After an AC unit Failure and 30 year old age, we recently replaced our Furnace with a 2 stage heat / 2 Stage cool unit. I am using the 3m-50 Wifi model, and trying to resist the tecnician's urging to replace the themostat, with OEM model as I've been so satisfied, with the 3m/Radio Thermostat model, which has worked great on our former single speed units.
I'm trying to understand the difference in function between the Economy Recovery and the Fast Recovery modes as defined in the manual. It seems to explain the Economy mode, as it works with the Temperature differential (mine is 2). For instance if i desire to cool the house to 72 degrees and it is 75, the stage 1 & 2 runs until temp is 74, and when it reaches 73, it turns off stage 2 and just runs stage 1 until it reaches 72. (This is resulting in an almost endless run time on stage 1 as the cooling load just doesn't quite ever make it to 72.)
So i've been trying to understand the algorithm for Fast Recovery.. If my house is 75, i have a 2 degree temperature differential, and i want to go to 72, does it run Full stage 1&2 until it reaches 72? If thats the case at what point then does it only run Stage 1? Is it time dependent? IE run stage 1 for 7 minutes and if no improvement then kick on both stage 1 & 2? I guess having a time factor in there for how long stage 1, can run without a temperature change so when the heat / cooling loads of stage 1 are equal to the house load, stage 1 just doesn't run forever without a cooresponding changing to the house temperature.
Here's the manual extract, but it doesn't articulate how it actually commands the furnace on Fast recovery and if that ever activates the first stage only.
NOTE: For 2 stage systems your 3M-50 can recover from a temperature setback in 2 ways: 1] Fast Recovery - This uses your 2nd
stage to bring the house to Target Temperature. This may use slightly more energy. 2] Efficient Recovery -This uses the 2nd stage to
bring your house to within a few degrees of the Target Temperature and then uses the 1st stage to go the last bit. (See setting the differential
in the operating guide). This is more efficient.
If you are outside the differential it will turn on the 1st stage and then one min later turn on the 2nd stage — and if in fast recovery use both till gets to set temp. If in efficient recover will use both till with in the differential and then just use the 1st stage. If you are not out side of the differential it will use the 1st stage and run it only unless it take more then 15 minutes to reach set temperature.
If you have any additional questions please don’t hesitate to contact us.
Your Radio Thermostat Support Team