Hi,
I am trying to work out the best way to model a heated (cold climate) bus storage facility in the baseline. The proposed has supply fans and exhaust fans with heat recovery and a heating coil to keep temperatures 50F. It also has purge fans that are modeled for a few hours a day when all the buses are traveling due to emissions. My proposed approach was the system in the baseline as Heating Only Storage (system 9) and then model the purge fan as process (like car parking fans). However i have a dilema as the baseline fan energy is significantly lower - primarily due to the 0.3W/cfm rate. The proposed is significant more that this (heat recovery/filters for emissions) and the baseline does not seem to have the same allowances that the other systems 3-8 have to add on. Any one have any thoughts or come across this before? It seems i am stuck in a sticky situation of being half parking garage / half heating only storage and am being penalized for it right now.
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Marcus Sheffer
LEED Fellow7group / Energy Opportunities
LEEDuser Expert
5907 thumbs up
August 28, 2017 - 10:32 am
I think the purge fans can be considered a process load and modeled identically if they are separate from the fans associated with the heating system. If they are not separate then they are not process and you have to pay the penalty for having heat recovery.
Victoria Watson
AECOM4 thumbs up
August 29, 2017 - 11:25 pm
Thanks Marcus, the purge fans themselves seem ok as process (separate) and for extreme operation to purge the space from noxious fumes. Its the standard bus storage ventilation and heating. It is still for the "parking garage" elements (e.g to remove the fumes from the buses and to temp the conditions in the space to 50F). I assigned a baseline system type to this initially due to it being a heated space. However the baseline system 9 is recirculating but car parking systems don't recirculate so it doesnt seem a good fit. ASHRAE 90.1 6.4.3.4.5 Enclosed Parking Garages states the ventilation systems shall automatically ramp down to 50% based on contaminant detection. This and the requirement to not recirculate just doesnt seem a fit for the baseline system 9 which is constant volume and recirculating. One of the exception to the 50% flow reduction is for spaces that arent heated. Implying this requirement relates to parking garages with heating. It seems odd the baseline heating type is not specified though for parking garage fans so that points back to using system 9. I think you are probably right on the fan power it should be 0.3cfm/ft2 (and we get stung for having much higher supply/exhaust/heat recovery) but i think the OA rates should probably be very high (0.75cfm/ft2 is required for the car park but then you factor in the demand control vent and it therefore varies in the proposed). I think this needs to be matched in the baseline. Then heat recovery isnt required as per 6.5.6.1 exception b) as heating to less than 60F. But should system 9 not be constant volume then and ramp down to 50%....as per enclosed car parking requirements....