In the world of building systems, where things that ain’t completely broke are lucky to get a bandage, decades can go by pretty fast. The results of a recent Building Operating Management survey offer a case in point: 27 percent of respondents have a building automation system that is 20 years old or older.Twenty years ago, BACnet and LonMark represented disruptive technology innovation. Systems using those open protocols quickly entered the market, but it took years before open-protocol systems became the norm for new BAS. Even today, a lot of buildings are run by BAS that aren’t interoperable: 61 percent of survey respondents said they have BAS that do not communicate with each other. No wonder the highest priority for a new BAS is compatibility with existing systems, according to the survey. With 47 percent of respondents calling that the most important factor in selecting a new BAS, it ranked well ahead of functionality and first cost.Long years of experience with BAS that don’t talk to each other have schooled facility managers in the importance of open systems. And that topic remains as relevant today as it was in the years when proprietary protocols dominated the BAS landscape.Consider access to data. To get the most out of the new generation of Building Internet of Things products, as well as familiar building controls, facility managers have to ensure that data flows easily from one system to another. But with sensors and cloud-based platforms, openness doesn’t mean an open protocol like BACnet or LonMark, as it does with a BAS. Rather, it depends on an open API, or application programming interface. Although many Building IoT products have an open API, some don’t. It’s pretty obvious which one you want.The point for facility managers is simple. With any new building automation or information system, whether it’s a traditional BAS or one of the new Building IoT options, it’s important to understand how data will be shared. The last thing any facility manager wants is to lock into a system today that constrains choices for the next 20 years.