Controls

A thermostat (Fig. 26-8) is a temperature-activated switch that turns heating and cooling equipment on and off in order to maintain a preset temperature. Thermostats also control the flow of water to radiators and convectors. The fans that circulate warm air also use thermostats. The thermostat triggers a low-limit switch, which turns fans and pumps on for the heat-distribution system when a preset low temperature is reached. An upper-limit switch shuts off the furnace when the

Figure 26-8 Thermostat.

specified temperature is reached. A safety switch prevents fuel from flowing to the heating plant if the pilot light or fuel-ignition system is not working.

A 1° reduction in the thermostat setting can save 2 percent of the heating bill for a home. Clock thermostats set back the temperature automatically at night, and turn back up one-half hour before the occupants get up in the morning. Clock thermostats pay for themselves in about one year.

The mechanical engineer determines the location of a thermostat based on the location of surrounding heat sources. Most thermostat malfunctions result from improper location, poor maintenance, or inappropriate use of the device. To work properly, the thermostat must be mounted on an inside wall away from doors and windows, so that it will not be affected by the outside temperature or by drafts. Do not place lamps, appliances, TV sets, or heaters under the thermostat, as their heat will affect furnace operation. If the thermostat is in a location where the space's occupants usually change the temperature, it should be in an accessible location, although there is no specific requirement in the Americans with Disabilities Act (ADA).

The interior designer should make it a point to know where the thermostat is to be located, as it could end up in the middle of a featured wall, right where the designer had planned to hang a piece of art. Thermostats are available with a flush-mounted wall plate, and with remote sensing wires that could be wrapped around a picture, sculpture, molding, or other decorative element. When thermostats must be concealed for aesthetic reasons or to avoid damage, they can be located in a return air duct.

Self-contained thermostats provide inexpensive room-by-room control for water or steam distribution systems. Self-contained thermostatic control valves can be mounted directly on cast-iron radiators, fin-tube radiators, FCUs, and unit heaters. They can be retrofitted in dormitories, apartments, and offices that have only one thermostat for each floor of the building. They provide highly cost-effective energy conservation by controlling the temperature locally, eliminating the need to open windows in overheated rooms. Self-contained microprocessor-based thermostats can be fine-tuned for flexible, simple control.

The HVAC controls for small buildings are usually thermostats. The American National Standards Institute (ANSI) and ASHRAE have published Standard 90.21993, Energy Efficient Design of New Low-Rise Residential Buildings, which set standards for thermostats. Thermostats must be able to be set from 13°C to 29°C (55°F-85°F). They must also have an adjustable dead-band, the range of which includes settings at 5.6°C (10°F) increments. The deadband is a range of temperatures separating a lower temperature that triggers the heat to go on from a higher temperature that starts the cooling system.

Workstation delivery systems (Fig. 26-9) offer personalized air-distribution controls. Some systems use conditioned air supplied through conventional ceiling systems, while others supply the air from a floor, wall, or column plenum. Both types of systems utilize a large under-the-desk fan and electronics unit that requires a single utility outlet. This outlet is equipped with telescoping ducts attached to desktop diffusers to distribute the airflow as desired. Individual users can control air temperature, airflow, under-desk radiant heat, task light level, and background noise from a desktop control unit. When the West Bend Mutual Insurance Company headquarters installed 370 of these units in the early 1990s, thermal complaints were immediately cut down from 40 a day to 2 per week.

Diffusers for air and masking sound

Control panel

System includes fan, air filters, air mixing box, masking^ sound. Control panel adjusts task lighting, sound, fan, air mix and radiant heating.

Figure 26-9 Workstation delivery system.

System includes fan, air filters, air mixing box, masking^ sound. Control panel adjusts task lighting, sound, fan, air mix and radiant heating.

Figure 26-9 Workstation delivery system.

One workstation delivery system provides each workstation with a fan, air filters, an air mixing box, and a masking sound generator. The control panel allows adjustment of task lighting, background sound, fan speed, air mixture, and radiant heating located below the desk. Another type of system uses ductwork integral to the workstation panels. Conditioned air flows from the building's HVAC system through a control box and the ductwork, then through dampers and down into the workstation. Workers turn the control dial within their workstation to regulate the volume of conditioned air flowing into the workstation. Research by Professor Alan Hedge of Cornell University indicates that having individual control of conditioned air results in reduced stress and increased productivity.

Building management control systems are designed to meet the needs of commercial office buildings, hospitals, hotels, schools, manufacturing facilities, universities, and other specialized facilities. Systems are designed to be easy to use and to have extensive reporting capabilities. Building management systems use direct digital control (DDC), with microcontrollers on each piece of regulated equipment. The DDC system can respond to the needs of specific users. DDC systems can be integrated with energy management systems for individual buildings, as well as centralized management of individual systems in separate locations. A central controller connects the operator's workstation to other controllers that handle specific task locations, such as equipment and machine rooms. These are in turn connected to the end devices, such as motors and sensors, which produce the desired action. Systems are designed for the specific application, and the manufacturer also provides training for facility staff.

Control systems for mechanical and electrical equipment can automatically warm up or cool down rooms in time for the occupants' arrival. Central automatic systems control fresh air quantities, adjust movable sun-shading devices, and adjust the intensity of lighting, promoting the maximum amount of on-site, renewable energy use. Control systems use little space, but must be accessible for upgrades. Where buildings use automatic controls for HVAC systems, the specifications for mechanical work usually require an operating manual and orientation session for the building manager on how the system works.

Building management systems for small buildings can be activated by remote control in anticipation of the owner's arrival. Door and window locks, security cameras, lighting, and appliances can be part of a comprehensive control system.

Central logic control systems are building management systems for large buildings, and are used in most new large buildings. The goal of central logic control systems is to maintain comfort with energy conservation. They coordinate relationships between the building's structure, systems, services, and management for improved productivity and cost effectiveness. The centrally regulated HVAC is tied into the lighting, electrical power, elevators, service hot water, access control and security, telecommunications, and information management systems. These systems alert building staff to malfunctions and can learn from past practice and keep records on performance.

The fume hoods in laboratories exhaust a large quantity of air, and may need to isolate hazardous substances, toxic materials, and disease or other biological organisms. The building control system can keep the lab under positive pressure and balance the needs for isolation and fresh air.

Hotels risk energy loss in unoccupied rooms or rooms with open windows. By tying the building control system into the registration desk, the system can respond to remote unoccupied rooms and open windows. A purge mode can clear the air completely for a new occupant.

Offices use building control systems to tie together VAV supply units, ventilating windows, daylight reflectors, venetian blinds, radiant heaters, electrical lighting, and insulating shades. A control panel allows an individual worker to interact with the control system.

Building management systems that include indoor air quality (IAQ) sensors automatically measure IAQ and control outside air intake. The HVAC system is then adjusted automatically.

Very sophisticated systems are currently under development for small buildings, such as residences, retail, and commercial occupancies. In buildings with varied and unpredictable use patterns, adaptive control of home environment (ACHE) systems anticipate users' needs and save energy. These ACHE systems use a neural network that adapts to its environment and anticipates users' needs to control lighting, air temperature, ventilation, and water heating, providing just enough energy when needed. Lights are set to the minimum requirement and heated water is maintained at the minimum level to meet demands. Only occupied rooms are kept at the optimal temperature. The control framework compares the cost of energy against a level of minimal acceptable comfort. The settings develop as the building is used over time. They adjust to overrule of the minimum levels, but test that minimum occasionally to make sure that a more energy-efficient level isn't acceptable.

Building management systems are not without problems. A study of 60 new buildings found that half suffered from controls problems, 40 percent had HVAC problems, and a quarter had malfunctioning energy management systems, economizers, and variable speed drives. Most shocking of all, 15 percent had missing equipment!

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