German OEM AGO GmbH Energie + Anlagen has found that its Calora ammonia (R717)/water (R718) heat pumps can achieve a temperature lift of up to 100K (100°C/180°F) with a higher coefficient of performance (COP) at a lower pressure ratio than its ammonia compression heat pumps.
“AGO’s Calora heat pump enhances the COP by approximately 20% and reduces the pressure ratio by one-fifth, outperforming traditional compression heat pumps under similar operating conditions,” said Klaus Ramming, Head of Thermal Engineering at AGO.
“While heat pumps with compression result in a pressure ratio of 15 and COP of about 2.3, AGO Calora’s absorption cycle heat pumps show a more favorable pressure ratio of 12.3 and a higher COP of approximately 2.8, achieving the same temperature lift under similar operating conditions,” he added.
Ramming presented the comparison at the Industrial Heat Pump Conference held in November in Prague, the Czech Republic. The conference was organized by Exergie, a Czech sustainable energy consulting firm.
AGO specializes in air conditioning and ventilation equipment and is located in Kulmbach, Germany, about 90 minutes north of Nuremberg. The company was founded in 1980 and has been a part of RheinEnergieAG, based in Cologne, Germany, since 2020.
During his presentation, Ramming highlighted the difference in the recorded pressures of the two heat pumps when raising temperatures.
“When we set the heat source inlet at 6°C (42.8°F) and the outlet at 2°C (35.6°F), and for the heat sink an inlet of 65°C (149°F) rising to 100°C (212°F) at the outlet, we observed a significant difference in pressure requirements between the two systems,” said Ramming.
“To achieve this same temperature lift, our compression-based heat pump required a condensing pressure of 63bar (913.7psi),” he said. “However, with an ammonia-water mixture, our Calora heat pump achieved the same temperature lift at a lower pressure of just 32bar (464.1psi).”
Ramming emphasized the importance of temperature lift in industrial applications requiring heat at high temperatures, such as the paper and pulp and chemical industries. He noted that AGO’s ammonia/water heat pumps are “well-suited for various industrial and energy-supply applications” thanks to their scalable output, which ranges from 1,000kW (284.3TR) to 10,000kW (2,843.4TR).
Ramming also noted that the Calora heat pump can operate in a broad range of temperatures.
“They handle heat source temperature ranges from -10°C (14°F) to 90°C (194°F) and have the potential to deliver heat sink temperatures from 40°C (104°F) to 160°C (284°F),” said Ramming.
In addition to the comparison between AGO’s absorption cycle and compression heat pumps, Ramming provided a detailed overview of the benefits of using an ammonia/water mixture in heat pump design.
“Integrating an ammonia-water mixture allows for a more efficient thermal exchange process,” said Ramming. This efficiency comes from the mixture’s ability to be cooled to lower temperatures during absorption, thereby reducing the necessary absorption pressure, which leads to an overall increase in the system’s efficiency.”
He further elaborated on the operational benefits and explained how temperature affects the system’s performance.
“Unlike heat pumps based on compression where the pressure ratio is dependent on the outlet temperature of the heat source and sink, heat pumps with a solution cycle depend on the mean temperature of these sources,” said Ramming.
“The ammonia/water solution allows for more versatile temperature management during the absorption and evaporation processes,” Ramming continued. “During absorption, the solution can be cooled to a lower temperature, reducing the necessary absorption pressure to achieve the desired ammonia concentration in the rich solution.”
The same principle also applies in the generator phase of the heat pump cycle, said Ramming
“As the inlet temperature of the heat sources rises, the ammonia/water solution can be heated to higher temperatures,” he said. “This results in an increase of evaporating pressure required to reach a certain ammonia concentration in the diluted solution.” “The ammonia/water refrigerant used in our heat pumps has zero global warming potential and ozone depletion potential, aligning with the global demand for sustainable and eco-friendly solutions,” said Ramming.
“Integrating an ammonia-water mixture allows for a more efficient thermal exchange process. This efficiency comes from the mixture’s ability to be cooled to lower temperatures during absorption, thereby reducing the necessary absorption pressure, which leads to an overall increase in the system’s efficiency.”Klaus Ramming, Head of Thermal Engineering at AGO