ASHRAE Journal - February 2023 - 16

COLUMN ENGINEER'S NOTEBOOK
FIGURE 1 Building B HHW load profile.
100%
30%
20%
10%
0%
40%
0%
100%
20%
0%
0%
Part Load Operating Point
(1x = Design Capacity, 4,500 MBH)
Option 1 is a fully electric option with an air-source heat
pump operating in heating-only mode to provide 100%
of the building's HHW needs. Although this machine has
cooling capabilities, it will be run only in heating mode.
This option will consist of two banks of six modules operating
in a two-pipe confi guration in heating-only mode
and will not be tied into the campus chilled water system
to reject the cooling water. This system is relatively simple:
it is stand-alone. The HHW supply temperature was
set to 135°F (57°C) to ensure the existing building coils
can meet the loads at the reduced temperature.
In this case, the COP at peak heating operation is
approximately 2.12 kW/kW (7.5 kW/ton). The COP will
increase if the system can operate at a lower HHW supply
temperature; however, the one-row coils within the
building require a HHW supply temperature of 135°F
(57°C) and further reset is not possible without modifying
the coils if the site experiences ambient temperatures
below 40°F (4.4°C). In this case, supplemental
heating would be required due to limits related to the
ambient lift capabilities of this machine.
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ASHRAE JOURNAL ashrae.o rg F E B R U A RY 2 0 2 3
Option 2 is a fully electric option with a water-cooled
heat pump operating in heating-only mode to provide
100% of the building's HHW needs. This option will consist
of a bank of six modules operating in a four-pipe
confi guration in heating-only mode that will tie into the
campus chilled water system to reject cooling water. The
HHW temperature was set to 135°F (57°C) to ensure existing
building coils can meet loads at the lowest possible
supply temp. The equipment COP is approximately 5.0.
This option requires pumps on the chilled water side to
ensure chiller modules maintain the required differential
pressure drop across the heat exchanger.
Option 3 is a hybrid option, which will include a watercooled
heat recovery chiller (HRC) operating in heatingonly
mode to provide 80% of the building's HHW needs
(roughly 25% of peak capacity). This option will consist
of a bank of modules operating in a four-pipe confi guration
in heating-only mode that will tie into the campus
chilled water system to reject cooling water. For peak loading,
supplemental gas-fi red boilers will be provided. The
HHW supply temperature was set to at 110°F (43°C) when
1.0x
(4,275-4,500 MBH)
0.95x
(4,050-4,275 MBH)
0.9x
(4,050-4,275 MBH)
0.85x
(3,600-3,825 MBH)
0.8x
(3,375-3,600 MBH)
0.75x
(3,150-3,375 MBH)
0.7x
(2,925-3,150 MBH)
0.65x
(2,700-2,925 MBH)
0.6x
(2,475-2,700 MBH)
0.55x
(2,250-2,475 MBH)
0.5x
(2,025-2,250 MBH)
0.45x
(1,800-2,025 MBH)
0.4x
(1,575-1,800 MBH)
0.35x
(1,350-1,575 MBH)
0.3x
(1,125-1,350 MBH)
0.25x
(900-1,125 MBH)
0.2x
(675-900 MBH)
0.15x
(450-675 MBH)
0.1x
(225-450 MBH)
0.05x
(0-225 MBH)
Heating Output
Operating Hours
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