Ducts And Efficiency

I just reread the May 27, 2002 issue with its four articles focusing on zoning. All recommendations seem to indicate that design allowing a considerable air bypass from supply to return when minimum airflows occur is acceptable. My concern with this procedure is that the EER and possibly the SEER of systems which permit enough bypass as to reduce return air temperatures significantly will be reduced to a much lower level.

I know that the kW input to a system goes down as the airflow is reduced and the suction temperature goes lower, but in one case I checked the EER ranges from 11.24 at 72 degrees EWB to 9.58 at 62 degrees EWB. We have always held that the supply ductwork should be capable of moving the air required at the system’s minimum capacity, i.e., low speed on a two-speed condensing unit.

I would be interested to hear any other views or evidence regarding this. Great magazine!

Fred G. Russenberger Jr., P.E., GRC Mechanical Services, Inc., South Hackensack, NJ

Real Zoning Control

My company, Comfort Solutions Inc., has been in the distribution business six years specializing in zoning. We sell zoning products to HVAC contractors in North and South Carolina.

I read all the zoning articles appearing in the May 27 edition of The News. However, I take exception to the notion that a thermostat with remote sensors alone is a substitute for zoning as claimed in the article, “An Alternative to Zoning.” And it certainly is not energy efficient, as the article implies.

The article stated that “the consumer can place control where it is needed.” Not so. This only places the “command” where it is needed, but does not actually “control,” since it fails to prevent the conditioned air from going where it is not needed nor wanted. This thermostat will continue to waste energy, not save energy as the article implies.

It might make one feel they are in “control” to able to select the temperature they desire while upstairs at night. Good luck on actually achieving it while the HVAC is still dumping unwanted air downstairs. In the morning, reality will set in when it will be freezing downstairs.

Zoning is all about control, real control. Zone thermostats are located in the best location for proper control. However, “real control” is only accomplished when thermostats are accompanied by zone dampers, a bypass damper, and the simple electronics that make it all work together. Conditioned air is delivered when it is needed, where it is needed, not where and when it is not needed.

The thermostat featured in the article is no alternative to zoning. It is merely an alternative to a less expensive thermostat. A better title would have been “A Zoning Wannabe That Isn’t.”

Scott McKinnon, President, Comfort Solutions Inc., Wilmington, NC

Publication date: 07/22/2002