Friday, January 20, 2012

HVAC temp sensor

Using a makeshift breadboard to wire up the resistor and temp sensor (aka: cut out a piece of plastic from HDD tray inserts)

The unmarked wire is for ground, the one with one line goes to the DQ pin of the sensor and will go to the channel pin of the control module. The wire with 2 markings is the VDD pin of the sensor and will go to the +5v line of the control module. I will be using cat6 to wire this to the module, so probably one pair for DQ and VDD and a single wire for ground. I can probably technically use the common wire of the thermostat as ground, but I rather use the one fed from the control module to be on the safe side.

I will try to shove this behind the existing thermostat which will save me from figuring how to put this on the wall and hide it.

There is also another sensor that will go outside, but not sure how I want to do that yet, and considering it's like -30 out there, I rather wait till spring to do any type of outside work. Chances are what I'll do is mount it on the house in some kind of small plastic box. Might even put it inside the phone nid.

The outside sensor will be used to help the system better calculate start times and run times to increase efficiency. For example, on a -30 day I might want the furnace to start earlier than a -5 day. the current indoor temp will also play a role in that calculation. The program will learn the heat gain/loss and then based on these values should be rather accurate in knowing when to start the heat.

There will also be other features such as over running past the set temp to avoid short cycling. So on a -30 day it may be better off to run the heat 2 degrees past what it's set to, and let it drop 3 degrees before starting again. The less short cycling, the more efficient things will be. Still lot of things to think about. At first the program will simply be an advanced temp scheduling program and I'll add more features over time. Being able to set the temp or change schedules from the office, or my playbook will be pretty cool.

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