PROJECT
INCORPORATING COLD CHAIN
important to optimise the fan speed and control to reduce power consumption to an absolute minimum .
Due to safety and as a result of the size of the facility , the decision was taken early on in the design phase to use secondary refrigerants in the field and limit the ammonia charge to the plant room . Noting the congestion in the roof void and the travel distances , it was a prudent decision and greatly increased the safety aspects of the overall facility and roof void .
Rainwater harvesting forms a key component of the overall system and facility design . This rainwater is treated to a high quality , to make it suitable for use in the evaporative condensers , as well as site potable consumption . This greatly reduces potable municipal water consumption and also provides a large back-up water source requiring municipal water as back-up / topup only . Of the total 350 000m ² site area , 250 000m ² is utilised for water harvesting . The total estimated water consumption for
The MT ( -8.75 ° C ) suction accumulator generating chilled glycol by means of four off thermosiphon PHEs . the whole site is 125 M litres , of which 69 M litres are consumed by the refrigeration plant . Although a total of 133 M litres are available for harvesting during a year , due to peak rainfall and demand mismatch it effectively results in a total amount of harvested water that can be consumed on the site of 75 M litres per annum
DESIGN CHALLENGES The professional team worked together in an incredibly efficient fashion and were all dedicated to the effective design and coordination of all aspects of the project . The use of BIM was effectively implemented to ensure good co-ordination and integration of all design aspects . This ensured that site clashes and problems were timeously identified and addressed and mostly resolved before the installation took place on site .
The client required an efficient , robust and sustainable design solution that speaks to Pick ‘ n Pay ' s journey of sustainability while also providing a world class facility for their centralised distribution operations .
The facility is divided into two massive chambers . The air distribution in these chambers was critical and formed part of a detailed design investigation . Heat loads were sub-divided into design compartments for various areas such as the docking bays and then central corridors . This informed the placement of the coils and air changes per hour in the various sub sections and regions of the large open areas .
The greatest challenge of this facility design was the appropriate selection of the refrigerant . During the concept design process a multitude of options were investigated . These ranged from primary ammonia to all areas , CO 2 central versus decentralised / distributed plants and even remote or multiple low charge ammonia plants with massive air handling units . Personnel safety , sustainability , efficiency and capex cost guided the final decision .
The three off MT glycol pumps , two duty , one standby each 75kW motors .
In the end the most cost effective and efficient solution was a primary ammonia plant operating at two temperature regimes with the lower of the two open flash economised on the high stage . The secondary refrigerants were water on the high temp side and a propylene glycol solution on the medium temperature side .
EFFICIENCIES AND RELIABILITY There were some specific efficiency decisions that AMC took on this project to ensure optimal energy efficiency . Two of the most notable aspects were a reduced condensing temperature and a tight approach on the secondary PHEs . The
Developing details with the contracting team on site to ensure an appropriate solution .
The plant room showing the HT reciprocating compressors and the HT suction accumulator . The HT reciprocating compressors .
28 www . coldlinkafrica . co . za COLD LINK AFRICA • May 2023