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Author Topic: Heat loss from under ground pipes  (Read 18131 times)

tbone

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Heat loss from under ground pipes
« on: February 28, 2012, 09:49:54 AM »
What's an exceptable number?  I know its all relative, but I believe I read somewhere that you typically lose x amount of degrees per 10 feet for 1.5 inch pex.  Not the triple wrap or the best that money can buy....just the standard insulated pex.
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RSI

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Re: Heat loss from under ground pipes
« Reply #1 on: February 28, 2012, 10:14:30 AM »
Just temperature drop along without knowing the flow rate doesn't mean much.
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TheBoiler

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Re: Heat loss from under ground pipes
« Reply #2 on: February 28, 2012, 11:16:09 AM »
Per 10ft, well that would have to be a fraction of a degree no matter what.

Some people on here have several hundred feet and would only be looking at a few degrees.
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tbone

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Re: Heat loss from under ground pipes
« Reply #3 on: February 28, 2012, 11:36:37 AM »
I am at 100 feet and loosing about 15 degrees...I'm guessing I need a redo.
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tbone

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Re: Heat loss from under ground pipes
« Reply #4 on: February 28, 2012, 11:39:51 AM »
RSI, not sure what my flow rate is...Ill check when I get home.
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tbone

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Re: Heat loss from under ground pipes
« Reply #5 on: February 28, 2012, 11:54:10 AM »
I should probably add that my circulator pump in non continuous, and I recently added a thermometer to my supply line, inside my house where I change over to copper.  I used electrical tape and with some insulation to attach, not sure how accurate it is, especially with the pump not running all the time.
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willieG

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Re: Heat loss from under ground pipes
« Reply #6 on: February 28, 2012, 12:14:43 PM »
15 degree loss in 100 feet of pipe and you are still able to heat the house i would guess flow would be in the 8 to 10 gpm and if that is right you are losing enough heat to heat your home at least half of the days of winter

ill bet that if someone was only heating their home (or at least heating thier home before anything else) that if the heat loss was measured at the outlet (return) of the exchanger in the plenum when the house was calling for heat and the blower was running that the heat loss between feed and outlet would be no more (likley less) than 15 degrees
« Last Edit: February 28, 2012, 12:33:35 PM by willieG »
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tbone

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Re: Heat loss from under ground pipes
« Reply #7 on: February 28, 2012, 03:33:48 PM »
Can't find my gpm...but its a taco 0011-f4.  Its an eighth hp @ 3250 rpm....amp 1.76.
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RSI

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Re: Heat loss from under ground pipes
« Reply #8 on: February 28, 2012, 04:51:57 PM »
Does the temperature drop stay the same when the pump runs for a while or does it slowly go up?
If you just have the thermometer on the pipe I would take it to the other end of the pipe and see what it reads there. It is real common for thermometers strapped on a pipe to read low.
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tbone

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Re: Heat loss from under ground pipes
« Reply #9 on: February 28, 2012, 05:30:39 PM »
Quote from: RSI on February 28, 2012, 04:51:57 PM
Does the temperature drop stay the same when the pump runs for a while or does it slowly go up?
If you just have the thermometer on the pipe I would take it to the other end of the pipe and see what it reads there. It is real common for thermometers strapped on a pipe to read low.
I'm not sure...its been so mild my pump doesn't stay on for long....I'm going to check it in the early morning after my pump has been running continuously throughout the night. I was guessing that my reading might not be very accurate.. I used my old thermometer from my stove that I replaced with the led.  I placed it on an elbow (just guessing that would be the most accurate).  I know I'm at least loosing 10 degrees as I checked it with a buddies heat gun not long after instal and that was the difference.
« Last Edit: February 28, 2012, 05:34:16 PM by tbone »
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willieG

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Re: Heat loss from under ground pipes
« Reply #10 on: February 28, 2012, 05:38:55 PM »
tbone check what the temps are on both sides of your heat exchanger for the furnace when the house is calling for heat. compare this difference to that of your underground pipes...this shoudl give you an idea of what you are losing
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RSI

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Re: Heat loss from under ground pipes
« Reply #11 on: February 28, 2012, 05:42:36 PM »
Infrared thermometers are hard to get an accurate reading on pipes too.
If you can use the same thermometer on the same type surfaces it will be fairly accurate. If you can, insulate around it to keep the air temp from giving a lower reading.  If you just compare the offset from the thermometer on the boiler should get you close.
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tbone

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Re: Heat loss from under ground pipes
« Reply #12 on: February 28, 2012, 05:49:50 PM »
Quote from: RSI on February 28, 2012, 05:42:36 PM
Infrared thermometers are hard to get an accurate reading on pipes too.
If you can use the same thermometer on the same type surfaces it will be fairly accurate. If you can, insulate around it to keep the air temp from giving a lower reading.  If you just compare the offset from the thermometer on the boiler should get you close.
ok I see what you are saying...good idea.  I'll check my pex temp before entering the ground versus my pex temp where it enters my crawlspace exiting the ground.i
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tbone

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Re: Heat loss from under ground pipes
« Reply #13 on: February 28, 2012, 05:51:25 PM »
Quote from: willieG on February 28, 2012, 05:38:55 PM
tbone check what the temps are on both sides of your heat exchanger for the furnace when the house is calling for heat. compare this difference to that of your underground pipes...this shoudl give you an idea of what you are losing
no heat exchanger....I'm h2o heat throughout, cental ac only
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tbone

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Re: Heat loss from under ground pipes
« Reply #14 on: February 29, 2012, 04:53:33 PM »
Anyone know an equation for calculating gpm that doesn't involve knowing BTUs?
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