# Using a PLC to "controlin a house ???



## OntarioMan (Feb 11, 2007)

Hello,

A PLC is a "programmable logic controller" (a computer) - initially designed for industry as a machine controller.

A PLC can be configured for many different input/output types. For example, you could measure temperature, pressure, light/dark, monitor limit switches, hand switches, motion detectors (the list is almost endless). You could control outputs such as lights, relays, heaters, fans, etc. etc.

Example : traditionally, a residential light switch is hard wired to the light - in a PLC scenario, the switch is an input to the PLC, and the PLC turns on the light. How is this an advantage? Well, you could configure the PLC to monitor the switch, when the switch is activated, the PLC would turn on whatever you like, one light, two lights, two lights and a fan, two lights and a heater in winter, two lights and a fan in summer, etc. etc.

Some PLCs are configured with a hand programmer, others can interface with your computer. So, not only could you configure the "logic" for your home, you could monitor it as well. 

The reason these have interested me as of late is the price. Some units which originally sold for many thousands of dollars new are available used for next to nothing on Ebay.


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## deaconjim (Oct 31, 2005)

I have worked with PLCs in industry for years, and they can easily be adapted for home use. Security systems are a good use for them, but they can be used for controlling HVAC systems, lighting, energy conservation, etc. There is a program called HAL 3000 that will integrate a plc with your home computer and makes a great system.


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## OntarioMan (Feb 11, 2007)

Yes, I did PLC work as well about 15 years ago - I've not worked with them since. AB, GE and Omron units.

I'll have to do some HAL 3000 research. Thank you.

Some folks might be wondering how this could save energy - below is another example.

In the summer, I run a central air conditioner. Sun shines during the day, house heats up, central air unit runs to keep the house cooler. As the sun goes down, the outside temperature may fall rapidly. At this point, my house is still hot from the days heat (thermal mass) and the central air unit continues to cool the house. Bottom line is that I have no way to automatically compare outside and inside temp., and no way to automatically shut down the AC unit and draw in cool outside air when the house is hot (aside from manually opening doors/windows). A PLC would allow me to automatically make logical decisions with regard to my central air unit - controlling exhaust/intake fans, etc. etc.



deaconjim said:


> I have worked with PLCs in industry for years, and they can easily be adapted for home use. Security systems are a good use for them, but they can be used for controlling HVAC systems, lighting, energy conservation, etc. There is a program called HAL 3000 that will integrate a plc with your home computer and makes a great system.


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## deaconjim (Oct 31, 2005)

Another way is to use motion sensors to detect movement in the home. If, after a predetermined time no motion has been detected, the PLC opens a contact preventing the water heater from energizing. As soon as any motion is detected in the house, the water heater contact is closed allowing the WH to funtion normally.


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## OntarioMan (Feb 11, 2007)

I think "home automation" is one of those technologies which we'll see much more of in the future. 

Here in Ontario, there is talk of "smart meters" - which basically boils down to charging folks a premium for electricity when demand is high (during the day) and giving them a discount when demand is low (during the night). Being able to "program" your home to take advantage of this is just another use of home automation.


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