Variability in Energy Factor Test Results for Residential Electric Water Heaters.
Variability in Energy Factor Test Results for
Residential Electric Water Heaters.
Healy, W. M.; Lutz, J. D.; Lekov, A. B.
HVAC&R Research, Vol. 9, No. 4, 435-449, October 2003.
water heaters; standards; residential buildings
Recent modifications to the minimum energy efficiency
requirements for residential water heat-ers have spurred
an investigation into the variability in testing
high-efficiency electric water heaters. While initial
interlaboratory comparisons showed excellent agreement
between test results from different labs, subsequent
interlaboratory comparisons show differences between
measured energy factors of up to 0.040. To determine the
source of these differences, analyses of various parts
of the test procedure are performed. For one case
studied, the uncertainty in test results can be as high
as 0.028 if instrument accuracies reach the minimum
level allowed in the test procedure. Other areas of the
test procedure where variability is introduced are the
optional use of pre-draws, the location of the lower
tank temperature-measuring device, the use of insulation
on tank fittings, and the use of a warm-up period before
the simulated-use test com-mences. The implications of
these issues on test results are discussed.