Whistling sound from new A/C zone damper

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Old 07-25-18, 01:25 PM
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Whistling sound from new A/C zone damper

We had a brand new AC (2 stage) and 2 zone Thermostat with mechanical dampers installed because our upstairs was way hotter than the lower levels (duh). Two ducts supply the basement/main level and one duct supplies the upstairs.

Whenever the upstairs is cooling, we can hear an [annoying] whistling sound coming through the lower levels' vents (as a result of those dampers being closed - my guess).

Questions:
1. How can I reduce/remove the whistling sound coming from the lower levels?
2. Is there an ideal level to set the cfm or pressure on the dampers?

Thank you!
 
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Old 07-25-18, 01:34 PM
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Zoned systems are very complicated. Sounds like the duct is the wrong size are bypass is not working. Best to call the company back and let them fix it.
 
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Old 07-25-18, 03:03 PM
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I agree entirely. The company is coming out tomorrow. I just wanted to educate myself to keep them honest. The individual I spoke to mentioned something about adjusting the cfm. I don't have anything to base my feeling off of, but that doesn't feel like the right solution. Thanks for your reply!
 
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Old 07-25-18, 04:34 PM
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The CFM for the entire system can't just be lowered. The entire system requires a certain CFM. One duct may only require half. There may be a way of adjusting the blower speed electronically. If not then a certain amount of air needs to be bypassed to keep the system from howling or whistling.

Adding multi zone control to an already installed duct work system is a comprise. When I've had to service an existing system with a problem similar to yours..... I wouldn't allow the primary damper (first floor) to fully close..... allowing some air flow to the system.
 
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Old 07-31-18, 07:09 AM
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There appears to be resolution....

The company came out and after troubleshooting and weighing options, lowered the CFM based on the number of registers and the size of the unit (there is an equation for an acceptable range). The diluted explanation is that too much air was being pumped to satisfy the up-stairs/zone 2 which caused whistling to be heard down-stairs/zone 1.

Without compromising time to comfort and without decreasing efficiency, the CFM was decreased to 900. (Zone 1 was at 1200 and zone 2 was at 1100) (The effective range for the unit for the size is 1800).

I will be keeping an eye on the energy usage as well as the comfort level.
 
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Old 07-31-18, 08:30 PM
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Stop back and let us know how it's working. In my opinion..... the system CFM may be too low now.
The ultimate solution is having it set up for two speeds based on one or two dampers open.
 
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