[Bldg-sim] RE : Infiltration effect in Climate 1

[Mehta, Gaurav]

Richard,

Are you using the default infiltration rate (0.038 cfm/ft2 of external wall area) for the perimeter spaces?

eQUEST calculates the cfm based on the external wall area and then converts this to an infiltration flow (cfm/ft2 of floor area of the space).

As Fredrick has pointed out this infiltration flow assigned by eQUEST to each perimeter space is not depended on the climate.

See the help section screenshot below:


[cid:image002.jpg at 01CC50FC.B0DA02C0]

It is a flat rate assigned to each space and does not include any wind speed correction and inside-outside temperature difference. The 0.038 cfm/ft2 (of external wall area) infiltration rate was included in the ASHRAE Standard 90.1-1989 as a beginning assumption and that's what shows up in eQUEST as default.

It is good that you are questioning the effect of infiltration on the energy use of building that you are modeling. In the absence of blower door test results it is difficult to imagine the real infiltration rate in a building as it depends on many factors such as the workmanship of the actual construction, stack effect, inside-outside temperature difference, wind-speed and how well the building is pressurized by the HVAC system.

I'll suggest go through the following study by PNNL: Infiltration Modeling Guidelines for Commercial Building Energy Analysis<http://www.pnl.gov/main/publications/external/technical_reports/PNNL-18898.pdf>

Although the report is Energy Plus specific but it can be applied to eQUEST as well. In a recent project I used the PNNL guidelines and further converted the infiltration flow for each space to air-changes per hour to take the wind-speed correction into account. This method still has limitation of not taking into account the inside-outside temperature difference (see above screen-shot). I found the rest of the methods that include both wind-speed correction and inside-outside temperature difference to be specific to residential buildings.

Hope it helps.

Thanks.

Best regards,

Gaurav

Gaurav Mehta, LEED® AP BD+C
Sustainable Building Analyst
Stantec
1932 First Avenue Suite 307
Seattle WA 98101
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From: bldg-sim-bounces at lists.onebuilding.org<mailto:bldg-sim-bounces at lists.onebuilding.org> [mailto:bldg-sim-bounces at lists.onebuilding.org]<mailto:[mailto:bldg-sim-bounces at lists.onebuilding.org]> On Behalf Of Genest, Frederic
Sent: Monday, August 01, 2011 6:03 PM
To: ROBERT GOMEZ; bldg-sim at lists.onebuilding.org<mailto:bldg-sim at lists.onebuilding.org>
Subject: [Bldg-sim] RE : Infiltration effect in Climate 1



Hello Richard.

I'm not used to eQuest, but since it is using DOE in the background, same as EE4 I'm using more frequently, I'll try to answer correctly.

Climate Zone has nothing to do with infiltration rates, except when in comes to wind speed and such. However, I don't think DOE is considering wind speed when calculating infiltration rates; it is usually defined as a constant, based on a value such as ACH or cfm/ft.sq. of wall area.

As such, I would start to check your infiltration inputs to see what is defined, first in eQuest and then in the DOE input file. I'm pretty sure you'll find your answer somewhere there.

Also note that design infiltration rate and "actual, under operating conditions" infiltration rate, are two different things. The average constant infiltration rate is adequate enough for the later one.

Also, if you ever need to model a real infiltration from blower door test results, I personnaly use the 50 Pa value divided by 20 for actual, normal operation conditions, while the 75 Pa value would be divided by 35 (in whatever units those values are provided).

Regards.



Frederic Genest, ing., M.Sc.A.
LEED AP, ASHRAE HBDP
fgenest at pageaumorel.com<mailto:fgenest at pageaumorel.com>

Pageau Morel et associés
210 Cremazie Ouest, suite 110
Montréal, Qc H2P 1C6
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www.pageaumorel.com<http://www.pageaumorel.com>


-------- Message d'origine--------
De: ROBERT GOMEZ [mailto:rsg4999 at yahoo.com]
Date: dim. 31/07/2011 23:05
À: bldg-sim at lists.onebuilding.org<mailto:bldg-sim at lists.onebuilding.org>
Objet : [Bldg-sim] Infiltration effect  in Climate 1

Hello all,

I'm currently involved in a project that is located in International Climate Zone 1 (Very Hot - Humid). The building has no heating system, HVAC systems are only for cooling. Infiltration effect is smaller than I expected from the eQuest energy model result. I know it has something to do with the climate. Can anyone tell me the reason why?

Thanks in advance!


Richard Gulli
Project Engineer
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