Q&A from HVAC Right-Sizing Part 3 Webinar

The January 20 webinar, the third and last in our 3-part series on HVAC Right-Sizing, dealt with Air Distribution and Duct Design and featured Arlan Burdick, Building Performance Specialist, as primary presenter. Arn is the author of Advanced Strategy Guideline: Air Distribution Basics and Duct Design, a publication created in partnership with the U.S. Department of Energy’s Building America program. Anthony Grisolia, Manager of Quality + Performance, acted as host.

This webinar covered understanding the effects of ducts and air distribution strategies on overall HVAC efficiency and sizing. The importance of integrated design was covered, including its effects on framing and space planning. Design principles for return air outlets, supply air and duct layouts were covered in detail, and the webinar also dealt with the importance of performace criteria such as temperature, noise and temperature uniformity.

Click here to access the slides and video of the webinar. 

Here's some Q&A from that session.

 Can this strategy be applied to multi-unit apartments?

[Arn] Absolutely. The integrated design phase is much more important when you start talking about multi-family.

 Does operating unnoticed include sound levels, and if so, what is the appropriate maximum db level for noise?

[Arn] We’re not going to get into db levels too much but there are noise criteria especially for registers and outlets, and yes, noise is a comfort issue.

 Can this also be applied to commercial construction?

[Arn] This is strictly residential. The Manuals we’ve mentioned from ACCA are residential manuals. There is a whole other series of procedures for light commercial.

 How can you identify if a bedroom is being overpressurized, in the field let’s say, like in a finished house?

[Arn] This is one of my favorite things to do when I’m out walking in the field with a builder, especially if we’re in a hot place and on a hot day. I try to wait until after lunch when the day is really hot. You get them to walk into one of those small rooms—happens faster in a small room—with a door undercut or no pressure relief, and take your hardhat off and stand underneath or next to the register and then close the door, and you can physically feel the air slow down in that duct work as the room pressurizes.

That’s the person, no-equipment way of doing it. You can take a manometer, put one tube in the hallway, and one tube in the bedroom, check the pressure and the difference will be zero. Close the door, and see how much the pressure changes.

[Anthony] Something that I’ve done is crack the door open about an inch and see if it closes on its own.

[Arn] Yeah, the self-closing door too.

 Air filters, do they affect pressure loss and air flow to rooms?

[Arn] They affect pressure loss in the entire system, and it needs to be accounted for up front in the design It should be part of the specifications: “this system was designed for use with this type of air filter.”

 So if the homeowner installed like a HEPA filter, that’s more restrictive, what could happen?

[Arn] If the system is designed very close with very little room for extra pressure loss, you could affect the system’s performance negatively.

 So some of those higher performance filters could suffocate rooms?

[Arn] They could.

Loss with exposed ducts. Does this apply to those kind of scenarios?

[Arn] The ductwork is within conditioned space. So it’s not going to affect your load on it, but the performance of the ducts will need to be addressed.

Why are direct returns from each room not desirable?

[Arn] Because of the additional ductwork required to get that air from the room back to the equipment. That’s additional pressure loss within the system. Better to use the pressure release method of the overdoor transfer or some method back to a central return. And simpler, if it’s that much more ductwork that needs to be run, it’s that much more expense.

 What effect does humidification have on the system? Humidifiers attached to the return?

[Arn] Humidifiers are going to be another pressure loss in the system, for starters. Then you have to be very careful about adding humidity to your house in any case.

[Anthony] Especially in a high performance home.

This is the third and last part of our webinar series on HVAC right-sizing.