A new propane (R290) cooling system developed by Tecumseh and retrofitted into vaccine storage and medical inventory management company TruMed’s AccuVax ES vaccine storage machine was 20% more efficient compared to the previous R134a system, according to the companies.
TrueMed, which specializes in designing storage systems for vaccines and medications, has partnered with Tecumseh to convert its AccuVax ES system to propane. The AccuVax ES can store 700 vaccines and includes a robot that picks and places them.
Akash Bhatia, Director of Systems Engineering & Masterflux Business Development at Tecumseh, and Prabhakar Doppalapudi, Chief Engineering and Technical Services Officer at TruMed Systems, presented the retrofit project at the ATMOsphere (ATMO) America Summit 2024. The summit, organized by ATMOsphere, the publisher of NaturalRefrigerants.com, took place June 10–11 in Washington, D.C.
According to Doppalapudi, the retrofit project arose due to strict environmental regulations, particularly those in California.
For the retrofit, Tecumseh fitted its VTCX419U and VTCX415U compressors to the AccuVax ES. The VTCX415U improved energy efficiency by 20% compared to the baseline R134a unit and operated at a maximum speed of 4,500rpm compared to the baseline system’s 3,000rpm. The VTCX419U was around 10% more efficient depending upon the rotational speed point. The cooling capacity of the VTCX415U was not shared.
“With the 415U, we were roughly around 20% more efficient than the baseline system, and we designed the system to operate with a reduced refrigerant charge, moving from 480g of R134a to 100g of R290,” explained Bhatia.
Design considerations
The project posed several technical constraints, such as the requirement to stay under a refrigerant charge of 150g and that the new system make no impact on the existing system’s hot gas defrost process and control parameters. Another key constraint was the requirement to maintain the existing evaporator design, which avoided additional tooling costs and ensured the system would fit into the existing machine architecture. The new refrigeration system also needed to use the existing 24-volt DC architecture.
One of the technical constraints was the requirement for a heat removal rate greater than 1,535BTU/h (0.45kW/0.12TR) at an ambient temperature of 40°C (104°F). Tecumseh’s upgraded cooling system, featuring the VTCX419U compressor, successfully met this requirement by achieving a cooling capacity of 2,368BTU/h (0.69kW/0.19TR).
The retrofit system has a refrigerator set point temperature of 5°C (41°F) and a freezer set point temperature of −15°C (5°F). The maximum evaporator temperature is at −25°C (−13°F).
Future plans
TruMed will convert all AccuVax machines to R290, according to Doppalapudi, who also noted that from 2025, new designs will use propane as standard, although it was not confirmed which manufacturer will supply the compressors. Existing machines using R134a will continue to operate until they are returned for servicing, at which point they will be retrofitted with either Tecumseh’s 419U or 415U compressor. The company will also look beyond the U.S. and will expand its use of propane refrigeration in Europe and Japan.
During the question and answer session, Doppalapudi shared details about the future of the retrofit project.
“Initially, only two units were converted as part of an evaluation process,” Doppalapudi said. “However, the team plans to build eight more units shortly, with the goal of converting 90 units [to R290] by the end of the year. Looking ahead, the intention is to scale up production significantly and build around 1,000 units per year initially, with a long-term target of increasing this number to between 10,000 and 20,000 units annually.”
“Looking ahead, the intention is to scale up production significantly and build around 1,000 units per year initially, with a long-term target of increasing this number to between 10,000 and 20,000 units annually.”
Prabhakar Doppalapudi, Chief Engineering and Technical Services Officer at TruMed Systems
