Simultaneous Heating and Cooling HVAC
I came across the question below and am not sure I understand the logic behind the answer. My understanding is that having terminal heat will allow you to heat cool air which will allow both heating and cooling within the same system. Terminal reheat will also allow for lesser ductwork. Why would we choose dual duct instead of reheat then if dual duct is going to significantly increase ductwork?
mermann I would really appreciate if you can elaborate on the logic. Thank you!
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Where on earth did you see that question? Dual duct is never the correct answer unless it’s 1956 and we don’t care about wasting googobs of energy. It would be akin to opening a window while the heat was on in the winter if you wanted to cool…No practice problem is perfect but this one is bad enough that I’d question the whole source and probably stop studying from it.
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Found the question…it’s in Ballast. Definitely a bad practice test item. If you come across it, ignore it.
Terminal reheat can heat and cool at the same time. As can variable refrigerant systems (VRS), which may not have been common when that question was written.
A building with dual duct is like a car without a seatbelt or a doctor suggesting that a pregnant woman should smoke: not done anymore and was probably always a bad idea, even with what we knew at the time.
—Michael Ermann
Amber Book creator
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