7 Steps to Commissioning a New Home & HVAC System

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hvac system static pressure measurement new home design and commissioning

Ken Fonorow is a friend of mine whom I've known since my days on the Gainesville Energy Advisory Committee when I was in grad school in the mid-'90s. He's also helped build the market for ENERGY STAR and high performance homes in Florida. When I saw him last year at the Southeast Building Conference, he told me about a paper he'd written with the folks at the Florida Solar Energy Center about commissioning new homes and their HVAC systems, and it's got some great advice for ensuring that good design is leads to high performance. (It also helps maximize the performance of bad design, but let's not discuss that.)

In the paper, they discussed how they worked with two production home builders in the Building America program. The purpose was to develop methods that would lead to more energy efficient homes, and here are the 7 steps they identified for commissioning new homes:

  1. Testing for Air Leakage. A leaky house doesn't perform well, as it loses conditioned air and allows unconditioned air into the house.
  2. Testing for Duct Leakage. Same applies to the ducts.
  3. Pressure Mapping. A home that has pressure imbalances has more air leakage. For example, when you close a bedroom door and the conditioned air that your HVAC system pumps into the room has no return path to the air handler, it'll find holes to the outside more easily. This test looks for those pressure imbalances.
  4. Outside Air Flow Measurement. A high performance home brings outside air into the house intentionally with a mechanical ventilation system. The amount of air you bring in must meet the design or your heating and cooling system could be overwhelmed and your home inefficient and uncomfortable.
  5. Total External Static Pressure. A forced air heating and cooling system has two parts: the equipment and the distribution system (the ducts). If the ducts aren't designed or installed properly, the blower in the equipment fights against a high static pressure cannot push enough air out into the duct system to keep the house comfortable.
  6. Temperature Drop for Air Conditioners. An air conditioner working properly should have a temperature drop (ΔT) of about 20° F. This is an easy way to find problems. (Furnaces also should be tested for temperature rise, but the Floridians who wrote this paper didn't address that.)
  7. Exhaust Fan Air Flow Measurement. Because of numerous installation problems, most bath fans get about half their rated air flow. Find this problem before anyone moves in.

You may notice in reading the list that some of the items are clearly in the HVAC contractor's bailiwick, but others are not. There's usually not a single person assigned to looking at the house as a system to ensure that the principles of building science don't get subverted.

If the home builder makes sure that someone does this commissioning, whether it's the HVAC contractor, a home energy (HERS) rater, or someone else, the home is much more likely to perform well. That's good for the people who live in the home and good for the builder and trade contractors, as they'll have fewer callbacks.

Of course, commissioning must be preceded by integrated house design and good HVAC system design. In the bigger picture, the steps are:

  • Design
  • Execute
  • Commission


Download the FSEC commissioning paper.

 

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Comments

M. Johnson

Those FSEC ideas are simple and good. It would be a big plus if everybody understood them.

John Poole

Nice summary, Allison. And thanks for providing the white paper.

Allison Bailes

M. Johnson: I'm with you 100% there. Let's spread the word. 
 
John P.: Thanks and you're welcome!

Bob

A big problem is equipment is typically oversized to cover up problems. Stop the oversizing and it forces the building to be done right.

Thomas Anreise

This is a great synposis, Allison. I think it captures a good deal of the v3 requirements that are currently being balked at or written off as dubious. In the NW, we have a well-established approach to the commissioning requirements via our PTCS (Performance Tested Comfort Systems) program, which integrates well into the v3 checklists/requirements here. For more info, see our website.

Allison Bailes

Bob: Good point about oversizing. That should be set in the design phase, so in a true high performance home, the commissioning of that part should just be verifying that the HVAC contractor installed what they were supposed to install. 
 
Thomas A.: Yes, the new ENERGY STAR Version 3 checklists do include this stuff, which is great. As I wrote on Friday, I'm not crazy about all the prescriptive requirements they've loaded up the program with, but I do like the ones that relate to commissioning. Thanks for the invitation to check out your Performance Tested Comfort Systems in the Pacific NW (one of the places I used to live).

Jim Bergmann

Watch rules of thumb for air conditioning temperature drop across coils. The split (difference between supply and return air temps) can be easily from 16-24 degrees depending upon the latent load (humidity. There are tables that can be used to determine the required split which involves measuring return air wet bulb, return air dry bulb and supply air dry bulb. Using this information you can quickly determine if there could be airflow or refrigerant charge issues.

Allison Bailes

Jim B.: Yes, you're absolutely right. The list above is meant only as a rough guide to the tests you should do, and the 20° F ΔT I listed was not meant as THE number someone should look for.  
 
Thanks for commenting, Jim, and thanks for selling a lot of great tools for those who make these kinds of measurements!

ABC

Unfortunately, not all HVAC service providers actually have a list like this. As a Dallas HVAC contractor, it is a good idea to have this list in order to make sure that the system works as a whole. After all, what we must consider is of course the quality of products and service for our clients. Good read!