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10 building. "Those days are gone because you cannot scale if it takes so long for a technician to install something," Mohan says. "Making the process quick and easy for the installer is important." Another constraint is that most businesses lease the space they occupy. Installing core building automation systems, such as heating, ventilation, and air conditioning, could involve costly building alterations that would require permission from building owners. "A tenant has little control," Mohan says. "As a solution designer, you can have much great success with smart control systems that work on top of existing equipment. Now, you're talking about tailoring sensor hardware and controls to the solution. Focus on use cases that don't require core, building framework–level changes." Designers have many choices when creating smart building control systems. One of the most important is where to put computational power. Does it belong in the cloud, in sensors, or somewhere in between? Packing compute power into sensors has disadvantages, as well. One is that the more processing power and RAM you have in the sensors, the more power they consume, which means that you will need to plan for hard-wired sensors or frequent battery changes. Mohan says, "As much as we talk about user experience from a user interface point of view, having a customer change a battery every 12 months is a no-go for market acceptance." Another problem with smart sensors is software and firmware upgrades. Wireless sensors in a commercial building often connect through a mesh network for communications. "Software upgrades on those tiny sensors can take hours," Mohan explains. "Many of them don't have one-to-one connectivity because they are mesh connected. Running a software update in a mesh network takes a long time. It's technically possible, but it's not something you want to do every month or even every quarter." "You have one edge gateway or compute box in a corner of the building with an internet connection. It talks wirelessly to all the sensors. It becomes the brains of the building."

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