Italian manufacturer Dorin has said that its new compressor design is expanding the application envelope of CO2 (R744)-based air-to-water heat pumps by overcoming the challenges associated with operating in low ambient temperatures.
According to Giacomo Pisano, CO2 Compressors Business Development Manager at Dorin, the company’s compressor design improves thermal insulation to reduce discharge temperature. In turn, this enables heat pumps to work more efficiently in colder climates.
“With our novel design, we are able to provide a single-stage CO2 transcritical compressor capable of working down to −22°F [−30°C],” he explained. “This is a real game changer, especially for air-to-water heat pumps because you are able to deliver a good heat with very low ambient temperature and no need for electric heaters.”
Pisano delivered these remarks during his presentation in the Heat Pump Case Studies session at the ATMOsphere (ATMO) America Summit 2024. The conference took place June 10–11 in Washington, D.C., and was organized by ATMOsphere, publisher of NaturalRefrigerants.com.
Dorin’s 160HP CO2 industrial reciprocating compressor was named Innovation of the Year 2024 at the conference’s ATMO Awards. According to ATMO, this award is given to the company that has produced a natural refrigerant-based product that has had, or is expected to have, a significant impact on the market.
“With our novel design, we are able to provide a single-stage CO2 transcritical compressor capable of working down to −22°F [−30°C].”
Giacomo Pisano, Dorin
Improving heat pump performance
As efforts continue to decarbonize heating, heat pumps are becoming a crucial part of the process, offering a sustainable alternative to fossil fuel-based boilers, said Pisano. However, challenges like operating limits in low ambient temperatures are impacting the adoption of air-to-water heat pumps.
“Heat output decreases with decreasing ambient temperature, [and] heat pump mode at −22°F is a big challenge,” he explained.
In these conditions, standard compressor design offers limited capabilities for CO2 in heat pump mode due to its very high oil and discharge temperatures. This leads to issues with heat dissipation and compressor lubrication, creating a bottleneck in the system, he added.
According to Pisano, ejectors can help alleviate the problem by increasing the saturated suction temperature of the compressor to reduce the pressure ratio and discharge temperature. However, ejectors do not fully address the main issue of compressor limitation in low ambient temperatures. For this, Dorin has created a new compressor design for use in CO2 heat pumps. The company has based the design on those used in automotive technologies and combustion engines, which work at much higher discharge temperatures.
“For CO2 heat pumps, Dorin is implementing the same solution in its compressor with a larger external discharge manifold that can completely isolate the high-temperature, high-pressure CO2 from the drive gear,” he explained. “With this, you have [improved] thermal insulation, which results in lower oil temperature, lower discharge temperatures and an extended application envelope.”
“While there are challenges, there are solutions to tackle them,” he added.
During his presentation, Pisano noted that there are several of these compressors currently in operation. However the company is ramping up its testing efforts, with a focus on this year’s winter season.
“There are multiple locations here in North America where heat pumps will be tested throughout winter time with no ejector,” he said. “There will be no help to the compressor in terms of reducing the pressure lift so that will be extremely interesting.”
Dorin is also testing its hot gas defrost functionality, with previous tests indicating that it can completely de-ice a coil in just 15 minutes, he added.
In addition to its efforts in North America and Europe, Dorin is present in China, with sales of its transcritical CO2 compressors tripling in the last five years.
