HVAC Help

B

bfisher

Active Member
I know this is slightly off-topic, but looking for ideas...

Switched over to cooling mode yesterday, and I'm noticing very little air is getting to the upstairs bedrooms.

Background: I have 3 zones (one for each floor), each with an automated damper that opens/closes to allow air to the appropriate zone.

I made sure the two bottom zones were off (set thermostat temp higher than room temp) and I could verify both dampers closed (I watched them close). The 3rd zone damper opened - so I would expect air to be blowing upstairs and not the downstairs 2 zones.

However, both of the downstairs zones are "bleeding" air - more than the upstairs zone is! (If I set the thermostat so that the zones are supposed to blow air - a lot comes through, therefore I'm calling this "bleeding air" or "leaking air")

Therefore, I assume I have something wrong... :D

Questions:
- is it normal for a damper valve to not close all the way? Could this be normal?
- The system has a mechanical damper (I assume to keep pressure from an overflow situation). I've manually moved it - no change.
- Could it be that the upstairs is too far away for the air to get to? (I moved in the house in August so we really didn't use the AC much before)
- If this is the case, recommendations? hire a pro? add a fan blower in the ducts?

Sorry - I know this isn't a normal thread... but everyone here seems pretty handy, thought maybe someone would have some ideas for me. Thanks!
 
Did you do all this work or did it exist? Is the return nearer the other 2 dampers? If so it may no be getting enough air in to blow out. One warning. As simple as air conditioning seems it's a bit more complex than most think. I would hire a pro. I had a friend who put in some electronic dampers and ended up burning up a brand new 5 ton Trane unit. I had a guy out about a month ago checking my new Trane unit that was installed last fall. The compressor had already burned out. He warned me that my RCS Tstat will cycle the unit way to often and could have resulted or assisted in the burnout. I promptly took it off that system. Hire a pro.
 
It was a preexisting house with an existing system in place. I'm very pleased with the HVAC system except for this first issue. I think I will call in our local AC company and let them take a look...

You are making me nervous about adding HVAC controls to my HomeVision Pro system (comes next after my UPB install). I really want my HA setup to be able to automatically adjust temps as we leave/enter the house, etc. I'm surprised about the warning, guess I'll make sure to do my homework.
 
It's all about airflow. The system needs a certain amount of "return air" to stay balanced. If you close one damper, anotherone needs to open.

Don't give up on automating it, find a pro you feel comfortable working with, explain your plans, and follow his advice.
 
I am paranoid about this stuff as well now, after hearing all these stories of zoning projects going wrong. I actually gave up on this for a while, if I do anything, a thermostat will be it, no dampers.
 
Rupp said:
I had a guy out about a month ago checking my new Trane unit that was installed last fall. The compressor had already burned out. He warned me that my RCS Tstat will cycle the unit way to often and could have resulted or assisted in the burnout. I promptly took it off that system.
Click to expand...
Compressors need a few minutes between power cycling [OFF, then ON] to allow the Freon to "equalize" (IIR the term correctly) on both the inlet and outlet of the compressor. Otherwise, you would be trying to compress a liquid instead of a gas. This usually trips the internal breaker on room A/Cs and refrigerators, sparing the compressor from overheating and burning out. Although frequent cycling was bad, I'm surprised that the new Trane didn't have an internal circuit breaker to "take the fall". How often was it cycling?

Does the RCS Tstat provide any DELAY between OFF/ON cycles? If not, I would create a macro (or condition) that disabled turning the compressor back ON for ~5 minutes after it was turned OFF. [You can easily hear when a compressor is "liquid bound" - the motor strains, lights dim, and if you're lucky, breakers click off.]

Rupp said:
I had a friend who put in some electronic dampers and ended up burning up a brand new 5 ton Trane unit.
Click to expand...
Was there any relationship between the new electronic dampers and the "burn up"? What burned up? Is there any "failsafe" that requires at least one damper to be open when the fan is running?
 
bfisher said:
Switched over to cooling mode yesterday, and I'm noticing very little air is getting to the upstairs bedrooms.

Background: I have 3 zones (one for each floor), each with an automated damper that opens/closes to allow air to the appropriate zone.

I made sure the two bottom zones were off (set thermostat temp higher than room temp) and I could verify both dampers closed (I watched them close). The 3rd zone damper opened - so I would expect air to be blowing upstairs and not the downstairs 2 zones.

However, both of the downstairs zones are "bleeding" air - more than the upstairs zone is!
Click to expand...
  • Does the airflow in Zone 3 ever increase (i.e. if Zone 2 or Zone 1 are enabled)?
  • Are all the registers in Zone 3 open?
  • How many returns do you have?
  • If you trace the ductwork to where Zone 3 meets Zones 1 & 2, is there ANY possible obstruction between that point and the first Zone 3 register?
[Just thinking out loud how I would troubleshoot it...]
 
My geothermal heat pump compressor has a delay built into it. Even if the Stat turned it on in 5 seconds after it commanded off, the compressor still wouldn't turn on.
 
My tstat (RCS TX15-;) has a 5 minute minimum run time but the guy working on it said that an air conditioner should exchange the air in the entire house about 4 times per hour. This means it needs to run about 10-12 minutes. He also stated that if the air wasn't conditioned at least 4 times per hour that mold could start growing. I don't think that the 5 minute run times burned up the compressor but it definitely isn't good for it.
 
If your A/C is only coming on for 5 minutes then I would think that your system is oversized. I had that problem with my old unit that I just had replaced. It would cool so quickly that it wouldn't take the humidity out of the air. But my problem had nothing to do with the thermostat. The RCS tstat is not going to quit calling for A/C before the temp drops to the setpoint. The RCS tstats also have short-cycle prevention. The TXB16 won't come on again for 6 minutes and the TX15B has a 5 minute short cycle.

Now I wish the RCS tstats could be customized. I would like to have a bigger deltaT than 1 degree. I noticed on the TXB16 that you can optionally have a 2 degree deltaT. I think it should be user settable.

Eric
 
ClearToLand said:
  • Does the airflow in Zone 3 ever increase (i.e. if Zone 2 or Zone 1 are enabled)?
  • Are all the registers in Zone 3 open?
  • How many returns do you have?
  • If you trace the ductwork to where Zone 3 meets Zones 1 & 2, is there ANY possible obstruction between that point and the first Zone 3 register?
[Just thinking out loud how I would troubleshoot it...]
Click to expand...
Thanks for your ideas.

Best I can tell, I can't get any more airflow in zone 3 no matter what I do. I've made sure zones 1 and 2 were both off, no change. I tried turning them on, no change. Closed the registers in zones 1 and 2, no change.

I tried closing a couple registers in zone 3 to see if I could boost airflow through the open ones, and didn't see much change.

Zone 1 has 2 returns, zone 2 has 1, and zone 3 has 1 return. None of the zones have their own air filter, they all flow through a common Electronic air filter. I can put my hand in front of the returns and feel air being pulled.

I'll have to look at the ductwork again. I can't remember any issues but who knows... I don't remember any problems during the winter, it was always plenty warm (but it is upstairs so it could just be convection heating keeping upstairs warm).

I'm suspicous of the "overflow damper" (not sure if that's the name). Its a weight on a rod that opens a damper when (I assume) the pressure gets high enough. I think the overflow goes to the upstairs but I need to verify. I'm wondering if it's not sticking shut which is forcing the air through to the other zones.

thanks for the ideas...
 
In case anyone was following this - I finally got the AC guy over today to look at this. The issue turned out to be my first instinct - the main floor damper wasn't closing all the way. We adjusted it and it improved the flow to the top floor - but it's still not enough (in my opinion) - it could probably maintain a cool floor, but not cool an already warm one.

Asking the tech some questions - there doesn't appear to be much we can do about it. Increasing the ducts and return size is one recommendation - but that is major work. The big problem is that the AC is in the basement and needs to push cold air all the way up to the top floor.

<edit: anybody have experience with InLine Duct Fans? I'm just starting to research this as a solution >
 
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