Heat Loss from Copper Pipe

[Hunderliggur]

Ever wonder what the heat loss is from uninsulated copper pipe? I found this table online. http://www.engineeringtoolbox.com/copper-pipes-heat-loss-d_51.html It looks like 1" of insulation reduces the heat loss by about 88% according to this table http://www.engineeringtoolbox.com/copper-pipes-insulation-heat-loss-d_52.html

My assumption is that these figures are for pipes in air, not water, so these tables probablly won't work for an in tank heat exchanger.

For 1 1/4 copper (which I use) at 99F delta T the losses are 93 BTUH/ft uninsulated and 11 BTUH/ft insulated. For my 80 foot run in my basement from the outside (underground) entry to the storage, the losses from the supply and return combined are about 13,000 BTU/hr. Now that my heat exchanger is up and running I don't need to heat the basement anymore so the insulation is going in today! Insulation is eligible for the 15% tax credit to boot! (just put more in my attic yesterday).

[Edit: Another site for LOTS of tools of interest http://www.builditsolar.com/Tools/tools.htm ]

 

[jebatty]

Good info, and use it to advantage. No or little insulation when you want the heat in an area and plenty of insulation when you don't.

 

[Chris Hoskin]

great info, thanks. My Dad has a long run of 1 1/4" between his Multi-Heat pellet boiler and his oil boiler. We left the lines uninuslated in order to keep the workshop/garage/mudroom warmer, but the rooms are too warm and he is getting too much short cycling on the oil boiler so we are planning to insulate the lines this weekend. At this point we are just going to insulate the supply lines and leave the returns uninsulated because we want SOME heat loss into the mudroom especially. Kind of knew this would improve things, but its nice to have the math behind it!

Chris

 

[Jeff S]

It,s incredible how much heat can be lost to unlivable areas.I insulated all my pex tubing in my crawl space.If in the future I decide to heat my floors I will do it on purpose with pex and transfer plates and carefully insulating under them,its poor economy to just leave those pipes uninsulated and hope that the heat loss will accidentally warm my floors and not escape out the side walls.

 

[Jeff S]

I bet those pipe don't recognize whether they are surrounded by air or water but only notice the temperature difference and will transfer those same BTU,s to your storage water.

 

[Hunderliggur]

I bet those pipe don't recognize whether they are surrounded by air or water but only notice the temperature difference and will transfer those same BTU,s to your storage water.

Probably true, but the still air around a pipe will rise in temp lowering the delta T. Water has better conduction so the sustained heat transfer would probably be greater. So I guess for sizing an in tank HX, these figures would be sufficient. I wonder how this compares to some of our users in tank coil heat exchangers. It would be nice if the math actually worked out.

 

[Floydian]

I don't know Jeff, I think the difference would be huge. In the heat transfer game conduction is king. When water gets involved when you don't want it to heat loss can become staggering. Like a heated uninsulated slab with a high water table or underground insulated pipe gone wrong.

Just my thoughts,
Noah

 

[Jeff S]

It would be nice to find some hard data on this subject.

 

[kabbott]

I get about 600 btu/hr per foot with my in tank coil (200 feet 3/4 copper) at ~30 degree exchanger in - storage water top delta. I think this is about what fin-tube is
rated at in air but at a much higher delta?

 

[DaveBP]

Take a piece of styrofoam and a piece of copper and put them in your freezer overnight. Now they are the same temperature. Pick them up in your bare hand and tell me which one is colder. Your nerves in your fingers are sensitive to heat difference and heat loss. The copper feels much colder because it is drawing heat away from your skin much faster than the foam plastic, even at the same temperatures.

Fill a bath tub with 50F water on a day that is 50F outside. Take off your clothes and stand outside for a minute (best to do this in the dark after the neighbors have retired for the night). Now go inside and get down into the tub. Feel the difference?

Those are two dramatic ways to get a personal experience of heat loss and how the surrounding medium can effect it at the same temperature. A temperature difference will only make it more noticeable and the same lesson applies.

 

[Fred61]

I'm sending this post from jail. Tried the bathtub experiment and apparently the neighbors didn't like what they saw or had trouble seeing. Posting bail soon. Almost time to light my daily fire. I light one fire a day , usually start it at four o:clock or so and charge my tank. The boiler master switch is usually in the off position by 9:30. I insulated the pipes and tank over time to maintain about 65 °F in my unfinished basement for the hours that the boiler isn't running. When the boiler is running, the temperature in the basement gets up to 72 °F and that slowly stratifies up to the living space for the next few hours. Therefore my room thermostats usually don't call for heat until the wee hours of the morning. The only exception is my mudroom which is over an unheated portion of the basement and has in-floor radiant. Pretty scientific, I would say!

 

[DaveBP]

You're lucky your neighbors busted you, Fred. I forgot to warn about having your wife see you experimenting like this. That could make jail seem fun.

 

[Fred61]

I bet those pipe don't recognize whether they are surrounded by air or water but only notice the temperature difference and will transfer those same BTU,s to your storage water.

Which is a better conductor, water or air? Would you be happier standing in water or air when a lightning bolt hits 50 yards away?

 

[Fred61]

I bet those pipe don't recognize whether they are surrounded by air or water but only notice the temperature difference and will transfer those same BTU,s to your storage water.

Which is a better conductor, water or air? Would you be happier standing in water or air when a lightning bolt hits 50 yards away?

Ever get tired of waiting for a pipe assembly that you just soldered to cool and picked it up and threw it in Fido's water dish. Cooled alot faster didn't it? If that pipe had hot water running through it there would be many more BTUs dumped alot faster than if it was in air.

 

[Jeff S]

That's what I like about this forum,guys bouncing their thoughts off each other,I was only taking the account of the temperature difference of the pipe and its surroundings with no regards to the conductivity (or lack of it) of the surrounding material.Looking into my Modern hydronic heating book by Siegenthaler I re-learned that the heat capacity of water is 62.4 Btu/cubic ft./deg.F compared to Air that has a heat capacity of .018 Btu/cubic ft.deg.F. Siegenthaler has coined the non scientific phrase (Water is 3500 more times more"Thermally concentrated " than Air).Thanks guys for your persistent illustrations.

Can I take those same Btu loss figures that were shown in the chart for air and multiply them by 3500 for a heat exchanger in water ?This I'm not sure of but if it is that's an incredible amount of heat transfer.I'm open to your thoughts.

 

[Hunderliggur]

Emperically, kabbott is getting 600 BTU/Hr/ft at delta 30F with 3/4 Cu. The chart says 29 BTU/Hr/Ft at delta 40F for 3/4 Cu. So based on kabbott's experience I would say multiply by 20 to 30.

 

[Hunderliggur]

Emperically, kabbott is getting 600 BTU/Hr/ft at delta 30F with 3/4 Cu. The chart says 29 BTU/Hr/Ft at delta 40F for 3/4 Cu. So based on kabbott's experience I would say multiply by 20 to 30.

 

[Jeff S]

How much does Kabbott's boiler produce? surely you can't transfer more heat than you have all though you may have the capability of doing more if it were available.I believe his delta was 30*,what if it were 100* ?
I don't even know if you even apply heat capacity to heat transfer,would still like to see some hard data on the subject.

 

[kabbott]

How much does Kabbott's boiler produce? surely you can't transfer more heat than you have all though you may have the capability of doing more if it were available.I believe his delta was 30*,what if it were 100* ?
I don't even know if you even apply heat capacity to heat transfer,would still like to see some hard data on the subject.

Boiler output = 112,000 rated... it peaks over 120,000. The boiler temp stays about 30 degrees higher than the storage over a period of several hours. If the coil
was capable of transferring more heat it would pull the boiler temp down making the delta less until the heat transferred matches the boiler output. No doubt the copper will
transfer much more heat at 100 degree delta.

Raising the flow through the coil will transfer more as well. It's hard to get good solid numbers because the coil goes from the top to the bottom of the tank which may be
20-30 degrees cooler.

I am using tank average temp to calculate the stored btu, and lbs/hour x boiler delta to calculate boiler output. This is all done via a "math" rule on my nfcs system and the 2
figures are pretty close to each other... that said the btu numbers are most likely not that accurate but make a good gauge of whats going on with the system.

Off to watch the Ravens beat up on the steeltown boys :coolsmile: