In energy modeling, a lot of you have asked about how to match utility bills (because the owner requested that they match). In many cases, this is quite difficult, and experience is really the best tool.
Why is it so difficult? The reason is that when you change 1 item in an energy model, it might impact everything else. For instance, if you choose a smaller sized fan, (assuming a VAV fan) you might increase your fan energy, because the fan does less unloading, and then you create more heat, which causes more cooling and a bit less heating. Complicated huh? I have helped a huge number of people match rates, and I know first hand that this can be very complicated, but for most cases we can solve the problem with 4 key factors (in climates with a heating season and cooling season - in cooling or heating only, it’s actually easier to solve anyway):
4 Important factors in the energy model
1) July Energy Bill (is it high or low?)
2) January Energy Bill (is it high or low)
3) Peak Energy use (month to month)
4) Annual Bill (high, low, or even)
From these four details, you can match most projects:
Example 1:
1) July bill is higher than reality
2) January gas bill is lower than reality (if you have electric heat, you may find that that the electric bill is correct in January)
3) Peak Energy (demand) is more steady than reality
4) Annual Bill is not too far off but slightly high
Solution:
The receptacle loads or lighting loads are probably too high.
Explanation:
Lights and receptacles give off heat, and consume energy.
1) This will increase the cooling load and thus your July bill will be high.