Maninga Engineering assists WITS in its strategic vision

By Phuti Sheela, engineer at Maninga Engineering, edited by Eamonn Ryan

The University of the Witwatersrand’s Commerce Law and Management (CLM) Building is an award-winning facility that features both a Thermally Activated Building System (TABS) system and chilled technology.

All images supplied by Maninga Engineering

The project stands out for incorporating energy saving methods for heating and cooling. All these were achieved while meeting the acoustic requirements of the building. Wits University had a requirement to free up academic and office space for various schools in anticipation for increased enrollment of post-graduate students as per Wits 2022 Strategic Vision.

The precinct redevelopment was through a space optimisation strategy which included the development of a new building to accommodate its administrative function in a new centralised location. The architects had created a three-story office building with a magnificent atrium to accommodate Wits’ requirement, which was to adhere to its urban design framework. Construction started in March 2021, and it was commissioned in December 2022.

The university requested a highly energy-efficient building which incorporated the latest technology to heat and cool offices. The professional team has explored the use of radiant heating and cooling system by using TABS to control the internal environment of the new building. The system must significantly reduce operating costs for the university. The proposed design solution takes into place the health and safety of the occupants in the building. The success will be measured by the level of comfort, making the environment conducive to end-users.

DESIGN CRITERIA

The following design criteria were applied in the design and configuration of all technical systems and services:

• Adequate capacity: load handling capabilities to meet present and future
• Reliability: under all
• Adaptability: ability to cater for changes in future technology and expansion without infrastructure
• Flexibility: simplicity of operation and ability to cater for changes in
• Maintainability: ease of maintenance and totally serviceable with locally available
• Cost-effectiveness: minimised capital and long-term operational
• Energy efficiency: the systems must operate at optimum efficiency and minimum energy costs.
• Sustainability.
• Safety: the designs must be performed with due consideration given to the circumstances of the occupants and the environment.
• Security: consideration must be given during the design process to potential incidents of equipment vandalism and improper use and handling.

The HVAC system comprises two elements: the ventilation element and the temperature control element. The ventilation requirement is a compulsory element which is essential for building occupation. The rooms’ ventilation design was guided by SANS 10400 Part O Table 1, which tabulates the minimum air required which was used in heat load calculations. The room population was calculated in accordance with the class occupancy of each building as stipulated in Table 1 below.

TABLE 1: DESIGN POPULATION

The below table tabulates the occupancy class for each room aligned to the population.

Filtered fresh air was to be introduced to all spaces according to the National Building Regulations. The fresh air systems consist of weather louvers, attenuators, filters, fire dampers, fresh air fans diffusers, ducting and volume control dampers. Various extraction systems are also included in the scope of works. The second part of the HVAC system is the temperature control. This element is purely for comfort purposes. Hourly Analysis Program is software that is used to calculate the amount of cooling and heating energy required in a space. The system factors both sensible heat and latent heat. To achieve the cooling and heating of the CLM building, an HVAC system consisting of the following was installed:

• Chilled beams
• Mini VRV outdoor unit
• Two air-cooled chillers
• Rooftop package unit
• An extraction system
• All these systems form part of a complete HVAC system for the

MEETING ROOMS’ AND OFFICES’ AIR- CONDITIONING SYSTEM

The CLM building is a three-story building which has meetings and boardrooms placed on the west side of the building throughout the three floors. In the meeting rooms and board rooms, a chilled beam system is used to achieve the required heating and cooling through chilled water. The chilled water is generated from the chiller which is placed on the roof and is dedicated to supply all the meeting rooms and boardrooms placed on the three floors. The chiller uses an R32 refrigerant gas which is able to achieve heating in the cold months and cooling in the hot months.

The roof-top package unit supplies fresh air into the area using ducts. The fresh air is dehumidified to prevent the formation of condensate. Hence the chilled beams do not require any condensate drain pipe. The fresh air from the roof-top package unit extends through the building to supply offices located in the centre of the building. This is because the offices in the middle of the building do not direct fresh air from the outside. It is worth noting that fresh air supply is necessary as per SANS 10400 Part O. In the atrium, there are two extraction fans that ensure there is air circulation throughout the building. Temperature control is achieved through TABS. The design for the TABS system is guided by ISO 11855-4. The standard gives guidance as to how the TABS system should be designed for optimum performance.

TABS is a system comprising of pipes installed in the slabs of the building and a chiller to supply chilled water into the pipes. Water is circulated through the pipes, and in turn conduction takes place to transfer energy onto the slabs. Emissivity then occurs with the aid of air circulation. For the offices located on the perimeter of the building, windows need to be opened for the TABS system to take effect. For the offices located in the middle of the building, the fresh air supplied from the roof-top package unit aids in the transfer of temperature from the slabs into office spaces. The communication between the chiller and the TABS control unit is through sensors that are installed in the slabs throughout the building. This in turn communicates as to how much chilled water can be generated from the chiller and in turn, the chiller does not run at 100% capacity – to save energy consumption.

ELECTRICAL ROOM AND SERVER ROOM AIR- CONDITIONING SYSTEM

The electrical room and the server room require cooling at all times to prevent overheating of the equipment being stored in the rooms. The cooling is achieved by means of two midwall split units installed in each room. An outdoor VRV system was ideal in this case as it reduced the need to have two outdoor units. This reduced the footprint of the installation. Furthermore, this meant that longer pipe runs could be achieved.

All floors at the CLM building have toilets. Due to space constraints, the system was forced to use one extraction air fan for both sides of the toilets. That is, one fan extracts from the male and female sides of the building.

SUNDRY FACTORS AND RISK MITIGATION

During the design phase, Maninga Engineering highlighted that the TABS system uses thermal comfort as a way of temperature control. As part of risk mitigation, the design opted for the route of increasing the fresh air system air flow in order to increase the system’s efficiency.

For the server room and the electrical battery room, a VRF system was ideal because it has longer pipe run allowance. This was crucial in a sense that otherwise the façade of the building would be tainted with pipes running from the roof plant. The usage of chilled beams eliminated the noise generated by conventional HVAC systems. The chilled beams seamlessly met the requirements of the acoustic engineer for the meeting rooms and the recording room. The chilled beams, coupled with the roof-top package unit, also eliminated the formation of condensate.

The two chilled beams used on this building are hydronic module chillers and they use R32 refrigerant gas. The refrigerant gas meets the Global Warming Potential (GWP) requirement as it is not part of the group of hydrofluorocarbons (HFCs) refrigerant gases. Occupants’ thermal comfort is the primary objective in radiantly heated or cooled space. To provide an acceptable thermal environment for the occupants, the requirements for general thermal comfort shall be taken into account by using the index of predicted mean vote (PMV) or operative temperature (OT), and local thermal comfort, for example, surface temperature, vertical air temperature differences, radiant temperature asymmetry and draft.

The operative temperature range corresponds to 20-24°C for cooling season and 23-26°C for heating season in spaces with sedentary activity.

The main advantages of using the TABS system are:

• Reduced building height (saving 500-600mm per story of building height)
• No suspended ceiling is needed to cover air ducts which results in a significant saving of building materials
• It is also possible to operate the system at 30-50% lower peak loads allowing reduced plant sizes and possible operation of heating/cooling systems with temperatures close to room temperature – allowing increased plant efficiency
• No noise levels