The Radio Park buildings are air-conditioned by central dual duct and variable air volume (VAV) Air-Handling Units (AHUs) located in plant rooms. One central chilled water plant (three centrifugal chillers with total cooling capacity 5600kW) supplies chilled water to all the Radio Park AHUs. Four boiler plants serve the respective AHUs with hot water (8 electrode boilers with total heating capacity of 2300kW) via four independent distribution networks.
The TV Centre buildings are air-conditioned by central VAV and reheat AHUs located in plant rooms. Two chilled water plants supply cold water via two separate distribution networks to the respective TV Centre AHUs. The TV Office plant consists of 3 screw chillers (total cooling capacity of 4200 kW) and the TV Studio plant of 3 centrifugal chillers (total cooling capacity of 8820kW). One boiler plant serves all the respective TV Centre AHUs with hot water (4 electrode boilers with total heating capacity of 6800kW).
The Lighting and Heating, Ventilating and Air-conditioning (HVAC) are scheduled and controlled by Johnson Controls’ (JCI) Metasys Building Management System (BMS). The SABC purchase electricity from City Power at Medium Voltage Time of Use tariff rates. The site operates currently at an average maximum demand of approximately 11,500 kVA and an electricity account of R18 million per year.
SEM Solutions performed a detailed energy audit during 2006 to identify energy savings opportunities and calculate the potential for electricity cost savings. An energy balance of the facility is displayed in Figure 2. The graph indicates that the HVAC system consumes more the 60% of the total facilities energy. The audit’s main focus was therefore on the HVAC system during the investigation. The findings of the investigation are summarised as follows:
- Office air-conditioning and lighting systems were on after hours when the respective areas were unoccupied even with a BMS in place for remote switching from the main control room.
- The Variable Air Volume (VAV) and reheat AHUs supply at constant air temperature throughout the year irrespective of the change in building cooling and heating loads. This resulted in over cooling and unnecessary re-heating.
- Although air economiser cycles were in place on the AHUs, to utilise free cooling during winter, the systems were decommissioned to reduce the intake of dry outside air during winter.
- The dual duct AHUs of the Radio office block supplied cold and hot air at a constant supply air temperature throughout the year irrespective of the change in building cooling and heating loads. This resulted in unnecessary cooling and heating at the same time.
- The chilled water pumping systems consume a total electricity demand of 800kW constantly throughout the year irrespective of the change in building cooling and heating loads.
4 Savings Strategies
As a result of the findings during the energy audit the following energy savings strategies were proposed to reduce the electricity cost of the facility:
- Extend the BMS with a phone switching module to switch lighting and air-conditioning remotely via phone (including cell phone) when required. This strategy implies fixed operating hours during office hours and remote switching after hours on demand with automatic shutdown on a rundown timer.
- Reconfigure and reprogram all the AHU cooling and heating controllers to a logic minimising over cooling and unnecessary reheating.
- Re-commission the air economiser control cycles and install dry mist evaporative cooling in the plant rooms at the outside air inlets to pre-cool and humidify the dry outside air during winter (see Figure 3 and Figure 4).
- Install Variable Speed Drives (VSDs) on the chilled water pumps to reduce the flow and energy consumption of the pumps during part load conditions.
5 Estimated Savings
A building and HVAC model of the facility was configured in the simulation program VisualDOE to calculate the potential for electricity cost savings of the proposed savings strategies. The estimated change in winter electricity demand of the chilled and hot water systems is displayed in Figure 5. The table below displays the estimated savings, implementation costs and payback periods:
Energy Saving: Estimated energy saving (kWh) per year.
% Saving: Percentage energy saving per year.
Cost Saving: Estimated electricity cost saving per year.
Installation cost: Excludes all audit, development of specifications and project management costs.
DDP: Direct Payback Period in months.
The installation of the savings strategies is currently in progress and should be completed by the end of August 2007. The savings values showed here are therefore estimates calculated by simulation. The actual savings will only be revealed one year after the completion of installation.
SEM Solutions however believes that the saving calculations are fairly accurate since they are financing the project and receives only 50% of the actual savings as payment to recover and generate a return on their investment. The success of any energy management project lies however in correct commissioning and operation of the savings equipment over time, which highlights the word management in energy management.
Implementing efficient control is one of the most cost effective savings strategies in the commercial sector.
The author of this article would like to acknowledge the efforts of:
- The Building Technology team at the SABC under the leadership of Mr Bruce Phipson.
- Johnson Control Facility Management under the leadership of Mr Neil Cameron.
- Shared Energy Management under the leadership of Mr Rip Wyma and technical support from Mr Roland van Leeuwen.