ASHRAE Journal - September 2022 - 44

TECHNICAL FEATURE
FIGURE 8 Baseline energy consumption vs. energy cost reduction.
70%
60%
50%
40%
30%
20%
10%
0%
Conventional Units
Neutral Deck
Units
Conventional Units
0 100,000 200,000 300,000 400,000 500,000 600,000 700,000 800,000 900,000
Baseline Energy Consumption (kBtu)
CERL AHU-2
CERL AHU-1
Bragg AHU-1
Bragg AHU-2
Bragg AHU-3
mode comparisons. The difference between the two retrofi
t modes (Mode 1 and Mode 2) and the baseline mode
(Mode 0) was used as the experimental energy savings
of the retrofi t. These energy totals were then divided by
average equipment effi ciency estimates (for the chiller,
boiler and water distribution system) to attain energy
impact at the utility bill.
Table 3 presents the calculated energy savings at the
AHU. These percentage changes in energy use represent
the the energy impact of the retrofi t technology. Table 4
presents the resultant calculated upstream savings at
the boiler and chiller plant and the impact on the utility
bill. For the conventional hot deck/cold deck units at
Construction Engineering Research Laboratory (CERL),
boiler plant savings accounted for most of the savings.
For the neutral deck units at Fort Bragg, reductions in
fan energy were the primary savings. These savings are
MZ AHU
CERL 1
CERL 2
BRAGG 1
BRAGG 2
BRAGG 3
VV W/ FIXED VENTILATION (MODE 1)
Simple
Net
Incremental Retrofit Cost
$13,000
$9,315
$7,200
$7,200
$7,200
Present
Value
$4,452
$48,685
$2,673
-$1,055
$1,191
Payback
(yr)
11
2
11
17
12
calculated for regular building operating hours (e.g.,
Monday through Friday 6 a.m. to 6 p.m.) for these particular
facilities. The annual energy consumption of the
demonstration units is lower than typical (compared to
the Commercial Building Energy Consumption Survey
[CBECS] data) and is not representative of typical multizone
systems. Potential causes for the variation from
typical CBECS consumption may include: off-hours
energy use was not taken into account, which could be
signifi cant in some applications (such as units providing
for conductive heat losses through the building envelope
at night), the CERL units serviced fully interior zones
and did not experience building envelope loads at any
time during operation and the Fort Bragg units maintained
more limited space conditioning than typical
buildings in America by heating only to 68°F (20°C) and
cooling to only 75°F (24°C).
Retrofi t of a MZ system will require repair or replacement
of components that are preventing correct operation
(e.g., failed sensors, broken dampers). Additionally,
the control sequence for the retrofi t requires functional
direct digital control (DDC) hardware and software.
Accordingly, retrofi t costs can vary widely among retrofi
t candidates. The cost analysis for the demonstration
system retrofi ts was limited to the fundamental new
components for the control scheme to accomplish the
basic retrofi t including: the VFD(s) on the fan(s), the
airfl ow measurement array (AFMA) and the controls
programming. Additionally, occupancy or CO 2 sensors
were added to those costs for the DCV option. As such,
the economic analysis treats the retrofi t as an " add on "
or incremental addition to a system that is already being
TABLE 5 Economic impact of an incremental (as an " add on " task to an existing DDC conversion or upgrade) retrofit.
`
Savings to
Investment
Ratio
1.4
6.6
1.4
0.9
1.2
Energy
Savings
($/yr)
$1,208
$4,083
$683
$420
$579
Incremental Retrofit Cost
$13,823
$9,690
$7,584
N/A
$7,334a
VV W/ DCV (MODE 2)
Simple
Net
Present
Value
Payback
(yr)
$10,394 8
$52,193 2
$3,020 10
$989a
13a
Savings to
Investment
Ratio
1.8
6.7
1.5
1.2a
Energy
Savings
($/yr)
$1,684
$4,357
$734
$574a
Production effi ciency corrections applied to hot water load: distribution losses = 10%; boiler cycling losses = 15%; boiler combustion
effi ciency = 87%. Production effi ciency factors applied to chilled water load: 0.71 kW/ton. Real discount rate = 3%; life of retrofi t = 15
yr, blended energy costs used. Fuel escalation rate = 3%; CERL unit energy costs were $0.0636/kWh and $0.84/therm. Bragg unit
energy costs were $0.0733/kWh, $0.62/therm.
aLimited DCV (one conference room only).
44
ASHRAE JOURNAL ashrae.o rg S E P T E M B E R 2 0 2 2
Modes 1 & 2 Energy Cost Reduction

https://ashrae.org/

ASHRAE Journal - September 2022

Table of Contents for the Digital Edition of ASHRAE Journal - September 2022