OWB thermostat question

[jimdad07]

You know guys and gals, I work on big steam boilers with Power Flame burners, commercial and industrial heating, air conditioning and rack refrigeration for a living all day every day and I have seen a lot over the last six years in the field, but you guys have got to be some of the best temperature control people I have read. Not being a smart $$$ in any sense, there are just some good minds here. I am learning reading through some of these outdoor boiler threads.

 

[Steveguy]

You can get programmable temp controllers from someone like love controls (dwyer instruments) or others that have relay outputs, programmable setpoints, dead bands, and alarms that you can have high limit, low limit or deviation from setpoint, or absolute value upper and lower limit. using deviation or absolute upper and lower limit, you can create a window in which draft will operate normally, above or below which the output will turn off. If I remember correctly, when you cycle power to them , the output will come on when temp is low, allowing draft to open to get up into the working range. This would allow for cold start, but if it goes low again, the alarm becomes active, turning off output. They are about $100


Table of Contents -- Temperature Controls

http://www.amazon.com/Temperature-Control-Universal-Input-Outputs/dp/B003NVGF9I

 

[applefarmer]

OK so now that this thread is active again, and I still have not done anything yet, I have decided to add another challenge. My owb has a selinoid controlled damper which opens and closes via input from the aquastat which also turns the blower fan on and off. How could I seperate the fan from the selinoid?

Here are my thoughts.
120 degree water (out of wood) = fan off, damper closed. This would be low limit.
bypass switch would allow damper to open and fan to run to mid setpoint (165)
At 165 fan would stop but damper would remain open until water hits (190)
At 190 damper would shut.
When water temp falls to 150 damper would open.
If water temp continues to fall to 140 fan would run till 165 then shut.

I think all I would need is another aquastat and a snap disk for low limit and a bypass switch. By the way I don't plan on doing any of this until the weather warms, and I hope I am not trying to reinvent the wheel.

 

[Stihl310]

OK so now that this thread is active again, and I still have not done anything yet, I have decided to add another challenge. My owb has a selinoid controlled damper which opens and closes via input from the aquastat which also turns the blower fan on and off. How could I seperate the fan from the selinoid?

Here are my thoughts.
120 degree water (out of wood) = fan off, damper closed. This would be low limit.
bypass switch would allow damper to open and fan to run to mid setpoint (165)
At 165 fan would stop but damper would remain open until water hits (190)
At 190 damper would shut.
When water temp falls to 150 damper would open.
If water temp continues to fall to 140 fan would run till 165 then shut.

I think all I would need is another aquastat and a snap disk for low limit and a bypass switch. By the way I don't plan on doing any of this until the weather warms, and I hope I am not trying to reinvent the wheel.

I'm not an expert by any means, but I think the easiest way to achieve what you want is to incorporate multiple snap disc theromstats, that are NC that open on high or low. There may very well be a controller out there that would do what you want it to do, and what Steve recomended may be the best way to go about it. I'm not real familiar with off the shelve units, as most of my background and schooling has been taking examples like you just posted and figuring out a way to get them to work, whether it be by mechanical sensing devices, or PLC's... If it were me right now I'd just try to use snap disc thermo's to achieve your high/low temp on and off's. the parts in between may prove to be slightly more difficult. I'm going to snoop around and see if I can't find something that would work, or pieces parts you could put together to achieve what you want.

 

[Steveguy]

The love controls type controller has two outputs, so you could control the damper and fan independantly, but in your last post you are aking the damper to work differently on dropping temperature than it does on rising temp. That would be pretty involved to do. You do rremember were just dealing with wood, fire, and hot water right?:hmm3grin2orange::hmm3grin2orange:

 

[Steveguy]

Thinking about it some more though, if your damper door setpoint is around 180 and you put a fairly large deadband setting in the program for that output, the controller won't respond until temp goes outside the deadband setting, although the controller may allow the same amount of overshoot as well, say you set a 180 setpoint with 20 degree deadband, the output won't come on till 170 and will shut off at 190, the controller won't change state within the deadband. If I'm remembering right.

 

[boyland]

You can do this using 2 ranco controls one running on hot and the other running on cold. They are wired in series as far as the fan connection the first will supply power to the second fan control. The first will run in cold mode turn off the power when the temp is below 120 the second will run in hot mode turnoff at 180.

2 ranco can do the job.

 

[Steveguy]

Here is a website and an item number that should work. You would want to talk to an application specialist to make sure it will do what you want.

Series 16B - 1/16 DIN Temperature/Process Controller - Dwyer Instruments


16B-33 1/16 DIN temperature/process controller, relay outputs 1 and 2. Same Day $99.00

 

[Steveguy]

You can do this using 2 ranco controls one running on hot and the other running on cold. They are wired in series as far as the fan connection the first will supply power to the second fan control. The first will run in cold mode turn off the power when the temp is below 120 the second will run in hot mode turnoff at 180.

2 ranco can do the job.

So if you want to control the fan and draft door independantly, you will need four of these units?

 

[boyland]

no run the damper control off the cold also.

 

[Steveguy]

The OP said he wanted to have the draft door and the fan act separately on the way up to setpoint, so you would need at least a third one to turn that off at 165.



"At 165 fan would stop but damper would remain open until water hits (190)"

 

[boyland]

Yeah but I can tell you that is a waste of time. You will not get enough draft if the unit is actually being used to go on up.

IMO.

 

[Steveguy]

Yeah but I can tell you that is a waste of time. You will not get enough draft if the unit is actually being used to go on up.

IMO.

Yeah, I think its more involved than needed. Thats the purpose of having a large volume of water is so you don't need real close control of the heat source, you can't turn it on and off like a propane burner.

 

[applefarmer]

Ok how about this, if I set the damper to open at 165 and close at 190, then set another independent aquastat to turn the fan on at 140 and off at 165? The damper would remain open all the time from 140-190 since it would not shut until it hit the upper setpoint. The thought was I could save some electric and maybe some wood, since maybe the fan would not have run if the natural draft could keep up.

 

[boyland]

you are going to create a creasote monster IMO

 

[Stihl310]

Ok how about this, if I set the damper to open at 165 and close at 190, then set another independent aquastat to turn the fan on at 140 and off at 165? The damper would remain open all the time from 140-190 since it would not shut until it hit the upper setpoint. The thought was I could save some electric and maybe some wood, since maybe the fan would not have run if the natural draft could keep up.

My concern would be once you cut power to the fan that there would not be sufficient air flow to keep the fire going. I witnessed this myself this morning when I replaced my blower. Initially the blower was running, kicking the heat back up when I went to work on it, so I flipped the switch and unbolted the unit, as it was unbolted the entire orifice was open to the inside of the firebox, and not once did it ever ignite whatsoever, just sat there smoldering.

I think if you had a larger opening to allow for more air flow this would not be an issue, however after what I saw this morning on my own unit, I could see as the previous poster said a creosote monster in the making. I think your best bet is to run both the fan and solenoid in sync with one another to avoid any other unforseen issues that may pop up.

You may be able to wire in an additional solenoid that would kick on an stay open from 165-190 that would open up a larger orifice to allow for more flow, however you would have to compare power usage from the fan to the addtional solenoid to see if you would actually save any electric to make it worth your while.

 

[war-wagon]

tried it, wanted to save electric. woodmaster 440 became creosote 440. not worth it. just sharing my stubborness and experience. only thing was that the wood was not completly seasoned. i'm considering better wood and maybe an early/late season modification when demand is less.