ASHRAE Journal - September 2014 - 19

TECHNICAL FEATURE

77
77

Zone Temperature (°F)

76

ZONE 117
ZONE 134B

ZONE 119
ZONE 134C

76
Zone Temperature (°F)

ZONE 116
ZONE 120
ZONE 134D

75
Adjacent Zone Was Running
In Heating Mode

74
73
72

75
74
73
72
71

71

70

70

69

69

7a

10a

1p

4p

7p

7a

10a

ZONE 103
ZONE 109
ZONE 112
ZONE 140A

FIGURE 6 VRF zone temperatures for units running in cooling mode on April 3, 2013.

1p

4p

7p

ZONE 140B
ZONE 147
ZONE 105
ZONE 111

ZONE 145
ZONE 104
ZONE 110
ZONE 134A

ZONE 139
ZONE 140C

FIGURE 7 VRF zone temperatures for units running in heating mode on April 3, 2013.

1.2

GSHP

1

VRF

Three Indoor Units
Switched On In
Heating Mode

0.8
W/ft2

zone temperatures in the other 10 zones floated between
70°F and 75°F (21°C and 24°C) during occupied hours as
shown in Figure 5.
Meanwhile, all 22 of the VRF FCUs ran, 14 exclusively
in heating mode and 8 exclusively in cooling mode.
Figures 6 and 7 show that the zone temperatures in the
zones with FCUs operating in heating mode were generally maintained between 74°F and 76°F (23°C and
24.4°C), while in the zones with FCUs operating in
cooling mode temperatures were usually between 70°F
and 73°F (21°C and 22.7°C) during occupied hours.
At first, this may seem counterintuitive, but the FCUs
for zones with lower setpoints (72°F [22.2°C]) ran in
cooling mode to satisfy the cooling demands of those
zones, while the FCUs for zones with higher setpoints
(74°F [23°C]) ran in heating mode to satisfy the heating
demands of their zones. The zone temperatures show
that the FCUs were meeting the demands of their specific zones.
This example demonstrates the energy expense associated with trying to maintain each individual zone
temperature at a single independent setpoint by the VRF
system. It is not clear whether the precise temperature
control in each individual zone offers any benefits of
thermal comfort. A thermal comfort survey may be necessary to answer this question.
Given the precise temperature control offered by the
VRF system, the interaction between the DOAS and the
VRF systems is sensitive and can cause some FCUs to run
in heating mode even on hot days. The next example
illustrates such operation.

0.6
0.4
0.2
0
12a

3a

6a

9a

12p

3p

6p

9p

12a

FIGURE 8 GSHP and VRF system power use on June 14, 2013.

Example 2
On Friday, June 14, 2013 the ambient temperatures
were warm with a morning low of 68°F (20°C) and an
afternoon high of 86°F (30°C).
Ten of the 14 heat pumps in the GSHP system operated intermittently in cooling mode for an average of 5.5
hours each during the workday. Meanwhile, all 22 of the
FCUs in the VRF system ran. Eleven of the FCUs operated
in cooling mode for the entire time when the building
was occupied between 6:45 a.m. and 6:45 p.m. Six other
FCUs operated intermittently in cooling mode, four
FCUs operated in heating mode for a short period in the
morning and in cooling mode later in the day, and the
FCU for the library operated in heating mode only for a
SEPTEM BER 2014

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ASHRAE JOURNAL

19



ASHRAE Journal - September 2014

Table of Contents for the Digital Edition of ASHRAE Journal - September 2014

Contents
ASHRAE Journal - September 2014 - Cover1
ASHRAE Journal - September 2014 - Cover2
ASHRAE Journal - September 2014 - 1
ASHRAE Journal - September 2014 - 2
ASHRAE Journal - September 2014 - Contents
ASHRAE Journal - September 2014 - 4
ASHRAE Journal - September 2014 - 5
ASHRAE Journal - September 2014 - 6
ASHRAE Journal - September 2014 - 7
ASHRAE Journal - September 2014 - 8
ASHRAE Journal - September 2014 - 9
ASHRAE Journal - September 2014 - 10
ASHRAE Journal - September 2014 - 11
ASHRAE Journal - September 2014 - 12
ASHRAE Journal - September 2014 - 13
ASHRAE Journal - September 2014 - 14
ASHRAE Journal - September 2014 - 15
ASHRAE Journal - September 2014 - 16
ASHRAE Journal - September 2014 - 17
ASHRAE Journal - September 2014 - 18
ASHRAE Journal - September 2014 - 19
ASHRAE Journal - September 2014 - 20
ASHRAE Journal - September 2014 - 21
ASHRAE Journal - September 2014 - 22
ASHRAE Journal - September 2014 - 23
ASHRAE Journal - September 2014 - 24
ASHRAE Journal - September 2014 - 25
ASHRAE Journal - September 2014 - 26
ASHRAE Journal - September 2014 - 27
ASHRAE Journal - September 2014 - 28
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ASHRAE Journal - September 2014 - 33
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ASHRAE Journal - September 2014 - 35
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ASHRAE Journal - September 2014 - 38
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ASHRAE Journal - September 2014 - 40
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ASHRAE Journal - September 2014 - 54
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ASHRAE Journal - September 2014 - 56
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ASHRAE Journal - September 2014 - 70
ASHRAE Journal - September 2014 - 71
ASHRAE Journal - September 2014 - 72
ASHRAE Journal - September 2014 - SCover1
ASHRAE Journal - September 2014 - SCover2
ASHRAE Journal - September 2014 - S1
ASHRAE Journal - September 2014 - S2
ASHRAE Journal - September 2014 - S3
ASHRAE Journal - September 2014 - S4
ASHRAE Journal - September 2014 - S5
ASHRAE Journal - September 2014 - S6
ASHRAE Journal - September 2014 - S7
ASHRAE Journal - September 2014 - S8
ASHRAE Journal - September 2014 - S9
ASHRAE Journal - September 2014 - S10
ASHRAE Journal - September 2014 - S11
ASHRAE Journal - September 2014 - S12
ASHRAE Journal - September 2014 - S13
ASHRAE Journal - September 2014 - S14
ASHRAE Journal - September 2014 - S15
ASHRAE Journal - September 2014 - S16
ASHRAE Journal - September 2014 - S17
ASHRAE Journal - September 2014 - S18
ASHRAE Journal - September 2014 - S19
ASHRAE Journal - September 2014 - S20
ASHRAE Journal - September 2014 - S21
ASHRAE Journal - September 2014 - S22
ASHRAE Journal - September 2014 - 73
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ASHRAE Journal - September 2014 - 75
ASHRAE Journal - September 2014 - 76
ASHRAE Journal - September 2014 - 77
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ASHRAE Journal - September 2014 - 100
ASHRAE Journal - September 2014 - 101
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ASHRAE Journal - September 2014 - 103
ASHRAE Journal - September 2014 - 104
ASHRAE Journal - September 2014 - Cover3
ASHRAE Journal - September 2014 - Cover4
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