Page 236 - Facility Piping Systems Handbook for Industrial, Commercial, and Healthcare Facilities

HEAT TRANSFER, INSULATION, AND FREEZE PROTECTION

5.20 CHAPTER FIVE

Substituting in Eq. (5.5)

HF = 200 − 80 = 120 = 120
.
.
( 249 /023. ) + 068. 92 + 068. 9.888
⋅
= 12 1Btu/h ft 2
.
To find the actual heat loss per linear foot, use the formula:
HL = HF × A

⋅
×
.
.
.
= 12 1 3 34 = 40 4 Btu/h ft (5.6)
To find the heat loss from the entire system, find the total length of run and multiply
that figure by HL. In order to do an accurate calculation, the different lengths of pipe run in
various temperature-controlled areas will each have to be calculated separately.
To find the surface temperature of the insulation exterior, use the formula:
×
ST = T 2 + ( HF SFR)

+
= 80 + 12 1 0 68(. × . ) = 80 8 2 88 2. = . F ° (5.7)
In order to calculate the heat loss from a tank, the only substitution in the above formula
should be AT instead of ET, and there is no need to find HL. To find the heat loss from the
whole tank, multiply HF by the area of the tank.
When calculating the heat gain for a cold line, the same formula as for a hot pipe is used,
except that the result is the amount of heat gained by the pipe from the ambient air.
General Design Considerations

The following paragraphs describe the general selection criteria for different materials
under average situations.
1. Domestic cold water or chilled water service. Fiberglass with ASJ should be secured
with staples. The reasons are that fiberglass is the least expensive insulation to install
and the staples can be applied in any weather and regardless of the dust conditions
on the job. Fittings should be covered with plastic-fitting covers. The staples must be
coated with a vapor barrier mastic. If the working conditions are reasonably dust-free,
self-sticking lap joints are a cost-saving alternative.
2. Domestic hot water, hot water return, and other services under 240°F (114°C). The
same materials as for cold water service (see number 1 above) are used.
3. Hot tanks under 240°F (114°C). Stiff fiberglass board covered with a breather coat of
mastic or fiberglass cloth should be used. Insulating cement can be used if additional
protection from abuse is needed.
4. Cold (not cryogenic) tanks. Rubber insulation with no jacket can be used if the area
where it will be installed is reasonably clean. A jacket is not required and the surface
can be painted. If there is a problem with dust or dirt, the material of choice would be
fiberglass boards with a coating of cut back mastic as a vapor barrier.
5. Outdoor service. Rubber insulation with an ASJ should be used in order to resist mois-
ture penetration into the insulation. The final cover should be aluminum secured with
bands or a lock seam. Field experience has shown that screws often fall out if subject
to vibration.
6. Sanitary exterior. The best choice is a stainless steel jacket if the cleaning is to be
severe. If not, a plastic jacket is more cost effective.

Downloaded from Digital Engineering Library @ McGraw-Hill (www.accessengineeringlibrary.com)
Copyright © 2009 The McGraw-Hill Companies. All rights reserved.
Any use is subject to the Terms of Use as given at the website.