Compiled by Ntsako Khosa | All images by Ntsako Khosa
Centrally located in the business district of Rosebank, is 144 Oxford – a Growthpoint owned and developed building with an air-cooled chiller system serving 17 large zoned central air handling units.
144 Oxford is an 8-storey premium grade office development in the heart of Rosebank. The design incorporates many environmentally sustainable initiatives in line with the Green Star SA Office v1.1 certification from the Green Building Council of South Africa (GBCSA).
One of the 17 AHUs that serves a dedicated
thermal zone of the building.
These include zoned lighting, energy-efficient building services and systems, water efficient fixtures, rainwater harvesting for use in toilets and landscape irrigation, water-wise landscaping, abundant fresh air and low volatile organic compound (VOC) interior finishes to ensure high level of indoor air quality. The performance glazed façade will let in generous natural light and offer views to the exterior. The façade is made up of full height glazing with insulated spandrel panels at low level to leave 1.8m of viewing panels. “These are coated and baked with a variety of different chemicals which improve thermal performance. So, you allow natural light in, but at the same time reflecting different wavelengths of the light, which is heat, back out of the building. The façade is double glazed (made up of two glass panes with a vacuum between), which gives much better thermal properties than you would get with normal low-e single glazing,” explains Brandon Huddle, technical director in the Built Environment Unit at Aurecon.
Variable speed secondary pumps circulate chilled
water to satisfy the building load.
CLIENT BRIEF
Aurecon worked closely with Growthpoint Properties, Paragon Group as architects, and the professional team through the various iterations of the building’s design to ensure that the mechanical services and the sustainability objectives were aligned seamlessly with the ultimate design. Aurecon was appointed in 2015 for the mechanical and environmentally sustainable design (ESD) consulting services.
ENVIRONMENTALLY SUSTAINABLE DESIGN
The key sustainability aspects of the building include:
- Energy and water efficiency strategies,
- Indoor environment quality features,
- Environmental and waste management commitments,
- Use of environmentally-friendly materials, and
- Transport and GHG emissions reduction.
While the design of the building incorporates various sustainability strategies and features, it is imperative that the building is managed and operated in a way which achieves and even outperforms the sustainability targets set out during design. Improved environmental performance of the building during the entire life cycle yields benefits to occupants, owners, and ultimately to the neighbouring communities.
One of four basement ventilation shafts.
Reduction of energy consumption contributes to reduction of greenhouse gas and other emissions. The energy efficiency strategy incorporates:
- Performance glazing – allowing optimal light to penetrate without the solar heat gain,
- Effective thermal insulation throughout the office area,
- Efficient building systems for reduced energy consumption – HVAC, lighting, domestic hot water heating, lifts and escalators,
- Management and monitoring of building services through a Building Management System (BMS),
- Efficient lighting – Average lux levels of approximately 400Lux and lighting power densities of less than 1.5W/m² per 100Lux for office usable area,
- Appropriate lighting zoning and occupancy sensors to ensure lights are switched off in unoccupied spaces,
- Heat pumps for domestic hot water generation, and
- Electricity generation from renewable source (PVs).
“The expected energy consumption is 148.1kWh/mÇ/year, while expected annual emissions are 76.5kgCO2/mÇ/year,” he says.
INDOOR ENVIRONMENTAL QUALITY
Various aspects have been carefully considered in order to achieve optimal Indoor Environment Quality (IEQ) for the development. The enhanced indoor environmental quality strategy looks at air quality, smoking, lighting, temperature, noise, daylight and glare. “Outside/Return Air Filtration is at 70% Arrestance. This is a typical filter specification for this type of building. Dust problems often revolve around housekeeping; dust and air conditioning borne dust at this level of filtration usually results in acceptable dust counts in terms of environmental standards,” Huddle explains.
The air cooled chillers are positioned on the roof
nine levels above ground.
AIR QUALITY
- Energy efficient air-conditioning system proving fresh air at rates of 12.5l/s/person for 100% of the Usable Area giving a 66% improvement on SANS 10400-O:2011,
- Low/no volatile organic compounds (VOCs) interior finishes,
- Exhaust risers to extract pollutants of copy areas.
Outside air is provided to the 144 Oxford building at rates much greater than the requirements of SANS 10400-O, namely greater than 12.5 ℓ/s/person for 98% of Usable Area. It is recommended that the tenants keep to the occupancy rates to what the building was designed for, should the occupancy rate increase the air conditioning system can be upgraded accordingly. The air-cooled chilled water system is made up of four chillers each supplying 800kW of cooling throughout the entire building. “We’ve got 17 air handling units that serve thermal zones in the building for example, there is one AHU serving the entire southern façade. It’s all thermally zoned,” he says.
Smoking
Smoking is prohibited in the building to reduce related health risks and protect the indoor air quality.
No-smoking signs have been placed at all entrances, and no provisions have been made for a dedicated smoking area.
Temperature
There is a high level of thermal comfort for 95% of the office usable area, measuring 31 883mÇ. The buildings’ design and mechanical system implemented are designed to provide thermally comfortable interior spaces. It is recommended that the design temperature bandwidth is monitored through the building management system, for deviation from set-point. The building owner can also do annual surveys to check if tenants are still satisfied and thermally comfortable.
Noise
Acoustic measures in the design to achieve appropriate internal noise levels between 40 and 45dB.
Daylight and glare
Façade with high performance glazing for increased daylight levels,
- Over 60% of the usable area has external views,
- Blinds installed through the office floors to reduce any discomfort caused by glare.
HVAC SYSTEM
The air conditioning systems consists of a chilled water, zoned variable volume system. Chilled water is generated by four air cooled chillers located on the roof. Chilled water is distributed via a primary/secondary pumping system.
The chilled water plant operates on a constant primary and variable secondary system.
Approximately 17 appropriately zoned air handling units (AHUs) on the roof distribute air to the various zones via externally insulated sheet metal ducting. The units are complete with dry economy cycles. Variable air volume (VAV) ceiling diffusers supply air to the space to suit the load.
The master diffusers are connected to the Building Management System (BMS) and room temperature sensors are integrated within the diffusers. The complete system (including diffusers) are controlled and monitored by a server based BMS system. The BMS provides monitoring features for a number of integrated services within the building, in addition it provides full heating, ventilation and air-conditioning (HVAC) control.
Basements are mechanically ventilated. The extract fans are high temperature fans which also act as smoke extract fans. CO sensors control the fan VSD’s. In addition, impulse fans supplement ventilation in the basement.
The following environmentally sustainable strategies have been included in the 144 Oxford HVAC design:
- High efficiency equipment
- Low pressure ducting and pipe sizing
- CO2 monitoring and control of the fresh air
- CO control of basement ventilation fans
- Full fresh air economy cycles
- Small footprint diffuser zone control
- Zero ozone depleting potential (ODP) refrigerants and insulants
Offices
The air conditioning system consists of the following:
- The central Chilled Water Plant will consist of multiple air-cooled chillers located on the roof utilising 2-pipe chilled water reticulation.
- Four chillers will be provided, each with 25% of the total design capacity of the building.
- Chilled water is distributed via a primary/secondary pumping system.
- Appropriately zoned air handling units on the roof distribute air to the various zones via externally insulated sheet metal ducting. The units are complete with temperature controlled dry economy cycles.
- Variable air volume (VAV) ceiling diffusers supply air to the space to suit the load. Perimeter diffusers have electric terminal heaters.
- The master diffusers are BMS addressable and room temperature sensors are integrated within the diffusers.
- The air handling unit supply temperature is determined by the diffuser demand.
- The complete system (Including diffusers) is controlled and monitored by a PC based direct digital control (DDC) BMS system. In addition, electrical and wet services are monitored by the BMS.
Ventilation
Toilets are mechanically ventilated to meet the building regulations. Smoke extract is also provided on the office floors, staircases and fire lifts will be pressurised during a fire scenario.
Control system
- The air conditioning and ventilation system is controlled by a PC-based DDC system.
- A base-building BMS is provided by the Landlord as an extension of the HVAC controls installation for the purposes of base-building energy management and metering.
“Designed initially to incorporate a hotel and office component, 144 Oxford Road was later changed to a multitenant office building.”
Air-conditioning and ventilation systems are integrated as follows:
- Central cooling/heating plant – to allow central scheduling, after hours operation and system optimisation.
- Individual AHU’s and VAV zone master controllers – to allow centralised space temperature, setpoint and operational monitoring.
- Ventilation and fresh air monitoring scheduling and
- optimisation.
GETTING THE JOB DONE
Each floor in the building is almost identical. The project was completed at the end of 2019. “It was about a 24-month construction period,” says Huddle. Changing part of the design due to a major change in the building use was a bit of a ‘setback’ – according to Huddle. “Because we then had to make the best of the building’s existing structure and vertical risers, however, working closely with the architects cushioned any delays that we could’ve experienced.”
LIST OF PROFESSIONALS
