Magnetic Expansion Valve May Increase R290 Heat Pump Output by 21% Over Traditional EEV, Says Siemens – Natural Refrigerants

Siemens said its new MVL702 magnetic expansion valve (MEV) has the potential to increase the heating output of propane (R290) heat pumps by 21% using 14% less energy than conventional electronic stepper motor technology, based on tests conducted by Lithuanian OEM Refra.

Refra tested the new MEV on one of its R290 heat pumps: a double-circuit reversible air-to-water unit with a total capacity of 60kW (17.1TR). One circuit was equipped with the MVL702 valve and the other with a traditional electronic expansion valve (EEV). The variable-speed compressors on both units operated continuously at full load to maintain outlet water temperatures between 30 and 32°C (86 and 89.6°F) at an ambient temperature of −6°C (21.2°F).

Alexander Jekimow, Global Product Manager at Siemens, told NaturalRefrigerants.com that the testing took place over several weeks with the heat pump operating nonstop throughout. Jekimow said this was because Refra and Siemens sought to find an ideal six-to-eight-hour time window with a roughly constant temperature – ±0.5K (0.5°C/0.9°F) – to run three heating and defrost cycles.

Siemens said that over the entire heating cycle, including defrost, the COP of the circuit with the MEV increased by 16.5% compared to the circuit with the EEV. “These results underscore the benefits and economic advantages of enhancing overall heat pump performance,” the German OEM said.

“Thanks to the speed of response and accurate positioning of the [MEV], we can achieve lower superheat values without suffering control stability,” Siemens said. “The analysis shows the impact of better superheat control on the efficiency of the heat pump, with the MEV circuit operating on average at 6.3K [6.3°C/11.4°F] superheat and the EEV at 9.5K [9.5°C/17.1°F].”

Ilona Pavšukova, Head of Marketing at Refra, told NaturalRefrigerants.com that the valve has already been integrated into the company’s line of propane heat pumps.

In interviews with NaturalRefrigerants.com, Jekimow outlined the operating details and advantages of the MVL702 valve, with Pavšukova detailing Refra’s partnership with Siemens and the company’s introduction of the technology to the market.

These interviews have been edited for length and clarity.

Are MEVs common in the HVAC&R industry?

Alexander Jekimow: Siemens is the only company in the HVAC&R industry offering refrigerant valves with modulating magnetic actuators. For over 30 years we’ve manufactured different valves based on the technology. Our MEVs offer mechanical ,normally closed functioning, positioning in less than one second, precise 1:1,000 resolution, active position feedback and simple control interface.

Rather than adopting MEV technology, the competition in the light commercial segment 30‒150kW [8.5‒42.7TR] results in some OEMs compromising product performance.

Why did Siemens develop a MEV for propane heat pumps?

AJ: With Siemens Smart Infrastructure as a leading company in building technology, natural refrigerant heat pumps support the trend for decarbonizing comfort heating. We questioned developing an expansion valve using stepper motor or modulating magnetic actuator technology. Given our experience with both, we decided to advance on an MEV based on its control performance and normally closed valve operation, which, with propane’s high solubility in common oils, protects the compressors without additional components like solenoid valves or battery modules.

Can you provide more information about the “rapid response” and “highly accurate” positioning of an MEV compared to an EEV?

AJ: The MVL702 completely opens and closes within one second. Small position commands of 1‒5% are executed within a part of a second, with direction from a superheat loop controller. A built-in active position sensor with a 1:1,000 resolution measures and adjusts the MEV every 50 microseconds.

In comparison, the positioning speed of a traditional EEV ranges from 2.5‒10 seconds. Moreover, in a continuous control case, due to a duty cycle limitation of 30‒50%, EEVs frequently stop to avoid overheating or extensive wear. Furthermore, stepper motor valves do not have a positioning sensor and, in addition, generate 2‒3% hysteresis from converting rotary motion into linear, resulting in continuous over- and undershooting of the valve position.

Can you walk us through the Siemens/Refra partnership to test the new MEV?

Ilona Pavšukova: We have a common goal with Siemens: to increase efficiency in refrigeration products. As such, we have cooperated closely with the manufacturer for five‒six years, including integrating Siemens Climatix Controllers into our products with management and monitoring programs.

Vytas Jurėnas, a Siemens representative in Lithuania, noted our ability to respond to market changes with unique solutions. With our desire to integrate the latest innovations, we offer facility and unit flexibility to analyze new components and, as such, partnered with Siemens to conduct extensive testing of its new MEV under real conditions.

How is Refra introducing this new tech to customers?

IP: Refra started communicating this new technology to our customers at the 2024 Mostra Convegno Expocomfort held in March. At that time, the test reports showed huge benefits for Refra propane heat pumps. Our customers are interested in and waiting for the first units to incorporate this new technology. Of course, some prefer traditional technology, but we encourage them to give innovative cooling solutions a chance.