single zone / multizone

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Good afternoon,

Because I am working in fenestration I hope a mechanical systems expert can help me out. If I have the DD Wizard floor plan as below (core/perimeter default is now 18 zones) - why is the Base Case with Multizone Packaged Units kWh almost 3x the Base Case with Single Zone Packaged Units (both electric reheat)?

What is the reasoning behind the multizone electric being so high? When I dig into the details I see that even with tstats at 60 (and in Hawaii) the multizone has significant space heating whereas the single zone has zero space heating.

At the end of the day, I think A/C savings are overstated because it seems like one version has simultaneous heating/cooling but would like to know the 'why'?

The facts are that it's multizone - so it is what it is ... I just want to learn from this and bring the best solution to my customers.

Thanks and take care


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You are correct - in this case the "Multizone" type system has a hot deck and cold deck, and these are combined to produce the air supplied to the zone, so there is simultaneous heating and cooling taking place as you surmised.

A "Multizone System" is not the same as "a system with multiple zones, and which might be VAV."

But to be clear, if you are using a single-zone system in the building as shown below, the fair comparison would be one single-zone AHU per zone, and not one serving all of the zones. If that's not the case, check the unmet load hours for both cases in the AHU summary sheet. That may also be one reason why one case is lower energy use than the other - the zones may need some reheat if supplied from a single AHU.


David S. Eldridge, Jr., P.E., LEED AP BD+C, BEMP, BEAP, HBDP
Grumman/Butkus Associates

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