ASHRAE Journal - October 2021 - 13

TECHNICAL FEATURE
on heat recovery. In Santa Clara, Calif., where the design
heating temperature is 29°F (-2°C), one market leader's
product yields a heating coeffi cient of performance
(COPh) of approximately 2.1 when generating 120°F
(49°C) water at design ambient dry bulb.
The effi ciency of heat pumps is highly dependent on
ambient air temperatures. While a design COPh above 2
is possible in mild west coast climates where the author
practices, effi ciency and capacity both drop rapidly as
ambient temperature falls. Currently available air-towater
heat pumps cannot generally be used when ambient
temperatures are below about 0°F (-18°C) while
producing hot water of approximately 120°F (-49°C)
(assuming R-410A refrigerant).
ASHPs are also very expensive per unit capacity
(roughly $150/MBH to $200/MBH [$511 000/MW to
$682 000/MW] vs. $15/MBH to $30/MBH [$51 000 MW to
$102 000 MW] for high quality condensing gas boilers).
And, because they use ambient air to extract heat, they
require multiple units with large footprints to generate
heat at scale. On large high-rise projects, it can be nearly
impossible to fi nd suffi cient roof space for ASHPs.
The use of multiple units in large installations necessitates
costly piping and controls for each unit. Most
ASHPs on the market have very high minimum fl ow
rates, which usually requires providing a primary pump
dedicated to each unit, further adding to fi rst costs.
ASHP plants are also likely to experience higher ongoing
maintenance costs than other plant options because of
the quantity of devices involved and the complexity of
the equipment itself; large ASHPs typically have four to
six scroll compressors, at least two refrigeration circuits
and multiple condenser fan motors, increasing the likelihood
of some device failing or requiring service.
One benefi t of ASHP designs is that almost all ASHPs
inherently can provide cooling as well as heating; they
require the ability to defrost the outdoor coils when
operating in cool weather, which is usually accomplished
by reversing the cycle, i.e., becoming a chiller.
Thus, ASHPs can switch to cooling mode in the summer,
reducing the size of the cooling plant serving the same
building and offsetting some of the fi rst cost from the
ASHPs. Unfortunately, currently available ASHPs are
not very effi cient in cooling mode, commonly yielding
effi ciencies of about 9.5 EER to 10 EER (1.2 kW/ton to
1.3 kW/ton [0.34 kW/kW to 0.37 kW/kW] or 2.8 COP to
2.9 COP) at AHRI Standard 550/590 conditions.
FIGURE 1 Cooling full-load efficiency of typical water-cooled and ASHP chiller
plants.
1.26
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0.0
0.61
Water-Cooled Chillers, Towers,
Condenser Water Pumps
Air-Source HP/Chillers
Contrast this with a well-designed water-cooled chiller
plant that operates at about 0.60 kW/ton to 0.65 kW/ton
(0.17 kW/kW to 0.18 kW/kW) or 5.4 COP to 5.9 COP at
design conditions, including condenser water pumps
(CWP) and cooling towers. This reality makes it almost
impossible to comply with either ASHRAE Standard
90.1-20192 or California Title 243 using the performance
approach when replacing water-cooled plant cooling
capacity with ASHP capacity since the baseline cooling
system for large buildings under both standards is a
chiller plant with water-cooled plant variable speed centrifugal
chillers.
Figure 1 shows a typical effi ciency comparison. On one
recent project where our company used AHSPs for heating,
we were able to use part of the available ASHP cooling
capacity to provide 30% of the design cooling plant
capacity, with the rest provided by a high-effi ciency allvariable
speed water-cooled plant; using any more of the
ASHPs in cooling mode resulted in not complying with
code and increasing energy costs.
Electric Resistance
Electric resistance-based electric heating options such
as electric boilers and wire-to-air coils do not present
the same spatial or mechanical fi rst-cost challenges
as ASHPs. Relative to ASHP plants, which are typically
limited to supply temperatures of around 120°F (49°C),
electric boilers can generate 160°F to 180°F (71°C to
82°C) supply temperatures like conventional natural gas
boiler plants, and thus can benefi t from the higher hot
water delta Ts (e.g., 40°F [22°C]) and smaller pipe and
pumps sizes that result from supplying hotter water.
O CTO B E R 2 0 2 1 ashrae.o rg ASHRAE JOURNAL
13
kW/Ton
http://ashrae.org

ASHRAE Journal - October 2021

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

Contents
ASHRAE Journal - October 2021 - Intro
ASHRAE Journal - October 2021 - Cover1
ASHRAE Journal - October 2021 - Cover2
ASHRAE Journal - October 2021 - 1
ASHRAE Journal - October 2021 - Contents
ASHRAE Journal - October 2021 - 3
ASHRAE Journal - October 2021 - 4
ASHRAE Journal - October 2021 - 5
ASHRAE Journal - October 2021 - 6
ASHRAE Journal - October 2021 - 7
ASHRAE Journal - October 2021 - 8
ASHRAE Journal - October 2021 - 9
ASHRAE Journal - October 2021 - 10
ASHRAE Journal - October 2021 - 11
ASHRAE Journal - October 2021 - 12
ASHRAE Journal - October 2021 - 13
ASHRAE Journal - October 2021 - 14
ASHRAE Journal - October 2021 - 15
ASHRAE Journal - October 2021 - 16
ASHRAE Journal - October 2021 - 17
ASHRAE Journal - October 2021 - 18
ASHRAE Journal - October 2021 - 19
ASHRAE Journal - October 2021 - 20
ASHRAE Journal - October 2021 - 21
ASHRAE Journal - October 2021 - 22
ASHRAE Journal - October 2021 - 23
ASHRAE Journal - October 2021 - 24
ASHRAE Journal - October 2021 - 25
ASHRAE Journal - October 2021 - 26
ASHRAE Journal - October 2021 - 27
ASHRAE Journal - October 2021 - 28
ASHRAE Journal - October 2021 - 29
ASHRAE Journal - October 2021 - 30
ASHRAE Journal - October 2021 - 31
ASHRAE Journal - October 2021 - 32
ASHRAE Journal - October 2021 - 33
ASHRAE Journal - October 2021 - 34
ASHRAE Journal - October 2021 - 35
ASHRAE Journal - October 2021 - 36
ASHRAE Journal - October 2021 - 37
ASHRAE Journal - October 2021 - 38
ASHRAE Journal - October 2021 - 39
ASHRAE Journal - October 2021 - 40
ASHRAE Journal - October 2021 - 41
ASHRAE Journal - October 2021 - 42
ASHRAE Journal - October 2021 - 43
ASHRAE Journal - October 2021 - 44
ASHRAE Journal - October 2021 - 45
ASHRAE Journal - October 2021 - 46
ASHRAE Journal - October 2021 - 47
ASHRAE Journal - October 2021 - 48
ASHRAE Journal - October 2021 - 49
ASHRAE Journal - October 2021 - 50
ASHRAE Journal - October 2021 - 51
ASHRAE Journal - October 2021 - 52
ASHRAE Journal - October 2021 - 53
ASHRAE Journal - October 2021 - 54
ASHRAE Journal - October 2021 - 55
ASHRAE Journal - October 2021 - 56
ASHRAE Journal - October 2021 - 57
ASHRAE Journal - October 2021 - 58
ASHRAE Journal - October 2021 - 59
ASHRAE Journal - October 2021 - 60
ASHRAE Journal - October 2021 - 61
ASHRAE Journal - October 2021 - 62
ASHRAE Journal - October 2021 - 63
ASHRAE Journal - October 2021 - 64
ASHRAE Journal - October 2021 - 65
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ASHRAE Journal - October 2021 - 70
ASHRAE Journal - October 2021 - 71
ASHRAE Journal - October 2021 - 72
ASHRAE Journal - October 2021 - HR1
ASHRAE Journal - October 2021 - HR2
ASHRAE Journal - October 2021 - HR3
ASHRAE Journal - October 2021 - HR4
ASHRAE Journal - October 2021 - HR5
ASHRAE Journal - October 2021 - HR6
ASHRAE Journal - October 2021 - HR7
ASHRAE Journal - October 2021 - HR8
ASHRAE Journal - October 2021 - HR9
ASHRAE Journal - October 2021 - HR10
ASHRAE Journal - October 2021 - HR11
ASHRAE Journal - October 2021 - HR12
ASHRAE Journal - October 2021 - HR13
ASHRAE Journal - October 2021 - HR14
ASHRAE Journal - October 2021 - HR15
ASHRAE Journal - October 2021 - HR16
ASHRAE Journal - October 2021 - HR17
ASHRAE Journal - October 2021 - HR18
ASHRAE Journal - October 2021 - HR19
ASHRAE Journal - October 2021 - HR20
ASHRAE Journal - October 2021 - HR21
ASHRAE Journal - October 2021 - HR22
ASHRAE Journal - October 2021 - HR23
ASHRAE Journal - October 2021 - HR24
ASHRAE Journal - October 2021 - 73
ASHRAE Journal - October 2021 - 74
ASHRAE Journal - October 2021 - 75
ASHRAE Journal - October 2021 - 76
ASHRAE Journal - October 2021 - 77
ASHRAE Journal - October 2021 - 78
ASHRAE Journal - October 2021 - 79
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ASHRAE Journal - October 2021 - 81
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ASHRAE Journal - October 2021 - 83
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ASHRAE Journal - October 2021 - 85
ASHRAE Journal - October 2021 - 86
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ASHRAE Journal - October 2021 - 90
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ASHRAE Journal - October 2021 - 92
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ASHRAE Journal - October 2021 - 94
ASHRAE Journal - October 2021 - 95
ASHRAE Journal - October 2021 - 96
ASHRAE Journal - October 2021 - Cover3
ASHRAE Journal - October 2021 - Cover4
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