New R4BN Oceans mall Umhlanga gets chilled water plant

By Ashlee Moodley Pr.Eng, director: RPP KZN Consulting Engineers, edited by Eamonn Ryan | All photos by RPP KZN Consulting Engineers

The Oceans Umhlanga development is a mixed use billion-rand development situated in the Umhlanga Village. The consulting engineers were RPP KZN Consulting Engineers and ADX Consulting Engineers.

Development at the R4-billion mixed-use Oceans Mall has reached a critical phase allowing it to open to the public. Two of the proposed three phases are complete with the five-star Radisson Blu and Oceans Mall open to the public. The third phase is made up of two residential towers with +/- 500 residential apartments. The mall comprises of a world-class shopping mall with over 100 stores.

Two of Africa’s largest state-of-the-art retailers anchor the mall, while it also promises to offer a variety of speciality stores and including international superbrands, such as Burberry, Versace, Armani and Paul & Shark. Apart from retail, the mall will provide a range of leisure and entertainment activities such as Fit 24 (24-hour gym), and 20 world class restaurants.

The project initially commenced in 2015 with the first phase of construction beginning in 2018 with the Hotel. The project was then put into a sleep period for various reasons, starting up again towards the latter part of 2020. When the Hotel was midway through, work began on phase 2 ­– the Oceans Mall. The Hotel was completed in October 2021 and the Mall in November 2022.

The design brief was to design a central chilled water plant similar to that of a district cooling plant that would service the various buildings as part of the development. This required multiple chillers, each with standby and duty pumps sets. Efficiency and space requirements played a major role in the selection of the chilled water system. Being less than a kilometre from the shoreline, a water-cooled chilled water system was selected for its efficiency and longevity as there are less components exposed to the elements when compared to air-cooled systems.

Maintenance costs reduced

The central chilled water system was the system-of-choice based on lowest overall energy consumption, lower maintenance costs and most economical plant space requirements. The same type of system is used extensively for mixed use developments in Dubai. The use of a central system allows better provision for redundancy without duplication in numerous separate systems. It also allows better use of diversity which is substantial in a mixed-use development.

The system provides a long lifespan, in the region of 25 to 30 years with proper maintenance. Overall maintenance costs are reduced as there are fewer moving parts when compared to air cooled alternatives.

The bulk of the power supply is centralised, which is more cost effective and economical. The challenge of recovering energy usage and maintenance is achieved by the installation of energy meters for all users as follows:

• Hotel at main supply
• Residential at each apartment
• Retail at each zone Air Handling Unit

The energy meters accurately measure chilled water flow and temperature to summate kW cooling, allowing apportionment of running and maintenance costs according to actual usage. Each of these meters transmit the readings to the central BMS/Billing System to be provided by the electronics engineer.

Air conditioning – central plant

The installation consists of a centralised water-cooled chilled water system with multiple chillers consisting of a mix of base load high efficiency centrifugal chillers and intermediate step load high efficiency screw chillers. The chillers together with the Chilled Water and Condenser Water Pumps are positioned in an enclosed plant room on Level 4 of the development.

The chillers are served by a number of open-circuit cooling towers which are mounted in an open plant area situated at the back of the site so as to avoid noise pollution to the Hotel and residential blocks.

Each chiller is interconnected with one or more cooling towers by means of galvanised steel condenser water piping and condenser water pumps including standby pumps. Chilled water is circulated to each building by means of insulated medium black steel ring main piping and chilled water pumps including standby pumps.  At various plantrooms, there is a dedicated heat exchanger and a tertiary chilled water pump station which services each building. This includes each residential block, Hotel block and retail.

Three identically sized pumps with variable speed controllers, two run and one standby, are provided for each. Chilled water shall then be circulated within its own loop per building/user thereby eliminating the risk of a water leak affecting the entire main plant and avoiding unnecessary pumping power losses.

An energy meter is installed in the primary leaving chilled water piping to record the amount of chilled water supplied to the building by the chillers and to track the thermal energy used by the plant.

Chiller control

• Primary Chilled Water Circuit: All four chillers are able to run simultaneously to provide the full load for the chilled water system to the building and controlled by a central chiller plant controller as well as an electronic BMS control system. An excess/deficit meter is installed in the primary/secondary decoupler piping which dictates how many chillers are required via the electronic control system. On start-up of a chiller, its primary chilled water pump starts up. After a 20-minute time delay the excess/deficit meter dictates if the primary flow is still in deficit and whether another chiller is required to start up. This process is repeated to start all four chillers if required. While chillers are in the run mode they maintain a chilled water leaving temperature of 5°C. When the excess/deficit meter is in excess mode (too much chilled water in the primary circuit) it stops the chillers as required in a timed delay manner. When a chiller stops its primary and condenser water pumps also stop.
• Secondary Chilled Water Circuits: When the primary chilled water system is requested to start up the chillers by the electronic control system, the first secondary chilled water pump starts up. When flow is established, and after a short time delay, the second and third secondary chilled water pumps start up in a similar manner. Only a maximum of three pumps run and one pump is a standby. The secondary chilled water pumps provide chilled water to various heat exchangers in the building through a system of insulated steel piping. The heat exchangers have two-way or three-way control valves in the piping system to regulate the amount of secondary chilled water flow through them to maintain a constant chilled water leaving temperature. To accommodate the varying secondary chilled water flow, the secondary chilled water pumps have VSD drives for the pump motors which are controlled by a differential pressure monitoring system in the secondary chilled water piping and this varies the speed of the pumps. Each heat exchanger system has an energy meter installed in the secondary chilled water piping to record the amount of chilled water supplied to the heat exchanger.
• Tertiary Chilled Water Circuits: The tertiary chilled water is provided from the heat exchangers and provides chilled water to the various air handling units and fan coil units serving the various buildings. Tertiary chilled water is pumped by a pump adjacent to the heat exchangers through an insulated steel piping system to the various units. Pumps on the tertiary loop are in a standby and duty configuration. The air handling units and fan coil units have a two-way valve control valve at each unit to vary the flow of tertiary chilled water through them to control the air temperature leaving the units. Some units at the ends of the tertiary chilled water pipe runs have three-way control valves to ensure that there will always be water flow at the ends of the piping system. Since the water flow through each unit shall vary according to their load requirement the tertiary chilled water pumps have VSD drives on the motors to vary the speed of the pumps according to the varying flow requirements.

Hotel and residential apartments tertiary systems

• Hotel and retail areas: These areas are served by constant and variable air volume chilled water air handling units all installed in enclosed masonry plantrooms and ceiling voids. Air distribution is through P3 ducting with a mixture of ceiling diffusers and side wall outlets.
• Hotel bedrooms: Each bedroom is served by an in-ceiling chilled water fan coil unit. Air distribution is via P3 ducting and single deflection side wall grille. Fresh air is preconditioned via an energy recovery wheel and is distributed to each in-ceiling fan coil unit position via externally insulated galvanised ducting and volume control dampers. Return air back to the fan coil units is via a single deflection return air grille complete with volume control damper and sound baffles mounted in the ceiling. The showers and ablutions in the Hotel bedrooms are serviced via the heat recovery wheel. Disk valves are installed in the flush plaster ceilings and used to extract the steam from the showers and odours from the ablutions. This air is then returned via insulated ducting back to the heat recovery wheel. The heat recovery wheel has a cooling coil and hot water coil for pre-treating of fresh air. During winter months, when the temperature drops below 20°C ambient, a dedicated heat pump will supply hot water and the ambient air will be heated and delivered to the in-ceiling fan coil units in the bedrooms.
• Back of house offices and ancillary: Back of house offices, conference venues and server rooms are served by variable air and constant air volume chilled water air handling units installed in enclosed plantrooms and within ceiling voids all as shown on the drawings. Air distribution to each area is through P3 and ceiling mounted diffusers. Storerooms and refuse rooms are ventilated via extract ducting, inline axial fans and discharge weather louvres complete with vermin proofing.
• Kitchens: Fresh air into the kitchen areas are via externally positioned vermin-proofed weather louvres connected in line with a primary filter bank, axial flow fan, sound attenuators and discharge grilles. Kitchen canopy extract air is via associated axial flow fans and 1mm thick galvanised ducting, with 300°C duct sealer which discharges to atmosphere.
• Public ablutions: All toilets are mechanically ventilated through axial flow fans and associated ducting systems, which are discharged to atmosphere.

Retail tertiary systems

• Major and mini-major stores: These areas are each served by chilled water air handling units (AHUs) situated in closed plant rooms. Chilled water is supplied from the main central chilled water system via the retail tertiary pumping system. Conditioned air from each unit is supplied through systems P3 ducting and distributed to the areas through ceiling type diffusers. Re-circulated air is returned through grilles positioned at the rear of the store and the ceiling void is used as return air plenums back to the AHUs. The required quantity of fresh air is introduced through external louvres mounted in each plant room. The plant is automatically controlled to provide the required temperature conditions in summer and is switched on and off automatically at the plant control. A manual override control, which allows each plant to operate for a maximum of two hours when actuated, is positioned at a remote-control point in each store.
• Majors and line shops: The line shops are divided into a number of zones, each served by chilled water air-conditioning units positioned in closed plant rooms. Conditioned air from each unit is supplied through systems of P3 ducting and distributed to the areas through ceiling diffusers. Re-circulated air from the line shops pass into the Mall areas from whence the air is ducted back to the plant areas. The required quantity of fresh air is introduced through external louvres mounted in each plant room.
  The plant is automatically controlled to provide the required temperature conditions in summer by means of averaging zone sensors, two per zone, and is switched on and off automatically at the plant control panel at each unit.
• Restaurants: The restaurants shall each be served by dedicated chilled water AHUs positioned in closed plant areas adjacent or within each restaurant. Conditioned air from each unit is supplied through systems of P3 ducting and distributed to the areas through ceiling diffusers. Re-circulated air is returned through grilles in the ceiling over the seated area and is ducted back to the plant area. The required quantity of fresh air is introduced through external louvres mounted in each plant room. The plant is automatically controlled to provide the required temperature conditions in summer and winter, and is switched on and off automatically at each plant control panel. Kitchen extract and make-up air is provided by the tenant in accordance with SANS regulations.
• Mall areas: The mall area is partially air-conditioned with re-circulated air from the line shops, as well as dedicated AHUs to the atriums in order to maintain acceptable temperature conditions in summer. In addition, a minimum amount of conditioned air is supplied to the mall areas from the plants serving the line shops.

Building monitoring systems (BMS)

• Chiller control: The BMS time schedule starts and stops the chillers and chilled water pumps. After receipt of the start signal, the chillers operate via their inherent control systems. As this is a mixed-use development the plant runs 24 hours, seven days a week with selected chillers being switched off overnight. Outside of the programmed occupation period, the chillers can be started if any of the AHUs are started and the chilled water control valve more than 10% open. Supply and return water temperatures and chilled water pumps’ status are monitored and controlled from the BMS operators terminal.
• Variable volume AHUs (gym) and constant volume AHUs (retail): The BMS time schedule starts and stops air handling units at the programmed times.
• Supply air temperature control: Averaging zone temperature sensors in each zone modulates the cooling control valve to maintain a constant supply air temperature. The temperature set point, fan air flow switch and safety thermostat status are monitored or adjustable from the BMS operator’s terminal.

Elements of difficulty

As with any project, on site services co-ordination becomes a challenge especially on large scale projects. The speed at which the installation had to be completed in order to meet the programme requirements meant regular site visits and quality inspections were undertaken to ensure smooth progress of all HVAC related services. The most difficult part of this project was managing the expectation of the client as the Hotel and retail were being built simultaneously. The chiller plant had to be part-operational to service the Hotel and residential apartments as this was completed first. Timeous approval of equipment submittals was imperative to meeting the sectional completion dates of the project which placed a lot of pressure on us as the consulting engineers.

The retail component of the project brought its own complexity as the leasing team was chopping and changing tenant boxes to accommodate an array of different tenant requirements. This required close cost control and timeous design changes in-order for the mall to be completed on time.

Product selection

The equipment specified was, as far as possible, selected for efficiency and quality, while still ensuring the client did not have to spend over their limit to achieve the same end goal. Budget constraints always dictate the type of equipment that is installed on any project. Together with the HVAC contractors, we were able to use some new to the industry technology such as making use of Siemens Intelligent Valves which combines the functionality of a two-way valve as well as a balancing valve into one valve. The balancing of the valve is easier and more accurate as this is programmed rather than manually set with standard balancing valves. We also used P3 ducting to speed up the installation of ducting as well as to reduce the impact of other trades damaging our services which is always the case when using FRK on ducting.

The chiller plant has a total capacity of 12MW of cooling. Cooling requirements were calculated using the Carrier HAP software and BSIMAC energy modelling software to assist with glazing specifications and required shading devices to meet the SANS XA requirements for the development.

Fresh air plays a vital role in any building and is a statutory requirement for compliance to the National Building Regulations. The opportunity to use an energy recovery wheel on the Hotel was taken, which provides the hotel bedrooms with pre-treated fresh air. This allows the in-ceiling fan coil units in the bedrooms to be selected at a lower cooling capacity. This in turn reduces the capital costs for chilled water piping as this can be made smaller and assists with in ceiling services co-ordination.

This is the first billion-rand mixed use development in Umhlanga which is serviced by a central cooling plant similar to that of a district cooling plant. The scale and complexity of the cooling plant makes it unique.

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