using sensor on/off electronic equip

Consider what the equipment will cost to run that will be monitoring the conditions. Several years ago we installed sensors to turn off lights and exhaust equipment. Unfortunately if everyone was sitting at their computers and doing paper work, the sensors would see no movement and turn off. At that point people would start bitchin and waving arms to have them turn back on. So we ended up installing bypass switches for normal hours of operation. But if you didn't take it out of bypass they stayed on anyway. We ended up placing BIG labels by the switches to remind people to turn off the lights when leaving. Cycling everything on and off constantly cost as much as just running everything normally.

Eventually we replaced everything with energy efficient equipment and saved money.

Good response, especially about the issue of using energy efficient equipment.

However, I don't agree with this one small part;

"Cycling everything on and off constantly cost as much as just running everything normally"

This has been proven time and time again not to be true except in some very rare occasions. There is no better energy saver than the Off switch. The idea that it takes more energy to restart something than it does to leave it running is for the most part a myth that came from very old days when some types of early vacuum tube type electronics equipment had "warm up" times where energy useage was high in the early moments of use, dropping off later. The age of solid state electronics put and end to that issue long ago, yet the concept persists as a myth now.

Thanks for objecting to power cycling myth. This has even been covered by the Mythbusters TV series. Regardless of what kind of lighting you are using you still save some power by shutting the lights off even if only for a few seconds.

Sorry about that. Yes I agree the off switch works best. We had lights and ventilation and whatnot hooked up to 10 minute timers. Everything would cycle on and off unless someone was actually moving about. Although we did get exercise waving our arms about and jumping out of chairs to start everything up again.

No sweat, it's just one of those little "facts" that everybody "knows" that makes me want to bang my head into a wall whenever I hear it.

Yeah! we banged our heads alot too. But they weren't sensitive to sound unless you bounced your head about a foot or two. Screaming didn't help either. When your fingers are close to a ten ton press, you need and want lights. At least they didn't connect the computers to the switches!!!!

I've been in offices with motion sensors as well. The proliferation of this "brilliant power saving scheme" was obviously the result of salesmen touting sensors to office managers who were more than willing to buy anything that looked high tech hoping they could impress a customer without considering the potential drawbacks. Hopefully anyone who has ever been in a room with lighting controlled by a motion sensor or combo MS and timer is now well aware that motion detection is not a good way to control lighting (except in a closet).

With more advanced technology an engineer could put together a "smart lighting system" that would actually work the way you would want it to:

A lighting scheme could be setup using a couple of infrared cameras placed in the room to detect occupants. The cameras could detect body heat, so both moving and stationary occupants would be recognized (except for maybe my ex-girlfriend). The cameras would have to have a little logic capability so they could be taught to ignore fixed objects such as computer power supplies or light bulbs, but this is very do-able with existing "vision system" software.

Of course, the payoff time for this system would be impractical if the only return is $1 a week in power savings, but the IR cameras could also be used to repace or supplement security cameras, so you can kill two birds with one stone and soften the initial cost.

how will you put a motion sensor on a fan