ASHRAE Journal - October 2021 - 22

TECHNICAL FEATURE
simplified charge and discharge profile for this
scheme on a design day.
The TIER design allowed us to provide two
ASHPs totaling 3,530 kBtu/h (1 MW) where 10
ASHPs totaling over 16,000 kBtu/h (4.7 MW)
would have otherwise been required. The relative
footprints of these two designs are shown
in Figure 8 and Figure 9.
TIER TES tanks are invariably taller than
the ASHPs they replace (height is desirable to
improve tank storage efficiency since thermal
stratification yields a thermocline
of at least a few feet in height; the
shorter the tank the more volume is
trapped in the thermocline, and thus
the greater the total tank volume must
be)-40 ft (12 m) taller in this case
study-so finding an optimal location
for the tank can be a challenge.
We have thus far found success
siting these tanks in parking garages. Typically, the
TES tank is smaller than the fire water storage tank
needed for a high-rise. On one high-rise we have been
preliminarily approved to use the TES tank as the fire
water tank, further reducing project costs and spatial
requirements.
EQUATION 1 Cascaded chiller heating efficiency.
COPh
=
Cascade
1−
1
+
COPh
heat recovery chiller
COPh
COPh
heat recovery chiller
cooling chiller
more time down from 60°F (16°C) to 40°F (4.4°C). The
overall delta T with the TIER design is therefore 40°F
(22°C), allowing for a compact tank.
Efficiency
Spatial analyses also illustrate one of the unique benefits
of condenser water TIER relative to other forms
of TIER, including HW and CHW: while a HW or CHW
TES tank's capacity is limited by the delta T of the loads
it serves, a condenser water tank serves as a source for
heat recovery chillers, so it can have a much higher delta
T. For a CHW TES system, delta T is typically in the range
of 18°F to 25°F (11°C to 14°C). A HW TES tank storing
120°F (49°C) water achievable by the ASHPs trim changing
the tank might similarly be limited to a 25°F (14°C)
delta T without multirow heating coil selections.
A condenser water TES tank by contrast can readily be
sized for 40°F (22°C) delta T or more. While the tank is
intended to operate with a 20°F (11°C) delta T between
60°F (16°C) and 80°F (27°C) on most days to minimize
the lift overlap between cooling-only machines and
heat recovery machines to maximize cascade efficiency,
on design heating days, the tank can cycle through one
The condenser water TIER solution-and all TIER
approaches for that matter-are significantly more
energy efficient than a conventional ASHP plant.
Consider first that the IPLV of a typical variable speed
centrifugal chiller that would be used to cool a large
building and charge the TES tank in a TIER design is on
the order of 0.35 kW/ton (0.10 kW/kW); this corresponds
to a COPh of 11. The COPh of heat recovery chillers boosting
water from 60°F to 125°F (16°C to 52°C) should be
greater than 5. The cascaded COPh is therefore roughly
3.7 (Equation 1).
Contrast this to the COPh of one representative ASHP
product, which varies from 2.1 at design ambient conditions
(32°F [0°C]) to 3.1 under more mild ambient conditions
(60°F [16°C]) when supplying 120°F (49°C) water.
Perhaps most important, any energy extracted from the
building and stored in the TES tank for later or concurrent
heating use effectively provides " free " cooling-it is
simply a by-product of the heating process.†
†The typical paradigm is to view the recovered heat from heat recovery chillers as a " free " by-product of the cooling process. With TIER
designs we prefer to flip the paradigm since the objective is to recover as much energy from the building on cold days as possible to
minimize the use of trim heat sources. This recovered heat makes the associated cooling in turn " free. "
22
ASHRAE JOURNAL ashrae.o rg O CTO B E R 2021
1
FIGURE 8 1.1 million ft2 building conventional ASHP
farm.
76 ft, 6 in.
FIGURE 9 1.1 million ft2 building TIER
TES tank and ASHP alternative.
30 ft, 6 in.
TES Tank
1
59 ft, 0 in.
53 ft, 6 in.
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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
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ASHRAE Journal - October 2021 - 42
ASHRAE Journal - October 2021 - 43
ASHRAE Journal - October 2021 - 44
ASHRAE Journal - October 2021 - 45
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ASHRAE Journal - October 2021 - 48
ASHRAE Journal - October 2021 - 49
ASHRAE Journal - October 2021 - 50
ASHRAE Journal - October 2021 - 51
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ASHRAE Journal - October 2021 - 53
ASHRAE Journal - October 2021 - 54
ASHRAE Journal - October 2021 - 55
ASHRAE Journal - October 2021 - 56
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ASHRAE Journal - October 2021 - 58
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ASHRAE Journal - October 2021 - 60
ASHRAE Journal - October 2021 - 61
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ASHRAE Journal - October 2021 - 63
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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
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ASHRAE Journal - October 2021 - 75
ASHRAE Journal - October 2021 - 76
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ASHRAE Journal - October 2021 - 95
ASHRAE Journal - October 2021 - 96
ASHRAE Journal - October 2021 - Cover3
ASHRAE Journal - October 2021 - Cover4
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