Omnistat2 RC-2000 Protocol Discrepancy

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Product: Omnistat2
Model: RC-2000
Firmware: 1.03d

Item #1: Possible Documentation Error
According to the "Serial Protocol Description" (April 2008, page 5), Group 2 Data contains:

1. Indoor Humidity (162)
2. Dehumidify setpoint (135)
3. Humidify setpoint (134)
4. Outdoor temperature (68)
5. Filter Days left (15)
6. Energy Level (169)

When I parse Group 2 Data I get everything in the list with the notable exception that the order is not the same as documented. My observations show that Humidify setpoint (134) comes before Dehumidify setpoint (135). My thermostat clearly indicates Humidify=22% and Dehumidify=55% and that is the precise order the values are returned by Group 2 Data ... Humidify comes before Dehumidify.

Can someone confirm that the documentation is in error?

Item #2: "Days until reminder" does not change
When viewed on the thermostat's display, Filter Reminder displays two properties :

1. Filter Reminder
2. Days until reminder

In my case, the value is 90 days for both properties and "Days until reminder" has not changed since I installed the thermostat about six weeks ago. What activity does the thermostat measure in order to decrement "Days until reminder"?

Would a momentary loss of power to the thermostat cause it to reset "Days until reminder"?

Does it count hours that the fan is activated by the thermostat (G terminal) as opposed to purely heating hours (W1 terminal)?

My gas furnace automatically activates the Fan when Heat is called so the RC-2000 is not programmed to explicitly activate the Fan when calling for Heat. In addition, the Fan mode is "Auto" so it runs only when the furnace is Heating. There have been at least 150 heating hours in the last 4 weeks (indicated by the thermostat's RunTime graph) so that should've made a dent in "Days until reminder". Either I've misinterpreted the operating theory or something is not working correctly. Can someone explain why "Days until reminder" isn't decrementing?

 

[jharrell]

My days until filter reminder seems to be decrementing properly. It could be date based and not runtime based, that is when you set the reminder days it stores the date, then compares it to the current date when it shows you the days left, and if you reset the date on the thermostat by accident to something earlier it will not decrement until the date exceeds the stored date. Just a guess, I am not sure how it is counting days.

One of my issues is the runtime graph only has data on week 0, week 1,2,3 are all at no runtime recorded, not sure why that is.

 

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I'm glad to hear that it works. I wish I knew why it doesn't work for me. What is your thermostat's model (RC-1000/RC-2000) and firmware version?

It would be disappointing to learn that it is date-based. If the HVAC is off, no air passes through the filter so there's no usage and no need to decrement "Days until reminder".

 

[jharrell]

I have an RC-2000 with 1.00b firmware.

Days until reminder denotes to me that is it is not runtime based, as I would imagine that would be a runtime hours until reminder setting.

I could be wrong but it would be strange to count runtime in days instead of hours also most filters recommend being change on time intervals and don't list how much runtime they support before being changed.

Hopefully HAI can chime in and let us know exactly what it is doing.

 

[RArbour]

You are correct, there was a discrepancy in the protocol. The Humidify setpoint does come before the Dehumidify setpoint. I hope this typo did not cause you much problems.

The filter reminder should be working as intended (no reported bugs). The filter reminder is counted as long as the fan is activated, so that is probably why the filter reminder is not decremented in your case. Would turning "Fan On with Heat", conflict with your furnace?

Some notes about the filter reminder:
Only decrements when fan is active.
Does not have anything to do with date.
Does save status during power failure (does not reset).
Pressing "OK" in the filter reminder page, will reset the reminder.

Ryan

 

[123]

Ryan,

Thank you for your reply.

... The Humidify setpoint does come before the Dehumidify setpoint. I hope this typo did not cause you much problems.

It didn't cause any problems (just surprising to discover the documentation hasn't been corrected since 2008).

...The filter reminder is counted as long as the fan is activated, so that is probably why the filter reminder is not decremented in your case. Would turning "Fan On with Heat", conflict with your furnace?

Nuts! That's what I was afraid of ... it tracks fan time and I use "Fan Off with Heat". I'll activate the fan manually and have it run for a day or two to see if it decrements the counter.

Seeing that the Runtime graph works properly for me, the thermostat does know how to log "heating hours" (i.e. Heat activated) instead of just Fan hours. The "Days until reminder" logic should be a summation of heating/cooling hours plus fan-only hours.

Regarding the use of "Fan On with Heat", I have no idea how my furnace will behave if the G (fan) terminal is activated concurrently with the W1 (heat) terminal. I'm hoping there'll be no ill effect of activating the fan when it is already automatically activated by the furnace. Can you describe what the Omnistat2 does when it activates the fan? I assume all it does is apply 24VAC to the G terminal?

 

[jharrell]

So when my filter says it should be replaced every 6months, I should *not* set the filter reminder to 180days, instead I should somehow figure my average runtime hours per day multiply 180 days then divide by 24 to get the approximate runtime days for changing?

How do you guys figure out how many runtime days should be entered for a filter?

 

[cornutt]

Regarding the use of "Fan On with Heat", I have no idea how my furnace will behave if the G (fan) terminal is activated concurrently with the W1 (heat) terminal. I'm hoping there'll be no ill effect of activating the fan when it is already automatically activated by the furnace. Can you describe what the Omnistat2 does when it activates the fan? I assume all it does is apply 24VAC to the G terminal?

Yep, that's the way it works. I'm pretty sure it won't hurt anything to set it to Fan On with Heat. If it's like gas furnaces that I've seen, the only difference will be that the fan will come on when the thermostat calls for heat instead of waiting until the heat exchanger warms up, which means the system will blow cool air for a minute or so at the start of each cycle.

 

[RArbour]

So when my filter says it should be replaced every 6months, I should *not* set the filter reminder to 180days, instead I should somehow figure my average runtime hours per day multiply 180 days then divide by 24 to get the approximate runtime days for changing?

How do you guys figure out how many runtime days should be entered for a filter?

Jharrell,
The frequency that you should change the filter is unique for each house. It is a factor of how much airflow that filter sees and how much sediment is in the airflow in your house. The filter recommends a certain time, but I would try different values to see what is best for you. If you do not have the fan on with heat (radiant heat), the filter would obviously not get as dirty as fast so the filter will last longer. It is really not time based.

Ryan

 

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Ryan,

I set Fan=ON (normally set to AUTO), let it run for over a day, and the Omnistat2 decremented the "Days until reminder" counter. The Filter reminder does work properly however, as mentioned, it is based on counting fan hours exclusively. If set to "Fan Off with Heat", it will not count the hours when the furnace is on. I suggest that a future firmware version handle this calculation differently.

Although my gas furnace automatically activates its fan when there's a call for heat, I followed your suggestion and switched the Omnistat2's setting to "Fan On with Heat". I'll monitor it over the next day or so; the reminder counter should now be including the hours when the furnace is activated.

There appears to be no negative affect on my furnace; it operates exactly the same way as before when set to "Fan Off with Heat". It always paused the fan (if already on) when starting up and it continues to behave the same way with "Fan On with Heat".

 

[cornutt]

There appears to be no negative affect on my furnace; it operates exactly the same way as before when set to "Fan Off with Heat". It always paused the fan (if already on) when starting up and it continues to behave the same way with "Fan On with Heat".

So if the fan's already on, it shuts it off while the burner starts? Interesting. I don't think I've seen one do that.

 

[123]

So if the fan's already on, it shuts it off while the burner starts? ...

It's a ten-year old RUUD Silhouette II (mid-efficiency). When the Fan=ON and there's a call for heat, I noticed the fan gets turned off, the furnace goes through its ignition/warmup phase, and after a minute or so it'll re-activate the Fan.

I thought that "Fan On with Heat" would activate the fan during the furnace's ignition/warmup phase. However, it appears that the furnace's controller has the final say and deactivates the fan during ignition/warmup. Overall, I'm happy that it has the smarts to handle the fan correctly.