First Fire with Storage - Basic Questions

[Tennman]

Well I'm excited that now going into our 6th season we finally have storage! I'm looking forward to experiencing the benefits you guys talk about. The system is a BioMass 60, two 500 gal vertical tanks, and a Laddomat 21-100. Here's my first batch of storage newbie questions:

1 - I thought there was something wrong with my boiler last nite. After burning for an hour the boiler temp was barely increasing. Boiler temp was at 120F for a long time. Way below the 157*F Laddomat turn-on temp set in the RK2001. Flue temp was at ~220--230*F. So I presumed boiler output was choked somewhere, maybe the new nozzle protector. After about an hour I touched the pipes in and out of the Laddo. The pipe going to storage was warm, about 120*F (as shown on by the RK). Got a ladder and touched the storage manifold at the top of the tanks, warm. The water in storage was about 50*F at the start of the burn. So this must be the thermosyphoning I've read about but until now never concerned me. I closed the cold return valve into the Laddo and almost immediately started to see boiler temps rise. Is this normal? I was surprised that the Laddo allowed apparently a pretty sizeable thermosyphoning flow, enough that the BioMass couldn't get a good head of steam with 50*F water being pumped in.

2 - I opened the Laddo cold inlet valve right before the boiler hit the pump-on temp (157*F). With the Laddo on it seemed to manage circulation and the boiler climbed up into the 180's. Normal? This may be a first fire of the season issue. Obviously we'll be keeping storage between about 130*F - 180*F during the heating season.

3 - This morning the FUEL light was on probably due to bridging. I'd guess the boiler ran for ~5-6 hrs before that shutdown. Top tank temp is ~ 130*F, bottom ~ 70*F. What's the equation for how many hours it takes at some assumed output to get 1000 gal of 50*F water up to uniform temp. From last nite's experience that looks like it could be a long time. Good news to me is clearly there's energy going into the tanks, but to get the whole tank up to 180*F from 50*F could take a long time.

4 - I'm not circulating any flow to the house, so for the first time I have a pretty good means of calculating the boiler's output since all the energy is going to storage right now. I'd like to calculate real boiler output based on the time to get to a uniform stored energy in the 1000 gal.

5 - Is thermosyphoning is a good/normal thing between the boiler and storage with a loading unit? I'm sure once I get and keep storage in the 130-180*F range the thermosyphoning flow will be reduced. Since there's a pump to make this happen, you'd think boiler/storage thermosyphoning would be a good thing.

Thanks guys.

 

[ewdudley]

The laddo circulator pump should be putting back pressure on the internal back flow preventer flapper valve, so thermo siphon through laddo should not be possible while the laddo circulator pump is running.

My guess would be that the laddo internal thermostatic valve was stuck open starting out and that you exercised it by forcing some flow of hot water through it, and now it's working OK.

The other possibility is that you have the laddo pump tied to launch temperature. The laddo pump needs to run throughout the burn cycle regardless of supply port temperature.

 

[salecker]

Interesting piping on your tanks.
What's the theory on all of the ties across the tanks?And where does the hot go in and cold come out?
When i did mine i was told to reverse the hot and cold runs to keep the tanks equalized.By this i mean the hot feeds into tank 2 then tank 1 at the very top.The cold comes from tank1 then tank 2at the very bottom.So looking at my tanks #1is left#2 is right.I have checked the temps in both tanks and they stay equal.
To bring up my storage it takes a good day of burning.I usually do it on a day that i will be around all day.
Thomas

 

[Tennman]

Makes sense EW. The Laddo manual suggests a flue thermostat to start and stop the Laddo which would give immediate control linked to the fire. I left the pump launch temp at what I used for my demand circ pump (157*F). Tonight I'll set Laddo launch temp in the RK to kick it off way sooner. There's no power to the Laddo until the RK hits that launch temp. I have no idea what that thermosyphoning's gpm was but it must be a bunch.

 

[avc8130]

I'll take a stab at the plumbing.

It looks to me like the boiler supply and load feed are at the top of the tanks.

My guess is the boiler return is at the very bottom of the tanks and the load return is at the 2nd to bottom set of tees.

I bet the crossovers are an attempt to keep perfectly stratified tanks.

ac

 

[Tennman]

Salecker, The piping schematic was provided by the Laddomat supplier and attempts to make the system act as one big tank. Boiler in and out at the very top and bottom respectively. House supply and return at the top and bottom dome/cylinder joint respectively. The middle manifold helps to thermally balance the middle region. Great, I had no idea how long it would take. Sounds like what I'm experiencing is normal.

 

[Tennman]

AC, yep.

 

[ewdudley]

Makes sense EW. The Laddo manual suggests a flue thermostat to start and stop the Laddo which would give immediate control linked to the fire. I left the pump launch temp at what I used for my demand circ pump (157*F). Tonight I'll set Laddo launch temp in the RK to kick it off way sooner. There's no power to the Laddo until the RK hits that launch temp. I have no idea what that thermosyphoning's gpm was but it must be a bunch.

You can expect a couple gpm or more. You can get a pretty good idea of what the gpm must be if you can come up with a reasonable estimate of net boiler output and a measure of deltaT from boiler return to boiler supply. For instance (110,000 btu) divided by (60 degF deltaT times 500) would be 3.6 gpm.

 

[Clarkbug]

Makes sense EW. The Laddo manual suggests a flue thermostat to start and stop the Laddo which would give immediate control linked to the fire. I left the pump launch temp at what I used for my demand circ pump (157*F). Tonight I'll set Laddo launch temp in the RK to kick it off way sooner. There's no power to the Laddo until the RK hits that launch temp. I have no idea what that thermosyphoning's gpm was but it must be a bunch.

EW hit this one on the head. Definitely run your pump whenever your have your combustion air fan running. That will keep your boiler in the sweet spot of no condensation. And it does take a long time to get things up to temp at the beginning of the season, but once the tanks are warm, its not an issue.

 

[maple1]

Yes indeed.

My loader is primarily controlled by a flue stat, but power also goes through an aquastat on top of the boiler. That way, if the boiler gets hot say in the case of a flue stat failure, the aquastat will start it when the boiler gets up to its setpoint.

I have noticed some variation in the operation of the flue stat - sometimes it will seemingly take a hotter flue to click on the pump than at other times. In those instances, thermosiphoning will occur until the pump kicks in, and during that thermosiphoning the return temps are whatever temp the bottom of storage is. And when the pump kicks in, return goes right to 140 (more like 145 I think) and stays there. I don't get enough thermosiphoning to prevent the boiler from getting up to temp, so it eventually kicks in one way or the other.

 

[ewdudley]

But with systems that use a thermostatic return protection valve without a loading unit I would think that the charging pump could be controlled by the 'launch temperature'. Is that right?

 

[Clarkbug]

I think that's the case EW. I only am familiar with the loading unit from my own experience though.

 

[Tennman]

Good news and info guys. I've read about ghost flows, thermosyphoning, etc and always seemed like something to prevent.

Maple, reassuring that some thermosyphoning doesn't hurt anything and is normal. I'm going to get the Laddo kicked off sooner.

I'll look for a simple equation that computes hours to charge 1000 gal to some deltaT assuming a given output. Be useful if you miss the computed charge time by a mile.

 

[goosegunner]

But with systems that use a thermostatic return protection valve without a loading unit I would think that the charging pump could be controlled by the 'launch temperature'. Is that right?

Yes that is correct.

gg

 

[Armaton]

Would there really be much thermo-siphoning with both supply and return higher than the storage?

 

[Floydian]

Congrats on the storage, Tennman!

Would there really be much thermo-siphoning with both supply and return higher than the storage?

I don't see how.

Noah

 

[ewdudley]

Would there really be much thermo-siphoning with both supply and return higher than the storage?

There's no heat trap on the supply path so it would thermo-siphon because nothing is being lifted on the return path.

 

[jebatty]

Calculating boiler output based on change in storage temperature, result will be average boiler output over time period.

1) You will need to calculate your average storage temperature before and after the burn, and this isn't easy unless the tank is fully mixed to a uniform temperature. Assume three sensors -- top 140F, middle 120F, bottom 100F. If you have good stratification, you don't know how far down into the tank each of the temperatures extend. The 140F could be the very top and 120F could extend to just below the top, or the 140F could extend to just above the 120F, etc.
2) Assume you can determine average temperature, then 1000 x delta-T x 8.34 / hours = btuH (average) over the time period, and btuH / 500 / delta-T = gpm (average) flow rate between boiler and storage. In other words it takes 8340 btu for each 1F change in average tank temperature.
3) Next you can calculate approximate boiler efficiency based on btu transfer to storage, if you do a weighed wood burn. One pound of wood at 20% MC provides 6050 btu at stack temperature of 400F. BtuH from previous calculation / btu in weighed wood burn = efficiency in transferring wood energy to storage. This is a pretty good place to start, and once you get your system performing as you think it should you can refine the calculation based on actual average stack temperature, water in the boiler and plumbing, etc.

 

[easternbob]

Tennman,
Looking good. I also just got my storage running after many years without. I was shocked at how long it took to warm up. Was starting to think what did I do wrong?? It's been warm and then cold around here so I haven't been keeping it to full temp so I think that is causing me some problems.
Good luck.

 

[Tennman]

Yeah, thanks for all the congrats. I've hung around here long enough I'm sure ya'll were wondering if I'd ever "get're done".

Able to change the Laddo start temp to under 100*F in the RK last nite. So that will cure essentially all startup thermosyphoning. Laddo off will use the RK FUEL or pump off temp settings. Not as efficient as a flue thermostat, but I have bigger fish to fry at the moment so for the time being I'll use the RK to manage the Laddo.

Yeah.... talk about a long time to charge. What I learned last nite was just using the Laddo doesn't stir those tanks like having the Taco 0013 on to mix temp in those vertical tanks. Running just the loading unit the tank temp was really stratified. Running the demand pump dropped the temp at top, but increased the return temp.... which I guess in not a great thing since I guess you'd like a large deltaT going into the boiler. Anyway working with Controlbyweb to control the 0013 out in the barn with the tstat call for heat in the house. I'll post my solution once I get it ironed out.

Been burning small to medium fires with boiler temps getting into the 180's and have seen 170 on top and ~130 on bottom. Long way to go to completely charge those tanks and the weather is pretty mild at the moment. Finally can focus on tuning the boiler for maximum output, whereas always before trying to stretch out the burn time since there was no place for excess energy to go. Made a small change to the secondary opening this morning before leaving and OMG! big stinking roar/flame. Because peak efficiency could never be used before I'm sure it was not well tuned. I'm motivated to tune this thing now to get all I can out of each stick of wood.

Got a lot of exposed black iron at the moment which is wasting a bunch of energy. Gonna get some fiberglass pipe insulation hopefully today.

Thanks Jim, I just knew one of you guys had some basic math. Now that I see using the demand pump helps to mix the tanks, it kinda muddies the math in capturing boiler output. Mainly I want to see the system capture excess energy now during mild temps. I'll play with your calcs above and see if I can get a spreadsheet working to simulate my system. Really I want some clues if my boiler is only putting out... say 100kbtu instead of it's rated 180-205kbtu. With all the idling in the past that was nearly impossible.

Someone should plan a "Boiler Room Convention" up nawth. I sure would like to shake the hand of all you guys who've helped me over the years. I suggest EW, Jim's, or Heaterman's place.

 

[jebatty]

I'm "up nawth but the "nawth" is northern Minnesota! Yah, come on over, ya betcha.