ASHRAE Journal - August 2021 - 59

COLUMN ENGINEER'S NOTEBOOK
FIGURE 1 Baseline Design Approach. Medical office building with dedicated heat
pump water heaters.
FM
T
dP
BTU
T
HRC HRC HRC HRC CH CH CH
FM
T
dP
dP
BTU
T
VFD
VFD
BTU
T
HHWS
VFD
VFD
DHW
HPWH HPWH HPWH HPWH
CW
HWR
Storage
Tanks
CW
HWR
E
E
HHWS
dP
VFD
VFD
CHWR
HRC HRC HRC HRC
HHWR
CH CH CH
T
FM
BTU
T
CHWS
FIGURE 2 Proposed Design Approach. Medical office building dhw production
integrated with HRCs.
FM
T
VFD
VFD
CHWS
CHWR
HHWR
DHW
Dual Source
Storage Tanks
supplemental air-source chiller (CH) modules to accommodate
peak cooling demands. Each heat-recovery
chiller and cooling-only chiller module is furnished with
a set of integral automated isolation valves that are controlled
by a factory controller to modulate output and
prevent bypass of chilled and heating hot water through
inactive modules under normal operation. Four identically
sized air-source heat pump domestic water heaters
(HPWH) with remote storage tanks are provided to meet
the demand for domestic hot water.
The owner's RFP encouraged design-build teams to
consider and propose alternative design solutions based
on merit to the project and owner. To that end, our team
considered options that had the potential to achieve as
many of the following attributes as possible:
* Lower fi rst cost;
* Lower maintenance;
* Better or similar energy-effi ciency performance;
and
* Reduced mechanical room space requirements.
The integrated domestic water heater design approach
shown in Figure 2 provided a compelling option to simultaneously
achieve as many of the aspirational goals
listed above as possible. The proposed approach consists
of two identically sized dual-source tank-type water
heaters that use the HVAC heating hot water utility to
preheat the domestic cold water (CW) feed from ~60°F
(~16°C) to ~110°F (~43°C) with auxiliary electric resistance
element heaters as the second heat source to lift
the water to its storage temperature of 140°F (60°C).
The heat-recovery chillers were initially sized to provide
an aggregate heating capacity of 2,495 MBtu/h
(731 kW) based on a selection of four equally sized
" 60 ton " modules to meet a design heating load of
2,106 MBtu/h (617 kW) during a design heating condition,
providing a peak heating hot water supply temperature
of 115°F (46.1°C). This yields 389 MBtu/h (114 kW)
of " spare " capacity that enables consideration of the proposed
approach of integrating the domestic hot water
production.
Additionally, because the chiller modules have hardware
similar to that of the heat-recovery chiller modules,
it is possible to consider conversion of cooling-only
chiller modules to heat-recovery modules to provide
additional heating capacity, if needed, without adding
extra compressors or heat exchangers to the proposed
system.
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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
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ASHRAE Journal - August 2021 - Cover3
ASHRAE Journal - August 2021 - Cover4
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