ASHRAE Journal - August 2021 - 62

COLUMN ENGINEER'S NOTEBOOK
FIGURE 5 HVAC HRC COP vs. HHWS reset with fixed CHW setpoint.
FIGURE 6 HHW HX% of design DHW load vs. HHWS reset.
5.0
4.5
4.0
3.5
3.0
2.5
2.0
1.5
1.0
85
90
95
100
105 110
HHWS Temperature (°F)
OAT at 37°F
OAT at 65°F
FIGURE 7 Baseline DHW design (top) and proposed DHW design (bottom) in plan
view.
115 120
100
90
80
70
60
50
40
30
20
10
85
90
95
100
105
110
HHW Supply Temperature (°F)
FIGURE 8 Baseline DHW design (top) and proposed DHW design (bottom) in
axonometric view.
115
120
heating hot water was simultaneously reduced by a substantial
amount (Figures 5 and 6). Given that the building
heating and cooling loads are orders of magnitude
greater than the domestic hot water load, it is prudent
to reset heating hot water and chilled water supply temperatures
based on demand to achieve the best overall
building energy performance. To accommodate the
reduced heat transfer done by the heating hot water
heat exchanger within the dual-source domestic hot
water system, the author recommends sizing the auxiliary
electric resistance heater to handle the full domestic
hot water load with silicon-controlled rectifier (SCR)
modulating output control to both allow for maximum
flexibility in heating hot water supply temperature
62
ASHRAE JOURNAL ashrae.org A U G UST 2021
turndown and provide a margin of redundancy in the
event of a service outage from the HVAC heat-recovery
chillers.
Reduced Mechanical Room Space Requirements
Our team found that the proposed dual-source domestic
hot water heater design yielded a substantially more
compact layout than the baseline design using dedicated
air-source heat pumps piped to remote storage
tanks. Although this matches our expectations based on
the fundamentals of air-source heat pumps requiring
Coefficient of Performance (COP)
DHW Heating Load (%)
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ASHRAE Journal - August 2021

Table of Contents for the Digital Edition of ASHRAE Journal - August 2021

Contents
ASHRAE Journal - August 2021 - Intro
ASHRAE Journal - August 2021 - Cover1
ASHRAE Journal - August 2021 - Cover2
ASHRAE Journal - August 2021 - 1
ASHRAE Journal - August 2021 - Contents
ASHRAE Journal - August 2021 - 3
ASHRAE Journal - August 2021 - 4
ASHRAE Journal - August 2021 - 5
ASHRAE Journal - August 2021 - 6
ASHRAE Journal - August 2021 - 7
ASHRAE Journal - August 2021 - 8
ASHRAE Journal - August 2021 - 9
ASHRAE Journal - August 2021 - 10
ASHRAE Journal - August 2021 - 11
ASHRAE Journal - August 2021 - 12
ASHRAE Journal - August 2021 - 13
ASHRAE Journal - August 2021 - 14
ASHRAE Journal - August 2021 - 15
ASHRAE Journal - August 2021 - 16
ASHRAE Journal - August 2021 - 17
ASHRAE Journal - August 2021 - 18
ASHRAE Journal - August 2021 - 19
ASHRAE Journal - August 2021 - 20
ASHRAE Journal - August 2021 - 21
ASHRAE Journal - August 2021 - 22
ASHRAE Journal - August 2021 - 23
ASHRAE Journal - August 2021 - 24
ASHRAE Journal - August 2021 - 25
ASHRAE Journal - August 2021 - 26
ASHRAE Journal - August 2021 - 27
ASHRAE Journal - August 2021 - 28
ASHRAE Journal - August 2021 - 29
ASHRAE Journal - August 2021 - 30
ASHRAE Journal - August 2021 - 31
ASHRAE Journal - August 2021 - 32
ASHRAE Journal - August 2021 - 33
ASHRAE Journal - August 2021 - 34
ASHRAE Journal - August 2021 - 35
ASHRAE Journal - August 2021 - 36
ASHRAE Journal - August 2021 - 37
ASHRAE Journal - August 2021 - 38
ASHRAE Journal - August 2021 - 39
ASHRAE Journal - August 2021 - 40
ASHRAE Journal - August 2021 - 41
ASHRAE Journal - August 2021 - 42
ASHRAE Journal - August 2021 - 43
ASHRAE Journal - August 2021 - 44
ASHRAE Journal - August 2021 - 45
ASHRAE Journal - August 2021 - 46
ASHRAE Journal - August 2021 - 47
ASHRAE Journal - August 2021 - 48
ASHRAE Journal - August 2021 - 49
ASHRAE Journal - August 2021 - 50
ASHRAE Journal - August 2021 - 51
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ASHRAE Journal - August 2021 - 53
ASHRAE Journal - August 2021 - 54
ASHRAE Journal - August 2021 - 55
ASHRAE Journal - August 2021 - 56
ASHRAE Journal - August 2021 - 57
ASHRAE Journal - August 2021 - 58
ASHRAE Journal - August 2021 - 59
ASHRAE Journal - August 2021 - 60
ASHRAE Journal - August 2021 - 61
ASHRAE Journal - August 2021 - 62
ASHRAE Journal - August 2021 - 63
ASHRAE Journal - August 2021 - 64
ASHRAE Journal - August 2021 - 65
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ASHRAE Journal - August 2021 - 70
ASHRAE Journal - August 2021 - 71
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ASHRAE Journal - August 2021 - 76
ASHRAE Journal - August 2021 - 77
ASHRAE Journal - August 2021 - 78
ASHRAE Journal - August 2021 - 79
ASHRAE Journal - August 2021 - 80
ASHRAE Journal - August 2021 - Cover3
ASHRAE Journal - August 2021 - Cover4
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