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From HFC to natural ahead of Kigali phase-down

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By John Ackermann | All images by John Ackermann

The Woolworths store at the V&A Waterfront, the jewel in the crown of South Africa’s tourist attractions, has been converted from HFC 404A to natural CO2 refrigerant.

The V&A Waterfront is visited by thousands of tourists, local and overseas, each year and delegates of the Kigali Amendment Workshop held in Cape Town, were taken on a guided tour of the new Woolworths CO2 refrigerant plant on 5 December 2019.

The V&A Woolworths store on two floors in the Victoria and Alfred Shopping mall was opened in 2008. To enhance the convenience of the growing number of shoppers, the trading area was extended across three floors in 2019. The food market on the ground floor was moved to the basement into a space gained from the parking area. A new refrigeration plant room, back up cold stores, freezers and display cabinets, were installed and only once operational, was the food market on the ground floor, with a R404A charged refrigeration plant, decommissioned. The changeover was done without any interruption to the trading of perishables and welcomed with awe by shoppers when completed.

Journey to green cooling

The conversion to CO2 refrigeration plant is in line with the policy of Woolworths to have all new supermarket refrigeration systems charged with CO2 and have the lowest energy usage.

The refrigeration plant has two similar trans-critical parallel booster racks designed, manufactured and installed by Mainstream Refrigeration. The swing to CO2 from HFCs started at a slow pace in 2008 with cascade subcritical systems. Although not the first in Woolworths, Mainstream Refrigeration installed a sub-critical CO2/R134a plant at the new Woolworths store in Palmyra Junction in 2010. The plant is still operational and in 2013, Mainstream Refrigeration installed a trans-critical plant at the new Waterstone store in Somerset West. To reduce energy usage further, a trans-critical parallel booster CO2 plant was installed in 2016 at the Woolworths Cascades store in Pietermaritzburg.

Mainstream Refrigeration have installed in excess of 42 trans-critical CO2 sites for Woolworths in Richards Bay, Bloemfontein, Pietermaritzburg, Durban and Cape Town. Commercial Refrigeration have installed the many trans-critical plants at all the new Woolworths stores in the densely populated Gauteng and Northern regions.

Each of the racks at the V&A can handle 75% of the refrigeration load of the 37 medium temperature (MT) (2 to 4oC),display cabinets, 5 low temperature (LT) (-25oC) cabinets, three back up cold stores (2 to 4oC), two freezer stores (-25oC) and a holding store (2 to 4oC) at the receiving bay on the ground floor.

Each rack has six Frascold semi-hermetic compressors, two on the medium temperature circuit (-5oC suction), two on parallel compression/MT and two much smaller compressors on the low temperature. The installed refrigeration power on each rack totals 98kWr on MT/Parallel and 15kWr on LT.

Built and tested at the Mainstream Refrigeration factory in Ottery, the overall dimensions of racks fit through a standard height doorway.

Reduction in energy usage

CO2 as a refrigerant with zero ODP and a GWP of 1, has reduced the environmental carbon footprint of Woolworths’s refrigeration plants and with other interventions, has reduced energy usage.
Variable speed drives on each rack compressor to balance the temperature set point closely with the refrigeration demand of all the cabinets and cold freezer rooms is one of many design features to reduce energy usage to a minimum. Floating suction temperatures to match demand, electronic expansion valves, parallel compression, EC variable speed fans (4 x 800mm diameter) on each of the two roof mounted gas coolers, air defrost on the MT cabinets, alarms to warn when cold room doors are left open, all contribute towards lower energy usage. For food safety and quality control, the temperature of product in the different cabinets are closely monitored by probes in artificial ‘hams’ which have the same thermodynamic properties as the actual product in the cabinets, for example chicken, cheese, milk.

“As part of our environment policy at Woolworths, refrigeration plants need to be green within due financial consideration and low on energy usage. Trans-critical CO2 refrigeration has also meant our plants do not consume any of that very valuable natural resource, water. LED lighting in cabinets, double glazed doors on all LT cabinets and acrylic doors on MT cabinets, except those with fresh produce, have been introduced to conserve energy usage, which is a major contributor towards global warming,” was said by Alex Kuzma of Woolworths during a tour of the V&A store.
Continuous improvements and added design features have reduced energy usage of Woolworths stores to an average of 50% of the total store usage. A separate power meter to monitor the total power usage of the entire refrigeration plant is a standard feature at Woolworths supermarkets.

CO2 leakage is a safety concern as it will cause asphyxiation by replacing the oxygen level in confined spaces. The plant room, cold stores and freezer stores are fitted with CO2 alarms and outside mounted buzzers and lights to indicate levels of CO2 by different coloured lights. The plant room sensor also activates an exhaust fan in the event of a severe CO2 leakage. The trading area has no CO2 sensors. In the most unlikely event of the entire CO2 charge of 500kg discharging into the trading area, because of its size, the concentration will not exceed the safety limit for human occupancy.

Safety and noise pollution

The CO2 safety levels, operating parameters, temperature alarms, power usage, cabinet temperatures are all monitored and controlled by the Guardian Controls Plant Management System with visual monitors for management staff and with remote access by senior staff of Mainstream Refrigeration. The RH and ambient temperature in the store is also monitored by the Guardian Controls PMS to keep store management informed of shopper comfort.

Being close to the Table Bay Hotel, the noise level of the roof mounted gas coolers at the V&A store was of concern and was overcome by fitting ebmpapst Axitop and EC variable speed fans.
The relocation of the food market at the V&A started during the first quarter of 2019 and was commissioned before the end of November.“Replacing 1250kgs of R404A (GWP 3922) with a CO2 plant at the V&A and all the energy saving features, has provided further proof that CO2 refrigeration is the best solution to achieve our green policy.” Kuzma concluded.