Electrical equipment and industrial instrumentation supplier Magnet says it has designed and installed South Africa’s first energy efficient ammonia heat pump.
The hot water project at poultry farmer Rainbow’s chicken processing plant in Hammarsdale, KwaZulu-Natal, entailed the installation of a system to harness the waste heat generated by ammonia compressors to produce hot water in the existing refrigeration plant.
The site previously relied on an electrode boiler to generate steam from water supplied by the municipality. The generated steam would heat the water entering the two hot water tanks used for site ablutions and washing.
“The installation of an ammonia heat pump has significantly improved the efficiency of the hot water system at the plant and, as a result, has reduced steam consumption,” says Magnet MD Brian Howarth.
The new heat pump, which was installed in the existing refrigeration plant, consists of a suction intercooler, a six- cylinder reciprocating compressor with a variable-speed drive, a plate-and-shell condensing heat exchanger and a programmable logic controller.
The operating principle of this system is the hot ammonia gas, which has already been compressed by the high stage compressors, and is further compressed in the heat pump before being condensed in the plate heat exchanger.
As the gas condenses, it transfers heat to the water on the other side of the plate, where the water outlet temperature is controlled by varying the compressor speed.
The water is heated to just below the condensing temperature of the ammonia, which is typically 32 °C at that operating pressure. The heat pump then heats the water to 55 °C.
In addition, power-monitoring equipment on the power supply calculates power consumption and the coefficient of performance of the heat pump.
A new water make-up valve is used to control the operating level in the hot water tanks. Hot water is mixed with domestic water in a mechanical temperature-regulating valve to ensure a constant preheated supply to the boiler.
The company reports that the project has resulted in an average saving of 300 kW, based on the plant’s current average water consumption rate, and has a payback period of just under two years.