The benefits of injection technology for cold climate heat pumps

Heat pump growth in North America and globally is fueled by the megatrends of electrification, decarbonization, and energy efficiency, which are core values for Danfoss.

In North America, there are programs in place to offer rebates for the purchase and installation of 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 is a key initiative supported by the government. Injection into the compressor is necessary to permit operation at these low ambient operating conditions.

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, where the units can operate in the field without 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 energy efficiency.

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 increased system efficiency, capacity, and cold-climate heat pump operation now and in the future.

Danfoss applies the injection technology in the PSH scroll compressors

Danfoss reaffirms its dedication to environmental sustainability and the global push towards decarbonization by introducing products designed to facilitate the transition to electrification for air conditioning and boiler manufacturers.

In line with this commitment, the Danfoss PSH scroll compressors, specifically tailored for low ambient heat pumps, have been optimized to operate seamlessly with the R454B refrigerant, boasting a lower 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.

PSH scroll compressor’s different types of 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 discharge temperature. Crucially, the flow rate throughout this process is meticulously controlled by the Liquid Injection Valve (LIV), which responds to variations in the discharge temperature, ensuring optimal performance and efficiency.

Vapor injection

Vapor injection is a method for increasing refrigeration capacity and system efficiency in 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 quality of the evaporator is lowered by first passing through the economizer heat exchanger.

A compressor optimized for vapor injection not only provides additional refrigeration capacity for the system but also increases energy efficiency. By managing the injection through a 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 pumps intensifies and reductions in fossil fuels 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 efficiency or capacity.

Learn more about our compressors and our entire portfolio for heat pumps: Heat pumps for air conditioning | Energy-efficient components | Danfoss