GLOBAL COOLING PRIZE | GREE ZERO CARBON Installation is fairly straightforward, in the same way that any household air conditioning system is fitted. The ventilation system needs to be installed on an exterior wall or window, while the photovoltaic panels would typically be installed on the roof. Parallel compression cycle with dual evaporation temperature Traditional unit air conditioners employ single-stage compression refrigeration. There is only one suction pressure for the compressor and, during cooling, there is only one evaporation temperature at the corresponding evaporator. Using the innovative cascade heat exchange and parallel compression refrigeration cycle means there are three suction pressures while the triple-cylinder rotary compressor is working in cooling mode. The three suction inlets are connected with low- and high-temperature evaporator and flash tank discharge outlets, from low to high pressure, respectively. The indoor air return flow passes through both evaporators in turn, creating cascade heat exchange, while the refrigerant at the condenser outlet entering into the flash tank achieves sub-cooling through the first-stage throttle. The cascade heat exchange and flash tank sub-cooling both improve the efficiency of the refrigeration cycle and, therefore, the overall energy efficiency of the air conditioning system. Zone Outdoor climate Control strategy 1 Low temperature, low humidity Mechanical ventilation 2 High temperature, low humidity Evaporative cooling + vapour-compression refrigeration (when needed) 3 High enthalpy, low humidity Ventilation (for dehumidifying) + vapourcompression refrigeration (when needed) 4 Others Vapour-compression refrigeration Figure 1: Control strategies in different climates Evaporative condenser Flash tank Compressor Electronic expansion valve Microchannel condenser HT evaporator Climate adaptive residential air conditioning Climate adaptive means the system can intelligently select one or more of the three modes of vapour-compression refrigeration, evaporative cooling and ventilation, depending on the outdoor weather conditions. For example, ventilation is selected when the temperature and humidity are low, and evaporative cooling when the temperature is high but the humidity is low (see Figure 1, Control strategies in different climates). When it is available and appropriate to do so, the mechanical ventilation system brings in cool, dry air directly. If the outdoor air is warm but relatively dry, and the evaporative cooling mode requirements are met, the water pump will be switched on to create a wet film in front of the ventilator fan, cooling the high-temperature outdoor air before it enters the room. If the indoor temperature and humidity requirements cannot be met with these free-cooling modes, the system will turn on vapour compression in joint operation with evaporative cooling. A new type of compressor The triple-cylinder, rolling-rotor compressor has three suction inlets and one discharge outlet. Together, combined with other components of the refrigeration system, a cascade heat-exchange, parallel-compression refrigeration cycle is achieved, improving the efficiency of the refrigeration cycle. Figure 2: Vapour-compression refrigeration LT evaporator Vapour compression refrigeration explained The ultra-efficient vapour-compression refrigeration system consists of the triple-cylinder rolling-rotor compressor, as described above, separate falling film evaporative finned-tube condenser and microchannel condenser, first-stage expansion valve, flash tanks, two secondary expansion valves, and two evaporators, which are connected to form a completely enclosed refrigeration system. The outdoor finned-tube condenser is sprayed with evaporator condensate or tap water to reduce condensation temperature. Photovoltaics The air conditioning system uses the PV power preferentially, but can seamlessly switch between PVs and the grid when required. The prototype entered into the Global Cooling Awards was not completely net zero because of the size limits, but with further adoption of energy storage and PV grid connection, zero carbon emissions is achievable. CJ Visit globalcoolingprize.org for more information about the Global Cooling Prize. Gree will publish a paper about this new technology at a later date www.gree.uk.com TIM BOXALL is technical sales support manager at Gree UK 54 July 2021 www.cibsejournal.com CIBSE July 21 pp53-54 Gree Global Cooling Prize.indd 54 25/06/2021 17:03