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2010-08-06 00:00
in Computers, Linuxha
Introduction
So, my plan was to be able to use outside air to cool the house at night during the summer without leaving doors and windows open on one hand, while being able to boost or shutoff air to the master bedroom depending on the time and boost HVAC air to the family room which gets the warmest but is also the hardest to cool since it's at the end of the line. Boosting air is simply done by adding booster fans to the right ducts, but controlling the fans at the right time is where it gets interesting: I wanted to be able to decide not to turn on the booster fan to the bedroom during the day (waste of air) and not bother with trying to heat/cool the family room at night either since the master bedroom needs the air more than the family room.The astute reader will note that this is usually done with dampers, but the furnace we have is older and would require a pressure return for extra air if only one room were targetted, and dampers just add more money and complexity when I already wanted booster fans. The trick is that booster fans can act as semi dampers when they're not running, which is good enough. Now, the main goal was however to be able to pull air from the outside and bring it in the house. This was accomplished with the same 2 booster fans to create suction this time and 2 dampers do redirect the air from the furnace output to ducts that go outside the house.
damper opened (notice the 2 small wires which got to my 1-wire 8 channel IO board)
If so, how many hundred dollars is it and do you need to call an HVAC person with proprietary software to reprogram it?
Do the inside and outside temperature probes cost $3 each, or more? :) If you want to skip ahead, this is the misterhouse hvac code I was able to write to control the hvac system.
Implementation with Misterhouse
This is where misterhouse comes in again, I can program absolutely any logic I want and mostly with sensors and actuators that cost a lot less than typical overpriced HVAC parts.The bits that came in play were:
Yes, booster fans do require some electricity to run (150W a piece or so), but for comparison, AC is 3000W just for the AC, to which you have to add 1000W for for furnace whole house fan and then the 150W for the booster fan: At least, as a bonus, we do now get more cold air to the family room with the booster fan when we do run the AC, so we reach our target temperature more quickly.
Top/Hvac Damper Open to Close Video (click me)
Scripts/code
Here is my misterhouse hvac script that controls the booster fans and outside air intake depending on inside, outside temperature and HAI thermostat status.
See more images for Booster Fans and Heating/Cooling with Outside Air with Misterhouse