[Equest-users] OA schedule

[David Reddy]

For LEED or other rating systems referencing ASHRAE PRM, it does seem 
that the 90.1-2007, appendix g, table 3.1 statement is misleading.

However, the mandatory shutoff damper controls in section 6.4.3.4.3, I 
believe, clarifies that the outdoor air should be 0 if cycling system 
during unoccupied hours, except if the use of OA reduces energy costs 
(night purge, economizer).

If you specify 0.001 in your MIN-AIR-SCH (enables use of economizer), I 
would review your system's hourly OA levels to make sure it is behaving 
as expected, especially for multizone systems.  I have found that this 
can lead to a significant amount of additional heating, as the 
economizer will be used to achieve the SAT control setpoint, even if 
this is not appropriate in the middle of the winter...  As such, I 
typically set the unoccupied MIN-AIR-SCH value to 0.

- David

On 4/27/2012 9:57 AM, Patrick J. O'Leary, Jr. wrote:
> depends on the modeling requirements.  90.1?  owner requirement?  
> leed?  something else?
>
> for 90.1-2007, appendix g, table 3.1, no. 4 schedules, specifically 
> states the "hvac fans that provide outdoor air for ventilation shall 
> run continuously whenever spaces are occupied and shall be cycled on 
> and off to meet heating and cooling loads during unoccupied hours."  
> 90.1-2004 doesn't specify fans specifically for outdoor air for 
> ventilation, it just says hvac fans - which is the same as the system 
> supply fan in a non-doas/economizer capable of completely closing the 
> outdoor air damper system so the outdoor air can't be shut off.
>
> so for a 90.1-2007 simulation the minimum oa should not be zero during 
> unoccupied hours.
>
> On 4/27/12 9:44 AM, sambhav tiwari wrote:
>> Hi All,
>>            It is necessary to specify the min OA schedule as -999 for
>> occupied and 0 for unoccupied hrs at either system or zone level or it
>> can be skipped.
>>
>>
>> Thanks
>> Sambhav
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