Fault Detection and Diagnostics for Rooftop Air Conditioners

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where β is a degradation factor for cooling capacity due to faults and
Q & Cap, Normal
is the
RTU cooling capacity for normal operation Substituting equation (5-6) into equation (5-
5) gives
E
α
= Q& Cap, Normal
(1 − β T
(5-7)
(1 −α)
EER
Savings
)
Normal
Neglecting demand costs, the utility cost savings (UCS) are calculated as
UCS ( α
= Q& Cap,Normal
(1 − ) T ) Ce
(1 −α)
EER
β
(5-8)
Normal
where
C
e
is the cost of electricity ($/kWh). Neglecting demand savings is a conservative
assumption. Significantly greater utility cost savings would be possible if demand costs
were considered. Roughly, the weighted average utility rate between on-peak and midpeak
periods in North California is 0.08$/kWh and that in South California is around
$0.21/kWh.
According to the simple relationship given in equation (5-8), the utility cost
savings associated with automated FDD applied to an individual RTU depend on the
following factors:
1. the normal ERR ( EER
Normal
) and the degradation in EER due to the faults, α .
The lower the normal EER and the greater the EER degradation, the greater the
opportunity for utility cost savings. The savings are particularly sensitive to
the EER degradation factor.
2. the normal cooling capacity ( Q &
Cap, Normal
) and the degradations in cooling
capacity (β). Greater savings are associated with larger cooling capacities and
cooling capacity degradations.
3. runtime (T ). Utility cost savings increase linearly with increasing runtime.