[Equest-users] Exhaust fans in appartment

[Nathan Miller]

Julien,

I don’t have time to dig into your questions at this moment (deadlines!), but just a quick check for you, are you modeling electric resistance heat via the system-> baseboards entries? If so, I don’t believe eQUEST ever autosizes baseboard heat, you always have to manually input (or use a formula based on space square footage…).

To get around this I often use the PTAC system, zero-out the fanpower, and then select electric resistance heat as the primary system level heat source. eQUEST should autosize that for you, and it would seem to be a thermodynamically similar system to inputting via-base-board (though I’m sure somebody can point out why it is better to use baseboards).


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: Julien Marrec [mailto:julien.marrec at gmail.com]
Sent: Friday, February 20, 2015 7:14 AM
To: David Reddy
Cc: Nathan Miller; equest-users at lists.onebuilding.org
Subject: Re: [Equest-users] Exhaust fans in appartment

Hi again,

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 separately.
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 1.
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 favor soon.

Thanks a bunch,
Julien

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

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

2015-02-20 13:04 GMT+01:00 Julien Marrec <julien.marrec at gmail.com<mailto:julien.marrec at gmail.com>>:
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<tel:%2B33%206%2095%2014%2042%2013>

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

2015-02-19 20:35 GMT+01:00 David Reddy <david at 360-analytics.com<mailto: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<mailto: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<mailto: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<tel:%2B33%206%2095%2014%2042%2013>

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


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