Q&A From IBACOS/Department of Energy’s Webinar

Presented by IBACOS’ Arlan Burdick, Building Performance Specialist and Anthony Grisolia, Services Manager, with the support of the Department of Energy’s Building Technologies Program, this webinar highlighted the importance of creating accurate heating and cooling load calculations and examined the criteria required to do so. Current industry rules of thumb, and perceptions and barriers to right-sizing HVAC were also discussed. This is the first in a 3-part series, to be followed by Part 2, Choosing Equipment Size and Part 3, Choosing the Right Distribution System.

Watch the archive or download the slides here.

Take a look at some of the great questions attendees posed during this session below. Anthony hosted the session, while Arlan served as commentator. Both answered questions.

[Anthony] So, if you’re asking an HVAC contractor to go on walk in production, let’s say he walks a house and there’s no draft-stopping behind a kneewall scenario, what is he supposed to do with his Manual J calculation?

[Arlan] You can downgrade just that portion of the home, just that kneewall portion, and address the load change that way, but this can really be a point of entry for a collaborative discussion between the builder, the HVAC contractor and the other trade partners to gain confidence in the execution of those building details. I’d like to add that IBACOS has seen builders on both coasts and across the country work with HVAC contractors who were initially skeptical about this, or resistant to change, but they’ve seen real success, they’ve seen it in the East Coast humid, West Coast dry, and Mid-country.

[Anthony] So from your experience, is there a type of insulation that needs to be looked at more closely in understanding how it’s installed?

[Arlan] I would say that probably the most common type of insulation that we see is fiberglass batts, I would also say that fiberglass batts are probably the most difficult type of insulation to install. Insulation only works if it’s installed in contact on all 6 sides, and insulation works best when it’s not compressed, or there’s not gaps. RESNET® has a classification to classifies various insulation quality levels, 1, 2 and 3, simply put, 1 is occasional or very small gaps, 2% or less of the area, all the way up to 3, which is substantial gaps. Going back to Anthony’s question before, an area without draft stopping, no draft stopping gets classified as a 3 under the RESNET standards.

 [Anthony] How do I get the Manual J?

[Arlan] ACCA. Air Conditioning Contractors of America. ACCA.org. And you want to be using Manual J, version 8. There are still some versions 7s floating around, but version 8 is the most up-to-date version. IBACOS recently updated our library here, and we ordered a new Manual J and I was surprised to see there was an ACCA manual J, edition 8, version 2. And they’ve changed the layout of it, it’s a little easier to read and understand, so if you’re buying a new manual, you’ll get that version that’s a little easier read and to understand. And I should also mention that there’s an ACCA Manual J version 8AE, or Abridged Edition, that simplifies the calculations, but there are very, very strict parameters for where that abridged version works, and you have to be working within those parameters to get accurate numbers.

[Anthony] Is there a simple residential HVAC calculator software that you would recommend, or an online calculator?

[Arlan] I can tell you what we use. We use WrightSoft. When we did that poll initially, it was about  20% who use WrightSoft, and there was over 30% who use other software, and there was a significant number who use their own spreadsheet.

[Anthony] But that’s what we use and that’s what we’ve been feeling comfortable with for the last 6 or 7 years.

[Anthony] We made a comment that insulation only works if it’s enclosed on all 6 sides. Does that mean that if one side is left open, is that the same as no insulation in the cavity?

[Arlan] RESNET grades it down to a grade 3 if it’s not draftstopped up on the back side. Insulation is not an air barrier, and if air is passing through insulation, it’s not as effective. 

[Anthony-] But I guess if you have, let’s say, spray foam, where it doesn’t allow any air movement through that insulation product, then you may not need draftstopping in that scenario. Something to think about.

[Anthony] Can REM/Rate™ be used to estimate cooling and heating loads for system sizing, or is the peak load from REM/Rate calculations different from the loads you get from the Manual J?

[Arlan] You’re not going to get the orientations, you’re not going to get the different parameters just off of REM/Rate. You’re just going to get that peak load.

[Anthony] We’ve typically seen REM/Rate just as a HERS rating tool, an energy costing tool.

[Anthony] For existing homes, how do you know the thermal enclosure?

[Arlan] You need the data. A blower door is a good way to get air infiltration rates. On existing homes, it matters what level of retrofit you’re doing. If you’re doing an insulation retrofit, you’re going to know what level of insulation you’re adding to it. If you’re doing window replacements as part of it, you’re going to know what the window specs are. But otherwise you have to possibly do some exploratory to see what’s in those walls.

[Anthony] You can buy those little camera probes where you can drill a hole into the wall and see if there’s any insulation in there, and if there is, you can look at how thick it is, and estimate the R-value.