[Equest-users] OA schedule

Patrick J. O'Leary, Jr. poleary1969 at gmail.com
Fri Apr 27 11:07:19 PDT 2012


good point david, considering a baseline (i.e. minimally compliant 
building) would have to meet the requirement i think the intent of the 
appendix g requirement is to simulate a worst-case scenario concerning 
outside air scheduling and energy consumption.  not unlike the 
simulation requirement for a proposed building that a thermal block not 
specified with a cooling or heating system must simulated with one that 
is the same type used in the baseline building simulation (app g, table 
3.1, no 10, d).

your reference to 6.4.3.4.3 (2007) would explain why a usgbc/gbci 
reviewer could comment on the oa schedule, even though app g is pretty 
specific on how the oa should be scheduled for simulation purposes.

Sambhav, if you're working on a leed project can you ask the review team 
(thru the project on leed online) to clarify which oa requirement method 
should be followed in the simulation - app g or 6.4.3.4.3?

On 4/27/12 10:32 AM, David Reddy wrote:
> 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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