Heat Loss in a Hot Water Pipe System

  • Thread starter Ouabache
  • Start date
  • #26
FredGarvin
Science Advisor
5,066
8
Ivan Seeking said:
Not possible. And I would add that graduation is the beginning of learning. Nothing is more dangerous in the real world than a new graduate.
Yeah. By "very tough" I meant impossible.

I do think recent graduates do come in two flavors; Those that have spent 4 years learning that they know squat and those that think they learned everything in 4 years. The latter are the dangerous ones.
 
  • #27
Ivan Seeking
Staff Emeritus
Science Advisor
Gold Member
7,213
176
FredGarvin said:
I do think recent graduates do come in two flavors; Those that have spent 4 years learning that they know squat and those that think they learned everything in 4 years. The latter are the dangerous ones.
Fair enough. I still don't know squat but at least I know that...and I have forgotten half the squat that I used to think I knew...:biggrin:
 
  • #28
FredGarvin
Science Advisor
5,066
8
Ivan Seeking said:
Fair enough. I still don't know squat but at least I know that...and I have forgotten half the squat that I used to think I knew...:biggrin:
I agree. The more I learn, the more I realize just how much I don't know.
 
  • #29
Ouabache
Science Advisor
Homework Helper
1,340
7
Thanks Artman and Astronuc for your recent suggestions on this analysis. I will also try and find a recent ASHRAE Applications Handbook. It sounds like a useful reference for these sorts of questions.
 
  • #30
1,490
22
Ouabache said:
Thanks Artman and Astronuc for your recent suggestions on this analysis. I will also try and find a recent ASHRAE Applications Handbook. It sounds like a useful reference for these sorts of questions.
It is.

Also, why don't you post the specifics of the project, such as the lengths of pipe of various sizes (such as 10' of 3/4" and insulated or not) and the amount of time the system stands idle, expected ambient temperature around the pipes. For life cycle costs you will also need the length of time for payback, the cost expected to do the project, and the type of water heater energy (natural gas, LPG, electric, oil, heatpump, etc) and, if you want to determine the cost of that energy we can all use the same information.

It would be a fun exercise for us and we could check your calculations.
 
  • #31
2
0
Hi

I hope you do not mind me joining this discussion, but I found this thread on a Google search. I have a related problem.

I am thinking of installing a set of Glass tube heat pipe solar pannels to help run my underfloor heating system. My only problem is that they can only be situated about 50 meters from the house, so the flow and return pipes will have to be burried underground. What I would like to know is how much heat loss I can expect in the pipes?

The pipes will be 30 - 40 mm diam Polyethylene water pipe, burried 0.75 m below ground. I am not sure how I could insulate these - I would need some type of waterproof foam plastic lagging as glass fibre would pass ground water. When the system is working (sun shining) the flow temperature will be 40-50 C with a return of 10-20 C lower. When it matters, in the winter, I assume a ground temperature of 2-10 C . This would effectively be a steady state system as the main issue is how much heat can I get during a winterday when the sun is shinning.

Any help or advice would be most welcome.

PJG
 
  • #32
1,490
22
pjgregory said:
Hi

I hope you do not mind me joining this discussion, but I found this thread on a Google search. I have a related problem.

I am thinking of installing a set of Glass tube heat pipe solar pannels to help run my underfloor heating system. My only problem is that they can only be situated about 50 meters from the house, so the flow and return pipes will have to be burried underground. What I would like to know is how much heat loss I can expect in the pipes?

The pipes will be 30 - 40 mm diam Polyethylene water pipe, burried 0.75 m below ground. I am not sure how I could insulate these - I would need some type of waterproof foam plastic lagging as glass fibre would pass ground water. When the system is working (sun shining) the flow temperature will be 40-50 C with a return of 10-20 C lower. When it matters, in the winter, I assume a ground temperature of 2-10 C . This would effectively be a steady state system as the main issue is how much heat can I get during a winterday when the sun is shinning.

Any help or advice would be most welcome.

PJG
Fill the trench around the pipes with perlite insulating concrete.
provides a k factor range of 0.58 to 0.66 Btu-inch/h-ft2-F (0.085 to 0.095 W/m-k).
 
  • #33
2
0
Hi Artman

Thank you for your response. Let me see if I understand this.

The heat loss in Watts is

Watts = k * Area * Temperature Differnce / Thickness Material (L)

So assume k for Perlite concrete is 0.09. Then simplifying for one pipe laid in a cylindrical tube of concrete radius 0.25m (L), the area per unit length would be 1.57 so for 50m of pipe and a 40 degree K temperature difference, the loss would be:

Loss = 0.09*1.57*50 *40/0.25 = 1130 watts.

So I will need to add about 1Kwatt to estimated load for the house to compensate for the heat loss in the underground pipes.

I have found a supplier of Perlite products in Italy. Now all I have to do is work out how to explain this to my builder in Italian.

Thanks again

PJG
 
  • #34
1,490
22
Here is another possibility to consider. Preinsulated pipe. I don't know which would be cheaper or easier.

http://www.maxx-r.com/?gclid=CP-Z4IiN3YQCFRs1Swod6jZ6Ww" [Broken]
 
Last edited by a moderator:
  • #35
1
0
copper water interface heat transfer

Hello,

Great discussion. Any references for a similar problem?

Copper pipe is bathed in a hot material.
Copper pipe has cooler water flowing through the pipe.

How to calculate heat flow through the copper pipe to moving water?

Non laminar flow is thought to improve heat transfer to water.
 
  • #36
1,490
22
Hello,

Great discussion. Any references for a similar problem?

Copper pipe is bathed in a hot material.
Copper pipe has cooler water flowing through the pipe.

How to calculate heat flow through the copper pipe to moving water?

Non laminar flow is thought to improve heat transfer to water.
What you are describing here is a unit called a "heat exchanger". The calculations for a heat exchanger can be rather complex. Dealing with the mediums, the temperature difference entering to leaving of both the transfer medium and the product being heated, the materials used in the exchanger, the insulating/transfer values of the tube side and shell sides. For references to this problem try searching for information on "Copper tube heat exchangers."
 

Related Threads on Heat Loss in a Hot Water Pipe System

  • Last Post
Replies
2
Views
999
  • Last Post
Replies
6
Views
1K
Replies
2
Views
921
  • Last Post
Replies
15
Views
2K
Replies
1
Views
3K
  • Last Post
Replies
2
Views
5K
Replies
4
Views
5K
Replies
12
Views
29K
Replies
1
Views
3K
Replies
1
Views
5K
Top