Boiler piping design

VirginiaBoiler

Hello, I'm currently in process of desigimg my OWB system and looking for any solid advise I can get.

Here's the deal:

The house: I'm not going to perform a heat load test on my house as this is a supplementary system. I have a 2 level rather large home with a basement that is very well insulated. Last winter, (very mild compared to most in this area) (I've lived in this house one winter) my 100,000 btu gas furnace (severs the 1st floor) kept up with the entire heat demand. With that said my 2700 sgf basement went without heat as there is currently no heat source. The basement is partially below grade and it didn't get below 55 degrees (give or take). I don't plan on providing heat to the 3rd floor from the boiler as it will naturally rise and if more is needed it has a zoned heat pump. I figure I need at least 150,000 BTU with 100,000 to a ducted heating coil to serve the 1st floor and 50,000 for the basement. The basement ceiling is unfinished, so I plan on finding used radiant fin tub to hang in the ceiling and reflect it downward.

Shop: If I get 50,000 BTU, I'll be happy

The Boiler: I picked up a 3 year old Portage and Maine Optimizer 250 for $4500.

Piping: The run will be 300' to the house and a separate 100' run to my shop. I could make it 250' to house and 150 to shop to save money on pipe, but it would be further from water supply, power supply, and less convenient for me to access.
I figure I need 1 1/4" to the house and 3/4" to the shop. I'll probably be using Performaflex unless I find a better deal on quality piping. I haven't decided if I want to do a separate loop inside the house and run through a heat exchanger. The boiler is open to the atmosphere so I would at least need a air separator in the house, so I'm not fight air in the lines.
I'm planning on continuous running pumps on each loop.

Questions:
What would be an optimum gpm target?
Does my pipe sizing look right? What is he potential btu with the 1 1/4" at say 5 gpm?

Ironman

To get 150k btu with the normal 20* delta T would require 15 gpm. A well sized hot water coil could very easily produce sufficient heat with somewhat cooler SWT and a 30* delta T. At 100k btus with a 30* delta T, the coil would need almost 7 gpm.

Fin tube radiation probably would need to be sized at a 20* de;ta T unless you over-size the emitters. 50k btus at a 20* delta T would require 5 gpm.

One thing you may not have considered: with an unpressurized system, the wood boiler needs to be at the same level or above the piping and heat emitters. If not, it will need to be pressurized with a heat exchanger between the boiler and the system. Hydronic circulators are just that: circulators, not pumps. They are only designed to create a small pressure differential to move the water through the system. They don't pressurize the system, so don't rely upon that if pressurization is needed.

An 1 1/4" pex line is good for about 12 gpm.

Where are you at in VA?

VirginiaBoiler

Thanks for the response Ironman,

I didn't even consider the elevation difference, although it looks like the boiler will be higher, but not sure how much. I actually have to cross a wooded ravine, so I'll need a transit or something to figure the difference. So with everything you said, do you think I should go with 1 1/2"?

I'm in Haymarket VA

Ironman

Your talking about 800' round trip from the boiler to the house, shop and back. That's gonna produce 35 ft of head @ 15 gpm with 1 1/2 pex. You'd need a very large circulator to accomplish that.

I'd recommend that you do an actual heat loss calculation to determine just how many btus are actually needed instead of guessing. An accurate heat loss calc is the foundation for everything in heating design.

SlantFin has a free app that you can download and is easy to use.

I'm near Staunton.

VirginiaBoiler

I'm doing 2 separate loops for the house and shop, each with their own pump with Tees at the boiler

VirginiaBoiler

BTW, my wife is a big fan of Polyface, we get regular deliveries

hot_rod

Is the 300' to the house round trip, or one way? That will make a difference in pipe sizing.

It is possible to run an open type boiler with piping and heat emitters above the level of the boiler, it does bring some concerns and challenges. You cannot use air vents on the open piping systems

Plate heat exchangers are cheap on E-bay and it solves a lot of issues.


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

VirginiaBoiler

The 300' is each way. My basement ceiling looks to be at about the same level or a little lower than the boiler, so elevation shouldn't be an issue.I did get a 50 plate HX from the guy who sold me the boiler, but not sure of the btu transfer potential. I'll dig into that some more tomorrow, just didn't think I would need it.

Ironman

The btu transfer rate of the heat exchanger depends not only upon its surface area, but also upon the temperature differential between the circuits and their flow rates. A lot of them only show the output with hot boiler water and cold domestic coming in. Naturally, that will give the highest rating.

Look at the ratings where both sides have high temps (160 - 180*). A fifty plate 5 x12" will probably give about 140k btus under those conditions.

EBEBRATT-Ed

@Ironman, I visited the old Dunham Bush plant in Harrisonburg, lets see 43 years ago. We were a rep for Iron Fireman burners back then.

If I remember right I flew into Staunton airport and then drove to Harrisonburg. Is that where the airport is??

Ironman

It's a little north of Staunton at Weyers Cave.

The Dunham Busch factory is gone; moved to South America. Home Depot shopping center is there now.

hot_rod

VirginiaBoiler said:

The 300' is each way. My basement ceiling looks to be at about the same level or a little lower than the boiler, so elevation shouldn't be an issue.I did get a 50 plate HX from the guy who sold me the boiler, but not sure of the btu transfer potential. I'll dig into that some more tomorrow, just didn't think I would need it.

You can use a free heat exchanger sizer at www.flatplateselect.com

Enter some temperatures and GPM flow and it will size a HX for you. 50 plate, if it is a 5X10 is a very large HX, it should be plenty.

Here is an example of a design for 18 GPM, 180 boiler side, 175- 160 B side, with a 20 plate.

VirginiaBoiler

Great, do you have a source for calculating gpm? I'm still a little confused, because I would think it would depend mostly on the pump. I guess, I need to determine a target gpm based off my duct coil and go from there?

hot_rod

IF you in fact need 150,000 BTU/hr total at a 20° ∆T, divide by 10,000 to get 15GPM required flow.

Ideally you would run a load calc for the home and shop and determine the exact gpm. The manufacturer of the coil you will be using will have data for pressure drop at various flow rates or BTU output.

Since you already have the 50 plate HX, you have plenty of HX capacity. Knowing the exact required gpm flow and head of each building would be desirable to properly size the circulators for the two distribution requirements.

Also since the boiler is an open system, steel construction, you will need an ongoing chemical regiment to lessen O2 corrosion, maybe a stainless circ on the boiler loop if you can find a good $$.

VirginiaBoiler

OK, Im going to take Ironman's advise and try the slantfin app.

VirginiaBoiler

Any suggestions on determining the pressure loss on the piping?

Ironman

We use engineering tables to determine the head loss of piping. It depends upon the gpm. The higher the gpm, the higher the head loss. It also involves taking into consideration all the fittings, valves and other components in the circuit.

Using primary/secondary piping also allows circuits to be pumped separately so that each pump only sees the resistance in its own circuit. An example of this would be to pipe and pump your ODWB loop as one primary circuit and and the system in your house as the secondary circuit. The secondary circulator could probably be a small one since it would not see any of the resistance of the long boiler loop.





The first factor to consider is the velocity: it should be kept between 2-4 fps. Then, we generally would look to keep the head down enough to use the smallest circulator reasonably possible. This involves using pump performance data from the manufacturer.

VirginiaBoiler

I assume the boiler itself has a pressure drop and the manufacturer should be able to provide or is it typical?

Ironman

If it's your typical large water content ODWB, then there's no pressure drop.

VirginiaBoiler

Update: I've been doing this in my spare time and designing as I go. I know, not smart, its just how I work.

So I've installed 250' of 1-1/4" Performa Pex. Its triple insulated in a casing. It's 500' round trip from the house to the boiler. I have a 50 plate HX in the house to provide a separate indoor loop and purchased a 20x20 duct coil that performs at 145,000 btu at 15 gpm. This coil will provide heat for the primary living area of the house. I also installed 34' of used 3/4" finned tube in the basement. Its unfinished and just wanted to throw some extra heat down there. I have 2 - 12' sections and 1 - 10' each in a different area of the basement. I'm going to install a zone controller and prioritize the duct coil.

The thing I'm trying to figure out now are the pumps. Based on previous replies, I've figured 10,000 btus per gpm. Considering I'm basing my design on 150,000 btus my boiler loop would be running at 5.4 fps with 19.55 pressure loss (this doesn't include the PD for the 50 plate HX).

I sized my indoor loop at 1" and its only 150' round trip, My duct coil pressure drop is 3.67 fthp.

Any pump recommendations?

Any idea the PD on the 50 Plate HX?

Thanks, Kevin

VirginiaBoiler

FYI, I found a good deal on a used TACO 0013. Thought it might be a fit for the boiler loop?

hot_rod

So 500' of 1-1/4 pex with a plate HX? Any other valves or fittings in the circuit?

Here is an example of a pressure drop chart for Rehau. Enter your flow rate, over to 180°. Note the multiplier is for 100'
Also try and stay around 4 fps velocity.

I think you may be looking at a more realistic a 12 gpm flow rate

VirginiaBoiler

Only other valves would be full port shut off at POC at boiler and HX, only fittings would be a couple 4 - 90 degree elbows. Everything else is long radius pipe bends. I have a SMT HX BL26C. Can't find any info on it, although it appears identical to the Baode BL26C, but I can't find any performance info on it. When I look at the B&G plate HX, they look to perform at a much higher flow rate. Any recommendations on a pump?

Ironman

You're probably looking at 2 - 3 psi pressure drop on a 5x12 50 plate at 15 gpm. So, 5 - 7 ft. of head.

leonz

Was the cost of a new coal stoker like the AHS S130 coal gun the reason you invested in a used P+M forest eater?

The B+G NRF35 circulator with an internal check valve is well within what you need.

Its better to leave the circulator in the basement so there is little chance of it freezing and you can have isolation valves in place to change it in the home with no water loss and the best isolation valves will have gauge ports so you can have leave a vacuum gauge on the inlet side and a pressure gauge on the output side to always be aware of the circulators condition.
A circulator that is drawing a vacuum means that the circulator needs to be replaced with a new one.

I stopped burning wood in a hand fed boiler after 33 years and bought a keystoker KAA-4-1 dual fuel coal stoker- the digital controls and gauges were bad twice and I wish I had purchased an AHS S130 coal gun instead as I would have been able to leave my oil boiler in place and set the S130 next to it.

VirginiaBoiler

Thanks for your response Leonz. I went with the wood boiler because I live on 10 acres of hardwood (mostly oak and hickory) I chose the P&M after much research I found them to be very reputable and I went with a gasification series to save on my time. Makes sense to me to heat my home with fuel thats laying on the ground. I suppose if I had coal laying around, I'd be burning that. Plus if I run out of wood, most my neighbors would be glad to let me take fallen trees as they don't even know how to use a chainsaw.

Interesting about the vacuum, I would think you would have a vacuum on the inlet side. I am planning on putting it in the house. My boiler appears to be about 8 or 10' higher than where my pump will be located in the basement. Does that factor into the head pressure or is it equalized in the loop?

Zman

The location of the pump is an interesting conversation.
To move 10 gpm through 500' of 1 1/4" pex pipe and heat exchanger you are going to generate over 30' of head (using uphoners numbers and siggy's software). Of that around 12' will be on the suction side if you put the circ in the basement. If the boiler is only 8'-10' higher than the basement It would actually be easier on the pump to put it on the boiler.

VirginiaBoiler

Zman, I don't understand how I could have pressure loss on the suction side if its pulling downhill? Should have positive pressure that would assist he pump.

Gordy

leonz said:

Its better to leave the circulator in the basement so there is little chance of it freezing and you can have isolation valves in place to change it in the home with no water loss and the best isolation valves will have gauge ports so you can have leave a vacuum gauge on the inlet side and a pressure gauge on the output side to always be aware of the circulators condition.
A circulator that is drawing a vacuum means that the circulator needs to be replaced with a new one.

Huh?

Zman

The pressure drop created by the circulator has nothing to do with the vertical head. The circ converts electrical energy to mechanical. If it is at the boiler, The pressure is all additive as that is the point of no pressure change. When you put it in the house, the resistance in the piping between the boiler and the house has a subtractive effect. Because it is an open system, you do need to consider the vertical element as well. In my example the benefit of putting the circulator low in the system is outweighed by the friction loss in the suction side.

VirginiaBoiler

How is friction loss in the suction even a factor when it is flowing downhill?

VirginiaBoiler

Let me rephrase that: Wouldn't the head pressure on the suction side be subtracted from the total friction loss of the suction side? Considering its flowing downhill?

Zman

You can look at it that way.
You would have 12' of friction loss partially offset by 8'-10' of head. This is only an issue because it is an open system and you would be going 2'-4' negative to atmosphere.

DZoro

Not sure on the P&M boiler, but some like a Heatmor ODWB. Provide a easy place for the system pump on the back of the boiler. Usually enclosed and even a pump outlet.

VirginiaBoiler

Zman, Okay good, I'm learning as I go. With that same logic, I'm going to leave the elevation out of the equation completely, rather than add it back into the pressure side. Thanks to all who take the time to respond!