How does a heat pump work?

Question

If you collect a large amount of heat at low temperature, say from underground piping, how do you convert it to useable heat for domestic purposes like cooking and central heating?

I'm thinking of a domestic scale operaton with reasonable capital cost and DIY maintenance.

Answer 1

Heat engines (e.g. a car engine, an aeroplane jet engine, a power station steam turbine) all work on the same thermodynamic principle. A gas (air, steam, or whatever) is compressed, heated, expanded, and cooled - heat is transferred from the hot side of the engine to the cold side and work or power is produced by the engine.

A heat pump, or refrigerator, does exactly the same thing but in a reversed cycle. Power is put in and heat is transferred, or pumped, from the cold side to the hot side.

The heat pump principle is practical, and efficient, when the temperature difference between the hot side and the cold side is small. For example a refrigerator operating in a room at +20 C may have a freezer temperature of -20 C (a 40 C temperature difference). A house central heating may work at a temperature of +35 C with an outdoor temperature of -5 C (also a 40 C temperature difference).

But a cooking system would need to have a temperature of at least 120 C and if the base heat supply is 20 C this is a 100 C temperature difference, and this is too great for a heat pump to be practical. Even if you used a windmill and got your power for free, it would still be more practical to couple the windmill to a power generator and use the electric power for your cooking. So you should consider a heat pump for your heating but not your cooking.

Answer 2

A heat pump works exactly like an air conditioner or refrigerator, except it's reversible. Keep in mind that BOTH air conditioners and refrigerators produce NET HEAT. If you go outside and stand above the air conditioner exhaust or feel behind your fridge when it's running--it's hot. A heat pump can allow you to switch what side you're on, hot or cold. Usually some form of compressible gas, e.g. freon, is allowed to evaporate into a gas in one section and then compressed into a liquid into another. This phase change allows one to extract/deposit heat. I've never heard of anyone cooking with a heat pump--they are useful only in milder climates, as the efficiency of the pump is inversely proportional to the temperature difference of the two temperature reservoirs. This means you want the difference in temperature between your house and outside to be as close to zero as possible. This is the reason people bury the pipes, as the temperature of the earth remains more constant throughout the year, around 40deg F.

Answer 3

I am not aware of a way that you do this cheaply. Heat pumps that use underground sources, work in the same way as a domestic fridge. They pump refrigerant through a pipe and it converts into heat in a boiler, this is then pumped through the ground to cool, and the whole thing starts again. Apart from the cost of electricity to run the pump, the whole operation is zero carbon. The cost of the heat exchanger is very expensive. The water produced all year round is hot enough to shower in and produce heating for a well insulted dwelling..

Answer 4

Laws of thermodynamics say that to convert it to high-temperature heat, like for cooking, requires a large energy input and isn't worth doing. But you can usefully "pump" heat up a little bit to the temperatue you might require for central heating.
If you put your hand on the back of your domestic refrigerator, it should feel warm. That is partly from heat "pumped" out of the refrigerator to cool it (the rest is from the electricity your refrigerator uses).
Think of an array of pipes buried in your garden as the inside of a refrigerator, and the warm pipes inside your house as like the back of your refrigerator, and you have a heat pump warming your house.

Answer 5

depends what type of heat pump. Mini split systems like Fujitsu can produce heat even when it's -21 outside I can attest to this many will not believe me but my energy cost for 12 months to heat and cool 1600 sq feet is under $300 the 1600 sq feet is on one floor with 1 head being used

Answer 6

Hello,

Simply

"a heat pump is a device that uses a small amount of energy to move heat from one location to another. Not too difficult, right? Heat pumps are typically used to pull heat out of the air or ground to heat a home or office building, but they can be reversed to cool a building. In a way, if you know how an air conditioner works, then you already know a lot about how a heat pump works. This is because heat pumps and air conditioners operate in a very similar way."

Are you clear?If not then check here-http://www.air-conditioning-companies.com/

Answer 7

Some more detailed information is given in link below.