ASHRAE Journal - October 2014 - 13

TECHNICAL FEATURE

the majority of an HVAC system's
carbon emissions, maintaining or
improving the efficiency of HVAC
equipment relative to current technology is an important consideration when developing equipment
with low-GWP refrigerants.

FIGURE 1 U.S. building sector HVAC primary annual

energy consumption, by technology.1

Annual Primary Energy Consumption (Quadrillion Btu)

and Mexico announced a proposal
in April 2013 to reduce HFC consumption by 85% between 2016 and
2033.³ In addition, several institutions within the European Union
endorsed an agreement to reduce
HFC consumption by roughly 80%
by 2030.⁴ The U.S. Environmental
Protection Agency (EPA) announced
in February 2014 the development of
two rulemakings: one to expand the
list of low-GWP refrigerants, and a
second to de-list several high-GWP
refrigerants for use in air-conditioning and refrigeration applications.⁵
As Figure 2 illustrates, meeting these
agreements will require significant
action within the HVAC industry to
balance the phase-down of highGWP refrigerants with the rising
consumer demand for HVAC and
other refrigeration systems.
Researchers have identified several low-GWP alternatives; however,
many of these refrigerants suffer
from other undesirable characteristics such as flammability, which
poses a significant concern under
current safety standards. Moreover,
alternatives for HFC-134a and
HFC-410A may have lower volumetric capacities, while options such as
carbon dioxide require complete
system redesign due to their transcritical cycle properties.
Additionally, design changes
required to address the characteristics of low-GWP refrigerants may
significantly raise the costs of vaporcompression systems and could
affect overall system efficiency.
Because the energy consumed during system operation accounts for

Alternatives to Vapor Compression
Although work is underway to
develop alternative refrigerants and
improve refrigerant management
strategies, the phase-down of HFCs
will impose constraints on vaporcompression equipment that will
require trade-offs among cost, efficiency, and safety. These constraints
could present market opportunities
for alternative space-conditioning
technologies.
A recent U.S. Department of
Energy (DOE) study⁷ characterizes
alternative technologies based on
their development status (some
technologies are in very early
stages of development), potential
for energy savings, and other factors that may affect their ability to
compete with vapor-compression
systems. Figure 3 groups 22 nonvapor-compression technologies
analyzed in the DOE study, classified by energy source and primary working fluid or material.
Although vapor-compression systems are also used in refrigeration,
transportation, and process cooling applications, the DOE study
focuses solely on building HVAC
applications.
Some alternative technologies are impractical for spaceconditioning applications due to

8
7

11%

6
5
4
89%

3

99%

2
1
0

Space Heating

1%
Space Cooling

Vapor-Compression Technologies
Non-Vapor-Compression Technologies, Including
All Electric Resistance Heating and All Fuel-Fired
Technologies

low efficiencies and capacities
(e.g., pulse-tube and vortex-tube
cycles), and some are too early
in their development cycle to be
fully evaluated (e.g., Bernoulli
heat pump, critical-flow cycle, and
electrocaloric heat pump). The
DOE study focuses on the remaining 17 technologies that could serve
as viable alternatives in vaporcompression space-heating and
space-cooling systems, with some
additional development.
In general, the studied vapor-compression alternative technologies
fall into three categories: solid-state,
electro-mechanical, and thermally
driven technologies.

Solid-State Technologies
Solid-state technologies produce
useful temperature differences
based on the intrinsic material

*Primary energy accounts for the losses in generation, transmission, and distribution. These losses are only accounted for electricity, as the transmission and distribution losses for natural gas and other
fossil fuels tend to be small. Primary energy does not account for the losses associated with extraction.
†The authors developed these estimates using the Energy Information Administration's (EIA) Annual Energy Outlook (AEO) 2010¹ to forecast baseline energy consumption in the buildings sector, segregated
by geographic location, end use, and fuel type.
‡These GWP values are expected to change upon the publication of the UNEP 5th Assessment Report.

O CT O B E R 2 0 1 4

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