40 All Electric Variant Refrigerant Flow with Air Source Heat Pump This all electric system is gaining traction an many new buildings, especially in temperate climates such as Washington State, where heat pumps operate at high coefficients of performance throughout the year. According to a 2022 survey by AMCA International and Applied Marketing Knowledge, VRF units were installed in 14% of new, non-single family home construction projects in the United States, a number that is expected to continue to grow.1 Fresh air requirements for this dedicated outdoor air system are met through the rooftop air handling unit (AHU) in Fig 4.2. Fresh air enters the building through the AHU, is distributed via vertical shafts and horizontal ducts and enters individual spaces through supply grilles (Fig 4.4.) The outside air is conditioned through electric resistance heating and direct expansion (DX) cooling coils. The AHU system can accommodate heat recovery. Heating and cooling loads are met through a series of roof-mounted variable refrigerant flow (VRF) outdoor units and delivered through refrigerant lines to the VRF indoor units in each space (Fig 4.4). Indoor air is circulated through the units to provide heating and cooling. Any condensate is collected within the units and pumped out. Multiple indoor units can be served by one outdoor unit with some modern systems allowing for simultaneous heating and cooling. References 1 Applied Marketing Knowledge, 2022, HVAC Terminal System Selections: A Real-World Project Data Survey, AMCA International
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