CO2 (R744) heat pumps are “really good” for district heating applications, and the best available technology in the 0.5 to 5MW (142 to 1,422TR) capacity range, according to Kim G Christensen, CEO of Danish OEM Fenagy.

Christensen shared these views during the HVAC and Heat Pumps session at the ATMOsphere Europe conference, held online September 28-29.

Some of the benefits of CO2 heat pumps, according to Christensen, are low sound levels and vibrations, making them a good fit for smaller plants in cities. They have small footprints making them suitable for small spaces, and they maintain nearly constant capacity during defrost and stable supply temperatures. They also “lose” less capacity when the ambient air temperatures drop. 

Fenagy manufactures R744 heat pumps and refrigeration systems in capacities from 300kW to 2MW. The company started operations in the summer of 2020, and currently has 14 projects underway, according to Ebbe Nørgaard, Sales Manager at Fenagy, speaking at the Refrigeration and Heat Pump Forum 2021 in Copenhagen on October 4.

“In a heat pump we have to heat water, and there is a glide from, for example, 40°C to 70°C, and that glide matches pretty well with the glide you have on the CO2 side,” Christensen explained. “That match is brilliant for district heating, because if you compare [CO2] to a condensing refrigerant like ammonia, for instance, you have this condensation plateau where you have a pinch point in the heat exchanger line . You have to push the condensation pressure pretty high to get the 70°C, so CO2 is really good for heat pumps and district heating systems here in Denmark.”

Graph from Kim G. Christensen’s presentation at ATMO Europe.

Denmark has a very well-developed district heating network, which meets around 70% of heating demand, with heat pumps becoming ever more prevalent in these networks.

“In Denmark we call [the use of heat pumps] smoke-free heating, because we want to go fossil-fuel free, and also move away from burning biomass, so the final answer is to electrify our heating systems, and that is what we do with electrical heat pumps, and this is why it becomes extremely popular,” Christensen said.

Currently there is about 350MW (99,520TR) of heat being supplied into Denmark’s district heating systems from heat pumps, Christensen said. Most of the larger industrial heat pumps are ammonia and the smaller ones include various refrigerants. Lately CO2 has begun making inroads in this market.

Christensen predicts a marked expansion of heat pump usage in district heating. “We do expect that in just eight years from now, in 2030, there will be 2,000MW (568,690TR) installed just that year, so we believe that the heat pump segment will be just as big as the industrial refrigeration segment,” Christensen added.

“Industrial refrigeration will eventually also include heat pumps, at least that is our philosophy,” he added. “We believe that we will no longer see refrigeration system reject heat to ambient air, but use it in our heating systems.”

“We believe that the heat pump segment will be just as big as the industrial refrigeration segment.”

Kim G. Christensen, Fenagy

Improving COP

The challenge for Fenagy while developing its heat pumps has not been about finding the right components; they are already available, according to Christensen. The challenge has been to enhance the COP.

“You are never good enough, so we will definitely try to improve the future systems as well,” Christensen noted.

Working to solve this challenge, Fenagy has developed its own ejector system and controls, including algorithms. To further improve the COP, Fenagy is developing a new expander and is currently testing a prototype with the Danish Technological Institute, according to Nørgaard.

You can read more about Fenagy’s heat pumps here.

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