ASHRAE Journal - September 2022 - 42

TECHNICAL FEATURE
TABLE 3 Energy savings at air handler (combined Btus of fan and coils).
MZ AHU
BASE CASE CV
CERL 1
CERL 2
BRAGG 1
BRAGG 2
BRAGG 3
Energy Use (kBtu/yr)
514,434
581,926
123,991
118,266
138,899
meter (measuring water flow and temperature differential);
electric energy was measured with an electric
meter at each VFD to capture the the energy used by the
combination of the VFD and motor. The system boundary
of the air-handling unit was chosen for energy monitoring
to determine the impact of the retrofit alone and
not be impacted by efficiency of primary heating and
cooling equipment (such as a boiler or chiller), which
would vary depending on the application. Further, site
fuel use at the primary heating and cooling equipment
was not measured because that equipment served multiple
AHUs, which would obscure the energy impact of
the retrofit. Gathered data were sorted into their respective
operational modes, described previously in the
" Demonstration Modes " section.
Figure 6 shows the energy analysis of this field data.
These data sets for each mode were then normalized by
equipment runtimes and weather conditions to allow a
valid side by side comparison of energy use between the
three modes.
Data from off-hours operation, unoccupied holidays
or known equipment or controls maintenance and
TABLE 4 Energy cost impact by operational mode and equipment type.
VV W/ FIXED VENTILATION (MODE 1)
MZ AHU
CERL 1
CERL 2
BRAGG 1
BRAGG 2
BRAGG 3
BASELINE
UTILITY COST
$4,561
$6,906
$1,113
$1,069
$1,160
Mode Cost
Savings
26%
59%
61%
39%
50%
Fan Cost
Savings
5%
1%
45%
33%
37%
Chiller Cost
Savings
5%
0%
14%
6%
8%
Boiler Cost
Savings
17%
57%
2%
0.4%
5%
Mode Cost
Savings
37%
63%
66%
N/A
49%
VV W/ FIXED VENTILATION (MODE 1)
Energy Use
(kBtu/yr)
391,676
257,910
66,135
88,423
94,775
Energy Savings
vs. Base Case
24%
56%
47%
25%
32%
Energy Use
(kBtu/yr)
367,642
233,881
61,084
N/A
94,086
VV W/ DCV
(MODE 2)
Energy Savings vs.
Base Case
28%
60%
50%
N/A
32%
malfunctions were eliminated. Data were sorted into 5°F
(2.8°C) outdoor air temperature bins. Although both dry
bulb and wet bulb conditions affect HVAC energy consumption,
it was established through regression analysis
of local weather data that outdoor air dry-bulb temperatures
were sufficiently correlated to outdoor air enthalpy
at the demonstration sites (with a linear regression
correlation coefficient, R2 = 0.97, Figure 7), and therefore
dry-bulb temperature could be an adequate indicator of
outdoor air conditions, and dry-bulb weather bins were
adequate for data groupings.
A Kruskal-Wallis analysis of variance (ANOVA††
) test
was used to evaluate whether the weather data from
each mode were statistically similar enough to allow
comparison, and data records were pared down to balance
the distribution of records for each mode of operation
to avoid skewing performance assessment. Hourly
savings (for both basic variable volume [VV] and variable
volume with DCV) were mapped to the corresponding
5°F (2.8°C) temperature bins then multiplied by
the number of hours of each bin according to (historic)
weather data for a typical year and totaled for the two VV
VV W/ DCV (MODE 2)
Fan
Cost Savings
6%
1%
45%
N/A
36%
Chiller Cost
Savings
3%
1%
14%
N/A
8%
Production efficiency corrections applied to hot water load: distribution losses = 10%; boiler cycling losses = 15%;
boiler combustion efficiency = 87%. Production efficiency factors applied to chilled water load: 0.71 kW/ton.
††Analysis of variance (ANOVA) is a statistical method for the evaluation of variance between two groups. The Kruskal-Kruskal-Wallis test
with a significance level of α = 0.05 was used in examining weather data.
42
ASHRAE JOURNAL ashrae.o rg
S E PTEM B E R 2022
Boiler Cost
Savings
28%
61%
7%
N/A
5%
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ASHRAE Journal - September 2022

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