Today, skyscrapers are springing up like mushrooms after rain, with individual building areas constantly expanding from several thousand square meters to hundreds of thousands of square meters. To ensure the normal operation of these buildings, various equipment is installed, including central air conditioning systems, lighting, and security systems. While providing a comfortable and beautiful environment, skyscrapers are also huge energy consumers, as all equipment requires electricity to operate; electricity costs account for a large portion of building management expenses. Building managers constantly face the question of how to conserve energy, making "energy conservation" an eternally relevant topic for skyscrapers. The emergence of building automation control systems has facilitated energy conservation in buildings.
1. Introduction to Building Automation Control Systems
Building automation control generally refers to the process within a building where environmental conditions are monitored through on-site monitoring and sensing equipment. Signals are transmitted via lines to the central control room, where the central control computer analyzes and processes the signals before transmitting them back to the relevant on-site actuators for control. Building automation control systems typically include fire automation (FA), closed-circuit television monitoring systems, office automation (OA), and building management automation (BA), but here we specifically refer to building management automation. The objects controlled by building management automation include: central air conditioning systems (cooling, heating, and ventilation), lighting systems (indoor lighting, courtyard lighting, building floodlighting, etc.), and water supply and drainage systems.
The building automation control system uses field digital computers (DDCs) to collect relevant data, which is then transmitted to a central computer via lines. After calculation and comparison, the central computer returns the information to the field DDCs and outputs corresponding signals (commands). These commands are then executed by the field actuators (or controllers) to complete the entire automatic control process. Alternatively, control can be achieved directly from the central computer to the field controllers. For example, in a lighting system, the central computer can issue commands according to set time periods, and the field controllers can directly switch on and off the power.
The purpose of establishing a building automation control system is to provide a safe, comfortable, and efficient office and living environment for buildings, and to ensure the economic efficiency of the building's operation and reduce the workload of management personnel.
2. Building Automation Control Processes and "Energy Saving"
Early high-rise buildings lacked automated building control systems, resulting in a common problem: some offices were set too low due to human error, causing nearby DDO air conditioning systems to operate under constant overload, even when no one was inside; at night, property management staff could only watch helplessly as lights remained on in some offices; and public area lighting was forced to switch on and off simultaneously. All of this led to significant energy waste. In the past two years, various "smart" buildings have emerged in large numbers.
The following is an introduction to the building automation control process of a 22-story, 30,000 m2 mixed-use building.
2.1 Central Air Conditioning System Automation The building's central air conditioning system supplies 7°C chilled water from the chiller room in summer and 60°C hot water in winter, with the hot and cold water continuously circulated by pumps. The total cooling load in summer is 750 refrigeration tons, and the heating load in winter is 6.998 million kWh. Cooling is provided by one 800-ton and one 400-ton centrifugal chiller unit, and heating is provided by an oil-fired boiler and a steam-water heat exchanger. Individual rooms use fan coil units with a fresh air system, while larger public areas use modular air conditioning units as a supplement. The central air conditioning automation control system collects temperature signals by floor and installs electric valves on the terminal pipes of the air conditioning system. A field digital computer inputs temperature signals and fresh air valve opening signals, outputting control signals for the electric valves to control the chilled and hot water flow rates of the fan coil units and the speed signals of the air conditioning fans, thus achieving automatic room temperature control.
The automatic control principle of a single fan coil unit: This automatic control system uses room temperature and fresh air control valve as signal acquisition targets. By collecting signals from the fresh air valve, the system monitors the fresh air supply. It also compares the room temperature with the set temperature value for that room, collected by the central computer. In summer, the system controls the chilled water flow by adjusting the opening of solenoid valve V, and together with the fan speed, precisely regulates the room temperature. In winter, the system similarly adjusts the room temperature by controlling the flow of circulating hot water by adjusting the opening of the solenoid valve.
The chiller, boiler, piping, and hot and cold water supply of the air conditioning system are also interlocked and controlled by on-site digital computers to monitor the operation of the chiller, boiler, and water pump status, reducing the human intervention required for management during the entire system operation.
From the above, we can see that the control of the air conditioning system largely avoids the human factor. In the control room, staff set the room temperature via a central computer, providing different working environments for the building by differentiating between working and non-working hours. Generally, the central air conditioning system automatically turns on 30 minutes before working hours; during non-working hours, a standby unit provides cooling or heating, or the central air conditioning system can even be turned off. During working hours, because the temperature can only be set by the central control room, it avoids excessively cold room temperatures caused by human factors, and prevents the system from continuously operating under overload, thus effectively avoiding energy waste.
2.2 Automatic control of the lighting system The building is equipped with functional lighting, mainly including general lighting, emergency lighting, evacuation lighting, decorative lighting, high-power floodlighting of the building facade, courtyard lighting, and sign lighting.
To facilitate building automation, the lighting system was designed with specific goals in mind: different circuits were to be set up for each function and area, with separate lighting for offices and public areas on each floor, and electricity metering implemented for all lighting circuits. For floodlighting, courtyard lighting, and signage lighting, photosensitive sensors were introduced, while for security areas such as stairwells and corridors, motion-sensor sensors were used. The automation system inputs photosensitive signals and motion-sensor signals into a local digital computer and outputs corresponding lighting power on/off signals. See details for control methods.
The automatic control principle of the computer-controlled lighting system: This lighting system uses the set signals from the central computer as the main parameters. Based on the work schedules and calendars of each department, the central control room staff sets the working and non-working hours. Signals are transmitted from the central computer to the field digital computers, which output power on/off signals to activate the lighting on the relevant floors. The system collects external sunlight signals and automatically activates courtyard lighting and building facade floodlights; it also receives human motion induction signals and automatically activates lighting in relevant public areas, such as stairwell lighting and corridor lighting, and then shuts off the power after a delay.
In addition, staff can directly turn on the lighting power in relevant office areas on specific floors to meet special needs. The automated control of the lighting system virtually eliminates the phenomenon of lights being left on all night, resulting in significant energy savings.
Energy Engineering - 47 Building Management Energy-Saving Measures: The construction of building automation control systems has created conditions for energy conservation. Generally, the energy consumption of the central air conditioning system accounts for 60% to 70% of the total building energy consumption, while the energy consumption of the lighting system accounts for about 30%. Many energy-saving measures address these two aspects.
3.1 Energy-Saving Measures for Central Air Conditioning Systems To ensure energy-efficient operation of the system, consideration should be given from the initial construction phase. For example, the selection of chiller capacity should include both large and small units to meet different needs; the selection of circulating water pumps should prioritize proportional variable pumps, and air conditioning units should also be variable air volume (VAV) units. System management should also be handled differently for each control object, including the chiller, piping, and terminals. In addition, the insulation effect of the entire piping system should be considered, and regular system maintenance and management should be strengthened. Specific measures include: minimizing the operating time and output power of energy-intensive cold and heat source equipment such as boilers and chillers, reducing reactive power operation of equipment, and keeping the energy source system in an energy-saving state.
During air handling, minimize the cancellation of heat and cold. Regularly inspect the fresh air system to maximize the use of fresh air, and use a fresh-to-return air ratio method to control the supply of cooling and heating from fresh air.
By utilizing variable flow control technology and employing variable air volume and variable water volume equipment, the optimal state point control and optimal start-stop time control of water pumps and fans can be achieved, thereby reducing the energy consumption of transmission equipment such as feeders, returners, and water pumps.
For air-conditioned devices that operate continuously, the setpoints and control target values for working and non-working times are manually changed; optimal energy-saving control is achieved by reducing operating parameter values.
For comfort air conditioning systems, under the premise of meeting comfort and hygiene requirements, the indoor temperature and humidity settings are automatically changed to maximize the temperature and humidity control range of the air-conditioned object. For example, in summer, an increase of 1 degree in the temperature setting can save about 8% of the cooling capacity, which is of great significance for reducing investment and saving energy.
By employing the latest technologies in control systems, such as adaptive control and fuzzy control software, control accuracy can be improved, thereby further expanding the allowable control range of temperature and humidity and achieving energy-saving optimization. For example, improving the control accuracy from 1°C to 0.5°C can increase the setpoint of the air conditioning system, thus achieving economical operation.
Make full use of outdoor meteorological conditions and take into account indoor temperature and humidity loads to determine the optimal temperature and humidity control scheme and the optimal air handling process.
While making full use of the building automation control system, we should strengthen the patrol work of on-duty personnel to ensure the normal operation of the central air conditioning system.
3.2 Energy-saving measures for lighting systems Similarly, energy-saving measures for lighting systems should also be considered from the construction stage. Specific energy-saving measures are as follows: During the lighting design stage, reasonably estimate the building's electrical load and determine the transformer capacity; strengthen the selection of backup equipment and select transformers with low no-load losses; reduce the no-load losses during transformer operation.
The lighting system is designed and installed separately according to area and function to solve the problem of excessive lighting control range.
Choose an appropriate illuminance standard; for general offices, choose 500 LX. Select a suitable light source, prioritizing fluorescent lamps and energy-saving lamps; using energy-saving lamps can save more than 15% of energy.
During the design and installation phases, electricity metering devices should be configured appropriately for each floor, and electricity management should be strengthened to control the electricity consumption of each leased unit.
Strictly set working and non-working hours, and control the switching time of lighting power supply; in particular, the switching time of courtyard lights and floodlights should be adjusted at any time according to the changes in calendar time.
Of course, there are many other energy-saving measures, but the key is to give full play to the role of "humans" under the accurate operation of the building automation control system, so that the system can operate in an energy-saving and healthy manner.
The building is now in use, and the energy-saving effect is very obvious, judging from the operation of the building automation control system. It has been well received by users and property management personnel.
