some comments
even lower slab temp 35-40 would be plenty. the slab will certainly be safe at that (think how hot it gets in the sun with low ground temp under!). problems arise when there are large differentials between areas. but higher temps are avoided as its just uncomfortable and very noticable.
But If your house is well designed (layout, orientation and insulation) you wont need to be constantly crtanking the slab heating at high temps the lagre area will take care of it. basicaly slabs are not reactive i.e. you do not want to get home and go "its cold lets crank the slab" thats wrong and wont work as the slab is too slow...
slab heaitng (and cooling for that matter) should hold or balance the temp which works best if your house will not fluctuate too much (goes back to house design inc. insulation under the slab!)
if your house aint too good you need a system more reactive like maybe radiators or more reactive and faster still an air handler which will be the fastest way to use hot water.. but also has the additional energy requirment of the fan...
I work in HVAC design and Energy area and have some solar design exp and generaly people have a heat back-up somehow (i.e. NG).. but you dont have too just have to do good modeling if you want to know for sure your solar fraction.
solar hydronic slab heating revisited
(108 posts) (41 voices)-
Roger K
MemberPosted Saturday 2 Jul 2011 @ 5:12:04 am from IP # -
Moondyne
MemberI installed hydronic heating tubes into my house slab - 20mm low density polyethelyne tubing @ approx 400mm tube spacing . I have had it in for 15 years and have only connected it since last winter. First connected it to 40 x Evacuated Tube solar collectors. I found that this could only supply limited heat to one area - approx 4m x 4m. When the system was designed the target was to have 45oC water circulating which would give a Slab temp of around 27oC which should give a room temp of between 18 - 20oc. After some closely monitored trials I have found that the heat from the 40 X ET's would only provide between 3 - 4 kilowatts/hr on a bright day in winter when the sun was shining without any cloud cover. This heat was only produced for a few hours at the peak sun times and tapered off quickly after that.
This winter I have connected a wood fired boiler and this puts in about 12kw/hr of heat when fired up. This manages to heat the slab (approx 100m2) from 140c to 20oc after 8 hours of continual running. The temperature difference between the water into and out of the slab was approx 14oC.The circulation rate was approximately 15 litres/min.
I have decided to connect the Evacuated Tubes to provide domestic Hot water only.
I will purchase a 25kw Wood fired boiler to give me enough heat for the hydronic floor heating. (Rule of thumb is approx 1kw per 6m2)
The house has a 100mm concrete slab and there is no insulation under or at the edges. The walls are 350mm limestone and has 2.6m ceilings.
Winter overnight temperatures where I live sometimes get to nearly 0oC (20 days per year) although the days can often be clear and not much below 150c.
I hope this information assists.Posted Saturday 2 Jul 2011 @ 1:33:28 pm from IP # -
Thanks for sharing your hydronic data. There is so little real information out there that it is difficult to judge whether the idea is worth pursuing. Could you provide a little more information?
Is your house well insulated and gap sealed or would you consider it to be a difficult space to heat?
Did you use a storage tank within your system or just a direct solar collector/floor loop system?
Is the pipework between the collector and any storage or floor usage highly insulated?
Can you advise what part of Australia you are in?We are still deciding what heat source to use in our in-floor hydronics and hearing the experiences of others helps us make this decision.
Our climate in Sydney is mild and our building will be well insulated with double glazing and will have good passive solar gain. I'm wondering whether with this building design the additional load for the floor heating will be sufficiently low to allow us to use solar thermal collection (or possibly a heat pump coupled with renewable electricity).
Posted Monday 4 Jul 2011 @ 3:59:51 am from IP # -
sue03
MemberWe are trying to decide about installing in slab hydronic pipes for an area of 9m x6m (family room and kitchen) for our new house in Canberra. Is this area small enough to power the biolers with solar panels? If we use gas boilers I am told it will constantly be cutting in and out and will not be efficient -i.e. that the area is too small for gas boilers to power the inslab heating. Please advise.
Posted Sunday 24 Jul 2011 @ 7:29:34 am from IP # -
dymonite69
MemberLet us assume that you have a 100mm concrete slab which you want to keep within a comfortable 5 degree temperature range e.g. 17-22 degrees.
To heat the 100mm slab from 17 degrees at the beginning of each day during winter, you would need about 1030 KJ/m2 of energy.
A 300 tube solar panel during winter provides about 19000 KJ of energy. This would heat the about 17m2 of slab e.g. 4.4x4.4m room.
Assumptions
Volumetric heat capacity = 2086 kJ/m3/Kelvin
Canberra June Insolation= 2.3 kWhr
ET panel efficiency = 80%
ET Aperture area = 2.8m2
Water inlet temp = 13 degreesAssuming the heat stored in the slab during the day is lost into the subsoil by the next day. Which is suggested by Catopsilia's graph.
2 KJ/m3
Posted Sunday 24 Jul 2011 @ 9:48:50 am from IP # -
ghostgum
MemberIf you have enough sun to heat the slab (more likely in Canberra than where I live in Melbourne), then can you arrange for the sun to fall on the slab itself?
The days on which you really want the heating are when it is overcast for several days, and solar won't help much.
Would an air sourced heat pump do the job instead?
Posted Sunday 24 Jul 2011 @ 12:25:17 pm from IP # -
TonyT
Memberdm69
Following from your post:
"300" tubes seems very high: Did your typing finger add an extra zero ?
In a Canberra winter the heat captured by 30 Evacuated Tubes would total 19,000kJ = 19MegaJoule per day = 5kWhr/day. (because one kWhr = 3.6MegaJoules)
If the solar heat was used to replace heat from an electric resistance heater using electricity that costs 20cent/kWhr, then 5kWhr is worth 5kWhr x 20cent/kWhr = $1.00/day.
A heat pump can deliver 3kWhr of heat by using 1kWhr of electricity.
If the heat captured by the ET solar water heater replaces heat provided by a heat pump that uses low tarrif electricity then 5kWhr of heat uses 5/3 = 1.7kWhr of electricity which is worth 17 cents/day if electricity costs 10cent/kWhr.
Without a tank and excluding any installation costs, the cost to buy a 30 evacuated-tube solar collector complete with a manifold and a mounting frame is $1,500 to $2,000. The price depends on whether the ET tube is filled with water or has a copper pipe holding a fluid that evaporates and condenses.
More data is posted at
http://www.ata.org.au/forums/topic/2135#post-20095
A 100mm concrete floor-slab could be insulated underneath by pouring the slab on top of a layer of ? 50mm styrene foam.
For 50mm thick styrene foam the cost ranges from $20/sqm for expanded foam with a low compressive strength of 60kPa and a thermal resistance R = 1.22 up to to $40/square metre for extruded foam with high compressive strength of 300kPa (will support a forklift) and R = 1.78. The cost of 50mm glass fibre insulation is ? $5/sqm but it has zero compressive strength so that a frame is needed to support the weight of the concrete.
For R = 1.5, the heat loss, U = 1/R = 0.7Watt/sqm/degC.
I am investigating attaching the in-floor hydronic pipes to ? ringlock sheep fencing mesh that is laid on ? 50mm thick polystyrene foam then covered with a thin layer ? 20mm of ? concrete/mortar/Dri-bond (small aggregate perhaps re-inforced with glass-fibres) then topped with a wood "floating" floor or with masonite then carpet.
My goals are (1) to minimise heat loss to the ground and (2) to minimise thermal mass so that I can more quickly vary the temperature of the floor and hence of the room.
When our room is not being used it does not need to be kept warm and costing us for the lost heat.
Posted Sunday 24 Jul 2011 @ 9:56:25 pm from IP # -
Samo
MemberFolks
My solar hydronic system has been running over winter, and now my control system is collecting the information I need to prove just how hard it's working for me. There's a graph along with the story that shows the temperature fluctuations as this system works. Next winter I'll have full temperature stats...http://www.shmeco.com/shmeco-story/1282/Automating-and-controlling-things-you-build/
The details of this system are
60 evacuated tubes
315 litre tank (max 75 degrees C)
24 litre expansion tank
9 Radiator panels
domestic hot water loop
pool heating loop
Control System with Smart Phone ControlSo bottom line is we can collect around 20kw of heat during the day, doesnt matter if the heat is used for hot water or house heating - as long as we use solar heat before burning gas...
My system definately works well... payback time will be long but it has been so much fun to build I don't really care!
Samo
Posted Monday 19 Sep 2011 @ 10:47:29 am from IP # -
That looks like a very cool project. I would really like to learn more about what you did and how you did it. Some time before next winter I'd like to go through the process of installing the heat supply side of our new hydronic heated slab here in Sydney. I was thinking about putting in a very basic evac tube and storage system controlled by thermostats but your Control by Web features would just make it so much more awesome. Do you have a web page showing more information?
Posted Tuesday 20 Sep 2011 @ 1:45:50 am from IP # -
Samo
MemberHi Munter
Sure that sounds like a good project too. I don't have a detailed technical description in the form of a web site yet, just some design drawings and spreadsheets. I do plan to publish more, but I need more stats to show the real story and that's going to take some time.
Samo
Posted Tuesday 20 Sep 2011 @ 8:32:30 am from IP # -
bholmberg
Membergreat forum... i'm convinced and have purchased my radiator panels, and 2x quantum titan heat pump hot water systems. (i've got solar panels up at the 66c rebate and have all day off-peak for hot water being in country victoria with no natural gas)
my question is what do i need to do now. here is my thoughts (beast on web research) below, please correct me if i'm wrong, I want to be clear on how the system works before going ahead with the installation:
- I need to fill the tanks with water and some glycol product to inhibit any corrosion.
- I need an expansion tank somewhere high to remove any air in the system so it needs to be higher than everything else?
- then I need 2 circulator pumps for my 2 zones, each switched on off manually?
- pipe through to the panels (I have thermometer controlled taps for each panel)
i've done a little sketch which may help which is here: http://99sg.com/brett/hyd_details.jpganother question... is this expansion tank something special? if so can someone provide me with an example or a size i would need. or is it just the same as an expansion tank in a car just a little tank to hold extra water with expansion? i did consider putting a car radiator cap that would open under pressure and suck back from the expansion tank again if needed. Also is it better for me to put the expansion tank on the return line to reduce heat loss?
i'm planning to simply turn off the heat pumps during summer. is this going to create maintenance issues?
as a side not, i purchased rusty old second hand radiator panels and got them acid dipped and powder coated. they look better than new and cost me $900 for 10 large panels (which leaves me with spares). I also picked up the 2x 2 year old quantum titans from a friend who runs a hotel and is switching to natural gas as 8x of the quantum titans weren't providing enough hot water for all the rooms. brings me to total cost so far of $1500. great value if you ask me!
keep up the posts guys. I really see huge potential in solar hydronic, and hope if gains some more main-stream momentum
Posted Friday 10 Feb 2012 @ 11:56:59 pm from IP # -
TonyT
Memberbholmberg asked:
" is this expansion tank something special?"
When the temperature of water changes, its volume changes.
The pump-system that is fitted to provide the pressure for a house that uses rainwater includes a small tank fitted with an internal membrane. A similar tank is fitted in the hydronic heating circuit. The size of that tank is chosen to compensate the change in the volume of water as the temperature varies in the closed hydronic heating circuit.
The hydronic circuit also needs to include automatic air-release valves and fittings so that it can be topped up (preferably automatically) if any water is lost from that circuit.
Posted Saturday 11 Feb 2012 @ 10:10:52 pm from IP # -
bholmberg
Memberthanks Tony. so the details in my drawing are correct? do I need a particular type of expansion tank? if so what size?
are the are release valves the ones on the panels themselves? or is this a separate system that i've missed? can i simply 'top up' the system through the expansion tank in my design? is there a better design available? i've heard something of open circuit hydronic heating systems. does that just mean its open to the air and the expansion tank is unpressurised?
appreciated.Posted Sunday 12 Feb 2012 @ 5:44:49 am from IP # -
bholmberg
MemberMaybe, but that sounds like no fun at all, and i've tried to find a 'professional' in the area, all i can find is 'I'll give it a go' tradies. Plus i'd really love to really understand the system so I can run and maintain it with excllence and efficiency. Maybe even revise and perfect the system over the years. Still Tony, I appreciate your input.
Posted Sunday 12 Feb 2012 @ 10:29:40 am from IP # -
TonyT
Memberbholmberg
If you use the search tool at the top right of this forum you will find the many threads that discuss hydronic heating.
Here are some starters
http://www.ata.org.au/forums/topic/2135#post-18652
http://www.ata.org.au/forums/topic/7#post-17267
http://www.ata.org.au/forums/topic/1832#post-17158
http://www.ata.org.au/forums/topic/635#post-16519
http://www.ata.org.au/forums/topic/1713#post-16204
http://www.ata.org.au/forums/topic/620#post-15492Posted Sunday 12 Feb 2012 @ 8:50:47 pm from IP #
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