Hello,

I'm using the DOE Commercial Reference Buildings to perform simulations
involving the cooling coil-fouling module introduced in EnergyPlus v8.3.
For the purposes of this question, I'm going to talk about the Large Office
building in Phoenix AZ.

I have modified the rated UA via the coil fouling operational fault
modeling to approximately 86% of its "clean" value for cooling coils. This
produces some expected effects, e.g. pump energy goes up due to a reduced
waterside dT across the coil for an equivalent load. Another "expected"
effect is that the amount of cooling energy use goes up. I put "expected"
in quotes because I am not aware of what effect fouling has on the chiller
models used in EnergyPlus. As a wholly unexpected effect, the gas heating
energy goes up. This occurs over the summer months, not the winter months,
and appears to be reheat. My question is "Why does this occur?"

A few thoughts thus far:

1) When I convert the cooling energy to cooling load (via COP) and the
heating energy to heating load (via boiler efficiency), the amounts just
about even out. Is the heating load a result of compensating for
over-cooling? Why would over-cooling occur in a situation when UA is
reduced?

2) Are the increases in cooling and heating energy unrelated to one
another? If that is the case, how does changing the cooling coil UA
increase the heating?

3) For the Large Office Commercial Reference Building, the increase in
heating seems to be occurring in the warmer (1A through 4A) and drier (2B
through 6B) climates, though it is more pronounced in the climates that are
both warm and dry (2B and 3B).

Presently, I have been unable to formulate a system operating condition
where these results make sense to me. Am more than a bit puzzled, and any
help would be appreciated.

Joseph Firrantello, PE
PhD Candidate
Architectural Engineering
Penn State University