ASHRAE Journal - September 2022 - 41

TECHNICAL FEATURE
FIGURE 6 Energy analysis of field data.
FIGURE 7 Example correlation of OAT with enthalpy at CERL.
R2 = 0.9677
50
40
30
20
10
0 5 10 15 20 25 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100
Outside Air Dry-Bulb Temperature (°F)
through modulation of the outside air damper. Heating
and cooling coils were enabled (modulating to setpoint)
or disabled (control valve forced closed) based on the
demand for heating and cooling as indicated by the signal
to the zone dampers. As with the Base Case, economizer
control and equipment start/stop schedules were
used. The binary reset on the deck temperature setpoint
was implemented as described above.
Mode 2. Variable Volume with Demand Control
rate to meet zone heating load and resulting in additional
fan energy savings. The lower temperature setting
improves temperature control because it better matches
the capacity of the coils with the reduced heating loads
in warmer weather, and it reduces overheating common
in older systems that often have oversized control valves,
leaky control valves (e.g., worn valve seats), leaky dampers
(e.g., bad or nonexistent damper blade edge seals),
etc.
Demonstration Methodology
The variable volume retrofi t was demonstrated on fi ve
air handling units in two different climate zones. The
multizone types included the conventional two-deck
(hot deck/cold deck) and the neutral deck (triple deck).
Table 2 shows system descriptions. Three operational
modes were analyzed.
Mode 0. Base Case. Replicated preretrofi t multizone
operation with constant volume fan and typical energy
effi ciency control schemes including hot deck temperature
reset (based on outside air temperature), airside
economizer control (free cooling using outside air) and
time-based equipment start/stop scheduling.
Mode 1. Variable Volume (VV) with Fixed
Ventilation. Variable fan speed based on the most open
zone damper. Fixed ventilation rate was maintained
Ventilation (DCV). Same as Variable Volume with Fixed
Ventilation above, except the ventilation rate was based
on space ventilation demand (according to CO2 or occupancy
sensors, depending on the system), by adjusting
the outside air airfl ow setpoint.
The operation of each unit was rotated through the
three modes, switching modes each day at midnight for
approximately one year. The rotation of modes allowed
for determining energy impact of each control scheme
(mode) under a variety of environmental conditions
and with comparable distribution of days for each mode
within the limited time frame allotted for the demonstration.
Operational data for each AHU and the zones it
served, as well as local weather data were gathered at 15
minute intervals. These gathered data were processed to
generate energy savings as described below.
Performance Analysis
The retrofi tted AHUs were evaluated for energy and
economic impact and ability to maintain comfort conditions
in the spaces they serve. These evaluations are
presented below.
Energy Calculation Methods
For each operational mode, thermal energy transfer
was measured at the hot and cold deck coils with a Btu
S E P T E M B E R 2 0 2 2 ashrae.o rg ASHRAE JOURNAL
41
Outside Air Enthalpy (Btu/lbair)
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ASHRAE Journal - September 2022

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