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GreenChill webinar explores NH₃ retail refrigeration in the US - part 2

2010-08-26 - ammonia21.com

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In the second part of the webinar on ‘Ammonia Use in Commercial Refrigeration’ organised by the Greenchill Partnership, Eric Smith of the International Institute of Ammonia Refrigeration discussed theoretical and actual layouts of ammonia supermarket systems. The subsequent Q&A session was much focused on the possibility of heat recovery.

GreenChill webinar explores NH3 retail refrigeration in the US - part 2

GreenChill webinar explores NH3 retail refrigeration in the US - part 1

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The use of ammonia in US supermarkets has to be in secondary loop systems, with ammonia being the primary refrigerant restricted outside the store. Keeping the ammonia charge as low as possible is also an important aspect to take into account.

That being considered, Eric Smith, Technical Director of the International Institute of Ammonia Refrigeration (IIAR) discussed different ammonia supermarket refrigeration system layouts that could be applied in US supermarkets:

Propylene glycol for the medium temperature (MT) and CO₂ for the low temperature (LT): the high side secondary loop would be placed on the roof, while the CO₂ cascade system would either be located on the roof or inside the building. In this concept, the number of limited charge water cooled NH₃ modules would be adjusted to meet the load required by the store.

CO₂ used for both MT and LT: For the MT an evaporative brine system is used whereby both liquid and gas returns back to the receiver.

Coles supermarket in St. Mary’s, Australia employing an ammonia/CO₂ refrigeration system, whereby the LT side uses a CO₂ DX cascade system while the MT uses a CO₂ secondary coolant system. Two flooded NH3 modules for the primary system are placed on the roof and employ 50kg of ammonia refrigerant each, with the CO₂ system is located in the mezzanine below.

Ammonia air-cooled chillers with weatherproof housing and scroll compressors developed by MAYEKAWA installed in Japan: Japan is still embracing the idea of using ammonia systems for supermarkets despite being a seismogenic country.

Components for the NH₃ modules

The presenter discussed the latest trends with regards to components used in NH₃ modules:

Compressors: open drive compressors are currently available, though they usually apply to larger systems, while semi hermetic drive compressors and scroll technology for hermetic constructions are being developed. Although copper may not be used in an ammonia system, many manufacturers are looking into using aluminum windings and miscible oil along with the system.

Heat exchangers: there could be several different scenarios in terms of layout of the high side heat exchanger, which takes heat from the ammonia, rejects it into the water and which in turn is piped to a fluid cooler. For example one could have the ammonia discharge to an evaporative condenser or even to air cooled condensers. Regarding the low side, Smith noted that microchannel heat exchangers are becoming cheaper and more prevalent thanks to improved manufacturing techniques, allowing the industry to create packages with much smaller footprint yet still very efficient.

Heat recovery: would it make sense with ammonia supermarket systems?

Replying to a question posed by a webinar participant on whether there is any thought given to using the fluid cooler to reheat either the store or water, Bruce Badger of the IIAR argued that although the technology is already there for industrial applications, it may not by economically feasible in supermarkets, as a separate sub system would be needed to increase the quality of the discharge heat such that the temperature difference between the water and the discharge gas would be greater.

On the same topic, another webinar participant confirmed that the technology for industrial applications is rapidly advancing to enable the use of compressors to take the discharge pressure to much higher levels, corresponding to much higher temperatures for full heat pump duty and full reclamation of the total heat rejection. However, how these advancements on the industrial side would convert over to the commercial side remains to be seen.

A final comment on the same topic by another participant pointed out that water heating has been broadly used in supermarkets as a way to increase efficiency and supply hot water. He noted that with ammonia refrigerant it would make even more sense than with traditional refrigerants such as R404A and R407, as the discharge temperature is much higher with ammonia. However, on the downside, the ammonia charge would have to be increased.