Meet Dr. Atila Novoselac, the Mechanic of HOMEChem. More at: https://HomeDiagnosis.tv/homechem
Home performance articles and stories from the field with internationally respected building forensics guru Corbett Lunsford at the Building Performance Workshop. Hear new episodes of the Building Performance Podcast, see new videos from the Home Performance YouTube channel, and learn all about how diagnostic testing (more than an 'Energy Audit') can make home improvement and new home construction a proven process!
Filtering by Tag: airflow
See bits of four episodes from Home Diagnosis Season 1! More at: https://HomeDiagnosis.tv
Corbett likes tools that are sexy and scary at the same time. This flow hood is both. Measure CFM, Drybulb, Wetbulb, Dewpoint, Velocity, and more with this very affordable tool that will help revolutionize the HVAC industry.
Watch home performance testing guru Corbett Lunsford test the pressure, airflow, and velocity performance of some beautiful custom carved wooden return grilles, using just a blower door kit, a homemade box, and an anemometer. Grilles made by Stellar Engraving by Vencor Inc. (http://vencorinc.com). Test performed out of the back of Corbett's pickup truck in Atlanta GA! Yeehaw!
I was going thru the videos in the training portal. Overall, I like your videos. However, every now and then, a portion of one leaves me less than satisfied with the answer. Usually, my disatisfaction is because you are rushing through and just skimming the details and explainations. I realize that your trying to limit the video's length and accept it.
However, I found one video that had something that you brought up, but didn't explain that frustrated me enough to write. The video is in the training portal, 'Mastermind Series Jan 2015' at 30:01 minutes in. Your talking about system airflows and you bring up NCI. You go to say how they add up supply airflows, return airflows, and compare it to what the airflow should be to get leakage. You say that that is wrong but don't explain. You finish by saying that system airflow needs to be measured at the blower.
So, the question I have is: Are you objecting to comparing either the supply or return airflows to what the system airflow SHOULD be (i.e. not measured) or something else?
Would you agree with the following?
(Equipment airflow) - (sum of supply register airflow) = (supply side leakage)
(Equipment airflow) - (sum of return register airflow) = (return side leakage)
Equipment airflow to be measured at or near the blower by one of the several methods. I am calling it equipment airflow and not system airflow just to be clear that it is what the fan actually produces.
Finally, are you doing full manual J's or just block load calculations to get ballpark numbers?
Great question, and I'm happy to clarify what I meant! Thanks for letting me know when my broad strokes don't actually answer your question and leave you frustrated- I always want to give a full picture of what home performance testing actually means.
My issue with measuring the supply airflows and return airflows, and inferring duct leakage from that is:
- How do you know what airflow the equipment is producing unless you measure the actual airflow at the equipment? You can use a calculation like 400cfm x tons of A/C, but what if it's heating season, 20 degrees outside, and the NEST thermostat won't let you disable the compressor's service disconnect and still run the air handler? Also, what if the installer targeted 350cfm per ton, or 450cfm?
- Even if you measure the equipment airflow, you won't be measuring the equipment cabinet air leakage, which is almost always there. In fact, the IECC duct leakage test assumes that 25% of all the duct leakage will be in the cabinet in new construction.
- The only way to measure duct leakage is to perform a duct tightness test, or for a quicker and more localized look, perform a pressure pan test during blower door testing.
- Measuring airflow is notoriously difficult. What tool and technique are we using? Pitot tube has high user error, passive flow hood (balometer) is not accurate for residential grilles and low flows, and anemometers need to be corrected for net free area of the grilles. Lots to scratch your head about, and it turns out the best way to measure airflow in the 21st century is still a plastic garbage bag.
To answer your final question, if all you need is a ballpark number, a block load is fine, but I always do a full room-by-room load calculation if I'm being paid to do an actual Manual J.
Hope that helps, and keep the questions coming!
Grace and I have been trying to make a TV show about home performance testing for years- we've tried three times so far! This is how it works traditionally:
- You get a network executive to want to see you as a couple onscreen because they think you're quirky or weird or otherwise compelling in a I-can't-look-away kind of way
- You work with a production company and pay out of your own pocket to shoot a 'sizzle reel' that shows off the personality of the hosts
- You remind yourself and everyone else that your show is about SCIENCE, not about relationship drama and being quirky or weird
- They remind you that no one cares about the topic in reality TV
- You feel frustrated and you throw the whole idea in the garbage because you don't want to play their stupid game
So we've decided to make the show ourselves, without asking anyone's permission. We find that works best for us- whether self-publishing a book (Home Performance Diagnostics) or making a feature film (The Other One), it always seems to work perfectly when we don't have someone breathing down our neck to conform to 'the way things get done around here normally.' Here's the show that will actually make it onto mainstream television: HOME DIAGNOSIS.
In 2014, we pushed hard for a show called PRESCRIPTION HOME PERFORMANCE to get made, but it went exactly nowhere. We went to the national RealScreen Summit, a non-fiction television programming conference (yeah, I know!), met with all kinds of networks to pitch the idea, and finally had Science Channel interested until they finally said, "wait, we don't want to compete with HGTV." And that was that. But you can still see what the show was like here:
And way back in 2009, we worked with our friends and client Sandy Gordon to make OUR GREEN COMPANY, which resulted in all of us being told by the Discovery Green channel that 'green' was a fad. Look at these kids- so young, so fresh, and maybe clueless!
Stay tuned for developments on HOME DIAGNOSIS- at the very least, it'll show on PBS just like This Old House does, and at most, it'll be running 24 hours a day on every channel there is. Probably it'll be somewhere in between!
If you'd like to participate in the making of this show, please reach out to us about it!