Heat Pump COP: Air-to-Water Explained

In summary: The COP of a heat pump can be expressed as COP_{heating}=\frac{T_{hot}}{T_{hot}-{T_{cold}}}As higher is better, the value of this can be improved by reducing the temperature gap at which the system works. I'm just a little unsure about which temperatures are being talked about. The heat pump in question is air-to-water. Does T_{cold} refer to the outside air temp? And is T_{hot} the water leaving the heat pump on the other end? These are my guesses anyway.Thx :)All correct.
  • #1
TSN79
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The COP of a heat pump can be expressed as [itex]COP_{heating}=\frac{T_{hot}}{T_{hot}-{T_{cold}}}[/itex]
As higher is better, the value of this can be improved by reducing the temperature gap at which the system works. I'm just a little unsure about which temperatures are being talked about. The heat pump in question is air-to-water. Does [itex]T_{cold}[/itex] refer to the outside air temp? And is [itex]T_{hot}[/itex] the water leaving the heat pump on the other end? These are my guesses anyway. Thx :)
 
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  • #2
All correct.
 
  • #3
Well, there is obviously something I'm not getting. Take the attached heat pump for instance. The smallest one has a listed COP of 3,14. [itex]T_{hot}[/itex] is said to be 45°C and [itex]T_{cold}[/itex] is 7°C. Using the formula from above this becomes 1,18 - which is obviously not right. What am I not getting?
 

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  • #4
Kelvin...
 
  • #5
Thx, I should have seen that one :)
Still, 8,4 is the theoretical maximum COP for these temperatures, isn't that right? So how do they arrive at 3,14?
 
  • #6
TSN79 said:
Still, 8,4 is the theoretical maximum COP for these temperatures, isn't that right? So how do they arrive at 3,14?
8.4 COP would require a perfectly efficient compressor, expansion valve, no fan for the condenser, etc., so the lower efficiency comes from taking into account those extra losses.

Though if you are asking how they calculate it, they don't; they measure it.
 
  • #7
the equation you gave is for the carnot COP that for a perfect heat pump where there is no temperature differences across heat exchanges to the heat sinks. The COP of a real heat pump is the heat output divided by the energy input and the carnot efficiently is the ratio of the real COP divided by the theoretical perfect carnot COP. And yes for the perfect carnot COP equation to work you have to enter the temperatures in the absolute kelvin scale. That is degrees C plus 273 as absolute o is -273 degrees C.
 

1. What is the COP of an air-to-water heat pump?

The COP, or Coefficient of Performance, is a measure of the efficiency of a heat pump. For air-to-water heat pumps, the COP typically ranges from 3 to 5, meaning that for every unit of energy used to power the heat pump, it can produce 3 to 5 units of heat energy.

2. How does an air-to-water heat pump work?

An air-to-water heat pump works by extracting heat from the outside air and transferring it to a water-based heating system. This is achieved through the use of refrigerant, which absorbs heat from the outside air and is then compressed to increase its temperature before being circulated through a heat exchanger to transfer the heat to the water system.

3. What is the difference between air-to-water and air-to-air heat pumps?

The main difference between air-to-water and air-to-air heat pumps is the type of heat distribution system they are compatible with. Air-to-water heat pumps are designed to transfer heat to a water-based heating system, while air-to-air heat pumps transfer heat directly to the air inside a building.

4. Are air-to-water heat pumps more efficient than traditional heating systems?

In most cases, yes. Air-to-water heat pumps can be more efficient than traditional heating systems, such as gas or electric furnaces, because they are able to extract heat from the outside air rather than generating it themselves. This can result in lower energy bills and reduced carbon emissions.

5. What factors can affect the COP of an air-to-water heat pump?

The COP of an air-to-water heat pump can be affected by several factors, including outdoor temperature, the size and efficiency of the heat pump, and the efficiency of the heat distribution system. It is important to properly size and maintain your heat pump to ensure optimal performance and efficiency.

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