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Since infiltration is a function of indoor-outdoor temperature difference and wind speed, the theoretical minimum is 0 i

I don't believe EnergyPlus will do this for you. You will have to schedule infiltration and ventilation amounts yourself

Just for a bathroom? Why are you targeting just this space for a single air leakage value? You can look at average house

Hello! I helped create the Measure. It should work, if you can edit the .idf before simulating. Can you do that? If so,

Yes, that is what the Measure is assuming. That when the system is on, the infiltration (Idesign in the ZoneInfiltration object) is reduced to 0.25 of the full value because it's assumed that when the system is on, the building is pressurized. When the system is off, it is assumed that infiltration can move freely into the building.

I will say that our research has shown that this isn't necessarily the case. We (the National Institute of Standards and Technology) have released a Measure called "Adding infiltration correlated for weather and building characteristics" which will take into account weather (wind and outside temperature), physical characteristics of the building, and system operation when calculating infiltration.

If you have the blower door results, you could convert that to an I_design value @ 4 Pa (equation in ASHRAE fundamentals) to be used in the ZoneInfiltration:DesignFlowRate object and the coefficients in the report @Stuart Dolsmentioned: http://www.nist.gov/manuscript-public...

I submitted a comment on the Prototype Buildings page. Hopefully we'll hear that they'll fix the mistake, if there is one. THANKS!!

Thank you, I will contact them directly. I tried this forum first since it's members are very responsive.

I think you're right, that in the grand scheme of things, perhaps the difference of 10m in this case is not significant. Also, there are advantages in modeling and simulation time when using multipliers, especially really tall buildings. But in the case of airflow modeling, we model all the floors since infiltration will be different at each. Guess the real crux of my question is: "is the Large Office Prototype model wrong in its height, or should I go ahead with the 37.5 m height?"

I think it does matter that the height is off since the "local wind" calculated by EnergyPlus will be different between 37.5 m and 47.6 m. From what I gather, this local wind affects (and local temperature) infiltration as well as external heat loss/gain calculations. If anyone can correct me, please do.

That link is for the "Reference Buildings" and I agree, that is 47.6 m high. Another set of buildings, updated for newer energy standards called "Prototype" buildings (here) has a Large Office at is only 37.5 m. Am I reading the model wrong or missing something?

The DOE Commercial Reference Building of the Large Office type was 47.6 m high. When I open the Large Office Prototype Building, in EnergyPlus and Google Sketchup, its height is only 37.5 m.

Just recently, we developed an Open Studio Measure that incorporate those infiltration relationships into your model. You do need to input system flow rates (total building supply, return, and any exhaust fans). You can find the Measure on BCL hereor look for the Measure titled "Adding infiltration correlated for weather and building characteristics" within the Open Studio program. Subscribe to updates on this Measure by sending an email to infiltration-request@nist.gov (Subject: Subscribe).

@xfang Here at NIST, we've done work in correlating infiltration, modeled with CONTAM (a multizone model airflow simulation program), with weather, HVAC operation, and building characteristics. We developed a set of equations to calculate coefficients in the EnergyPlus ZoneInfiltration:DesignFlowRate object. You need the building height, exterior surface area, volume, and system pressurization (supply, return, exhaust fans). You can find the equations in this article.

No, no, thank YOU!

Thanks, Dan! I will do that.

@macumber, thank you! I will submit that!

I want to change the minimum value required for the Space Infiltration object, which requires editing the .idd file. However, when I go to save my edits, I am giving a warning that I do not have access to this file even though I am the administrator for this computer. Has anyone else come across this (or similar) problem? How do I resolve it?

Yes, please do!

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.

Hello, based on my understanding of energy modeling, eQuest included, infiltration is an input, not a calculated output. Therefore, you use the built-in infiltration models to specify how you want infiltration "modeled". No matter the balance of air in the building/zone, infiltration remains as you input it. There will be no change because you have exhausted an extra 50 cfm of air. The infiltration you input will impact the thermal loads only, not the balance of air. Balance of air is done by the user.

To overcome, you may use a method developed at NIST (Ng et al.). It takes into account building characteristics, central system flow (including exhaust), and weather. The report can be found here http://dx.doi.org/10.6028/NIST.TN.1829. You can also find the method in the ASHRAE Journal July 2014 Issue.

Good luck and let me know if you have further questions.

You could also model the building in CONTAM (http://www.bfrl.nist.gov/IAQanalysis/...) which the airflow visualization is built into the user interface.

Agreed, tracer test is most accurate for determining infiltration rates. Or performing a multizone model simulation.

But you'd still have the issue that a constant infiltration rate does not reflect actual variation with weather and system operation. See my article in the July issue of ASHRAE Journal for calculating coefficients to use in EnergyPlus that varies infiltration with weather and system operation.

Regarding the PNNL report, it was based on a square 3-story building, so to use the method, one should recalculate the wind pressure coefficients to find a envelope leakage. Further, the baseline envelope leakage was assumed to be 1.8 cfm/ft2, which a particular building may or may not be. Only a blower test can tell you.

Regarding infiltration in energy models: the energy model only performs thermal balance using supply, return, and exhaust air volumes. Whether or not infiltration is zero or non-zero, it is not included in the thermal balance and energy models don't perform air balance either.

I agree with a comment above, that no matter which model you choose in an energy model, there will be coefficients/constants that are not attainable without further testing such as blower door and tracer gas tests. And if you enter a constant infiltration rate, you don't capture the effects of weather and system operation on infiltration. In real life, infiltration is not constant.

I published an article in the July issue of ASHRAE Journal which outlines equations to calculate coefficients in one of the EnergyPlus infiltration models. You use building height, surface-to-volume ratio, and net system flow (supply-return-exhaust) normalized by surface area, to calculate those coefficients. You do have to assume a baseline leakage value (like m3/s/m2 @ 4Pa) but having these coefficients allows infiltration to vary with weather and system operation (building pressurization, essentially). In the buildings I simulated, sometimes doing this saved energy, sometimes it increased energy. But it was still better than using a constant infiltration.