INDUSTRIAL & COMMERCIAL HEATING HEAT PUMPS
A domestic air-source heat pump installation. Such equipment is highly sensitive to how it is used
have been disappointing. Unlike established technologies such
as gas central heating, there has been little in the way of standards for heat pump installations to adhere to. Understandably, installers have been on a learning curve, so it is no surprise that some installations have had problems. The EST did not publish much detail
about the installations in its study. But according to a report by Delta Energy and
Environmental, most of the heat pumps on the EST trial were retrofitted into existing buildings (some recent, some older). So it is reasonable to assume that these installations might be typical of the wider UK picture. The crucial fact is that any heat pump is
very sensitive to the way it is utilised. Its real- world performance will only be as good as the system it is part of. This not only relates to the way the heat pump is installed, but also to the way it is used.
designers and installers to assess system ratings
heating produced]/[Electrical energy supplied]. So a one-star system may
not perform any better (in carbon emission terms) than a properly operated gas condensing boiler system. However, as the radiator
oversizing increases and the star rating goes up, so does the predicted SPF. For ground- source heat pumps a two-star rating score will raise their SPF to more than 3, and for air source a star rating of 4 is needed that is equivalent to radiators being oversized by a factor of three to four. This may seem a ridiculously large oversize factor; however, for older systems there is a good
www.cibsejournal.com
The guide is an excellent resource for those who simply want a ‘ball park’ estimation of the potential of heat pumps
chance that the building heat loss may have been reduced by improving insulation and reducing air infiltration, so rendering the radiators larger than needed.
New-build For new buildings the guide provides a look up table to assist in the selection of heating systems that are likely to operate at an appropriate SPF with an aim to
reduce carbon emissions. This uses a combination of room heat loss, heating emitter types and heating flow temperatures to assess the likely SPF for air- and ground-source heat pumps. The table includes radiators, convectors, fan-assisted convectors and variants of underfloor heating systems. The combination of heating system type, heat loss and heating system flow water temperature is used to give a temperature star rating and an SPF. A traffic-light colour- coding system helps to steer the designer/installer to a correct combination to ensure a high seasonal performance factor. The document provides an
excellent resource as a guide for those who are either not able to undertake an in-depth analysis or simply want a ‘ball park’ estimation of the potential for heat pumps. However, the real SPF will be influenced by the heating load calculation and the assessment of the existing heating system – not so difficult for new-build, but for individual older properties, it provides more of a challenge. If the heat pump system is additionally used to provide domestic hot water, then the SPF will be reduced below those suggested in this heating-only guide. Prof Tim Dwyer is technical editor of CIBSE Journal
October 2011 CIBSE Journal 53
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