Book - School of Science and Technology

374 Air-conditioningBecause refurbishment of buildings will have to comply with Part L, a set of slightly lessdemanding standards are defined for newor refurbished systems in existing buildings.This is in recognition of the fact that there is less design flexibility in such situations. Asimilar set of design targets is provided for buildings that are mechanically ventilated.Because the calibration data only exists for office buildings, the so-called Carbon PerformanceRating is only applicable to office buildings.For buildings other than offices, the only requirement is in terms of specific fan power.This is defined as `the sum of the design total circuit watts, including all losses throughswitchgear and controls such as inverters, of all fans that supply air and exhaust it back tooutdoors (i.e. the sum of supply and extract fans), divided by the design ventilation ratethrough the building'. Again, different target values have been defined for ventilationsystems in newand refurbished buildings. Consideration is being given to the developmentof similar targets for pumps and refrigeration equipment, so that appropriate energyefficiency standards can be developed for a wider range of building types.Other important newfeatures of the 2001 Approved Document are the emphasis oneffective commissioning and on the provision of adequate energy metering. Considerationof both these issues is required at the design stage, so as to ensure the building user is ableto operate the systems reasonably efficiently, and to monitor on-going performance as ameans of ensuring the required performance is maintained.Whilst statutory regulation may not be appropriate, there is already a quite discernibletrend to question whether air-conditioning is a necessary prerequisite for quality commercialpremises, for example, Chapter 13 deals with the suitability of natural ventilation solutions.Some years ago in response to a Code of Practice on Environmental Issues by theEngineering council CIBSE stated the following which still holds good today:If the requirement for air-conditioning has been fully established, the following principlesshould be adopted and adhered to:. the system should be energy efficient (with due regard being given to the inclusion of costeffective energy saving methods such as free cooling) and also controlled to minimise energyuse.. operation and maintenance strategies should be devised and the necessary reÂgimesadopted to deliver economy, efficiency and effectiveness in the working of systems throughouttheir life cycles.. system design, construction and commissioning should be carried out in accordance withcurrent national and European standards, codes of practice and statutory requirements.. cooling system refrigerants should be used in accordance with the policy laid down in theCIBSE Guidance Note on cfcs, hcfcs and halons.General principlesThe desired atmospheric condition for comfort applications usually involves a temperatureof 18±22 C in winter and 21±24 in summer; a relative humidity of about 40±60%and a high degree of air purity. This requires different treatments according to climate,latitude, and season, but in temperate zones such as the British Isles it involves:In winter. A supply of air which has been cleaned and warmed. As the warming lowers therelative humidity, some form of humidifying plant, such as a spray or a steam injector,with preheater and main heater whereby the humidity is under control, is generallynecessary.