Troubleshooting Tarm temps.

[dirttracker]

How much pipe (and what kind/size) do you have between you boiler and storage? You should be getting significantly less idling now as opposed to the balancing valve fully open. I suspect if you have a fair amount of head loss in you piping to storage then you will have to close down the bypass even more. Just be careful you don't close it down too far or you will end up with the situation I described previously.

If you close the balancing valve all the way, the termovar will shut down the feed from storage in an attempt to regulate the boiler inlet temperature. In this condition you will not have much flow out of the boiler and should have a lot of idling.

The mixing will never completely stop due to the design of the termovar. It never closes off the bypass port, even with temperatures over 160 coming from storage.

The reason behind the balancing valve is to provide additional resistance to the branch of the loop. From the perspective of your boiler, the bypass and storage look like 2 loops in parallel. The loop with the least resistance will get the most flow. If you have a long loop or something creating a lot of pressure drop in your storage loop, the majority of the flow will head for the bypass until it is closed a fair amount.

I get idling with my tarm 40 when the bottom of storage is at 150 - 160 depending on how much heat the burn is producing. It does not idle for long at this point. I suspect it would not idle at all if the bypass was completely closed - I have always wanted to try using a zone valve with a cheap temperature controller to close off the bypass loop under these conditions.

Your system is idling because you cannot get the BTUs out of the boiler fast enough at these return temperatures. I suspect this is a combination of how much is going though the bypass loop and the characteristics of the pump performance and the storage loop.

BTW, I checked my termovar and it is also stamped 72 C. I believe this is the temperature where the storage port is fully open, but I may be wrong.

 

[in hot water]

Here is a handy formula. Q= 500 X flow rate X (delta T)

Q being the rate of heat transfer, 500 is the density of water at 60F (a nice round number that decreases a small amount as the temperature rises)
f is the flow and the delta T is the difference in temperature going into the tank vs the return

So with boiler supply of 190 and return from the tank at 140F and a 10 gpm flow rate 500 X 10 X 50 = 250,000/ hr. btu moving into the tank.

As the tank warm the transfer rate slows down, the delta t is closing up, 500 X 10 X (190-170) = 100,000.

So with a cool tank, say 140F it heats much faster than when the tank rises to 170.

To heat 1000 gallons of water from 140 to 190 use 8.33 X volume x delta t So 8.33 X 1000 x 50 = 416,000 BTU
From 65F to 190F = 1,041,250 btu.

Coast time from that tank 8.33 X v X delta t divided by the load 8.33 x 1000 x (190-140) with a heating load of 40,000 BTU/hr would give you 10 hours. Not counting any loss from the tank, pipes etc. if they are not within the heated space.


We see our storage tanks rise in temperature quickly when you start them from a cool temperature, then as they hit 160 or so you think something is going wrong because the temperature rise slows way down, but it is just the laws or thermodynamics at work. Hot goes to cold, and the rate of this transfer changes with the delta T. That is when you see the boiler hit high limit, and go to idle. Once you get the hang of this you can load the wood accordingly.

The wrench in the works is how much energy is being used to heat the home as the tank is charging. That is a moving target and makes the formula a bit more complex.

hr

 

[Reggie Dunlap]

I just read through this whole thread and I'm more confused than when I started. I have a Tarm 40 with the Termovar valve and 750 gallons of storage.

My boiler hits 190 every day and idles on and off as the tank heats up to 175-180. Sometimes the boiler is at 190 and the tank is still at 160-170 and the boiler idles on and off for hours. Is this idling bad? It seems as though the heated water isn't going to the tank fast enough? Or the return water is too warm? Is the Termovar adjustable?

This is my fourth winter with the Tarm and it's done this since new. Maybe this is just the way the Termovar is supposed to work? It just seems like I could burn less wood if the energy transferred to the tank quicker.

Any feedback is appreciated.

 

[Singed Eyebrows]

The loading units do not seem to have these problems & as Chuck172 says they are considerable. My Laddomat 21G is problem free & I hear very few problems with the Termovar LU. There are members here that do get the balance close(still needs to be adjusted from what I have read), personally I would just as soon pay a bit extra & have one less thing to troubleshoot & worry about, Randy

 

[chuck172]

With the above formula in mind, "Q= 500 X flow rate X (delta T)"
Seems to me that larger, low temperature open storage would be much more efficient, as far as wood consumption, than smaller, high temperature pressurized storage.

 

[jebatty]

My boiler hits 190 every day and idles on and off as the tank heats up to 175-180. Sometimes the boiler is at 190 and the tank is still at 160-170 and the boiler idles on and off for hours.

I originally had this situation with my Tarm Solo 40. It's helpful to diagnose the problem. Start with a diagram, post it here, and let's see what your system looks like. Second, get some meat or "milk frothing" probe thermometers, if you don't now have thermometers at key points on your pipes. You want one on each pipe going to/from the Termovar; also supply to system, supply to tank, return from tank, return from system. Fix the probes with cable ties and insulate them well. Third, and what ended up being the biggest part of my problem, was that I had only 1" pipes to/from the boiler, and also to/from the tank, and my circulator (007) could not handle the Tarm output. Also part of the problem was the setting on the Termovar balancing valve. That's where your thermometers help out. That valve does not need to be open much to get return after Termovar and to boiler at 140+.

Since I redid my system and moved to my new shop, I have 1-1/4" lines, a very short round-trip run directly to storage, and a 15-58 on M to supply the tank. My boiler never idles until return from tank goes above about 175F, that being the very bottom of tank, and at this point everything above is 190+F. During tank charging I have practically no mixing.

Since i started "weighed wood burns" early winter this year, I never have idling any more. I know exactly how much wood to burn to reach the temperature I want with no idling at all.

 

[Willman]

I know exactly how much wood to burn to reach the temperature I want with no idling at all.

Do you go by the weather forecast for the time period of the load to determine the amount of wood used?

Will

 

[jebatty]

..."I know exactly how much wood to burn to reach the temperature I want with no idling at all...."

Do you go by the weather forecast for the time period of the load to determine the amount of wood used?

This starts with the premise that all wood of the same moisture content, with small variation, has the same BTU's per pound. A pound of oak has as much heat energy as a pound of pine, for example. My wood is very well-seasoned, so I assume 20% MC, and that means that at 400F flue temp, each pound of wood has 6050 BTU's.

The next step is to calculate how many BTU's you need to charge your storage to the desired end temperature, say 185F, which is my usual target. I use 185F because unless I plan to be gone and need maximum tank BTU's, the 185F provides sufficient boiler/storage delta-T to avoid any idling without taking some extra measures. I am able to charge the entire tank up to 193F +/- with a little extra burn/flow management and still avoid idling.

To calculate needed BTU's, you need to know your average tank temperature, which takes some sensors. For my horizontal tank my sensors are 1/3 from top, 2/3 from top, and bottom. In a normal situation when the storage has been drawn down and is ready to be recharged, the sensor 2/3 from top is pretty accurate as to average tank temperature, or I can average the 1/3 and 2/3 sensors.

I have radiant in-floor heat supplied by a plate HX from my boiler/storage system (in-floor has antifreeze, which is the reason to separate the in-floor from the boiler/storage), so assume I've run my 1000 gallon storage (+ 55 gallons in the boiler/tank loop) down to 110F, which is a 75F delta-T. Then, to raise the tank/boiler from 110-185F, I need 75 x 1055 x 8.34 = 659,903 BTU's, assuming no system draw during the burn. Divide that by 6050, and that equals 109 lbs of wood.

From experience I know that an in-floor radiant draw nearly always drops the tank temperature by about 10F, or 10 x 1000 x 8.34 = 83,400 BTU's, which is another 14 pounds of wood. When I start a burn, I check the temperature of the in-floor sensor, and from that I can tell whether or not the in-floor will "demand" during the burn. If I expect it will, I add 14 lbs to the prior 109 lb calculation, new total 123 lbs. If I don't think it will, my total remains 109 lbs.

A wrinkle, now. You also need to know or estimate your boiler efficiency. I use 80% for mine. So now take the calculated weight of wood and divide it by the efficiency to get the actual weight of wood you need. 109 / 0.80 = 136 lbs actually needed.

It takes just a couple of minutes to load the splits on a scale and weigh out 136 (or 154) lbs of wood, which is what I do. Then start the burn, and for my boiler 136 (or 154) lbs will be 2-4 wood loads, since I burn aspen/pine, which is light in weight compared to volume. Complete the burn, and no idling.

In my system, I have sufficient flow through 1-1/4 pipe, short loop to/from storage, pump head about 2 feet, to handle my boiler maximum output at delta-T=20 (140,000 BTUh / 500 = 14 gpm), but keep in mind that as storage moves towards the 185F target, the last wood load in the boiler is burning down, and boiler output is substantially less than maximum, so even at 14 gpm and delta-T < 20, the entire boiler output is being moved to storage.

This is part of the beauty of weighed wood burns. No guessing as to how much wood you need for that last load. Your last wood load is burning out, boiler BTU output is falling, storage temperature is reaching the target maximum, delta-T is falling, and yet idling is avoided.

Your system may be more complicated than mine, but by watching a few things, you can easily determine how much wood to burn. For example, after doing weighed wood burns this season, I also know my heat load/hour at various temperature ranges. BTUh heat load / 6050 / efficiency = wood lbs/hour. Factor that into your determination of how much wood to burn to supply demand and charge storage, and you achieve the same no idling result.

You also need to know your gpm flow based on pump head and the curve for your circulator. Pump head is calculated, which is subject to possible error, but after a few burns you will know how close you were on your calculation and you will know pretty close what your flow rate actually is. It all comes together.

I reduced all of the above to a simple chart I have on my boiler. Now, all I do is look at storage delta-T, and the chart tells me how much wood I need to burn, plus an extra 18 lbs if I expect a radiant demand during the burn. And with the 185 storage target, if I'm off a little, there is "buffer" room on the high end, and if I'm under a couple of degrees, so what? Every burn is efficient without idling.

 

[Rick Stanley]

..."I know exactly how much wood to burn to reach the temperature I want with no idling at all...."

Do you go by the weather forecast for the time period of the load to determine the amount of wood used?

This starts with the premise that all wood of the same moisture content, with small variation, has the same BTU's per pound. A pound of oak has as much heat energy as a pound of pine, for example. My wood is very well-seasoned, so I assume 20% MC, and that means that at 400F flue temp, each pound of wood has 6050 BTU's.

The next step is to calculate how many BTU's you need to charge your storage to the desired end temperature, say 185F, which is my usual target. I use 185F because unless I plan to be gone and need maximum tank BTU's, the 185F provides sufficient boiler/storage delta-T to avoid any idling without taking some extra measures. I am able to charge the entire tank up to 193F +/- with a little extra burn/flow management and still avoid idling.

To calculate needed BTU's, you need to know your average tank temperature, which takes some sensors. For my horizontal tank my sensors are 1/3 from top, 2/3 from top, and bottom. In a normal situation when the storage has been drawn down and is ready to be recharged, the sensor 2/3 from top is pretty accurate as to average tank temperature, or I can average the 1/3 and 2/3 sensors.

I have radiant in-floor heat supplied by a plate HX from my boiler/storage system (in-floor has antifreeze, which is the reason to separate the in-floor from the boiler/storage), so assume I've run my 1000 gallon storage (+ 55 gallons in the boiler/tank loop) down to 110F, which is a 75F delta-T. Then, to raise the tank/boiler from 110-185F, I need 75 x 1055 x 8.34 = 659,903 BTU's, assuming no system draw during the burn. Divide that by 6050, and that equals 109 lbs of wood.

From experience I know that an in-floor radiant draw nearly always drops the tank temperature by about 10F, or 10 x 1000 x 8.34 = 83,400 BTU's, which is another 14 pounds of wood. When I start a burn, I check the temperature of the in-floor sensor, and from that I can tell whether or not the in-floor will "demand" during the burn. If I expect it will, I add 14 lbs to the prior 109 lb calculation, new total 123 lbs. If I don't think it will, my total remains 109 lbs.

A wrinkle, now. You also need to know or estimate your boiler efficiency. I use 80% for mine. So now take the calculated weight of wood and divide it by the efficiency to get the actual weight of wood you need. 109 / 0.80 = 136 lbs actually needed.

It takes just a couple of minutes to load the splits on a scale and weigh out 136 (or 154) lbs of wood, which is what I do. Then start the burn, and for my boiler 136 (or 154) lbs will be 2-4 wood loads, since I burn aspen/pine, which is light in weight compared to volume. Complete the burn, and no idling.

In my system, I have sufficient flow through 1-1/4 pipe, short loop to/from storage, pump head about 2 feet, to handle my boiler maximum output at delta-T=20 (140,000 BTUh / 500 = 14 gpm), but keep in mind that as storage moves towards the 185F target, the last wood load in the boiler is burning down, and boiler output is substantially less than maximum, so even at 14 gpm and delta-T < 20, the entire boiler output is being moved to storage.

This is part of the beauty of weighed wood burns. No guessing as to how much wood you need for that last load. Your last wood load is burning out, boiler BTU output is falling, storage temperature is reaching the target maximum, delta-T is falling, and yet idling is avoided.

Your system may be more complicated than mine, but by watching a few things, you can easily determine how much wood to burn. For example, after doing weighed wood burns this season, I also know my heat load/hour at various temperature ranges. BTUh heat load / 6050 / efficiency = wood lbs/hour. Factor that into your determination of how much wood to burn to supply demand and charge storage, and you achieve the same no idling result.

You also need to know your gpm flow based on pump head and the curve for your circulator. Pump head is calculated, which is subject to possible error, but after a few burns you will know how close you were on your calculation and you will know pretty close what your flow rate actually is. It all comes together.

I reduced all of the above to a simple chart I have on my boiler. Now, all I do is look at storage delta-T, and the chart tells me how much wood I need to burn, plus an extra 18 lbs if I expect a radiant demand during the burn. And with the 185 storage target, if I'm off a little, there is "buffer" room on the high end, and if I'm under a couple of degrees, so what? Every burn is efficient without idling.

NICE!! I have an old, but perfectly, usable, serviceable, and "calibratable" platform balance scale in the old egg-room of one of my barns. I think it goes to 500lbs. Someday, when I get organized HA, that baby is going into the garnbarn. Not to prevent idling in my case, but boiling. I'll really will want high temps to have fewer burns when I get other buildings online.

 

[Willman]

Thanks Jim for the excellent explanation. I will copy and print out for future reference. I do have an old platform scale that will be pressed into service when the time comes.

Will