Understanding HVAC – The Next Step for Energy Auditors

HVAC For Energy Raters, Energy Auditors, And Building Analysts Class In Atlanta

In 2003, I finished building a high performance home and moved into it. Shortly thereafter, I enrolled in a HERS rater class and got myself certified as a home energy rater. So, with all that experience plus my background in physics plus the fact that I spent summers in my teen years helping my grandfather work on air conditioners, you might think I’d’ve had a good handle on HVAC.

In 2003, I finished building a high performance home and moved into it. Shortly thereafter, I enrolled in a HERS rater class and got myself certified as a home energy rater. So, with all that experience plus my background in physics plus the fact that I spent summers in my teen years helping my grandfather work on air conditioners, you might think I’d’ve had a good handle on HVAC.

If so, you’d be wrong. Oh, I knew the basics – that a refrigerant moved heat in air conditioners & heat pumps, that furnaces burned a fuel and then moved the heat to the living space, that duct systems in most homes have a lot of problems. But what I really found when I became a home energy rater was that I had waaaaayyy more to learn. Over the past seven years, I’ve mostly taught myself what I needed to know and have gotten to the point where I know HVAC issues pretty well.

Let me tell you a story about how incomplete knowledge could get a new home energy rater into trouble. About 6 years ago, I did a Manual J heating & cooling load calculation for a client, and they sized the systems on my recommendation (actually a bit larger).

A year later, I got the call. The house wasn’t cooling below 80 degrees F, and the air conditioners were running continuously. I went out and tested the house for infiltration. No problem there – it was as tight as I had modeled. I tested for duct leakage, and that wasn’t it either. Then I went out to the house with a flow hood (balometer) and measured the air flow. Ah ha! The 7 tons of air conditioning capacity was moving only 5 tons of air (2000 cfm instead of 2800 cfm).

The point of my story is that putting in a correctly sized air conditioner is only part of the story. The air distribution system has to be properly designed as well.

Another place where ignorance can get a new energy auditor in trouble is duct sealing. Most heating and cooling equipment is hvac air conditioner evaporator coilgreatly oversized and is attached to a duct system that’s too leaky and too small. Energy auditors know how to measure duct leakage, so it’s easy to go out and start telling everyone they need their ducts sealed.

The problem is that if the static pressure in the system goes up too high as a result of the duct sealing, the evaporator coil can freeze up. In fact, David Richardson, an EVER rater and HVAC contractor (and author of yesterday’s guest post on combustion safety), said that his local utility duct sealing rebate program inadvertently gave him a lot of business in the ’90s for this very reason.

I’ve been wanting to do it for a couple of years now, but last Friday, we held our first Advanced HVAC for Raters class here in Atlanta. Thirteen home energy raters & building analysts came to the class, and we covered a lot of the basics with them:

  • Identifying different system types
  • Understanding the refrigeration cycle (They acted it out!)
  • HVAC design fundamentals
  • Air flow and static pressure

We’ve got another Advanced HVAC for Raters class coming up on 24 September in Asheville, NC, so if you’re in the energy rating or auditing business and you want to improve your understanding of HVAC, sign up for it. (There’s a $30 rebate if you sign up by the end of next week!)

If you want to go even deeper, sign up for the 3 day class on HVAC Air Diagnostics and Balancing that we’re teaching 8-10 November. It’s a National Comfort Institute (NCI) class that we’re sponsoring and will be geared towards energy raters and auditors. David Richardson (mentioned above) will be teaching the class for us, so you’ll benefit from his HVAC knowledge and experience as well as his HERS and NCI expertise.

This is an area where anyone with expertise can find their services in demand. There are certainly some good HVAC contractors out there, but clearly many of them don’t understand air flow, and that’s why there are so many crappy duct systems. Whether you take our classes, someone else’s, or learn it on your own, as an energy rater or auditor, you NEED to understand HVAC on a much deeper level than you got in your initial training.

This Post Has 5 Comments

  1. Allison, this is a good read.
    Allison, this is a good read. But I’d like more details on why that 7-ton was only moving 5 tons. Can you expound?

  2. Good question, Matt. My trip
    Good question, Matt. My trip to the house to test the air flow was my last involvement with that project, but I’m pretty sure that the main problem was that the ducts were undersized. They used hard pipe and put in what was mostly a trunk-and-branch system (both good for air flow), but even with an installation that looks good, ducts that are too small restrict air flow.

  3. Many thanks, Allison. That’s
    Many thanks, Allison. That’s what I was thinking, judging from the flow of your blog’s article, but I didn’t want to make a faulty assumption. The next question in response is probably obvious, and it’s answer it probably obvious, but here goes: how does one fix that issue? Just simply change the ductwork, right?

  4. Yep, the ductwork needs a
    Yep, the ductwork needs a retrofit. Sometimes it’s as simple as adding another return duct with a new vent, because undersizing returns is more common than undersizing supplies. Sometimes it’s best to rip the whole thing out and start over. This is why it’s best to do the whole Manual J-S-T-D process up front.

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