[Equest-users] Exhaust fans in appartment
julien.marrec at gmail.com
Fri Feb 20 04:14:19 PST 2015
After implementing zonal exhaust, I'm still in a bit of a pickle.
For those familiar with it, I'm actually modeling a building per the ENERGY
STAR MultiFamily High-Rise Simulation Guidelines, slightly modified because
it may go for NYSERDA Multifamily Performance Program (MPP). MPP New
Construction, in its v6 version, has a different calculator that the MFHR
one for infiltration, and you have to model infiltration and local exhaust
Anyway, the calculator is telling me to put:
- 0.08 ACH in the space with hourly fraction at 0.5 (so 0.04 ACH...): it's
doing some kind of calculation to come up with 0.04 CFM/sqft of exterior
above grade surfaces (roof + ext walls)) that leads to the 0.08 ACH figure.
- Model the exhaust as about 40 CFM per apartment with a fraction of always
I don't know why, but this seems fairly low to me (0.38 ACH would seems
about right for a fairly tight building when you consider that
building-wide, but here I'm only entering it for the apartments right now).
What do you think?
Ultimately, I have one major problem: the heating consumption reported is
abnormally low. I've been banging my head since yesterday trying to figure
out why. I think I've ruled out pretty much everything (but I'm confident
that missing something is possible) aside from this ventilation thing.
If I add (or increase) Zonal exhaust to a zone:
- The attached system sizing doesn't seem to change
- but suddenly I'm getting unmet heating hours...
- And I do have *some* more consumption
*This make me think eQuest somehow doesn't really take zonal exhaust into
account when autosizing *(but does for consumption)*. Do you have the same
experience with it? Any workaround to avoid this problem?*
Finally, I think I'm in dire need of a pair of experienced yet fresh
eyes... I'd be extremely grateful if someone was willing to take a look at
my model. Ping me and I'll send you the file, and hopefully return the
Thanks a bunch,
Julien Marrec, EBCP, BPI MFBA
T: +33 6 95 14 42 13
LinkedIn (en) : www.linkedin.com/in/julienmarrec
LinkedIn (fr) : www.linkedin.com/in/julienmarrec/fr
2015-02-20 13:04 GMT+01:00 Julien Marrec <julien.marrec at gmail.com>:
> Thanks to both of you for your answers!
> You say its combined in quadrature. Is there documentation somewhere about
> 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?
> 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
> 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.
>> On Thursday, February 19, 2015, Nathan Miller <nathanm at rushingco.com>
>>> 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”
>>> *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
>>> 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
>>> 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.
>>> 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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