Rise and rise of renewables

Stephen Andrews, Technical Manager at Danfoss Heat Pumps, looks at how an increasing number of businesses are upgrading their buildings with microgeneration technologies, such as heat pumps, to provide a more sustainable and affordable energy source for the future.

Almost half of the energy consumed in the UK (49%) is in the form of heat, the generation of which accounts for around the same proportion 47% of our country’s Carbon Dioxide Emissions (source DECC). 

The Government’s drive is to make renewable energy more accessible, as part of its ambitious plans to move the UK from just 1% of heat energy being produced by renewables to 12%. The Renewable Heat Incentive represents over £860m of investment designed to help shift renewable heat from a fringe industry into the mainstream. This would help to save around 60 million tonnes of CO2 by 2020, as part of reducing the effect on climate change.

The scheme will be introduced in two phases and, in the first phase, long-term tariff support will be targeted to the non-domestic sector, such as business and the public sector – principally because they contribute most to UK’s carbon emissions at 38%. Here, the Government is encouraging the heavier users of energy to adopt renewable technologies, such as heat pumps to help them to reduce their carbon emissions.

The UK is currently still very heavily dependent on non-renewable sources, unlike some other European countries. However many organisations (both public and private) are taking the view that they had better act now to be able to benefit from a more sustainable, renewable form of heating and hot water. 

Operational efficiency

The use of heat pumps is increasing rapidly, especially where there is no mains gas supply or a building is dependent on oil, solid fuel or electricity. All heating systems, including heat pumps, work best when there is good insulation, where there are no draughts within a building and where the doors are not left open for long periods. A good heat distribution network is also essential – and this is why underfloor heating systems are so widely specified with heat pumps. 

The first stage is for a SAP calculation to be carried out, which determines the sizing requirements of the heat pump and how effectively this will meet the building’s space heating requirements. Often, where the project is a refurbishment, it may be necessary for insulation to be upgraded to ensure that the performance of the heat pump is optimised.

The key to designing a heat pump system is to keep it simple. We find that most issues with heat pump configurations come about because of an over-complicated layout. 

Part of the training we offer involves a module on system design and this is an area where we provide support for engineers, especially in the early stages of working with heat pump technology.

To gain a full appreciation of the efficiency of a heat pump system, it is important to understand more about how they work. A heat pump circulates a refrigerant fluid around a circuit containing four elements: evaporator heat exchanger, compressor, condenser heat exchanger and expansion valve. Heat absorbed from the ground or air is transferred to the liquid refrigerant which evaporates to form a gas. This gas is then compressed which causes its temperature to rise. The hot gas passes into the condenser, where it starts to change back to a liquid as heat is transferred into the building. After passing through the expansion valve, the liquid refrigerant returns to the evaporator and the cycle begins again.

Heat pumps involve a different approach to system design than any other heating system, such as gas boilers or solid fuel. As they are not reliant on a combustible fuel, it is therefore important to plan a long term strategy for the heat pump over the year. This includes studying the requirements for heating and hot water at certain times of the year and working out what the base load requirements will be. 

As with all good heating arrangements, we recommend that wherever necessary, heat pumps are cascaded, so that there is no over-reliance on any single unit. With a master and slave arrangement, heat pumps can be sized to meet the requirements of the project. This means that in the unlikely event of the master stopping working, the other heat pumps are unaffected and the system can continue to operate normally, with another heat pump reconfigured as the master. Problems are rare with heat pump systems if the installation procedure is followed correctly. 

Good practice within a maintenance schedule is to check the refrigerant level of a heat pump at least once a year. With our systems, the refrigeration units are hermetically sealed, which means the risk of any leakage is minimal. The weight of our refrigerant is also below the limit that is legislated by F Gas legislation, which means they are not subject to annual assessment by an external body.

Preventative maintenance

A well commissioned heat pump system by an MCS installer will require minimal maintenance when compared to a traditional fossil fuel combustion system. After some initial checks such as filter cleaning during the first few months it is expected that little invasive servicing will be necessary throughout the lifetime of the heat pump. The protection levels of the water and glycol mixture in ground source heat pumps should be checked at regular intervals.

There is often a misconception that heat pumps cannot provide both space heating and hot water in large installations. However, a typical heat pump can deliver water temperatures of 50-55°C and if higher temperatures are required for specific industries, then this can be boosted by use of a de-superheater in the refrigerant circuit, which is standard in all Danfoss’ light commercial heat pumps.

Weather compensation systems are one of the major advantages of some heat pump systems. Instead of being governed by heat sources through zone-controlled thermostats cycling on and off throughout the day, heat pumps should be left on constantly, selecting their temperature determined by conditions outside the building. This ensures a more comfortable environment for building occupants and more consistent temperatures, rather than experiencing the high and lows of traditional boilers. 

Early adopters

Schools have been early adopters of heat pump technology. This was largely supported by funding through the previous Government’s Low Carbon Buildings Programme (LCBP) which has now ended, so the RHI is set to be crucial to future installations.  

One such installation was at Bowland High School in Grindleton near Clitheroe where the pump was installed as part of a newly-built music block and provides space heating for the building, which includes a classroom, storeroom and toilet facilities.

Readings taken over a 12-month period, including the harsh winter of 2010/2011, show that the pump is achieving an average Coefficient of Performance (COP) of 3.39. This is above the system’s initial target of 3.08, based on calculations at the time of installation and is enhanced by the high level of insulation within the building.

The project was commissioned by Lancashire County Council which is one of several local authorities to cut its carbon emissions and energy costs by specifying heat pumps. With the amount of land available, ground source heat pumps were perfect for this project and it has provided the opportunity for young people to learn more about renewable energy systems, as they become a more widely accepted part of everyday life.

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