Iconic PwC Tower pulls out all the stops

By Pieter De Bod (Pr Eng)

The striking PwC Tower in Midrand is finally complete and its plant rooms are as impressive as the views from the top of this ‘twisty’ beacon of sustainability.

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Are you perhaps one of those inquisitive individuals who speculated what the weirdly shaped structure was that was going up next to Midrand’s Allendale off-ramp in 2015 and 2016? You wouldn’t be alone. Even some of the local radio stations conversed about the new structure. There were speculations of this new structure being a water reservoir, while others thought it was a fortress …

Over the past few years, many of us have witnessed the construction of the sensational PWC Tower, starting with a big hole in the ground in 2014 and slowly evolving into a mighty, shiny new glass edifice.

The PwC Tower is designed by LYT Architecture and located next to Mall of Africa, and the complex forms the ‘green’ heart of the new buzzing hub of Waterfall City. The developer is Atterbury and the building owner is Attacq.

Reception lobby featuring swirl diffusers. 
Image credit: Ilana KoegelenbergThe Samsung condenser serving the lift room on the 27th floor. 
Image credit Ilana KoegelenbergInnovative and cutting edge technology of the screw compressor inside the water-cooled Carrier Evergreen 23XRV chiller. 
Image credit: YouTubeDuring the first months of 2015: construction of the basements and the core well underway. There are five parking basements. 
Image credit: WSPThe Clivet air-cooled multifunctional chiller site delivery. 
Image credit WSPCetra dual air handling unit serving the treated fresh air to the building and extracting the toilet extract. 
Image credit: Ilana KoegelenbergThis photo was taken inside the lift core looking up towards the roof slab of the core. 
Image credit> WSPExtra A4.jpg

This iconic twisty tower is the first high-rise building in the Midrand–Waterfall–Kyalami district. The building comprises 27 storeys (25 of which are office floors), five parking basements, and an annexure building comprising numerous office floors, conference facilities, meeting rooms, commercial kitchens and canteen facility, recording studios, and archive rooms, totalling around 48 000m2. The unique tortuous shape of the building gently twists through in height, with the top- and ground floors rotated by 30 degrees.

The height of the new PwC Tower and the fact that it is situated on a high point in Waterfall City, will make it the tallest structure on the corridor between the Johannesburg and Pretoria CBDs. The PwC Tower is visible from almost anywhere within a 30km radius.

The project is registered with the Leadership in Energy and Environmental Design (LEED) council and targets the esteemed LEED Silver certification.

WSP was appointed as the mechanical consulting engineer on this project for heating, HVAC, and building management systems (BMS), as well as energy monitoring systems (EMS).


No electrical heating is installed anywhere in the HVAC system, as this is very inefficient and environmentally unfriendly.


DESIGN CRITERIA

Guy Steenekamp, a director at LYT Architecture, explains: “The brief for the PwC Tower at Waterfall City called for an iconic building form that would be unique to the development and which would mark the property as a new top-tier destination for business.”

The air conditioning for this building has been designed to meet the following criteria:

  • Commercially economical.
  • High operational efficiency, and high coefficient of performances (COPs) of the cooling and heating systems.
  • Good occupancy comfort.
  • Good thermal zoning.
  • Simple to maintain.
  • Simple to operate.
  • Good service access to all HVAC equipment.
  • Low electrical and water consumption.
  • Relatively high fresh air rates to occupants.
  • Good HVAC system reliability.
  • Long service lifespan.
  • High filtration efficiency.
  • State-of-the-art chillers.
  • Integrated heating and cooling recovery.
  • High-performance glazing.
  • Automated internal blinds system.
  • CO and CO2

SYSTEM DESCRIPTION

The air-conditioning system comprises a central cooling and heating system. Chilled water is generated on site by a combination of two state-of-the-art high-efficiency water-cooled Carrier screw chillers, plus three multifunctional air-cooled chillers and one heat pump chiller. These six chillers work in combination to provide the best energy efficiency and lowest water consumption, depending on the cooling demand and the ambient temperature conditions.

The chilled water is pumped by means of primary and secondary pumps to various fan coil units (FCUs) and air handling units (AHUs) in insulated steel piping. In the tower, on the typical floors, the FCUs are positioned in the ceiling in the perimeter zone (the 3 500mm zone from the glass), while the internal office areas and meeting rooms will be served by variable speed AHUs (one per office floor).


Chilled water is generated on site by a combination of two state-of-the-art high-efficiency water-cooled Carrier screw chillers, plus three multifunctional air-cooled chillers and one heat pump chiller.


Some meeting rooms and executive offices are also served by means of FCUs for individual control. The conference rooms and training rooms in the annex are served by means of FCUs or AHUs. The same FCUs and AHUs are also providing the space heating through hot water that is generated by the multifunctional and heat pump chillers. Each AHU has two separate coils: one for chilled water and one for hot water.

WSP has given special attention to proper service access. It is essential that all components of the HVAC system can be accessed easily and safely.

DPS intro

Each FCU contains the necessary washable removable filters, insulation, cooling and heating coil, and three-speed supply air fan. In most cases, return air is drawn into the ceiling voids and mixed with a regulated amount of filtered outside air. 

Chilled water is supplied at a temperature of ±8.0°C to the building to ensure that the internal space cooling equipment (that is, FCUs or AHUs) can cool the internal space to meet design conditions

Hot water is supplied at a temperature of ±40.0°C to ensure internal space heating.

No electrical heating is installed anywhere in the HVAC system, as this is very inefficient and environmentally unfriendly.

Variable speed drives serving the air handling units in the annex. The plant room is screened off by louvres. 
Image credit: Ilana KoegelenbergEvapco cooling tower in the foreground. 
Image credit: Ilana KoegelenbergInterlinking the lower and upper chiller plant room with chilled water, hot water, and condenser water pipes. 
Image credit: Ilana KoegelenbergCetra air handling unit serving conference rooms in the annex. 
Image credit: Ilana KoegelenbergTypical light lobby ceiling detail, featuring swirl diffusers served by a fan coil unit. 
Image credit: Ilana KoegelenbergAutomated internal louvres in the reception lobby, screening off the afternoon sun. 
Image credit: Ilana KoegelenbergClivet multifunction chiller, located on the annex roof. The plant room is screened off by louvres. 
Image credit: Ilana KoegelenbergThe reception desk with built-in low-pressure hot water pipes system. 
Image credit: Ilana Koegelenberg

EQUIPMENT SELECTION

In the office tower, the FCUs were specifically selected for the following reasons:

  • Optimal zone control: Compared to a central AHU system, FCUs provide superior independent indoor zone control for each facade, keeping in mind that the facade direction varies at each level as the building twists upwards: (a) on each office level the facade faces three different directions, (b) each FCU can control indoor temperature independently from other FCU.
  • Flexibility: Easier to deal with tenant changes/additions compared to central AHU system. To change, add, and remove FCUs to accommodate changes is easier compared to doing changes on central AHU systems.
  • Future proofing: Chilled and hot water piping will be provided in the ceiling and a limited amount of additional T-offs with isolating valves will be provided for future FCUs.

The air-cooled heat rejection equipment is sized based on ambient summer condition 35°C dry bulb, and the relevant components of the HVAC system to comply with ASHRAE Standard 90.1-2007 – Section 6.4 standard.

The internal design temperature for the office area is 22.5°C in summer and 21.5°C in winter. These temperatures are those at which the majority of people are considered comfortable, and which are accepted as standard indoor design conditions in South Africa. The temperatures would be controlled within a tolerance of ±2.0°C

A unique feature of the air-conditioning system is the incorporation of ultra-efficient water-cooled Carrier chillers. Carrier’s Evergreen 23XRV chiller is claimed to be the world’s first integrated variable speed, water-cooled, screw chiller. It incorporates significant breakthroughs in water-cooled chiller technology to provide excellent reliability and achieve superior efficiencies at true operating conditions, all without compromising the environment.

The 23XRV chiller provides:

  • Energy efficiency: Variable speed, positive displacement screw compressor. This refrigerant-cooled, variable frequency drive (VFD) chiller has the ability to reduce speed and optimise operation independent of ambient conditions. This unique capability permits the chiller to precisely match building load and conserve energy.
  • High part-load performance
  • High-performance tubing
  • Environment friendly
  • Versatile: Ideal solution for constant and variable flow pumping systems.
  • Advanced tri-rotor compressor: The tri-rotor compressor used in the 23XRV has been designed for extremely high reliability. It features balanced rotor geometry and shorter screw lengths, resulting in vastly reduced compressor bearing loads and a minimum L10 compressor bearing life in excess of 500 000 hours when operated at Air-Conditioning and Refrigeration Institute (ARI) standard conditions.
  • Superior oil management: All 23XRV chillers regulate oil temperature, viscosity, and pressure. Rather than relying on differential system pressure to lubricate the compressor, it uses a patented process to ensure that high-quality oil is delivered to the compressor bearings via a positive displacement pump. This allows continuous operation with cold condenser water at all loads. Should the input power to the chiller be lost, the system is designed to assure proper lubrication of the bearings during coast down.
  • Refrigerant-cooled VFD: Refrigerant cooling of the VFD minimises VFD size and ensures proper cooling of the transistors for extended life. Using R134a refrigerant instead of water also eliminates costly maintenance of the water cooling pump, heat exchanger, and rubber tubing used with water-cooled VFDs.
  • Cooler tube expansion: The cooler tube is fitted with expansion valves at centre support sheets to prevent unwanted tube movement and vibration, thereby reducing the possibility of premature tube failure.
  • Low harmonic distortion: The chiller generates less than 5% total harmonic distortion at the input to the VFD without the use of any external filters or line reactors. This ensures that the VFD cannot exceed IEEE-519 standard for distortion at the point of common coupling. The integrated VFD provides a soft start, further reducing stress on the compressor and inrush current at start-up.
  • Positive pressure design: This ensures that air, moisture, and other performance-degrading contaminants are not sucked inside the chiller. This eliminates purge units and their associated maintenance.
  • Product Integrated Control (PIC III): Carrier’s direct digital electronic controls (PIC III) provide great flexibility and functionality. Each unit integrates directly with the Carrier Comfort Network (CCN) system, providing a solution to controls applications.

In the tower, the male and female toilet areas are mechanically ventilated by means of respective extract air fans on the upper roof. The extract grilles above the toilet and urinal are connected by means of a flexible connection and sheet metal ducting to the main extract ducting. The extract air is discharged to atmosphere at high velocity. Toilets in the balance of the building are extracted the same way.

Black supply air diffusers serving the meeting room lobby area. 
Image credit: Ilana KoegelenbergAcoustic sound-absorbing panels on the wall dampen the noise in the chiller plant room. 
Image credit: WSPInside the air handling unit plant room. 
Image credit: Ilana KoegelenbergExposed soffit and ceiling void services on the third floor in the tower. 
Image credit: Ilana KoegelenbergThe twisty tower leaning over, as can be seen from the inside of the foyer to the annex facility. 
Image credit: Ilana KoegelenbergLower chiller plant room featuring the primary and secondary pumps as well as the Carrier 23XRV chiller. 
Image credit: WSPCarrier 23XRV chiller. 
Image credit: WSPLower chiller plant room with excellent service access. 
Image credit: WSP

The smoke extract system in the tower comprises three axial fans per office level, and are also doubling up as over-pressure relief during night-time flushing or an economy cycle. The ground lobby has separate smoke extract fans, of which one fan is doubling up as a hot air extract fan connected to a temperature sensor at high level.

Most of the AHUs in the building incorporate a night-time flushing mode to allow internal spaces to be ventilated with outside air. Night-time flushing is normally implemented to cool the internal space when outdoor temperatures and humidity conditions are appropriate. This energy-saving feature allows the free night-time cooling to remove the heat that was built up in the structure during the daytime; therefore, the chillers will have to work less hard the next morning to cool the building.

This building is equipped with an automated blind system linked to solar sensors. This system will automatically open and close blinds depending on the angle of the sun and the time of the day. This system is incorporated to control glare and minimise solar influx into the building.

Another special feature of the heating system is the low-pressure hot water heating system incorporated in the reception desks. A traditional hot water pipe is located in the footwell position. Receptionists may want to rest their feet on the hot water pipe to provide heating during cold days. Each receptionist desk has its own heater and thermostat.

Underfloor hot water heating is installed in the main lobby in the ground floor slab. This heating system is designed to combat the cooling effect of the large single-glazed glass in the lobby area, to make the space more comfortable for occupants. A stand-alone plate heat exchanger is used to transfer the heat from the hot water system to the low-pressure underfloor hot water piped system. The PEX piping is placed in the slab in the screed under the tile surface.

The energy monitoring system (EMS) dashboard was also designed by WSP. The purpose is to display, monitor, and record the electrical and domestic water consumption on the project, to understand the consumption pattern of the large electrical and water consumption components, and to manage this. There is a saying, “We can only manage what we measure.”


A unique feature of the air-conditioning system is the incorporation of ultra-efficient integrated variable speed, water-cooled, screw chillers.


The entire parking basement is mechanically ventilated with large axial fans, connected to the smoked detection system and a CO sensor system.

Stainless steel canopy hoods with UV lights and capture jet technology are installed in heavy cooking areas in the commercial kitchens. Special low noise, high-pressure backward curved fans extract the smoke and are located on the roof of the annex. A Kidde fire suppression system is installed in the canopies.

The lift shafts and fire escape staircases in the tower are pressurised by means of axial fans, which are located on the roof of the tower.

The server room, patch rooms, and other similar rooms are cooled by either FCUs or close control units and connected to a separate 24-hour chilled water system.

MODELLING

WSP has modelled the entire HVAC system on Autodesk Revit, which is a building information modelling software for architects; structural engineers; mechanical, electrical, and plumbing (MEP) engineers; designers; and contractors, and is developed by Autodesk. It allows them to design the HVAC system components in 3-D, annotate the model with 2-D drafting elements, and access building information from the building model’s database. Revit is 4-D building information modelling (BIM) capable, with tools to plan and track various stages in the building’s life cycle, from concept to construction and later, maintenance and/or demolition.

South Africa’s environmental challenges include water scarcity and limited electricity supply. Various sun studies and the energy modelling have led to a sustainable, innovative HVAC design, including selection of high-performance glazing, smart HVAC control design, pressure independent control valves (PICV), CO and CO2 sensors, night-time flushing mode, and occupancy sensors.

A clean-cut installation by Airgro in the lower chiller plant room. 
Image credit: WSPThe chilled water riser pipe anchor point in basement level 2. 
Image credit: WSPPioneer busy with the installation of the low-pressure hot water underfloor heating. 
Image credit: WSPThe hot water riser pipe anchor point in basement level 2. 
Image credit: WSPShowcasing the stunning colourful interior spaces on the typical tower floors. 
Image credit: WSPConstruction of the upper chiller and air handling unit plant room well underway at the end of 2016 (roof of the annex building). 
Image credit: WSP
The chilled water, hot water, and condenser water pipes in the lower chiller plant room.
Image credit: WSPWBHO is proud to display the lift core structure and first few office floors complete, towards the end of 2015. 
Image credit: WSP
The PWC HVAC and BMS Consulting team, from left: Pieter De Bod, Johan Botha, Gareth Astbury, Martin Roodt, Christopher Clack, and Steve Dickinson. 
Image credit: WSP

BMS

The building is equipped with a new building monitoring system (BMS). The BMS is a localised computer-based monitoring system that monitors the building’s HVAC system, generators, UPS, main electrical meters, main water meters, and fire detection system alarms.

All the information is transmitted to a central computer in the control room on level 1, and is then displayed in graphical format on a screen in the control room. The information on the BMS can be assessed remotely over the Internet. The BMS can be set to trend and store data for troubleshooting purposes.

The BMS will be used for alarm management. Critical alarms will be sent via SMS to the facility manager. Water and electricity consumption will be logged, and management reports will be generated. The BMS network uses dedicated LAN cables and is separate from the PwC network.

The HVAC subcontractor Airgro, under the leadership of experienced engineer André van Niekerk and his team, has done a sterling job with the HVAC installation on PwC Tower. Well done!

LIST OF PROFESSIONALS

Water-cooled chiller Carrier
Air-cooled multifunction chillers Clivet (Peter Groves AC)
Pumps Grundfos
Cooling towers Evapco
Fans Flaktwoods
FCUs Sinko
DX units Samsung
BMS Tridium (i.c.e.s)
AHUs Cetra
Underfloor heating Pioneer
Valves Belimo

ABOUT THE AUTHOR

Pieter De Bod (Pr Eng) is an accredited Green Star Professional and works as the technical director of WSP. He is a member of the American Society of Heating, Refrigeration and Air-conditioning Engineers (ASHRAE).


Click below to read the February 2018 issue of RACA Journal

RACA FEB2018

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