn't have a location close enough to the exisitng house plumbing inputs.
A second aside - those correspondants above who are using/considering flat panel hydronic heaters are really expecting the home's air and building mass to store their heat, way less effective at getting hot that the conc slabs with tubes in them, so the hold time, or thermal mass is way better with slab heating, if you can do or afford it.
So, having said all that, I guess none of the above correspondents had the flexibility that we had to choose system components and sizes.
Someone asked what would we do differently: this house is a big compromise on modern heating, built from a draftsman's plans, no architectual input at all, I suspect. No thought to passive solar design, heaps of huge french windows (some still in single glazing - but we're working on that) and a big % of it open plan rising 15 steps from bottom to top, with cathedral ceilings to 7m in parts. Heaps of air to move and heat.
But the performance of the solar heating, kicked in in early April to all slabs, cut down to one essential slab loop, topped up with the fire running quietly from about May to Sept, seems a pretty efficient system to me.
Yoday the bottom of the stroage tank is 35 deg, the peak input water temp from the collectors was only 54, and it's 19 now inside, 10 outside.
By the way, the heating conversion was only completed in 2008, so this is the first winter with it.
Anyone wanting more ought to send me an e-mail address with questions which I will try to answer, and i can send photos, specs of gear, etc to those who need it.
One day when i'm not busy I'll do some diagrams, and thermal calcs on yield, etc, but it's been decades since I did that part of my engineering quals.
JohnSamin
Member
An update on a solar hydronic installation I mentioned this post previously.
It's a lot of work! No wonder hydronics is so expensive!
At the half way point, 60 evac tubes installed and now heating. Installed 315ltr tank, controller + pump + built the custom hydronic controls. Taken 3 weeks - 1 week full time, remainder part time.
Pressure tested to 6bar and run it covered in 70% shadecloth to limit over heating.
System sitting at 60 degress tonight, not bad with 30% insolation - don't want too much heat/pressure too soon. Hot water is dangerous stuff...
Hydronic side next - Gas backup, 7 radiators, 100m Pex and loads of T joiners.
Will post link to pics and the temperature graphs soon.
Samo
IanHill
Member
On a recent open day of sustainable houses around West Gippsland, we saw a cheap room-heating idea that may be added to a home - a self-contained air-heating solar panel on the roof delivering through a bit of 50 x 100mm spouting reaching down low and into the living room, where it gently puffs in heated air, without any need for any other energy source. Can't tonite think of the concept's name.
Can e-mail a photo or 2 & perhaps dig up the owner/designer/installer's contact details if you're interested.
Andrew
Member
Does anybody have a view on using a in slab hydronic tubing to distribute the heat obtained by direct solar gain onto the slab. It would lower the temperature of the slab (and thus degrade the available energy) but also increase the heated thermal mass, and it may be possible overcome the energy degradation by increasing the window area (hopefully without overheating the rooms containing the windows)
ghostgum
Member
I did a calculation a few days ago on how much pipe I would need under a wooden floor for a solar hydronic system. I haven't got it in front of me, but I think with a 20C difference between water temperature and the outside of the PEX piping, the heat transfer was about 10W per metre of pipe. This calculation was based on the thermal resistivity of the PEX material, and working out an R value per meter of pipe. You would want 2 - 4 kW of heating, so 200 - 400m of pipe, at $500 per 200m.
With equalising the temperature between two areas of the slab, you are talking about a much smaller temperature difference. I expect that it would be no more than 5C, so you would need about 1km of piping.
A better method may be to use a heat shifter fan to equalise the air temperatures between the different areas.
Skysolarman
Member
ghostgum - Andrew
Rule of thumb for how much pipe you need for underfloor heating is 6 metres of pipe per m2 of flooring required to be heated , for efficient house heating you need approx 60-70watts per square meter...solar heating does not do it totally....to heat a 250m2 house for example you will need approx 16kw/p/h...a big ask in the middle of winter when you are asking your SWH to heat your domestic water supply as well , you would need about a 2500 liter tank to supply this amount of hourly output.
My belief is you can reach a compromise with solar water heating and other alternatives for hydronic heating..let me give you this case scenario..with a combo of double glazing , good drapes and specifically designed eves on your house that allows in all the winter sun to heat the space as well as preheat the slab and keeps out the summer sun will do the job . You would need a large solar hot water storage tank with a 10kw heat exchange coil to supply the underfloor its heat placed at a position where it would not suck heat away from domestic hot supply , you would need a reasonable solar array that could contribute 5-6kw/ph which equates to 25-30w per m2 input to the slab , your feet will be comfortably warm , the space temp a comfy 15-16 degrees and above all your ongoing costs at a minimum...
Note: Tank size V solar array is what its all about for desired output
ghostgum
Member
The required heat output depends on whether you run the thing all night, or whether you want to be able to come into a cold house and warm it up in a few hours.
In our case we have an existing radiant panel hydronic system heated with gas. This has about 12kW of panels for 220m2 of floor area. Last year's gas usage was $500 (plus the fixed service fees). We would probably only get half our heating from solar, so that's $250 per year. The cost of putting in a system would be $10k for a DIY system, and double this for commercial. It really isn't going to pay for itself.
A DIY system would be based on 8m2 home made panels on the north wall of the house, with direct water flow to a 2000l vented tank under the house, and direct water flow to hydronic pipes under a wooden floor. Putting insulation under the floor was hard enough. I don't like the thought of half removing it, inserting 400-1000m of stiff hydronic pipes, fixing these with aluminium plates to the underneath of the sheet flooring, then refixing the under floor insulation. The cost of electricity for the solar collector pump and hydronic pump is another issue.
Rather than using under floor heating, another option would be to use the existing radiator panels. For this I would need to heat the storage tank to 70C not 40C, and have a heat exchanger from the storage tank to the existing hydronic system (large coil of PEX piping in the tank), then add another hydronic pump and controller, and avoid it messing up the existing gas system. I might be able to do this for under $5k, which is still a 20 year pay back time.
dymonite69
Member
The main advantages of a hydronic system is avoiding the issues of a forced convection system. It is certainly no cheaper to run than using a conventional domestic heating system.
A standard commercial installation will cost $$$ particularly if coupled to a solar system.
The only way you can get enough solar energy during winter is to have a HUGE collector area. Even a 45 tube evacuated tube solar heater won't cut it.
What you need is a large absorber area and not the high temperatures that evacuated tubes can achieve. After all the floor only needs to be heated to around 27C. A solar pool heater covering most of the roof delivering moderately warm water is all you need to keep the floor heated adequately.
The better
JohnSamin
Member
Of course these systems are not cost effective at the moment. But I do expect that eventually energy costs will change that. But cost isn't/can't be the only reason you do something like this...
Some early pics...
EV Tubes (covered with shade cloth)
http://users.tpg.com.au/jksamin/hydronic2009/60_EV_Tubes.jpg
Home brew contoller and Hydronic pump...
http://users.tpg.com.au/jksamin/hydronic2009/Custom_Pump_Controller.jpg
Early days of install - hot water not connected
http://users.tpg.com.au/jksamin/hydronic2009/December2009.jpg
I have 60 tubes installed, even covered (70% shade cloth) the temp is hitting 70c on a good heating day. Though doesn't cut it fully covered when we have a cloudy day. So now I'm using one side covered one side open. Currently the solar pump is set to turn off at 85c, and get there every day. Zero Gas for hot water since commissioning. Seen the EV collector temp at 149c (Tank 85C at 3.5bar pressure) when cut off temp reached and still sun available. Pressure release at 6bar. Though this is summer....
My approach is designed to keep the large tank costs down by direct (excess) heat storage into the house at radiator temps (~70C). Even DIY its expensive at around $8K and counting.
System:
Small tank 315L + internal heat exchanger
Instant Gas heater
60EV tubes + copper + mounting hardware
2 pumps, 2 controllers. Controller 1 for Solar, 2nd for Hydronics.
7 Radiator Panels, Pex, T's, Expansion Tank, inhibitors, air bleeders, taps etc etc...
Plumber for hotwater connection to house.
Remainder labour DIY....
Winter:
Heat tank to predetermined temp maybe ~70C for hot water (have 50C valve).
Dump remaining day heat into house once tank reaches temp - the hydronic controller senses tank and house temp, won't allow the house to cook (wishfull thinking) or freeze. Thermostat + timed heating periods supported.
Instant Gas Backup on hydronic heating and hotwater.
Solar/Hydronic and hot water are separate systems joined via heat exchanger.
House Double Glazed, Roof R6, Walls Double Brick with insulated Cavity.
Doesn't require much heat.
Summer:
Cover the panels because I can't get rid of the heat at the moment
Maybe future heat source for ejector jet cooling or small pool.
http://solar-thermal.anu.edu.au/low_temp/solarac/index.php
The real test is yet to come...
ghostgum
Member
If the storage tank isn't pressurised, then a 2000l stainless steel water tank may be suitable. You then have to insulate it. My current thoughts are polyurethane spray on stuff, or standard batts with a wrapper of RFL. It depends on whether you can keep it out of the weather, which in my case is easy by putting it under the house.
Do you have slab or suspended floor? If the latter, you might be able to dump excess heat into the subfloor brickwork during Autumn to Spring.
With dumping excess summer heat, are you talking about heating a spa or small swimming pool?
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