Efficiency of electric residential heat pumps...

[Externet]

Hi.

Can someone explain how these units work, please ? As far as I understand, please correct :

 

In summer heat, the compressor liquifies the refrigerant, it is cooled to outside ambient and evaporated inside the dwelling to absorb heat.

 

In winter, the refrigerant flow is reversed by an electrovalve and the compressor liquifies the refrigerant and heats it, with its heat being released inside the dwelling. The cooled gas that delivered heat inside goes back to the compressor outside and is compressed/heated again...

 

About efficiency; how can these systems be claimed as more efficient in winter; if a kilowatt is a kilowatt. The energy the warm compressor uses is vented outside in the cold, plus any remnant heat in the refrigerant at the coil outside.

 

If the winter heating cycle was just inside with heating elements, like 'standard systems', zero heat is dissipated outside at the compressor unit. There is nothing getting warm outside, there is no wasted heat outside. Is this "heat pump in winter' a good idea?

 

Light please ?

[Endy0816]

The heat is being extracted from the outside air.

 

Warming up inside by cooling down the outside. Flipping around a window AC unit is probably easier to picture.

Edited March 4, 2017 by Endy0816

[Externet]

Thanks Endy0816

Understand the flipping of a window unit; but such comparison moves the compressor to the inside, and the heat generated by the compressor, fan motor and heat remmants in pipes is then kept inside.

 

In a 'heat pump' unit with a compressor unit outside, its heat is instead, wasted warming the ambient. In the link below, the heat losses generated by the compressor, fan motor, part of pipes is not considered. If that heat counts -say a kilowatt- ; it is a kilowatt wasted, is it ? :

 

----> http://www.allenhvacpro.com/Images/heat-pump-heating-ani.gif

 

How can this be called 'more efficient' than having the electric furnace heating elements inside, where 100% of energy heats the dwelling ?

[Strange]

The heat pump uses only a fraction of the energy transferred (less than 20% for the best ones), so that means, if I understand it, that the efficiency is far more 500% compared to directly using the electricity to heat the house.

 

I assume the main reason for having the pump, compressor, fan, etc outside is because of space and noise.

 

Perhaps realistic designs are arranged to allow some of the waste heat to be pumped back in, as one way of achieving high efficiency.

[studiot]

There was a thread about heat pumps a while back that had some useful information.

 

http://www.scienceforums.net/topic/84339-heat-pump-applications/?hl=%2Bheat+%2Bpump

 

I have since installed a residential heat pump and thought I had recently started a thread to record experience and for folks to discuss it, but I can't find it at the moment.

 

So here is a link to a really good book about them with lots of information tables and photos of real installations.

 

http://www.crowood.com/details.asp?isbn=9781847972927&t=Heat-Pumps-for-the-Home

 

You should be aware that residential heatpumps come in different types, depending upon their source of heat energy, which can be the ground, water (eg a stream) or the air.

Further the way the heat is supplied also comes in different forms.

So you can use the heat to heat water or air or even building fabric.

 

The link you reference is known as air to air since heat is taken from the outside air and added to the inside air.

 

Doing this costs less energy than using electric or gas (or other fuel) energy to heat the air directly.

This is because you are inputting work to drive a machine that achieves this.

 

Air to air types would be suitable for your area because you can reverse these to provide cooling in summer.

[Endy0816]

One issue I can see with an indoor compressor is that it is going to create a need for additional cooling in the summer.

 

Heat Exchangers would work to cool the compressor and warm up air going in/out, but adds to cost/complexity.

Edited March 5, 2017 by Endy0816

[Externet]

Endy: The 'indoor compressor' is related only to the example/comparison of flipping a window AC. Unrelated to the discussion.

 

A 'heat pump' outside unit always has compressor/fan/coils. And those outside components waste heat to the outside winter cold ambient.

[Endy0816]

Expansion valve can lower the fluid's temperature below ambient. A liquid to gas phase change can also be used to absorb heat.

 

Insulation and good design account for minimizing losses from the rest of the system.

Edited March 5, 2017 by Endy0816

[Strange]

And those outside components waste heat to the outside winter cold ambient.

 

 

The question is, how much that affects the efficiency. As the best are nearly 600% efficient then either they do recover the few percent that is lost that way or it is irrelevant.

[studiot]

Expansion valve can lower the fluid's temperature below ambient. A liquid to gas phase change can also be used to absorb heat.

 

Insulation and good design account for minimizing losses from the rest of the system.

 

Rather than concentrating your fire power on one small and relatively insignificant part of the design, you should consider all aspects of it.

The major influences on system performance come from elsewhere.

 

For instance, do you not wash more in the summer?

The industry reports that there has been a shift from the major energy user being home heating/cooling towards water heating in recent years due to greatly improved building insulation.

 

There are many other aspects of the installation to consider, before compressor siting.

 

We have two heat pumps in the family.

Both are air to water.

One is completely outside and only heated/spent water is transferred between the unit and the outside engine.

The other is completely inside and only natural air is transferred, via a duct.

This is because it is in a third floor London apartment and local planning regulations require it this way.

 

Both also utilise a part of the system you haven't mentioned; a heat store.

This type of system is gaining popularity.