Question about DOAS and Fan-Coil configuration

asked 2018-10-24 18:02:41 -0600

s_pourm gravatar image

updated 2018-10-25 13:19:48 -0600

For an office building, I have MUA ducted to each zone fan coils, So under the air loop, I have each zone connected on the demand side of air loop using duct VAV no reheat,

And I defined the fan coil under thermal zones for each zone,

So I made the availably schooled of the each fan coil unit to be zero all the time, and ran the simulation,

Results shows that I have zero fan energy after, does it mean the MUA is also off? what if I have supply the MUA air to the zone separate from the Fan coils, (Not ducted to fan coils), in that case, how should I model the MUA and fan coil to avoid them to behave as one system.

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how is the outdoor air rate controlled? that may dictate whether you want to model outdoor air directly at the terminal units or through a central air loop. Also, do you have energy recovery on the exhaust air? For the fan coils, if you set the availability schedule to zero, then they will be always off, and you'll get unmet hours. Instead, set the fan static pressure to zero or some negligible non-zero value like 0.01 Pa.

mdahlhausen gravatar imagemdahlhausen ( 2018-10-24 21:32:01 -0600 )edit

The outdoor air is coming from the central air loop and there is exhaust air ERV, well this is the design, but I am not how if my model exactly is representing that, For the fan coils, I have assigned a minimum air flow per floor area 1.8 CFM/Ft2, however when I look at the results for the zone air flow rates and divide those by my sq. ft., I will see a much lower number that 1.8 CFM/FT2, that's why I decided to put the fan availability to zero to see how the central air loop is doing alone, but then the total fan power became zero in the results.

s_pourm gravatar images_pourm ( 2018-10-25 08:55:25 -0600 )edit

what do you have set for your design specification outdoor air in your space types/spaces?

mdahlhausen gravatar imagemdahlhausen ( 2018-10-25 11:04:04 -0600 )edit

I have it defined as CFM/FT2 (ft/min), the method is maximum and all the other fields are zero, and no schedule, I used one of the design specification detentions, modified and renamed it and used under spaces/airflow .

s_pourm gravatar images_pourm ( 2018-10-25 11:36:26 -0600 )edit

can you tag the post with what software you are using? Have you tried adding output variables to show air flow rates on your air loop?

For the system you describe - a dedicated outdoor air system with an ERV, serving individual zone fan coils - I think the closest EnergyPlus approximation is a 100% OA loop with uncontrolled terminal units and separate zone fan coils with zero outdoor air and fan set to always on but zero static pressure.

mdahlhausen gravatar imagemdahlhausen ( 2018-10-25 11:50:49 -0600 )edit