Capitec wows with impressive new HQ in Stellenbosch

Capitec wows with impressive new HQ in Stellenbosch

By Wouter Seevinck, Executive: Practice Area Lead – Mechanical, Cape Town at Aecom | All photos by Terry February

Rated one of the best banks in South Africa and considering their tremendous growth, it made economic sense to construct and own a facility to house all their employees in one location to allow for future growth.

Capitec Bank set out to consolidate their staff and operations who were previously located in various buildings in Stellenbosch and around Cape Town in multiple offices.

The new headquarters, iKhaya, which means ‘home’ in Xhosa, involves a main campus building of 21 500m², capable of housing 2 000 employees as well as a stand-alone car park building. Both buildings have one level of partially below ground basement, a podium level, first and second floors.

The Architectural design completed by DHK Architects intended to create a collaborative space with a large focus on optimising internal flow and departmental interaction. This was achieved by the large atria spanning the length of the curvilinear building, interconnecting departments with a series of bridges and bespoke staircases.  

Capitec Building 07Bespoke wall art.

Building construction commenced in August 2018 and Practical Completion under the JBCC contract was achieved in February 2020. The HVAC installation had taken just over 12 months to complete. The construction programme was aggressive and despite further acceleration challenges, the project was delivered without delay.

The client brief in terms of the HVAC system was to provide an innovative HVAC system, optimising efficiency while ensuring the systems are simple to operate and easy to maintain. The design objective was not to achieve a Green Star rating, however best practice Green initiates had been implemented in the design. Acoustic performance of enclosed offices and boardrooms was also a priority.

The HVAC system and installation

Cooling / Heating / Ice generation Plant

The HVAC system for the main campus building involves a central air-cooled chilled and hot water generation plant combined with thermal ice storage which supplements the chiller cooling capacity.

To satisfy the 2 556kW peak cooling demand, two chillers were employed, one being cooling only with ice build capability (dual set-point), the other being a 4-pipe heat pump chiller capable of simultaneous heating and cooling, as well as ice build capability.

22 of the ‘Ice-On-Coil’ type Calmac thermal storage vessels were provided which contributes 35% of the peak instantaneous cooling demand. By utilising thermal storage, the peak cooling demand imposed on the chillers resulted in 1 678kW during peak electrical tariffs, as opposed to the total 2 556kW a conventional chilled water system would have had. The thermal storage system was designed to satisfy 50% of the peak day kW.

Hot water for space heating purposes is available at any time of the year, regardless of the cooling demand or plant cooling operating status. The peak heating capacity of the system is 870kW.

The sequence of operations relating to the various plant modes is achieved by the control system which is made up of various valves, actuators and controllers, and follows the dictates of the design.

Capitec Design 03 400Air handling plant arrangement around a typical core.

The plant along with ancillary components such as buffer tanks, glycol management, ice inventory and expansion/make-up systems are located on the roof of the main campus building.

Chilled and hot water hydronic circuits

The chilled water pumping arrangement is a closed loop constant-primary and variable flow secondary system de-coupled by means of a plate heat exchanger. The heat exchanger also allows for the glycol solution to be contained in the plantroom only.

Chilled water generated by the chillers is supplied at 4.5°C and -6.0°C for normal and ice production modes respectively. Chilled water is supplied to the building at 8.0°C by the N+1 variable flow vertical centrifugal pumps located on the roof plant.

Air Handling Units (AHU) and Fan Coil Units (FCU) are generally fitted with 2-way modulating control valves, except for the hydraulically remote units which are fitted with 3-way modulating control valves to ensure minimum circuit flowrates and to eliminate dead-leg scenarios.

Hot water is supplied to the building by means of a closed loop by N+1 variable flow, vertical centrifugal primary hot water pumps supplying hot water to the building at 45°C. The AHU and FCU heating control valve arrangement is similar to the cooling system.

Air-side system strategy

The majority of the building area is open-plan and is served by ‘All Air’ 4-pipe variable air volume air handling units located on the roof. Economy cooling has been employed in this system to optimise energy usage. The principle is such that when ambient conditions are favourable enough to satisfy the building demand without the need for mechanical cooling, 100% outdoor air is supplied to the building by actuating a series of dampers.

Insulated supply air ducts distribute conditioned air via riser shafts in each of the cores to the floors allocated to specific AHUs. The design of the system incorporates zoning of areas relative to their load characteristics with each zone assigned to respective AHUs.

Once the duct branches off onto the floor, it is equipped with a pressure control damper, which, via the control system will ensure that the branch duct pressure remains constant as the flowrates fluctuate on building demand. Swirl type variable air volume diffusers are strategically placed throughout the open plan floors to ensure adequate air distribution and eliminate draft effects.

The diffusers have integral temperature sensors that compare the actual room conditions to that of the set-point. Should the room conditions deviate from the set-point, the diffuser will react by supplying more or less conditioned air to the space, hence varying the air volume of the system.

Upstream of the diffuser, the pressure control damper and the AHU speed will modulate to meet set criteria as the system operates. All parameters are pre-set, and no manual operation is needed. Return air is drawn from the open plan areas via louvres located in the clearstory window line in the common atrium.

Capitec Plant 04Typical return air fan arrangement

The atrium is served by dedicated AHUs with air distribution achieved by linear diffusers strategically placed along the perimeter of the atrium and on bridges crossing the space. High volume radial type diffusers are also provided in the ceiling level of the atrium.

Boardrooms and large meeting rooms are served by dedicated 4-pipe fan coil units with treated fresh air supplied by fresh air tempering AHUs on the roof. Each boardroom/large meeting room is equipped with a dedicated fan coil unit able to provide heating and cooling to satisfy the demand in the room.

These fan coil units are independent of the central system and open plan areas in its vicinity. Boardroom air conditioning set points can each be set individually based on room load and desired occupant comfort or can be controlled via the building management system (BMS).

Units can be switched off if boardrooms are unoccupied, thus promoting energy efficiency. Treated fresh air is supplied to the FCUs. If FCU cooling capability is disabled, fresh air introduced to the space is de-humidified and cooled/heated to neutral conditions.

Ventilation

Fresh air supply to the building is provided to all habitable spaces in the building in accordance with local regulations – SANS10400 Part-O. Fresh air is introduced to the building via dedicated constant volume fresh air fans supplying each air handling unit which serves most of the floor space.

Each fan set is equipped with a filter bank at the intake. Powered fresh air supply was implemented to ensure minimum fresh air flowrates are supplied to the space regardless of the AHU supply air fan speed varying under the variable air volume control sequence. Fresh air to fan coil units is supplied by constant volume tempering air handling units.

Capitec Plant 10Plate heat exchanger and associated control valves

The Building’s smoke control system is incorporated into the overall air handling unit system. By utilising common systems and equipment, the system is economic yet functional. Each core has multiple air handling units connected to a single high-level return air point in the atrium. Each air handling unit system has a return air fan and economy cycle dampers.

Typically, one of the AHUs at each core has been adapted in such a way that it serves as a smoke exhaust system as well. The return air fan volume of the smoke facilitating AHUs return air fan matches the requirements for smoke exhaust – fire-rated in accordance with EN12101.

The economy cycle dampers and ducts were also specified with the required fire rating. In the event of a fire, the control system will ramp up the return/smoke exhaust fan, close the bypass damper in the duct stream and open the relief damper downstream of the fan, exhausting smoke to atmosphere and preventing it from entering the AHU.

Exhaust air systems for ablutions are provided to the building in accordance with local regulations – SANS10400 Part-O. Ablutions are typically situated around the building cores. Exhaust air risers serve the ablutions on each floor of the core and is connected to a Toilet Exhaust Air fan located on the roof.

Solving project challenges

A particularly challenging part of the design and implementation was the coordination of the large supply air ducts within the available ceiling void space and the other trades. Due to the large area per floor plate and the available cores to locate riser shafts in, the airflow rate per riser shaft was quite high resulting in large duct take-offs to the floor.

A high-rise commercial building by comparison has smaller floor plate areas resulting in smaller duct branches to the floors. This issue was mitigated by leveraging the capabilities of 3D modelling and clash detection, but with limited tolerances, site intervention was required in certain instances to make it work.

Another challenging aspect was the requirement for rooftop plant to be located away from the building line in order to minimise visibility of the equipment from the ground level. This resulted in the plant space being extremely condensed. The use of 3D modelling also greatly assisted with the planning of the plantrooms together with strategically placed cross-over bridges to allow access to all the equipment.

Ice storage selection

The ice storage system was selected based on Net Present Value (NPV) calculations performed against conventional systems to illustrate what the return on investment would be by implementing such a system. The result was positive and well received by the client who supported the implementation thereof. The supplier was very forthcoming in terms of assisting with the selection of the ice storage vessels based on the design load profiles and discharge capacities.

Capitec Plant 08 400Ice storage vessels and ice inventory meter.

Considering there are many options in terms of ice storage vessel design, we were looking for a solution which is a modular, low profile design that could be installed on the roof plant areas. The Ice-on-Coil solution was identified as being a best option as it met all these requirements. It was also favoured by the structural engineers due to the impact on the roof slab design considering the load is spread evenly instead of large point loads as other solutions would have had. 

Impact on electrical usage, efficiency and sustainable elements

By employing the thermal storage principle, the electrical peak demand was reduced by approximately 30% and due to the load shifting principle, 50% of total cooling kWh was shifted to off-peak electrical tariff periods, significantly reducing the energy cost of the system.

The project brief did not include any formal green star rating. Good practice energy efficiency strategies were however implemented and includes items such as heat recovery capabilities of the 4 pipe Heat pump chiller, economy cooling on all AHUs, variable water and air flow systems and supply air temperature reset based on the Variable Air Volume diffuser feedback.

Various building elements such as high-performance double-glazed facades and low energy light fittings were selected based on simulations done in thermal modelling software to promote energy efficiency and thermal comfort in the building.

Capitec Design 02Thermal Modelling conducted on the building

Unique elements

The simultaneous heating and cooling capability combined with the thermal storage is a fairly new concept and makes the system unique in a sense. The system as a whole is not unconventional, but the building shape made the implementation of the system challenging and one of a kind.

Project name:

  Capitec Head Quarters - Stellenbosch 

List of professionals:

Owner

Capitec Bank Holdings Limited

Developer

Capitec Bank Holdings Limited

Architect / Designer

DHK Architects 

Project manager

SIP Project Managers 

Consulting engineer

Electrical

AECOM 

Mechanical

AECOM  

Wet services

AECOM 

Civil

AECOM  

Structural

AECOM

Acoustic

SRL South Africa

 Contractors

Main building

WBHO Construction 

HVAC & R

AIRGRO Mechanical Contractors

Wet Services

RMI & PPEW Plumbing 

Electrical

JFE Group 

Fire

QD Fire

Product suppliers:

Chillers - Climaveneta

Intramech

Ice tanks - CALMAC

Airco

Heat exchangers

CIAT

Air Handling Units

TROX

Diffusers

Rickard Air

Pumps

Wilo

Fans

AMS

Fan Coil Units

Skyshot

HVAC Controls / BMS

SSD Controls


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