Solar-Assisted Heat Pump
Nobrainer
| Posted in Energy Efficiency and Durability on
Hi, I had a small question I haven’t seen anywhere, really.
Why don’t we use a heat collector/concentrator to pre-heat the incoming refrigerant before a heat pump?
effectivly a solar assisted heatpump, but more efficent.
And before anyone says, yes i live in Sweden.
95%+ of energy used to heat homes is electric radiators or electricity to heat domestic water or use a heat pump power by electricity to heat domestic water and radiant heating.
Nobody uses gas and few burn wood pellets or oil in older homes
Example, i have a Ground source heat pump. Right before the liquid goes to the heat pump i pass it through a solar heater raising the temperature from perhaps 8c ( or whatever temperature ground source heat have and increase it to let’s say 30c?
Would this not make it more efficient and raise the effective COP as the water now needs to be heated from 30c to 50c instead of 8c to 50c.
Or if I have an Air source heat pump right before the refrigerant is going to the compressor, i heat it up 30c more?
The ambient temperature might be 20c in the air, and then I can heat up the refrigerant from 20c to 40c? Or if it’s during winter and the outside temperature is negative -10c i could raise the temperature with the solar collector to 10c? Effectively increasing the COP as the target temperature is closer?
Perhaps you would need a few m2 of solar concentrators, but it should be relatively small compared to solar panels needed to decrease the heating bill.
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Replies
You mean like the the solar assisted heat pumps produced by SAHP systems in the UK? I believe Radiant Store in Troy NY sells these systems. I wonder if anyone has one and can comment?
You would actually want to preheat the refrigerant at the evaporator to help with heating, making it easier to flash the liquid refrigerant to a gas. Heating is the opposite of air conditioning with a heat pump :-) doing this might also help to reduce the need for an outdoor unit to run defrost cycles too, which would be an added energy saving plus.
I don’t see any reason why this wouldn’t work, you’d just have some additional system complexity. I would avoid running the refrigerant lines to the solar collector though (which you seem to have thought of too, since I see a heat exchanger on your drawing). More refrigerant lines means more refrigerant required to charge the system ($$), and also more places that risk leaks.
Bill
I think this is how the SAHP system works, no? sahp.info
Unfortunately the commercial solar assisted heat pump mostly use a heat collector instead of ground loop or air as far as I can find :/
It’s weird there is barely any real life examples of it, considering it must be an extremely cost effective way to increase a heat pumps SCOP.
I would likely use some kind of oil in the solar collector to allow much higher heat than water can take without risking it boiling in the loop.
Is there any way to easily calculate the size needed to pre heat the heat pump refrigerant as close to working temperature as possible?
Indeed, these have been designed. https://en.wikipedia.org/wiki/Thermodynamic_solar_panel Nobrainer could also draw warmed source air for an air to water heat pump from around the solar panels, given that the panels were in a 'greenhouse' like box.
Reducing the lift temperature (t1-t2) of your heating water will increase the performance of the heat pump. It is possible to use solar or wood fire energy to do so. Performance is t2/(t1-t2) e.g. https://en.wikipedia.org/wiki/Coefficient_of_performance#Theoretical_performance_limits It is possible that the solar system can heat the water high enough to bypass the heat pump during sunny periods. A buffer tank can help smooth out the added thermal energy.