OmniStat2 2 Stage Cool Normal Behavior

[ano]

Got a new AC system with an OmniStat2.  I'm trying to better understand how the OmniStat2 determines if it cools at stage 1 or stage 2.  From reading the instructions it sounds like its a simple decision based on how far the temp is away from the desired temp.  1 degree away and its stage 1 and 3 degrees away for stage 2.  But it doesn't seem to be working like that. 
 
I set it to 20 degrees below the actual temp.  It started at stage 1, then went to stage 2 for maybe two minutes then back to stage one.  Is this normal?  I'm guessing its more complex that a simple temp deference.  Anyway to force it to stage 2?
 
Thanks.

 

[jharrell]

I believe the EEC tries to be more intelligent than a simple temperature difference, which is why it says to disable EEC when testing the system stages.
 
Here is a snip from the Omnistat installation manual:
 
This thermostat is equipped with Energy Efficient Control (EEC) that continually monitors the performance of 
the HVAC system and uses Stage 2 (heat or cool) and Stage 3 (auxiliary heat) only when necessary. 
If the thermostat determines that Stage 1 is able to heat or cool at a rate of 5 degrees per hour or better, Stage 2 
will not be used. If Stage 1 is unable to heat or cool at this rate, the thermostat will use Stage 2 as needed. 
Under these conditions, Stage 1 will run continuously and Stage 2 will cycle on and off as needed. In extremely 
cold conditions, the auxiliary heating will be used when Stage 1 and/or Stage 2 is not heating at a sufficient rate. 
 
You can find the rest here on page 20: http://homeauto.com/Downloads/Products/Omnistat/RC-2000_Installation_Manual.pdf
 
I sort of wish there where some manual overrides both in the Omnistat itself and remotely through the Omni for testing, but after having an RC-2000 for a few years with a 2 stage heat pump, once it learns the system it's pretty much always done the right thing with the stages so I am satisfied as is.

 

[ano]

I'm understanding it better, but HAI could also do a much better job at explaining how it worked.  Like if you "disable EEC" by setting it to zero I presume, then what? Does it just base stage by temp difference?
 
I said "no" to four contractors that wanted to install proprietary HVAC units with proprietary zone controllers HAI can't control.  This is the direction that almost all systems are going to today.
 
But i did find a contractor that would listen to what I wanted and designed a system to do it.  Now the resposibility falls back on me to interface the OmniStats to what they are installing.  The zone control won't be installed until Thursday, but today my goal was just to get one Omnistat2 to control the unit directly.  It was a challange when they wanted to test it at stage 2, but the OmniStat2 didn't want to cooperate.  Challange 2 will be getting three OmniStat2's to talk correctly with a Honeywell zone controller which will talk to the system.  Honeywell's documentation isn't any better than HAI's.
 
I have my fingers crossed that it will all work when done.  I guess my fallback would be to do the zone control with Omni relays controlling dampers, but then I need to figure out a way to force the HVAC unit into stage 1 or 2 from the HAI.
 
The OmniStats are fine for some applications, but HAI needs to do a better job at helping me do what I am trying to do because the world is changing.  It reminds me of a time a few years ago when automakers made it almost impossible to replace an in-dash audio system. The OmniStat is Pioneer's in-dash cassette deck.

 

[jharrell]

Overriding EEC for testing is explained on page 8:
 
 
5. Press [HOLD] and select “On” to override Energy Efficient Control. 
6. Set the Mode to "Heat". Raise the desired heat setting 1 degree above the current temperature. Ensure 
that Stage 1 heat comes on. After a few minutes, raise the desired heat setting 3 degrees above the current 
temperature. Stage 2 heat should come on. Set the mode to "Off". Ensure that the heating unit goes off. 
7. Set the Mode to "Cool". Lower the desired cool setting 1 degree below the current temperature. Ensure 
that Stage 1 cool comes on. After a few minutes, lower the desired cool setting 3 degrees below the 
current temperature. Stage 2 cool should come on. Set the mode to "Off". Ensure that the cooling unit 
goes off. 
8. Press [HOLD] and select “Off” to enable Energy Efficient Control.
 
I agree it could be explained better, never been a big fan of how they separate Installer and Owners manuals etc, makes it harder to find the correct information.

 

[ano]

Thanks. I did not see that.  I guess I skipped over the Power Up section.  (maybe because they are using 5 point font) 
 
Today the AC people are installing the zone controller, and from speaking with them they don't have the foggiest idea how it works, so I need to learn about it so I can make sure they hook it up correctly.  (I don't think they have ever used this Honeywell controller, they have always used the proprietary Trane zone controller.)  I'm guessing it will be best to shut off the EEC on the thermostats feeding into the zone controller, but maybe not.  I have to learn better how this zone controller "thinks."

 

[ano]

I'd discovered another weird thing about the OmniStat2.  Every thermostat I've ever seen, including the older RC-80 worked like this: If you were using AC, lets say, and you set the temp to 78 degrees, the thermostat would turn on at 79 and would turn off at 77.  But not the OmniStat2. If the temp is 78, it turns on at 78, and off at 76. This means you need to set the temp 1 degree higher to match a "normal" thermostat. Strange.

 

[HAI_fjh]

My wife is OCD about the temperature and freaks out when the temp overshoots by a degree. I have explained to her many times that it is an energy saving thing and has to do with minimum run times and whatever, and please stop fiddling with it. If you REALLY want to know Ryan can give you a long detailed explanation about the patented energy saving routines, predictive and learning algorithms... Basically the OmniStat2 is trying to keep the temperature within the desired range in the most energy efficient way. It does save energy and unless you can actually feel the +/- 1 degree difference I would not worry about it. My wife only complains if she happens to walk by the thermostat and notice it. 10 seconds earlier she was perfectly fine and walking to the back of the house when she passes the thermostat and sees it has over shot by 1 degree... Drives me crazy.

Sorry about the rant. The short answer is yes, in order to save energy the temperature control may be a little "loose" and may occasionally overshoot by a degree or so. Don't try to compensate for the number, just set it where you are comfortable and let the OmniStat2 do its job. If it is too "loose" you can adjust EEC settings and minimum run times to tighten it up. But don't be too quick to keep changing the settings because the thermostat is trying to learn the heating/cooling characteristics of your environment. You may have seen a hint of this in the document excerpt above where it talks about the stage 2 operation being based on the rate of heating or cooling. The default setting usually work pretty good but give it a couple of days to learn your environment. We have come a long way from the early days of mechanical thermostats where 1 degree over meant full cool and consequently we are saving a lot of energy...

I hope this helps explain a few things.

 

[ano]

Thanks for the explanation.  That helps.  I'm not complaining about the operation, but just trying to understand it to know what is "normal" and what is broken and needs to be returned.  Keep in mind I am going from two single stage AC units with RC-80's (which were very reliable and stable) to two multi-stage AC units with four RC-2000's three of which are going through a Honeywell zone controller.  Generally I read and control the thermostats through CQC because it can do much more than HAI's programming.
 
The flakiest thermostat of all seems to be a new RC-1000 that is connected to my single-stage AC which will be replaced tomorrow.  This thermostat has two behaviors which are bad:
 
1) The temp reading often bounces up and down by a degree because it can't make its mind up. 
 
And this is another strange one:
2) When in cool mode, if you manually turn on the fan, or if the fan is turned on by setting it to "cycle," the temperature reading of the thermostat will instantly drop by one or two degrees.  The second the fan is turned off, the temperature returns to it's normal value. This occurs WITHOUT the AC running, just the fan.  This seems like a bug. If it's a "feature" I don't understand it.
 
I haven't seen this behavior with the RC-2000, just the RC-1000, and soon that RC-1000 will be on e-Bay and someone else's problem, so I'm not too worried about it.