Am I flowing enough BTU's?

the easy way to tell is if your boiler starts cycling as the bottom temp of storage starts to come up.
if the boiler runs flat out and no cycling when the return temperature is with in 20 degrees of the boiler set point, it's fine.
karl

Am I reading that chart right? I wanna say my head was around 7 or 8 going to my storage. Similar setup. My boiler is 60kw.. so about 250k BTU. I'm moving 22 to 25GPM at a 20degree delta T.

You're moving 5gpm?
5x8.3.x60= I'm seeing a 50 degree delta T only moving slightly over HALF of your BTUs

am I missing something there?

When I'm FLAT OUT.. I might be putting out 300k.. BTUs. 23 or 25 delta T. 22 to 25 GPM... my storage will get 195 top to bottom. very little cycling till I get way up on temps.

Tough to tell on sub par wood. first year is always tough. Do you have temp wells so you can SEE for sure your in/out temps? Keep hanging around here. Smartest thing I did was add temp wells EVERYWHERE after seeing guys on here have problems. Mark from AHONA had me dialed in perfect from the start, but I wanted to be able to WATCH exactly what was going on. Guess it's the geek in me.

JP

If that's your chart.. it looks like it. The boiler has resistance, and even though your plumbing run is short, it's still some more resistance. Like I said, I'm in the ballpark for your numbers, albeit with larger boiler and larger plumbing. It sure SEEMS to me, completely self taught, that you're way shy on pump performance. Math works out to close to 50 degree delta T at 9gpm for your peak output. I think your head is likely to be higher than that, making your numbers worse.

Chart is a bit tough to read.. but mine is a 0011
http://www.taco-hvac.com/uploads/FileLibrary/0011Sht.pdf

I think the best way to tell is to watch your boiler in & out temps, and watch the dT between them over a burn. I changed my procedures this year, not charging as high & depleting storage before burning. I am quite sure I saved wood - still have a cord or so left down there. That keeps the water that is running thru the boiler as cool as possible for as long as possible - thereby pulling more heat out of the gasses before they hit the stack. I guess also stack temps would be a good thing to watch too - too high might mean dirty tubes, or maybe even too much air. Aside from insulating everything as best as you can (pipes & tanks), likely not much else to do.

JP11 said:

Am I reading that chart right? I wanna say my head was around 7 or 8 going to my storage. Similar setup. My boiler is 60kw.. so about 250k BTU. I'm moving 22 to 25GPM at a 20degree delta T.

You're moving 5gpm?
5x8.3.x60= I'm seeing a 50 degree delta T only moving slightly over HALF of your BTUs

am I missing something there?

Click to expand...

What do you have for a pump or loading unit?

My LK810 has a Grundfos 15-58 3 speed, set on low. Which at 7ft of head, would be around 4gpm (an assumption on head - I don't know what actual head is - storage is right next to boiler but don't know how much the LK810 body would present). I know your boiler is bigger than mine, but 22 to 25gpm seems pretty huge to me. Mine keeps a 20°dT also - I don't run my storage that high, and usually start with it pretty depleted (maybe 120 at bottom?). First lap thru gets me to 160, but it takes quite a while since a lot of the flow is going around the bypass. Second lap gets me to 180. I did a burn yesterday that started at 105 at the bottom (120 at top - we were away for the weekend). Took me about 1.5-2 loads (3 cu.ft. firebox) of wood to get my 660 gallons to 190/180, over about 6 hours. Plus also heated our 80 gallon DHW tank from 115 to 150.

Boardroom said:

I don't have temperature wells on the in and out from the boiler. I have used strap-on gauges on the in to make sure my boiler protection was working but never anything on the out/supply side as I figured the reading on the boiler was always what was going out.
I never know if I am reading these charts properly either. Is my pump only capable of pumping max 10 gpm? Maybe if Bob is around he can clear this up.

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What is your boiler temp when you are charging storage from cold, for say the first couple of hours?

Sorry, it just doesn't make any sense. If you're moving 40k BTUs with 4gpm. In your example above.. you said you heated your tanks approx 80 degrees in 6 hours.. moving near double the BTUs per hour that the 20degrees at 4gpm works out to. Not to mention the BTUs that went into the DHW tank.

If you boiler is 40kw.. it just doesn't add up. you've GOT to be pumping more BTUs than that. either in delta T or in GPM. One or the other.

I never crunched numbers on my heat output. Just reporting what it does - and that's what it did yesterday.

(I think it is rated at 140,000 btu/hr - not 40,000?)

Boardroom said:

When I light the boiler my storage is usually around 100 at the bottom and 130 at the top. My boiler might read around 80. This time of year, my only draw is my DHW so not much load being drawn while I am firing. I fill the boiler about 1/3 full of wood which gets it up to about 160 in 45 minutes. I then load the box once and that is enough to charge my tanks to 155 at the bottom and 175 at the top, about a 2.5-3 hr burn.
I am really interested in understanding your numbers JP. I am not unhappy with how my system is running but don't want to be pushing only half my BTU's either.

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Does the boiler stay at 160 until your return (bottom of storage) gets above 140? Then creep up? Or does it go up to where it starts to idle, before it gets to say the 155?

JP11 said:

Sorry, it just doesn't make any sense. If you're moving 40k BTUs with 4gpm. In your example above.. you said you heated your tanks approx 80 degrees in 6 hours.. moving near double the BTUs per hour that the 20degrees at 4gpm works out to. Not to mention the BTUs that went into the DHW tank.

If you boiler is 40kw.. it just doesn't add up. you've GOT to be pumping more BTUs than that. either in delta T or in GPM. One or the other.

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OK, I did do some numbers on what it did yesterday. First time I did this, and rounded some things, so might have something off.

So 700 gallons, at 75° rise, would be 420,000 btu.

Over 6 hours would be 70,000 btu/hr. Thinking back more - I lit around 4pm. Went to bed at 10, with the fire not out. So trying to allow for the fire getting established & going good, and burning out while I was in bed, call it 7 hours. So 60,000.

At a 20°dT, that would be 60,000/60min/20° = 50lbs/8lbs = 6.25 gpm.

So maybe more than 4 - but not a lot more and certainly nowhere near the 20gpm range.

(As mentioned, I don't know what the head is my pump is seeing - but a 15-58 on low pumps no more than 11gpm, with zero head)

Boardroom said:

The boiler climbs to 180-185 in an hour with my pump on high. It may idle for a short time but maybe only once in the burn. Just to add one thing - Econoburn ships a Grundfos 15-58 with the boiler which is intended to run the near boiler loop. I switched it out for the Caleffi that I am using. Might give you some idea of size they are recommending.

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Just my uneducated seat of the pants input - you would likely gain some, then, if you could pump more in order to keep your boiler temps lower through most of the burn. The rather simplified way I thought about it was, if my boiler is 160 during most of the burn rather than say 180, that should give it the potential to pull 20° more out of the gases before they exit.

The best way for you to do that, and how much you would actually gain (i.e. would it be worth it?) - I don't think I could say or hazard a guess at. Also not sure how much you valve body would be comfy in flowing.

You discounted your delta T in the domestic. It just doesn't make any sense that you're getting 60k BTUs out of a 40kw boiler. You're rated at 136k Btus.

I'm not saying you NEED to move 21gpm.. But I've routinely seen 300k BTUs during a full burn from my 60. I always thought it would be nice to move your full capacity at a delta T of close to 20.. without getting your FPM of the water too high. Thus my pump and pipe sized to move the BTUs I have. I can't take any credit for the math, Mark at AHONA planned it. I think I've got a handle on what was done and how it works.

JP

Yesterday was hardly a controlled & fully data logged burn. That's about how long the fire burned, and about how much water was heated by about how much. I know there was a time in the middle between loadings that the fire was down to coals for a while (at which time the dT was also likely a lot less than 20), it also went to coals a while after I lit before I got the first load in (too many distractions), I'm not sure what time it was when it finally burned out - and I'm also burning junky wood this time of the year. Another factor is I don't quite get as hot a burn this time of the year with my naturally drafted boiler.

But even in the dead of winter when burning wide open, my loading unit is still on speed 1 and I'm pretty sure I haven't seen my dT over 20. I do get some convection flow around the loop - and when I'm burning in the winter my load pump (Alpha) is also pumping at the same time to usually more than one zone. So maybe the boiler/storage loop does get more flow from those 2 added factors at those times. Also, until the DHW tank gets up to temp, the load pump is also pumping when heating just DHW - but only about 1gpm (the display says). And I don't think for more than an hour.

Anyway - that's what happened yesterday, and that's always what my loading unit pump speed is set at and my dT is when I am watching it. And I also do think that Boardroom could use more flow.

If your boiler is not coasting (idling), then you are moving the entire btu output of your boiler to storage. Therefore, your system is working, you have found a load/burn pattern that minimizes coasting at the high end, and your system is performing as intended.

I usually set my boiler at 195 which means it coasts at 185. The hottest I ever get bottom of storage is 160 and by then I have timed it so that my wood load is starting to dwindle so not much chance of coasting at that point.... When I light the boiler my storage is usually around 100 at the bottom and 130 at the top.

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Next some assumptions: well seasoned wood (20% MC), full load of wood, 200,000 btuh rated output at high burn, about 30' equivalent of 1.25" piping, pump head of about 1.2', and flow rate based on your pump curve about 10-11 gpm.

Now the math. With bottom of storage at 100F to the boiler and assumed 10gpm, your entire 200,000 btuh output will be moved with only a temperature rise (delta-T) of 40F: 40 x 10 x 500 = 200,000. You set your boiler at 195F. This means that until water from storage rises to 155F, your 10gpm can continue to move 200,000 btuh. As return water from storage rises above 155F, you no longer have the flow rate needed to move 200,000 btuh, but also now your wood load is burning down and boiler output is falling. At assumed boiler output of 195F, you still can move 175,000 btuh at storage return temp of 160F; 150,000 btuh at storage return temp of 165F; 125,000 btuh at storage return temp of 170F; etc.

I would hate to be burning wood to create heat that is not making it to storage.

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Except when idling, you cannot be burning wood to create heat that is not making it to storage. All the heat has to go somewhere, and storage is your only destination (except what goes up the flue or escapes to the environment from the piping and boiler shell).

My conclusion is that with your wide delta-T's and method of operation, you are doing a very good job of operating your boiler system.

Except when idling, you cannot be burning wood to create heat that is not making it to storage. All the heat has to go somewhere, and storage is your only destination (except what goes up the flue or escapes to the environment from the piping and boiler shell).

I think the underlined part is not something to be assumed as insignificant. As mentioned above, I changed my procedures a bit this past winter to have the overall effect of keeping my boiler temps as low as possible for as long as possible, through a burn. I have never had this much wood still in my basement at the end of a winter. Hardly scientific, and inaccurately quantified - but I would guess I went from 7+/- cords consumed to 6+/-, just based on what's still down there. It kind of makes sense in my simple mind that 160 water would pull more heat out of the gas stream than say 195 water.

Interesting thread for sure.

This may be partially true but also more complicated. A lamda controlled boiler will have varying flue temperature as O2 is monitored/controlled to achieve an efficient burn. Trying to maintain the most efficient burn in a non-lamda boiler by controlling wood load or draft settings would be complicated.

Maple1, you may want to do some weighed wood burns with output only to storage (no system draw) while using different burn strategies which affect flue temperature, and measuring btu's transferred to storage with each burn strategy. The results would be interesting.

They likely would be quite interesting. Not sure I am as interested, though.

I only have 2 sensors on my tanks - so there's quite a bit of fuzziness there. They are at about 1/4 up and 3/4 up. So I never really know how warm the bottom of my tanks actually are, and the gradient between them amounts to about 1/2 of my storage volume so never really know where the stratification boundary is in that 1/2 volume. Also likely significant when trying to come up with BTU measures that are half ways accurate. I might be able to temporarily mount some on in other places to play with - I'll keep this in mind in case I get really bored at some point. Not likely in the foreseeable future with the length of my to-do list around the place.

On the lambda aspect - yes, the flue temp would very likely vary as the fire is O2-controlled for burn efficiency, and as the burn progresses. And that efficiency would be quite hard to duplicate with manual operation. But my thought was that that (burn efficiency) is completely separate from the temp of the boiler itself, and if all else was equal (or no matter how efficient the fire was or wasn't burning) - cooler boiler water would pull more heat from the gases (heat exchange efficiency?) at all points in the burn cycle. Or would at least have the potential to. But then would there be a point where cooler water would affect burn efficiency? Not sure, but would anticipate that if there was, the burn would also be controlled by water temp inputs along with O2 measures in the higher end controlled-burn lambda boilers. Which I don't think I have read about - but may have missed.

We're likely not some place the OP was intending to go when he started this.

Boardroom said:

Is it the old hot to cold thing where the bigger the delta T, the more heat that can be transferred? If those high gas temps can not be used by an already hot boiler, do they just continue up the flue?

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I think so. I remember some time in the past here, talking about this some on another thread, and another of our members who does this stuff for a living also mentiong somewhat the same thing. I'm more or less just telling what I think I'm seeing, with some seat of the pants reasoning thrown in. Seems to me I also remember someone saying 'cool boiler = happy boiler', or something like that. Of course - that is as long as it still stays above the point of condensing (min. 140 return).

Boardroom said:

I should probably start measuring flue temperature to find out. Can you lead me to a good temp probe?

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Mine came with a very good one, but I think it came from Europe. Not sure where to get one as I think I tried a Google search on it at some point - but would start a serious search for it at the place I got my boiler from (Smokeless Heat). Or another boiler/furnace vendor. They shouldn't be too awful expensive - mine's just a dial guage.

I'm also not sure you could detect or conclude a direct measurable correlation by watching flue temps either - because I think then you would have to take into account not only the flue temps, but varying speed of the gases out the flue. Example - if you dropped your boiler temp by 30°, and that did lead to correspondingly more BTU's into your water, it likely wouldn't show up as a simple corresponding 30°drop in your flue temps but I suspect something quite a bit less. Calcing this heat transfer stuff is hard enough (for me) for something as simple as a FPHX, let alone getting into a HX with varying flue gas temps & flows on one side of it.

JP11 said:

But I've routinely seen 300k BTUs during a full burn from my 60.

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So that would be 50% more output (+/-) than it is rated for? Routinely?

That is impressive boiler performance, indeed.