By Andrew Minnaar Pr Eng, AMC Engineers and Andre van der Merwe, managing director of Evapco South Africa; edited by Eamonn Ryan
Scale was the unique characteristic of the Pick ‘n Pay Distribution Centre HVAC&R project, being probably the largest such project of the past 12 months, as well as the largest distribution centre in the southern hemisphere.
While the project is predominantly a refrigeration one, so significant is its scale that the lesser HVAC component nonetheless represents a major project.
The development covers 36ha of state-of-the-art infrastructure and is currently being commissioned. It is part of a larger project to position the Eastport Logistics Park, near OR Tambo International Airport in Gauteng, and the broader R21 area, as South Africa’s prime logistics hub as allied industries and businesses seek proximity and rational integration into the country’s leading logistics ecosystem.
However, the complexity of the HVAC&R project stemmed less from its size as in having multiple different cold rooms, multiple different temperatures and multiple different smaller areas each with different considerations. This distribution centre is an undoubtedly sizeable one with large areas catering to massive amounts of product.
The Pick ‘n Pay Distribution Centre project at OR Tambo International Airport in Johannesburg is a state-of-the-art facility that serves as a hub for the distribution of goods to Pick ‘n Pay stores across the region. The project was designed to be highly energy-efficient, incorporating a range of innovative technologies to reduce energy consumption and minimise its impact on the environment. One key component of the project was the HVAC system, which was designed to be highly efficient and environmentally friendly.
The project serves as a model for sustainable building design and demonstrates the potential for the HVAC industry to contribute to a more sustainable future.
During the design of this facility special care and time were taken to optimally design the air side of the facility. As with most facilities or cooling designs where the heat is removed from the space via air, the flow and distribution as well as selected conditions of the air comprise a critical and often overlooked consideration.
The facility in its final configuration has 80 coolers in the +2°C area and 24 coolers in the +14°C area; each cooler is equipped with four 700mm EBM EC fans capable of delivering 18 850 m³/h (5.236 m³/s) of air. This results in a total of some 545m³/s of air being displaced in the facility, at a peak fan power consumption of 145kW, to provide the cooling required. It is clear that careful consideration is to be given as to how this air is distributed and optimised to provide the cooling to the facility.
As this facility was extremely high, some 18.9m at the centre and 11.6m at the dock faces, the air volume in the centre of the facility is much larger than at the dock faces. This was advantageous as the coils were equally spaced and thus created a higher air change rate at the dock faces where the instantaneous heat load could be quite high at times due to the infiltration loads. The design allowed an air change rate of some 16AC/h at the dock faces resulting in an average distribution velocity of 0.27m/s which sufficiently deals with the high peak infiltration loads. The inner half of the warehouse was designed to have slightly lower air change rate of eight air changes per hour and an average distribution velocity of 0.22m/s.
Crucial consideration was the actual airflow interaction between coils – initially the coils were placed in a three-row spine row orientation with two back-to-back coolers in the middle of the facility and a single row at each dock side, all blowing towards the dock. During the detail design phase it was recognised that there might be poor cooling by the dock row of coils as the cold air from the centre row will be blowing into the rear of the dock row of coils. This might result in a higher dT over the product and possible warm spots below. It was decided to move the centre back-to-back row towards the dock rows and rather make two back-to-back rows of coils on either side of the facility as shown in the schematics below. This resulted in a better air distribution in the space and completely eliminated the middle pipe run and pipe bridge.
Andre van der Merwe, managing director of Evapco South Africa, explains that for this project Evapco was the successful supplier of the system, including the industrial level, evaporative condensers.
“Evapco continually strives through its vast research and development programme to design and supply products focused on:
- Higher system efficiency
- Environmental responsibility
- Lower annual operating costs
- Reliable simple operation and maintenance
“The equipment was selected and specified by the consulting engineers AMC Consulting.
The units were supplied via the main refrigeration contractor Marine & Refrigeration Engineering (Gauteng). The units supplied were three off Evapco Model No. PHC S715. These are induced draft, counterflow, belt drive axial fan two stage evaporative condensers. The units are ‘twin cell’ configuration each,” explains van der Merwe.
These units are each rated for ammonia condensing at 2 300kW total heat rejection.
This is to be achieved at a lower than standard 30.0 °C condensing temperature for optimum system efficiency.
He explains that the PHC Range units offer the highest cooling efficiency and cost-effective solution in the industry.
Some of the unique features included in the unit supply are:
- Integral external access platforms
- ‘Sun Blocker’ inlet louvers to prevent biological growth and ingress of debris and water splash-out
- High Premium Efficiency fan and pump motors
- Non-fouling low maintenance ‘ZM’ spray nozzles
- Evapco unique patented ‘Oval Tube’ Sensi-Coil design
- Automated electric water level control package.
“The condensers were 100% manufactured locally in our facility in Isando, Kempton Park.
The order for the condensers was received mid-December 2021 and required delivery to site mid-April of 2022.
“This is most definitely a significant size project and fortunately this was after the main Covid lockdown, and we had a sufficient time frame of four months to complete manufacture. We did, however, like most local manufacturers, experience stock shortages of certain key components in our supply chain, but we succeeded in getting the units ready by the required deadline.
“Due to the size of these condensers each unit ships in four sections; two off basins and two off top casing sections, for a total of 12 sections. That meant that coordinating the logistics to site needed some careful planning. Over and above, these sections are all abnormally wide and so required special freight permits with an escort.
“The one beneficial factor was that the new site in East Port Logistics Park is less than 20km from our factory. Our own in-house Mr.GoodTower Service crews were on hand to assist with the site rigging and assembly to ensure the units went together without any delays or issues.
“Evapco is certainly proud of being parts and successful supplier of choice for this prestigious project for Pick ‘n Pay, our Main Contractor MRE and Consulting Engineers AMC,” says van der Merwe. Last year Evapco SA celebrated its 40th anniversary of operations in South Africa. Evapco SA manufactures and supplies the full range of Evapco products under licence to Evapco Inc. USA.
The consulting engineer’s description of the refrigeration component
The facility is one of the largest, if not the largest, temperature-controlled distribution centre in South Africa. The overall site is 360 000m², of which 150 000m² is distribution area. Of that, 45 000m² is the temperature-controlled distribution area and forms the portion of the development that AMC was involved in. For this project, AMC completed the design, tender and site supervision of the insulated structures as well as the HVAC to all ancillary buildings.
Provision is made for a future heat pump, utilising the discharge gas from the primary plant and compressing it to 70°C saturated conditions in order to generate hot water in the future, if required. The plant has been equipped with VSD on all major component motors to ensure that part load conditions are optimised and energy savings are being realised during part loads conditions.
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/top-up only.
Design challenges: The professional team worked together in an incredibly efficient fashion and were all dedicated to the effective design and co-ordination 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.
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 condensing temperature was selected at 30°C, resulting in a 9K approach on the design ambient wet bulb condition. All condenser fans were equipped with VSDs to ensure fan law efficiencies were maximised during low load conditions, exponentially increasing efficiencies as load decreased.
The PHEs were selected with a very tight 2K approach resulting in a 4K LMTD for the HT and MT systems. What this further allowed is for the system to be able to operate with a PHE out of service by reducing the suction temperature by only 0.7K on the MT system and 2K on the HT system.
System reliability and redundancy is absolutely critical for this type of facility, considering the centralisation of the client’s distribution and the associated business and product value that moves through this facility. Redundancy was incorporated as responsibly as possible while ensuring that single points of failure were eliminated as far as possible. A further aspect that was implemented in the design is that where redundancy was required, it was employed to increase efficiency during normal operation, that is running the compressors at lower speeds for recips, running a reduced number of screws at full load on the MT system and reducing condensing temps and fan speeds on condensers. These energy savings elicit significant paybacks on the required redundancies and make the overall installation significantly efficient.