This project started back in March as soon as I was able to ambulate after the back surgery and it started looking like the pandemic was not going to go well. I began by hauling a couple hundred dollars worth of PVC from Home Despot and putting up the prototype with a junk fan to test the hypothesis. A few months later we were inundated with wildfire smoke and the idea took on a whole new meaning.
Initial results were better than expected. The basement was no longer a stuffy, closed space without adequate air circulation. Temps edged closer between the up/downstairs and the air was noticeably cleaner throughout the whole house. That became quite obvious a couple weeks ago when it nearly got dark here in the middle of the afternoon. A permanently installed full-blown upgrade was called for.
That filter is the same thing you see hanging off the fender of a big dump truck, probably at least 100 times more efficient than most residential HVAC types. I believe it’s rated at around 15um single-pass. But more importantly, it runs continuously in this application. Something most people don’t realize about filters is they tend to filter better the longer they remain in service. Trapped dirt adds to filter depth making it more efficient. Leave ’em in there, as long as flow remains adequate. That is the same filter I now run on the CTD. It has not been changed in 5 years, still flowing great, per the filter minder. I believe the air filter on the Bimmer has been on longer than that.
The UV-C sanitizer is the really big idea here. I saw a news story a few weeks ago about one of the local private schools spending a quarter million dollars to upgrade their HVAC with these. Seemed like a good idea and the light was only $125 – much cheaper than a stay in the ICU. And again, it runs continuously, not just when the A/C or heat is on. The vertical column under that filter creates about a 3x larger internal volume per foot than the 4″ PVC running around the basement, so the air column moves more slowly past the sanitizer light, increasing efficiency there as well. The aquariums give us good humidity stability, so I would not be surprised to find the air quality in this house exceeding the controlled spaces in the best hospitals anywhere in the world.
Putting a 5″ hole in the stairwell wall was a non-trivial task, due to the location requirement – the hole had to be in that exact spot. There was just enough clearance by the floor joist to get it cut, but it needed a radical, not-well-aligned double 90° bend in the tubing to make it work (duct tape to the rescue). The PVC duct tees off to the far corners of the basement, where variable-speed fans pull filtered, sanitized air down from the upstairs ceiling. One basement leg is about 20 feet longer, so that fan runs a step higher to balance flow.
This project can be done in almost any 2-level house for a total of around $500 in materials and equipment. You might need to go through a floor, or come up with imaginative piping solutions, but the concept is simple – ventilate, filter and sanitize. It’s a pretty high-value system if you are Covid-sensitive living in a wildfire-prone area.
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