The existing condensers
above the refrigeration
room condense the
ammonia before it flows
to the liquid receiver
9 January 2012 – An energy efficient hot water project has been completed at Rainbow’s chicken processing plant in Hammarsdale, Kwazulu-Natal, South Africa.

“The installation of an ammonia heat pump, the first of its kind in South Africa, has significantly improved the efficiency of the hot water system at the plant and as a result, has reduced steam consumption,” says Brian Howarth, managing director of Magnet, a company that implements and supports electrical equipment and industrial instrumentation throughout Southern Africa to ensure optimum energy efficiency.

“The project encompasses a new system to harness the waste heat generated by ammonia compressors in the existing refrigeration plant to produce hot water. The site previously relied on an electrode boiler to generate steam from municipal supplied water. This steam heats water entering the two hot water tanks used for site ablutions and washing.”

The new heat pump, which has been 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 new PLC.

The operating principle of this system is the hot ammonia gas which has already been compressed by the high stage compressors, 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. 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 via the heat exchanger to 55°C.

Power monitoring equipment on the power supply has been installed to calculate power consumption and the COP (coefficient of performance) of the heat pump. An insulated panel structure encloses the heat pump and maintains the temperature within the heat pump.

A new water make-up valve is used to control the operating level in the hot water tanks. Liquid ammonia from the heat exchanger is sent to the existing liquid receiver in the refrigeration room. Hot water is mixed with domestic water in a mechanical temperature regulating valve to ensure a constant pre-heated supply to the boiler.

This project achieves an average saving of 300 kW based on the plant’s current average water consumption rate and has a payback of 1.8 years.