Modernized my controls, adding new features and adding data logger

[sgschwend]

I have added a Dwyer Instrument temperature switch to my 1989 Essex boiler. The switch is used to turn the boiler off when the fuel is gone. I found that my Honeywell dual set point thermostat was ready for replacing.

I had wanted to add circulator pump start temperature on this thermostat and it would have worked but my clumsy work overstressed the contacts. Since the Dwyer Instruments worked so well in the first application and it was less expensive, I decided to switch to one of Dwyer Instruments dual set point thermal controllers. It was easy to install, just hook up power, move the switch wires from the Honeywell, and connect the temperature probe. Then using the front panel keys I could program the set points. There is a bunch of functionality, but in my case I just want to get it into service.

Here is a picture of the new installation, the old Honeywell part is sitting on the top, the two Dwyer Instruments switches are on the front panel, as you see they also display the current temperature.


If you are thinking about replacing your older controller parts, or adding a shutdown controller for when the fuel is gone, then here is an option to consider.

New features and data logger on next post.

 

[deerefanatic]

There are also similar controllers on ebay for less than $30 that do the same thing.... Even with my NFCS system, I use several of these controllers in various places around my system.

In my opinion, these controllers are a MUCH better alternative to standard Aquastats.....

 

[sgschwend]

I have created a new schematic and then removed all of the obsolete parts. The picture also show the Control by Web data logger connected to a wireless router, I can either log on to that router or load the web page from any Internet connection (the data logger has security). Note how empty box looks now.

The new features are:
1) automatic shut down when out of fuel, using a K type thermocouple in the firebox (I tried flue gas which works too but I like the fire box measured temperature change better).
2) selectable circulator control
3) fan/pump run indicators
4) one button start, master power off switch

 

[sgschwend]

Here is the Essex boiler new schematic:

 

[sbleiweiss]

Is this the device that you used (TCS series)?
(broken link removed to http://www.dwyer-inst.com/Products/Product.cfm?Group_ID=125&Product_ID=289&sPageName=Specs)
I would love to have a more intelligent shut-down for my wood gun boiler.
Also what do you use for thermocouple probes that can survive inside the boiler?
Thanks,
Scott B.

 

[snowman49820]

You're getting me in more trouble with the wife. She keeps telling me to leave the stove alone, it works great now.

 

[Nofossil]

My experience with thermocouples is that nothing will survive in the secondary flame zone. Omega makes probes with stainless and/or Inconel sheaths that work fine as long as they're located outside the flame region. I use the models with ungrounded 1/8" diameter sheaths. They can be bent to position the tip wherever you want it, and the sheath can be ordered in almost any length. My combustion probe has a 12" sheath.

 

[lavs4x4]

Steve,

Looking good, I like the idea of the unit shutting down when out of fuel. Shutting the draft fan off is a great idea. I hate hearing mine knowing there is no wood left.

 

[sgschwend]

Yes, Scott that is the thermocouple version. Nofoss has a good point, when you put the probe in the chamber you want to get it close but not in the secondary burn. I used the sight tube and then move the probe in from there, at 3 inches in it isn't even up to the temps found in the flue. The probes I am using has a max temp spec of 2050F, which is right at the theoretical burn temp., it is not necessary to continuously measure that high. I purchased mine from Grainger, and went with 18" (I knew 3" was way to short, I wanted it to be too long).

The challenge with the flue measurement is that if you have the boiler at 180F then the flue temp will hold there even with the fuel gone (it resists going down any further), if your boiler is at a lower temp and it runs out of fuel it will drop to that temp and then hold. It is important to have a low set point so that when the high limit stops the burning process the flue gas temp will be above the fuel shutdown set point. I wanted a measurement that was less sensitive to the boiler water temp. When the probe is in the fire box it will have a lot larger swing and the temperature drop is slowed down by the refractory. All of this makes it easier to pick a temperature set point that will shut the boiler down when the fuel is gone.

With all of that said, a 180F flue gas set point (putting the probe in the flue) works pretty good. In that case I use 2 degrees of hysteresis (temperature must drop by before restart), which equates to about 10 minutes.

The above schemo should be applicable to any boiler.

 

[sbleiweiss]

Steve,
Thanks again for posting this. It has me thinking about what to do to replace the low temp shutdown on my Woodgun boiler. You bring up an excellent point about what happens when the boiler cycles from the high limit. Ideally the controller would allow a few minutes to re-establish the fire before trying to enforce the low temp limit. It sounds like you have figured out a threshold that lets you avoid this problem.

In my case, I generally don't let the boiler cycle. Once it has reached the operating set point limit, the storage is close to as hot as it is going to get and I usually just shut the boiler off at that point. In this case, preventing a re-start might be considered a feature, but I would not want to rule it out and many others run without storage and need this re-start ability.

The ideal setup would be one of these controllers with a timer in parallel with it. The timer would have to self reset every time power was applied. When power is applied it would pass power to the boiler for a programmable amount of time and then cut power off. By that time, the temperature control will have sensed heat and keep the boiler draft fan powered after the time-out. This would work for start-up as well. Anyone know of any timers that work this way? or temperature controllers that can power the load for a fixed time after power-up regardless of the temperature?

 

[Gooserider]

I think that is what Steve is doing - he has a "start" button up near the top of the schematic that triggers a timer.

You can definitely get timer relays and switches that will do a countdown for a preset time and then open - lots of different choices, simplest can be one of the electric light switch timers that people sometimes put on lights that are only used for short periods of time...

Gooserider

 

[sgschwend]

I do use an "Off delay" timer for start.

You would want a duty cycle type of timer (I don't know the real name). It would closed for a program period every so many minutes. I did remove one of these because the device had a fixed duty cycle of 15 minutes on and 180 minutes off. It was used to keep the fire alive in the case where the machine idled.

The thermocouple switch should handle this job; it should allow the boiler to stay on (idle) as long as there is fuel. In my configuration the circulator continues to run after the hi limit switch is reach (I also added a switch so that I could chose to let the circulator run full time even when the safety SW is open to help cool down the boiler or let the TC switch shut it down).

A quick search found this, go down to programmable relay:
http://www.nteinc.com/relay_web/relay.html

here is a Dayton one, a little overkill you can go to Grainger.com and use a time delay relay search:
(broken link removed)

you will find relays as low a $13, the lower cost ones tend to have low contact current specs, but would be OK if you were just closing another relay.

 

[sgschwend]

I watched my boiler run out of fuel tonight to see the difference between shutting down with a flue gas measurement and the fire box measurement.

The flue gas measurement is much more touchy, I normally set it at 180F and that works, but the boiler will hold the temp near there and that is why it is more difficult to use.

The fire box temperature (which is not in the turbulent gas) is a lot more forgiving. I set the shut down temperature switch at 200F the probe measured between 300-500F when it has fuel. When the fuel was gone the temp migrated down to 200F, in about 20-30 minutes. That is plenty of time for the ciculator to move the last bit of heat out of the boiler.

It should also be plenty of time for the case when the boiler needs to idle. During idling the drop in temperature should be even slower because the pyrolysis process (chemical decomposition in the absence of air) will continue to release heat energy. I will measure that tomorrow.

 

[sbleiweiss]

My plan is to mount the probe between the fire box and the heat exchanger. There is no active flame in the area where the probe will be, but the gasses should be very hot at this point. I am going to install the probe through the block off plate that is where the oil burner would normally be mounted. I hope it will survive in this area. There are no easy ways to get the probe into the woodgun fire box area. Maybe a sensor wire could sneak in between the air valve and the opening it sits in, but it's all sealed up with silicone so I am not sure what type of gap exists.

One of the first things I changed on my boiler control was to move the boiler circulator and relay to it's own power feed that is continually on. I have a heating controller to determine if the boiler water is hot enough to provide usable heat. When there is a call for heat, the boiler circulator will respond if the boiler temp is high enough. I have it set to come on at 150 degrees and a 30 degree differential. This allows me to shut the boiler off while it is still at full temperature (I use a timer for now) and the house draws heat from it for 4-6 hours overnight before it reaches the low limit and switches over to draw from storage. You might want to consider if this would work for you. I did not want to let the draft fan run while I was scavenging heat from the boiler because I thought too many BTU's would be lost up the stack. My boiler holds 80 gallons, so I am able to scavenge about 50K Btu's from it after shut-down.

 

[sgschwend]

Scavenging heat is a good move. I removed the glass window (about 2" around) in the rear of the boiler and mounted my probe on a steel replacement part. I only need to put the probe in about 6" so a 12" would have been a better choice than the 18" I purchased. Yes, I did not want to drill an errant hole.

I think my boiler hold about 50 gallons and after 24 hours it is down 50F. Where my storage, which is ten time bigger is only down about 15F (at the top) while it has supported the house load for almost 20 hours. I was thinking about scavenging the boiler heat for the DHW. I haven't decided what clever way to do this; I am currently thinking about using a zone valve to modify the path of the DHW floor heat loops (yes I have two small loops that heat the kitchen, bathroom, and laundry room floors). I kept the older system because it allows for backup heat. So now I am trying to trick it into dual function, floor heat and DHW (I do have 100 gallons of DHW storage to use).

 

[mole]

I watched my boiler run out of fuel tonight to see the difference between shutting down with a flue gas measurement and the fire box measurement.

The flue gas measurement is much more touchy, I normally set it at 180F and that works, but the boiler will hold the temp near there and that is why it is more difficult to use.

The fire box temperature (which is not in the turbulent gas) is a lot more forgiving. I set the shut down temperature switch at 200F the probe measured between 300-500F when it has fuel. When the fuel was gone the temp migrated down to 200F, in about 20-30 minutes. That is plenty of time for the circulator to move the last bit of heat out of the boiler.

It should also be plenty of time for the case when the boiler needs to idle. During idling the drop in temperature should be even slower because the pyrolysis process (chemical decomposition in the absence of air) will continue to release heat energy. I will measure that tomorrow.

Steve, I like your automatic shut down. Nice job. I considered using using the stack temperature to close my draft door at the end of the fire but changed my mind because of the way the water tubes "buffer" the temperature drop. Same as you. I never really considered using the firebox temp though. I settled on an Interamatic mechanical 6hr timer which I wired in series with the draft door ($24), so I set the timer to open the draft door for the estimated amount of time the fire will burn, usually for 4-6 hours. Sometimes I have to rewind to add an hour or two of burn time. It's generally working well for me, but it's not as wife-proof as your solution is......My wife threw a big round in the boiler one night (one of maybe 3 nights she's "helped" in 3 years) just before the timer closed the draft door. The end result was that the tubes fouled from an all night smolder with the draft door closed. So now I'm considering whether to change the controls or train the wife. Changing the controls will be easier! Thanks for sharing your ideas.

JR

 

[sgschwend]

JR, I did modify my method based on you idea. The control schematic I came up with has two modes: 1) off with fuel, 2) off with boiler temperature. I flipped the circulator to the switch so now it shuts off with the boiler temperature.

That gave me about an hour of circulator run time after the fuel was gone to collect more heat for the storage tank.

You timer idea would work automatically if you added it to the "fuel is gone" switch. Set the timer for one hour; in that time the boiler temperature would be lower than the storage temperature.