I’m using this standard formula for calculating soar heat gain BTU
qsol = A•SHGC•I
where : qsol –solar gain – [BTU/day]
A- area in - [sf]
SHGC – solar heat gain coefficient
I – insolation, solar radiation incident on the glazing system surface – [Btu/ft2/day]

So in order to find solar gain for heating season and cooling season, I’m averaging the insolation for heating months and cooling months, and multiplying it by the number of days in those respective months, and the result is in BTU.

Now, when I’m calculation annual energy losses , and dividing them by efficiencies of the equipment, I get confusing results :

Energy Cost of Heating ($) = (q_(sol )∙182∙1/η∙C_ng)/(100 000)
Energy Cost of Cooling ($) = (q_(sol )∙183∙1/COP∙C_ee)/(3 412.3)

Cng – price of natural gas – $/therm
COP – coefficient of performance for the cooling unit
Cee – price of electrical energy – $/kWh
100 000 – conversion from btu to therm – btu/therm
3 412.3 – conversion from btu to kWh – btu/kWh

Because of COP > η (1/COP <1, and 1/η >1) I have solar gain in winter time higher that in summer , which doesn’t make sense,

And when I’m calculating annual energy losses, I have to subtract winter heat gain from the energy of the rest of the year. When I do that, (because heat gain in winter is higher) the result is negative, which again doesn’t make sense to me.

How do you think I should do my calculation , where is my mistake, how I can handle this, taking in consideration that I need total annual losses ( per cooling and Heating seasons) in kWh and $.