ACR Journal

December 2021 | January 2022 AIR CONDITIONING 36 Harriet Evans, MHI sales director at Beijer Ref UK & Ireland, explores some of the key points to consider when designing a VRF system. Improving e ciency with heat recovery VRF Volume 8 No.1 Variable Refrigerant Flow (VRF) air conditioning is a system that delivers high performance in cooling and heating for all commercial applications. It regulates its capacity to meet demand and often covers larger design loads than splits or multi splits. MHI’s KXZ range of VRF includes both heat pump and heat recovery models, but what do they o er and how do you make the right choice for each project? There is one clear operational di erence between the two. A heat pump can operate in a single mode only, meaning that all indoor units are in cooling or heating at any given time. A heat recovery system, meanwhile, allows each indoor unit to be in either cooling or heating mode, irrespective of what the rest of the system is doing. Making the right choice When designing a system, the type of areas being served is the main consideration. Open plan o ce space, for example, would normally be considered one zone, regardless of how many indoor units are involved. For this reason, a heat pump system could be the right choice as all the units would be required to be in the same mode. When specifying for a number of di erent areas, such as a collection of small o ces or meeting rooms, or a collection of open plan spaces, then ideally each area should be able to regulate its own temperature and cool or heat as required. This is where a heat recovery system would come into its own. This additional flexibility is the main reason why heat recovery systems are chosen, alongside the ability to reduce carbon footprint, meet energy-saving standards and cut building operation costs. That must be balanced initially against higher initial capital costs because of more components and the VRF offering simultaneous operation of both cooling and heating installation of three main refrigerant pipes around the building from the outdoor unit, rather than two with a heat pump system. System efficiency Air conditioning takes energy from one area and rejects it elsewhere. Normally this would see heat energy from a room rejected outside, using electricity to power the system’s compressor and the associated fans which circulate air. E ciency, whether EER in cooling or COP in heating, is a ratio of energy consumed to energy transferred / rejected / introduced: 1 kW of energy consumed to 1 kW of capacity produced, equals an EER or COP of 1; 1kW consumed to 4 kW produced gives a ratio of 4. The higher the number, the more e cient the equipment is.