By ignoring one of the basic and efficient heat exchangers on the market, manufacturers across Australia, in a wide range of industries, could be paying excessive energy costs.
Developed more than 50 years ago, Peter Hendy, owner of Victoria-based Hendy Coils, said that air conditioning style coils are still one of the cost-effective heat exchangers available today. But many people just do not know about them.
According to Hendy, it is possible to have a custom-made heat exchanger designed and built in Australia for a particular application at about the lowest cost per unit of energy transferred when compared to other heat exchanger styles on the market.
Hendy said, “The coils can be used in a wide range of energy recovery applications, including food and timber drying, dehumidification, moisture removal and process heating.”
“They utilise aluminium fins on the air side to provide an extended surface that overcomes the poor heat transfer rate between air and a solid surface, and can use water, steam or other fluids inside the copper pipes.”
“Internal to external surface area ratios as high as 24 to 1 are available and the configurations used are flexible with regard to size, fluid flow arrangement and fin spacing,” he told Manufacturers ’ Monthly.
Hendy said that an industrial laundry is a good example of how the coils can operate.
Hendy said, “Hot water from washing machines must be cooled before disposal to the sewer. So rather than dissipating this energy to the atmosphere, an air conditioning coil can be utilised to transfer this heat to an incoming air stream supplying a drying machine.”
“By preheating this air, the energy requirement of the drying process can be substantially reduced. The hot moist air normally exhausted from the drying machine can also be passed over the air side of another coil and used to preheat the water supplied to the washing machines.
Hendy said that it is also possible to assemble a versatile air-to-air heat exchange system using these devices in a ‘run-around’ or thermal loop energy recovery system.
He said, “The basic system consist of two regular style air conditioning water coils placed in separate air streams of differing temperatures. A small pump circulates a coupling fluid, normally water, in a loop between the coils. Heat energy is thus transferred from one air flow to the other.”
According to Hendy, efficiencies up to 80% are possible, however recovery rates of 60 to 65% are usually more cost effective, he says.
The ‘run-around’ system is said to have a number of advantages over other forms of air to air heat recovery equipment, including no possibility of cross contamination of the air streams.
Hendy said, “Under certain conditions latent heat can be recovered, but no moisture transfer between the air streams can happen.”