# [EnergyPlus_Support] Re: Calculation method of heat loss due to mechanical ventilation

```Dear Xiangjing,

I already found this equation and the heat loss is equal to d(m_inf)/dt * C_p * (T_infinite - T_z) = heat transfer due to infiltration of outside air.
However, I can't find how EnergyPlus calculate the C_p of moist air and the d(m_inf)/dt. For this last item, I need the air density value but mine are different from those calculated by EnergyPlus.

Regards

Robin GENOUD

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "Zhang Xiangjing" <geshen516@...> wrote:
>
> Dear Robin
>
> You can look at the heat balance model of air mass inside a zone.
> The mechanical ventilation part should be one item inside that equation.
>
> Regards
> ZHANG Xiangjing
>
> --- In EnergyPlus_Support@xxxxxxxxxxxxxxx, "rgen1202" <robin.genoud@> wrote:
> >
> > Hello,
> >
> > I can't find in the engineering reference document the formula used to calcul the heat loss due to mechanichal ventilation. In fact, I have a constant mechanical ventilation rate set and I can't calcul on my own the same heat transfer as retourned by EnergyPLus. Indeed, I started by calculating the outdoor air density with the dry temperature, the atmospheric pressure and the relative moisture, but I already find different values. I used the magnus formula for the vapor saturation pressure, but my values are approximatively 0.1 kg/m3 higher.
> >
> > Is there a file in which I could find the formula used by EnergyPlus for air density calculation and heat transfert due to mechanical ventilation and infiltration (I assume it requires the air heat capacity too).
> >
> >
> > Best regards.
> >
> > Robin Genoud
> >
>

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