Outdoor Wood Boiler Setup

johnlons

First time joining although I have visited the site many times and I appreciate all the advice on here.

I have done service, repair, and installation on residential systems for 7 years (not long). However, I have never installed a wood boiler before. This system is being installed as the primary heat source for two shop buildings. They have a Crown Royal Pristine 7400E Outdoor Wood Boiler which is 390K BTU Output.

One building is 100ft away from the OWB and will have two Modine hanging heaters. They installed the insulated underground pipe which included 2 - 1" Pex tubes before I had got involved with the job. My opinion is the pipe will possibly be undersized to be able to run 2 - 120k BTU Modine Heaters but that is a different topic.

The second building is located within a few feet of the OWB. This will include 2 - 63K Modine hanging heaters and a small office area of in slab radiant that will require 18K BTU/HR

My thought is to have two independent pressurized systems one for the first building and one for the second building. The OWB has two separate outlets which should work well for what I'm thinking. I believe it would be impossible to pump water the distances and elevations that I need without doing it this way.

Please see the attached sketch of what I had in mind for the second building. Am I missing anything or should I change anything that I have planned. Second question is, how do I size my flat plate heat exchanger for this purpose? Most of them are spec'd for DHW, radiant, or snow melt which would require low temperatures where I'm trying to achieve higher temps to allow the Modine heaters to work properly. I have tried a calculator that I've found but I don't know If I'm getting the right output. Ideally the OWB would put out 180-190 degree water to the flat plate and as hot of water that I can get out and over to the Modine heaters.

Thanks I appreciate any input.

STEVEusaPA

No attached sketch...
But this is always a good source:
https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_10_0.pdf

johnlons

I apologize I dont know what happened. Let's try again. Disregard the zone that leads no where.

Jamie Hall

Other than needing an expansion tank on the boiler circuit, that should work. Make sure the heat exchanger is big enough. But you aren't showing really independent systems for the two buildings? They share the heat exchanger?

I too am concerned about the 1 inch PEX. You're looking at needing 15 to 20 gpm. Not that you can't push that through the pipe -- you can. But the pressure drop is going to be high -- at least 25 psi (55 feet or so) -- so you will need a real pump, not a conventional circulator.

johnlons

Thanks for the reply. In the sketch the expansion tank is a standing floor model. Does the wood boiler need an expansion tank its not a pressurized boiler? The first building is not pictured in the sketch but will be very similar except no radiant. It will have its own heat exchanger. I intended to buy 2 of these flat plates which are 5x12 100 plate and "rated" for 250k BTU. They don't list and real specs to determine if its actually capable of outputting that much realistically. Thoughts?  https://altheatsupply.com/100-plate-water-to-water-heat-exchanger.html

Jamie Hall

Each independent circuit is going to need its own expansion tank -- but I think that that's what you mean.

Reading the heat exchanger specs, they are looking at about a 50 degree temperature drop in the water -- 180 in and 130 out on the input side. If it is really piped as a counterurrent exchanger, you could reasonably expect the output side -- at that flow -- to have a similar temperature range, but offset slightly lower (say 120 in and 170 out) at the same flow rate.

That sounds doable for the radiant, but I'd be a little concerned about the Modines.

So... you really need to work with a mechanical engineer familiar with heat exchangers to be sure to get what you need.

STEVEusaPA

Won't work, or won't work well (or for long). Circulator is backwards on the wood boiler. Also you should have boiler protection so very cold water doesn't return to the wood boiler.
You should also have a buffer tank and/or dump zone for the wood boiler. I can't imagine the boiler's hot water production will match the emitters the whole time the wood boiler is firing.
Look at the link I attached in my first post.

hot_rod

here is a little cheat sheet for piping those. A @Jamie Hall mentioned, getting the amount of BTUs you want for those two 120K unit heaters will be a pumping challenge.

\200' of pex with some fitting, looking for 24 gpm... off the chart:)

psb75

Having more heat storage in the form of an insulated tank (hundreds of gallons) will improve the efficiency and convenience of firing the boiler. You can also use the tank as hydraulic separation from the heating 'load.' Outdoor boilers are not pressurized i.e. they are 'open' system --and that is their 'weak link'. They rust out before pressurized, 'closed' systems do. Wood (pellets or cordwood) heat and heat storage are a good 'marriage.'

hot_rod

I think that unit holds 300 gallons, so plenty of buffer. On your drawing, usually hot out the top, so flip that circulator around, flow out the top, return to the bottom.

johnlons

Jamie Hall said:

I too am concerned about the 1 inch PEX. You're looking at needing 15 to 20 gpm. Not that you can't push that through the pipe -- you can. But the pressure drop is going to be high -- at least 25 psi (55 feet or so) -- so you will need a real pump, not a conventional circulator.

I agree its not even close. It seems as if 1 1/2" pipe would have been a better option. Agreeing that we will never be able to get the GPM to support 2 - 120k heaters, and throwing out the heat loss for the building what could we do to compromise for the lack of pipe size. They do have a waste oil furnace in that shop which could supplement. The calculations that I came up with would be a max of 12GPM with a UPS26-150 am I correct? $$$ to run that pump for an extended period of time.

Do you think those heat exchangers run the 2 - 63k modines okay or is a buffer tank almost a must? I did mention the buffer tank idea but storage space was a concern for them.

STEVEusaPA said:

No attached sketch...
But this is always a good source:
https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_10_0.pdf

Thanks I appreciate the info there and will include a Caleffi Thermomix into the design at minimum.

Zman

Overall it looks good. You do not need the extra circ and the closely spaced tee for the radiant. Keep the circ in the radiant loop and pipe the supply and returns right into the header.
I would size the distribution piping to the actual load at 4 ft/sec and the headers to 2 ft/sec.

johnlons

Zman said:

Overall it looks good. You do not need the extra circ and the closely spaced tee for the radiant. Keep the circ in the radiant loop and pipe the supply and returns right into the header.
I would size the distribution piping to the actual load at 4 ft/sec and the headers to 2 ft/sec.

The radiant manifold is roughly 60 feet away from the main manifold in a remote closet. Seemed a bit far for me to only use a single circulator?

Solid_Fuel_Man

Do you have the room in the OWB for two plate exchangers and 3 circulators? 

What is the elevation between the boiler's water level and the far building?

You may be better off pumping boiler water to each building. Needing only 2 circulators in the OWB. Then have your plate exchangers in the buildings right at the pex entry. 

Have you done a heatloss of the buildings? I bet you will need nowhere near 240,000 btu/hr. But those fan coils like HOT water! Radiant in each building would have worked best with long runs of small lines. 

Solid_Fuel_Man

Also, typically OWB dont need return protection. Bang bang control is sufficient. You will likely end up running the circulators 24/7 to prevent freezing. And control the building side if the boiler temp is too low. 

Do what kind of conduit or wires are buried between the boiler and buildings? That will help a lot. 

There is a reason we call them smoke dragons or forest eaters..... the watts to run the circulators alone is significant. 

johnlons

The boiler sits only a few feet from the exterior wall of the first building which is where my sketch shows. There is not a whole lot of room inside the boiler casing. My thought was to plumb the lines from boiler into the first building and make the connections to the first heat exchanger then continue to the manifold for that particular building. The heat exchanger and pump for the remote building would also be inside the first building. I would come off the heat exchanger and into the underground line to the remote building. Might be hard to understand the way I'm explaining it but I could attempt to make another sketch showing both. The only thing I would have inside the boiler casing would be Ball valves, 2 stainless steel circulators, and strainers.

The buildings and OWB are on the same elevation. It is a pretty flat lot.

I figured it would be more reliable to have a pressurized system going that far through 1" pipe.

Unfortunately I have not been involved with this job from the start. They purchased this boiler with the salesman telling them everything would be fine with that pipe size and distance.

The heat loss came out to 160k. They do have a large over head door that will open frequently as it is a maintenance shop for trucks and equipment. They are convinced they need so much more but I'm happy to downsize the units as mentioned to the appropriate size or what ever size I can do considering the 1" underground line going there. At this point I'm thinking they will be stuck with another 2 - 63k units. Any experience with the Modine Lodronic units? The BTU ratings are based on 140 degree water temp

Also radiant is out of the question for all of the locations where Modine heaters are spec'd due to it being existing buildings with slabs. The radiant section is a new addition off of the one building.

Zman

johnlons said:

Zman said:

Overall it looks good. You do not need the extra circ and the closely spaced tee for the radiant. Keep the circ in the radiant loop and pipe the supply and returns right into the header.
I would size the distribution piping to the actual load at 4 ft/sec and the headers to 2 ft/sec.

The radiant manifold is roughly 60 feet away from the main manifold in a remote closet. Seemed a bit far for me to only use a single circulator?

I would change the tubing diameter or upsize the circ before I would add a second one.

johnlons

Solid_Fuel_Man said:

Do what kind of conduit or wires are buried between the boiler and buildings? 

If I'm understanding your question correctly, I believe the pipe is Thermopex 1"

leonz

johnlons said:

First time joining although I have visited the site many times and I appreciate all the advice on here.

I have done service, repair, and installation on residential systems for 7 years (not long). However, I have never installed a wood boiler before. This system is being installed as the primary heat source for two shop buildings. They have a Crown Royal Pristine 7400E Outdoor Wood Boiler which is 390K BTU Output.

One building is 100ft away from the OWB and will have two Modine hanging heaters. They installed the insulated underground pipe which included 2 - 1" Pex tubes before I had got involved with the job. My opinion is the pipe will possibly be undersized to be able to run 2 - 120k BTU Modine Heaters but that is a different topic.

The second building is located within a few feet of the OWB. This will include 2 - 63K Modine hanging heaters and a small office area of in slab radiant that will require 18K BTU/HR

My thought is to have two independent pressurized systems one for the first building and one for the second building. The OWB has two separate outlets which should work well for what I'm thinking. I believe it would be impossible to pump water the distances and elevations that I need without doing it this way.

Please see the attached sketch of what I had in mind for the second building. Am I missing anything or should I change anything that I have planned. Second question is, how do I size my flat plate heat exchanger for this purpose? Most of them are spec'd for DHW, radiant, or snow melt which would require low temperatures where I'm trying to achieve higher temps to allow the Modine heaters to work properly. I have tried a calculator that I've found but I don't know If I'm getting the right output. Ideally the OWB would put out 180-190 degree water to the flat plate and as hot of water that I can get out and over to the Modine heaters.

Thanks I appreciate any input.

=====================================================

Hello Johnlons,


Working with my past experience and feeding a wood boiler I can tell you that you need more hot water storage.
That salesman was no friend of theirs or yours.
The boiler they have will not keep up with the demand.

The folks below make insulated hot water storage tanks for hydronic heating.

Watson Research

www.wrboilers.com

You could employ three of these tanks in the closed circuit heating loops in the buildings heating that thermal mass of water for these buildings rather than feeding the water to air heat exchangers.

Forest eaters waste a lot/tremendous amounts of heat energy when idling.

I would rather see you have this "salesman" come out and design a heating system for them and I bet he would not be able to.

A heating load of that size would call for a 260,000 BTU coal stoker boiler running at 160 degrees. to heat the water.

Solid_Fuel_Man

Keep the big Modine's. Over sizing them will help on water temperatures. A 3rd unit (possibly in the future) may help too. That would allow you to not need to push so much water through the 100' pex. 

My question about conduit was for electrical. Did they bury and type of conduit or wire from the far building to the boiler or to the other building? I hope so, you will need it. 

For what worit's worth, you can save money and use iron circulators. The boiler is steel and and open system. It will be treated water, and is fine for iron circulators. 

Remember you must push the water from the boiler, this is the same as "pumping away" because the boiler itself is the expansion vessel. 

GroundUp

Back up the bus a little bit. What is the heat loss in the further away building? A 120k Modine will be derated to approximately half that with the 8-9 GPM and 173* AWT you'll achieve from that 7400E with that piping arrangement, so the two of them with a 120k pull would be fine with the 1" pex. 1" pex is incredibly common for OWB applications and if properly installed, it can still work well. Long story short, there is no need to pressurize anything but the radiant. Crown offers free annual water testing and will supply the proper chemical to treat the system. Absolutely do NOT need extra water storage, that will only harm the performance of the 7400E. Pipe the larger building with a 26-150 or similar on one of the LOWER ports of the OWB, pumping toward the building and just make a loop inside the building with closely spaced tees to feed the UH as secondary zones, all atmospheric system as designed and returning to the opposite top port. The other building, given the short loop, perhaps a 26-99 primary circ again at the boiler's other lower port to yet another pair (or two) of close tees for the UH, through a 10 plate 5x12 HX for the radiant, and return it back to the opposite top port of the OWB. Both boiler circs run 24/7 for water jacket mixing. No need to overthink this. I've installed hundreds of different OWB and was actually involved in the design of the Pristine E series and conventional MP series from Crown, the proper channel is to keep it simple. First things first though, we need the heat loss of the building.

johnlons

Solid_Fuel_Man said:

Keep the big Modine's. Over sizing them will help on water temperatures. A 3rd unit (possibly in the future) may help too. That would allow you to not need to push so much water through the 100' pex. 

My question about conduit was for electrical. Did they bury and type of conduit or wire from the far building to the boiler or to the other building? I hope so, you will need it. 

For what worit's worth, you can save money and use iron circulators. The boiler is steel and and open system. It will be treated water, and is fine for iron circulators. 

Remember you must push the water from the boiler, this is the same as "pumping away" because the boiler itself is the expansion vessel. 

My fear with having the bigger Modine heaters is that the fan on them will cycle on/off from cooling down rapidly.

To my knowledge there isn't any electrical that was installed with the Thermopex.This means the circulator would probable have to pump 24/7 between boiler and the far shop.

I intended to install the circulators pumping away

leonz

Its not a case of overthinking anything, there is not enough thermal mass in that forest eater.

if they are hell bent on using wood a Garn boiler would be a better choice as they have 4 models with the 2,000 and 3,200 gallon units being the largest and they can be equipped with electric heating elements to take advantage of off peak electricity to heat the boiler water.

www,garn.com/wp-content/uploads/2012/11/Garn_WHS_Design_manual.pdf

johnlons

GroundUp

Heat loss came in around 140,000 however I did add about 15% factoring in the over head doors opening frequently. This is a fairly large commercial shop with not so great insulation.

To be exact it is 180 foot loop from boiler to the far shop and back. Once in the shop there will be one heater directly above the entry point (30ft loop) and another at the furthest corner which is roughly an additional 190 ft loop. Not to mention these heaters will be mounted at the ceiling which in elevation is probably 15ft above the wood boiler. I'm just not confident the system would be problem free if it was not pressurized. How many PSI could I expect from the water mass of the Pristine boiler? Are there and precautions to take to avoid becoming air locked?

In the closest shop there would be no point in only pressurizing the radiant in my opinion. All the same components required no matter what besides needing a larger flat plate.

Thanks

leonz

johnlons said:

GroundUp

Heat loss came in around 140,000 however I did add about 15% factoring in the over head doors opening frequently. This is a fairly large commercial shop with not so great insulation.

To be exact it is 180 foot loop from boiler to the far shop and back. Once in the shop there will be one heater directly above the entry point (30ft loop) and another at the furthest corner which is roughly an additional 190 ft loop. Not to mention these heaters will be mounted at the ceiling which in elevation is probably 15ft above the wood boiler. I'm just not confident the system would be problem free if it was not pressurized.


"How many PSI could I expect from the water mass of the Pristine boiler?"

Drum roll please......................................................

13PSIG...........................................................


Are there and precautions to take to avoid becoming air locked?

In the closest shop there would be no point in only pressurizing the radiant in my opinion. All the same components required no matter what besides needing a larger flat plate.

Thanks

----------------------------------------------------------------------------------------------
With a poorly insulated buildings it were me I would still walk away.
I used a wood fired boiler for 33 years and they can get cold very quickly.
Get this boiler salesman to design a heating system and guarantee its high efficiency, HE WONT, HE CAN'T.

hot_rod

https://www.caleffi.com/sites/default/files/coll_attach_file/idronics_10_0.pdf

So additional info here on piping non pressurized OWF. An explanation on how heaters can be above the waterline of the unit

GroundUp

Pressure and water mass are not correlated one bit, but with the loop circ in the back of the boiler cabinet as designed will always have enough head on it to pump the loops. Properly sized circs on properly installed piping to the secondary UH loops would have no problems lifting that 15 feet or staying air free.

I think leonz is confused about what's going on here, he sure seems to be out in left field with all this thermal mass talk

leonz

UM, no I am not confused about this or about thermal mass; ask anyone that has cast iron steam or hot water radiators about thermal mass and what a benefit it is to heat an old home or a new one.

Why do you think people invest in Garn wood burning boilers? They take wheel barrow loads of dry wood below 25% moisture and run it through an induced draft firebox insulated with ceramic burner parts and use a 5 pass heat exchanger in the 3,200 gallon model to pull all the heat out of the smoke that they can to heat 3,200 gallons of water and have steam vapor for exhaust.

Zman

@leonz
They already purchased and installed one of these https://www.crownroyalstoves.com/outdoor-wood-furnace-pristine-series/
At 3,200 lbs and 290 gallons of water, it has a fair amount of mass.

I agree with you that more mass is better but, can we acknowledge that the owner is not going to throw away the boiler they have and buy a Garn?

The only thing that concerns me about the design is the 1" pex
I would probably oversize the fan coils so that it will function better with the high delta T you will see due to low flow.

Solid_Fuel_Man

The 1"PEX is soooooo commonplace in the OWB game. It's a matter of the pay now (1.25 or 1.5"PEX) or the pay later (with a bigger watt hungry circulator) philosophy. 

The 1" PEX can be made to work just fine in all reality. It will just cost some dollars to buy and operate the circ for that loop. It's the same with people running 500' 1/2" loops is a slab. It'll work with a big enough pump. What is saved on smaller pipe price will be paid for several times over in electric cost. 

But it's a moot point, the boiler is there and the lines are buried. Not it's just got to be setup to work. It's not the end of the world. 

People who like to burn wood......well they burn wood! If they get tired of it they will stop. 

leonz

I have seen folks use retired insulated railroad tank cars to store water in for thermal mass.

hot_rod

not to forget a high head circ with little NPSH, and high temperature  A perfect recipe for cavitation.
Show me some math  on moving 390,000 btu/hr through 1” pex

leonz

The one inch pex is rated for 80,000 BTU per foot isn't it Bob?
the pipe sizer example I saw for 1 inch pex showed 5.5 feet per second/8 gallons per minute so I think they are in deep doo doo.

hot_rod

Here is what 24 gpm would look like in 1" pex.

Also the math for determining when and how you pull sub-atmospheric conditions in an open system.
And Grundfos NPSH requirements

hot_rod

12 gpm in 1" pex, still beyond best practice velocities.

GroundUp

Why are we striving for impossible flow rates? The 140k design load can easily be attained with 8 GPM and a 35 degree delta. All done.

hot_rod

Guess we need to know which model Modine you have. I don't see a 120? Output is generally at 200°F SWT and 60° air temperature.

Modine has all the derate and optional ∆T math at their site.
Not sure an 8 gpm of 175F SWT with a 35° ∆ gets you 140K output on any of the models?

leonz

www.sterlingrail.com

Lots of insulated tank cars for sale here.


==============================================================================================================

Just for fun here: An insulated 20,000 gallon tank car has a lot of useable thermal mass and 2 circulators could be used for the system one for the boiler in a closed loop from the boiler to the tank cars steam coils(using the coils for hot water) and a smaller one to the heating load.

SO using the Metric formula to heat water in hours;

Pt = (4.2 * L *T)/3600=

Power= (4.2 * Liters * Time) * 3600

4.2 * 75,208 * (140-50)/3600

4.2*75,208 * 90/3600= 547 hours = 23 days (rounded higher)

20,000 gallons of 140 degree water

Pushing 8 gallons per minute of 140 degree water to the heating load will require 2,500 minutes(104 hours rounded to 4.3 days) to push that amount of 140 degree water through the heating loops if done in series.

Using the starting point of 140 degree water to heat the water mass the temperature could be raised gradually in ten degree increments on a continuous basis to 160 degrees as the returning water flow would be warmer requiring less energy to reheat a gallon of water to a higher temperature over time.

With the poorly insulated buildings maintaining a temperature of 160 degrees would probably be more efficient but as a lay person I do not know how well it could work.

Using the 490 gallon insulated tanks from New Horizon Corp. probably would work well if they were used to store heated water in each zone to be heated and having a separate circulator for each zone.

Larger storage with copper coils that can be moved through doorways are available from other suppliers.







I love math but I am not that good at it.