I am modeling an older greenhouse, assuming an infiltration rate of 3 ACH. The building will be upgrading all of the windows and as a result will also reduce the leakage rates. For modeling purposes, I am taking infiltration rates out of 2011 ASHRAE Handbook HVAC Applications. The greenhouse has perimeter steam radiation and no cooling. However, there is a ventilation fan for summer use to keep air moving through the building. I ended up modeling this as system heating/ventilation system with no heating coils installed, baseboard radiation, and an economizer to quantify the summer ventilation rates.

For the analysis, I created two parametric runs. One parametric run varied the glass characteristics. The second parametric run varied the glass characteristics and reduced the infiltration rate to 1 ACH. Parametric run 1, show the expected fan energy consumption, operating the summer months, and periodically during the shoulder months. However, parametric run two showed the fan operating year round at roughly the same energy consumption each month.

I do not have the baseboard heat scheduled; I am allowing the system to vary with changing load. Does anyone know why reducing my infiltration rate will cause the ventilation fan energy consumption to increase?

Thank you.

Daniel Kaler