Heat Gain In a Chilled Water Circuit
Heat Gain In a Chilled Water Circuit
(OP)
Hi
I'm new to the group, work in the HVAC industry and have a 'hopefully' fairy simple question for you all!
I am assessing the temperature rise of water running at 1 deg c through a copper pipe covered with SL grade styrene, which is located within the roofspace of a building. So far i have not been able to find any help in my thermodynamic texts.
Basically what i am trying to derive is the required thickness of the insulation to avoid getting an excessive temperature gain in my water circuit.
Could somone please point me in the direction of a formula which will allow me to work this out, or towards a piece of software that will be capable of working this out.
Thanks in Advance
Nathan
I'm new to the group, work in the HVAC industry and have a 'hopefully' fairy simple question for you all!
I am assessing the temperature rise of water running at 1 deg c through a copper pipe covered with SL grade styrene, which is located within the roofspace of a building. So far i have not been able to find any help in my thermodynamic texts.
Basically what i am trying to derive is the required thickness of the insulation to avoid getting an excessive temperature gain in my water circuit.
Could somone please point me in the direction of a formula which will allow me to work this out, or towards a piece of software that will be capable of working this out.
Thanks in Advance
Nathan





RE: Heat Gain In a Chilled Water Circuit
The formula you need for your situation is this:-
Q= T1-T3/((LOGe(r2/r1)/(2*3.142*L*K12))+..............
.......((LOGe(r2/r3)/2*3.142*L*K23))
where r1 is = inner radius of pipe
r2 is = outer radius of pipe
r3 is = inner radius of pipe insulation
r4 is = outer radius of pipe insulation
k12 and k23 are the thermal conductivities of the materials respectively
L is the length of pipe
T1 is the temp. inside the pipe
T3 is the temp. outside the pipe
Hope this helps
desertfox
RE: Heat Gain In a Chilled Water Circuit
http://www.pipeinsulation.org/pages/home.html
RE: Heat Gain In a Chilled Water Circuit
you should reference a heat transfer text or a mechanical engineering handbook such as Mark or Kent for the appropriate formulae on insulation. Thermodynamic texts do not deal with this type of problem. Bear in mind that too little or too much insulation will be incorrect therfore particularly check on the subject of the economic thickness of insulation which will require knowledge about the thermal conductivities of the three layers of the piping and heat transfer coefficient the latter of which will require knowledge about wind effects on the insuated piping. There may also be reflection effects from nearby objects such as ducting, air handling, aluminized coated roofing that you must also evaluated.
RE: Heat Gain In a Chilled Water Circuit
If the outer radius of insulation ro is smaller than k/h, heat transfer will increase by adding more insulation
As normally expected, for outer radii greater than the critical value an increase in insulation thickness will cause a decrease in heat transfer.
From my own experience ro is generally small enough so that any practical insulation is well above this critical value.
RE: Heat Gain In a Chilled Water Circuit
RE: Heat Gain In a Chilled Water Circuit
An interesting aside about the "critical value of insulation". I have seen a case where a company had a problem with calcium carbonate (lime) plateout in their heat exchangers. They would clean them out, and then get real good heat transfer for a couple of cycles before it dropped off sharply - because they'd exceeded the "critical value" of the calcium carbonate and it started acting like an insulator. They were having a dickens of a time trying to explain why there was such a sharp drop - they expected there would be a gradual decrease in heat transfer.
Patricia Lougheed
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