Trouble transfering heat to storage tank from Tarm

[Chris S.]

First, thanks to everyone for a great forum. I've learned a tremendous amount here- and hope someone might be able to point me in the direction of a solution for my current situation.

I've got a Tarm Solo Plus 60 set up with storage in the form of a 1,000 gallon dairy tank to heat the radiant slab of our small business. A local plumber set it up with the help of the good folks from Tarm in NH. This project has been a learning experience for our plumber who has maintained a good attitude through the project. We are having some issues at the moment and while I'm definitely not a plumber/engineer, I'm trying to help brainstorm and ask the right questions that might point him to the bottle neck.

Basically, our situation is this. I fire up the Tarm, the water jacket comes up to 140F and the circulators come on moving water jacket water through a heat exchanger which transfers it to the loop that takes the hot water into the storage tank's copper loop exchangers. Within 45 minutes to an hour the temperature of the Tarm water jacket reaches its upper limit and turns off the fan, stopping combustion. Slowly the water jacket temp drops as the pumps and exchangers do their thing, the fan kicks back on and burns again for a number of minutes before maxing out and turning off again.

This is a new system installed this spring. We did a test fire this summer with the plumber and a rep from Tarm USA there to hold our hands. We had the same issue then. Rene from Tarm hypothesized that since our storage tank temperature was only 68F the Termovar valve was not allowing much tank water to be pulled in and heated, so the Tarm quickly reached the temperature for fan shut-off. To alleviate this situation during the annual start up (we have limited DHW needs and decided to not heat the tank year round) the plumber installed a bypass to the Termovar to bring the tank water up to temp more quickly, and once in normal operating range we'd shut down the by-pass (perhaps this is a no-no??)

Well now we are in the heating season and even with the by-pass open, the Tarm water jacket is quickly reaching 180F+ shutting off the fan and smoldering.

We were really looking forward to high-efficiency, wide-open burns to charge our tank and are frustrated with the creosote dripping out the bottom of the chimney and from around the upper door gasket.

The plumber is operating on the thought that air is trapped in the tank's heat exchanger coil loops and preventing good heat transfer. He assures me the pumps/pipes and the heat exchanger that separate the Tarm from everything else are sized as specified by the Tarm USA folks.

Has anyone had similar troubles bringing their tanks up to temp? Do other people's wood-gasification boilers cycle on and off when operating with storage? Short of reviewing the details of every valve and pump can anyone offer any general advice of things to check?

We've got the tank temp up to 140F today, but the fan/combustion is still cycling on and off.

Thanks to those of you who made it this far down- any thoughts are appreciated.

 

[steam man]

I think most of us would need more info to make a correct assumption but I will try to make an educated guess on this one. It seems to me that it is obvious you don't have enough load on the Tarm. There could be air in the lines but I would think the pump would be noisy. Is 140 to 180 water reaching the inlet of the tank's heat exchanger? What is the outlet temp of the exchanger? I would think it should have been sized for 20 deg F drop at least. If not, could be the heat exchanger is not big enough. What is the estimated flow rate through the pipes to the exchanger? Installng a balancing valve (just a ball valve) in line with the Termovar back to the Tarm has been talked about in other threads. Basically you need to throttle the bypass back to the boiler. Start with the valve 1/2 open and see how it responds.

I wouldn't panic yet. There are plenty of people who are going to help you out around here. Your system is goingto work. Posting a diagram and some more detail info would help out.

Mike

 

[free75degrees]

What are the specs on your coils? (how long, how many, what diameter pipes?) Did the coils come from STSS, or some other company, or were they homemade?

When the tank circulator is on and the boiler water is at 180* and the tank is cool, how do the temperatures of the input and output pipes for the tank feel? How much hotter is the input than the output?

How is the Termovar bypass piped? There are 3 pipes that connect to the Termovar - which 2 of the 3 pipes is it connecting?

 

[mikeyny]

It is hard to give much good advice with out a little technical info from you. What size pipe goes to and from the tank? What type of heat exchanger, home brew ? How far is the boiler from the tank? What is the temp going out to the tank and coming back? Delta t? The tank and pipe are insulated? Is there an aquastat on the tank to control the circ? Some aquastats will shut off the circ if the water temp falls below a pre set temp. What size circ? Do you have the return and supply lines reversed? This info could narrow it down to a few things. Also the fact that it sounds like you have some proffesional people working on this is encouraging. From what I hear, the Tarm folks are VERY good at this type of wood boiler set up. AIR in the loop would cause little to no flow and cause the problems you have. Install an air scoop with a vent at the high end of the loop. Begin your trouble shooting with the easy and cheap things first. When you figure this out you will probably shake your head a few time and laugh. This is how we all learn.

 

[chuck172]

For the life of me, I can't figure out how you can ever get good flow from the storage tank through the circulator . If you're trying to heat 500-1000 gallons of water, your gonna be returning lots and lots of cool water to the tarmovar, keeping the mixing valve from ever opening fully.

 

[free75degrees]

For the life of me, I can't figure out how you can ever get good flow from the storage tank through the circulator . If you're trying to heat 500-1000 gallons of water, your gonna be returning lots and lots of cool water to the tarmovar, keeping the mixing valve from ever opening fully.

I'm trying to get my head around this too. Here are my thoughts...

I think the termovar is designed to allow the max amount of tank return water as is possible and still get a minimum water temp in to the boiler. I think it will always include some amount of the cold return water becuase if it didn't then you would just get 180* water circulating around the boiler and it would get too hot. So if the tank return water is very cold then it just adds a little bit of the cold water with the hot boiler water. As long as the water coming from the tank is cold then we are in good shape becuase we know we are removing cold water from the tank which is what we want to do (and replace it with hot water)

Another way to think of it is that the termovar only allows about a 20* drop in the water leaving the boiler vs. the water entering when the boiler is at 180* - i.e. if the water coming out is 180* the water going in will be 160*. Assuming the circ moves a constant volume of water per time then we are essentially supplying a fixed amount of btus per time from the boiler (the btus are a function of the volume of water and the delta in temp). This fixed amount of btus per time is basically all going into the tank. When the tank is cold we only need a trickle of water into the tank to accompilsh this. When the tank is warm we need to move more water through the tank. The termovar gives this automatic variation in flow, which is indirectly related to the tank temp.

 

[chuck172]

So when the tank water temp is very cold, you can expect very little tank flow through the circulator. Most of the return water will be from the already heated boiler supply water through the balancing valve. Were talking heating 500 -1000 cold gallons here. Only when the tank fully reaches aprox. 140 will the tarmover open increasing flow. Is this right?

 

[free75degrees]

So when the tank water temp is very cold, you can expect very little tank flow through the circulator. Most of the return water will be from the already heated boiler supply water through the balancing valve. Were talking heating 500 -1000 cold gallons here. Only when the tank fully reaches aprox. 140 will the tarmover open increasing flow. Is this right?

I think that when the tank return water is very cold the circ flow will about the same as when the tank return is hot, it is just that most of that flow will come from the hot input to the termovar.

 

[chuck172]

Right, most of the flow will come from the boiler supply bypass rather then the storage tank return.

 

[Chris S.]

thanks everyone for the encouragement and patience- obviously there are a lot of pertinent details here, and it can be hard to describe the whole system via a keyboard. Even when several trained professionals are standing in front of the system it causes some head scratching.. so trying to make sense of it in cyber space is daunting, but here I go!

I'll try and answer the questions posed so far more or less in order.

I've been firing the Tarm intermittently since Friday afternoon and as of this afernoon the tank is up to 155F at the top, 158 mid level, 157 towards the bottom. Currently the water jacket of the tarm is at 190 and the fan is off.

Water going into the heat exchange coils submersed in the tank is at 180F right now, coming out at 160F. There has been a 20 to 30 degree F difference between in/out consistently since we started the process.

I don't know what the flow rate through the pipes delivering and removing water from the in tank coils is- I'd have to ask the plumber about the pumps.

We do have a balancing valve, here is a photo of the Termovar, balancing valve and our "by-pass". Low quality from my camera phone but it is all I have handy at the moment.

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The balancing valve I believe some of you are referring to is on the right of the Termovar our little bypass route is below and left.

The size of the pipe to and from the coils in the storage tank is 1.25" in diameter, but it looks like it necks down to a smaller diameter to connect to the coils. The coils are from STSS. The Tarm and tank are only 5 or 10 feet apart. Both are inside at ground level in conditioned spaces. The stainless steel dairy tank has about 2 inches of foam insulation in its structure, I plan on adding more exterior insulation once we get everything set up and running.

There is an aqua stat on the tank, it is set at 110F. I'll have to inquire about the circulating pump sizes- supposedly they were spec'd by Tarm USA, but I'll have to double check some of these details to see if the plumber got the wrong ones or if something is over/under sized. Unfortunately I'm not the actual installer of the system- I know enough to be slightly dangerous but the plumber definitely was given the leeway to build what Tarm had specified with little intervention from me.

He did install an air scoop/spirovent in a high point above the tank yesterday, so maybe as I've run the system today we've gotten some of the air out.

Mikeyny, I'm looking forward to the chuckle and head shaking that will inevitably come at the end of all this, but the sooner it comes the better!

chuck172 and free75, I've puzzled over the termovar situation a great deal and I think you are both right. To me it was frustrating to have the Tarm be throttled back and smoldering b/c the termovar was only letting a trickle of cool water mix with the looping hot water. That is why we introduced the bypass- I'm not saying it was a great idea, perhaps having the return water to the Tarm too cool caused problems I don't know about, but there was so much creosote from the combustion being held back that I was willing to give it a try.

Now that our tank is over 140F the termovar shouldn't be so restrictive, right?

Since the tank is up to 155F it might be hard to tell now if transfer of heat is difficult simply because we've reached such a high temp or if something is wrong with the system. From your collective experience what tank temperature ranges should cause the Tarm fan (combustion) to cycle on/off due to high water jacket temps? When is it reasonable for that to happen? And what tank temps should allow the Tarm to burn straight out with no high-heat shut downs if the system is set up correctly?

Thanks! Chris

 

[free75degrees]

I wonder if the termovar is stuck in a position where it is supplying hot water to the boiler return. Maybe even with the bypass you are getting too much hot in the return - the path from the tank could have more head than the path through the termovar. You could test this by completely closing the balancing valve, essentially disabling the termovar and causing the bypass to be used exclusively.

 

[mikeyny]

Just a few thoughts. The rate of flow issue. The thought that the termovor may not be working properly is a very good point. That deserves a little attention. How do you check that?? I don't know. And the fact that the flow into the many feet of heat exchanger in the tank is quite different than the flow thru a few ft of pipe back into the boiler. Head pressure and resistance to flow into and out of that coil is much different than that loop back to the boiler. Pipe size vs pump size? I am really only a backyard boiler operator, not an engineer. Normaly I try to keep things simple, but to get the greatest efficiency's that these boilers can achieve it take's some complexity and real engineering ,but I still think it is a small oversight somewhere in the system. Hoefully some of the real engineers here will solve this for you soon. If not I suggest you offer up a six pack or two or even a good bottle of scotch to the soul who solves this for you.

 

[Chris S.]

free75- I like the idea of closing the balance to disable the termovar and bring in more water from the tank. I may give that a shot the next time I fire.

mikeyny- the whole pipe/pump sizing is way outa my league. I agree the devil could be in the details there, but I may have to punt and let the plumbing professionals work that out with TarmUSA's help. Tarm has been very supportive so far- two thumbs up for their customer support. 4pm on a Friday their tech staff was willing to delve into it with me the owner- very patient with my lack of technical language. They may get another call tomorrow or Friday when the plumber and I take another crack at this.

Thanks for the input, I'll keep you posted on how this develops.

 

[steam man]

Stupid question here-what is the output of the boiler? I just checked Bioheat site and it seems to be around 198,000 btu/hr. I may have that wrong but I am thinking that if the Termovar is operating correctly, the boiler may be oversized for the output of the coil in the tank. It seems like the numbers look ok its just that the boiler isn't working hard to maintain those numbers. What are the coil specs?

Mike

 

[Nofossil]

I posted an earlier reply that got lost in the ether. Lots more activity on this thread since then. I'm going with the idea that the Termovar is either (a) not working properly, (b) not allowing a high enough flow rate, or (c) not allowing a high enough delta T.

A little more data would be good. You mentioned a 20 degree delta T across the tank HX towards the end of the burn. When the heat transfer was not going well, what were the three temperatures at the Termovar?

I'm assuming that the hot in (recirc) was 180, and the cold in (from the storage HX) was close to the tank temp - say 120 when the tank bottom temp was 110. What was the Termovar output (I assume that's also the Tarm input)?

Seems like it *should* be 140 under those conditions - just high enough to provide input protection. If it was 160 or more, the Termovar is being part of the problem.

 

[jebatty]

FWIW, here is a description of my operation today. Tarm Solo Plus 40, 1000 gal LP pressurized storage, 5 x 12 x 30 plate hx, Taco 009 on the boiler side; Taco 007 on the tank side. I was operating the boiler solely to charge the tank, no other draw on the system. 3/4" line between the hx and the tank; 1-1/4" line on the boiler side of the hx.

Surface aquastat on the return line after the Termovar, set at 145. When return temp to boiler rises to 145, boiler circ and tank circ are on. Balancing valve on Termovar set by trial and error to allow a fairly low flow through the Termovar on return to the boiler, bulk of flow would be to the tank once the Termovar opens.

The maximum temp I could get out of the boiler was just over 170, and it moved around a bit between 160-170. Water from tank to hx was 80; water out to tank from hx stayed pretty close to 130; delta T about 50 degrees on tank side. Return water to boiler was about 130 or a little less, just high enough to prevent the aquastat from cycling the circs off. At no time did boiler ever reach the cycle off temp of about 185. After about 3.5 hours of operation, water from tank started to rise above 80.

I was running the Tarm fairly hot, with probe flue temp 500-600. I have some control over this as I added a manual motor speed control on the draft fan.

 

[free75degrees]

So I just lit my 2nd fire on my new Tarm setup. The 1st one was last night and I just put a few logs on as a warm up. Tonight I filled it up. Gasification kicked in within 10 minutes. Then the temp kept going up and the draft fan went off and it went into idle state. Not only that but even in idle state the temp kept going up and up! I eventually got to 100*C and I was getting nervous so I grabbed a couple buckets and started draining some hot water from the boiler to get the temp down. Once the temp was down to 80*C I turned the fan back on and the same thing happened again. So I was thinking that whatever happened to CJS was happening to me! And I figured it HAD to be the termovar.

I noticed that each of the flanges on the termovar had a little flat sided protrusion and i didn't know what it was so I thought maybe it was some adjustment and I used some pliers to turn it. When I did, I noticed the noise of water flowing through the termovar changed. Hmmm, I thought, what could that thing be. Then I remembered that I had an extra flange from port 2 which was the one where I broke the nut from overtightening and had replaced the flange with a black fitting. So I grabbed the unused flange and turned the flat sided thingy. To my surprise it was a built in ball valve! Well the ball valves on the installed termovar had all been open so it didn't seem liek that explained the problem. But after closing and opening the ball valves a few times something must have loosened in the Termovar because the boiler temp started dropping rapidly. I opened the tank top and was shocked to see that the temperature was really started to get hot. I think there must have been something stuck in the Termovar or maybe I was not using it right. Is there an instruction manual for that thing? CJS - maybe you have a similar problem.

 

[jebatty]

Excellent point on the integral ball valves on the Termovar. It has a built-in balancing valve. When I installed my Termovar, I noticed the valves, but I already had plumbed in a balancing valve. So I opened fully the integral Termovar valves and use the plumbed in balancing valve.

 

[chuck172]

you mention the integral ball valves on the termovar, are you talking about theTermovar Loading Unit?

 

[jebatty]

I guess I don't draw the distinction as I don't know whether these are different. All I know is that the Termovar that Tarm supplied to me included integral ball valves on the boiler input side and the return side from the system.

 

[chuck172]

I had no idea that those three flaps were adjustments. There should have been some more info with the valves.

 

[Huskurdu]

Damn, where's CJS??? I just read this entire thread.....I'm dying to know if that is his problem... It's like watching a soap opera unfold.... LOL

 

[Chris S.]

wow- I'm reading now and am going out to check my termovar.....

 

[Chris S.]

so are these the "integral ball valves" that are being referred to here?

Thanks for the tip free75... sounds like things got a little hot for you! I'm glad you had a happy ending so to speak. So by opening and closing those integral valves you think you freed something up and got it working better? I'm certainly wiling to give those a few twists back an forth. My tank is still at 155F today and the suns out so I may not fire again until we need some heat... but I'll give this a try and report back in the next couple of days after I fire it up again.

 

[chuck172]

I wish I had a termovar to take apart. I'd like to see what those "integral ball valves look like"