supply line temp drop

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Old 01-09-13, 06:42 PM
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supply line temp drop

What do you guys think an acceptable temp drop for a outdoor boiler supply line should be? I have 3/4" line double insulated and a run of 90 ft. It is 3 ft down and the boiler is set at 180 degrees.
 
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Old 01-09-13, 08:22 PM
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Only 3/4" ? I think that shoulda been larger!

How many BTU is your ODB rated for?

I dunno... maybe 10-15 ? Just a WAG...

What are you seeing?

Your drop will be higher if you don't have enough flow. 3/4" pipe is kinda smallish, so you will have some resistance there...

What pump you running at the boiler?
 
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Old 01-10-13, 01:02 PM
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My buddy had 200 ft of pex that i got really cheap so i used that. I think i am running at 8 gpm through that tubing.does that sound reasonable? I am not sure what the temp drop is...i am installing the 2nd thermo tonight. My concern its that my registrar air is only coming out at 93 while the boiler is set at 180.
 
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Old 01-10-13, 01:29 PM
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I think i am running at 8 gpm through that tubing.does that sound reasonable?
8 GPM through 3/4" pex? sounds quite high actually. 3/4" copper is larger ID than 3/4" PEX and 8 GPM is high for copper in 3/4...

How or why do you believe you are flowing that much?

What pump are you using?

You are doing 'hydro-air' then... how is the ODB connected into your system? (I think you've told us this in the past, but please forgive my laziness in not searching!) Are you using a heat exchanger tied into the existing system?
 
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Old 01-10-13, 05:54 PM
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I only have 2 gallons per minute I was way off.... I got the probes installed there is a 25 degree drop over that 90 foot run.

Iam using a grundfos 3 speed pump. It is 1/25 hp.

I an using this pump to constantly circulate the water in the loop. This includes the heat exchanger in my furnace plenum. do you think the root of my problem is too small of a pump?
 
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Old 01-10-13, 06:11 PM
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I only have 2 gallons per minute
How do you know that?

there is a 25 degree drop over that 90 foot run.
Is that out and back? So 180' of tubing?

using a grundfos 3 speed pump
What model?

think the root of my problem is too small of a pump?
Possibly, but I would like to look at the pump curves for the pump you are running...

I think another part is the fact that you are only running 3/4" tubing...


So you are not tying this system into an existing hot water system, is that correct?

You have installed a coil in your boiler plenum and are pumping the ODB water directly through that?

 
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Old 01-10-13, 07:32 PM
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I measured the flow by turning off the pump and letting the boiler water get really hot. I then turned on the pump and timed how long it took for the temperature at my inlet supply to start moving rapidly...this gave me the speed of the fluid. I multiplied that by the cross-sectional area of the tube to get the floor rate.

The temp drop is measured from the exit of the boiler to my supply inlet in my basement. It is now 15 degrees by the way...1st measurement was from cold start.

The pump is a grundfos CP3S15-62FC... I run it at the fastest setting.

This is an old indoor boiler that I have outside in an insulated shed. It holds 11 gallons of water at the boiler and then I have 160 gallons of water that are in water heaters in my basement that are tied to this...the loop goes from my boiler 90 feet to my basement to water tank 1 and then 2 then the heat ex changer in the furnace then into a 3rd tank and finally back the 90 feet to my boiler. I know it is kinda cobbled but I got it for free so I thought that I would try.

Thanks a lot for the help... I really do appreciate it.
 
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Old 01-10-13, 08:23 PM
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Interesting setup!

Is the system pressurized or atmospheric? (not that it means anything to the question, I'm just curious).

Grundfos? or Steibel-Eltron?

http://www.newhorizoncorp.com/PDF/St...umps_Flyer.pdf

The temp drop is measured from the exit of the boiler to my supply inlet in my basement. It is now 15 degrees by the way
I think this implies that you are losing about 15K BTUH over the 90' run of tubing... I think...check me on this...

Do the storage tanks ultimately get to 180 so that the water to the hydro coil is HOT?

Have you measured the delta T across that coil? If you are only flowing 2 GPM, with 180 water IN at that low flow rate, I would expect SIGNIFICANTLY cooler water coming out.

Looking at the pump charts, if you are in fact flowing 2 GPM, that would imply that there is appx 16 ft of head in the circuit to/from the boiler. Sounds possible.

A bigger pump might help, but then keep in mind if looking at pump charts that the 16 ft of head is a 'moving target'. Trying to flow 4 or more GPM and the head goes up exponentially...

How did you insulate the tubing?
 
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Old 01-10-13, 08:46 PM
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The system is pressurized....that leads me to another question. I set the pressure when it's cool at about 12 PSI... the system will hold pressure for a long time as long as the system stays cold. when I heat the system up to 150 or 160 and then days later if the fire cools back down to around 90 degrees I noticed that the pressure is gone. I don't see any leaks and I'm wondering why would only happen over a cycle of heating and cooling back down.

the pump is a grunfos.

the storage tanks never really get above 150... I'm having a hard time getting heat out of that boiler. I have not been able to measure the temperature drop across the heat exchanger yet.
 
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Old 01-10-13, 09:03 PM
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So then you must have quite a large EXPANSION tank on the system then?

If not, I would be wondering how come it hasn't blown up yet?

I'm having a hard time getting heat out of that boiler
At 2 GPM I can understand why!

Remember that for a 20 Delta T, flowing 2 GPM is only going to move about 20K BTUH of heat, and you are losing a good portion of that into the ground along the way.

You probably do need larger tubing, and or larger pump.
 
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Old 01-10-13, 09:10 PM
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I got two 10 gallon expansion tanks....i will try a bigger pump. What should the flow be? Any ideas about the loss of pressure?
 
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Old 01-11-13, 02:09 PM
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By the end of the night the temp drop was only 5 degrees. The system was of so it probably had to warm up the pipes and insulation.

What do you think about the pressure loses iam seeing?
 
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Old 01-11-13, 04:23 PM
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What do you think about the pressure loses iam seeing?
I would say that if you are ABSOLUTELY CERTAIN that there are no leaks, then it has to be temperature related.

Perhaps when you set the initial pressure up to whatever you set it, the system still has some residual warmth in all of that water. As it further cools to a temp that is LOWER than the temp when you adjusted the pressure, the pressure would drop down lower...

You must not have a 'pressure reducing valve' on the system? You are pressurizing manually?

Do you remember what brand PEX was used? I'd like to get some specs on it to try and determine how much 'head' you have, and possibly how big a pump you might need.

Problem is still that small-ish tubing though. Yes, you can throw a bigger pump at it and possibly force more flow than you really should through the 3/4"... but it certainly won't be an ideal situation... I don't know how much more than 4-6 GPM I personally would be comfortable in recommending!
 
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Old 01-11-13, 05:24 PM
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Yeah...i adjust the pressure manually.

I don't remember what kind of Pax I bought I just know that its oxygen barrier and it's kind of a redish more than orange.


the temp drop is now back to 20 degrees and has been there for about 2 hours now. I have the supply in return line insulated with black foam and then inside a6 inch drain tile... I think that drain tile got full of water it's. Its solid drain tile but it might a hole that filled with water and that's why it's taking so long for to heat up
 
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Old 01-11-13, 05:34 PM
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Can't guess at flow rate required from boiler until you know the size, btu gross output or doe output.
3/4" pipe would be between 40k and 60k boiler output.
If you keep raising the pump size you keep raising the resistance to flow. This means the pump will become noisy and prematurely fail.
 
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Old 01-11-13, 06:53 PM
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I think that drain tile got full of water
Well... that's as good as no insulation at all then... bummer.
 
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Old 01-11-13, 08:56 PM
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I am going to order 250' of 1" pex and in close it in that b;ack pipe foam (it's rated to 200f). I will leave it ontop of the snow until spring.

My buddy buried his lines by cutting a trench 1' wide by 2' deep and laying 1" pink foam down for a foundation and sides. he then filled it package peanuts and covered it with another piece of foam and filled it in with dirt. If any water gets in there it will seep right through.

Does anyone see any problems with this?
 
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Old 01-12-13, 08:44 AM
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Does anyone see any problems with this?
Yes. Wet insulation is absolutely worthless. It is no longer insulation at all.

The black foam stuff... you mean the stuff they sell at the big box stores? That stuff is probably worthless too... underground at least. The more expensive 'rubberized' stuff is a bit better but again, if it's wet, forget it. It's OK to use inside a building but unless you can keep the tubing dry, there will be excessive heat loss.

I know that the dual pex insulated stuff that they sell is very expensive but it is really the only way I've seen that might have any insulation quality at all. Of course, if you don't mind losing say 20K BTUH to the earth (sometimes there's an excess anyway...) your plan would be OK.

I have seen vids of installations where the guy bought a couple cans of that DIY spray foam, not the little 12 oz cans, but the big canisters... used the foam boards to line the trench, suspended the tubing in the foam 'box' inside the trench and then completely enclosed the tubing in CLOSED CELL spray foam... that would probably work, but again, expensive. Those kits ain't cheap!

By the way, since you already have the 3/4" installed, you COULD run it in parallel with a second 3/4" run and maybe save some $$$ on the tubing. Do what you need to do with the insulation if you choose, but you could just run another trench and two more runs of 3/4" in parallel.
 
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Old 01-15-13, 07:59 AM
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Thanks for all the help...

I ordered 300' of 1" tubing from Pexsuppy. I cancelled the black rubber pipe insulation for it...at a price of a dollar a foot the 1 R value was not worth it... My insulation plan is as follows....

Install the 1" lines on the frozen ground and let the hot water "soften" them up so I can work with them. I am going to let the water get as low as 70F.

Then...I am going to take a 4" - 10' PVC pipe cut in half the long way to use as a form. I am going to cut two end caps to fit inside of the PVC mold to support the lines on the ends...lay the pipes in the bottom mold, slide the end caps into position...maybe have to add something in the middle to support the pipes if they sag....then spray away with big gap "great stuff". Once the bottom mold is full I will heap up the foam on top of the pipes and apply the top mold and secure it to the bottom. I forgot to mention...you should spritz water on the pipe and molds to get the great stuff to set up faster.

After an hour...I should be able to remove the molds cleanly and have a 10' insulated section of pipe. I have to to do this 10 more times....but if it works for the 1st section I will complete it.

I figured that I will have...1 20oz can per 10' section invested at 6$ a can...60$ total. The R value is 7.5 per inch....I should have at least an inch from the end of the foam to the 1st pipe... Great stuff is closed cell....it will not absorb water. I calculated the heat loss to be less than 1F for my entire 110ft run.

This summer when I bury it I will enclose it in 5" drain tile.

I do not see any issues with this...does anyone else?

I will post pics when I am done.
 
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Old 01-15-13, 04:05 PM
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Sounds pretty ambitious... and don't be surprised if nothing you can do to clamp the two halves together holds... I'm guessing that the two halves will be forced apart by the expansion of the foam. I used that stuff to seal an unused floor drain one time... went out to dinner... came back to find the cast iron drain housing ripped right out of the concrete and sitting on a 'mound' of great stuff about 3-4 " off the floor.

OH... protect it from the sun... but maybe the top 1/8" really won't matter... the sun turns that stuff dark auburn color and dries it out to dust.

You are probably going to need to make some wooden spacers... and support the tubing in a couple places along the run of 10'. I can envision more 'stuff' on one side pushing the tubing 'off center'. When all is said and done, you won't have any way of knowing just how close the tubing is to the outside of the foam.
 
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Old 01-15-13, 04:12 PM
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This guy's idea has some merit, but compressing the pink insulation like that makes it worthless as an insulator:

DIY Outdoor wood burner Insulating Underground PEX Tubing Insulated HydroPex - YouTube

Google: "homemade insulated pex" (in quotes) for lots of ideas.

By the way, don't abandon the stuff you've already got in the ground! Connect it in parallel with the new stuff! The less 'head', the better...

Like the guy in the vid said that his Amish friend said; "don't bother with the insulation, just throw another log on the fire!"

If you are successful with the "Stuff", I think this corrugated drain tile looks like a pretty good idea.
 
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Old 01-15-13, 08:38 PM
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I will play it by ear....if the 1st section expands too much I will back off on the second one. even if stuff foam breaks through the mold I can always just trim that off when I slide it into the 5 inch drain tile. I'll let you know how it works hopefully send some pictures. Thanks Again.
 
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Old 01-22-13, 08:06 AM
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Here's a little update on my attempt to insulate my lines with grreat stuff. I got two 10' sections done before the real cold set in. For the most part...it worked fine although there is some spots that did not expand totally to close in the pipes. I will have some tough up to do on those...

The cold weather forced me to stop after the 2 sections and use fiberglass as a temporary solution. With just the fiberglass around my lines and the lines above ground I now have less than 5F drop through the 1" line...much improved.

I also have a new boiler coming on Monday....I decided even with an accpectable temp drop the boiler I am using is just too small to do the job. I ordered a Ridgewood Boiler. They are a company out of Michigan. I have heard good things about there boilers so I thought I would give them a try. You cannot beat there price or their firebox thickness...it is 3/8".

Anyone heard of them or have any reviews?
 
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Old 01-22-13, 05:48 PM
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I haven't heard of, but then have not spent a lot of time looking either, so that don't mean anything.

Yes, that sounds much better... now hook those 3/4" in parallel! No sense wasting all that work! (unless you think you will lose more heat than the benefit of the extra flow... could happen!)

Keep us posted, and if you get inclined, I for one would not mind seeing pics of your system!
 
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