FW: Modeling cabinet/unit heaters

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Jim Grady's picture
Joined: 2011-09-30
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Hi Nirupama,

So you have a classroom zone that is served by two unit heaters that you're trying to figure out how to model, and you're not sure whether their heat source is HW from the boiler because the systems might exceed the boiler capacity.
Based on the systems I've worked with, if you are seeing a building fed by HW and baseboards in perimeter zones fed by the same, then the cabinet unit heaters you're seeing in classrooms are likely HW systems as well. Some MER zones may have electrical resistance heaters for freeze protection, but regularly used zones like classrooms should be on the hot water loop.
Now regarding the boiler capacity, if your systems amount to a whole lot more capacity than the boiler can provide, double check your capacity inputs vs your mechanical schedule. The mechanical design uses "MBH" differently than eQuest, which could potentially trip someone up. (eQuest MBtu/h is 10^6 Btu while the mechanical schedule MBH is 10^3 Btu)
I've modeled schools with similar setups to yours, and I'd recommend modeling the cabinet unit heaters as Fan Coil systems. You can combine the capacity, fan kW, and cfm for the two systems and model it as one. This system can be attached to the hot water loop.

Holt Cutler, EIT, LEED AP BD+C

Holt Cutler's picture
Joined: 2011-11-12
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