Hello,
New member here interested in learning. I Googled and searched this forum for a few hours trying to find an existing answer to my question but couldn't find a discussion fitting my situation.
I'm getting a new (replacement) 4-ton Trane XV20i heat pump system installed in the southeast US and I wish to understand why my contractor says a modulating damper on the return air ducts are not necessary. In my situation I have 2 zones on the same floor with each zone having their own return air register and duct leading back to the return plenum. These 2 first-floor zones are separated by a standard size door (that will often be closed). Zone 1 is approximately 1000sqft with 11 ft ceilings, and zone 2 is about 1800 sqft with high vaulted ceilings.
My concern is that when only one zone is running, there will be negative pressure in the other zone unless there are dampers installed on the return ducts. My contractor says this negative pressure won't matter (but I have a leaky home built in the mid 90's).
The reason they gave me that installing modulating dampers on the return is a bad idea, is that supply CFM will be greater than the return CFM and therefore not enough air will be passing over the coil.
Now, I understand why in a single-stage, or even a 2-stage system the return CFM could be an issue if return air was restricted. But the XV20i has a variable speed blower and variable speed compressor with far greater control than a 2-stage compressor. According to Trane the 4 ton can do 35% - 100% capacity in .1% increments.
I'm a pretty technical person, and while I could just take their answer at face-value, somethings not adding up for me:
I'm wondering if they are just used to installing single or 2-stage systems that don't offer this kind of control. If I'm right about this (or I could be wrong), I greatly appreciate links to documentation or design guides that state modulating dampers on return ducts are okay or even suggested in multi-zone systems with variable speed blowers and compressors.
Thanks in advance.
New member here interested in learning. I Googled and searched this forum for a few hours trying to find an existing answer to my question but couldn't find a discussion fitting my situation.
I'm getting a new (replacement) 4-ton Trane XV20i heat pump system installed in the southeast US and I wish to understand why my contractor says a modulating damper on the return air ducts are not necessary. In my situation I have 2 zones on the same floor with each zone having their own return air register and duct leading back to the return plenum. These 2 first-floor zones are separated by a standard size door (that will often be closed). Zone 1 is approximately 1000sqft with 11 ft ceilings, and zone 2 is about 1800 sqft with high vaulted ceilings.
My concern is that when only one zone is running, there will be negative pressure in the other zone unless there are dampers installed on the return ducts. My contractor says this negative pressure won't matter (but I have a leaky home built in the mid 90's).
The reason they gave me that installing modulating dampers on the return is a bad idea, is that supply CFM will be greater than the return CFM and therefore not enough air will be passing over the coil.
Now, I understand why in a single-stage, or even a 2-stage system the return CFM could be an issue if return air was restricted. But the XV20i has a variable speed blower and variable speed compressor with far greater control than a 2-stage compressor. According to Trane the 4 ton can do 35% - 100% capacity in .1% increments.
I'm a pretty technical person, and while I could just take their answer at face-value, somethings not adding up for me:
- How is creating negative pressure in one zone to supply another not a problem in my situation?
- And in a system/situation like this, wouldn't the communicating zone controller and thermostat simply lower the blower and compressor speed to balance the static pressure based on the pressure sensors installed in the supply and return ?
I'm wondering if they are just used to installing single or 2-stage systems that don't offer this kind of control. If I'm right about this (or I could be wrong), I greatly appreciate links to documentation or design guides that state modulating dampers on return ducts are okay or even suggested in multi-zone systems with variable speed blowers and compressors.
Thanks in advance.
source https://hvac-talk.com/vbb/threads/2228719-Zoning-dampers-on-return-ducts-in-variable-speed-systems?goto=newpost
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