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Mr. Heat Mechanical Inc. Heating Cooling Electrical Hydronic Contractor Official Website

The Effects of Coil Selection with Outside Air Loads

HVAC and process heating/cooling must deal with the added tonnage created by using fresh air from outside. Most times, the requirement for fresh air is mandatory and can go from 10% all the way to 100 % of the system air flow. There are numerous rules and regulations written to eliminate air flow quality problems, including bacteria and other micro-organisms, that can cause health problems. Rarely is a system designed with more fresh air introduction than is required by law.

We have all heard the term “economizer”. However, many in our industry do not really understand this term. An economizer is used when the temperature of the outside air is at or near the temperature of the return air in the system. An example would be a design return air temperature to an HVAC unit that is 80 degrees F. When the outside air temperature is below or reaches the design temperature, some or all the return air can be exhausted (sometimes stated as “relief “), and an outside air damper opens to bring in fresh air. One must equal the other. Whatever you exhaust must be made up with the introduction of new fresh air into the system. If I exhaust 4000 CFM, then 4000 CFM must be introduced through the outside air damper.

 

Source : uscoil .com