Building heating and cooling control systems facilitate proper functioning of building heating and cooling systems so that the internal environment is comfortable at the optimal price. Control systems have become more sophisticated, enabling facilities managers to better maintain cost and energy efficiency.
Fundamentals of Control Systems
Sensor to Controller to Controlled Device. The operational design for building control systems uses a sensor to controller to controlled device (or feedback) system. The control system manages building temperature, humidity, pressure, or cleanliness. In temperature control, a sensor determines the desired temperature (set point), and a controller determines desired directional change. The modern thermostat fulfills both functions but requires a controlled device to activate the environment change. Regularly used controlled devices include airflow controls, electric switches, and automatic valves.
Feedback. Control systems require feedback to measure the changes activated by the communication between sensor, controller, and device.
Coordinated Operation. The building control systems enable monitoring and coordination of system efficiency. The goal of using a building control system is to maximize comfort, minimize facility wear and tear, and manage energy consumption.
Brief History of Automatic Control Systems Original Systems. Early buildings used manual heating systems (e.g., stoves and fireplaces) and were not cooled in warmer months. As buildings became larger, steam heat and individual windows for light, air, and ventilation were installed. Uniform heat distribution needs drove the creation of a more automated control system. An early system allowed an occupant to signal that the room was cold and needed heat by ringing a bell to signal the fire stoker to increase heat flow. In 1985, the first thermostat was created by combining a metal that would bend in the presence of heat with a temperature sensor and an electrical switch. The thermostat automatically rang the bell when the room dropped below a specific temperature. As building size increased, a fully automated control system was developed. Fans for building ventilation were interconnected with electric motors, which operated the valves that the thermostat signaled to open or close.
Around 1910, pneumatic control systems that provided proportional air control soon replaced early automated systems, which only allowed on-and-off device control.
Pneumatic Controls Period. Pneumatic control systems developed in the 1920s remained the industry standard into the 1990s. As the low cost of pneumatic controls facilitated widespread use in building control systems, demands emerged to control other environmental needs. The humidistat was invented and connected to the sylphons, humidifying building air.
Together, they formed a sensor to controller system that functioned like the heating system. Pneumatic control system capabilities were further enhanced by development of capillary sensing to monitor air conditions in air ducts rather than rooms.
As control systems quality evolved, so did the desire for system feedback to monitor the difference between desired result (set point) and actual outcome. Second- order feedback systems increased overall system efficiency by automating the system feedback loop to minimize set point (e.g., desired temperature or humidity) overshoot. Quicker system response times (derivative control) and greater system efficiency (integral control) enabled proportional-integral-derivative control. Pneumatic transmission (most common type of campus building control system) separated the sensor from controller by an air pipe, allowing multiple systems to simultaneously access and respond to sensor signals.
Electro-pneumatic systems emerged as control systems included clocks, switches, and lights. As systems became more complex and required more intensive monitoring and adjusting, costs rose, and control system specialists and technicians replaced building engineers.
In the 1970s, the integrated circuit and improved systems software made computerized systems viable, lowering cost and improving efficiency.
Into the Digital Age
Building Monitoring and Control Systems. System software and multiple energy crises created an even stronger case for energy efficiency. The growing need for cost containment and system control pushed facilities to include fire alarms, security systems, and lighting control in a comprehensive building monitoring and control system. Before the mid-1980s, buildings had separate pneumatic and control oversight systems. In the new integrated digital control systems, all sensors interfaced with one controller.
Digital Control Systems. Digital control systems have evolved beyond simple centralized control. As systems became smaller, distribution of system intelligence was possible. Input point information was available to all systems, and localized resources (rather than the central control system) could effectively respond to system adjustments. Graphical User Interfaces (GUIs) became more user friendly, enabling more effective system monitoring and fine-tuning. Converting from old building technology to digital control is cost-effective but requires a robust system design to take full advantage of system capabilities.
Managing Control Systems on Campus Most campuses combine three types of control systems: pneumatic transmission, separate building monitoring, and some digital control. Effective maintenance strategies require an in-depth understanding of system design, maintenance expectations, and hardware and software replacement options.
Understanding Control Systems. Campus control systems were most likely installed as needed over the years. Third-party control system suppliers provide extensive training opportunities and traditionally have produced control drawings that document system installation details and system specifications and capabilities. Control documents must be available to all relevant staff members.
Maintaining Control Systems. Control systems, especially pneumatic transmission systems, require maintenance. Facilities managers at smaller institutions are more likely to outsource maintenance to specialists; larger institutions usually establish in-house expertise. Systems integration must be seriously weighed when determining system upgrades or overhauls because individual control systems are proprietary and integration is often challenging. Limiting the number of system vendors can minimize integration issues but can affect cost (e.g., more limited bidding).
Replacement of Control Systems. Many institutional building control systems are more than 30 years old and soon will need a complete overhaul or replacement.
Hybrid systems are available that enable integration of still-functioning older units into a new system.
Complete system replacement can make the most functional sense, but cost is a strong consideration.
Applications of Control Systems
Control system design begins with determination of desired system functionality. Avoiding unnecessary system complexity and choosing a system that is understandable to users are vital. Other important factors in choosing a high-quality control system are compatibility with existing systems, availability of prompt access to service and parts, and ongoing maintenance expectations.
Energy Conservation Strategies
Efficient management of heating and cooling systems is an important element of an overall energy conservation strategy. The biggest savings from a more efficient control system result from optimizing and reducing energy use.
Occupied-Unoccupied. The best energy conservation strategy turns off equipment when a building is not in use.
Unoccupied Setback. Reducing or increasing the set point of individual room thermostats reduces energy consumption.
Temperature Compensated System Start-Up. The energy required to restart equipment that was turned off in an unoccupied building is minimized by allowing the control system to factor in outside weather and indoor temperature in determining optimal restart time.
Demand Control. A central monitoring and control system manages energy load demands to minimize peak energy cycles and reduce utility costs.
Duty Cycling (Load Cycling). Duty cycling reduces overall energy demand by turning off systems for prescribed short periods of time during normal operating times.
Zoning. Zoning is a modification of air distribution equipment that allows partial system shutdowns.
Individual Space Operation. Digital control systems can modify individual room temperature controls, enabling optimization of energy use room by room.
Automatic Set Point Adjustment. Individual rooms have different set point requirements for temperature control in different seasons. Automatic set point adjustment permits the control system to reset those set points automatically, resulting in increased energy efficiency.
Ventilation Control. Some ventilation standards require specific minimum levels of outdoor air ventilation.
Programming the temperature control system to use the temperature differentials between inside and outside air to facilitate more efficient internal climate control increases energy efficiency.
Common Control Strategies
Types of Control. System control can be effected in many ways, including two-position control, proportional control, proportional + integral control, and proportional
+ integral + derivative control.
Air Damper Design Strategies. Airflow can be controlled with a parallel blade damper (best suited for open-or-closed systems) or opposed blade damper flow (more efficient performance in an environment with a varying range of air flow demands).
Control Valve Pressure Drop Design. Control valve size affects efficiency in both air and water temperature control systems. Oversized or undersized valves impair airflow and water flow control, potentially damaging the system.
Future of Control Systems
Available control systems offer insights into future control systems and new features.
Systems Integration. Ongoing systems integration is likely. Buildings with individual integrated control systems will be connected with a network of other buildings and systems to create one universal campus system. Some common communication protocols allow different control systems to communicate. The result will be greater flexibility in system design and operation.
Distribution of Access. Facilities experts historically have managed control systems. As control systems advance, the management of individual systems will be in the hands of users.