Dec 05, 2008The City of London School for Girls is heating its facility more efficiently and more comfortably, thanks to a wireless sensor system that allows each room to be controlled independently, in order to maintain the optimum temperature. The system is intended to lessen the school's carbon footprint by reducing the tendency to overheat some rooms, with wireless sensor nodes that were easier and less expensive to install than a traditional wired system.
The system, developed by Control Technologies Ltd. (CTL), was provided by sister company ARO Performance Systems Ltd. Another of CTL's partner companies, Ambient Environment Solutions Ltd., is undertaking installation using Jennic's JenNet system and wireless sensors, based on the IEEE 802.15.4 standard. The school installed the system in one floor over the summer break, and is now deploying the wireless sensors throughout the rest of the five-story building during the December winter break.
A private day school for girls of all ages, the academic institution is considered one of London's more prestigious schools. It utilizes the city's enterprise-wide TAC Andover Continuum building management system (BMS) to control the temperature in its 120 classrooms and offices. The school has been struggling with inconsistent temperatures, whereby some rooms were overheated and the windows in those rooms were opened to cool them down, leading to energy waste.
Control Technologies Ltd. has been providing the City of London with building management service for its heating, ventilating and air-conditioning (HVAC) systems, both for restoration and maintenance purposes. In this case, faced with the challenges before the School for Girls, CTL found that a Jennic wireless system—which Control Technologies had been testing in other city buildings for the past two years—would be the optimal solution.
The five-story school, constructed with concrete, stone, masonry and a metal grid, did not lend itself to additional wiring, says Andrew Osborn, director of ARO and CTL. Running new wires through the building's walls was simply not feasible, but the school required an upgrade to its HVAC system. "The energy consumption at the school was very high," Osborn says, "and they needed to get that under control without disrupting the fabric of the building, and without disrupting school activities there." That meant there would be no drilling of holes or cable installation.
The school has under-floor heating mats and electric space heaters that warm the building in five heating zones. Until now, none of the heating elements within a specific zone could be controlled individually, leading to very little ability to regulate each classroom's temperature. With the new JenNet system, the school increased the number of individually controllable zones from five to approximately 130, using 160 Jennic wireless sensors.
Each Jennic device contains a 32-bit RFID chip wired to a temperature sensor, and is powered by two AA batteries. At preset intervals, the sensor node awakens, collects temperature data and transmits that information, along with its unique ID number and the condition of its batteries, to the wireless mesh routers at a distance of up to 100 feet, or through three partitions (such as walls). The sensor then goes back to sleep.
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.
