Because forced-air heating and cooling systems are assembled on site from a great many parts, there are many ways for installers to make mistakes. Researchers have repeatedly shown that a high percentage of residential forced-air systems have major problems, including duct systems that are poorly designed, poorly located, and leaky. Other problems include incorrect refrigerant charge and too much or too little airflow over the cooling coil.
The classic solution to these problems — in addition to the obvious step of better duct system design — is to insist on a more rigorous commissioning process. “Commissioning” refers to the process of testing and adjusting installed equipment to be sure that it performs in accordance with the manufacturer’s specs and the designer’s intent. Although commissioning is rare for residential HVAC systems, it is a routine step for commercial and institutional buildings.
As I noted in an earlier blog, The Energy Star Homes Program Raises the Bar with Version 3, the Energy Star program has decided to include requirements for the commissioning of forced-air HVAC systems, beginning January 1, 2012. The following commissioning steps will be mandated:
For years, energy experts have been advising HVAC installers to implement all of these time-consuming and tricky commissioning steps; yet few installers actually perform them — or even have the specialized equipment needed to do the required testing.
Until recently, I accepted the logic behind this package of commissioning recommendations, and advised builders to insist that these steps were followed. However, a recent conversation with Marc Rosenbaum, an engineer at South Mountain Company in Massachusetts, has led me to rethink the wisdom of residential HVAC commissioning.
Instead of forcing HVAC installers need to do a better job of commissioning their equipment, it might make more sense to conclude that conventional forced-air systems are so problematic that they shouldn’t be…