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Wireless Sensor Network Helps School Cut Its Energy Use

The City of London School for Girls is employing wireless sensor nodes to manage temperatures in about 130 zones set up in its building, reducing the tendency to overheat certain rooms.
By Claire Swedberg
Six routers are plugged directly into outlets on each floor and, in turn, transmit signals to a "coordinator" or "gateway node"—one per floor. The sensor nodes and routers transmit their 2.4 GHz signals according to an IEEE 802.15.4 air-interface protocol. Each gateway node is connected to the BMS system on the proprietary RS485 serial field bus, connecting data to the enterprise system via the City's Ethernet wide area network (WAN). In this way, the City of London can monitor HVAC data from the many zones within the school, to see how the heating system is functioning.

Each floor's gateway node is also cabled to the school's power distribution boards, which control the power running the floor heating pads at any specific zone, based on that zone's temperature sensor data. There are six routers installed on each floor, with about 30 in the building altogether.

The greatest obstacle to the mesh system, Osborn says, involves the elevator shafts, which are highly metallic and can obstruct the RF signal. Nodes are installed in such a way, however, as to transmit around those obstacles.

The installation cost was 80 percent less than that of a wired solution, says Tony Lucido, Jennic's VP of marketing, and installation time was 90 percent less. What's more, he adds, "there was no need to redecorate the building after installation of the wireless sensor network."

By the end of December, Osborn predicts the system will be fully installed with 160 nodes. The installation is being conducted outside of school hours, but in the zones where it is already installed, he says, "It is going blindingly well." This, he notes, is not a plug-and-play solution. There has been a lot of pain over several years, he says, experimenting with the technology in several City of London buildings (mainly due to read range issues involving the stone, masonry and concrete of London's larger buildings) and finding the proper frequency that would transmit appropriately in older buildings such as the girls' school.

Now that the preliminary research has been completed, Lucido says, the wireless system is proving to be a simple installation. "This is a very convenient way to retrofit," he states.

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