Quantifying multifamily infiltration savings in EneryPlus

asked 2015-03-13 16:02:07 -0600

xfang
163 ●1 ●6

updated 2016-10-20 11:19:24 -0600

We are trying to quantify energy cost savings with air sealing measures (7ACH down to 5ACH per unit, for now assuming all leakage to the outside) in a mid rise multifamily building using a whole building modeling approach. For the zoneinfiltration:DesignFlowRate object in EnergyPlus, the EnergyPlus IO manual lists I_design for two scenarios: 1. 7.5mph value and using Blast coefficients and 2. 10mph value and using DOE2 coefficients.

According to an earlier post on Getting Infiltration Correct, I presumed I_design is design value at 4pa rather than at 7.5 or 10mph wind speed. And I used the DOE2 coefficients 0.224 on wind speed difference, my predicted savings level is 4-5 times more savings on a per unit basis than savings level predicted by BEopt or Remrate. Is there any recommendations to align the savings number? Are there better coefficients to use for multifamily buildings as well, similar to @lisang 's publications?

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answered 2015-03-16 12:18:43 -0600

lisang
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The I_design is a presumed 4Pa airtightness value, which is not reflective of actual operating conditions. In a report, I compared results using both the BLAST (#1 you list above) and DOE2 (#2 you list above) and they are a lot higher than what you'd get using a multizone model, like CONTAM. Unfortunately, the study I posted previously did not include multifamily residences, and I know of no other set of coefficients in the literature. Nevertheless, using the coefficients I developed (using 7 commercial reference buildings) may be better than using BLAST and DOE2 since they take into account building characteristics, weather (both temp and wind), and whether the central heating/cooling system is on or off (which affects building pressurization). Hope this helps.

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