I think it's been a year or so since the last discussion on this in this forum and I'm keen to learn of anyone's success with heating a slab by mostly solar means - or heat pump. Currently at that stage of structural plans where I need to really decide on slab heating or not... maybe I should just put the tubes and manifold in and decide on the means to heat the water later... Evacuated tube with an electric booster seems most likely (no town gas - and suspect too much boosting required for bottle gas). Does anyone have any experience with the water temps required to maintain a slab to provide a room temp of say 20 degrees during a cold winter day? Will I even need it in a strawbale house? Keep up the good info and green thoughts!
solar hydronic slab heating revisited
(111 posts) (43 voices)-
ghostgum
MemberI have no experience with it, but I have read a little about it.
A solar hydronic heating system is effectively using sun falling on the roof area to heat the slab underneath. If you can get enough sunlight to heat via hydronic, then you can probably get enough sunlight through windows onto the slab to do it almost as well. In other words, by appropriate use of windows and eaves, you may not need a slab hydronic system in Australia. I would look first at a well insulated slab, double glazed windows (if using aluminium frames, use thermally broken frames if you can get them in Australa), and clerestory windows letting light onto an internal brick or stone wall to get heat into the middle of the house. You may find that these sort of measures are cheaper than a slab hydronic system. You may want an additional fast response heater for mornings.
I've read that radiator panel hydronic systems require the water heated to about 70C, while slab systems require the water to be heated to about 40C. If using a ground source heat pump (again not common in Australia), this difference changes the efficiency factor from 3 to 4.
Another heat source would be wood pellets.
http://www.ata.org.au/branch-news/melbourne-branch-next-meeting-15th-april-alternative-fuels-for-heating-and-transportI've got a radiator hydronic system driven by natural gas.
Posted Friday 15 May 2009 @ 1:13:05 am from IP # -
I too am interested in solar hydronic heating. The advances in evacuated tubes must make it more technically viable than it was previously due to the higher output temperatures achievable but from what I've read it is still not viable from a simple cost perspective.
I think the advice that using direct gain through architectural means is more efficient is probably correct. If you are at a design stage then you have an opportunity to realise this efficiency.
As I have limited opportunity to change the house design the thought of having a large thermal store of water sitting ready for use under the house at any time chosen by me appeals more than just going with daily heat/cool cycles.Posted Friday 15 May 2009 @ 2:21:40 am from IP # -
Mike,
The slab heating thing got a bit of a run recently in another thread - 'New green house, best way to heat and heat water'.Of course, it depends on where your site is, it's orientation and Winter cloud cover as to whether a slab heating system is likely to be required.
IF your site has a Northern outlook and Winters are generally sunny, then there's no reason not to do a typical passive solar house - with all the features ghostgum and munter mention. The main efficiency benefit of strawbale walls is their excellent insulation. So a sensibly designed passive solar place with your well insulated walls in such a location shouldn't need slab heating.
IF your main view axis is South, and it's sunny enough in Winter, and you still want a passive solar house your overall glass/floor area ratio will get driven upward as you want view windows and sun access windows. This is fine if you don't mind using very high performance windows. Thermally broken frames are available here, AWS (Vantage) have a range called 'Thermal Heart' http://www.awsaustralia.com.au/
In such a scenario a compromise between building performance and extra heat input may be reasonable.IF your site has limited Winter solar access because of overshadowing or near constant cool season cloud cover passive solar won't work. Then you really will need a supplimentary heating system. If your site falls into this category where there isn't enough sun for passive solar, then plainly solar anything else will be compromised as well.
A client of mine looked into a ground loop heat pump for their house at Gloucester in NSW - in the end deciding the near $20k price was too much for 2-3 months of the year. (The potential supplier was from Cooma, where such systems are probably very practical) If your site is cold for 6-7 months of the year too such a system probably makes more sense.The site really is the determining factor in these things.
Posted Friday 15 May 2009 @ 3:39:02 am from IP # -
hawk
MemberGhostgum, with your clerestory idea, wont you lose as much heat through them at night as you would gain from having them? If they are double glazed will that offset the loss, or will you need some sort of cover at night to stop a thermal updraft?
I have now been looking at Hydronic Slab heating after getting no solid advice on GS heat Pump to heat the slab and it being confirmed around the 20K mark.
I have a tall treed site, often under a cloud and am unsure that I will get full sun onto the North Slab so I dont want to freeze in winter.
I also find the installer/suppliers a little mysterious and I am not that confident to take the leap of faith for 20K.I am told solar slab heating 'doesnt work'(cant find anyone to back this up though either way), so I am also looking at an instantaneous Gas heater/or Heat pump directly into the Slab. (10-12k, installed) The Heat pump is green, but more expensive up-front, aparently delivering a 10% better efficiency, however its a long time to get a return on that, so maybe in the scheme of things, I'd be better putting that into more efficient product elsewhere.
The other thing is I havent found any info on running costs, although I am 'told' that its very efficient.
Does anyone have any stats/info/experience on running costs?Posted Thursday 28 May 2009 @ 11:11:06 am from IP # -
ghostgum
Memberhawk, yes you will need to use double glazing with well insulated window frames. It is a trade off for the heat gain during the day vs the heat loss at night.
Have a read of
http://www.ata.org.au/forums/topic.php?id=7&replies=5Posted Friday 29 May 2009 @ 1:28:22 am from IP # -
Greg
MemberGood to see other people interested in solar Hydronics. I'm looking at options for heating and I'm waiting on a quote from http://www.urbanenergy.com.au/ . They have affiliates in Germany and offer their products here. The LATENTO heat exchanger looks a clever solution to multiple hot water demands at different temperatures. They offer all the solutions to hydronic heating and I have my fingers crossed.
I attended a presentation recently by an eco-architect from Armidale where they installed a solar evacuated tube system to hot water radiators with good results.
I have had quotes for Ground sourced heat pumps and gas boilers to heat a slab and radiators. Like the comments made in this forum, the prices are far to high to warrant installation.
Since I was going to install solar hot water anyway, I am hoping the incremental cost to go for slab heating is not excessive. I have very good solar aspect and the building will be primarily strawbale (so good insulation)and timber framed double glazing will help. As information comes in I'll let the forum know if they are interested.
Posted Wednesday 3 Jun 2009 @ 5:46:16 am from IP # -
I think the incremental costs will still be reasonably significant. Using solar hydronics will require a larger collector area than a solar hot water system so you'll probably need multiple sets of collectors. There are some cheaper ones coming out of China which don't qualify for the rebates and perhaps you could use these to keep the costs down.
I'd be very interested to hear how it turns out - please keep us informed.
Posted Wednesday 3 Jun 2009 @ 11:26:08 am from IP # -
rosandcarl
MemberWe have a big, old, two storey, house with high ceilings and no original insulation in Southern Tasmania, we have insulated where we can and we burn over 15 tonnes of wood a year for heating and hot water and the house is still far from warm.
The good thing is that we have a hydronic system installed and a good solar aspect. What I want to do is boost the system with solar and or a heat pump. I have read that a heat pump will only operate 1 or 2 radiators but I believe heat pumps come in a range of sizes. I am interested in the Armidale presentation that Greg mentioned 5 days ago and if anyone has combined evacuated tubes with a heat pump to supply home heating quantities of hot water.Posted Monday 8 Jun 2009 @ 1:19:52 pm from IP # -
Joel
MemberWe are in the process of getting a solar hydronic slab system. We paid to get the pipes put into the slab before we were certain we would go ahead with it (a bit over $2000). In the end we went ahead with 60 solar tubes and a gas booster on a 750 litre storage tank. The system supplies hot water and heating to the floor.
So far we have not seen a great deal of benefit. The solar tubes are not supplying enough energy to keep the water hot let alone heating the floor. We may have been too adventurous trying to do everything in one system. We are hoping that the issues we are experiencing are teething problems and that eventually we will get the settings worked out. One of the biggest issues we have had is that the installer is so busy we are having real problems getting him back to look at what if anything can be done even though we still owe the bulk of the cost of installation.
Posted Tuesday 9 Jun 2009 @ 10:43:15 am from IP # -
Greg
MemberHere are a couple of sites that offer some technical information about evacuated tubes. Perhaps there are some mathematically inclined individuals that can do the math to determine how much hot water you can generate with your system (in theory)
http://www.solar-heating.cn/Tech.asp <- shows how much energy is captured and converted
http://www.apricus.com.au/collector.htm <- gives solar collector areaLots of variables like how much solar and for how long and also the cold water temp so trying to do the cals without this info means it can be radically out. If you can make the measurements and/or assumptions yourself you can get an idea of what the systems is capable of doing.
Posted Wednesday 10 Jun 2009 @ 12:35:24 am from IP # -
ghostgum
MemberJoel,
Some information that I've read in various places:
Hot water needs to be about 60-70C, reduced to 50C for bathrooms.
Hydronic radiator panels use water at about 70C.
Hydronic slab heating uses water at about 40C.
So the water temperature for your household hot water use and slab heating are different.The system I saw described in ReNew magazine (issue 95, pages 31-33) used a large open vented storage tank, and inside the tank there were heat exchange coils for the hydronic, hot water and evacuated tube panels.
One system used 8 by 12 tube panels, and 1200 litres of storage.
http://shop.ata.org.au/cart.php?target=product&category_id=300&product_id=16400Posted Wednesday 10 Jun 2009 @ 12:41:14 am from IP # -
Greg
MemberAnyone feel like becoming a solar tube importer ? Wonder if it would work out same or cheaper ?
# Triple Vacuum Evacuated Glass Tube 25- 40% more efficient. Not sure about that but web site is here...
http://ateliving.ecrater.com/product.php?pid=3767557prices on the web site are staggeringly inexpensive. (no shipping and USD of course)
http://www.heliosray.com/home.phpPosted Wednesday 10 Jun 2009 @ 2:29:22 am from IP # -
hawk
MemberJoel, thats sad news. There is so little information around on these things, other than mysterious websites, so its good to hear of your actual experiences.
I am told that insulating the slab, then installing the pipework makes it around 20% more efficient. Did you do that also?
In terms of the installer, would you have done things differently in retrospect?
Did you look at any actual installations prior to making the choice?
Would you recommend anything in hindsite?Posted Friday 12 Jun 2009 @ 10:39:10 pm from IP # -
norbert
MemberI believe when heating is required most (winter)the sun is not strong enough to heat the amount of water required to run a hydronic system during the day let alone at night.I suspect to make this system possibly work you would need a huge storage tank fed by a huge amount of glass tubes.
The cost for a system like this would be out of reach for most of us.
Our hydronic heating has a flowrate of some 30ltrs per minute.So even if you had a 1000ltr hot water storage tank and enough sun during the day to heat the water then on a night within half an hour the hot water would be used and then back up is required.
We have decided to go with a conventional hydronic system using an efficent boiler to heat the water and keep our domestic hot water seperate by using 30 evacuated glass tubes.Solar hydronics sounds great but at the moment I don't see how this could practicly work.Posted Saturday 13 Jun 2009 @ 3:22:10 pm from IP # -
Benny
MemberIt shouldn't be hard to estimate just how much heating effect you will get - or at least the max possible. Whatever area the tube array is will probably collect no more than 5-600 W/sqm. And thats peak - multiply by a cosine rule for angle of incidence, say 10hrs of insolation (winter), and the max possible would be about 3.2kWh per sq m. So like having a 1kW fan heater on for 3 hours. How much concrete slab or room air would that heat up ?
Posted Monday 15 Jun 2009 @ 12:20:43 am from IP # -
ghostgum
Membernorbert, I think the calculation should be different. The water is pumped from the tank to radiator panels, loses some heat in the panels, then returns to the tank at a lower temperature. You don't use up all the water in 30 minutes, but you do lose temperature from the tank. The hydronic system may also not pump continuously.
The specific heat of water is 4.186 joule / gram / degree Celcius.
Raising the temperature of a 1000 litre (kilogram) tank by 30C is 126MJ.
I use a temperature change of 30C, on the assumption that water at 40 to 70C would be effective in hydronic radiator panels.Collection calculation:
Assuming solar collection of 1kW/square metre and 4 hours of strong sunlight, gives 1000 * 4 * 3600 = 14.4MJ per day. So you'll need about 10 square metres of collection area to warm 1000l of water by 30C on an average day.Usage calculation:
My house has about 14kW of hydronic panels. These will consume 126MJ in 126000000 / 14000 / 3600 = 2.5 hours. I know from experience that about the house needs less than half this to maintain the room temperature in the evening, so you should get at least double this.There is also the question of whether you would use the heating more in the morning (before sunlight through the windows starts to help), or in the evening after dark.
The article in ReNew 95 effectively said that it doesn't make economic sense to use solar hydronic in the city, but if you were in the country in a sunny area and were paying for bottled gas, then it might be different.
Posted Monday 15 Jun 2009 @ 1:35:57 am from IP # -
ghostgum
MemberSome more rough calculations:
Specific heat of concrete is about 0.9.
Density of concrete is 2400kg/m3.
Slab 200m2 area by 0.1m thick = 20m3 volume.
If slab is warmed by 5 degrees (e.g. by the sun), then heat required is 20 * 2400000 * 0.9 * 5 = 216MJ.So this is of the same order of magnitude as a 1000 litre tank of water warmed by 30 deg C (126MJ).
Letting sufficient sunlight fall on the house slab is usually considered a better solution than add-on heating.
Posted Monday 15 Jun 2009 @ 3:43:11 am from IP # -
Interesting stuff folks.
The standard wisdom that a 'slab on ground' structure is the best option for efficiency only makes sense if the slab isn't freezing cold. If the location requires that the slab be thermally insulated from the ground, and the design doesn't allow Winter solar access to a large portion of the floor, then I wonder how much thermal good the 'cold' part of the slab is doing.
As Ghostgum's figures indicate raising the temperature of a whole floor slab by a small amount takes a pile of energy.
I've got a glassy little house nearing completion on an ideal North facing unshaded slope and the Northern half of the narrow floorplan is barefoot comfortable in the evenings, but the Southern half isn't! In our (relatively) mild climate it works fine.In a more difficult climate perhaps the ideal is a slab on the sunny Northern side of the floorplan and a lower thermal mass floor (which is more easily heated) on the 'cold' side of the house.
All this is fine if starting from scratch, but if presented with a real heating challenge like rosandcarl's it looks like a 'high tech' answer is the only solution.
Posted Monday 15 Jun 2009 @ 9:03:54 am from IP # -
beninthesouth
MemberHi Mike and others.
I have been working on the practicalities of thermal collection for the last few years.
The idea is basically to incorporate cost effective collection, into an insulated roofing panel.
I am about to start manufacturing functional prototypes in South Gippsland and can supply some components.
There is some more information at absorberroof.comPosted Saturday 27 Jun 2009 @ 6:07:26 am from IP # -
Camilla
MemberI had always assumed that solar would not provide enough for hydronic heating as well as domestic hot water, so had planned to use evacuated glass tubes for the domestic hot water, and an air source heat pump for the hydronic heating. Does anyone know anything about air source heat pumps for heating? I was hoping to use one (or 2) for the heating in winter and for the pool in spring/autumn. Thoughts?
Posted Sunday 5 Jul 2009 @ 12:22:18 pm from IP # -
Camilla,
Is your project in Sydney a refit/upgrade of an existing house or a new build?If it's an upgrade, a heat pump system (or two) may be cheaper than simply fixing the house to make it work properly, as is often sadly the case with older buildings.
Renovations cost money, and depending on the design, can decrease energy bills for the life of the building.
Bolt-on solutions cost money too, and nearly always increase energy bills for the life of the building.If it's a new build, unless your site is extremely compromised, I'd be surprised if a properly designed passive solar house didn't achieve all that you want to achieve.
A decent pool cover will extend your swimming season into Autumn, though it probably won't do much for Spring.
Posted Monday 6 Jul 2009 @ 12:25:06 am from IP # -
f2design
MemberWe have a solar domestic Hot water system 60 Apricus tubes, combined with hydronic slab heating using wood boiler backup with a 400l storage tank. The system is installed in an 8 star passive solar house with prime north solar access in the Cape Otway climate zone. The boiler a Farmar SV 20,000 has a peak performance rating of 20kcal/hr or 23.2KW with a burn efficiency of over 70% heating 640 l/hr to 70degC. It sits as a room divider fireplace with an exposed flue in the living room but as it is designed primarily as a boiler it contributes much less radiant heat to the room than a traditional slow combustion heater.
No backup was needed for hot water during summer. I even made a shade cloth for 1 30 tube panel.
Getting the building fabric thermal performance right is the most important starting point. This is the first winter season of occupation. The house has not needed any backup heating during the day yet. On clear sunny days the inside air temp gets down to 15C at sunrise warms throughout the day in sun to mid to high twenties and in overcast to around 20C. Night time boosting is not needed on sunny days. Night time boost on coldest overcast days can amount to a burn of approximately 3 hrs. This provides for evening comfort and ensures hot water for morning showers by turning off slab pump before going to bed.
Comfort is achieved with slab at 20C and air above 17-18C. High performance building fabric means that slab does not need to be heated as much as is our experience with designs of lower performance.
A reforestation program on the site will sequester more CO2 than will ever be emitted from burning sugar gum timber grown. CSIRO research indicates this scenario can work on sites of over 2 acres creating a totally self-contained energy system.
The full system for a 180sqm 3 bed house was not dirt cheap at $23,000 but the costs are almost zero (chain saw $) from here on.
Posted Tuesday 7 Jul 2009 @ 6:29:27 am from IP # -
springtide
MemberHey f2 design, gotta ask who did your system? - we are in the process of buying a block south of Hobart and would like to incorporate solar/combustion hydronic heating into our house design (not 100% passive solar due to north east views but R8 roof and walls with 4kw grid feed). Any names or links would be of great assistance.
Cheers!Posted Friday 31 Jul 2009 @ 1:50:18 pm from IP # -
f2design
MemberSpringtide
We worked with local contractor interested in sustainable installations, Sunworks Eco Plumbing. Concept of the system was part of our integrated house design and Joe brought his technical expertise to the project to deliver the completed system. It was his recommendation to use the Farmar boiler although it was the first time he had installed one. It was a good call as it is a high performance boiler, not just a slow combustion heater with a wetback and seems to work extremely efficiently.
Posted Friday 7 Aug 2009 @ 12:05:03 am from IP # -
I believe that heating with radiators instead of slab heating is the more efficient way of heating a house in a warm climate like Sydney. There is only a little bit of heating in the living room required. No need to heat the bed rooms. Just cover yourself.
I am importing radiators that can be connected to the hot water tank because the water comes only in contact with copper pipes inside the collector. It should work especially well with oversized slar hot water systems or with heat pump systems. Heat pumps can supply additional heat as required. The only downside is that the radiators do not have approval according to Australian standards (Watermark) yet.
I can also supply low cost collectors imported from China. Unfortunately they do not qualify for government rebates and RECs because they are not certified to Australian standards.
Posted Friday 7 Aug 2009 @ 6:36:44 am from IP # -
IanHill
Membersee also my reply on solar angles. Our solar system heats the living and entertaining parts of a large, multi-level home very well. It's boosted a little by a heat exchanger in the wood fire flu, and I seldom need to add gas to keep much of a 54 sq home at 18 deg or so right thru winter. We also power a 2m high water-heated towel rail.
the real tricks are getting the number of evac tubes right, getting a large water storage, getting the pump flow rate right, and sensible thermostat program settings.
Posted Thursday 13 Aug 2009 @ 12:10:36 pm from IP # -
IanHill
MemberP.S our hydronics, built in 1978, take water from the solar storage mixed to 25 deg C, and today the water is leaving the slab at 15 deg c. Flow rates thru the slab tubes are important for heating and keeping down electrical consumption. A bare foot test shows how even the slab heating is.
Posted Thursday 13 Aug 2009 @ 12:16:18 pm from IP #
