ASHRAE Journal - July 2024 - 68

in Compressors
D
environmental sustainability and the
global push towards decarbonization by
introducing products designed to facilitate the
and boiler manufacturers.
In line with this commitment, the Danfoss PSH
ambient heat pumps, have been optimized to
operate seamlessly with the R454B refrigerant,
boasting a low Global Warming Potential (GWP)
of 466, conforming to the EPA's latest
environmental directives. These compressors
have received approval for liquid, vapor, and
wet injection, allowing for the integration of
these technologies into a variety of heat pump
systems while guaranteeing peak performance
during the cooling process by incorporating
intermediate discharge valve (IDV) within the
compressors.
injection operating modes explained:
Liquid Injection
The PSH Liquid Injection fully equipped
compressor has been engineered to minimize
footprint, reduce time to market, and remain
cost-competitive while ensuring a reliable
design. This compressor comes equipped with
an injection valve and controller to precisely
regulate the amount of refrigerant. It is available
for capacities up to 15 tons.
Liquid injection operates as follows: Initially,
liquid-phase refrigerant is injected directly into
the scroll set and then it vaporizes, reducing the
throughout this process is meticulously
controlled by the Liquid Injection Valve (LIV),
which responds to variations in the discharge
temperature, ensuring optimal performance
Vapor Injection
Vapor injection is a method for increasing
various applications. The basic working
principle requires an injection-capable
compressor, a heat exchanger, an expansion
device, a solenoid or check valve, connecting
tubing, and a controller.
From the thermodynamic perspective, the
refrigerant leaves the condenser as a subcooled
liquid and passes through an expansion device
before entering the economizer heat exchanger.
It leaves the heat exchanger as a vapor or vapor/
liquid mixture, which is then injected into the
compressor, reducing work. This process also
increases system capacity, given that the inlet
passing through the economizer heat
exchanger.
is a key initiative supported by the government.
Injection into the compressor is necessary to
permit operation at these low ambient
operating conditions.
A compressor optimized for vapor injection not
only provides additional refrigeration capacity
for the system but also increases energy
controller, the compressor's operating envelope
is greatly enhanced compared to a traditional
compressor operating without injection. This is
extremely important as the transition to heat
are required.
Wet Injection
When the scroll requires additional cooling
beyond what vapor can provide, the controller
adjusts the injection superheat (SH) to zero and
monitors the compressor discharge gas
temperature (DGT) to control wet injection. This
mode, distinct from liquid injection, solely
increases envelope without enhancing
Heat Pump Market
Heat pump growth in North America and
globally is fueled by the megatrends of
In North America, there are programs in place to
heat pumps. There is also legislation prohibiting
gas furnaces for heating in several states, which
is anticipated to expand nationwide. New York,
for example, will ban the sale of new equipment
using fossil fuels beginning in 2026. Other states
and local municipalities have similar proposals
that would make heat pumps mandatory.
Within the heat pump market segment, the
ability of these units to operate in cold climates
The cold climate heat pump challenge allowed
manufacturers to receive funding from the
Department of Energy to expand the operating
map of heat pumps to frigid climate zones.
Historically, units in these low ambient zones,
such as the northern parts of the US and
Canada, would only have heating from natural
gas or propane. Without the ability to include
injection into the compressor, the internal
components (bearings, etc.) cannot withstand
the higher temperatures in these operating
conditions. This also limits the compressor map,
requiring supplementary heat sources.
With the success of this program, the focus on
heat pumps is only continuing to expand. It will
be scaled up to include larger capacity units,
with an additional emphasis on increased
For the end user, in areas where gas prices are
increasing, heat pumps will provide an
alternative to furnaces and other heat sources
and may lead to utility bill reductions. They will
decrease the natural gas or propane
requirement when heating is needed in frigid
climates, thereby reducing system complexity.
In many cases, rebates are also available for
cold-climate heat pumps with injection. Overall,
the injection solutions will be an enabler for
cold-climate heat pump operation now and in
the future.
ASHRAE Journal - July 2024

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