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Reduce CFM or buy new unit? 1

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HVACbegginer

HVACbegginer

Mechanical
Jan 23, 2023
1
Hello everyone!

I am having a problem deciding if I should (if it is possible) reduce the CFM of a 10T rooftop unit packaged, in order to save the owner money. He prefers not to change the RTU, so he does not have to spend "large amount of money". The point is that with new changes, the required RTU needs to be 5T. Existing 10T is double than required. So, is there a way to reduce the CFM? Existing unit(RGS119HDCA0AAAA) has only 1 compressor, and I think it cannot be used for VVT.

Thank you in advance.
 
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You should typically have about 350 to 450 CFM per ton. If you can't turn down the capacity, then you can't turn down the CFM. I would tell them that they can use the 10 ton but it's more than they need. Depending on the details of your situation, it may not matter much or it may be pretty uncomfortable at times. Just like anything with HVAC, you have to look at the entire system to make a judgment.
 
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Single speed unit may freeze, short cycle and so on. How did you determine you only need 5T? Did the use change from the time the 10t unit was installed?
 
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In addition to problems pointed out by previous posters, the 10T unit will NOT BE ABLE to control humidity in the space due to short cycling. The WB temp in the space will rise well above 50% if the space is occupied.
You want the cooling coil to run longer, to wring out the moisture.

Sorry, but I think you will need a smaller capacity unit.
 
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