# calculate energy cost of wasted heat

Hi folks, This isn't specifically an EnergyPlus question but I figured if anyone had worthy input, it would be this group. I'm trying to calculate the cost of having a leaky valve in a reheat coil on an air handling unit. I know the airflow in cfm and temperature differential between what's in the mixed-air box (post cooling) and discharge after exposure to the heating coil. I've calculated the BTU of the undesired heating, but given that the system is also in cooling mode, my logic is that the number of heating BTUs inserted into the building system are going to require similar amount of additional cooling to compensate. We have a commercial software package that is telling us for a particular time period, the cost is ~70 dollars. My calculation is closer to 120 dollars. I'm doing a rough ballpark calculation (i.e., using .075 pounds per cubic foot of air) but I wouldn't expect to differ by such a large amount. Does my methodology seem unsound (particularly the assumption of additional cooling BTUs as equal to heating)? Any feedback would be appreciated.