Heat Recovery Revisited
A properly designed heat recovery system can conserve 50 to 80 percent of this wasted energy and put it to work heating a space or a process. Why don't we do this? Possibly because most people are too busy and do not realize the potential savings. Do not lose out for 2013.
· An air cooled rotary compressor produces 2552 BTUs per horsepower which means that 100 hp produces approximately 250,000 BTUs of waste heat
· 70% recovery would give approximately 175,000 BTUs that are absolutely free to use for room heating or liquid heating
· A typical home requires approximately the same 175,000 BTUs to heat it on the 20° F day
· 175,000 BTUs of gas at $.80 per therm would cost $1.40 an hour for 4000 hours equaling $5600
The next question is what kind of heat recovery systems make sense and are relatively simple to implement? Some of these points were covered in the previous newsletter but are important enough to recap again for air cooled rotaries:
Simple Method:
Exhaust heat from the compressor room in the winter into an adjacent area being sure that there is enough makeup air so the room does not go negative. In the summer an exterior wall exhaust fan would have to be used to keep the room cool. This is especially effective for cold warehouses and loading docks. The ROI on this solution would be normally under one year.
Moderate Method:
Duct the output from your cool compressor to a manually operated Y diffuser, which allows the direction into the plant in the winter and outside in the summer. The ducting has to be designed properly to prevent back pressure, which could cause compressor overheating. The normal back pressure is .25 inches of water. Again the room has to have proper makeup air so a negative pressure is not created, which affects compressor operation. This more complex solution normally has a two-year or less ROI.
Complex Method:
Most often used in a new compressor room, a fully automated inlet and outlet damper system is designed to maintain constant compressor temperature as well as discharge temperature to the plant area year-round. The system requires engineering for the specific compressor(s). Many power companies offer additional rebates for secondary gas energy savings, which help bring the ROI for a complex system below two years.
What happens if you do not have use for the heat from a compressor in the immediate area? With air cooled rotary you can use small horsepower duct blowers with flexible tubing or engineered ducting to carry the heat to the areas that will benefit most.
Many people do not realize that a compressor running between hundred and 180°-190° F can also effectively heat hot water. A properly designed oil to water heat exchanger can be used on both an air cooled and water-cooled machines to carry the waste heat to a process or a remote area. Great care has to be taken to properly engineer the heat exchanger for each compressor so as not to affect oil system pressure.
Hot water heat recovery is used extensively in Europe. Examples are:
· Washroom water in a major foundry
· Hot water for the bleaching process and a paper mill
· Pre-heating of water for boiler applications for an automotive plant
· Feed water for humidification systems in textile weaving rooms
Again many power companies offer additional rebates for secondary gas energy savings which could bring the ROI to below two years.
If it's free or at least has a two-year ROI why don't we use it and be more efficient as well as adding to the bottom line? Let us know what you have for a heat recovery requirement application so we can review it with you. No concept should be considered too wild.
For more information please contact Frank at 508-351-1817 or e-mail him at flederer@hopeair.com
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