316 Energy Project Financing: Resources and Strategies for Success
vals can be short and occasional. Lighting fixtures provide an example
of constant power flow, assuming they have no dimming capability.
However lighting operating periods may not be constant, for example
outdoor lighting controlled by a photocell operates for shorter periods
in seasons of long daylight than in seasons of short daylight. Where a
parameter may change seasonally, such as this photocell case, measure-
ments should be made under appropriate seasonal conditions.
Where a parameter may vary daily or hourly, as in most heating
or cooling systems, continuous metering may be simplest. However
for weather dependent loads, measurements may be taken over a long
enough period to adequately characterize the load pattern (i.e., week-
day/weekend and weather-dependent characteristics of the load) and
repeated as necessary through the post-retrofit period. Examples of
such day-type profiling can be found in Katipamula and Haberl (1991),
Akbari et al. (1988), Hadley and Tomich (1986), Bou Saada and Haberl
(1995a, 1995b) and Bou Saada et al. (1996).
3.4.1.5 Option A: Sampling
Where multiple versions of the same installation are included
within the boundaries of a savings determination, statistically valid
samples may be used as valid measurements of the total parameter.
Such situation may arise, for example, where individual light fixtures
are measured before and after retrofit to assess their power draw, while
the total lighting power draw cannot be read at the electrical panel due
to the presence of non-lighting loads on the same panel. Providing that
a statistically significant sample of fixtures is measured before and af-
ter ECM installation, these data may be used as the ‘measurement’ of
total lighting power draw. Appendix B discusses the statistical issues
involved in sampling.
3.4.1.6 Option A: Uncertainty
Chapter 4.2 reviews the general issues surrounding uncertainty of
savings determination. However, specific factors driving the uncertainty
of Option A methods are:
- The magnitude of effects beyond the boundary of the retrofit
isolation. For example, the significance of the mechanical cooling
energy associated with a reduction in lighting power depends on
the length of the mechanical cooling season and the number of
hours of operation of the cooling equipment each day.