[Equest-users] Exhaust fans in appartment

Julien Marrec julien.marrec at gmail.com
Fri Feb 20 04:04:18 PST 2015


Thanks to both of you for your answers!

David,

You say its combined in quadrature. Is there documentation somewhere about
this?

Also, I'm confused about how it's more flexible to add HRVs when using
zonal exhaust. I thought the core principle of Zonal Exhaust was that it
was directly exhausted to outside, which means not going to the central
system and thus completely bypassing any Heat recovery.
>From the help file: "The SYSTEMS program simulates heat recovery from
central exhaust only, not from zone exhaust. If heat is to be recovered,
zone exhaust should not be entered but rather allowed to default to the
central system."
Am I missing something?

Thanks,
Julien

--
Julien Marrec, EBCP, BPI MFBA
Energy&Sustainability Engineer
T: +33 6 95 14 42 13

LinkedIn (en) : www.linkedin.com/in/julienmarrec
LinkedIn (fr) : www.linkedin.com/in/julienmarrec/fr
<http://www.linkedin.com/in/julienmarrec>

2015-02-19 20:35 GMT+01:00 David Reddy <david at 360-analytics.com>:

> I agree with Nathan's recommendation; that is also how we have
> also settled on modeling whole house exhaust ventilation.  With regards to
> infiltration, we do model a nominal amount that is calculated using PNNLs
> infiltration modeling guidelines and is input at the space as the
> component adjusted with wind speed. The EXHAUST-SOURCE = infiltration will
> automatically combine the space and zone exhaust in quadrature, which
> we believe is appropriate, at least with respect to what is readily
> available in Doe-2. The space component is assumed the same in
> proposed/baseline unless the intent of the analysis is to illustrate the
> impacts of reducing uncontrolled air leakage.
>
> In addition to other noted flexibility, it is also easier to incorporate
> modeling of variable flow and even HRVs.
>
> -David
>
>
> On Thursday, February 19, 2015, Nathan Miller <nathanm at rushingco.com>
> wrote:
>
>>  We model that type of system all the time, and prefer to model the
>> outside air as zonal-exhaust (infiltration).
>>
>>
>>
>> The primary reason is that it ensures the space conditioning system sees
>> the same vent load regardless of if you switch systems types (or have
>> different systems in a baseline vs. proposed case for example). On jobs
>> where I input it as OA on systems, I was never able to get the ventilation
>> load energy use to line up when I compared, for example, electric
>> resistance heat to PTACs, probably due to the slightly different algorithms
>> employed for each system type.
>>
>>
>>
>> The other nice thing is that it allows you to model the space
>> conditioning fans as cycling to meet the load (schedule = 0 all the time,
>> night-cycle-control allowed, fan operation = intermittent). If you
>> introduce the outside air through the system inputs, often it will force
>> the mechanical system fans to operate all the time to provide ventilation,
>> but in your case, you already have the whole-house-fan to do that.
>>
>>
>>
>> I believe any infiltration air assigned at the zone gets tacked on to
>> infiltration air assigned at the space. If you want greater control of the
>> net infiltration air, you’d probably have to do some math and decide when
>> those values should stack, and when they would be “double counting”
>> infiltration.
>>
>>
>>
>> *Nathan Miller, PE, LEED AP BD+C** – **Mechanical Engineer/Senior Energy
>> Analyst*
>>
>> *RUSHING* | *D* 206-788-4577 | *O* 206-285-7100
>>
>> *www.rushingco.com <http://www.rushingco.com/>*
>>
>>
>>
>> *From:* Equest-users [mailto:equest-users-bounces at lists.onebuilding.org] *On
>> Behalf Of *Julien Marrec
>> *Sent:* Thursday, February 19, 2015 11:44 AM
>> *To:* equest-users at lists.onebuilding.org
>> *Subject:* [Equest-users] Exhaust fans in appartment
>>
>>
>>
>> Hi,
>>
>> I'm modeling an apartment building that has toilet and bathroom exhaust,
>> and mechanical supply. Make-up air comes from trickle vents.
>> (Side note: the corridor has mechanical supply, much higher than 62.2 at
>> 0.6 CFM/ft²,  and no exhaust whatsoever, so I expect *some *makeup air
>> would come from there too, but I'm prohibited to capture this effect...)
>>
>> I have been thinking about the best way to do this: whether I should
>> assign this to a zonal exhaust fan (EXHAUST-FLOW) or whether I should
>> specify the CFM exhausted as an outdoor air flow (OUTSIDE-AIR-FLOW).
>>
>> I think the OUTSIDE-AIR-FLOW would be the least problematic if I only had
>> to deal with the baseline, but in my proposed building I only have
>> baseboards for heating, so this wouldn't work.
>>
>> First, Am I correct in the above statements?
>>
>> Second, if I do specify an exhaust fan in the following way:
>>    FAN-CONTROL      = CONSTANT-VOLUME
>>    EXHAUST-FLOW     = 50
>>    EXHAUST-FAN-SCH  = "Fraction Always 1 Yr"
>>    EXHAUST-SOURCE   = INFILTRATION
>>
>> (I'm also defining exhaust systems like this for mechanical rooms in my
>> basement)
>>
>> Will eQuest actually take into account that it (he?) should add 50 CFM of
>> outside air (through infiltration) as a load? Will eQuest also take that
>> into account for the sizing of my zonal equipment?
>>
>>
>>
>>
>>
>> Finally, will it interact in any way with the infiltration defined under
>> Internal Loads for the Space?
>>
>>   Thanks for any clarifications you can offer.
>>
>> Best,
>> Julien
>>
>> --
>> Julien Marrec, EBCP, BPI MFBA
>> Energy&Sustainability Engineer
>> T: +33 6 95 14 42 13
>>
>> LinkedIn (en) : www.linkedin.com/in/julienmarrec
>> LinkedIn (fr) : www.linkedin.com/in/julienmarrec/fr
>>
>
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