COWARD ENVIRONMENTAL SYSTEMS, INC.
500 Birchfield Drive,Suite 501, Mt. Laurel, NJ 08054
856-727-4400 -fax 856-727-4344
e-mail: cesi@cowardenvironmental.com

Heat Reclaim

Heat or Cool - Don't waste it - Reclaim it - Save the fuel and dollars that it represents! All legitimate demands.

We have the expertise and products to make it happen; if only it had no cost. We have coils for "Run Around" systems, "Air to Air" exchangers and "Total Energy" sensible and latent exchange wheels, with efficiencies to as high as 80%. Each type offers advantages, the establishment of which requires careful analysis.

Pay Back Time - The Pay Back Time usually relates to the level of the heat available for reclaim. This level is established by the Log Mean Temperature Difference available between the exhaust and intake air streams. Low level is found in exhaust air streams from structures used to house humans (perhaps 70°F). With an average intake air temperature of perhaps 40°F, the log mean temperature difference approaches 30°F, a small number. High level is found in exhaust air streams from heated processes that can generate much higher log mean temperature differences. Obviously the latter allows for a much faster pay back time and therefore is more important to consider. Of course, the quantity of heat reclaim is directly proportional to the number of operating vs. non-operating hours. The efficiency of any system is described as the ratio of the quantity of heat that is reclaimed vs. the total available for reclaim.

Run Around System - The "Run Around" system offers a slightly lower efficiency potential but does not require that the exhaust and supply and air steams be adjacent to each other.

It requires the added air side pressure drop against the fan and the horsepower required to circulate a heat transfer fluid. Both of these energy requirements must be subtracted from the total heat quantity reclaimed. The latent exchange that might occur requires careful consideration of handling the Ice formation on the coils. Care must be taken to assure that the external fin surfaces are cleanable in the instances where contamination is possible.Total Energy Wheels - The "Total Energy" wheels allow for much higher efficiencies because the heat from latent conversion becomes available. Care must be taken to guard against cross contamination between intake and exhaust streams that must be adjacent to each other. The fact that the wheel represents an excellent filter in itself leads us to believe that the wheel should be washable. Only certain types of desiccants allow for this feature.

In the determination of any reclaim efficiency and the Pay Back rates it is necessary that the intake air psychometric conditions be known on a year round basis. The ideal method of determining this quantity is probably the use of the ASHRAE Computerized Bin Weather Data. This will allow for the calculation of the log mean temperature difference on an hourly basis for 365 days per year. It is possible to make approximate calculations by averaging the monthly weather temperatures available from the local weather stations. We suggest that you allow us to assist you in approximating the reclaim rates available from each type system and the budget costs before you finalize your selection.

by:

Nick Musulin

7-99