Profile cover photo
Profile photo
Jesse Smith
48 followers -
Builder
Builder

48 followers
About
Posts

Post has attachment
Here's an excerpt of an email I wrote in support of adding large central returns in a finished basement directly adjacent the unit, with transfer grilles at the top of the basement stairs. The overwhelming majority of HVAC technicians reject this as something that can never work. One of the amazing things about trying this is that the effects are testable in advance of the work by temporarily removing the blower cabinet door and taping the door switch shut. (Danger warning - this will cause massive safety problems by spilling combustion appliances, so it requires a continuous return path. Don't mess around with this if you're not an HVAC professional!)

"The point of why I went there was to test if the hypothesis was right. In this case, it appears to be right. There are basically 2 parts to the problem:

1. Airflow is restricted, specifically on the return side. This causes a reduction in the total quantity of airflow. This statement is totally uncontroversial, and there are multiple ways to test it. Another way would be to check the total external static pressure of the duct system, then extrapolate what a reasonable future external static pressure would be after the duct changes. Then check those two values against the blower chart for the unit. PSC fan motors in particular have a pretty sharp airflow curve, so reducing static pressure increases airflow significantly. See here: https://hvacrfundamentals.blogspot.com/2013/09/blower-external-static-vs-cfm.html . Or just check the PSC blower motor tables for the equipment you sell.

2. Delivery temperatures tend to improve (especially in summer) through better mixing. I.e. we're (at least initially) moving the coldest air through the system.
Lots of technicians erroneously believe they can fix distribution problems by sucking on individual rooms. This is predicated on some false assumptions followed by confusing outcomes. In general, you can't suck your way out of distribution problems. In some instances you can increase total system airflow by adding return - much in the way I proposed on this job - but the localization of the return doesn't tend to do very much.

The way I tend to think about it is by thinking of Occam's Razor (see: https://en.wikipedia.org/wiki/Occam%27s_razor), wherein the simplest answer tends to be the correct one. Q: Why are rooms hot on the second floor in summer? A: Because there's not enough cold air being supplied to those rooms. At what point on a continuum of a room being too hot does one decide that instead of the room having insufficient supply that the problem is insufficient local return? Furthermore, how do so called 'hot air returns" know to suck back the hot air from the room and not the cold? When we suck air from a room, what temperature is the air that replaces the air we just sucked away? Doesn't the supply air displace the air from the room anyway, just by being supplied to the room (answer: yes or the room would explode).

I design the return side of the system to 1) support the system airflow effectively. And 2) ideally reduce pressurization/depressurization of rooms to less than 1 Pa. Local room returns are really good for reducing pressurization problems, which is what we should focus on.

If you still have skeptics in the wake of this, just start testing it under hotter conditions. Go to a customers home at 2pm on a really hot day. Record the temperatures on all 3 floors. Then take the cabinet door off like we did yesterday, leave the basement door open and watch what happens. Ideally record pre and post airflow if there's time. It might take a little while, but in most houses this will be highly effective.

One corollary to this is that the two sides of this argument are mutually exclusive. So if I'm right, then the other side is specifically wrong and vice versa. So either my entire framework for understanding HVAC airflow is wrong, or the other side is wrong. But one of us has a responsibility to dismantle some of our ideas about HVAC system airflow."
Blower External Static vs CFM
Blower External Static vs CFM
hvacrfundamentals.blogspot.com
Add a comment...

Post has attachment
Add a comment...

Post has attachment
Here's a quick update on our pursuit of a more fuel efficient fleet. One option we're considering is outfitting a vehicle to perform smaller energy retrofits - typically air sealing, duct sealing and small-scale spray foam jobs. Very preliminary, but a couple of vehicle options spring to mind: 

1) A fuel efficient tow vehicle with a small trailer. The VW Golf SportWagen TDI is EPA rated for >40 mpg hwy, and can tow up to 2000 lbs. 
2) A small fleet vehicle such as a Ford Transit Connect. 

Currently the VW wagon looks more appealing to me, both because of fuel savings and high passenger capacity. How much of a hit would we take on fuel economy when towing? Also, would the setup appear totally unprofessional to clients? I don't know the answer to these questions.  

Separately, we've also started measuring some stuff with a ScanGauge, recommended by the ecomodder website. Turns out people think you'll be more successful improving performance if you actually measure stuff. Who knew!
Photo
Add a comment...

Post has attachment
Something I'm very uncomfortable with is the impact of all the fossil fuels Tay River consumes. We'll travel up to an hour for building shell work, which means that we'll cover much of the Philadelphia suburbs, and as far north as Edison NJ. My guess is that our vehicles cumulatively travel about 600-1000 miles/week for shell work alone. 

Our current shell retrofit vehicles are 2 Isuzu NPR box trucks, and a Nissan Titan. One of my current goals is to reduce Tay River's fossil fuel consumption. I suspect that part of this involves looking broadly at the problem, and being open to a variety of solutions. 

I'm really impressed with the ecomodder website. There's something very impressive about people who uncompromisingly pursue a single idea to an extreme degree. The site is full of fantastic information on vehicle fuel reduction. 

As I see it, the problems Tay River face include: 

- The Titan is an absolute pig. We bought it for the towing capacity, but of course it fell into general use. 
- The Isuzu NPR's aren't bad as far as box trucks go, but newer box trucks are reported to be significantly better (25 mpg vs 15). Partly I wonder if we could modify the trucks to  improve gas mileage. 
- We carry a lot of material in the box trucks. In many cases (ex. cellulose) the material travels from Northern NJ to our shop, is loaded on box trucks, and then returns to Northern NJ to be installed on jobs. This seems pretty wasteful, and with better organization we could probably have material delivered to job sites directly, possibly allowing us to downsize vehicles. 
- The vehicles seat 2-3 people, and not very comfortably. Frequently we will send 4-5 guys to a job, which necessitates sending 2 vehicles simply because it exceeds our vehicle's passenger capacity. 
- We pick up materials too frequently. We seem to send trucks out for materials several x/week. I came through the trades believing this was a hallmark of inefficiency, and have never really shaken the feeling. Material runners are a death blow to job site efficiency. 

I'll keep you posted on our progress. If you have ideas, please share them with us! Thanks for reading. #homeperformance   #fueleconomy   #better   #dyfj  
Add a comment...

Post has attachment
Quick video of why you shouldn't install an attic exhaust fan.
Add a comment...

Post has attachment
Tay River built-ins. Abel is a good carpenter. 
Photo
Add a comment...

Post has attachment
SIPS failure. Pretty gross. #buildingperformance
Photo
Add a comment...

Post has attachment
Now who's your Daddy? Steve, June and Aaron show how to airseal houses. #NJHPwES   #homeperformance  
Photo
Photo
2013-09-06
2 Photos - View album
Add a comment...

Post has attachment
Just added a trellis to our deck project.
Photo
Add a comment...
Wait while more posts are being loaded