When designing for cold weather climates one area that has been largely disregarded is air stratification in the mixing box of an Air Handling Unit (AHU). The presence of air stratification is a threat to freeze and rupture hydronic coils and thus is the reason low-limit freeze stats are used to stop the unit from operating when freezing conditions are present. However, repeated “nuisance trips” are undesirable and the most commonly used technique to avoid this problem is having the control system abandon the airside economizer and switch the unit to heating mode. It is often assumed this fix is not highly impactful to energy use because it only happens on the coldest of days. However, in most cases the air stratification within the AHU mixing box is so prevalent the airside economizer ends up being abandoned when the outside air temperature drops below 40°F. Therefore in an effort to be energy conscious, system designers should strongly consider the benefits of a high-performing static air mixer to eliminate the air stratification. A well-mixed airstream would allow most airside economizer systems to operate until an outside air temperature of -5°F, which increases the functionality of the system design a significant amount of hours in cold climate locations. Thus the use of a high-performing static air mixer to extend economizer operation provides even greater system benefits that just eliminating “nuisance trips” and protecting the coil. This paper serves to detail the significant opportunity for energy savings by installing a high-performing static air mixer in AHUs using airside economizers coupled with hydronic coils.
Citation: Cold Climate Conference, 2012
Product Details
- Published:
- 2012
- Number of Pages:
- 8
- File Size:
- 1 file , 2 MB
- Product Code(s):
- D-CCC12-27
