ACR Journal

21 ENERGY RECOVERY BEYOND THERMAL ENGINEERING LORDAN • Unit 1 North Road, Penallta Industrial Estate, Hengoed, CF82 7SS • 01443 812222 • stuart@lordan-uk.com Design and manufacture Small to Large coils MADE IN BRITAIN ACR-SEP19-LORDAN.qxp_Layout 1 12/08/2019 16:18 Page 1 While purposeful in terms of designing systems to broad operational envelopes, these options add complexity by involving third-party integrations to the design and operation. Recent developments improving the low ambient operating ranges of direct expansion products (air conditioning) means that there is now a rise in cooling and heating solutions using DX heat exchangers with either third party or integrated heat pumps. Previous DX cycle logic and associated technology would restrict operation to a particular ambient range. More so in the UK, these restrictions in heating would be felt when the supply air ambient dropped below 10 o C. Advances in technologies such as vapour injection, which maintains compression temperatures, and tighter refrigerant flow control through inverter technology; has allowed the reduction of costly electrical preheat elements usually used to raise inlet air temperatures. Integrated heat pumps generally have a self-contained refrigeration circuit within the AHU chassis. A heat exchanger is positioned in the supply air stream and one in the extract air stream. The position of these heat exchangers is paramount to system operation and eciency. To aid the heating process, the condenser, which is in the supply air stream, is placed downstream of the thermal wheel and the evaporator, located in the buildings extract, is before the thermal wheel. This means that heat energy removed from the building is transferred to the refrigeration cycle, raising refrigerant suction temperature/pressure and requiring less work from the compressor to raise the head pressure/temperature to ,in turn, increase the air temperature. Further energy is recovered from the thermal wheel passing to the supply air stream, tempering the ambient air in really low outside temperatures before passing through the condenser. Increased Demand The current instruction from industry bodies to prevent transmission, infection and contamination is to turn o thermal wheels and remove air recirculation from the central plant. Whilst thermal wheels provide a very low mixing of air streams; further air sealing is present to reduce possibilities further for applications where hygiene is a priority. However, this still is not enough to satisfy the advice being provided. A further energy recovery system applied to air handling units is a run around system. This is a hydronic system of very similar principles to that of the DX, but rather than exchanging energy through refrigerant, it uses water as a medium and a circulation pump instead of a compressor. Run around systems are particularly useful for transferring energy between separate extract and supply systems as we see applied in clinical environments. The ability to reuse energy in this manner improves the system, and in turn, building eciency. It reduces the requirements for additional equipment to meet building demand and reduces operational costs. The application of DX cooling and heating within air handling units and smaller energy recovery ventilation systems is becoming the popular choice for maintaining broader climate control within a building as designers are pressing to use higher ventilation rates with no recirculation. www.exi-tite.com Integrated heat pump air handling unit showing direct expansion coil in supply air stream.