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Environmental Issues
Going Green

By Alan J Hartley

Heat Pumps



The principal of a heat pump can be a little hard to grasp as the inside of the building being heated is being warmed by taking heat from its even colder surroundings, but it operates like many commercial air conditioning systems, or exactly the same way that a Refrigerator works, only in reverse. As in the operation of a fridge, all heat pump systems use quite a bit of electricity to operate, but for every 1 KW used they will produce more or less than some 3 KW of heat depending on their efficiency. This means that you are getting 3 times as much energy out of the system as you put in. The “FREE” energy comes from the energy in the surroundings that has been put there by the Sun. With heat pumps that use the ground as a source of heat it is tempting to think of it as coming from the heat given out by the Earth’s core, but in most ground heat sources the pipe-work is only a few feet down and is affected more by the atmosphere. In places such as Iceland of course they really do use Geo-Thermal heat. 

The cost efficiency of heat pumps as compared to other fuels depends largely on the price of electricity as so much is used in their operation. From this aspect domestic Heat Pumps cannot be considered to be a truly “GREEN” energy source, but apart from that most of the energy does come from a renewable source instead of burning fossil fuels such as gas, coal or oil.

To work at optimum efficiency heat pumps need to extract heat from a source that has a steady temperature. This means that pumps extracting heat from the surrounding air outside a building are not usually the best option due to the Summer/Winter variances. Having said that many of the better air conditioning systems used for cooling commercial buildings can operate in reverse and become air based heat pumps to provide some background heat in winter. Ground based heat extraction is generally more efficient as there is always a steady temperature and a high water table or wet ground will improve their efficiency even more. Pipes containing refrigerant fluid are buried in the ground and may last well over 50 years, so not only do you need a clear and suitable area for them to be installed easily, but you must be sure that they will not be disturbed in the future by other development etc. The cheapest way to install a system is to lay the pipes horizontally, but if space is restricted they can be installed vertically at greater expense by boring down.

Instead of using the ground as a heat source you can use water. A lake, river, or a spring would be even better, if one is close by, as it will have a steadier temperature being warmer in the winter and possibly cooler in summer. However, you might have problems with water authorities depending on the installation and the impact the system has on the watercourse. Several very large commercial water based systems have been on trial in recent years in London. It is said that when the Royal Festival Hall opened in London back in the 1950's it used the Thames as a water source. In 2007 the Festival Hall was again used for testing a very large Thames water based Air Conditioning system. Trials have also been conducted using ground water based systems for the London Underground.

To actually heat a house it is best to use under floor heating or warm air ducting throughout the building. This makes installation difficult in most existing buildings and is best done in a new build house, or one that is being gutted and done up.

Radiators can be heated by a heat pump system, BUT they need to be at least double the conventional size and would require larger bore piping than is usual to prevent heat loss. This is because water heated by heat pumps needs to be at a lower operating water temperature than that of conventional heating system to maintain the efficiency of the heat pump. Again, a heat pump system can be used for general hot water in the house, but it is best with a storage tank and not so good for showers as there would be no pressure. Newer systems can operate like a conventional boiler, but they are expensive and may require re-plumbing throughout the house with larger pipes to prevent heat loss.



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Alan J Hartley