How Vapor Injection Technology is Enabling Cold Climate Heat Pumps

Vapor injection is a method to increase refrigeration capacity and system efficiency in a wide range of applications. The basic working principle requires an injection-capable compressor, a heat exchanger, expansion device, solenoid or check valve, connecting tubing and controller.?

From the thermodynamic perspective, 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 vapor or vapor/liquid mixture where it is then injected into the compressor, reducing work. It also provides an increase in system capacity since the inlet quality to the evaporator is lowered by first passing through the economizer heat exchanger.

A compressor optimized for vapor injection will not only provide additional refrigeration capacity for the system, but it will also increase energy efficiency. By managing the injection through a controller, the operating envelope of the compressor 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.?

Heat pump growth in North America and globally is fueled by the megatrends of electrification, decarbonization and energy efficiency. These 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 that prohibits 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 a necessity 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 very cold 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 having the ability to include injection into the compressor, the internal components (bearings, etc.) are unable to withstand the higher temperatures at 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 focus 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 requirement for natural gas or propane when heating is needed in very cold climates, thereby reducing system complexity. In many cases, rebates are also available for cold climate heat pumps with injection as well. Overall, vapor injection will be an enabler for increased system efficiency, capacity and cold climate heat pump operation now and in the future.

Nick Mislak will discuss vapor injection, along with additional injection technologies, and more in Trends and Market Drivers in Commercial Heat Pump Development for North America, an exclusive RETHINK Live webinar on Wednesday, October 16, 2024, at 12:00 PM EDT. All of the sessions in this year's RETHINK Live series will also be available on-demand following the event. Learn more and register: RETHINK Live Returns to North America for a Third Edition | Danfoss