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15/11/2012

 

Energy costs are a major concern of any food producer. One of the most overlooked factors that food manufacturers should consider to make their facilities more energy efficient is waste heat recovery in freezing field.

 

Most processing facilities use refrigeration systems for blast and spiral freezers, chillers, processing rooms, and cold storage. The heat removed by the refrigeration systems is usually dumped to the atmosphere as wasted heat. At the same time, facilities are paying for fossil fuels to heat water for processing and clean up. The enormous amount of wasted heat from the refrigeration system can be efficiently recovered and used to meet the hot water needs of the facility.

 

Waste heat recovery on this scale was not possible just a few years ago because the temperature of the rejected heat was too low to be used directly. Now, low-grade heat can be economically recovered and raised to a useful temperature with ammonia heat pumps and single-screw compressors.

 

Heat pumps are widely used in commercial and residential HVACV applications to harness heat. The cost of electricity to run a heat pump is much lower that the cost of fossil fuels to heat water, because of the inherent efficiency of the refrigeration cycle to move heat from one location to another. Producers can use a lot less fossil fuels in their boilers if they capture the heat they paid for, rather than throwing it away to the atmosphere.

 

Facility managers focus on payback and the long-term energy savings, and include energy rebates and efficiency incentives in the decision. A waste heat capture system will pay for itself quickly and continue to save money for many years.

 

Recent screw compressor design improvements are what enable these new high-pressure heat recovery systems. Using a single-screw compressor heat pump with ammonia, waste heat can be captured and converted very efficiently to heat water up to 195°F. Even if the captured heat cannot provide all of the water heating needed, it can still offload the boilers by preheating the water and feeding it to the boiler.

 

To use ammonia at temperatures and pressure required for large heat pump applications, the screw compressors must be able to handle a minimum of 750 psia at 195°F. The unique Vilter single-screw compressors with cast steel housings are designed for 1100 psia at 230°F. This allows the compressor to generate higher condensing temperatures, producing water up to 195°F.