TonyBrobston
commented
2 years ago It's working pretty well. To try and draw a better picture I'll explain some of what I've seen.
I live in a three-level-split, so I have two zones (which does not have any traditional zone stuff going on). One zone is the main floor, which has four 4x10 vents; two rooms with two vents each. The other zone is the basement and upstairs. The basement has one room with three 6x10 vents and the upstairs has four rooms with one 4x10 vent each. Also, my basement is only half below ground.
It is currently 68-95 F here (Des Moines, IA). From what I can tell, the upstairs is the hardest to keep cool when it's 90+ F (mid-day on a hot day); especially my office (smallest bedroom) and our master bedroom (which has a sunroom off of it, hot air leaks from the sunroom to our master bedroom). The short answer is, I can now get both of these rooms down to at least 70 F; but tend to prefer 72/73 F.
I wondered for the longest time why my office would get so hot. Part of that is two PC's, two large monitors, lighting, my 3d printer, body heat, southern exposure, etc. But also, the ducting for this room is second in line; counting ducting runs for this zone, my office has another five ducting runs after it (two upstairs and three in the basement). When all 6 vents in this zone are open, it seems like my office is getting less than 1/6 of the airflow. When all or a few of the five ducts past my office are shut, my office gets substantially more airflow, and as a result, cools down. I can now get it to be colder than I like, even with my computers and printer running.
On the other hand, I would prefer my basement at 70-72, but it tends to sit at 68-71, even when the basement vents have been closed for days. I attribute this to being half below ground, having rooms that are cooled above it, and possibly some cool air leaking from the HVAC (I've noticed if I feel around the main plenum above the furnace, there are small air leaks). In theory I could make mqtt-hvac-vent-control smart enough to compensate by pushing some heat to the basement, but I'm not sure that's something I want to do. But, this sort of concept could make sense if the situation was inverted and you had a room creating a lot of heat (like a server room/closet); it might be winter, but maybe you want to push cold air to one room to keep server temps down, though I have no idea the implications of running A/C in the winter 🤔 .
The vents do open/close often. They aren't silent; I'm not sure it's possible to have a motor that is silent? As I explore battery options, I may experiment with some sleep mode options, which will inherently cause the vents to open/close less often.
As for the static pressure, from what I've gathered there's really only two options:
- A variable speed blower, which would allow you to match CFM to the system based on how many vents are opened or closed. However, I'm not sure how this accounts for blowing enough air across the coil to keep it from freezing; I also don't know if that's an actual thing, but have heard others mention it.
- Installing a Static Pressure Regulating Damper between the main return and the main plenum. This would still move the required amount of air across the coil, but I'm not sure if recirculating cold air would cause the coil to get too cold or not. From what I saw in this video, it does not seem like a concern. https://www.youtube.com/watch?v=WSJUQ2qEb3w
- Installing some sort of diverter. Similar to the solution above, but not recirculating. This seems like the safest, but not exactly the most efficient.
If anyone else has suggestions on how to deal with the static pressure issue, please comment.
wjcarpenter
kamermans
Not really an issue. Just a question. This is a well-organized project with a lot of thought behind it. It looks like you are reasonably far along. I am curious if you are actually using this to balance your HVAC airflow yet.
I'm not "an HVAC guy", but I've been trying to figure out an economical (or completely DIY) way to balance my single-zone system so that my upstairs rooms are similar to my downstairs rooms. My impression (from Internet searching and reading) is that the "close off some vents" schemes are trickier and less desirable than the "booster fans in ducts or registers" schemes, mainly because the increased static pressure is harder to manage. But I'm no expert, and I wonder how your system works in practice.
Are you far enough along to be able to draw any conclusions?