Towers Main: rejuvenated and award-winning

By Pieter de Bod (Pr.Eng.) LEED BD+C

This project is a breath of fresh air for the city of Johannesburg.

Johannesburg’s old ABSA Towers building has not only received an impressive modern makeover but has also received multiple awards and a warm welcome by the city, the ABSA staff, and the apartment’s residents.

Not only does this skyscraper boast a new vibrant vortex pattern façade that can be seen from miles away as one of Johannesburg tallest buildings, but a new shell and core air-conditioning, heating and ventilation system was installed.

This landmark mixed-use redevelopment further received two SAPOA (South African Property Owners Association) Property Development Awards for Innovative Excellence in 2020.

Introduction

WSP were appointed as the MEPF (Mechanical, Electrical, Plumbing and Fire) consultants on this significant project. To be part of the redevelopment of this 1970s building made it an interesting but very challenging project. I remember very clearly when I visited the Towers Main building for the first time in the spring of 2018. The project team was gathered in the lift lobby on the ground floor, and we made our way to the roof of the building. I was impressed by the strip windows that provided an unforgettable and breath-taking 360-degree vista from the upper floors. I also remember the good condition of exposed concrete structures and all the down-stand beams.

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There are so many factors to consider when recommending a suitable shell and core air-conditioning system to the development team. Retrofitting air-conditioning systems in old buildings like this is very challenging and requires careful consideration and planning.

WSP strives to implement mechanical systems that render buildings more environmentally friendly and resource-efficient throughout its entire life-cycle, starting with design and followed by construction, operation, maintenance, renovation and eventually demolition.

The Towers main building is located on the corner of Main Street and Troye Street, Johannesburg, and comprises the following:

• Three basement levels (each between 3150m² and 4000m²)
• Retail, reception spaces and a coffee shop, public art gallery, crèche, and piazza on ground floor
• Multiple A-grade office floors on the first nine floors
• New stylish residential apartments on the tenth to twenty ninth floors
• A sky-deck and mechanical plant rooms on the fifteenth floor
• Roof with numerous MEP plant rooms.

The mixed-use building includes several amenities for tenants including a coffee shop, art gallery, day-care centre, and gym.

The concept design

The current building did not have any air-conditioning system installed when we arrived on the project. The previous tenant or building owner had removed all remnants of the old air-conditioning system.

A new four-pipe chilled and hot water system was designed by WSP and installed by Ductech with new air- cooled heat pump chillers. The new chillers are installed in a new secure open chiller plant room on ground floor.

The motive to install the new chillers on ground floor is to provide easy maintenance friendly access from road level. A key factor in ensuring a successful air-conditioning system design for this building was to coordinate the position and size of the brand-new chiller plant room with the developer and architect very early on in the project.

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A chiller plant generally is noisy and not aesthetically pleasing and is typically pushed to the back side or the roof of a building, away from building entrances. Since the roof of this building is on the thirtieth floor it did not made sense to house the chillers there due to maintenance concerns and installation challenges related to the building height (in excess of 140 metres high).

Air-cooled heat pump chillers were carefully specified and selected taking their noise levels into account. The chillers draw air from the side and discharge vertically up onto the atmosphere.

New chilled and hot water pipes are installed in the existing riser shafts in the building and terminate on level fifteen. Chilled and hot water pipe tap-offs are installed on every level and terminated by balancing valves, shut-off valves, a strainer, and flushing bypass at approximately 1 metre into the internal space.

The chilled and hot water system is a primary constant secondary variable system to allow for lower power consumption when the cooling and heating needs are in part load while utilising variable frequency drives on secondary pumps and multiple scroll compressors in the heat pump chillers.

A new dedicated outside air filtration unit is installed on the mechanical floor on level 15 to provide ducted filtered fresh air to the new offices and retail levels below. Two new ducts are installed in the existing riser shafts because a single duct would not have fitted into the existing riser shafts. Balancing dampers and fire dampers are installed on every tap-off to the floors they serve.

A new toilet exhaust system is also installed on levels one to nine to cater for the various gang toilets on every floor. The toilet exhaust system is a standalone system per floor, each consisting of two axial fans with sound attenuators and exhaust weather louvres.

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The main reason for designing standalone exhaust systems on every floor in lieu of a central exhaust system is due to lack of space in the existing riser shafts. The existing riser shafts are taken up by the life safety systems like the new stair pressurisation systems, the outside air system, chilled and hot water pipes and other electrical, fire and plumbing systems.

A brand-new basement ventilation system is installed in compliance with the local and national building regulations. Large exhaust fans are strategically installed in two corners of the basements while outside air is pulled in from large vertical concrete shafts and louvres on the opposite side of the basement.

Multiple jet fans are utilised to force air flow from the air inlet point to the exhaust air point. This arrangement allows cross ventilation while minimising the need for long duct runs. Each basement had their own set of fans. Old stale air from the basement is exhausted vertically up into the atmosphere on street level and their positioning was carefully coordinated with the architect to hide and obscure a view of the basement ventilation ducts. The basement ventilation system doubles up for smoke evacuation of the basements.

Several Carbon Monoxide (CO) sensors are installed in the basements and connected to a central control panel. The CO sensors are an energy saving feature that prevents basement fans to run continuously and consume unnecessary power. When there is a fire or smoke alarm signal, all basement fans will start and override the CO monitor system.

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New staircase and lift pressurisations are installed to ensure compliance to the local and national life safety building regulations. Twelve new stair-case pressurisation fans were installed – of which 6 are duty and 6 are standby. The stair pressurisation systems were designed so that some ducts serve levels fourteen down to basement 3, while other systems serve levels fifteen to level twenty-nine. Two new lift pressurisation fans are also installed.

A new central exhaust system is installed for the apartment laundry and bin exhaust. The system comprises a new exhaust fan on level 30, and new exhaust ducting extending to level 10.

A sustainable feature of this air-conditioning system is that it does not consume any water to reject heat (no cooling towers are used), which is a criterion highly regarded by the GBCSA.

The chilled and heating water systems are closed-loop systems. Fresh water is a delicate commodity that should be treated with care. In future, it will become even more of a critical factor to consider in the design of air-condition system solutions. Also, the additional benefit from not using cooling towers for heat rejection is that there is no chance for Legionella bacteria to form.

The four new hermetic scroll R410 air-cooled chillers were carefully selected and controlled to allow either chilled water generation or heating water generation, or both at any given time. Each chiller offers over 300kW of cooling or 340kW of heating, two refrigeration circuits and an on-board primary pump. The refrigerant has an Ozone Depletion Potential (ODP) of 0.

Project challenges

The design team was confronted with numerous design challenges and constraints. It is not a trivial task to design a basement ventilation system for an existing building. Several basement ventilation design strategies were studied during the concept design stage, but the strategy that involved the least amount of structural and financial implications was chosen.

Careful coordination with the structural engineer and architect was necessary to ensure the execution of a successful basement ventilation system. It is always imperative to make sure that the intake and exhaust positions are a sufficient distance apart from each other to minimise the effect of air short circuiting or cross contamination.

The space in the existing riser shafts were very limited. A decision was taken by the mechanical design team to have localised toilet exhaust, as there was no space for the central toilet exhaust duct. It was not practical to add new riser shafts in the existing structure, so we had to use the riser shafts what were already there. Many internal coordination sessions with WSP’s electrical, plumbing and fire engineers made it possible to arrange all services successfully within the existing riser shafts.

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Commissioning and fine-tuning

Comprehensive pre-commissioning, commissioning, as well as quality monitoring were performed by the HVAC contractor on all the new shell and core mechanical systems. This was done in a systematic manner.

After completion, the HVAC contractor was required to provide training and system knowledge to the building owner/manager by submitting the following documentation:

• Design intent report
• As-built drawings
• Operational and maintenance manuals
• Commissioning records
• Commissioning reports for each system.

The commissioning records by HVAC contractor included:

• Demonstrating that the services were commissioned
• Commissioning dates, records of all functional/ commissioning testing undertaken, a list of any future seasonal testing, and a written list of outstanding commissioning issues.
• The outcomes and changes made to the building as a result of the commissioning process, accounting for all the recommendations.

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Modelling

WSP modelled the MEPF (Mechanical, Electrical, Plumbing and Fire) systems in Autodesk Revit, which is a modern building information modelling software for architects, structural engineers, mechanical, electrical, and plumbing (MEP) engineers, designers and contractors and developed by Autodesk.

Revit allows designing and coordinating the MEPF system components in 3D, annotate the model with 2D drafting elements, and access building information from the building model’s database.

BMS

A new simple BMS is installed to monitor key components of the MEPF systems. All the monitored information is transmitted to a central computer in the control room, and the information is displayed in graphical format on a screen in the control room. The BMS can be set to trend and store data for troubleshooting purposes. The BMS is mainly used for alarm management.

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Awards

SAPOA presented this project with two awards in 2020. The first award went to the developers of this project Atterbury and Ithemba Property for the winner in the mixed-use category.

Towers Main also won the prestigious overall transformation award.

List of professionals:

List of Mechanical Equipment Supplier and manufacturers:

Equipment installed:

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