CO2 Air to Water Heat Pump w Solar Pre-heat

[rQb]

Hi,

Does anyone have experience with CO2 heat pumps and the use of solar pre-heat feed to the heat pumps? I'm being advised that solar pre-heat is not preferred as a larger delta T is better. If above 35DEG C pre-heat performance drops? New to heat pumps and have not been able to easily find an good explanation. Some documentation online makes same statement but doesn't provide a simple explanation.

Thanks in advance.

RQB

 

[EnergyProfessional]

I think you should explain more what you attempt to do. Heatpump to heat what? And Northpole, or Dubai?

When it is cold at night, you don't have solar. so the system also has to work without solar. Solar should just be a supplement to save energy.

 

[nuuvox000]

Could you define "performance"? That might help you answer your question.

 

[GT-EGR]

The way this information is being presented I think is the confusing part.

Yes as the entering temperature gets higher, you get less heat pump heating output aka lower efficiency. This is just due to the ability to transfer heat from the refrigeration cycle if the water starts off warmer/closer to the refrigerant temps.

However, your solar pre-heat is mostly “free” - so even though your heat pump does the remaining work at a lower rated efficiency, it overall has less heating to do.

But theoretically yea, if you could switch things around somehow (I don’t know the nuances of solar preheat) and somehow make it so the solar does the higher temp heating work and the heat pump does the lower end then yes that would be more efficient. But I would bet that is much more complicated to control the highly variable solar contribution to do the final temperature control.

 

[chicopee]

A heat pump has a similar cycle to the refrigeration cycle which you can familiarize yourself by getting a book on thermodynamics for engineers. The term refrigeration is synonymous with air conditioning (A.C.). On the low pressure side of the refrigeration cycle, the state of the liquid CO2 changes to a vapor as the evaporator is heated by the warm liquid that was flowing thru the solar panels. The state of the liquid CO2 changes to a vapor which is compressed by the refrigeration or air conditioning compressor otherwise liquid CO2 will damage the compressor. The compression of the vapor will raise its pressure and temperature from a low pressure to a high pressure known as the heat of compression. Three things that you have to familiarize yourself to answer your inquiry. First learn the Mollier diagram of CO2; the Mollier diagram shows the relationships of temperature, pressure, enthalpy, specific volume, quality of the CO2 within its saturated region and the more esoteric concept of entropy. Secondly, familiarity of the heat pump cycle using as a medium CO2; lastly know the minimum temperature required to heat the low pressure side of the A. C. cycle from the liquid heated by the solar panel. You should be aware that a heat pump used as a heating and cooling system will have a life time about half of an air condtioning or refrigeration system.

 

[EnergyProfessional]

Heatpump = refrigeration cycle. It pumps heat from cold to warm (instead of heat moving from warm to cold) and requires work (motor-driven compressor) to do that

All the odd terms like chiller, AC, refrigerator just describe specific applications, fluids, typical temperatures etc. But all of them are heatpumps employing a refrigerant.