Filter or Treat Ventilation Air Supplies

Ideally, green buildings have simple lighting equipment and minimal HVAC systems since their form, structure and envelope inherently provide comfort. Most modern urban buildings, with their site and program constraints, require more extensive electrical and mechanical systems with automatic control.

The best control strategy allows occupants to directly manipulate simple and understandable building features, such as windows or shades. Controls should provide immediate feedback on their effects, but should not require occupant attention for safe, healthy indoor conditions, low energy consumption and operating costs. Occupants should be able to control their own surroundings, but automatic building controls must ensure the building operates efficiently regardless of occupant behavior.

Direct Digital Control Systems

Direct digital control (DDC) allows precise, flexible management of electrical and mechanical systems, and allows monitoring and management of energy consumption and demand. Rapid advances in computer technology have provided improved digital control systems at moderate cost. Many of the Recommended Practices of this chapter are technically and economically feasible because of these advances.

Larger climate-responsive buildings are often best served by a digital control system that tunes and adjusts electrical and mechanical systems to supplement natural light and cooling. Digital controls can easily respond to occupancy and schedule changes throughout the life of the building.

Daylighting controls can allow the electric lighting energy to be reduced by as much as 80%. Properly designed, they are essentially unnoticeable, and provide occupants with the ability to adjust space lighting to their own needs. Reduced lighting power translates into lower cooling loads, smaller HVAC equipment and reduced energy consumption.

Digital control coupled with occupancy sensors for lighting and HVAC systems ensure that if lighting or space conditioning are not needed, they are not used. This helps to reduce the energy consumption and equipment needs of a building, and offset control costs.

Similarly, variable-speed motor controllers ensure that energy is not wasted providing air or water flows that are unnecessary for comfort. Speed controller costs are falling quickly, and are now economic in much smaller applications than before.

HVAC Control Strategies

DDC systems also allow optimal HVAC control strategies that were difficult or expensive to do with older pneumatic controls. One example is load-shifting to periods of low utility demand. Correctly programmed energy management controls can substantially reduce energy costs, by operating HVAC equipment during periods of lower gas or electricity demand charges.

Night cooling in particular uses the building structure for thermal storage, allowing HVAC equipment to operate more efficiently when outdoor temperatures are cooler and demand charges lower. As well, operating costs are reduced, since high-demand fans and pumps are used less during peak demand periods.

Requirements for Best Controls Performance

However, DDC systems have some disadvantages. Poorly designed systems can be inaccessible or incomprehensible to occupants. DDC systems require careful design to allow occupants simple, understandable local control without disturbing safe and economical electrical and mechanical system operations.

Design efforts to control solar gain, natural lighting, ventilation and cooling will be wasted unless the systems are set up and commissioned properly from the start. Proper testing, commissioning and documentation are essential for efficient operations, preventive maintenance and occupant satisfaction.

To use digital control systems to their full potential requires trained building operators motivated to provide healthy, comfortable indoor conditions and efficient operations. This has led to a trend towards professional building management by “building service companies”, staffed by controls technicians, often operating many buildings from a remote central location.

Older digital control systems have suffered from incompatibilities between different manufacturers, limiting design and operator flexibility and greatly complicating building operator training. Recently there has been much progress on “interoperability” - integrating building controls, sensors, and actuators with security, communications and computer local area networks (LANs). Two protocols have been established that allow equipment from many different vendors to communicate and work together: Lonworks; and BACNet, sponsored by the American Society of Heating, Refrigerating and Air-Conditioning Engineers. These will greatly ease the task of controls integration in new designs and in future retrofits.