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Comments on small-duct high-velocity delivery systems?

I am currently evaluating HVAC systems for a new "showcase" custom home in a hot humid climate (Central Florida). One of the systems we are evaluating is a small-duct high-velocity system that claims less than 2% leakage and superior dehumidification, but with SEER less than I would consider in an energy efficient home.

The home is around 5,500 s.f. "under-air". Planned ICF wall system with spray foam insulation in a closed attic. I'm looking for any comments or experience that may help me with the evaluation.

Asked by Greg Hardwick
Posted May 31, 2011 8:23 PM ET
Edited Jun 1, 2011 8:16 AM ET

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2 Answers

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1.

I would not call small duct - high velocity systems green. By thier nature they have a high pressure drop which uses more fan energy for the same cooling effect. The "dehumidification" they refer to is because there is less airflow across the cooling coil. A standard air conditioner would get the same effect by reducing air flow across the coil by slowing the fan down (thus saving more energy).

As for air leakage, I don't buy that thier systems have less air leakage. Properly installed ductwork will have low air leakage, improperly installed ductwork will have high leakge. If small ductwork/high velocity fiberglass ductwork is installed improperly, it will have air leakage problems. These systems can have thier uses, but a energy effecient house is not one of them.

Answered by Frank R
Posted May 31, 2011 9:56 PM ET

2.

i'm guessing their claim on less air leakage is because they sell a package system with sealed hoses which do probably tend to leak less than a typically installed system. they pretty much only can leak at the unit connection and outlet connection if they don't use trunks.

the only more 'green' feature is that you may be able to run all the ducting inside the envelope because it is so small whereas traditionally many homes run in in an unconditioned attic or basement.

you could probably hit better effeciency with a better a/c condenser which is seperate from the blower, depending on which company you go with and what they install, but the high speed blower will use more juice and not help matters

Answered by bob coleman
Posted Jun 1, 2011 1:36 AM ET

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