Fustrated with OWB

[92rslt1]

Hi guys, I was researching technical data and it led me here.

I have a central boiler 1400 (200k max btu) and I am looking to solve this ongoing problem I am having getting this thing to heat my house.

The problem: Its not heating the water in the indoor boiler hot enough, not enough exchange I believe.

I think It could be:
a clogged or dirty exchanger
lack of flow
undersized OWB.

When I installed it the all 3 (used) HX were cleaned with Acid and were looking clean so chances are it didn't clog since october. I let them all soak one day with straight muriatic acid.
Its running a single 00r taco circ pump mounted on the OWB, 1 inch pex lines.

I originally thought my house didn't have enough baseboard, it was engineered to have exactly 65 feet of BB on the main floor loop which according to what I was told was perfect for the SQ feet. I was thinking maybe they didn't take into account the taller ceiling, so I added 1000ft radiant heated flooring in 250ft loops running off the indoor boilers manifold.

Didn't solve the problem, but helped a little.

The Out door boiler says its water temp teeters between 180-190.
The indoor boiler is constantly calling for heat and outputting 140-150* water. Its just not hot enough for my baseboards or flooring to work proper.

If I cut the wood boiler off and turn on the 130k btu gas boiler it will cycle at 170* and my house will be 75* in -20 windchill weather. So I know with the proper temp It should work.

The question is do I need another pump on the OWB? How can I get this thing to exchange more efficiently like everyone claims they do. I hear 20* heat loss through an w2w exchanger, but I'm not even getting close to that.

Its eating wood like nobody's business and I'm not getting the house over 65. (10 cords so far since October)

 

[92rslt1]

here is my exchangers.
mini 10 plate to heat incoming water heater heat, plus side arm.
50 plate for house boiler:wood boiler exchange.

 

[maple1]

Need accurate temps in & out of everything to give much help.

How long is the underground? 1" pex isn't very big. What type is it?

Edit: if the owb maintains 180-190, you should be able to cross undersized own off the list. And 3 hxs? Might need a piping diagram too...

 

[92rslt1]

Im not sure of brand but its O2 barrier, the under ground run is about 40ft thermopex. Then it runs down the inside the wall 30ft, makes a turn then another 30ft into the basement, then ten = 15 more feet, Its wrapped in foam insulation.

 

[heaterman]

An 00R is probably a little light for pushing that much head. According to your diagram, all the loads are on one big loop and I'd wager that's going to drop the little Taco down to the 2-3 GPM range just eyeballing the total length of tubing + the flow resistance in the HX's.

You can either up size the pump or reconfigure the piping as follows.

Leave the 00R in place but make it just feed into the house and back out in a loop to the wood boiler.
Install separate pumps for your various loads on a secondary loop(s).

 

[hondaracer2oo4]

We need all if the temp readings in/out at boiler, house and heat exchangers. How many plates is hx? 10 full cords or face?

 

[92rslt1]

Yea, 10 full cord of wood. Im a little nervous because its only feb and I only have 2.5 cord left.

I will try to get a few readings, the problem is they always change depending on the weather. For example last night, it was cold and the incoming water on the house side was hitting the exchanger at 130 and only warming to 140 because every zone was calling, but when its warmer (30+) outside it will enter at 130 and exit at 150-160.
It seems to work fine in 30* weather, but it drops right off in the cold weather where I need it most.

Its entering the first exchanger at the water heater around 180* after passing through all the exchangers it usually returns to the OWB at around 150.

The readings on the house side are from the gauges on the boiler and the reading on the OWB side are taken at the elbows with an infrared thermometer.

Another thing too is that the house side of the 50 plate exchanger is 1 1/4 galvanized so when all the zones call for heat, the water is really moving through it. The OWB side is 1 inch pex, or about .8 inches of flow.

 

[leon]

Can you provide us with a plumbing diagram?

Is the piping plumbed in series to the "in house boiler" and then the heating load with the
return header entering the base of the fossil fuel boiler??

Where is you circulator?? Have you checked the bladder tank to
make sure it is not water logged and failed.

The thing is that the more you add the more the circulator must push the water through.

Ideally you want the circulator in the home and on top of the fossil fuel boiler to take
advantage of pumping away and eliminating air bubbles.

Where is your point of no pressure change??

 

[92rslt1]

I uploaded a few pictures and diagrams in post #4 and #2, not sure if they are not showing up or just not very good.

On the Wood boiler loop it goes. Wood boiler -> water heater 10 plate -> side arm -> 50 plate HX -> back to wood boiler.

On the Fossil fuel/house side there is 6 zones with zone controls. 1. Upper master. 2. Upper master #2. 3. Main floor BB. 4. Office & laundry & bedroom. 5. Sub floor heat. 6. vacant zone.
The pump on the house side is a large bg unit that moves the water very well. It pushes from the return side down through the gas boiler. I purged all the zones last week and there was no air, I even installed automatic purge valves on each baseboard to get any tiny bubbles out.

What do you mean when you refer to no pressure change?
The bladder has 12psi of air. Boiler has 25 psi of water.

I honestly wish I could just direct connect my OWB to the house, I would love to get the max btu out of the wood boiler, however the upper floor is 10ft over the top of the wood boiler, so the water would probably just run out the top.

 

[maple1]

I don't really think that first HX is doing much for you. Should only need one for DHW.

That said I would bet dollars to donuts your circ is too small. The pump curve for the 00r says flow goes to zero at 15ft. of head. You have around 250' of 1" pex in the round trip, give or take. That is likely presenting all of that 15' of head - 1" pex is on the small side for OWB piping. Let alone 3 HXs and misc. other fittings.

Here's a link to help you figure out how much pump you need:

(broken link removed to http://www.taco-hvac.com/uploads/FileLibrary/SelectingCirculators.pdf)

 

[hondaracer2oo4]

We need to figure out why you are only boosting your temp 10 degrees across the hx. It makes no sense that you only are getting a 10 degree drop on the owb side and a 10 degree rise on the house side but you never gain traction. If you were moving water slow on one aide or the other you would see a big drop on the owb side for slow moving water there or big rise on the house side for a slow pump on that side. Close a ball valve on the house side down on the return or the supply to slow te water down and see how much of a rise you get then. Try te same on the owb side.

 

[92rslt1]

The big drop is on the OWB side at 30* and it was only elevating the indoor temp 10*
Last night it was entering at roughly 176 +- and returning around 147+- on the OWB side.
House side was raising only 10*.

I will go check it now and see what it is today, where it is operating ok because it is warmer outside. Its hard because it fluctuates so much with demand.

 

[hondaracer2oo4]

Yeap I understand it now. Size your pump via the taco manual. That's your problem trying to exchange. Next step is to figure out your wood problems. What is your wood that you are burning? Moisture content, species, split size etc.

 

[92rslt1]

Yeap I understand it now. Size your pump via the taco manual. That's your problem trying to exchange. Next step is to figure out your wood problems. What is your wood that you are burning? Moisture content, species, split size etc.

The wood is oak, hickory, cherry and ash. Some of it has 40% but most of it is dry and the bark as fallen off.
Im thinking its related to the pump issue, if its returning 150* to the boiler then it needs to work hard to and constantly to heat it back to 180+.

Is is correct to assume once I get the correct size circulator on this, the water should return to the OWB hotter as it isn't spending as much time in the HX?

 

[hondaracer2oo4]

Yes that is correct but it is only returning probably 1-2 gallons per min at 150. Do you have the fire star controller with the online software so you can see how often it is having to fire? I think the water jacket is 200 gallons? If so that means that it takes 100-200 mins to drop the water from 180-150. If the house is constantly taking that much heat out of the owb. So how much is 40% moisture and what is the moisture content of the other wood? The 40% wood is almost useless in the gasser. It is having to spend so much time just burning out the water. How many sqft are you heating? What is the construction like, insulation and tightness?

 

[92rslt1]

My firestar is the older model that doesn't track history. The jacket is 200 gallons.
My wood is various moisture content, its all over the place, because it came from several different places and species. I started using a digital tester to test it as it came in, but stopped because it wasn't consistent at all, I could test each end of the same piece and have two completely different readings. The extremely dry wood I use on really cold days, that makes up probably 50% of my wood. The wet wood was oak that was split last year, but down for 3 years (or so they claim) When its gassing there is no smoke, which is most of the time. The 40% wood will gas too, I just have to make sure it gets loaded on top of the dry wood in the stove, so that it has time to dry out before it hits the bottom. Not exactly conducive to a long lasting firebox though.
my splittings are 18-24 inches long, once or twice split 4-5 inch radius pieces.

It was a tough year for wood this year, because it was my first year, so I couldn't do my own, I had to buy it off someone in order to get enough in time. The guys selling the wood don't understand me when I tell them what a gasser is. The second load I got was huge oak, probably split this year. I tell them 5 inch max radius otherwise twice split and they look at you like its spanish. They hear wood boiler and assume incinerator. After I got on him about it he started splitting it better and chilled out with the green stuff a little.

The house is newer build with 2x6 construction, fully insulated. However it has several large windows and doors on one side and the living room has about a 25ft cathedral ceiling. So, Including the basement which isn't heated, but is hot from all the piping is about 4000sq ft.

 

[92rslt1]

So when calculating the head, how do I know what flow rate I need? I see the range of 1 inch pex only goes up to 7.5, then I see the charts only take into consideration what to add for copper elbows and 90*s. I know the ID of a pex brass elbow is very small, only about 1/2 inch or so considering the ID of pex is only .87.

Have about 240 ft pex
4 ball valves
9 straight brass pex barbs.
13 90* elbows

Thats not including the HX. I cant imagine the 50 plate or side arm is restricted in anyway.
If I was to guess with max flow rate I am getting.
.00223x1x295(7.5^1.75) = 22.33 of head.
but I added 1 foot per copper unit as a guess because I know the pex is much smaller ID. For example the copper 1 inch elbow is 2.62 I added it as 3.62.
Is there data somewhere for pex connections so I am not throwing darts?

 

[Fred61]

I could test each end of the same piece and have two completely different readings.

You will get different readings if you check the ends. The only way to check moisture is to split the piece and immediately check the split face. Oak must be split and stacked undercover for at least 2 years preferably 3. Firewood that has been down for any length of time is not drying until it is split and stacked so when your wood vendor tells you it has been cut for some time, he has told you nothing. Don't let that statement register.

 

[hondaracer2oo4]

You can move more than 7.5 gpm through 1 inch pex but 7.5 is the max number before it starts to get difficult to move the water because the headloss from friction loss gets real high. Use the 7.5 number for now. I don't know where to find pex fitting numbers, they are restrictive, I would use copper numbers but maybe double them? As far as wood goes you have a lot of sqft to heat. You said 65 feet of bb just on floor one , that is 39000 btus at 180 just on that floor. You are going to go through 10 cords on a good year with good wood.

 

[goosegunner]

I cut oak without bark all the time. I have split fresh cut trunk pieces with no bark and cracks and still found 35% moisture.

Not really drying it by putting it on top. The steam has to go somewhere, it gets forced through the nozzle.

 

[92rslt1]

I cut oak without bark all the time. I have split fresh cut trunk pieces with no bark and cracks and still found 35% moisture.

Not really drying it by putting it on top. The steam has to go somewhere, it gets forced through the nozzle.

Agreed, but thats the only way it will gas the wood. If I load green/wet wood into it on the bottom its not pleasant. Putting it on top of dry wood will still result in a good burn. Its not an ideal situation, but its what I have to deal with until I can do it myself.

 

[Bob Rohr]

You can move more than 7.5 gpm through 1 inch pex but 7.5 is the max number before it starts to get difficult to move the water because the headloss from friction loss gets real high. Use the 7.5 number for now. I don't know where to find pex fitting numbers, they are restrictive, I would use copper numbers but maybe double them? As far as wood goes you have a lot of sqft to heat. You said 65 feet of bb just on floor one , that is 39000 btus at 180 just on that floor. You are going to go through 10 cords on a good year with good wood.

Here are some pressure drop numbers from Viega, I imagine other brands would be similar.

I agree that 7.5 GPM is right at 4 feet per second velocity. Exceeding that and you start to get velocity noise and excessive wear in the fittings, especially those close turn ells.

At a 20° ∆T you could expect about 75,000 BTU delivered. If the building heats fine with the 130,000 gas boiler, call it 105,000 at 80% efficiency, you are not going to be able to move that much energy from the OWF. You may sneak up on it a bit by upsizing the pump, but will will have excessive velocity.

By far the most common error we see on this site is undersizing the pex from OWF to the loads. You are covering a portion of the load, on mild days you may be fine, so the rest of the wood is heating the great outdoors from where it came

 

[leon]

I uploaded a few pictures and diagrams in post #4 and #2, not sure if they are not showing up or just not very good.

On the Wood boiler loop it goes. Wood boiler -> water heater 10 plate -> side arm -> 50 plate HX -> back to wood boiler.

On the Fossil fuel/house side there is 6 zones with zone controls. 1. Upper master. 2. Upper master #2. 3. Main floor BB. 4. Office & laundry & bedroom. 5. Sub floor heat. 6. vacant zone.
The pump on the house side is a large bg unit that moves the water very well. It pushes from the return side down through the gas boiler. I purged all the zones last week and there was no air, I even installed automatic purge valves on each baseboard to get any tiny bubbles out.

What do you mean when you refer to no pressure change?
The bladder has 12psi of air. Boiler has 25 psi of water.

I honestly wish I could just direct connect my OWB to the house, I would love to get the max btu out of the wood boiler, however the upper floor is 10ft over the top of the wood boiler, so the water would probably just run out the top.

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You have a circulator not a pump.

You have too much operating water pressure in the boiler.

Your circulators need to be pulling water off the top of the boiler not pushing it into the sump of the boiler.


The point of no pressure change is where your bladder tank is located in your system.

Where is your air scoop?????


Ideally you want to pipe the boilers in series then to the heating load then from the return header back to the boiler or boilers
Can you install a domestic hot water coil in the fossil fuel boiler??

Are you able to bypass the wood boiler when the heating season ends??

You have to much plumbing and that is making a mess of things

A simple one pass circular domestic hot water coil would solve most of your issues.

By the looks of your system replacing it with a storage tank would solve all most all your heating issues and eliminate the HX mess completely

 

[heaterman]

That little mini HX is your bottle neck for flow.

 

[hondaracer2oo4]

Flat plate hx are pretty restrictive by nature so they certainly add head loss into the system. I bet that with two flat plates and a side arm you are pushing near 30 feet of head. You are going to need a Bell and Gosset NRF36 3 speed or a Grufundos 26-99 3 speed pump to move the max gpm and there for max btus to the house. People don't realize that 1 inch pex can only move 75k btus max with any efficiency. That is why I ran 2 1 inch pex lines each way when I built my system. I was new to the home and it had a 200 btu oil furnace, I didn't know if the house really needed that or if it was way oversized. You will be fine with 75k btus, you just need to get it to the house.

As far as your wood usage goes you are going through as much wood as you have because of moisture content. If you are getting 40% mc and you are only checking the ends of the wood then you likely have 50% plus mc. You need to take a piece of unfrozen wood, split it again and measure the fresh face of the wood that just split from inside the wood. I bet you are running not much better than 30% mc in any of your wood.