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. 

2)This will decrease the heating load because of the extra heat and the heating equipment will operate less in January.

3) The lights or receptacles will be high every month

And guess what, if the answers are the opposite, then the receptacles/lights are probably too low!

Example 2:

1) July Bill is Higher than reality

2) January Bill is higher than reality

3) Peak Energy is consistently higher than reality.

4) Annual Bill is Higher than reality

Solution:check items like Domestic hot water, or parking lot lights (items that spin the meter but don’t affect the building loads). Common occurrence is that these are too high (or that someone used a 24/7 operating schedule for them).

Explanation 

Lowering an item like Parking lot lights (or the operating hours) will lower the energy every month of the year. No further explanation needed.

Example 3:

1) July Bill is Lower than reality

2) January Bill is correct

3) Peak Energy is close for all months but  is low in May-September

4) Annual bill is lower than reality

Solution:

Check your cooling efficiencies, or some form of cooling equipment. If the cooling equipment is modeled as “too efficient”, this would cause this issue. Decreasing the cooling efficiency (or heat rejection equipment, or some form of cooling equipment)

1) July bill will increase

2) January bill should not be affected and remains correct

3) Peak Energy will only increase in cooling months

4) Annual Bill will increase

In any case, this won’t solve all issues. I’m sure I’ll hear some sort of criticism, but this will solve the most common cases.