Riding Under the Thermostat

Gordy

Indoor feedback already exists with the thermostat right?

Gordy

I think the onboard outdoor reset can go to another level using those two devices without more third party intervention.

Solid_Fuel_Man

Tekmar has several indoor feedback systems.

The two stage thermostat is really the simplest approach to the "I'm cold switch". You can add a resistor in series with the ODR to boost the tempo if the boiler only has one temp input such as the ECO and many others.

I can post a simple wiring diagram if anyone is interested.

Gordy

That’s why I like your method @Solid_Fuel_Man . Why add more third party devices to complicate.

But I still think the outdoor reset programming on the boiler could be taken to the next level with most of the simple sensors that are normally already in place. Wind sensor would be a nice option, but a maintenance nightmare I believe.

flat_twin

Solid_Fuel_Man said:

Tekmar has several indoor feedback systems.



The two stage thermostat is really the simplest approach to the "I'm cold switch". You can add a resistor in series with the ODR to boost the tempo if the boiler only has one temp input such as the ECO and many others.



I can post a simple wiring diagram if anyone is interested.

That's one approach I was thinking about. Fool the ODR sensor with whatever value would make it look like it's colder than the actual outdoor temp. It wouldn't be as abrupt as demanding 180 SWT. I'd sure like to see what wiring scheme you have for the Eco sir.

The Honeywell 8000 I have is a TH8320R1003.

Eastman

I like Solid_Fuel_Man's approach, too. But at the end of the day, the thermostat and boiler should be communicating the requested room temperature and the actual temperature somehow. It shouldn't require a workaround or 3rd party device. I mean, when are thermostats going to advance beyond just on/off?

Check this out:
http://www.honeywelluk.com/Documents/ReferenceGuide/pdf/OpenTherm_Fact.Sheet_FINAL_WEB.pdf

In Europe, they've put together an open standard for this. We need something comparable.

NY_Rob

Le John said:

@NY_Rob do you have a wiring diagram of how you wired the timer. I’d like to try the same approach!

It's actually really simple...

NY_Rob

Eastman said:

Furthermore...
It would be nice if the control system could receive temperature forecasts. That would be helpful for high mass systems.

Some t-stats do that now IIRC.

Eastman

I think the Ecobee can use weather. Not sure to what level of sophistication, though.

Solid_Fuel_Man

Sorry, I've had several middle of the night emergencies and not been on here in a few days.

This is how to use a 2 stage thermostat on any boiler with outdoor reset. The resistor or better yet potentiometer tools the boiler into thinking its colder outside and ups the CH temp. This shows the terminals for W-M ECO

Eastman

@Solid_Fuel_Man
Maybe the resistance could be controlled in some manner by a proportional thermostat?

flat_twin

Solid_Fuel_Man said:

Sorry, I've had several middle of the night emergencies and not been on here in a few days.



This is how to use a 2 stage thermostat on any boiler with outdoor reset. The resistor or better yet potentiometer tools the boiler into thinking its colder outside and ups the CH temp. This shows the terminals for W-M ECO

Thank you. My Honeywell tstat is capable of two stage heat and I can see how opening relay 2 puts the resistor in the path of the ODR sensor. By golly I think even a retired telephone man can do it!

Solid_Fuel_Man

I've actually done this and it works well. You can adjust the resistance to "adjust the boost". Just connect the middle and one end of a typical 3 wire potentiometer.

I made a standard Tekmar injection control a two stage this way just did it to the supply sensor, worked well. Same can be done with the OAT sensor on your boiler.

Solid_Fuel_Man

@Eastman I think one could make a more sophisticated system, but with a well balanced reset curve, a two stage system has worked exceptionally well for me.

Several boilers I've installed accept a 4-20ma or 2-10Vdc input which is generated by a building management system with true proportional feedback from a slew of sensors and data. But that may be beyond our scope for a 1-6 zoned home.

nicholas bonham-carter

If the Ecobee can use weather, then so how accurate is that?
Can anyone rely on the weatherman, who has the same information as the Ecobee?—NBC

Eastman

Maybe it's just grabbing the current temperature over the internet.

Gordy

The current temperature from someone else’s personal weather station..........

If you are going to go that far in being a control freak, may as well have your own weather station. Then You know

ratio

If you know which thermistor is being used for the outdoor sensor, you can cypher up a close approximation of the desired reset magnitude with a resistance chart for the sensor. Pretty likely it's a 10k sensor. There are two main flavors that differ enough at the point wher we're interested in the make it important to know which one we have. Here is a resistance chart that covers a good number of thermistors & RTDs. (I carry a printed copy of this in my truck.)

Gman66

Solid_Fuel_Man said:

Sorry, I've had several middle of the night emergencies and not been on here in a few days.



This is how to use a 2 stage thermostat on any boiler with outdoor reset. The resistor or better yet potentiometer tools the boiler into thinking its colder outside and ups the CH temp. This shows the terminals for W-M ECO

SFM, I use this very method on my Tekmar strap on ODR attached to my old dumb CI boiler with one exception: I use an array of 3 thermistors, identical to the one in the Tekmar, in parallel with each other to replace your one resistor. The problem with the resistor is that thermistors are highly non-linear and a single resistor might fool the ODR by 20 degrees when it is 45 degrees outside but only 5 degrees when it is 15 outside. The three identical themistors in parallel increases the resistance by 1/3 at any temp which for my thermistor fools the temp by 12 to 16 degrees at any temperature.

BoilOver2

> @Solid_Fuel_Man said:
> Sorry, I've had several middle of the night emergencies and not been on here in a few days.
>
> This is how to use a 2 stage thermostat on any boiler with outdoor reset. The resistor or better yet potentiometer tools the boiler into thinking its colder outside and ups the CH temp. This shows the terminals for W-M ECO


This is a nifty idea. Link to an example potentiometer that might work for such a setup?

I'm trying to fine tune an odr curve, and it seems like in the very coldest periods of the night I'd like to boost ch temp by 5-10 degrees for a couple hours. I have an ecobee so I could program it to say fire second stage from 2-4am or something like that.

Thanks!

flat_twin

Per the ODR curve chart NY_Rob posted earlier in this thread, a 5 degree increase in SWT for me would mean I have to fool the ODR into seeing about 10 degrees less than actual temperature. I have some electric guitar parts laying around including spare volume pots. As SFM mentioned, wiring the middle and either side of the pot makes a variable resistor. I'll mount it in a small electronics utility box and sticky tape it to the inside of the boiler cabinet, then clearly label it in case I'm not here to explain it.

ratio

Look at the thermistor curves I posted. Like @Gman66 noted, thermistors are non-linear, the resistance change that corresponds to 10° is dependant on what the temperature actually is. That said, if you know about what temperature you're going to want to reset at, you should be able to find something reasonably suitable; or do something clever with multiple thermistors & resistors. I don't know if I have the patience to sit down & figure that out!

flat_twin

I made a copy of those charts, thank you! Yes I could only set the potentiometer when the OAT was about where I think the need for 2nd stage heat would be or select a resistor by the chart.
I'm also intrigued by the idea of a 2nd ODR sensor that would maintain the original SWT curve, just a few degrees higher. Increasing the SWT by 4-5 degrees would be plenty to deal with extreme wind or the door being opened more than normal.