In Control of R-744

Michael Englebright, global key accounts manager, Carel, presented on the “Sustainability of CO₂ Technology and the Role of Control Systems,” which examined improvements regarding such refrigerants in secondary systems.

For example, regarding secondary systems developed in the 1990s, he said there were advantages (reduced refrigerant charge, applications on the high side, use with brine, and a wide acceptance by retailers), along with what he called ‘barriers’ (high energy regarding pumps, maintenance costs, and efficiency losses).

The early 2000s, he said, brought subcritical cascade with its pluses (reduced refrigerant charge, advancement in controls, and medium-temperature evaporator efficiency improvements), but still with some barriers (cabinet evaporator development, pump flow and capital costs, as well as a need for training of installers and technicians). But, with the recent development of transcritical booster SX systems, there comes, he said, use of a single refrigerant, evaporator optimization, medium- and low-temp COPs [coefficient of performance], and hot gas defrost — while still dealing with issues related to such systems being used in warmer climates, capital costs, and training.

“The main barriers (now) are training and education,” he said. “In emerging countries there is a need for centralized training, and industry support (in training) is a must.” He noted the need for e-learning platforms as well as hands-on training.

Focusing on some specifics, he said, “An additional benefit which CO₂ systems deliver is utilization of useful heat. There is integrated management of heat pump valves during the defrost requirements, and there is a swift, short defrost duration.”

He noted, “Research results today demonstrate that applying a CO₂ transcritical ejector in the system is a promising method to increase system efficiency.”

Mainstreaming CO₂/Ammonia Systems

The use of ammonia and CO₂ in a system is a mainstream solution for creating refrigeration, according to presenters Benoit Rodier, director of business development, Cimco Refrigeration and Jim Hower, industrial refrigeration sales manager, Danfoss. They specifically looked at it for use in a Canadian distribution facility for fruits and vegetables. “Reaching this correct balance dictated its future direction of warehousing and delivery freshness,” the presenters said.

The presentation focused on what Hower and Rodier called simplicity and reliability for the system.

It was noted, “The ammonia charge is relatively small and restricted to the engine room only. CO₂ pumped emphasizes simplicity, control, and maintenance of modern plants. NH₃/CO₂ components are readily available for 754 psig, making design and construction accessible to OEMs and contractors.”

The result was a “wide range of room temperatures from one CO₂ temperature loop, faster pull downs, limited ammonia charge, and easy startup — within 48 hours.”

This results in what the presenters called a “formula for repeated success” when “supplier’s help and support is crucial, a project is scalable and repeatable and (there is) an integrated approach with measureable results.”

Transcritical Trends

The trend toward transcritical CO₂ systems is becoming “reliable, affordable, and more efficient,” said Brian Porter, corporate director of sales, Blissfield Mfg., who discussed double-stage transcritical compressors.

“This new range (of compressors) features a wide operating envelope being suitable for many applications,” he said. “This two-stage technology allows for several advantages such as split low- and high-temperature systems in typical rack applications so you have less risk. You get the advantage of floating heat pressure also for low-temperature units. There is heat pump operation for low-temperature ambient thanks to high maximum speed.”

He noted, “Two-stage compressors offer interesting solutions to decrease supermarkets’ capital and running costs.”

Propane in Room Air Conditioning

The development of a low-charge propane room air conditioner using smaller-diameter copper tubes was presented by John Hipchen, president, Exel Consulting Group, on behalf of its author, Wenson Zheng, of Copper Alliance Asia.

He noted, “China has aggressively and successfully combined MicroGroove small-diameter copper tube technology with R-290 refrigerant in window and room air conditioners.” He noted that Chinese OEMs are using MicroGroove technology in RAC systems both within the country and for export.

He asked, “Can R-290 MicroGroove RAC in North America be far behind? With R-290-approved by the U.S. Environmental Protection Agency’s (EPA) Significant New Alternative Program (SNAP) and R-290 costs a fraction of R-22 and R-134a, significant reductions in refrigerant charge from MicroGroove technology can make R-290 systems economically viable in North America.” He did say the flammability aspect of R-290 is a concern.

Publication date: 9/2/2013

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