Studies of a novel ejector-based refrigeration cycle using an “ultra-low” ejector entrainment ratio of 0.105 ‒ developed and patented by Bechtel University in St. Paul, Minnesota, with a prototype built at Purdue University in West Lafayette, Indiana ‒ indicate a possible 5% energy saving in HVAC applications.
“The collaboration with the Bechtel team led to the development of a state-of-the-art hydrocarbon-based experimental setup to demonstrate the feasibility of the technology,” said Dr. Davide Ziviani, Assistant Professor of Mechanical Engineering at Purdue.
Working fluids used in the model included R134a for a baseline, propane (R290), ammonia (R717) and R152a (HFC). According to the paper, R-290 was the best-performing fluid due to its thermophysical properties.
However, the technology, dubbed Crescendō for marketability, has a potential application anywhere energy is used for HVAC systems, said David Ladd, Senior Solutions Analyst at Bechtel, in a press release. The demonstrated energy recovery potential from capturing available energy through a “regenerative” cooling cycle could increase the adoption of CO2 (R744)-based refrigerant systems.
The ejector provides free compression, with high-pressure liquid from the pump discharge meeting vapor evaporated in the cooling levels. “The energy transfer accelerates the fluid to near supersonic speeds, with the precisely tapered diffusing section increasing the pressure on the outlet stream,” Bechtel said in a Crescendō press release.
According to the research published in the Proceedings of the International Congress of Refrigeration, Crescendō improves evaporator performance by subcooling the refrigerant at the evaporator inlet for better distribution. “The benefit achieved by better refrigerant distribution is quantified by a slightly different pinch point temperature in this paper, and the results show nearly 5% of power savings can be made possible when the difference in pinch point temperature reaches 1K [1°C/1.8°F].”
The paper indicates that energy efficiency increases at higher pinch point temperatures, with the pinch point being the temperature difference between the refrigerant and the surrounding air. As such, applications in refrigeration systems could unlock higher energy savings, with more than 10% COP improvement at cooling temperatures below -40°C (-40°F), according to the Crescendō press release.
“Additional research is needed to optimize the cycle and its components,” said Ziviani. “However, the initial promising results can open the doors for next generation environmental-friendly refrigeration systems for many applications.”
The Betchel and Purdue team are continuing the research by building a commercial prototype using the technology inside a small building air conditioner. Ladd invites anyone interested in the project to contact him. “We believe in a community approach to achieving efficient cooling.”
According to Bechtel, the current research supports applications operating from refrigeration (5°C/41°F), freezer (-5°C/23°F) and low-temperature (-25°C/-13°F) through ultra-low temperatures (-80°C/-112°F). Within three years, researchers expect to add applications for warm temperatures (20°C; 68°F) and liquefied natural gas (-160°C/-256°F), with Cyco cooling (-273°C/-460°F) applications within four years.
“Crescendō technology has the potential to reduce a cold storage facility’s annual [greenhouse gas] emissions by more than 400 metric tons of CO2e and is projected to have a specific energy consumption of less than 2 kWh/m³/year [compared to current facilities using 15‒25 kWh/m3/ year],” the Crescendō press release said.
Bechtel feels the novel system eliminates temperature excursions and could lower logistics costs by 38%.
“The results show nearly 5% of power savings can be made possible when the difference in pinch point temperature reaches 1K [1°C; 1.77°F].”Purdue/Bechtel Published Research