The heat is on – with a low carbon solution

Heat pumps supply more energy than they consume by extracting heat from their surroundings. Consequently, they now form an essential part of the solution for reducing both energy consumption and carbon emissions, and can also provide their heat from renewable sources such as the ground and solar heated ambient air.

A heat pump is an efficient and space saving means of heating a wide range of premises. It can also provide cooling to these premises should there be the requirement.

Where heat pumps are used for heating, they are capable of highly cost-efficient energy applications because they tap into a limitless supply of ‘free’ heat – either the surrounding air or heat captured in the ground or water, such as a lake.

How they work

The vast majority of heat pumps work on the same principle as the domestic refrigerator utilising a vapour compression cycle, but for heating the heat hump utilises the hot end of the process. The vapour compression process utilises low grade heat that is normally too cool for human or process requirements and lifts the same quantity of energy to a higher temperature that is then suitable for human comfort.
Depending on the application and type of heat pump, gains of 300-500 per cent are normal.

When dealing with heat pumps, and because efficiency cannot be defined as above 100 per cent, the term used is actually Coefficient of Performance (COP), so the COPs for the above example would be 3 to 1 and 5 to 1. In its simplest form a COP is calculated by taking the HEATING OUTPUT divided by the POWER INPUT.

Heat pumps are normally classified by their heat source and means of delivery, for example
• air to air
• air to water
• water to air
• water to water
• ground to air
• ground to water.

Use in schools
Heat pumps offer a robust solution for heating in schools. Despite the demise of the Building Schools for the Future programme, the use of heat pumps in schools offer a number of advantages:
•    a simple and cost effective installation compared to some alternative technologies
•    ongoing schools building programmes can benefit from heat pump systems that improve the environmental footprint and reduce running and operational costs
•    a low carbon technology that helps to reduce CO2 emissions
•    a renewable heat technology to satisfy the UK’s renewable obligation.

Also, installed in places of education, heat pumps will provide a valuable learning tool for students who will gain awareness of the use of low carbon and renewable heating systems and see this as the norm in their future careers.

As an example of the worth of heat pumps, according to the U.S. Department of Energy, ground source heat pump systems in schools in the USA reduce energy use by 25 per cent to 50 per cent compared to traditional systems and although no such similar study is available for the UK, the expectation is the same.

Positive outcomes
The education authorities that have invested in this area have been very positive as to the outcomes. We shouldn’t forget the financial considerations either as the lower energy costs, while an ongoing advantage, also result in good payback periods due to the fuel savings.

All types of heat pump, as listed above, can offer a solution for schools and the choice may well depend on factors such as cost, available space, hours of operation, availability of heat source, and layout of the building.

If the schools of the future invest in heat pump systems they should consequently provide more energy efficient operation, generate less CO2 and utilise heat from renewable sources thus addressing most of the green agenda. Importantly they will also have lower operating costs.

Case study

A school has just been completed in North Wales to accommodate 220 children from nursery age groups through to Year Six. The exterior of the single storey building, although extremely pleasant, is conventional in style. But the method of heating both the building and the water for pupils, staff and kitchens is anything but. With an eye to the future – in terms of both energy costs and environmental considerations – the education authority opted for a system utilising the heat always present at a more or less constant temperature in the ‘near-surface geothermal layer’ underground.

In a system designed by NIBE Energy Systems Ltd of Chesterfield, 11 boreholes 100 metres deep were drilled into the school grounds before landscaping. Each borehole contains a plastic tube in an elongated u-shape, within which circulates a glycol/water mixture in a closed circuit, working in rather the same manner as a car’s cooling system.

Energy from the warm ground is absorbed in the mixture and translated to two inter-connected NIBE Fighter 1330 heat pumps situated in the school’s boiler/utilities room. These, with a capacity of 30 kW, convert the latent energy into heat for the water in a fully insulated tank situated near the Fighter units. This in turn feeds the entire under-floor central heating system and the hot water supply for all the school buildings. Back-up heating, if required to act as a boost in times of maximum peak usage, is supplied by a gas boiler.

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