E = [(Aper × U) + qvent] ΔT × hr (10.1)
where
E =
Aper = surface area of perimeter envelope, ft2
U = effective U-value of thermal envelope,
Btu/hr ft2°F
qvent = ventilation load, Btu/hr°F
ΔT = night setback temperature difference,
degrees F
hr = heating season unoccupied hours