Hi! I just asked a question about solar HWSs and now I'm moving onto home heating. The house I am building near Wollongong is only 100sqm, and is light-weight construction but will be well insulated. I am thinking about heating it with hydronic radiators powered by an electric heat pump. Does anyone have any tips on what I should look out for when choosing my system? Or, for that matter, any alternative options I should consider to heat this little house? I am not planning on having gas connected to the house. Thanks very much!
Hydronic radiator heating using electric heat pump
(31 posts) (13 voices)-
David
MemberI'd use a heat pump or chiller system store the heat having it driven by Solar power, storing the hot water or coolant in a large insulated storage tank, then simply use the hot/cold liquid at night to maintain temperature accordingly.
In fact I'm doing a version of this for both heating and cooling in our house which is still to be finished.
However our slab is no longer using hydronics embedded in it. I found an alternative that is more cost effective and the installed cost is slightly lower to boot.
My design, also used for cold room refrigeration as well house cooling, house heating (there's 2 sides to a heat pump/chiller system) all only using power derived from Solar during sunlight hours to drive the entire system, except for after sunlight hours where at most a couple small circulating pumps move water or coolant or fans as needed do the rest of the work using only very small amounts of power. Stored heat and cold adds up to an excellent place to store lots of excess energy that would otherwise be unused and therefore wasted.
It's a lot more cost effective to store electrical energy in the form of heat/cold if you can do it, not to mention a lot cheaper in the longer term rather than buying much larger capacity batteries.
Posted Tuesday 3 May 2016 @ 12:06:31 pm from IP # -
scott drew
MemberIf you are getting a heat pump for hydronic perhaps use it for your hot water too instead of solar. Use the space you save on the roof for solar electric panels to power the heat pump.
Posted Tuesday 3 May 2016 @ 11:06:35 pm from IP # -
Bushwalker
Memberscott drew said:
If you are getting a heat pump for hydronic perhaps use it for your hot water too instead of solar. Use the space you save on the roof for solar electric panels to power the heat pump.Good plan.
Also worth thinking about using PV to run the heatpump for storing hot water. Timeshift the energy for evening and morning use. Needs a big and highly insulated tank.
Has anyone done this yet?
Posted Wednesday 4 May 2016 @ 2:20:43 am from IP # -
scott drew
MemberVLJhouse,
I have a siddons solarstream heat pump for hot water heating. I've had it for 8 years so its a different model to what's available today, but same principle.
Its a stainless tank, well insulated, for the hot water storage. It sits in my garage. The compressor unit, much like an air conditioning system, sits outside the garage in open air.
I have a 2.2kw solar pv system on my roof which almost covers the electricity required by the compressor. I can set it on a timer for turning on during daylight hours or have it running at night on off peak, or a combination of both during a 24hr period depending on my hot water needs.
They're an Australian company based in Victoria, although not all components are made here... I doubt many heat pump bits are made here... but I could be wrong.
I think their solarstream may be hydronic friendly. A google search will find them or just give them a call.
I used a local to me solar installer who had been in business for over 25 years. Stayed away from young companies just in it for subsidies, but that was in the days of crasy feed in tariffs. Not sure there's many companies like that still around. I'm in Sydney so that installer probably no use to you.
Posted Wednesday 4 May 2016 @ 4:35:08 am from IP # -
arttt
MemberIm also interested in answers about combined domestic hot water and hydronic heating from a heat pump.
Last time i looked the heat pumps seemed expensive (to me) just to run for an hour a day to cover domestic hot water needs but if they ran much longer to do double duty for space heating then the cost seems more reasonable.
The sanden heat pump has a COP of 4.5 in its brochure. If it ran 24 hours a day it could provide about 100kWh of heat. My house uses well less the 10kWh of heat for domestic hot water so there is about to 90kWh of spare capacity. Assuming the heatpump is ok running on a high duty cycle.
You would need to do a heat load calculation for your house to be sure there was enough capacity in the system. It starts getting more complex and expensive if you need bigger or multiple units.
Posted Wednesday 4 May 2016 @ 5:25:15 am from IP # -
VLJhouse
MemberThanks again Scott. I really appreciate your contribution. I've made contact with Siddons so hopefully I'll hear back from them soon. I would be interested in getting the name of your installer off you just in case they come down this way - or they may recommend someone who does. Thanks, Vanessa
Posted Wednesday 4 May 2016 @ 10:40:03 am from IP # -
I'd keep away from domestic hot water units for hydronic heating - they're aren't designed for the work load and something like the Siddons won't give you nearly enough heat to run a decent system.
I had a 10kw heat pump installed for our hydronic system and it's working well. We are in Bowral so much colder than Wollongong.
I learnt a lot from the install - PM as there is a long story!
Posted Wednesday 4 May 2016 @ 6:43:35 pm from IP # -
Oh and you can't 'run' a hydronic heat pump off solar unless you have a huge pv system. They draw too much power and often when you need heating the most it's because the sun ain't shining! For domestic hot water sure, but not hydronic heating.
Posted Wednesday 4 May 2016 @ 6:46:08 pm from IP # -
arttt
Memberdarrynm said:
I'd keep away from domestic hot water units for hydronic heating - they're aren't designed for the work loadIs that just a guess or do you have a data point or 2 for that? Ive seen online examples of people doing this and photos of rather complex looking installations with multiple domestic hot water units set up for hydronic heating.
I think your correct to be wary of the work load/duty cycle issue but its not much different to a RC air con running 24/7 in the tropics.
The issue of producing enough heat just depends on the house. It sounds like darrynm needed a 10kW system so he is right a DHW is unlikely to suit him. However, it is just a case of making sure the system is sized for the heat load of the house on the coolest most overcast days. I cant see any reason that a small well insulated house cant have a heat load that is well below what these DHW heat pumps can produce.
All that said im no expert and haven't jumped in and brought/built a system yet. Its a lot to get my head around. radiator sizing, pumps,valves, heat exchanger, storage tanks, control system to make sure hot water needs are met before heating etc etc.
Anyone interested in this its worth looking through some of darrynms old threads. He asked questions around this a few years ago and got some good responses including some helpful calculations.
Posted Thursday 5 May 2016 @ 1:30:07 am from IP # -
Bushwalker
MemberSiddons bolt-on details: http://www.siddonssolarstream.com/wp-content/uploads/2015/07/Siddons-Bolt-on-Heat-Pump-details.pdf
Rated input power: 0.97KW
Rated input current: 4.4ASo basically, we are looking at a 1000 watt load @ 240V
Our solar is currently putting out over 4000 watts. I think a Siddons bolt-on heatpump would do the job on a sunny winter day as long as you have adequate solar panels installed.
For tanks, there is a well known 'Run on Sun' supplier. You can find lots of toys including tanks on their Hydronic heating page:
http://www.runonsun.com.au/yes/Hydronic_heating.htmlPosted Thursday 5 May 2016 @ 2:29:30 am from IP # -
arttt said:
Is that just a guess or do you have a data point or 2 for that? Ive seen online examples of people doing this and photos of rather complex looking installations with multiple domestic hot water units set up for hydronic heating.I don't have anything I can quote, but it's the conclusion I came to after talking to several well known heat pump sellers in Australia. You certainly can daisy-chain smaller units designed for DHW to achieve an output equivalent to a hydronic heat pump but I think it's reasonable to expect decreased life span of the units....which are pretty expensive to start with!
As you mentioned I have asked a lot of heat pump related questions in the past on this forum and went through quite a process to have one installed at our place. The expense was well on the high side even with an exisiting radiator setup - putting a few reverse cycle air con units or just running small fan heaters might have produced a similar result purely on cost
Happy to answer any questions about what we did.
Posted Thursday 5 May 2016 @ 3:27:03 am from IP # -
arttt said:
The issue of producing enough heat just depends on the house. It sounds like darrynm needed a 10kW system so he is right a DHW is unlikely to suit him. However, it is just a case of making sure the system is sized for the heat load of the house on the coolest most overcast days.Indeed. You've got to look at this very carefully and it's generally considered better to oversize your units and run them easier than the other way around. A Siddons draws around 1KW so at say COP 3 it will be producing 3KW of hot water being outputted every hour.
Sure you might be able to get a big water tank and run the heat pump overnight for example to store some heat and release more than 3KW in an hour, but realistically I think you're expecting a 3KW output unit to heat a whole house! If you have a VERY small house and/or it's super insulated or gaining heaps of passive solar it might work....but I'd be quite sure 3KW ain't going to effectively heat 99% of homes in Australia.
In terms of practical use most people want to turn on their heating and within 15mins the room to be warm right? A 3KW unit is not going to achieve this, even with storage. Remember also that a DHW heat pump will max out at 60 degrees, whereas most radiators are rated for 80 degrees....so you'll need to supersize your radiators = cost & more space taken up in the house.
Posted Thursday 5 May 2016 @ 3:37:20 am from IP # -
It would be interesting to find out their pricing. I sourced a heat pump from China direct - cost around $3500 including shipping and duties. It's a 10kw unit = draws 2.5-2.9 kw when running x COP average around 3.5 = 8-10kw output. I very much doubt an Aussie based business can get close to that on price but obviously warranty and maintainence issues might make any saving void if there are issues.
Posted Thursday 5 May 2016 @ 8:06:42 am from IP # -
Benny
MemberIs there any reason for using a heat pump to produce hot water, then pumping that water through pipes in to the house so that the hot water radiates heat to warm the air/building - rather than just directly using a reverse cycle AC to heat the air ? I know a warm floor (concrete) is nice to walk on, the heated floor would be better at supplying heat in the evening after the main heating was done during the day from a PV system - but is this worth the reduced efficiency and costs (hydronic plumbing etc). The heat pump HWS's typically have a lower efficiency than heat pump AC's as they heat the water to 60C rather than just 22-24C - which is the final required temp of the air. My split AC has a CoP of over 5.
I can understand underfloor/hydronic heating in really cold climates where the heating is on 24/7 but is this necessary in Wollongong ? The response time from hydronics especially through a slab would be much slower than for direct air heating so if its mainly on in the evening this could be an issue.
You could use a air heater to pre-heat the hose in the same way if you want to make use of excess PV supply - run the AC at 25 during the day and get he walls/furniture all warm and then coast through the evening - maybe not as comfortable as using the slab but much cheaper for installation and better efficiency.Posted Friday 6 May 2016 @ 9:22:37 am from IP # -
arttt
Memberall good points benny.
cant speak for the OP but for me i see a couple of benefits.
1) I dont really like the RC units blowing air around
2) one hydronic heat pump can heat a few different rooms just by adding a radiator in each room. and selecting which rooms you want heated (not all at the same time).
3) It would be nice to only pay for one unit for domestic hot water and space heating combined. Only makes sense if your heating needs can be met by the one unit.Posted Friday 6 May 2016 @ 1:47:50 pm from IP # -
Canberra Mark
MemberAll points of interest for me. We are looking at building a 180m2 passive solar design house in Canberra in the next few years. I am interested in using the same Air source heat pump for potable hot water as well as in slab hydronic heating. Slab will be earth coupled on the Northern side of the building with perimeter insulation to 1.2m. Southern side of building envelope will be under slab insulated. Benefit of in slab hydronics over radiator panels is the lower temperature requirement- 40 degrees vs 60 degrees.
According to anecdotal evidence from a few sources in the CBR region, a slab on ground with adequate perimeter insulation maintains winter temps of 24 degrees on the northern side, to 18 degrees on the southern side. We are thinking of running limited hydronic loops in the slab on the southern side to service 2 bathrooms and a kitchen. We have roof space to accommodate a 10kw/hr solar PV set up so should have more than adequate generation capacity to meet the needs of the heat pump.
Met a guy from Laros technologies who said that he had seen a set up where the same unit was used for potable and in slab heating duties. It was one of the Sanden Supercritical Co2 pumps. He did say, however, that Sanden will not honor the warranty if it is set up in this manner. Need to get to the heating load number crunching point before I have any quantitative info to add to this discussion.
mark
Posted Saturday 7 May 2016 @ 4:08:12 am from IP # -
d.darroch
MemberBenny said:
So if your adding a heat pump and hydronic heating its not really "passive solar" ? If its all powered by PV then I suppose it would be described as "active solar". ?Why not? Just because a house needs some auxiliary heating, it doesn't mean it's not passive solar. Yes the heat pump & PV are active elements, but Canberra Mark hasn't described the actually design. I'm sure there's passive design elements in the house relating to orientation, glazing, shading etc. A passive solar house doesn't have to be zero carbon, or zero energy. It just needs to use these passive design elements to reduce energy consumption for heating/cooling.
From yourhome.gov.au,
"Passive design reduces or eliminates the need for auxiliary heating or cooling, which accounts for about 40% (or much more in some climates) of energy use in the average Australian home."
Posted Saturday 7 May 2016 @ 11:47:56 am from IP # -
Eco
MemberPassivhaus and 100% passive solar design are usually expensive in terms of money and also embodied energy. Passive solar and energy efficiency principles should be incorporated into all new house designs but in most cases won't eliminate the need for additional (auxiliary) heating/cooling. If that additional heat/cool can be provided by active solar system(s) that is great and could achieve a house that does not need any (or only a little) fossil fuel based heating or cooling energy. This house should not be considered inferior to Passivhaus or 100% passive solar especially if the embodied energy to achieve this outcome is less.
Posted Sunday 8 May 2016 @ 12:12:24 am from IP # -
axess
MemberCanberra Mark,
Why not insulate the whole slab? A 4 degree temperature difference across the whole slab might introduce movement stresses that might exacerbate the risk of cracks.
The anecdotal evidence you mention seems pretty exact for maintained temperatures from 18 to 24 degrees. These temperature differences (not measured by sensors in the slabs I presume) might be caused by other parts of the building elements(insulation variations for example).
This seems to be analogous to having 32MPA concrete in one part of the slab because you wish to polish that part, and having 20MPA in the rest. You would be better off having 32MPA throughout given the relatively small extra cost of the higher strength concrete. The same goes for insulating the slab. You will also have local temperature controls to adjust comfort levels as well I presume.
Posted Sunday 8 May 2016 @ 4:53:18 am from IP # -
Greg
MemberHey Canberra Mark. I curious to know if the earth coupling of the slab will work as suggested. Personally I'd insulate the lot, after all its about heat loss. If the ground temp is below your slab temp then surely you have to heat that entire mass of earth. I've read material that suggests it takes 5 to 7 years to get the benefit of ground coupling.
Wish you success.Posted Monday 9 May 2016 @ 5:27:51 am from IP # -
Greg
MemberBenny, another reason for heating a slabis for thermal storage. That's what you're doing with passive solar, using insolation to heat a mass which radiates at night. When there's no sun an alternative heat source can be used.
If you have the slab already for passive solar it makes sense to keep it warm. It would be unlikely that warm air from an AC would transfer much heat to the slab and be effective.
Now if you don't have that exposed thermal mass slab and just have a well insulated home, i can see AC being the way to go.
Which way is most cost effective???that would be hard to determine easily and then you get individual preferences as well. Just my thoughts.Posted Monday 9 May 2016 @ 5:38:17 am from IP # -
I think there would be nothing cosier than walking around on a heated slab - even if our house is 20 degrees on the thermostat you dont feel warm unless you have socks or ugg boost on as the floor has a chill.
Passive solar is a must with a slab and would greatly reduce your overall heating cost as you're getting free heat from the sun. It would be unlikely to provide all your heating but that's where your heat pump comes into it. And as someone above mentioned you're working with 40 degree maximum temps so it's within a more efficient range for your heat pump vs cranking it up to 60+.
If I was designing a house I'd have a concrete living area with hydronics, but radiators in bedrooms with carpet on a timber floor. For the heating just run a manifold to separate the radiator loops with the slab loop and have a temp reducer / mixer so you don't overheat the slab.
Posted Monday 9 May 2016 @ 11:18:39 pm from IP #
And you've probably got insulation under your floors....I'm about to starting crawling around to make our timber a little warmer but need to dig my way under as the house is old and quite low to the ground