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unmet cooling hours for 5 zones in MURB

asked 2020-07-07 23:27:44 -0500

mbebawy's avatar

updated 2021-04-17 13:50:28 -0500

i am facing a persistent unmet hours issue in energyplus 8.9. i have 5 zones, lobby and corridor spacetypes. served by the same Make up air unit with a cooling coil. there are separate DSOA objects defining OA as per space type. i have attempted varying the zone cooling sizing factor with no result. code requires those zones be set on NECB G thermostat schedule, ie: set to 22 degrees C during occupied hours. i have also attempted changing the heating & cooling sizing factors simultaneously to make sure airflow is sized properly. bear in mind, that same MUA unit is serving many other zones with no unmet hours.

any thoughts what can be attempted to fix this?

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-Different internal/solar gains that cannot be handled by a unique MUA?

-How is air flow rates and supply air temperature set?

Ag's avatar Ag  ( 2020-07-08 12:50:19 -0500 )edit

thank you for the quick response!

4 of the 5 zones are internal zones. 1 is an external bridge which connects two buildings. you are right, that zone will likely have significantly higher solar gains than the other zones. as for internal gains, occupancies and loads are fairly similar for those 4 zones.

as for temperatures, using NECB G schedule for heating and cooling in a dual setpoint thermostat (24 C for cooling, 22 C for heating)

for airflow rate, the MUA has a variable speed fan which is always on. For OA, its specified as flow per area and occupancy as per code

mbebawy's avatar mbebawy  ( 2020-07-08 12:59:48 -0500 )edit

It could be that 4+1 zones with different characteristics cannot be handled by a MUA with a supply air temperature that is the same for all 4+1 zones. Do you have any other HVAC zone equipement other than DOAS?

Ag's avatar Ag  ( 2020-07-10 09:51:09 -0500 )edit

i managed to tweak the thermostats by allowing a higher cooling temperature setpoint and it seemed to fix the issue. its not the best solution but i think you are right. if the mechanical setup was more of a unitary nature for each zone, those unmet cooling hours wouldnt pop up. thanks for your help

mbebawy's avatar mbebawy  ( 2020-07-10 09:53:52 -0500 )edit

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answered 2020-07-10 09:56:00 -0500

mbebawy's avatar

after examining the ESO files, it seemed that the only option to resolve this was to allow the cooling setpoint thermostat a couple of degrees more of buffer. given that the system serves a multitude of zones, its unfair to expect meeting all cooling hours demand. recommendation to design to split out the zones to be served by a larger number of smaller units ie:unitary system design

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Asked: 2020-07-07 23:27:44 -0500

Seen: 131 times

Last updated: Jul 10 '20