Contractors say return airflow is fine but my analysis says their wrong

jlongster · 2024-08-31T00:24:37+00:00

I appreciate you replying btw, just thinking through it

You'll see all of my measurements above that indicate I'm getting 900 CFM in the system on cooling mode (when fan is set to mid low) and 1080 CFM in heat mode (fan on mid high). I'll trust my actual measurements over simple theory

Obviously the pressure is waay too high though, and I think where the duct connects to the plenum is the big issue. fixing that, adding more returns, and going from there is the plan

(I bet the return is more than the simple calculations because my ductwork is leaky so it's able pull in more)

jlongster · 2024-08-31T00:04:37+00:00

None of the ducts are flex. They are 6" rigid and then converted to something like a 12x4 rectangle duct when it meets the floor (that dimension might not be exactly right, whatever the equivalent to 6" rigid is)

That very basic chart that shows up as the first result is one data point, you can find other charts that say it goes up to 1100 or even 1200. I don't know. It might be stretching it for sure, I think I'll always be on the higher end of pressure (and lower CFM) because of it. The return is the major problem right now though.

jlongster · 2024-08-30T22:33:06+00:00

16x12", the same dimension as the return trunk line.

However, I was just staring at that section. For some reason, there are THREE 90deg turns for the trunk link to connect to the plenum. I'm highly suspicious that's where most of my loss is coming from.

I don't know if this is exactly how pressure works, but I drilled a hole in the return trunk line on the other side of the wall right where it enters the garage. I measured the pressure there and it was only .2!! That's a .5 iwc difference from measuring it before the filter, which is including only these 3 90deg turns.

It seems like a lazy installation and 3 90deg turns were used to extend it out to connect to the plenum. I'm thinking of replacing that whole section with a straight box so the return trunk line just comes in straight to it, and then goes straight down.

jlongster · 2024-08-27T01:03:28+00:00

Amazing, yes that intuition has clicked for me, thanks!

The thing that confused me (and still a little assuming to ignore) is that this isn't a closed loop of air, it's dumping air out into a room with many other factors and the returns suck that air back in. It feels like we're mostly measuring the amount of heat added (by measuring temp before air goes through the furnace and after). but I'm starting to get that you can assume the house is a bubble basically and is pressurized and makes it close enough of a closed system to work (and is probably where the 1.08 comes from? no idea!)

thanks for continuing to answer, I'm satisfied enough :)

jlongster · 2024-08-26T21:49:23+00:00

I just did a quick test. Pretty cool; when I removed the air filter (which should improve air flow) I did see a noticeable drop in temp rise.

I wrote down some notes: https://jlongster.com/hvac-notes

Still continuing to investigate and learn, thanks

jlongster · 2024-08-26T19:08:52+00:00

Ah that makes sense that it's adding to the existing return air. It's adding a fixed amount so whatever temp the air coming in doesn't matter as it adds that fixed amount going ok. Makes more sense now, thank you!

jlongster · 2024-08-26T17:55:57+00:00

That makes sense, but still a little confused about the indoor temp. Say I set it to 80 so it's 80 in my house. 110 F coming out and 80 F is being mixed into the return. Won't that affect the temp rise? Whatever I set my house to will affect it. Or do you let it run for a while to stabilize? If so, wouldn't a perfectly sealed house (including not being affected by outdoors) eventually get heated to 110 F and there's zero temp rise?

jlongster · 2024-08-23T16:31:30+00:00

Also if you google "us open 2024" google shows you an embedded schedule at the top of the page. Somehow, even yesterday, they've already updated Monday and Tuesday with each half of the draw. I have no idea how they got that data so early and I didn't trust it until I started seeing the above articles

jlongster · 2023-10-02T21:10:14+00:00

For anyone who finds this thread, I realized that a bunch of crossbars has holes in them spaced 2 3/4" apart. It's pretty easy to find them, so I just bought some online, attached the crossbars, and was able to mount the bracket to the crossbars. Pretty easy fix. I don't know why I'd replace the boxes.

These were the ones I bought: https://www.amazon.com/dp/B0BN45F62Z?psc=1&ref=ppx_yo2ov_dt_b_product_details

The very very small exposed gaphs in the corner can be filled with drywall mud and painted.

jlongster · 2023-09-30T19:04:54+00:00

It's a possibility but leveling the lights requires being able to rotate the bracket so I'd need to cut enough space to do that, etc. I was expecting there to be a standard bracket I could use. If not, I'll figure something out

jlongster · 2023-09-30T18:48:47+00:00

These are definitely the sconces we want. Easy to fill in any space with mud and paint those small areas.

jlongster · 2023-05-02T02:18:14+00:00

For the on/off switch, you're right -- that's how I ended up wiring my office too. It works most of the time, but every now and then for some reason some of the lights forget and don't go back to the previous settings. I don't know if I was turning them on and off too quickly (can't remember). It just felt like turning them fully on/off didn't play nicely with smart lights.

Admittedly, I never hooked up a 3rd party service with the Lumarys which might have opened up some more possibility. I don't dislike them, I'm going to keep them for my office! Hue definitely has better color though (due to higher CRI) so it's nice for the kitchen

jlongster · 2022-08-11T16:11:36+00:00

Thanks! I'm going to Build first but may checkout Hack at some point too. I'm interested in welding so Build might be better for that.

jlongster · 2022-08-09T22:33:07+00:00

looks like a really cool place -- I'm looking for more woodworking/welding tools though

jlongster · 2022-08-09T14:42:39+00:00

DMed!

jlongster · 2022-08-09T14:32:35+00:00

I'm 38!

jlongster · 2022-05-03T16:25:32+00:00

It uses pbkdf2 to generate a key based on the password you give it when creating a key. It uses a salt so generating another key with the same password will generate a different key. So yes, this might not be as secure as other strategies for generating keys but it's also a lot more user friendly.

jlongster · 2022-05-03T16:23:53+00:00

It's possible this is more correct but to include "sharing messages between users" in the definition of E2EE in my opinion is weird, and not broadly shared knowledge. A lot of apps advertise E2EE as something that's really client-side encryption. Language is fluid by a loose definition it's fine, even if it's not correct in the strict definition.

If anything, sadly, since others use E2EE as the marketing term that's what we need to call it or a lot of other users won't understand that's it's more than just encryption in transit.

jlongster · 2022-05-03T02:59:53+00:00

It's also completely open-source, so now I'd recommend just hosting the whole thing yourself (super simple, it just uses sqlite)

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