Last December, U.S. retailer Hannaford began orchestrating its first CO<sub>2</sub> transcritical retrofit.
Last December U.S. retailer Hannaford, which has installed transcritical CO<sub>2</sub> booster systems in two new stores since 2013, began orchestrating its first transcritical retrofit at a 50,000-sq.-ft. supermarket in Raymond, New Hampshire.
The 27-year-old store’s racks (R507 for low-temperature and R22 for medium temperature), piping, condensers, evaporators and display cases were all “at the end of their useful life,” said Harrison Horning, director of energy and facility services for Delhaize America, a subsidiary of the newly formed Dutch company Ahold Delhaize; he focuses on supporting Hannaford’s 181 stores in five Northeastern states.
One of the fortunate features of the store from a retrofit perspective was that “there was ample space to put a new system while the old system was running next to it,” said Horning. The space came from moving an old emergency generator outside and removing an old air-conditioning rack.
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<strong>First with parallel compression</strong>
The Raymond store retrofit, which provides 1.8 million BTUs/hr. of total heat of rejection, is Hannaford’s first transcritical system with parallel compression. It is also the first transcritical system to use hot high-pressure CO<sub>2</sub>gas for direct heat reclaim in a main HVAC unit.
In the store’s walk-in freezers and coolers, and in its compressor room, Hannaford has installed CO<sub>2</sub> leak detection, “respecting ASHRAE 15 and 34 requirements,” said Horning.
A notable construction challenge in the retrofit was that the transcritical rack needed to be simultaneously hooked up to low-temperature and medium-temperature loads in new cases overnight to allow start-up.
“In a new store, you don’t think about that because it happens when nobody is looking,” said Horning. “In this case, it happened overnight, because we needed to be open and operational the next morning.” But the operation was “planned well and it worked OK”. Subsequent cases were phased in over the ensuing weeks.
Hannaford decided not to run some of the store’s display cases on CO<sub>2</sub>, and those were linked to a separate R407A condensing unit. “So, the store is not 100% CO<sub>2</sub> but it’s well over 90%", Horning noted.
Horning offered some caveats about doing a transcritical system retrofit. One was to “make sure that when the equipment leaves the factory, it’s ready”. In May, the system sprung a refrigerant leak after a fitting cracked. This was because the system was intentionally designed with additional pressure transducers on the high side and thus more threaded connections. “So, pay attention to factory engineering.”
He also advised having round-the-clock technical support available. This was true at the Raymond store, which also required skilled welders to work on stainless-steel piping as well as people with controls expertise.
Hannaford would like to find at least one store every year or two that similarly meets the criteria for retrofitting to a transcritical CO<sub>2</sub> system.
Source: <a href="http://www.r744.com" target="_blank" rel="noopener noreferrer">www.r744.com</a>