With the excitement being created by rapidly growing application of heat pumps in the residential sector to replace conventional central heating boilers, it is often mistakenly thought that this is a recent innovation, this is not the case; heat pumps have been with us for over 50 years, indeed they are a dominant feature in the commercial buildings sector.
What we are seeing in the residential sector is the emergence of air or ground source-to-water heat pumps, which can satisfy space heating and domestic hot water requirements utilising conventional heat emitters - radiators, fan coil units or underfloor heating and hot water storage cylinders. Heat Pumps being part renewable, part electric technology, achieve far greater operating efficiencies than all electric or fossil fuel (gas or oil), combustion based boilers. Heat pumps have been recognised as being capable of helping us reach our carbon emission reduction targets not to mention greatly reducing our household heating bills.
In the commercial sector the pre-eminent heat pump is the air source air-to-air type, which can satisfy the space heating and cooling requirements, however, the sanitary hot water services are still mainly provided by secondary systems such as all electric or gas/oil fired boilers.
Pre 1990's most commercial buildings were cooled by air or water-cooled chillers circulating chilled water to wall mounted or ducted fan coil units and heated by conventional 'wet' central heating systems, either utilising the same fan coil units or radiators. In the mid 1980's, Daikin Industries developed an ingenious new heat pump technology called Variable Refrigerant Volume or VRV. This revolutionised the commercial air conditioning market because, for the first time there was a single system that could efficiently cool and heat commercial buildings, reducing dependence on energy guzzling boilers, which would now only be needed, in smaller capacities, for providing hot water.
What's more, VRV could offer simultaneous cooling and heating from the same system by re-distributing waste or rejected heat that would otherwise discharged to atmosphere! VRV offered many other benefits apart from superior energy efficiency, it was a modular concept so proved much more flexible in terms of the space it occupied and in programming the installation works.
Daikin Air Heat Pumps
Electrical loads were reduced and the speed with which VRV was able to respond to demand was far quicker than any chilled water/secondary heating system.
No surprise then that modular VRV (and later derivatives known as VRF) overtook central chiller systems in terms of popularity in the commercial sector.
However, certain commercial applications remain better suited to chiller systems, for example in large areas with a single temperature set-point or where response times are less critical, spaces with larger cooling loads or very high ceilings.
So has chiller development learned any lessons from the success of VRV? - Heat pump chillers have also been available for some years but at a premium that hindered their success. Such chillers could only operate in cooling or heating. In heating mode, there were limitations and in certain conditions a secondary heating source would still be required to satisfy the heating demand. This has been largely resolved with the more recent introduction of inverter technology (which VRV/VRF had adopted years earlier). Inverter technology enables the heat pump chiller's compressor/s to be boosted, in more extreme conditions, with a frequency increase that exactly follows the required thermal load, resulting in a wider operating range and reducing or eliminating the need for secondary heating.
Heat recovery, heat pump chillers manage to get a little closer to VRV/VRF capabilities because, the chillers offer cooling and heating as before - but - in cooling mode, heat absorbed from the conditioned space and from the compressors, instead of being rejected to atmosphere, is recovered and directed to a second heat exchanger. The recovered heat energy can then be used in areas calling for heating or passed to a thermal storage facility for hot water. In this way chillers can offer simultaneous heating and cooling, a common requirement in commercial buildings, at remarkably high efficiencies.
To manage the heating and cooling requirements of our commercial buildings it's not so much a question of why install heat pumps rather than other technology? More the fact that no other systems offer anything like equivalent energy efficiency and cost effectiveness. A fact that we in the industry trust will be acknowledged in the government's soon to be announced Renewable Heat Incentive.
