The Hole' in Whole' House Performance

June 1, 2007
Over the past year or so, my organization has been training an increasing number of home energy raters. As a result, we're learning a great deal about

Over the past year or so, my organization has been training an increasing number of home energy raters. As a result, we're learning a great deal about home performance, energy ratings, and how that community tends to look at the HVAC system. For the most part, building performance folks view the HVAC system as a part of the "house as a system," focusing primarily on duct leakage and its effect on energy usage.

Today's energy programs view the HVAC system as a static system, and have little understanding of the dynamic effects of a live, working system. Outside of providing incentives for higher equipment SEER and tight ducts, little attention is given to the operation of the system itself. Some attempts have been made to include refrigerant charge in these programs, but unfortunately because they assume air flow, they also miss the mark, often by as much as 20% to 30%.

Interestingly, the energy rating software used to rate newly built homes (REM/Rate) has a field where you can include a performance adjustment for the HVAC system. The default however is 100%, and raters are taught to leave it there, assuming 100% performance since the ducts are sealed. The truth is, when we measure a "live" system in terms of Btus to and from the conditioned space, typical system performance is 50% to 70% — with tight ducts and a tight envelope.

To put this in perspective, even if we used a 70% HVAC performance factor, the system would fail any energy efficient home standards. Tim Hanes, a rater with Cenergy, in Iowa, found that to get an equal performance reduction from the building envelope, he had to input 1/4-in. of attic insulation in the REM/Rate software. That, of course, would not only fail any energy rating, it wouldn't even meet code!

So what is this "hole" I'm talking about? Put simply, it's the HVAC system's inability to deliver the BTUs it needs to move in and out of the home for the Watts or therms it's consuming. This deficiency isn't just from duct leakage. It‘s the result of a host of system defects including poor design, poor duct sizing, poor register selection and placement, improper installation causing restricted airflow, and no air balancing — in other words, poor total system performance.

While over the past 15 years or so there has been an increasing focus on the "house as a system," many seem to have lost track of the "HVAC system as a system." While all the interactions a structure has with the HVAC system are important, it's more important to get the HVAC system right first. After all, the building industry looks to us as the experts in HVAC.

Your work affects the biggest energy usage in a home. With this power comes responsibility. But also with it comes a great opportunity to do the right thing and be profitable at it.

Let's stop taking half measures such as just sealing ductwork, or just replacing boxes with higher SEER or AFUEs. The future is in proving delivered BTUs. After all, Btus translate directly to Watts or therms. This is truly where the rubber meets the road in HVAC system performance. In the near future, Btus will be the new currency of utilities, of carbon emissions programs, and of other energy reduction programs.

The other benefits of delivering the right Btus and airflow to the right places include improved comfort, safety, equipment life and reliability. These are all things we strive for as an industry. But often with great frustration, we miss the mark. How many times have you installed new equipment and a customer complains he never saw his bills go down, it's less comfortable than the old one, and now he must turn the TV up when the air comes on?

When you get a system performing properly it's amazing how these problems go away.

We recently tested a 15-EER heat pump in a brand new, energy efficient Texas home with tight ducts that had 1.2-in. of static pressure and over 10 amps of current draw from the variable speed blower. We measured operating efficiency at 10 EER. This home passed all other energy ratings with flying colors. Do you see a problem here?

The silver lining in all this is that YOU, the HVAC contractor, are in the driver's seat totake that average performance rating from 60% to more than 90%. The energy and building industries need your help to fill in the "hole in whole house performance." Do it right, and you'll reap the rewards. Do nothing, and miss the boat. The choice is yours; it always has been.

Dominick Guarino is chairman/CEO of National Comfort Institute, a national training, certification, and membership organization focused on a variety of expertise including Carbon Monoxide, Combustion, Air Diagnostics and Balancing, Performance-based Contracting, and more. Contact him at [email protected] or call NCI at 800/633-7058.