Temperature lift of a heat pump

In summary, systems that involve a heat pump need to be designed for a delta T of about 10C, not the more usual 20C, apparently because the pump can't lift the temperature more than this.
  • #1
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I've always been told that systems that involve a heat pump need to be designed for a delta T of about 10C, not the more usual 20C, apparently because the pump can't lift the temperature more than this. Is this correct, and why is this so?
 
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  • #2
What is "usual"? Water-based heat exchangers (ie, in chillers, water source heat pumps, cooling towers, etc) are typically designed for 10-14F delta-t's. Even for airside heat exchangers of the cooling variety (dx or chilled water air conditioning coils) 20C is a huge delta-T for air for an HVAC application: 20 F is more typical.

The approach temperature would be the reason for all of that and for a heat pump in particular, the efficiency is highly dependent on the difference between the hot and cold sides.
 
  • #3
"Usual" is my opinion of a system that uses boilers, gas, or whatever for heating. Here I use a delta T of 20C. But, as soon as a heat pump is to take care of it all, I'm always told it must be designed with a lower delta T, i.e. 10C. I was just wondering why this is.
 
  • #4
Some devices are more sensitive to temperature variations than others: whether you send 90 C water or 80 C water to a radiator, the difference in performance will be small - maybe 10%. But if you send 0 C water instead of 20 C water to a heat pump (in heating mode), you will utterly destroy your efficiency. Refrigeration cycles require very specific operating temperatures to run efficiently - fuel-fired heating systems are a completely different animal. Many heat pumps list performance at different temperatures - have a look at how fast the output changes with it.

Still, it surprises me that you would design a boiler plant for a 20 C temperature rise. They are typically rated for much less for safety reasons: I've seen boilers melt their burners due to insufficient water flow and you also don't want to accidentally boil the water.

A gas furnace, on the other hand (if that's what you are talking about) is designed to operate at an extremely high temperature (stainless steel burner), so it can handle a very wide range of temperatures: you might see a 40 C delta-T for the air going through a gas furnace. As long as you keep the output temp below about 60 C (so you don't burn anyone), you can do just about whatever you want with it.
 

1. What is the temperature lift of a heat pump?

The temperature lift of a heat pump refers to the difference between the temperature of the heat source (such as the ground or air) and the temperature of the heated space that the heat pump is providing heat to.

2. How is the temperature lift of a heat pump calculated?

The temperature lift of a heat pump is calculated by subtracting the temperature of the heat source from the temperature of the heated space. For example, if the heat source has a temperature of 50 degrees Fahrenheit and the heated space has a temperature of 70 degrees Fahrenheit, the temperature lift would be 20 degrees Fahrenheit.

3. What is a good temperature lift for a heat pump?

The ideal temperature lift for a heat pump can vary depending on the specific heat pump system and the climate it is being used in. However, a general rule of thumb is that a temperature lift of 40 degrees Fahrenheit or higher is considered efficient and effective for most heat pump systems.

4. Can the temperature lift of a heat pump be adjusted?

Yes, the temperature lift of a heat pump can be adjusted by changing the settings on the heat pump or by changing the heat source. For example, if the heat pump is using air as a heat source and the temperature outside is very cold, the temperature lift will be higher. However, if the heat pump is using a geothermal heat source, the temperature lift may be lower.

5. How does the temperature lift of a heat pump affect its efficiency?

The temperature lift of a heat pump is directly related to its efficiency. The higher the temperature lift, the more work the heat pump has to do to provide heat to the heated space. This can result in lower efficiency and higher energy costs. Therefore, it is important to choose a heat pump with a temperature lift that is suitable for your climate and heating needs.

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