COILS, COOLERS AND CONDENSERS
recovery, heat pumps and photovoltaics). The solar system on the roof of the supermarket is designed to fully cover own electricity consumption needs on Sundays. During opening hours, the solar collectors cover some 40-55% (distributed throughout the day) of the demand. Around 70% of the heat energy is derived from waste heat from the central commercial refrigeration, while the heat pump covers peak heat loads.
Transcritical CO2 cycle
Because the cooling and lighting systems are the largest energy consumers in supermarkets – together accounting for some three quarters of the entire energy requirement – special attention was paid to energy-effi cient operation and environmentally friendly refrigerants when it came to the refrigeration in Norderstedt. The innovative cooling concept is based on a central transcritical CO2
process which, in turn,
supplies decentralised refrigerant cycles in the individual cooling units by means of circulating water. A Güntner S-GVH FLAT Vario gas cooler with a capacity of 119 kW transports the unusable heat from the transcritical CO2
cycle to the
ambient air. CO2
The evaporator in the transcritical CO2 multi-compressor cycle is used primarily as a
evaporator integrated in the buffer tank
A further special structural feature of the transcritical CO2
evaporator used in the transcritical CO2
system in Norderstedt is that the process is
surrounded by a cold water buff er tank. When the CO2
evaporates, the cold transmits directly to the water in the buff er tank without the CO2
the water.
Because cold water from the buff er tank supplies cooling water to the condenser of the connected “Epta Blue” refrigerated cabinets and is available in a suffi cient or redundant quantity, the supermarket’s entire cooling technology can be supplied from this tank without loss in the event of a fault in the CO2
cycle, allowing adequate grace period for service call-outs. entering
heat pump. This means that the condensing temperature of the connected refrigerated cabinets and condensing units in the cold rooms can be kept low to increase effi ciency.
Heat recovery for heating and raw water The usable heat on the high pressure side downstream of the compressors is directed in heat pump mode via a plate heat exchanger which is connected to the heating network. Raw water can therefore also be heated effi ciently, owing to the high discharge gas temperature. In addition to the heat pump, the waste heat from the refrigerated cabinets serves as the main energy source for heating the supermarket. The Epta refrigerated cabinets used are fi tted with
“blue boxes” for this reason. The entire waste heat is delivered to a central cooling water system and can be used in this way for the heating.
Energy-saving refrigerated cabinets The refrigerated cabinets on the operator side were also optimised to ensure the lowest possible energy consumption. All refrigerated cabinets (normal and deep freezing) are thus enclosed by glass doors in chest or shelf form in the REWE green building, so as to avoid cooling losses from the outset.
The anti-glare glazing of the deep freezers is additionally fi tted with anti-fog coating, which prevents the panes fogging up when the doors are opened, thus in turn eliminating the need for an electrical window heater.
Axair
www.acr-news.com October 2017 41
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