Pipe Insulation

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B

ACK

TO

B

ASICS

:

P

IPE

I

NSULATION

Todd Jekel, Ph.D., P.E. Assistant Director, IRC INDUSTRIAL REFRIGERATION CONSORTIUM

RESEARCH & TECHNOLOGY FORUM

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• Basics of insulation & insulation systems

1

• Industry insulation recommendations

2

• Annual energy simulation

3

• Conclusions

4

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Why do we insulate piping?

• Preserve the refrigerant state by limiting heat

loss or gain

• Limit temperatures of jacketing to

– protect personnel (high temperature)

– protect product/space/system (low temperature)

from free water (condensation) or weight (ice formation)

• Protect the underlying piping from corrosion by

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How Insulation Works

• Uses low thermal conductivity materials

• Material manufactured

with trapped bubbles of

low thermal conductivity

blowing agents

• Reduction of surface temperature

relative to ambient further reduces

convection & radiation and inhibits

condensation & ice growth

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Heat Transfer

• One-dimensional, steady-state, conduction

heat transfer in cylindrical coordinates

𝑄̇ =

2𝜋𝜋𝜋 ∙ 𝑇

_{ln 𝑑}

𝑠,1

− 𝑇

𝑠,2

2

⁄

𝑑

1

• 𝜋 is a property of the insulation chosen

• 𝑑

₂

= 𝑑

₁

+ 2 ∙ 𝑡

• 𝑄̇ is a heat rate, i.e. units of Btu/hr, tons, kW

_t

d₂ d₁

T_S,2 T_S,1

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Heat Transfer, continued

• Convection

𝑄

_𝑐

̇ = ℎ ∙ 𝐴

₂

∙ 𝑇

_𝑠,2

− 𝑇

_𝑜

– ℎ is a property of the orientation, diameter,

velocity, and temperatures

– 𝐴₂ = 𝜋 ∙ 𝑑₁ + 2 ∙ 𝑡 ∙ 𝜋

– 𝑄_𝑐̇ is a heat rate, i.e. units of Btu/hr, tons, kW_t

h k

𝑄_𝑐̇

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Heat Transfer, continued

• Radiation

𝑄

_𝑟

̇ = 𝜀 ∙ 𝜎 ∙ 𝐴

₂

∙ 𝑇

_𝑠,24

− 𝑇

_𝑜4

– 𝑄_𝑟̇ is a heat rate, i.e. units of Btu/hr, tons, kW_t

– 𝜀 is the surface emittance

– 𝜎 is the Stefan Boltzmann constant

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Heat Transfer, cont.

• Increasing the insulation thickness

– increases the conduction resistance, reducing

heat transfer & surface temperature relative to surroundings

– increases the area over which convection &

radiation acts, increasing relative heat transfer

– Does an “optimum” exist?

• Energy Balance on jacket surface

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Design Analysis

• Assumptions:

– Ambient conditions: quiescent, 95°F, outdoors

– Pipe at uniform temperature

– Insulation 𝜋 = 0.0195 Btu/hr-ft2-°F

– Aluminum jacket (weathered) 𝜀= 0.3

𝑄_𝑟̇ _𝑄 𝑐̇ 𝑄̇ 𝑇_𝑜 𝑇_𝑠,1 𝑇_𝑠,2 𝑑₂ 𝑑₁

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Observations

• Used NAIMA’s 3EPlus (v. 4) to verify the

analysis with good agreement

• For the range of insulation thicknesses in our

industry, an “optimum” insulation thickness

doesn’t occur

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I

NDUSTRY

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Industry Recommendations

• Outdoor horizontal piping

– 100°F dry bulb, 90% relative humidity,

wind velocity 7.5 mph, metal jacket

• Indoor horizontal piping

wind velocity 0 mph, PVC jacket, or

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IIAR Recommended Thickness

Nominal Pipe Size (in) Service Temperature (°F) -40 -20 0 +20 +40 2 3.5 3 3 2.5 2 2-½ 3.5 3 3 2.5 2.5 3 4 3.5 3.5 3 2.5 4 4.5 3.5 3.5 3 2.5 5 4.5 4 3.5 3 2.5 6 4.5 4.5 3.5 3 2.5 8 5 4.5 4.5 3 2.5 10 5.5 5 4.5 3.5 3 12 5.5 5 4.5 3.5 3

Table 7-3 IIAR Ammonia Refrigeration Piping Handbook Extruded Polystyrene insulation on outdoor piping

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IIAR Recommended Thickness

Nominal Pipe Size (in) Service Temperature (°F) -40 -20 0 +20 +40 2 2.5 2 2 1.5 1.5 2-½ 2.5 2 2 1.5 1.5 3 2.5 2.5 2 2 1.5 4 3 2.5 2 2 1.5 5 3 2.5 2.5 2 1.5 6 3 2.5 2.5 2 1.5 8 3 2.5 2.5 2 1.5 10 3 3 2.5 2 1.5 12 3.5 3 2.5 2 1.5

Table 7-4 IIAR Ammonia Refrigeration Piping Handbook Extruded Polystyrene insulation on indoor piping (90°F)

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IIAR Recommended Thickness

Nominal Pipe Size (in) Service Temperature (°F) -40 -20 0 +10 2 4 3 2 2 2-½ 4 3 2 2 3 4 3.5 2.5 2 4 4.5 3.5 2.5 2 5 4.5 3.5 2.5 2 6 4.5 4 3 2 8 5 4 3 2.5 10 5 4 3 2.5 12 5.5 4.5 3 2.5

Table 7-5 IIAR Ammonia Refrigeration Piping Handbook Extruded Polystyrene insulation on indoor piping (40°F)

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Energy Analysis

• Previous analysis was for design conditions,

but what about the energy impact over the

year?

• To estimate that, will need

– Weather data, including wind & solar

– Model that accounts for the solar gain

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Weather Values

• Data excerpt for Madison, WI TMY2 data

Month Day Hour GHR DB DP WS Btu/hr-ft2_°F _°F _mph 1 1 6 0.00 34.0 28.9 13.87 1 1 7 0.00 33.6 29.7 13.20 1 1 8 2.54 33.4 30.2 12.30 1 1 9 12.05 33.1 30.0 11.63 1 1 10 26.31 33.4 30.9 10.74 1 1 11 43.11 33.6 31.5 10.07

• Descriptions

– GHR = Global Horizontal Radiation (solar),

Btu/hr-ft2_-F

– DB = Dry bulb temperature, deg F

– DP = Dewpoint temperature, deg F

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Model Description

• Split insulation in half

– Upper half is exposed to solar radiation

– Lower half is not

– Both halves get the same convection coefficient

• Horizontal cylinder in cross-flow or natural convection depending on wind speed

• Hourly calculation to determine the total load

on the piping due to heat gain through

insulation

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Model

𝑄_𝑟,𝑢̇ _𝑄 𝑐,𝑢̇ 𝑄_𝑢̇ 𝑇_𝑜 𝑇_𝑠,1 𝑇_𝑠,𝑢 𝑑₂ 𝑑₁ 𝑄̇ _𝑙 𝑄_𝑟,𝑙̇ 𝑄_𝑐,𝑙̇ 𝑇_𝑠,𝑙 𝐺𝐺𝐺 WS

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Results for Piping @ -40°F

Pipe Size [in] Insulation Thickness [in] Annual Heat Gain [ton-hrs per 100 ft] Annual Cost per 100 ft 8” 5” 1,014 $180 8” 3” 1,456 $260 4” 4.5” 707 $125 4” 3” 907 $160 2” 3.5” 562 $100 2” 3” 610 $110 Assumptions • Madison, WI • 2.4 HP/ton • $0.10/kWh

Pipe Size [in] Insulation Thickness [in] Annual Heat Gain [ton-hrs per 100 ft] Annual Cost per 100 ft 8” 5” 3,730 $670

Failed Insulation Estimate†

Properly Maintained Insulation Estimate

† Factor of 2 loss of insulation thermal conductivity on top, factor of 6 on the bottom

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Results for Piping @ +20°F

Pipe Size [in] Insulation Thickness [in] Annual Heat Gain [ton-hrs per 100 ft] Annual Cost per 100 ft 8” 3” 540 $36 4” 3” 224 $22 2” 2.5” 165 $16 Assumptions • Madison, WI • 0.9 HP/ton • $0.10/kWh

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Results for Piping @ -40°F

Pipe Size [in] Insulation Thickness [in] Annual Heat Gain [ton-hrs per 100 ft] Annual Cost per 100 ft 8” 5” 1,340 $240 8” 3” 1,920 $340 4” 4.5” 935 $170 4” 3” 1,200 $215 2” 3.5” 740 $135 2” 3” 805 $145 Assumptions • Tampa, FL • 2.4 HP/ton • $0.10/kWh

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Results for Piping @ +20°F

Pipe Size [in] Insulation Thickness [in] Annual Heat Gain [ton-hrs per 100 ft] Annual Cost per 100 ft 8” 3” 1,010 $68 4” 3” 625 $42 2” 2.5” 465 $31 Assumptions • Tampa, FL • 0.9 HP/ton • $0.10/kWh