Acceptable levels of heat leak into a process cooling system 1

[jari001]

I am looking for some guidelines on how much heat leak is deemed reasonable for a -20°C glycol distribution system via the piping network. The piping network is mainly indoors and ranges from 4" sch. 40 pipe to 1" sch. 40 pipe (carbon steel) and will have 2" of either PIR or cellular glass type insulation. For the sake of running these lines in a congested area of the plant, I'm trying to determine if going to 1.5" or 1" of insulation would pose an unacceptable amount of heat gain.

I can show I will operate above the area dewpoint temperature with relatviely little insulation so I don't think that's a limiting case.

 

[georgeverghese]

Try this:
Work out an average of the TOTAL installed cost of insulation per year- $/year, ( spread out over say a short payout period of 3years) for various thicknesses ( 2inch, 1.5inch, 1inch, 0.5inch) - say each value is A. Ask an insulation contractor for these budgetary values.
Work out the heat leak per metre of piping for each of these thicknesses( kJ/m2/year), which would also include the average annual solar radiation heat leak component. This step would be the trickiest to compute.
Work out the refrigeration duty required to compensate for each of these heat leak values (kJ/m2/year).
Work out the operating cost (OPEX) of the utility enable this refrigeration for each case ($/year)- say B

Plot a graph of A+B (total of OPEX + CAPEX)on the y axis vs insulation thickness on the x axis. You will see a minimum total cost in the graph, which would be your optimum thickness. To choose between 1.5inch and 1inch, select the one with the lower total.

This method does not include the additional CAPEX of larger refrigeration equipment to make up for increased heat leak for the thinner ins cases, on the assumption that the refrigeration duty is within the duty range of a given refrigeration unit for all ins thicknesses in the range considered.

 

[shvet]

chap. 9

https://a.co/d/ddnvdk4

 

[jari001]

Thank you for the suggestions, I will look into them.

 

[LittleInch]

The other way is just to see what the temperature ends up with that level of insulation.

If you need amax of say -15C, but you end up with -12, then it won't work. The economic issue is secondary if you can't supply the users with the temperature they want.

Also at low or no flow the system will heat up faster so this might be an issue?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[IRstuff]

pose an unacceptable amount of heat gain.

Only you, the designer, and the consumers of the coolant system can answer that question. My approach would be to hunt down each of the consumers and get their usage specs for the coolant and that would dictate the heat gain allowable. I'd guess, however, that everyone that has a spec, has the design value, and no additional heat gain is tolerable without a lot of re-analysis of each of their usages.

One typically has control of insulation type, thickness, area, and coolant flow. So while decreasing insulation thickness increase heat gain, it might be possible to compensate the gain by increasing flow rate, since it's the cumulative exposure time to the thinner insulation that results in the cumulative heat gain, so faster flow means less heat gain per unit volume of coolant.

TTFN (ta ta for now)
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[georgeverghese]

For Solar radiation heat component
Heat absorbed (1) + heat re radiated out(2) + heat reflected out by cladding(3) = total annualised average incident solar radiation
Subcomponent 2 is a function of the cladding surface temp.
Check if subcomponent 3 (total reflectance) is also dependent on surface temp. See narrative in Perry Chem Engg Handbook or your text on radiative heat transfer.