Toilet Exhaust Allocation

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I know fan energy has been talked about before but I can't find the
exact answer to my question.

What do you guys find is the best way to deal with point source exhaust.
Especially when it is going to be running intermittently, and not
necessarily associated with main equipment.

1. A simple example is an apartment unit with a fan coil and then
kitchen and bathroom exhaust that will run intermittently. Do you feel
that you need to take the 0.3 W/cfm and distribute it between the supply
and exhaust? Then schedule the exhaust to run explicitly for 2 hours (or
whatever time) per day.

If the fans are not being required to supply the ventilation air. I feel
like the easiest approach would be to model the exhaust fan as a direct
load on the electric meter in the proposed case. And leave the baseline
supply at 0.3 w/cfm.

Or is there any case to be made that you could consider either the
bathroom or kitchen exhaust a process load and model it the same in the
baseline and proposed (in addition to the 0.3 W/cfm).

2. A more complicated example would be a school. Where you have some
continuous exhaust systems for pressurization. You can also have makeup
exhaust for the kitchen. And intermittent exhaust for the labs.

Do you feel you need to model these all explicitly? Also, is it
necessary to include all of the fan power from the exhaust as part of
your appendix G allowance based on supply flow rate, then distribute it
based the ratio of exhaust, return and supply. Again, I feel it is
easiest to take some of the smaller exhaust systems and model them
directly on the electric meter. I also feel large, intermittently
running exhaust systems will distort the fan power allocation in the

I would appreciate hearing how the community deals with these issues.


Steve Jacobs's picture
Joined: 2012-11-12
Reputation: 600