ASHRAE Journal - October 2021 - 24

TECHNICAL FEATURE
Note that on a design day, when the ASHPs
are charging the TIER tank with tepid 80°F
(27°C) water, their COPh will increase to
approximately 3.75, yielding a cascaded COPh
of 2.4. In other words, even on a design day
when both the ASHPs and heat recovery chillers
are operating, the TIER design will still
yield superior energy efficiency to a conventional
ASHP plant.
TABLE 1 Condenser water and hot water TIER design lift heating efficiency comparison.
CONDENSER WATER HEAT RECOVERY
Cooling Only Chiller
Heat Recovery Chiller
NET HEATING EFFICIENCY
TIER also improves water efficiency in designs with
water-cooled chillers since any heat recovered from the
building for later or concurrent heating use is avoided
cooling tower heat rejection and evaporation.
Cost
Not only are condenser water TIER designs significantly
more efficient than ASHP designs, but they also
cost less. Since water-cooled chillers (typically 250 ton
to 400 ton [879 kW to 1407 kW] screw chillers or larger
centrifugal machines) are used as the primary heating
machines in a CW TIER plant, they can efficiently
serve double-duty as cooling machines for the plant. For
instance, in the example plant discussed previously with
two cooling-only chillers and two heat recovery chillers,
on a hot day one of the heat recovery chillers swings to
cooling duty and operates in parallel with the cooling
chillers as shown in Figure 6.
On a design cooling day, both heat recovery chillers can
swing to cooling duty. Owners, therefore, avoid paying
for nearly as much redundant tonnage as they do when
using a separate ASHP plant for heating. In effect, a
TIER design swaps out multiple ASHPs for a TES storage
tank and converts cooling-only chiller capacity-which
already needed to exist for cooling duty-to heat recovery
chiller capacity.
Preliminary pricing from the 1.1 million ft2
(102 000 m2) project discussed previously indicated the
conversion to TIER would yield mechanical equipment
savings on the order of $900,000. These savings do not
account for the electrical, controls, piping or opportunity
cost savings from reclaimed space that will result
as well. The TIER redesign replaces eight ASHPs, with
a budget price of $1,840,000, with one TES tank with a
budget price of $960,000. And as noted above, the tank
is basically free if it can double as the fire water storage
tank. Chiller cost per ton is lower for the screw heat
recovery machines in this plant than the cooling-only
24
ASHRAE JOURNAL ashrae.o rg O CTO B E R 2021
DEVICE SOURCE (°F) SINK (°F)
40
60
140
80 12.72
4.2
3.36
-
40
COPh SOURCE (°F) SINK (°F)
HOT WATER HEAT RECOVERY
COPh
-
140
-
3.5
3.5
variable speed centrifugal machines, showing that large
heat recovery chillers are not necessarily more expensive
than their cooling-optimized counterparts.
Condenser water TIER saves space, improves energy
and water efficiency and reduces costs relative to a conventional
ASHP plant, making it an all-around win for
owners and the environment.
Alternative Storage Approaches
While the author believes that condenser water (CW)
TES is the most promising TIER approach for most applications,
hot water (HW), chilled water (CHW), ice and
phase-change materials (PCM) all have their own benefits
and shortcomings.
Hot Water Storage
Hot water (HW) storage is perhaps the most intuitive
alternative for a system used to solve a heating problem.
The energy flows were conceptually shown in Figure 2.
A supposed advantage of HW storage relative to condenser
water (CW) storage is that it eliminates the
cascade chiller configuration and allows for greater
morning peak shifting in locales with higher utility rates
in the morning warm-up hours where that matters.
Eliminating the cascade configuration would seem to
yield a significant energy benefit, but in practice the difference
is relatively small as Table 1 illustrates.
Consider an application requiring 40°F (4.4°C)
chilled water and 140°F (60°C) hot water. COPh for one
manufacturer's 300 ton (1055 kW) heat recovery screw
chillers for such an application is approximately 3.5. In
a condenser water storage design for the same application,
a variable speed cooling-only centrifugal chiller
would operate at 40°F (4.4°C) chilled water supply
temperature (CHWST) and 80°F (27°C) condenser water
return temperature (CWRT), and a heat recovery screw
chiller would operate at 60°F (16°C) CWST and 140°F
(60°C) hot water supply temperature (HWST). At the
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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
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ASHRAE Journal - October 2021 - 49
ASHRAE Journal - October 2021 - 50
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ASHRAE Journal - October 2021 - 53
ASHRAE Journal - October 2021 - 54
ASHRAE Journal - October 2021 - 55
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ASHRAE Journal - October 2021 - 58
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ASHRAE Journal - October 2021 - 60
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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
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ASHRAE Journal - October 2021 - 96
ASHRAE Journal - October 2021 - Cover3
ASHRAE Journal - October 2021 - Cover4
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