Unmet heating hours and space loads don't match up

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Hi all,

I need some help figuring out the source of unmet heating hours right now. Using RTU 4-2 as the example (only 2 zones), here is the load summary for these spaces (spaces are highlighted in black):

[cid:image002.png at 01CD44CE.0B3EA8E0][cid:image005.jpg at 01CD44CC.99A7CAA0]

The best I can tell from this report (correct me if I'm wrong) is that the spaces require approximately 38.5 kBtu/h total of heating to satisfy the load. The unit has 430 kBtu/h (or rather, MBH) of heat. Yet, I still have a ton of unmet heating hours. The unit is constant volume. Thoughts?

Kristy M. Walson, PE, LEED AP BD+C, BEMP

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You are using "Single Zone Reheat" as the system type for RTU-4-2 and others and you have multiple conditioned zones on the system. This will not work. When using a single zone system (whether it be PSZ or SZRH) you specify a control zone. This control zone tells the unit what temperature to supply the air at. If you put two conditioned zones on one single zone system the non-control zone will be subject to the whims of the control zone. Hence the large amount of unmet load hours in E5 NNW Perim Zn (G.NNW1). Either combine the zones into one zone (Really it is one zone even if there is a wall separating them) or if there are some other reason why they can control the supply air temp independently you will need to select a different system type or create two systems.


Timothy Howe, MS, LEED? AP BD+C

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