Transcritical CO2, leveraging waste heat and supported by solar energy, was found to be the lowest-cost option for South Coast Stores.
Adiabatic gas cooler for transcritical CO2 system
South Coast Stores, an Australian wholesaler in the remote town of Nowra, New South Wales, has opted for a CRS/Sphere transcritical CO2 system that uses solar energy and employs the waste heat from the refrigeration system for hot water and heating requirements.
The cold-storage component was commissioned in January, followed by the retail space in February. Other refrigeration options, including ammonia and HFCs, were rejected.
South Coast Stores is a joint venture between V&C Food Distributors, and Cream of the Coast, the Streets Ice Cream distributor in Nowra. The aim of the venture was to replace the aging facilities of these two companies, both of which were nearing the end of their lives, with a new, modern building.
The new facility includes an extensive dry-storage area, large freezer storage primarily for ice cream, a large cool room primarily for dairy products, an ante room with truck-loading bays, a meat-processing area with a work-in-progress cool room, and an extensive retail area with chilled and frozen display cases and an aged-meat display case.
The facility has many design features to limit energy use, including thick concrete walls, well-insulated roofing, under-slab heating with refrigeration waste heat, underfloor heating in the retail area, domestic hot water (from waste heat) and a 100kW solar installation.
South Coast Stores hired Australian engineering consultancy Minus40 Engineers to assist with the design of the facility. Its task included assisting the builder during the early design, selecting the insulation paneling and the refrigeration, air-conditioning and hot-water services, assisting with the selection of refrigeration and paneling contractors, and inspecting the site work of both contractors.
South Coast Stores was sensitive to the risks associated with HFC use and the future availability and cost of candidate HFCs, such as R407F and R448A. It was therefore open to the idea of using long-term replacement refrigerants such as CO2 or ammonia, said Michael Bellstedt, Managing Director of Minus40. “Minus40 advised against the use of any HFC refrigerant at an early stage of the project, based on the known phase down and environmental risks of synthetic refrigerants.”
Minus40 conducted an extensive budget analysis and modeled the expected annual energy consumption of both considered options, ammonia and CO2. Ammonia is more energy efficient, but not enough to compensate for its higher capital costs. (He did not provide energy consumption data.)
“The commercial viability of an ammonia plant versus a CO2 plant with solar PV was found to be unattractive, and therefore a full CO2 plant with booster and parallel compressors and an adiabatic gas cooler was chosen as the lowest-cost option,” said Bellstedt. The CO2 system provides 256kW (55.8TR) of total cooling capacity.
Small- to medium-sized refrigeration systems are relatively more costly with ammonia than with CO2 (though this differential reduces for larger plants), according to Bellstedt. “The payback on the additional capital cost, both of the CRS/Sphere transcritical CO2 rack refrigeration plant and enhanced building requirements, was found to be in excess of the expected life of the [ammonia] plant, and therefore the decision was taken to go down the CO2 path only for tender purposes.”
“Transcritical CO2 in this application made sense over freon for obvious reasons and is far more cost effective over ammonia in this application,” noted Shaun Davis of MB Refrigeration, the refrigeration contractor for the project.
The CO2 system had a “negligible incre- mental upfront investment cost relative to a freon system,” added Mark Brennan, Director of Cream of the Coast.
Bellstedt noted that he is an “avid proponent” of natural refrigerants for all applications of refrigeration and air conditioning. Moreover, he believes that ammonia will provide “the most energy efficient solution in nearly every application, and I consider this statement to be indisputable.”
However, he added, every application needs to be considered individually, as the energy penalty associated with the use of CO2 “can in some cases be small enough to render the additional cost of implementing an ammonia system unviable.” Often, spending only some of the cost differential on a solar PV system “can negate the energy penalty or render the remaining energy benefit of an ammonia system even less viable.”
In this case, due to the relatively mild summer climate in Nowra, operation of the CO2 system in less efficient “transcritical mode” is expected to be rare, even in Australian summer months of January and February, explained Bellstedt.
In addition, other site considerations and even end-user prejudices can render an ammonia system unsuitable or unpalatable, said Bellstedt. “Hence, whilst my first preference will always be an efficient, charge-minimized ammonia system, situations in both commercial and industrial applications exist where a CO2 system can be preferred.”
THE RIGHT CONTRACTOR
Finding the right contractor to assist with the installation was critically important, explained Cream of the Coast’s Brennan. “Making sure the contractor had experience with CO2 systems and the support of the manufacturers/suppliers was a key factor in selecting our partner,” he said. Contractor MB Refrigeration was the choice.
“The choice of location (Nowra) for such an innovative project was unfortunate as it limited the choice of interested contractors,” explained Bellstedt. “MB Refrigeration must be applauded for their enthusiasm for the project, and for the competitive pricing submitted by them. This made the project commercially attractive to the client.”
MB Refrigeration made the commitment during the tender phase to work with a preferred local refrigeration contractor during the installation and commission to ensure that local skills are developed to support service work after the warranty period. This was a key factor for South Coast Stores in its decision to choose MB Refrigeration.
This was also the first transcritical CO2 installation in Australia using Frascold Controls for transcritical CO2 rack compressors, confirmed Giovanni Lo Nero, Sales Area Manager for Frascold. Frascold came on board when the contractor MB Refrigeration insisted on using its compressors.
One of the major challenges during the project was unrelated to the refrig- eration system. Significant delays were experienced during the building approval process, ultimately delaying the project by more than 12 months. This delay coincided with a change in local arrangements for the preferred supplier of evaporators, resulting in a dramatic and unacceptable increase in local pricing. Therefore, the system design had to be switched to other suppliers, further delaying the project’s completion, explained Bellstedt.
MB Refrigeration used this opportunity to offer hot-gas defrost as opposed to the specified warm-glycol defrost, significantly simplifying the site installation. “The wisdom of the decision to move to hot-gas defrost will be evaluated in the coming months, but initial observations indicate that the technology works well,” said Bellstedt.
Freezer (low-temperature) capacity: 108kW (13.7TR) at −25°C (13°F) SST
Medium-temperature capacity: 148kW (42.1TR) at −7°C (19.4°F) SST
Compressor supplier: Frascold (Italy)
Rack Manufacturer: CRS/Sphere (South Africa)
Rack arrangement: Six medium-temperature compres- sors, three booster (low-temperature) compressors, two parallel compressors
Gas cooler, desuperheater and evaporator coil supplier: HC Heat Exchangers (South Africa)