ASHRAE Journal - August 2013 - 67

Technical FeaT
FeaTure

deviation in energy consumption (%)

in a minor reduction in the
Figure 1 Deviation in the annual energy consumption compared to the benchmark system.
carbon footprint compared
to the benchmark system as it
20
18 17
16
contains a significant charge
15
of high GWP refrigerant.
10
The second was a cascade
6
3
5
system with R-404A chilling a
2
1
1 0 0
brine loop on the MT side and a
0
0
–1
–3
CO2 DX loop on the LT side. The
–5
–6
main objective of this system is
Quebec
–9
–9
–10
–9 –10
–10 –11
New York
to minimize the R-404A charge.
–15
Atlanta
R-404A is contained in a chiller
–18
–20
that cools a secondary brine loop
(1)
(1)
(2)
(3)
(3)
(3)
(4)
and CO2 cascade condenser.
Alternative
R-404A/CO2 R-134a/CO2
R-404A
Propane
Ammonia
R-134a
Transcritical
System
The third was a cascade sysCascade
Cascade
Chiller
Chiller
Chiller
Chiller
CO2 Booster
tem with R-290 (propane),
MT
R-404A DX
R-134a DX
Prop. Glycol Pumped CO2 Pumped CO2 Pumped CO2
CO2 DX
R-717 (ammonia), R-404A or
LT
CO2 DX
CO2 DX
CO2 DX
CO2 DX
CO2 DX
CO2 DX
CO2 DX
R-134a on the high pressure
side (all alternatives were
analyzed) chilling a pumped CO2 secondary loop on the The highest efficiency gain was achieved by the tranMT side and CO2 DX on LT side. For hydrocarbons and
scritical booster system in the coolest climate, resultammonia, this system represents the safe solution, as the ing in an annual power savings of 18% over the R-404A
flammable refrigerant is isolated in the machinery room benchmark. In contrast, choosing a cascade solution
or in an outside container, and the charge can be signifi- with pumped glycol on MT and CO2 on LT would have
cantly decreased compared to DX systems. Likewise, for resulted in a penalty of 18%. While there are other factors
affecting the efficiency of the individual system, such as
HFC refrigerants the cascade arrangement allows for a
the quality of commissioning and daily operation, these
drastic reduction in charge.
The fourth was a CO2 transcritical booster system with figures are indicative of the average savings that can be
CO2 DX on the MT and LT sides. The system has been
achieved.
gaining popularity due in large part to the simplicity of
To validate the efficiency analysis results, a simple
the single-refrigerant system and high efficiency in tem- COP calculation was made for all cycles. Using only the
perate climates.
average annual ambient conditions and not considering
losses or inefficiencies, deviations between the simple
Methodology
calculation and those of the software were approximately
The core of the efficiency analysis was Pack Calculation 30%. The simple cycle calculation confirmed the general
II software. The software was designed to compare the
trends and, by introducing an isentropic efficiency of 0.7
performance of different refrigeration system architec- to the simple model, the deviations fell to within 10%.
tures based on manufacturer compressor models and
Comparing the COPs to what has been reported from a
hourly climate data for locations worldwide. For valida- variety of sources in the field (Table 1), the trends are also
tion, the results also were compared to simple cycle cal- confirmed.
culations and to available efficiency data. For more about
The most surprising result of the comparison was the
the assumptions used in the study, see Reference 1.
performance of the transcritical booster system, which
even in the Atlanta climate slightly outperforms the
Results
benchmark system. The three factors that impacted
Figure 1 shows the results of the simulations for three
this result most are: the condensing pressure ability
representative climates: Quebec, New York and Atlanta. to float to a lower temperature; direct cooling, which
Au g ust 2013

ashrae.org

ASHRAE JouRnAl

67



ASHRAE Journal - August 2013

Table of Contents for the Digital Edition of ASHRAE Journal - August 2013

Contents
Commentary
Industry News
Letters
Meetings and Shows
Feature Articles
Presidential Address: Shaping the Next
Technical vs. Process Commissioning: Owner’s Project Requirements
Energy Codes & Standards, Part 2
Shaping the Next: Indoor Air Quality
Cutting-Edge Renovation
System Efficiency for Natural Refrigerants
Standing Columns
Building Sciences
InfoCenter
Data Centers
Emerging Technologies
HVAC Applications
Energy Modeling
Refrigeration Applications
Product Showplace
People
Classified Advertising
Advertisers Index
ASHRAE Journal - August 2013 - Cover1
ASHRAE Journal - August 2013 - Cover2
ASHRAE Journal - August 2013 - 1
ASHRAE Journal - August 2013 - 2
ASHRAE Journal - August 2013 - Contents
ASHRAE Journal - August 2013 - Commentary
ASHRAE Journal - August 2013 - 5
ASHRAE Journal - August 2013 - Industry News
ASHRAE Journal - August 2013 - 7
ASHRAE Journal - August 2013 - 8
ASHRAE Journal - August 2013 - 9
ASHRAE Journal - August 2013 - 10
ASHRAE Journal - August 2013 - 11
ASHRAE Journal - August 2013 - 12
ASHRAE Journal - August 2013 - 13
ASHRAE Journal - August 2013 - Letters
ASHRAE Journal - August 2013 - 15
ASHRAE Journal - August 2013 - 16
ASHRAE Journal - August 2013 - 17
ASHRAE Journal - August 2013 - 18
ASHRAE Journal - August 2013 - 19
ASHRAE Journal - August 2013 - Meetings and Shows
ASHRAE Journal - August 2013 - 21
ASHRAE Journal - August 2013 - Presidential Address: Shaping the Next
ASHRAE Journal - August 2013 - 23
ASHRAE Journal - August 2013 - 24
ASHRAE Journal - August 2013 - 25
ASHRAE Journal - August 2013 - 26
ASHRAE Journal - August 2013 - 27
ASHRAE Journal - August 2013 - 28
ASHRAE Journal - August 2013 - 29
ASHRAE Journal - August 2013 - 30
ASHRAE Journal - August 2013 - 31
ASHRAE Journal - August 2013 - Technical vs. Process Commissioning: Owner’s Project Requirements
ASHRAE Journal - August 2013 - 33
ASHRAE Journal - August 2013 - 34
ASHRAE Journal - August 2013 - 35
ASHRAE Journal - August 2013 - 36
ASHRAE Journal - August 2013 - 37
ASHRAE Journal - August 2013 - 38
ASHRAE Journal - August 2013 - 39
ASHRAE Journal - August 2013 - Energy Codes & Standards, Part 2
ASHRAE Journal - August 2013 - 41
ASHRAE Journal - August 2013 - 42
ASHRAE Journal - August 2013 - 43
ASHRAE Journal - August 2013 - 44
ASHRAE Journal - August 2013 - 45
ASHRAE Journal - August 2013 - 46
ASHRAE Journal - August 2013 - 47
ASHRAE Journal - August 2013 - 48
ASHRAE Journal - August 2013 - 49
ASHRAE Journal - August 2013 - Shaping the Next: Indoor Air Quality
ASHRAE Journal - August 2013 - 51
ASHRAE Journal - August 2013 - 52
ASHRAE Journal - August 2013 - 53
ASHRAE Journal - August 2013 - 54
ASHRAE Journal - August 2013 - 55
ASHRAE Journal - August 2013 - 56
ASHRAE Journal - August 2013 - 57
ASHRAE Journal - August 2013 - 58
ASHRAE Journal - August 2013 - 59
ASHRAE Journal - August 2013 - Cutting-Edge Renovation
ASHRAE Journal - August 2013 - 61
ASHRAE Journal - August 2013 - 62
ASHRAE Journal - August 2013 - 63
ASHRAE Journal - August 2013 - 64
ASHRAE Journal - August 2013 - 65
ASHRAE Journal - August 2013 - System Efficiency for Natural Refrigerants
ASHRAE Journal - August 2013 - 67
ASHRAE Journal - August 2013 - 68
ASHRAE Journal - August 2013 - 69
ASHRAE Journal - August 2013 - 70
ASHRAE Journal - August 2013 - 71
ASHRAE Journal - August 2013 - Building Sciences
ASHRAE Journal - August 2013 - 73
ASHRAE Journal - August 2013 - 74
ASHRAE Journal - August 2013 - 75
ASHRAE Journal - August 2013 - 76
ASHRAE Journal - August 2013 - 77
ASHRAE Journal - August 2013 - 78
ASHRAE Journal - August 2013 - 79
ASHRAE Journal - August 2013 - 80
ASHRAE Journal - August 2013 - 81
ASHRAE Journal - August 2013 - InfoCenter
ASHRAE Journal - August 2013 - 83
ASHRAE Journal - August 2013 - 84
ASHRAE Journal - August 2013 - 85
ASHRAE Journal - August 2013 - 86
ASHRAE Journal - August 2013 - 87
ASHRAE Journal - August 2013 - Data Centers
ASHRAE Journal - August 2013 - 89
ASHRAE Journal - August 2013 - 90
ASHRAE Journal - August 2013 - 91
ASHRAE Journal - August 2013 - Emerging Technologies
ASHRAE Journal - August 2013 - 93
ASHRAE Journal - August 2013 - 94
ASHRAE Journal - August 2013 - 95
ASHRAE Journal - August 2013 - HVAC Applications
ASHRAE Journal - August 2013 - 97
ASHRAE Journal - August 2013 - Energy Modeling
ASHRAE Journal - August 2013 - Refrigeration Applications
ASHRAE Journal - August 2013 - Product Showplace
ASHRAE Journal - August 2013 - 101
ASHRAE Journal - August 2013 - People
ASHRAE Journal - August 2013 - Classified Advertising
ASHRAE Journal - August 2013 - Advertisers Index
ASHRAE Journal - August 2013 - Cover3
ASHRAE Journal - August 2013 - Cover4
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