If I have a 165' (one way) run from house to OWB, do I use the 165' or 330' figure when calculating head?
Head calculations
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330' plus whatever the heat exchanger adds. If there are a lot of fittings, they might become significant.
Tom in Maine said:
Correct. Be careful with the HX. They can develop pretty significant head when you start getting flow rates over 5 GPM. (typical 30 to 40 plate with 1" tappings)
That's my problem, I listen to a hack plumber and the OWB dealer and they all suggested 1" pex. The plumber had me running a Taco 014 which started to cavitate (marble sound) due to the high head and 185 * water temp. I'm running 160' from boiler to house plus another 60' indoors with 1" copper, 28-90's, 1 50 plate HX, 1 check valve, 1 Y-strainer. I'm pretty pissed off that I listened to these guys and didn't try and figure this out myself. The guys at Taco recommended an 011 or 013. I still think I'm in trouble. Last heating season, the boiler kept up and had no problem heating the home. The BTU output from the manufacturer states 200,000. I think that's pretty high? Can someone help me figure out a solution besides the obvious....digging up the pipe and laying down 1.25 or 1.5".
What's the difference between pex and pex-al-pex. I would imagine the latter has a bigger ID? The pipe I was given is the blue and red stuff.
Did the 014 cavitate all winter or just when the water was above a certain temperature?
They system worked okay otherwise?
How close do you think you are to 200,000 btu's/hr?
They system worked okay otherwise?
How close do you think you are to 200,000 btu's/hr?
It didn't cavitate all the time. I even noticed it around 165* though. The system did work fine as is. I Kept the house at 72* during the day, 2700sqft, 6 year old home. I can't get a firm answer from the dealer on BTU's. EPA site claims just over 100,000 on the next size up model E3400. I'm thinking if I was at the 100,000 btu mark, things would make alot more sense, hence the reason why the system is keeping up as is. My plumber I believe assumed the 014 was a "bigger" # therfore a bigger pump, when in reality it doesn't match the head or gpm I need. The lower BTU's will definitely bring me down within range.
This is a dilemma with unpressurized systems. The vacuum that is created at the center of the pump impeller is making the water boil after you go past the 165F point. I suspect you have the pump at the boiler, pumping away to the house. Relocating the pump might solve the problem.
The pump has to see more pressure on the inlet side to help keep the boiling from occurring at the impeller.
I don't think this is as much a pressure drop issue as a function of the system being unpressurized.
It might be helpful to relocate the pump at the lowest point of the system.
The pump has to see more pressure on the inlet side to help keep the boiling from occurring at the impeller.
I don't think this is as much a pressure drop issue as a function of the system being unpressurized.
It might be helpful to relocate the pump at the lowest point of the system.
The calculations show I should be using a 009 pump for the highest head and lower flow rate. The 014 is for just the opposite...high flow low to medium head. I'm going to replace the pump, when I do maybe I'll put it in the basement vs the boiler.
330' of 1" plastic pipe has about the following head, plus fittings, hx, etc:
10 gpm = 30' head (100,000 btu at delta T = 20)
15 gpm = 64' head (150,000 btu at delta T = 20)
I agree that locating the circ away from the boiler and at a low point may work well. That was exactly my setup when I used an OWB, since sold and now use a gasser.
10 gpm = 30' head (100,000 btu at delta T = 20)
15 gpm = 64' head (150,000 btu at delta T = 20)
I agree that locating the circ away from the boiler and at a low point may work well. That was exactly my setup when I used an OWB, since sold and now use a gasser.
If your heating load is under 50,000 btu a 009 with your present tube might be able to keep up. The numbers I crunched using your list of pipe tube and fittings, I came up with 19.5 ft of head at 5.3GPM with a 009. A 0013 will do 6.3 GPM but the head goes to 28.6 requiring a minimum of about 6.5PSI at the impellor to keep it from cavitating. Not gonna happen no matter where you locate the circ unless the boiler is located about 30' higher than the circ.
As a general rule the only time 1" is suitable would be for loads under 70,000 btu and lengths under 125' total. Pretty safe to say that trying to get more than that out of 1" whatever tube is an exercise in futility. Sad to say but I've never met an OWB seller that realized there were more tubing sizes than 1".
Long story short. I'd spare myself about 5 burned up pumps over the next couple years, dig it up and drop in some 1-1/4". Doing that will allow a 15-58 to give you just under 7GPM which should be plenty for your house. I'd guess offhand that your actual load is less than 60,000 on 2700 sq ft of new construction.
As a general rule the only time 1" is suitable would be for loads under 70,000 btu and lengths under 125' total. Pretty safe to say that trying to get more than that out of 1" whatever tube is an exercise in futility. Sad to say but I've never met an OWB seller that realized there were more tubing sizes than 1".
Long story short. I'd spare myself about 5 burned up pumps over the next couple years, dig it up and drop in some 1-1/4". Doing that will allow a 15-58 to give you just under 7GPM which should be plenty for your house. I'd guess offhand that your actual load is less than 60,000 on 2700 sq ft of new construction.
Don L said:
The calc I ran was for standard 1-1/4" pex. No I.D./O.D. stuff. Just plain pex. When you get into larger bore stuff there can be confusion generated by different companies using different methods of calling out sizes along with the occasional metric designation thrown into the mix just to keep things interesting. That being said, the program I use to crunch the flow rate and head works with standard designations of sizes. 1-1/4" pex would have a rough I.D. of about 1-1/16" IIRC.
Heaterman, what if I use my existing 1" for say the return and install another insulated dual 1" for the supply. This way they are seperated and I do not have to worry about heat transfer. Will I run into a problem at the other end of the spectrum by going to large(doubling pipe diameter)? How do you handle connecting to the boiler and the 1" copper in the house, do I just T them together. I'd love to run a smaller pump as well!
MyOutdoors said:
Basically the head will stay the same and you'll get almost double the flow ......all other things being equal. If the single 1" gives you 5 you'll probably get about 9-9.5 with a pair.
When bring two lines into one it's usually best to set it up like a manifold where each line comes into the side of a tee. The tee's are joined end to end. This keeps the head very similar in each line rather that bringing both lines into one tee in a side and end configuration. It's important to do as much as you can to keep the head exactly the same in each line for maximum flow.
Now I'm really confused! I thought if I doubled the lines I would get the obvious flow rate, but thought the head would also drop do to the "new" calculations using the flow rate. If I used the Taco formula:
HL = k x c x L x (f1.75)
Where:
HL = the head of the piping system (feet of head)
k = a number based on tubing type/size (found in Table 3)
c = correction factor for fluid type and temperature (found in Table 4)
L = total equivalent length of piping circuit (feet) (from Step 3)
f1.75 = flow rate through piping (gpm) raised to 1.75 power (selected values found in Table 5)
I can now use between .0001 or .00036 for K? Instead of the original .00223 for the 1" pex.
Here are my old calculations: .00223 x .933 x 615 x 56.234= 72 head loss
Dual 1" lines: .00036 x .933 x 615 x 128= 26 head loss
HL = k x c x L x (f1.75)
Where:
HL = the head of the piping system (feet of head)
k = a number based on tubing type/size (found in Table 3)
c = correction factor for fluid type and temperature (found in Table 4)
L = total equivalent length of piping circuit (feet) (from Step 3)
f1.75 = flow rate through piping (gpm) raised to 1.75 power (selected values found in Table 5)
I can now use between .0001 or .00036 for K? Instead of the original .00223 for the 1" pex.
Here are my old calculations: .00223 x .933 x 615 x 56.234= 72 head loss
Dual 1" lines: .00036 x .933 x 615 x 128= 26 head loss
Heaterman, did I calculate this right? I'm going to use my existing insulated 1" supply & return combined as a "dual line return", then I will purchase another insulated 1" Dual line and use that as my Supply. I just want to make sure this is the way to go. I will have to purchase another pump (help size please) and 2 manifolds (interior of home & exterior of Boiler). Where is the best place to purchase a pumps, manifolds, crimpers & clamps. Thank you heaterman.
Survey SAYS!
Using 2 loops, 1" pex, 330 feet long (165 each way) with some misc fittings thrown in;
AND 1-1/2" common piping
8.92 GPM, 11.01 Ft head, 4.64psi differential driven by a Grundfos 15-58 (not the FC model)
11.5 GPM, 17.8 ft head, 7.24 psi differential when using a Grundfos 26-64
7.85 GPM, 8.81ft head, 3.71psi differential with a Taco 007
7.37GPM, 7.89 ft head, 3.32 psi differential with a Taco 009
8.8 GPM, 10.86 ft head, 4.54psi differential running a 0010 Taco
Now, just fer kicks...........it's interesting to see the following numbers when you run one of the big boys through that tube set.........
Taco 0011---------- 12.67GPM, 20.34ft head and 8.57 psi differential
Grundfos 26-99----13.43GPM, 22.53ft head with 9.5psi differential
As you can clearly see, with tubing lengths in the area you are using, 6gpm (per tube) is about max flow rate. The larger circs will move a tad more water but basically the extra energy burned is just used to create head.
What did you say your heating load was again?
Using 2 loops, 1" pex, 330 feet long (165 each way) with some misc fittings thrown in;
AND 1-1/2" common piping
8.92 GPM, 11.01 Ft head, 4.64psi differential driven by a Grundfos 15-58 (not the FC model)
11.5 GPM, 17.8 ft head, 7.24 psi differential when using a Grundfos 26-64
7.85 GPM, 8.81ft head, 3.71psi differential with a Taco 007
7.37GPM, 7.89 ft head, 3.32 psi differential with a Taco 009
8.8 GPM, 10.86 ft head, 4.54psi differential running a 0010 Taco
Now, just fer kicks...........it's interesting to see the following numbers when you run one of the big boys through that tube set.........
Taco 0011---------- 12.67GPM, 20.34ft head and 8.57 psi differential
Grundfos 26-99----13.43GPM, 22.53ft head with 9.5psi differential
As you can clearly see, with tubing lengths in the area you are using, 6gpm (per tube) is about max flow rate. The larger circs will move a tad more water but basically the extra energy burned is just used to create head.
What did you say your heating load was again?
Thank you again for your input, This is my second time around and I want to get this right. I'm basing this installation on your input! Manufacturer claims 200,000 BTU output (Very high in my opinion), my home is approximately 3000 sq ft with 3 heating zones and DHW. I'm using a 50 plate HX with a Taco 007 continuously circulating through the boiler. I've never pinned down my exact heat load, but I can tell you my wife and kids like it around 72* in the winter! LOL. My home is new construction and 6 years old.
MyOutdoors said:
If your house is 3000 sq ft total I doubt if your heat load is much more than 80K, if that much. If so........... you really should do a heat loss........... 8gpm will be sufficient flow provided the rest of your heating system is up to the task and designed right. The numbers are from the software program I use to design the piping for all my jobs so I have no reason to doubt they are valid. Keep in mind that when you are at the "edge" of what should be pushed through a given size tube, as you are, a few extra fittings can make a substantial difference in flow rates.
How do I conduct a heat loss calculation? I also have 60' of 1" copper inside the home (oneway). With all the fittings (alot of 90*'s) and plate HX, I figured 615' total. So if I read your post right, am I still pushing it even with the dual 1" lines?
MyOutdoors said:
I went back to the beginning of this thread and re-read your list of fittings and tube. I definitely did not include everything you have listed there in the quick calc that I did. I would want to do something a lot more detailed before I'd tell you to pull the trigger because, as I said, you are at the edge of what a pair of 1" tubes will handle without making some serious head. Seeing that you are working with an open system (OWB) it's imperative that you keep the head and pressure differential as low as possible. If you don't you will have problems with suction boiling and burned out pumps for the life of the system. I will try to find time to plug in your complete list of tube and fittings along with the HX and rerun the numbers.
Given what you are trying to do with the pair of 1" tubes it's really important to get a good handle on your heating load so I'll say again, do a heat loss calc. You might try Don Sleeth at HVAC-CALC.com He has a very good manual J based program that is easy to use and understand. Last I knew he sold one time use copies of it pretty reasonable. Have you looked for a good local contractor that could lay an eyeball on your situation and make a recommendation?
I would appreciate your calculations if you have time. I will check out the site you gave me as well. I don't have any good contractors in the area...one of the reasons I'm in this mess right now. This web site and the help I've gotten from people like you have been great. When you have time, let me know what you come up with. Even if I can get into an 009/11 range (high head pumps), I'll manage the energy cost. Installation is like a catch 22...Due to local codes, I had to install the distance away from my residence, now it' causing more problems. I hope I can get this figured out soon! Thank god I have my own backhoe to dig up the pipe, at least that will be fun!
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