Human Sensing Air Conditioner Control

I won't give you any suppliers since you can easily do that yourself. What I'm going to do is try to dissuade you from doing this. At least not the way you're thinking about doing it.

People move around (it's what they do) and switching an air-conditioner on and off when people move in and out of the room will destroy your air-con in a short time. If a person enters a room to get something and leaves in just, say 20 seconds (the thing he wants is on a table top), your air-con will start up and shutdown before it has a chance to cool the room.

If this was an office building, you could switch on the airconditioning about an hour before people start coming in. Then switch it off about an hour or thirty minutes before quiting time. On Sundays, the system disables itself so it stays off. A lot of office buildings do it that way.

Sorry for raining on your plans. I just don't think it's a good idea.

Dissuade says it all without even reading the whole thread starter. But if you must do this why sense motion or anything else physiological. Simply use switch an relay that removes/connects AC power whenever the door is open-closed. Simpler still, a wall switch by the door, and ready hand, to do the same. No door? Two electric eye beams across the doorway.

Hello the best way is to use an ifrared detector PIR and add a timer function so the aircon will cycle ok. Ask the maufacturer how long it needs to prevent any troubles.

I also think that cycle the eir con is not a good idea. For energy saving, it's even better to improve the room insulation, regulate the thermostat some degrees up, and let it work normally in auto mode.

If you still want to do so, the IR detector with timer to ensure a minimum time turned on, is a good solution. If a person enters the room again and again for short periods for an hour, for example, the air con would stay on in the auto position, switching on and off in its own cycle normally. If no moves are detected after the hour, it would be cutted off.

This can be easily done with IR detector, a timer and a contactor properly sized, if your air con does not allow auto timer function. All off-the-shelf parts that you can find in a hardware store near you. Pretty easy, if you think about it.

I once stayed in a motel that had the heating and air conditioning controlled by movement. I would go to sleep and the outside temperature would go below zero. I don't move when I sleep and the temperature would go to 35 degrees F. I would wake in a very cold room. I also stayed in this same motel in the summer and the same thing, I would go to sleep in a 70 degree room and wake in a room that was over 90 degrees (I was working nights).

Control based on movement is just a really sorry way to try to save money. It is more economical to maintain a steady state than to try to recover from temperature extremes.

I have made this equipment for the hotel and motel industry for 15 years. What you have to do, and why you got uncomfortable while sleeping, is use a switch on the entry door to perform a detection sequence. Door opens and closes followed by PIR events = room occupied and remains occupied until door opens and closes followed by no PIR activity then room is unoccupied. Start a timer so you don't enable temperature setback for say 15 minutes then go to a setback temperature and not full off. If you use 55 or 60 degrees for heating and 85 for cooling you can cut equipment run time from 30 minutes per hour in peak season to 5 minutes per hour. I have the stats to prove that. You must also be cognizant of other equipment issues like not short cycling the compressor - a two minute lockout if it just shut off in setback and the room becomes occupied to require operation immediately. Most equipment has a feature to prevent damage (even your refrigerator for example) but older equipment uses essentially a self reseting thermal circuit breaker to prevent damage to a compressor attempting to start into a full head of pressure (it will stall until pressure equalizes between the high and low side) but it's not a good idea to repeatedly use this. I have completed designs for several configurations of both retrofit devices and complete full blown thermostats including wireless systems. My designs are in operation in thousands of rooms around the country. They work very well, do not behave in a way that impacts equipment life (except in a positive way due to less usage time) and save a tremendous amount of money with only minor guest inconvenience. Properly done there is no reason not to use this technology.

Uh huh, I assumed he was going to use this in a house.

In a hotel room, you don't usually come and go so your system is fine for that application. If used in a house that has centralized airconditioning, your system will also work.

For a house with an airconditioner in every room, perhaps not. You could set a 15 minute start delay on your unit but what if the occupant leaves after 15 minutes and 5 seconds? You could put a 30 minute minimum run time but that's 30 minutes wasted if the occupant leaves soon after it just started.

I still say (with a variation this time) that this scheme will not work...for a house...with individual aircon in each room...whose occupants come and go...

Well of course, and unless there is a door that stays closed it would be even more pointless.

So when my wife goes out and I am still there - the heat or cooling still cut back?

You can get a lighting control that senses occpancy. The ones that use both IR and ultrasonic to detect motion and are ceiling mounted work best. They are set to switch with an adjustible time delay after they cease to detect motion (to prevent short cycling). Pets, hanging decorations that move, running ceiling fans, etc. will defeat the sensor. They are available with a circuit to control lighting and optionally an auxiliary dry contact. You would have to interrupt either the window AC unit's control circuit or provide a contactor between the outlet and plug. Most newer window AC units are microprocessor controlled and could prove to be a challenge.

Hi,

You want to see how this is working! I can show you which I implemtended in one of my home automation project in Delhi. My Mobile No. is 9810082259

regards,

A K Saseendran