Hi every one
We are working on a gymnasium and using demand control ventilation based on CO2 sensors, Occupancy sensors and monitoring switch at the front desk for some spaces.
In spaces where the strategy is based on CO2 sensors ASHRAE is clear on how to apply the max and minimum according to Appendix C. but with occupancy sensors it is not clear. The occupancy sensor will determine if the space is occupied or not therefore if the space is deemed unoccupied by the occupancy sensor do we have to maintain the minimum rate for the square footage Ra or not.
The same for the monitoring switch at the front desk that is controlling the two vav terminal unit that are supplying the play area where the Rp = 0 and Ra = 0.3 CFM/sqf.
Has any one experienced this case?
Thanks
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Rudolph Carneiro
HVAC consultantOptimized Systems
26 thumbs up
October 3, 2012 - 8:08 am
Hi Housine. I'd say that according to 62.1, the rate can literally be zero when unoccupied since all non-occupiable spaces literally require no ventilation. The gymnasium, when unoccupied would be similar to a corridor that requires no ventilation unless you have employees working in the corridor for long periods. Question: How can a play area RP be zero? I'd imagine play areas to be occupied for long periods.
HOUCINE TLEMSANI
Mechanical DesignerMEP Engineering Solutions, Inc
14 thumbs up
October 3, 2012 - 10:03 am
Yes that’s my take on it, but ASHRAE 62.1- 2007 ADDENDA g, r and t has changed section 6.2.7.1.2 Demand Control Ventilation (DCV) as follow.
The breathing zone outdoor airflow (Vbz) shall be reset in response to current occupancy and shall be no less than the building component (Ra*Az) of the DCV Zone.
Examples of reset methods or devices include population counter, carbon dioxide (CO2) sensors, timers, occupancy schedules or occupancy sensors.
The part that is odd is that you have to provide the minimum O/A to the zone even when the space is unoccupied during the building occupied time. The occupancy sensor wills sense if there is a transient occupancy in the spaces.
Furthermore according to this section you cannot use any strategy for spaces that have only a requirement per sqf.
Is there something I am missing?
Rudolph Carneiro
HVAC consultantOptimized Systems
26 thumbs up
October 3, 2012 - 10:55 am
Ok. I didnt know that you were using an addenda. I think the purpose of the mínimum is to appropriately ventilate the VOC emissions of finishing materials in the gym. In this case, I'd imagine there would be alot of polyurethane applied to the floors that would emmit gases and in turn, someone entering the gym would be unconfortable for a certain period until the gym gets reasonably ventilated. However, addenda is optional for use for LEED NC. Reducing the ventilation rate to zero would seem to be OK in my opinion.