Heat Pumps – their pros and cons

The Energy Savings Trust has been testing heat pump performance in 83 homes for the past year. It seems that the EST has reached the conclusion that like the parson’s egg a heat pump is good in parts. Many of the heat pumps made no difference to energy cost or carbon dioxide emission reductions, some made energy more expensive and others produced real savings. Why then, should anyone install a heat pump when it seems such a hit and miss affair?

Heat pumps draw low grade heat from the surroundings – underground or in the air – and pass the heat into a gas which is compressed and expanded. This process releases heat into the building that needs to be heated. The technology is identical in concept to that of a refrigerator, so it is hardly ground breaking or novel.

Heat pumps leave cold areas, often covered with ice, around the places from which they draw heat. If your heat source is underground a poorly designed heat pump will create an underground ice lake; if your heat source is the air a heat pump may leave ice forming around the place where the air is drawn into the system. These problems can be eradicated by reversing the cycle to put heat into the ground to defrost it, or into the air to de ice the aperture but these processes use energy.

Every heat pump has a coefficient of performance – a COP. Many manufactures claim a COP of three or four, but these COPS apply to heat pumps working in warm conditions. As the weather gets colder (when you need more heat) the COP declines often to a COP of 1, which is just as efficient or inefficient as if you were heating your home with electricity and may end up costing more than using white electricity storage heaters.

The EST drew the following conclusions from their trials:-

  • heat pumps are sensitive to design, commissioning and use
  • simple designs work best
  • the impact of hot water production on performance is unclear
  • instructions and information for users and installers are poorly explained and need to be improved
  • clear lines of responsibility and a contractual guarantee for installations are needed to ensure consistency after sales and services
  • further study is needed on an installation by installation basis.

I would differ from these conclusions, but not materially. Like all renewable energy installations you need to produce a high quality product. This is the key to a good heat pump, not the simplicity of design. Complicated designs work very well, but they must be installed correctly and they must be capable of being managed by the end user without having to read through pages of a manual and keep on resetting the controller of the heat pump.

The “interface” between the device and the consumer is all important and this, and poor quality workmanship and work seems to be at the heart of the problems identified by the EST.

Genersys’ sister company, ThermoSolar, has had a sophisticated and highly successful heat pump on the market for more than two years. It not only exploits the underground temperature differentials but is linked to an array of Genersys flat plate evacuated panels thereby getting a solar heat boost for central heating and hot water.

We have not marketed the product in the United Kingdom because it requires a great deal of training for correct installation and is more expensive than the existing heat pump systems. We judge that there is not enough heat pump expertise in the United Kingdom to set up our systems correctly. The installation trade will need a long learning curve.

Eventually there will be a place for sophisticated heat pumps in the United Kingdom, but for the time being they will be like the parson’s egg, good in parts

 

3 Responses

  1. My customers that I have installed a heat pump for seem to be happy with the result.

    Cody

  2. The low carbon footprint of the heat pumps are a great way to help the environment, not to mention the fact that the system literally pays for itself.

  3. a well rounded simple and cohesive summary of the current progress of heat pump technology in practice

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