Heat Pumps

On paper a heat-pump is a compelling proposition. With efficiency ratio of three or four to one you can't argue with the economics. Few City bankers would pass up the opportunity to get the kind of return a heat pump offers and yet they are still relatively rare fixtures in our homes. This is set to change as fuel prices rocket. Everyone is now looking at ways to cut their bills but is a heat pump a practical alternative to a gas or oil boiler?

Heat pumps, which are simply air conditioning units working backwards, are not new but historically we have struggled to find a way to integrate them into whole house central heating without back up. The heat pumps typically produce 40 or 50 degrees centigrade which isn't quite enough to heat radiators. Two recent changes have made heat pumps viable.

Firstly the greatly improved insulation levels and draught proofing in housing now means that a lower temperature is all that many houses now need. Secondly under floor heating is now seen as the best way to utilize lower flow temperatures without compromising comfort levels and thirdly manufacturers have begun to produce dedicated systems that optimize the heat pump output through computer control interfaces.

The main choice in heat pumps is between ground source and air source. The ground source pumps give a higher efficiency ratio typically of 4 to 1 and the air source gives around 3 to 1. The drawback with ground source is that you have to bury the pipe underground. With an air source unit you simply put it outside the house. Whichever way you collect the heat the storage and utilization of that heat through the heat pump is the same.

STORING THE HEAT

Many of the systems around today use buffer tanks. These are essentially cylinders that provide a thermal store of water which can then be drawn upon by the under floor heating or by the hot water system where it is topped up to the usual 60 degrees centigrade needed to combat legionella. Buffer tanks are usually the same size as a very large hot water cylinder and you still need a hot water cylinder as well. Provided you have the space this is a good option but if they are being placed upstairs you also need to consider the considerable weight of 2 cylinders full of water. This could be as much as 400 litres at 1kg per litre.

A space saving alternative is the Gledhill heat pump package which uses a dedicated variation on the well established Gledhill thermal store. This is coupled with a Mitsubushi air to water heat pump.