1、外文资料 Energy-saving solution for commercial buildings Commercial buildings energy-saving solution for the status quo of Chinas electricity industry government agencies, enterprises, universities, hotels, hospitals and other buildings have we can not ignore the cost, that is, high tariffs, and we ofte
2、n spend a lot of energy through administrative means to Energy management and energy conservation announced Analog-to-digital (A/D) converter: The part of a microprocessor- based controller that changes an analog input signal to a digital value for use by the microprocessor in executing software pro
3、grams. Analog input values typically come from temperature, pressure, humidity, or other types of sensors or transducers. Application software: Programs that provide functions such as direct digital control, energy management, lighting control, event initiated operations, and other alarm and monitor
4、ing routines. Configurable controller: A controller with a set of selectable programs with adjustable parameters but without the ability to modify the programs. Digital-to-analog (D/A) converter: The part of a microprocessor- based controller that changes digital values from a software program to an
5、alog output signals for use in the control system. The analog signals are typically used to position actuators or actuate transducers and relays. Direct digital control: A control loop in which a digital controller periodically updates a process as a function of a set of measured control variables a
6、nd a given set of control algorithms. Microprocessor-based controller: A device consisting of a microprocessor unit, digital input and output connections, A/D and D/A converters, a power supply, and software to perform direct digital control and energy management routines in a HVAC system. Operating
7、 software: The main operating system and programsthat schedule and control the execution of all otherprograms in a microprocessor-based controller. This includes routines for input/output (I/O) scanning, A/D and D/A conversion, scheduling of application programs, and access and display of control pr
8、ogram variables. System-level controller: A microprocessor-based controller that controls centrally located HVAC equipment such as variable air volume (VAV) supply units, built-up air handlers, and central chiller and boiler plants. These controllers typically have a library of control programs, may
9、 control more than one mechanical system from a single controller, and may contain an integral operating terminal. Zone-level controller: A microprocessor-based controller that controls distributed or unitary HVAC equipment such as VAV terminal units, fan coil units, and heat pumps. These controller
10、s typically have relatively few connected I/O devices, standard control sequences, and are dedicated to specific applications. BACKGROUND COMPUTER BASED CONTROL Computer based control systems have been available as an alternative to conventional pneumatic and electronic systems since the mid 1960s.
11、Early installations required a central mainframe or minicomputer as the digital processing unit. They were expensive, and application was limited to larger buildings. Reliability was also an issue since loss of the central computer meant loss of the entire control system. Advances in microtechnology
12、, particularly in large scale integration (LSI), provided answers to both the cost and reliability issues. Introduction of microprocessors, i.e., a computer on a chip, and highdensity memories reduced costs and package size dramatically and increased application flexibility (Fig. 1). Microprocessor
13、programs include all the arithmetic, logic, and control elements of larger computers, thus providing computing power at a cost/ performance ratio suitable for application to individual air handlers, heat pumps, VAV terminal units, or the entire equipment room. Microprocessor-based controllers allow
14、digital control to be distributed at the zone level, equipment room level, or they can control an entire building. A more detailed definition is provided in the ASHRAE 1995 HVAC Applications Handbook. “A digital controller can be either single- or multiloop. Interface hardware allows the digital com
15、puter to process signals from various input devices, such as the electronic temperature, humidity, and pressure sensors described in the section on Sensors. Based on the digitized equivalents of the voltage or current signals produced by the inputs, the control software calculates the required state
16、 of the output devices, such as valve and damper actuators and fan starters. The output devices are then moved to the calculated position via interface hardware, which converts the digital signal from the computer to the analog voltage or current required to position the actuator or energize a relay
17、. In each of these definitions the key element for DDC is digital computation. The microprocessor unit (MPU) in the controller provides the computation. Therefore, the term digital in DDC refers to digital processing of data and not that HVAC sensor inputs or control outputs from the controller are
18、necessarily in digital format. Nearly all sensor inputs are analog and most output devices are also analog. In order to accept signals from these I/O devices, A/D and D/A converters are included in the microprocessor-based controller. Figure 2 shows several inputs and outputs. The microprocessor usu
19、ally performs several control functions. DIRECT DIGITAL CONTROL Inherent in microprocessor-based controllers is the ability toperform direct digital control. DDC is used in place ofconventional pneumatic or electronic local control loops. Thereare several industry accepted definitions of DDC. DDC ca
20、n be defined as “a control loop in which a digital controllerperiodically updates a process as a function of a set of measuredcontrol variables and a given set of control algorithms”. ADVANTAGES Digital control offers many advantages. Some of the moreimportant advantages are discussed in the followi
21、ng. LOWER COST PER FUNCTION In general, microprocessor and memory costs keep coming down while inherent functionality keeps going up. Compared to earlier systems, physical size of the controller is also reduced while the number of discrete functions is increased. Digital control, using a microcomput
22、er-based controller, allows more sophisticated and energy efficient control sequences to be applied at a lower cost than with non-digital controls； however, simple applications are less costly with non-digital controls. APPLICATION FLEXIBILITY Since microprocessor-based controllers are software base
23、d, application flexibility is an inherent feature. A wide variety of HVAC functions can be programmed and, in addition, the controller can perform energy management, indoor air quality (IAQ), and/or building management functions. Changes in control sequences can easily be accommodated through softwa
24、re whether dictated by system performance or by changes in the owners use of the facility. COORDINATED MULTIFUNCTION CAPABILITY Although basic environmental control and energy management operate as independent programs, it is best to have them incorporated as an integrated program in order to provid
25、e more efficient control sequences. For example, sensing the temperatures of several zones to determine the average demand, or the zone with the greatest demand for cooling, will provide improved efficiency and control over merely sampling a representative zone for a chiller reset program. An added
26、feature is that the sensors providing zone comfort control can serve a dual function at no added cost. These benefits require controller-to-controller communications which is discussed in the Building Management System Fundamentals section. PRECISE AND ACCURATE CONTROL Proportional control has the i
27、nherent problem of offset. The wider the throttling range is set for control stability, the greater the offset. With the microprocessor-based controller, the offset can easily be corrected by the simple addition of integral action. For even more accurate control over a wide range of external conditions, adaptive control algorithms, available in some microprocessor-based controllers, can be
