RACA Journal March 2020 | Page 56

Projects 1 Each rack has six Frascold semi-hermetic compressors, two on the medium temperature circuit (-5 o C suction), two on parallel compression/MT and two much smaller compressors on the low temperature. The installed refrigeration power on each rack totals 98kWr on MT/Parallel and 15kWr on LT. Built and tested at the Mainstream Refrigeration factory in Ottery, the overall dimensions of racks fit through a standard height doorway. REDUCTION IN ENERGY USAGE 2 3 CO 2 as a refrigerant with zero ODP and a GWP of 1, has reduced the environmental carbon footprint of Woolworths’s refrigeration plants and with other interventions, has reduced energy usage. Variable speed drives on each rack compressor to balance the temperature set point closely with the refrigeration demand of all the cabinets and cold freezer rooms is one of many design features to reduce energy usage to a minimum. Floating suction temperatures to match demand, electronic expansion valves, parallel compression, EC variable speed fans (4 x 800mm diameter) on each of the two roof mounted gas coolers, air defrost on the MT cabinets, alarms to warn when cold room doors are left open, all contribute towards lower energy usage. For food safety and quality control, the temperature of product in the different cabinets are closely monitored by probes in artificial ‘hams’ which have the same thermodynamic properties as the actual product in the cabinets, for example chicken, cheese, milk. 1. 2. 3. 4. 4 5. In the event of a severe CO 2 leak in the plant room a fan automatically exhausts the CO 2 from ground level via a duct. A CO 2 sensor is mounted close to the inlet to the exhaust duct. Backup cold stores are fitted with Thermo Coil CO 2 evaporator blowers. The store has two backup low temperature stores. Cold room doors are fitted with a ‘talking’ alarm to warn when doors are left open and buzzers to warn when CO 2 levels are high. Open doors and high CO 2 levels are also indicated on the monitor of the Guardian Controls PMS. Entrance to the food market is directly from the basement car park. 5 54 RACA Journal I March 2020 www.hvacronline.co.za