# Tekmar control or product   -   wood boiler return water temperature protection



## PassionForFire&Water (Feb 1, 2012)

I'm not familiar with Tekmar controls.
Was reading a lot of good stuff on them on this forum, but I do have a question I don't know the answer to.

*Is there a TEKMAR control or product that can be used as wood boiler return water temperature protection (like a Thermovar LK820)?*

I have an issue with one of my indoor wood boilers installed in the field having excessive condensation and creosote build-up.
I do not have a detailed schematic or exact temperature readings, only bits and pieces.
The wood boiler is charging a water storage tank.
The water storage feeds a floor radiant system
The water from the water storage tank is mixed down in temperature before it goes into the radiant manifold system
I do not know the temperaturess of the water entering/leaving the floor radiant manifold, but I know radiant floor systems run normally at temperatures between 80F-130F

I suspect that the return water from the radiant floor system is around 80-90F, and that this cold water is entering the storage tank and then gets fed into the wood boiler.

Don't quite understand how any of the TEKMAR controls can prevent this, that's why we always recommend and use a Thermovar LK820.

Any input is appreciated


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## jebatty (Feb 1, 2012)

There are many reasons for condensation and creosote, as I am sure you are aware. You might be better off by getting some accurate information as to what and why before deciding you need a particular control. Maybe the user is just burning green or wet wood, or the air settings on the boiler need adjustment, or ....


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## PassionForFire&Water (Feb 1, 2012)

Hi Jim,
You are right.
The air settings / draft of course are important but an unknown. Is 99% not the issue in this case.
Assuming the MC is between 18-25% and knowing that we advised an Thermovar LK820 but some sort of Tekmar control was installed instead, I'm trying to figure out if there is a Tekmar product that can act as return water temperature protection like an LK820 does.


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## DaBackBurner (Feb 1, 2012)

Several Tekmar controls can provide return boiler water protection with correct plumbing practices. The 361 will provide this with injection loop. The 363 can provide boiler protection with a 4-way mixing valve. I'm sure there are others, these two just come to mind as I was looking at them the other day.


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## jebatty (Feb 1, 2012)

I'm not aware of a Tekmar that serves as a loading unit. But Tekmar makes controls which will operate a motorized mixing valve based on temperature and the combination can provide return water protection. Why not inquire specifically what was installed? And get a plumbing schematic so you know the system? Without full facts it is nearly impossible to suggest a solution because everything is speculation.


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## afblue (Feb 1, 2012)

I have a Tekmar 356 injection mixing controller. It has "boiler protection" but its not going to help your situation. The boiler protection has a temp sensor that can be put at the boiler return, and can reduce the heat demand of the house until the boiler recovers to a set return temp in a conventional boiler system. But if you have a mixing system with storage, the only way you can have boiler protection with storage and a low temp manifold, is to have a thermovar valve that let's the boiler bypass in a loop to heat itself up. 

What I did with my Paxo 25 was set my boiler circulator was turn setpoint up to 170, so it will always have hot water sending to the storage, and if cold ever does get past the thermovar, it will shut off until the boiler heats up.


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## ALASKAPF185 (Feb 3, 2012)

What about a simple boiler bypass. Some boilers have them built in for cold shock protection and are required in many manufacturer's installation specs for warranty. Also a hydraulic separator. The Tekmar boiler control is a great product but maybe overkill for protection.  Maximum efficiency & comfort comes from maintaining the designed Delta T, Usually 20 degrees


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## dogwood (Feb 3, 2012)

Look for a post from HR that RobC recently pointed out to me in https://www.hearth.com/econtent/index.php/forums/viewthread/40804/.


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## in hot water (Feb 4, 2012)

The only way to provide boiler return protection is to have a device that can sense the temperature at the return connection to the boiler.  Boiler bypass piping or bypass pumps alone cannot provide this protection.  They lack the temperature sensing function, and cannot adjust to ever changing conditions that the boiler sees.

Several choices include the thermostatic mixing valves or valve pump assemblies.  With this arrangement the thermostatic element is inside the unit and adjusts the flow to allow hot supply from the boiler to temper the return temperature to the boiler.  Simple and effective.  You need to confirm the valve has the capacity to pass the gpm that the boiler requires.  The Cv of the valve and the size of the pump installed will need to be considered. See the attachment to understand how thermostatic valves operate.

Return temperature protection can also be accomplished with a motorized mixing valve.    Either a 3 or 4 way valve would have a motor to move the position of the valve.  A strap on sensor at the boiler return connection is the "decider".

Yet another method is a variable speed pump that adjust the "mix" temperature by modulating the pump speed.   tekmar controls can drive either device, the motorized valve or the injection pump.

I'd guess the thermostatic valve would be the least expensive method, the motorized valve or variable speed pump require an additional control, maybe two.

But there are some delta T pumps on the market that are variable speed.  Usually they have a tekmar built board built into them to modulate their speed.  There are other manufacturers of mixing valves and controls.  I believe HeatTimer and HBX are still in this market.

Return temperature protection is a must on wood fired boilers.  Your boiler will have a miserable life and reward you in expensive and possibly dangerous way without proper protection. 

hr


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## ALASKAPF185 (Feb 4, 2012)

Never seen a boiler bypass when adjusted correctly that could not maintain a set delta T. I don't care if it has 200 going out and 35 degrees coming back. Its the cheapest, easiest, most reliable and most common way of protecting boilers from cold shock and condensing problems. Used on many car wash boilers for snow melt and or with space heating applications where large temp swings are the norm. 1 less component to fail.


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## PassionForFire&Water (Feb 4, 2012)

ALASKAPF185 said:
			
		

> Never seen a boiler bypass when adjusted correctly that could not maintain a set delta T. I don't care if it has 200 going out and 35 degrees coming back. Its the cheapest, easiest, most reliable and most common way of protecting boilers from cold shock and condensing problems. Used on many car wash boilers for snow melt and or with space heating applications where large temp swings are the norm. 1 less component to fail.



Can you please explain, maybe a schematic?
Just a bypass valve is not gone do the trick. See explanation from "in hot water"
I'm not sure that i'm understanding you correctly. Are you refering to a Thermovar with bypass valve or something else?


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## ewdudley (Feb 4, 2012)

PassionForFire&Water; said:
			
		

> ALASKAPF185 said:
> 
> 
> 
> ...



Here's an example.  It has two injection pumps for when storage is already fairly hot and more flow is needed to reduce supply temperature, but the second pump is not essential because, as you'll see below, I've since decided that I'm is just as well off simply to heat storage to the maximum desired temperature on the first time around and then shut down.

I control mine using on-off pumping with a $35 PID controller, with another relay other than the one in the PID controller to switch the pump because the controller relay is a pretty dinky.

The recirculation pump is a 007 good for about 17 gpm, and the normal injection pump is a 15-58 on low speed.  You need to run the numbers for your particular situation, but the idea is that the recirculation flow is overwhelming enough to absorb intermittent injections of cool return water with no problem.

I have mine running on an 80 second cycle, and at about 70000 btu per hour net heat output the injection pump runs about 25 seconds per cycle.  Return temperature dips about 10 degF while the injection pump is running.

A compelling advantage of this setup is that the return temperature can be changed with the push of a button, and therefore so can supply temperature.  Normally I run mine with return temperature set to 165 degF and supply runs around 175 degF.  This means that the tank is charged with 175 degF water from the get-go, instead of filling with 160 degF water on the first lap around and then going up to the final fill temperature on the second lap.

--ewd


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## ALASKAPF185 (Feb 4, 2012)

vdt 


http://comfort-calc.net/Bypass_Piping_Explaination.html

there is plenty of info & diagrams here, and even if its necessary on larger volume boilers


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## PassionForFire&Water (Feb 4, 2012)

Thanks guys! Appreciate your input.
Being a mechanical guy, i need to say that i like the thermovar concept above all these other alternatives. Easier to explain to customers and DIY installers.
Also, this devise not consuming electricity is a big plus because a lot of our units are installed in off grid situations and zero energy buildings where electricity use is a big issue/topic.
Thanks again.


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## ewdudley (Feb 4, 2012)

PassionForFire&Water; said:
			
		

> i need to say that i like the thermovar concept above all these other alternatives. Easier to explain to customers and DIY installers.



You may want to take note that the big mixing valves have a choice of temperature setpoint.  Although 140 degF may be the minimum return temperature, it's not necessarily the optimum temperature for a particular application, so depending on the installation a higher temperature model might work better.  Or not.

--ewd


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## in hot water (Feb 5, 2012)

here is a good read on boiler protection.

www.pmengineer.com/Articles/Feature...-Boiler-Protection-in-Your-Next-System-Design

All cold start boilers will condense until the heat exchanger warms above the dewpoint of the fuel.  The same thing happens in the flu pipe until it is warmed.

A few minutes, maybe 10 is about as long as you want to allow them to sweat.  If the boiler is connected to a low mass distribution system it may get out of condensing mode quickly.

Generally wood boilers are high water content, high mass and connected to large thermal storage.  Without a sensor to acknowledge the return temperature you would be guessing.

For many years we were told copper tube boilers could run with  return temperatures below 140F.  But I have seen many failures of the flu and HX when they run extended periods with cold return.

In one case two folks were poisoned by CO spilling from a boiler with a plugged HX from running cold connected to a radiant system.

I've replaced dozens of failed boilers due to cold return temperatures, best to protect you and your boiler with a well designed return temperature protection device.

hr


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