[Equest-users] OA schedule

Patrick J. O'Leary, Jr. poleary1969 at gmail.com
Fri Apr 27 11:48:16 PDT 2012


the app g, 3.1, no 4 text (2007) states:

"HVAC Fan Schedules.  Schedules for 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."

so separating outdoor ventilation from fan cycling does not appear (to 
me) to be the intent of the app g requirement.  why would a fan that 
provides outdoor air for ventilation be required to operate if it is not 
providing outdoor air?  e.g. doas system or outdoor air supply fan 
separate from fan in the ahu, or even if the outdoor air ventilation fan 
is the ahu supply fan (per app g, 3.1, 4).

how does the requirement (6.4.3.4.3) apply to an evaporatively cooled 
system with zero return air? i.e. no return air path.  or an evaporative 
system with no return air path in cooling mode but 80% return in heating 
mode when mated with a furnace section?  app g, 3.1, 4, sounds more 
logical (to me) without even getting into the debate about how to 
properly simulate a baseline building system of system type 3 or 4 when 
the proposed building system is an evaporative cooler with 100% outside air.



On 4/27/12 11:23 AM, David Reddy wrote:
> Yes, thanks Bill, these are exactly the same points that I was going 
> to follow up with...
> -DR
>
> On 4/27/2012 11:19 AM, Bishop, Bill wrote:
>> I don't see any conflict between App. G and 6.4.3.4.3. I interpret 
>> the "cycling" language as requiring that the fans cycle to meet 
>> heating and cooling loads but without providing ventilation. 
>> Providing ventilation when cycling conflicts with the G3.1.2.5 
>> requirement that ventilation rates be the same - you won't get the 
>> same ventilation during cycling since the proposed and baseline cases 
>> will differ in the frequency and duration that they cycle.
>>
>> Regards,
>> Bill
>>
>> -----Original Message-----
>> From: equest-users-bounces at lists.onebuilding.org 
>> [mailto:equest-users-bounces at lists.onebuilding.org] On Behalf Of 
>> Patrick J. O'Leary, Jr.
>> Sent: Friday, April 27, 2012 2:07 PM
>> To: David Reddy
>> Cc: equest-users at lists.onebuilding.org
>> Subject: Re: [Equest-users] OA schedule
>>
>> 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.
>>>>>
>




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