Ž . Energy and Buildings 32 2000 81–87 www.elsevier.comrlocaterenbuild Smart occupancy sensors to reduce energy consumption Vishal Garg ) , N.K. Bansal Center for Energy Studies, Indian Institute of Technology, Hauz Khas, New Delhi 110016, India Received 20 April 1999; accepted 23 July 1999 Abstract Ž . Occupancy sensors have long been used for control of various devices like artificial light, HVAC devices, etc. . Past research has shown that use of occupancy sensors for control of lighting can save up to 30% electrical energy used for lighting. However, most of the Ž . Ž .Ž sensors, which are currently being put to use, have a preset sometimes user adjustable time delay TD the time after which the lights or . any other load will be switched ‘‘off’’ after the last motion is detected by the sensor . If this TD is long then, it will have less energy savings, as the load will remain ‘‘on’’ during unoccupied period also. At the same time, if the TD is kept short then it may result in Ž . unwanted switching ‘‘off’’ False Off of the lights when no motion is detected during periods of occupancy. It has been observed in our research that the activity level of a user changes over the time of the day. Also, it is seen that activity level of different users is different. Hence, single TD for all the users and for all times of the day is not desirable. The commonly used sensors do not adapt to changing activity levels. In this paper, we present design of smart occupancy sensors which can adapt to changing activity levels. A model is also proposed for ‘‘human movement’’ of a person working at a computer. Smart occupancy sensor can learn the variation in activity level of the occupants with respect to time of the day. With this information, it can change the TD with time of the day. Experiments conducted have shown that about 5% more energy can be saved by using smart occupancy sensor as compared to non-adapting fixed TD sensors. q 2000 Elsevier Science S.A. All rights reserved. Keywords: Occupancy sensors; Energy; Time delay 1. Introduction Occupancy sensors have a potential to significantly reduce energy use by switching off electric loads when a normally occupied area is vacated. While occupancy sen- sors can be used to control a variety of load types, their most popular use has been to control lighting in commer- cial buildings. Although occupancy sensors have been used in many commercial facilities over the last decade, pub- lished third party performance data is surprisingly sparse. Ž . Both the Electric Power Research Institute EPRI and American Society of Heating, Refrigerating, and Air-Con- Ž . ditioning Engineers ASHRAE estimate an average 30% savings from this technology in generic assessments for w x commercial buildings 2,6 . With occupancy sensor con- trols for lighting equipment in one or two person offices, wx the estimates of energy savings vary from 25% to 50% 5 . ) Corresponding author. Tel.: q 91-11-6861977 ext. 5066; fax: q 91- 11-6581121; e-mail: gargvishal@hotmail.com These data are supported by a utility evaluation by Consol- idated Edison who found a 30% reduction in average lighting demand for its projects that installed occupancy wx sensors 3 . Measured data from case studies suggest that good performance from occupancy sensor installations can be realized. A retrofit of an office building with passive infrared occupancy sensor controls in South Australia yielded a 40% reduction in lighting energy use with a wx simple payback of 2 years 4 . Energy saving potential is highly dependent on baseline assumptions and operations wx but values of 35%–45% are typical 1 . Also, several case studies of occupancy sensor installations show savings of wx 25%–75% in variety of spaces 7 . These savings are dependent on average or peak occupancy rates. Stannard et w x al. 15 in their work provide a brief discussion of the impact of occupancy profiles on the reduction in peak demand and energy use due to lighting controls. The result of a survey by Lighting Research Center discusses the importance of considering occupancy use patterns in pre- w x dicting potential savings 10 . A detailed study of occu- pancy sensors used in a US national laboratory found a 0378-7788r00r$ - see front matter q 2000 Elsevier Science S.A. All rights reserved. Ž . PII: S0378-7788 99 00040-7