Heating and Ventilating

 

Heat Pump Review: Is it time to wash our hands of commercial boilers?

Mitsubishi trial demonstrated how heat pumps can be used to provide a building's hot water - in its own kitchen
Heat Pump Review: Is it time to wash our hands of commercial boilers?
With the latest advances in heat pumps, it is now possible for all of a building's hot water to be supplied as a by-product of the heating and cooling system.

Heat pumps can therefore be used to help hard-pressed businesses to save energy (and therefore cost) by removing the need for separate plant to provide hot water to any building with air conditioning.

To demonstrate the possibilities of the system, manufacturer Mitsubishi Electric has installed its PWFY heat pump water heater to serve the kitchen in its Hatfield headquarters in Hertfordshire.
The three-storey building is the base for more than 300 staff, and the kitchen serves a busy breakfast and lunch cafeteria as well as providing catering for the regular conferences and seminars the company holds.

A constant and reliable supply of hot water is therefore a must for the kitchen. The PWFY utilises the waste heat energy from the air conditioning system that regulates the temperature in the kitchen area. It uses cascade refrigerant technology, which increases the heating of the incoming water supply.

This is then stored in a copper insulated tank located next to the PWFY, near the kitchen. The hot water is then supplied directly to the kitchen from the tank at a temperature of up to 60ºC.

The installation includes two indoor fan coils in the kitchen, a hot-water tank, piping, an outdoor condensing unit and the PWFY indoor unit. It took three working days to complete, and disruption was kept to a minimum with the kitchen being shut for only one working day (Friday) when the work began. The kitchen was then ready for the Monday morning normal opening hours.
The unit has been in operation since the end of August, and Mitsubishi Electric is closely monitoring the energy savings from the system and will publish the results after a couple of months' normal operation.

At 800mm x 450mm x 300mm, the unit occupies about the same size as a commercial boiler - so, while it has not freed up any internal space, it is effectively providing free hot water to the kitchen.

It outputs water up to 70ºC to a dedicated Manco high-efficiency tank with a capacity of 200 litres. The kitchen gets through around 650 litres a day. The PWFY is inverter operated so that it reaches the set point temperature in the most efficient way.

The set point for the tank is 60ºC, and the PWFY will go into standby when this temperature is reached to conserve energy.

The whole system is currently being monitored by Mitsubishi Electric's M2M technology, which enables data on the temperatures and power consumption to be collected and stored so the energy savings being made by the system can be worked out.

Air conditioning is a necessity in today's commercial buildings and nowhere more so than in a busy kitchen. By taking heat rejected from electrical equipment and offices and using it for further heat recovery and energy reduction, these heat pump water-heating units offer the potential for free hot water and greater energy reduction for many of the UK's commercial premises.

Figures from Defra's Market Transformation Programme (2006) show that the provision of heating and hot water accounts for more than 50% of energy consumption in non-domestic buildings. Initial modelling from the Defra study of gas- and oil-fired water heating boilers and warm air and radiant systems resulted in annual carbon emissions of 10.8M tonnes of carbon.

The model also shows there is a link between gas boiler efficiency and age, ranging from 50% efficiency for a pre-1979 gas boiler to 81% for boilers from 2007 onward.

Mitsubishi Electric is confident that using the heat recovery process of heat pumps to provide hot water can offer average coefficients of performance of 4 (or efficiency levels of 400%) in comparison.

It is difficult to find accurate figures of the size of the commercial boiler market but, even when the general inefficiencies of the national grid are taken into account, it is obvious that something delivering a performance of 400% will give a better carbon reduction performance and a much more efficient delivery system than something working at 81%.

If all VRF air conditioning systems were optimised in this way, we could completely replace the need for carbon-based water heating systems. This could have a substantial impact on the energy efficiency levels of the country - and the energy bills of the nation's hard-pressed businesses.

Call 01707 282880 or visit www.mitsubishielectric.co.uk/aircon.
1 October 2008

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