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Infiltration rate using energyplus

asked 2014-11-26 22:51:29 -0500

Gilles CR gravatar image

updated 2014-11-28 10:46:40 -0500

I found hard to estimate a correct infiltration rate in energyplus. The heating load results are such dependant on those rates that I am not sure what to use. Following the guide, there are some suggestion as to what number to use for coefficient such as wind speed, etc...I am used to work it out based on air change rate (1 ac/h would be a leaky building and 0.25 a tight one). Some have used 0.05cfm/ft2 of exterior wall. Others would assume a 10 feet zone around the building perimeter with 1 ac/h. Could someone have an insight of a correct method?

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answered 2014-12-01 09:44:28 -0500

If you are trying to represent the actual physics of infiltration, then you need to look at values of infiltration that are appropriate for your building type (see more info below). If you are using infiltration rate as a calibration parameter that you adjust so that your energy predictions match reality, then I advise you to find other parameters to adjust and go back to a more physically appropriate infiltration rate.

Infiltration is one of the parameters with the highest uncertainty for several reasons including 1) it changes in time and varies around the building, 2) there can be lots of leakage points on buildings that are not well known, 3) opening and closing of doors for people and equipment entering/leaving can sometimes dwarf actual infiltration but is often left out of the model. This is one reason why I advocate for using probabilistic modeling and actually propagating the uncertainty through the model.

Besides PNNL 18898 "Infiltration Modeling Guidelines for Commercial Building Energy Analysis " mentioned in a previous answer, there are several places to get information about infiltration in real buildings and modelling

Alex Berge of Chalmers University, did an MS thesis on the topic.

A good list of resources for measured infiltration can be found in AIVC TN 66:Building air leakage databases in energy conservation policies: analysis of selected initiatives in 4 European countries and the USA

Malcom Orme and Nurul Leksomono put together a ventilation modeling guide in AIVC Guide 5: Ventilation Modelling Data Guide.

Unfortunately, the AIVC papers/reports are not publicly available, but if you are in the right country, you can get free access.

Good Luck!

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answered 2014-12-01 10:59:41 -0500

ChrisBalbach gravatar image

Although no longer published in the current ASHRAE Handbook of Fundamentals (HOF), the 1997 version included a 1 page table in Chapter 25 that provided Best Estimates, Minimum Estimates, and Maximum Estimates of Eeextive Leakage Areas of over 100 different building elements. The table is described as applicable to low-rise residential, and states that ELA are are based on a pressure differential of 0.016 inches H2O and a Cd of 1.0

I recall seeing this table (or a variant of it) included in Wrightsoft software, used to fully document the determination of initial and final building level ELA. I have also seen custom spreadsheets which used this table, or a variant of it, to accomplish the same. While certainly not perfect, it is the best example I can point towards for the development of a transparent estimate of ELA, pre and post.

At the other extreme, I am aware that Canam/ZeroDraft uses a hybrid inverse/forward model (proprietary software) called ALCAP which performs monthly savings estimates of savings (peak demand and consumption) associated with descriptive infiltration improvements. Some of the algorithms used in ALCAP are described here: http://www.regie-energie.qc.ca/audien...3671-08/C-9-12GRAME-1Annex73671_14nov08.pdf

Canam/ZeroDraft has claimed that the ALCAP calculation methodology is both conservative in nature and has been validated via numerous case studies. They certainly have the experience and data to mine from many, many projects. At a first glance, it does not seem difficult to extend the basic ALCAP approach to calculate infiltration savings estimates at a daily level, based on unique daily operations. This might be useful to generate upper/lower bounding levels for savings that could be claimed.

I personally think from a practical perspective, in addition to transparency, our community needs open-source tools that can provide a layer of quality assurance on top of our savings estimates, to prevent excessive claims of savings performance which cannot be substantiated without great expense, such as infiltration reduction. Perhaps these two methods can be applied in creative ways to help us move closer towards this.

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Could you edit the link pointing to the document including the algorithms used in ALCAP? I am interested but I can't find the right link. Thanks!

EDIT: Ok, found it! An underscore is missing! Link.

Jeremy gravatar image Jeremy  ( 2014-12-01 11:15:54 -0500 )edit
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answered 2014-11-28 13:58:21 -0500

Gilles,

There is a publication from the PNL that provides guidelines on how to model infiltration for commercial building using Energy+, you can find the publication here. Also you can set the infiltration flow rate to "AirChanges/Hour" in the ZoneInfiltration:DesignFlowRate object.

I hope this can help!

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answered 2014-11-28 16:07:29 -0500

In Canada, the standard is 0.05cfm/ft2 for perimeter zones, as per the MNECB.

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Asked: 2014-11-26 22:51:29 -0500

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Last updated: Dec 01 '14