Re: [EnergyPlus_Support] Infiltration

You might check how this feature works when natural ventilation is set to calculated and scheduled-- It would make since that when calculated is checked the AFN infiltration objects are used on all external surfaces but when scheduled is checked than infiltration is modeled ZoneInfiltrationDesignFlowRate..

Jeremiah D. Crossett | Senior Analyst | Phase Change Energy Solutions

120 E. Pritchard St. | Asheboro, NC 27203 | Mobile 503-688-8951

www.phasechange.com

On Fri, Feb 1, 2013 at 10:40 AM, Edward G. Lyon <eglyon@xxxxxxx> wrote:

Thanks, we have Design Builder in the company, but I don?t use it myself. When I have some time I?ll check out what they do exactly.

Ned Lyon, P.E. (MA, WV)
Staff Consultant

SIMPSON GUMPERTZ & HEGER
781.907.9000 main
781.907.9350 direct
781.907.9009 fax
www.sgh.com

From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Jeremiah Crossett
Sent: Friday, February 01, 2013 1:34 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: Re: [EnergyPlus_Support] Infiltration

I agree with Ned, but also think it is worth mentioning that Design Builder has a simple input from blower door to Energy Plus that might be worth looking into, and I have attached a screen shot of the input. I am not 100% sure how DB applies this to its E+ file generation but assume it uses the ZoneInfiltrationDesignFlowRate Object pasted from another file below. I think there is a better way to do it with airflow network as well.

Name Infiltration

Zone or ZoneList Name     Zone

Schedule Name       On

Design Flow Rate Calculation Method     Flow/zone

Design Flow Rate    0.018

Flow per Zone Floor Area

Flow per Exterior Surface Area

Air Changes per Hour

Constant Term Coefficient 1

Temperature Term Coefficient     0

Velocity Term Coefficient   0

Velocity Squared Term Coefficient          0

Jeremiah D. Crossett  | Senior Analyst  | Phase Change Energy Solutions

120 E. Pritchard St. | Asheboro, NC 27203 | Mobile 503-688-8951

www.phasechange.com



On Fri, Feb 1, 2013 at 10:15 AM, Edward G. Lyon <eglyon@xxxxxxx> wrote:

In my opinion, the answer to your question is very complex. I am not sure what you mean precisely by 50Pa test. Usually this means ACH50 (air changes per hour at 50 Pa), but you could have a complete test that reports Coef and Expon for the flow equation Flow = Coef*Pressure^Expon.

In either case there is no short cut way I see to put this data directly into EnergyPlus.

I also think different procedures may apply to different types of buildings. If you have a small house, and ACH50 result divided by 20 (sometimes other factors) is a fair approximation of the infiltration air exchange rate for a small building. You could define Infiltration as an ACH and juggle the coefficients to give you a better guess for seasonal temperature and wind conditions. Or you could study the research on ACH50 correlations to infiltration and schedule something appropriate for your location. If you have a commercial building, your test data should be unit area based and you would use Infiltration with a surface area calculation.

Infiltration in EnergyPlus has a sophisticated set of input parameters intended to vary infiltration by site conditions, and I have done a lot of whole building testing. Perhaps others can provide a good reference for integrating measured data into the energy model, but I have not seen it. I think there may a way to approximate the pressure from the temperature and wind in order to recalculate coefficients for Infiltration in EnergyPlus. Perhaps I need to study this in more depth myself.

From my testing work I also know that not all parts of the building leak the same. There may be different results for different zones (roof to wall edges leak more than field of wall). This is likely to influence some zones more than others. Also a very leaky roof above very tight walls will give you a very leaky test result, but the actual infiltration affecting energy could be much less.

For a recent model that looked at temperature conditions and not energy, I was able to use an air flow network. The equations there are more easily adaptable to the results of a building blower door test and the analysis automatically calculates pressures based on wind and temperature. This can get complicated for larger buildings, and may not work with other fans in a mechanical system.

Now it is not my intention to offend all the serious and dedicated energy modelers out there who put infiltration into their models. I just don?t see how it is currently much more than a guess or accepted practice, and I would be interested in any available information on correlating test data to models. I get asked that question a lot, and each energy model calculates infiltration in a slightly different way.

Ned Lyon, P.E. (MA, WV)
Staff Consultant

SIMPSON GUMPERTZ & HEGER
781.907.9000 main
781.907.9350 direct
781.907.9009 fax
www.sgh.com

From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of FrancescoP
Sent: Friday, February 01, 2013 12:09 PM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Infiltration

I wonder what the best ways to model infiltration in these two cases are:
1. you know the result of the blower door test (50Pa)
2. no blower door test was made but you know how the building was built
Any idea?
With Regards