Coefficients for DesignFlowRate in OpenStudio?

asked 2022-02-11 18:57:59 -0500

Vasco Figueiroa's avatar

updated 2022-02-19 08:04:48 -0500


I'm trying to set a DesignFlowRate to establish some sort of forced ventilation in the single thermal zone of my OpenStudio model.

When looking at the Input Output Reference, there are 4 coefficients: A, B, C and D. It says that a custom set of these coefficients should be determined "using methods such as those laid out in Chapter 26 of the ASHRAE Handbook of Fundamentals". But that chapter is dedicated to tables regarding material properties related to heat and moisture. What sort of methods are laid out in this Chapter that are remotely related to Ventilation? The chapter that is mostly related to this is the 16th, called Ventilation and Infiltration, is devoid of this information as well.

Looking at the Reference again, there are 3 stated sets for these coefficients, with highly varying values, some of them coming from EnergyPlus predecessors, which state their sources as the following: “Empirical equation and the coefficient default were determined from ASHRAE journal articles and other data on the effects of outdoor weather conditions.” and "... based on examining the infiltration relationships described in the ASHRAE Handbook of Fundamentals". Again, not really helpful...

Finally, looking at the Engineering Reference of this object, it it said that the equation is based on a measurement from Coblenz and Achenbach 1963, which measured another set of values (Equation 2)! At the very least, this was the set which was closer to the default set used in OpenStudio.

Can someone provide me some guidance for a rationale behind the decision of these coefficients?

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