[Equest-users] FW: Modeling cabinet/unit heaters

Holt Cutler HCutler at EMEGroup.com
Mon Mar 5 07:36:31 PST 2012

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

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From: equest-users-bounces at lists.onebuilding.org [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of Jim Grady
Sent: Friday, March 02, 2012 7:13 PM
To: equest-users at lists.onebuilding.org
Subject: [Equest-users] FW: Modeling cabinet/unit heaters

From: Nirupama Laskminarasimhan [mailto:nirupama at lightec.net]<mailto:[mailto:nirupama at lightec.net]>
Sent: Friday, March 02, 2012 3:44 PM
To: equest-users at lists.onebuilding.org<mailto:equest-users at lists.onebuilding.org>
Cc: Jodie Lucci; James Michael Grady
Subject: Modeling cabinet/unit heaters

I'm modeling a school building with unit heaters and cabinet heaters. There is a central boiler serving these heaters. The rest of the school has fin-tube radiation all along its exterior walls. I'm trying to create thermal zones to match the interior space types (classrooms, corridors, etc.). But for classrooms with 2 unit heaters, I'm not sure how a system could be created-

1.       Can I create a forced air hot water heater that runs on the hot water loop, and specify the BHP of the motor and the cfm's the fan handles?


2.       Baseboards with MBH capacities running on the hot water loop + w/sf on the misc. loads to compensate for the fan electricity consumption?

If I went ahead with option 1, I would account for the systems, but I do not understand if the heating capacity in MBH for the unit heaters comes from the boiler? (based on the boiler's capacity)

If I went ahead with modeling unit heaters as baseboards with misc. electric load, wouldn't I run into ventilation issues, as I'm not accounting for the cfm's of air moved by the fans in these heaters?

Also, can someone tell me how a thermal zone on eQuest behaves? Do the walls of the zone represent the "vertical walls" in the building interior?

Thank you.

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