value for cp Specific heat of air

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@mdengusiak great catch on $c_p$ using the wrong units ($J/kg$ should be $J/kg-K$) in the EnergyPlus documentation. You can mention this in the ongoing documentation issues list on Github where the EnergyPlus source code is hosted.

Aaron Boranian ( 2021-12-01 10:00:25 -0600 )edit

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answered 2021-12-01 14:13:58 -0600

MJWitte

9740 ●6 ●10 http://www.gard.com/

In general, EnergyPlus uses variable specific heat of air. The psychrometric function PsyCpAirFnW calculates specific heat as a function of humidity ratio.

But there are a few instances of 1005. lurking in the code, in the ecoroof module (as noted above), the Mundt room air model, baseboard heat standard rating calculations, and the VRF DX controls.

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this is great! especially link to the source in code thanks! so when I want to calculate manually infiltration based on the mass flow Q = m * cp * dt [W] Q = Zone Infiltration Mass Flow Rate * cp * (Zone Outdoor Air Drybulb Temperature - Zone Air Temperature) I should recalculate cp for each hour from Zone Outdoor Air Drybulb Temperature and Site Outdoor Air Humidity Ratio ? or a should use different variable? I am referring to https://unmethours.com/question/65256...