XML. Standard solution.
A few years ago, the integration of BAS (Building Automation System) ) into any computer system was such a difficult task that successes in this area were separately reported in specialized thematic publications.
Today this has become a widespread phenomenon.
A college in Pennsylvania collects data (water, electricity, gas consumption, CO2, CO levels) from a large number of systems to a remote field station, compares it with a modeling program and publishes the results on its website.
Company An aviation research company in Texas collects data from a large number of chillers and air conditioners and puts it into an Excel spreadsheet for analysis and troubleshooting.
In an office complex in Melbourne, such data is used to issue invoices for the provision of additional services to each of the users.
If there is any doubt about the amount of bills, a detailed report is immediately submitted, which records the exact time the air conditioners were turned on and off and the dates when all requests for their use were received.
In the US, a building automation contractor collects data from all variable air volume (VAV) air conditioners and heating circuits in a new building and includes it in the commissioning report.
All these projects were implemented using a new standard for data exchange — XML (eXtensible Markup Language).
This is an information technology standard that is being actively implemented in a wide variety of industries.
It can be considered the successor to the DDE, OLE and OPC specifications, but the successor is more powerful, more popular and much more compatible with the Internet than all previous ones.
Today, the XML standard is jointly and very successfully supported by such bitter competitors as Microsoft, Apple and Linux!
Does this mean that BACnet, LonWorks and many other protocols are losing their relevance? Not at all! XML was created to exchange information between computers at the top level.
The corresponding data files contain readable text, and the structure of this data includes fairly lengthy (for a computer) descriptions of exactly what data is contained in the corresponding files.
This allows programmers to relatively easily find the information they need and quickly establish connections between computer databases.
But this also means that transmitting information requires significantly more channel capacity than using any of the specialized protocols used in BAS.
XML is well suited for data transfer over local IP networks such as Ethernet, but can create excessive load when used in field controller networks. And if XML is ever used in air conditioning controllers, it will be in the very distant future.
The XML standard itself does not contain any provisions that would standardize communication in BAS, so in this regard, using XML would be a step back to the days before the development of the BACnet and LonWorks standards, when each manufacturer created its own communication standard.
Test point data, graphs, warning messages — all this can be presented in any format the manufacturer chooses, and such data will still comply with the XML standard.
ASHRAE and other groups are working to correct this problem by developing a standard for representing BAS data in XML format.
If BACnet and any other specialized protocols for BAS are better developed and more efficient than XML, then why is there so much fuss about this protocol?
XML provides a standard method for BASs to communicate with other computers, whether those computers belong to other BASs or to completely different systems.
The original version of the BACnet protocol did not support IP addressing used on the Internet because the Internet was not yet very mature when the BACnet standard was created.
This situation changed very quickly.
Currently, BACnet and other protocols for BAS support communication over the IP protocol, as it has become the de facto standard for high-level communications.
Today, BAS manufacturers are similarly introducing XML support into their web servers and carriers. workstations, since it was XML that became the standard for communication with other systems at this level. XML is a logical extension of building automation system protocols.
XML also allows for high-level abstraction of BAS data and its transformation into a format that facilitates communication with other systems.
For example, a programmer creating a computer program for a utility company might need information about equipment turn-on schedules from the BAS, or the program would need to send a command to the BAS to limit utility consumption.
By using XML, you won’t need to learn all the intricacies of BAS’s internal protocols to perform these simple operations. The same can be said about computer programs used in accounting, for managing hotel rooms, for scheduling school classes, for monitoring patients in hospitals, etc.
There are also many programs that building owners can integrate into their BAS, but most often they do not even provide a BACnet standard interface, let alone simultaneously support BACnet, LonWorks and other specialized proprietary protocols used in modern BAS.
Typical BAS network
There is also a problem for integrator programmers working in poor companies that need to collect data from a large number of computer systems scattered throughout the city, or in large corporations where it is necessary to prepare reports for management summarizing the accumulated information.
Do such programmers need to learn the internal data formats of all applications from which the information they need will be obtained?
XML allows such data to be provided through a standard, self-documenting interface that is independent of the data structure or internal communication protocols of the BAS.
When XML is combined with a standard service provisioning protocol such as SOAP, it creates a universal interface that can be used to communicate across thousands of individual computer applications.
How universal is such an interface? Dan Traill of U.E.S. Controls (Houston, Texas) provides two examples.
The school district asked his company to collect utility usage data from several schools, conduct a month-by-month audit of energy use, compare actual energy use to local weather data, and rank those schools according to energy efficiency.
Since the BAS in these schools was supported by network services, the company’s engineers had no problems creating the requested report.
“It was a very simple process,” Dan stated.
“They used the built-in XML support to create a Microsoft Excel spreadsheet, automatically loaded data into it, and based it on it created a report in Excel format.”
A more complex situation arose when the company was asked to develop a program that would allow 2,000 workers to extend their office hours but would account for the associated additional use of HVAC systems.
To develop this program, the company entered into an agreement with a firm, and its programmers submitted to U.E.S. – a fairly large preliminary estimate for the development of this program using a special interface for data exchange. When Dan told the programmers that BAS supported XML and SOAP, this estimate was cut in half.
The combination of XML and SOAP has already gained wide acceptance in the world of information technology. At Microsoft, this combination was called .NET, at IBM — WebSphere, at Sun — SunOne.
Other manufacturers use different names, but they can all be classified under the general category of «network services» that can be used to read data from one computer and write it to another. They can also be used to run applications on remote computers.
A standard has been developed for information technology that supports data exchange, but it does not cover the entire volume of data and services that systems can exchange.
It would be nice if it also allowed you to search for the necessary data.
Even better, it could extract the data it needs without requiring the services of a separate programmer.
Such a standard should include not only protocols for packaging and sending data, but also protocols that define the format of the data itself.
Because the range and variety of data generated by BAS is large, the standard must be flexible and comprehensive, integrating the information model of the entire building and its constituent systems.
This problem is not limited to the BAS industry.
Network services have been used to transfer data between companies for several years. As in the BAS industry, network services were initially seen as the solution to all B2B communications problems and as a universal tool for data exchange.
It soon became apparent that although network services were a very useful tool for speeding up such data exchange, the process of transferring data still required writing a large number of special programs to find and connect the data that was to be exchanged.
The problem could be greatly simplified if every industry adopted a standard information model that allowed programs to automatically find the data they needed without human intervention.
And today, many standards already exist or are in the process of being developed in dozens of industries, such as biometrics, electronic shopping, legal records management and security systems.
ASHRAE has been developing an XML building information model for several years.
It is not surprising that the BACnet standard development committee also takes a significant part in this process, because the letters BA in the name BACnet stand for Building Automation, i.e. «building automation».
The new information model, called BACnet/WS (BACnet Web Services), is intended for use beyond this protocol. In essence, this is a universal model capable of operating in BACnet, LonWorks and other control protocols. It can provide a common basis for high-level interoperability and data exchange between these protocols.
In June 2004, the proposed model was opened for public comment at the ASHRAE convention, where it was adopted as part of the ASHRAE/ANSI/ISO standard for automation of control of building utility systems.