【 Weak current College 】 go; how the introduction of new technologies such as LONWORKS BA system design---Power By 【 China power house network 】

BA system design is the key?
Owners in introducing building automatic control system for attention?

BRIEF:HOWWECANDESIGNBASYSTMWITHLONWORKSTECHNOLOGY.

WHATKEYISDESIGNINGOFBASYSTEM.

WHATPROBLEMISOWNERPAYATTENTIONTOINBA.


Currently, many modern building, especially inside the tall tower building automation installed (BA) system, not only greatly improve the efficiency of the building environment, but also the building energy consumption in quantitative control, ensure that the building energy cost reduction possible.

But it is undeniable that, for various reasons (such as designed is not perfect, and so on) also did cause some BA project not too successful, or even total failure.

In this article, would I Division in the BA engineering experience, lessons learned, as well as some new ideas written and peer exchange.

1, LONWORKS technology in BA system design

Currently, LONWORKS technology in the industry response larger BA, this control technology to traditional BA system configurations will have significant impact:

ECHELON LONWORKS technology is the United States launched the company in 1991, local action network has a complete development system platform that contains all of the design, configuration and support control network elements, is currently the most advanced control network technology.

LONWORKS technology consists of the following three core components:

(1) MC143150 or MC143120NEURON (neuron) chip

(2) implementation of the agreement, LONTALK ISO/OSI reference model and provides all of the seven-layer services

(3) Web development tool (LONBUILD) and node development tools (NODEBUILDER)


LONWORKS network's greatest advantage is its complete openness, its main findings in the following areas:

(1) LONWORKS communication protocol used by LONTALK provides ISO/OSI reference model is defined by all of the seven-layer services.

(2) supports avariety of communications media LONWORKS and any free topology network architecture.

(3) LONWORKS communication medium has support for twisted pair and coaxial cable, fiber optic and wireless microwave etc.

(4) the LONWORKS network topology can be any format that can be a star, tree, mesh-type, true-to-peer communication.


We can thus assume that when a building area is large, the control equipment (such as air conditioning units, pumps) decentralized distribution, if you are still using the traditional BA networking topologies, the implementation of on-site DDC controller communication connections ("hand") cabling not only tedious, and even some environmental impact by site to wiring. If you use DDC with LONWORKS technology, you can select any of the following situations in the field of communication network topology, system configuration flexibility, visible LONWORKS technology advantage.

But everything is differentiation, split in two, in engineering design we obviously felt:

(1) Although physical forms of LONWORKS on free topology, but each LONWORKS node requires a connection to a channel (CHANNEL), it must be a network segment (SEGMENT), system configuration, you must add a router (ROUTER), the inadequacies of the main problems:

-Increase the complexity of system management

-In fact logically increased control grading system, System classification number, the more system reliability values high, reduce system stability

(2) all vendors of components (such as various types of sensors, controllers) only and must be inserted into the curing a NEURON chip LONTALK Protocol and in accordance with the provisions of the LONWORKS control networks consisting of arbitrary topology truly intelligent network.


To sum up, from technical, LONWORKS technology for building automation system configuration provides another choice, but there are various restrictions on LONWORKS technology advantage is also not fully into play. We believe that if size-control system is not very large, for engineering design configuration best not LONWORKS technology.

2 BA key engineering design

A successful BA works must have two elements:

* System is stable and reliable, failure probability drops to lowest possible limit.

* System provides accurate quantitative control mode for building energy control provide reliable guarantee.

Any owners for building installation BA system directly to motivation is to achieve a significant reduction in energy consumption of buildings in order to achieve savings in operating costs for the purpose of the building. This requires the control of BA system as much as possible precisely as a whole.

In what follows we want from engineering design explore how to ensure precise control of BA.

2.1BA system model

In theory, a control system has the following equipment:

(1) testing transmitting equipment: will be charged objects transferred parameter detected and converted into various types of signal energy.

(2) control adjustmentSection unit: will detect the device delivered was transferred parameters signal and set value, when comparing the deviation of the issuance of certain rules of control signal to perform adjustment device.

(3) implementation of the regulation device: under control regulator (Controller) to control signals in the size and orientation, large or small valve door open and change adjustment parameter values.



Obviously, building automatic control system (BA) the main unit are:

-Testing device: various types of sensors (such as temperature sensors, pressure, pressure sensor, etc.).

-Direct digital controller: short for DDC, using the computer to the digital output signal directly control electric water valve valve to open degree.

-Actuator and electric valve



2.2BA system accuracy factor



It is clear from the above, the following conditions (factors) will have a direct impact on the degree of BA system precisely control:

(1) system front-end measured signal accurate especially like temperature this analog signal must be as accurate as possible.

How to ensure the system front-end signal accurately, we take the following measures:

* Reasonable configuration front-end sensor number. Detection points set too small, you will not be able to obtain precise front-end signal; the front sensor number (numbers table) too many words easily cause signal coupling between the system cost increase.

* The right to choose where to install the sensor. For example, to install the air duct temperature sensor if you install the air near the unit, sensor detection is the low temperature values may be; if the install in far away from the air, the sensor temperature values may be measured. This must be based on the actual situation of wind tube selection sensor installation location.

(2) system to control link small, can provide a rich control of integrating software.

At present the BA manufacturers DDC (direct digital controller), the use of a computer digital output signals to directly control the electric water valve valve to open degree, without intermediate regulator; in addition, DDC contains a wealth of integrating control procedures, (P) algorithm, PI (PI) algorithm, proportional integral differential (PID) algorithm.

Because different PID coefficient, charged objects generated different reactions characteristic curve:

PID coefficient is higher, then the object response characteristic curve is steep, the shorter the transitional process reaction; PID coefficient is lower, then the object response characteristic curve is relatively flat, that is, the response is relatively long transition process.

In theory, the shorter the transitional process, the system responds quickly, in other words, the system control precision is high, but this does not say that the higher precision of control system, the better: as the air conditioning system itself inertial larger, such as BA system control accuracy is higher, the more easily lead to oscillation system, the system the more unstable.

This requires in engineering design and debugging of the process correctly software configuration, select the appropriate sampling cycle and control functions, ensure the system response output optimization, system control accuracy and system stability and balance.

(3) to ensure that the valve to open degree "zero"

All kinds of electric water valve is the main implementing agency BA system, in the air conditioning running control valve opening is BA system is mainly regulated content. Of these, guarantee the valve to open degree "zero" is BA system control accuracy is an important guarantee. In other words, select the correct flow characteristics and the appropriate diameter of electric water valve is BA system guarantee of success.

* Electric regulating valve flow refers to the air conditioning of water flow through the valve and the valve of relative relative aperture function between, currently works on commonly used mainly in the linear flow rate characteristic, equal percentage flow characteristics of electric water valve.

Unit itinerary changes due to changes in relative flow and point of relative flow proportional relationship is equal percentage flow characteristics of water valves. The type of water valves, adjustable range relatively wide, more suitable with balancing hydronic systems, therefore a large number of applications in BA systems is equal percentage flow characteristics of electric water valve.

* Electric water valve diameter determines the adjustment precision valves. Water valve diameter selection is too large, not only increase the owners of the investment costs and make the valve basic stroke units larger lead valve adjustment precision cut, to saveenergy; water valve diameter selection is too small, often occur even if the water valve all open systems are difficult to reach the set temperature value to achieve control objectives.

So how to compute your electric water valve diameter?

Projects we commonly used is by calculating the electric valve flow coefficient (Kv/Cv) values derived electric water valve caliber, because flow coefficient and water valve caliber is a correspondence, in other words, discharge coefficient set, water valve diameter size is defined.

Water valve flow coefficient (Kv/Cv) using the following formula:

Cv=Q/ΔP1/2

Where Q-equipment (air conditioning/air supply unit) of cold/heat or air flow Δ P-valve before and after the pressure differential ratio

In theory, in different air conditioning circuit, Δ P values are different, is a dynamic change of value ranges generally from 1-7. But because flow coefficient calculation process Δ P is evaluated, and so on of radicals Cv calculation is not very big. Therefore, in engineering design general elections Δ P value is 4.

For example, 1 air conditioning unit specification values are as follows:

◆Maximum air flow: 8000M3/H cooling capacity: 47.17KW calories: 67.55KW

Residual pressure: 410PA power: 2KW

How to adjust water valve selection?

First, we calculate the flow coefficient Kv/CV

Cv=Q/ΔP1/2=67.55*0.685/2=23.14

Kv=Cv/1.17=43.92/1.17=19.8

Then calculated flow coefficient Kv/Cv selection and adjustment of suitable diameter water valve.

3, owners should be aware of several issues

3.1 is a pragmatic view of BA's energy-saving

Investment for building owners to install BA system mainly look at BA system can save energy costs, lower operating costs, improve building building economic efficiency.

But a significant number of owners exist error: think building energy-saving is relying on a system, BA BA system can save a lot of money. This perspective although understandable, but apparently overlooked BA system prerequisites: as long as reasonable in HVAC design, in combination with rational and effective automatic control of BA, can we truly achieve savings in manpower, energy saving. In other words, the building of energy-saving is a comprehensive systems engineering, not solely rely on BA system can achieve. For building energy-saving relationship with BA system has specialized literature analysis, this article does not do an in-depth discussion.


3.2 procurement equipment should be considered when BA interface

In theory, BA on the control device model, brand, functionality, there is no limit, but this does not mean that BA on the device is not required: owners purchase controlled electrical equipment must have secondary control loop or BA BA interface, otherwise the system is unable to carry out effective controls.

I Division in engineering practice found many owners did not take into account in procurement of equipment, electrical cabinet BA requires no secondary circuit, had to restructure electric control cabinet, causing owners investment waste.

Because of the different brands of BA systems to secondary control circuit requirements vary, so it's best to go ahead with BA contractors.

4, summary

The above just in BA engineering practice and experience of some experience, experts and peer humour.

5. references

(1) of the East China architectural design, the intelligent building design technique of Tongji University Press, October 1996

(2) is editor in Chief, Chen of the intelligent construction electrical design handbook, Chinese building material industry press in August 1999

(3) land great good, the intelligent building guide pulley of China construction industry press June 1996

(4) land great good, the smart building mainstream technology Outlook August 1998

(5), the wish King Air-conditioning energy saving and building intelligent act in December 1999