what is the dats set at ?
please add a 5 min delay to the outdoor condenser to stop short cycling
skinny the 2 floor damper open just a touch
the heating season may be ok, beacause the heat rises and won't run so much
How big is the bypass damper and duct?
Originally Posted by andrewskevr
Most zoned systems I find in the wild have a grossly over sized bypass duct because many people mistakenly size them like it is a normal duct, instead of following the zoning manufacturers instructions.
The system can likely be made to operate acceptably with a reasonably sized and adjusted bypass, and for the zone dampers set so they don't close all the way, so air can be relieved to the other zone(s) when the small zone is calling.
This is assuming that the system is not significantly over sized. If it is significantly over sized, you can basically abandon all hope of it ever working acceptably.
Hopefully the indoor coil has a TXV, or the compressor is doomed to early failure.
The DATS is set at 45, and is not adjustable on the honeywell 311, would it be worth investing in a 321 where I could adjust the DATS down to 40, or is 40 too risky?
Also, how do I add a 5 minute delay to outdoor compressor? Is that something done on the zoning panel, the thermostat or the compressor itself? Sounds like a good idea, might take a long time to cool, but atleast it will give my compressor a breather between cycles along with all the damper tweaks.
My bypass duct is large, its the same size as the return duct going to the blower, what size should a bypass be?
All- this is a great forum and I really appreciate all the support and responses, keep any other ideas coming.
Your bypass is 16 or 18" round? Wow.
to many contractors zoning a system is just a matter of cutting the duct and adding dampers and then they very rarely work properly .
I would add some ductwork to the small zone. Not sure of the setup, but at least 2 duct runs, increasing amount of ductwork and decreasing the size of the bypass would alleviate some of this problem. You might even try to run a small duct from the supply plenum to the j-box feeding the lower floor, bypassing the damper, that way you'll be moving some of the air when the top floor calls, but not so much as to affect the temperature on the lower floor a lot. Not sure you'll be able for it to ever have long run times and never go off on DATS, but it should minimize it. The heat may not run as much since it rises.
I like DIY'ers. They pay better to fix.
The HVAC guys came out and were unsure what to do and are suggesting a bigger bypass, but I think that would make it worse because recycling more chilled air and supercooling will only bring the temp lower. So, I played HVAC Technician, found my paperwork on the dampers and played around. By adjusting 2nd floor damper to relieve a bit of air from during 3rd floor only runs, and adjusting the bypass damper to bypass less air, the DATS is now not tripping, I measured with temp probe and its 48 degrees (DATS shuts off compressor at 45). I have strong air flow to my 3rd floor and it cools down quickly, my 2nd floor isnt affected too much by the 3rd floor relief air flow, do overall I am quite happy.
I realize it is still not ideal, but my 3rd floor is a rec room that will not be used daily, the 2nd floor relief cooling shouldn't be much of an issue, plus the wife always wants the house cooler anyway. I am sure my third floor is cooling too hard and too fast, but being that I keep it at 85, and then only cool it when using it, it is nice to get a lot of cool air quickly to get to temperature, although i guess the downfall is possible moisture issues, but I'll have to monitor it, so far so good.
Now I have to see how the winter goes with heat, hopefully less issues being that heat rises.
A bigger bypass won't help. The systems needs to move more air to somewhere else in the house. Not back through the coil.
A BIGGER bypass?!? Really?
That system shouldn't have more than a 10"-12" bypass. From what I am hearing it sounds like you are bypassing too much already and you have done what I would have by setting a minimum position on the 2nd floor dampers. next step is to try and find a way to add ductwork to the 3rd floor or a dump zone on the 2nd.
If your system has the capability then setting the thermostat to constantly run the blower on low speed will help with humidity issues on the 3rd floor.
I would love to see pictures of the setup.
I lift things up and put them down.