Expansion makes Fourways Mall biggest in South Africa

By Martin Davis, Pr Eng  B.Eng (Mech) – Spoormaker & Partners

The Fourways Mall project consists of various smaller renovations and additions, but the major portion is the addition of 90 000m² of retail space.

The new mall construction started in 2016, although the planning started more than 10 years ago. It was to open mid-2018, but due to project delays only opened in August 2019. The addition to the existing 87 149m² construction makes Fourways Mall the largest mall in South Africa.

The design specification was to provide an overall cost-effective and practical HVAC system suitable for a modern mall operation. Important design specifications, among others, were:

life cycle costing

system flexibility due to constant tenant churns

Per-tenant energy measurement and billing

The HVAC system information

The concept chosen was a closed-circuit condenser water system with DX water cooled package units, and decentralised un-conditioned fresh air. The main reason this system was chosen was for the system’s relatively low life cycle cost, high level of flexibility and capability of per-tenant billing.

The new mall development section consists of the following systems:

2097kW Evapco closed circuit cooling tower (eco-ATWB-H 12-4L18-U22). Imagecredit: RACA Journal

Central closed-circuit condenser water plant

The main cooling tower plant consists of five towers with dry cooling capacity to reduce water usage and allow for partial cooling during domestic water shut-down periods. Closed circuit cooling towers are used to ensure that the water circulated to the DX package units is clean and does not foul the heat exchangers on the DX units in the shops. This ring main consists of more than 8km of piping.

Condenser water is circulated through a ring main pipe system on the mall levels. The various shops are each provided with tap-off valves into the main condenser water pipe ring in direct proximity to the shop, enabling each tenant’s DX package units to obtain its cooling water from the ring.

Two air-cooled heat pump chillers are installed in the main cooling tower plantroom to introduce heat back into the condenser water circuit for when there is a net heating demand within the mall or if the condenser water temperature drops too low.

Shop/tenant air conditioning system

The DX package A/C units consist of an air-filter, refrigeration circuit with compressor, evaporator and water-cooled condenser, and supply air fan. Two types of units are distinguished – for smaller shops, in-ceiling type A/C units are installed, while the larger shops are provided with floor standing, up-blow A/C units positioned in a plantroom within the tenant-area.

The units supply filtered and conditioned air into the shop via externally insulated galvanised sheet metal ducting installed within the ceiling void. Air is deposited into the shop via CAV type ceiling diffusers.

The return air passes through return-air grilles and a shop’s common ceiling plenum space. The DX package A/C units are energised from the tenant’s electricity distribution boards (DB), and the energy consumed by these units is thus measured and can be paid for directly by the tenant. The indoor air temperature is controlled through a wall-mounted set point adjuster that allows for individual temperature set point control.

Shop/mall ventilation system

There are four central fresh air plants, each with three fresh air units that provide filtered, un-conditioned fresh air to the central shop and mall walkway areas. Filtered fresh air is distributed to the central zones through galvanised sheet metal ducts routed above the shop ceilings. These common ventilation systems can also be used in reverse for smoke clearance. Ablution blocks are mechanically ventilated with dedicated extraction systems.

The induction jet fan for smoke clearance in the lower parking area. Image credit: RACA Journal

Parking area ventilation system

The parking areas are mechanically ventilated. These systems are also used as a smoke clearance system, together with the use of jet/trust fans.

Project challenges

An element of difficulty experienced in this development was related to services co-ordination. In a constantly changing retail environment the various designs and services needed to be updated and coordinated before being installed on site.

Another item was the fact that the new mall is constructed from precast hollow core concrete panels, which means that vertical penetrations had to be planned for long in advance. The meticulous coordination process that was followed, led by the architect, allowed for these challenges to be overcome.

Unique project element

What essentially makes the system unique is the sheer size of the installation and volume of components involved in the installation.

The applied design allows each shop to have its own A/C unit, thus allowing for a high level of redundancy throughout the mall. This is a vast improvement from systems that have one large centralised A/C unit that serves multiple tenants, which often have different heat load profiles.

The centralised condenser water plant and ring main piping system allows for diversity to be maximised and further improves redundancy. The main cooling tower plant consists of five cooling towers with dry cooling capacity to reduce water usage and allow for partial cooling during domestic water shut-down periods

“Changing of user habits generally yields more energy saving than just having an overall energy efficient system.”

The primary condenser water pump assemblies. Image credit: RACA Journal

Energy Saving

To a large extent, per-tenant billing is catered for with this design – energy consumption can thus be reduced due to tenant accountability. Changing of user habits generally yields more energy saving than just having an overall energy-efficient system.

This system provides the user with a system where they can benefit directly from improving on their energy usage habits.

This system also makes use of individual A/C units, which allows for certain areas to be switched off if they are not trading. This then ensures that energy is not wasted on cooling un-occupied areas.

The HVAC system itself is simple and robust. The system was designed this way so that it would allow for maximum flexibility, be easy to operate and easy to maintain.

Taking into account all the variations necessitated by tenant-extras and tenant-changes, the project was run within budget. 

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