BACK TO BASICS:PIPE INSULATION

Todd Jekel, Ph.D., P.E.Assistant Director, IRC

INDUSTRIAL REFRIGERATION CONSORTIUM

RESEARCH & TECHNOLOGY FORUM

MAY 2-3, 2012

• Basics of insulation & insulation systems1

• Industry insulation recommendations2

• Annual energy simulation3

• Conclusions4

Overview

INSULATION BASICS

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 keeping the piping cold & dry (vapor retarder)

How Insulation Works• Uses low thermal conductivity materials• Material manufactured

with trapped bubbles oflow thermal conductivityblowing agents

• Reduction of surface temperature relative to ambient further reduces convection & radiation and inhibits condensation & ice growth

Heat Transfer

• One-dimensional, steady-state, conduction heat transfer in cylindrical coordinates

��𝑄 =2𝜋𝜋𝜋𝜋𝜋𝜋 � 𝑇𝑇𝑠𝑠,1 − 𝑇𝑇𝑠𝑠,2

ln ⁄𝑑𝑑2 𝑑𝑑1• 𝜋𝜋 is a property of the insulation chosen• 𝑑𝑑2 = 𝑑𝑑1 + 2 � 𝑡𝑡• ��𝑄 is a heat rate, i.e. units of Btu/hr, tons, kWt

d2

d1

TS,2TS,1

k

Heat Transfer, continued

• Convection𝑄𝑄𝑐𝑐 = ℎ � 𝐴𝐴2 � 𝑇𝑇𝑠𝑠,2 − 𝑇𝑇𝑜𝑜

– ℎ is a property of the orientation, diameter, velocity, and temperatures

– 𝐴𝐴2 = 𝜋𝜋 � 𝑑𝑑1 + 2 � 𝑡𝑡 � 𝜋𝜋– 𝑄𝑄𝑐𝑐 is a heat rate, i.e. units of Btu/hr, tons, kWt

hk

𝑄𝑄𝑐𝑐

TS,2

Heat Transfer, continued

• Radiation𝑄𝑄𝑟𝑟 = 𝜀𝜀 � 𝜎𝜎 � 𝐴𝐴2 � 𝑇𝑇𝑠𝑠,2

4 − 𝑇𝑇𝑜𝑜4

– 𝑄𝑄𝑟𝑟 is a heat rate, i.e. units of Btu/hr, tons, kWt

– 𝜀𝜀 is the surface emittance– 𝜎𝜎 is the Stefan Boltzmann constant– 𝐴𝐴2 = 𝜋𝜋 � 𝑑𝑑1 + 2 � 𝑡𝑡 � 𝜋𝜋

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��𝑄 = 𝑄𝑄𝑐𝑐 + 𝑄𝑄𝑟𝑟

Design Analysis

• Assumptions:– Ambient conditions: quiescent, 95°F, outdoors– Pipe at uniform temperature– Insulation 𝜋𝜋 = 0.0195 Btu/hr-ft-°F– Aluminum jacket (weathered) 𝜀𝜀= 0.3

𝑄𝑄𝑟𝑟 ��𝑄𝑐𝑐

��𝑄

𝑇𝑇𝑜𝑜

𝑇𝑇𝑠𝑠,1

𝑇𝑇𝑠𝑠,2

𝑑𝑑2

𝑑𝑑1

Analysis (Load v. 8” Pipe Temperature)

Analysis (Load v. 4” Pipe Temperature)

Analysis (Load v. Pipe Size @ -40°F)

Analysis (Surface Temperature)

Analysis

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

INDUSTRYRECOMMENDATIONS

Industry Recommendations

• Outdoor horizontal piping– 100°F dry bulb, 90% relative humidity,

wind velocity 7.5 mph, metal jacket

• Indoor horizontal piping– 90°F dry bulb, 80% relative humidity,

wind velocity 0 mph, PVC jacket, or– 40°F dry bulb, 90% relative humidity,

wind velocity 0 mph, PVC jacket

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 HandbookExtruded Polystyrene insulation on outdoor piping

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 HandbookExtruded Polystyrene insulation on indoor piping (90°F)

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 HandbookExtruded Polystyrene insulation on indoor piping (40°F)

SIMULATION

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– Refrigeration system efficiency

Weather Values

• Data excerpt for Madison, WI TMY2 dataMonth Day Hour GHR DB DP WS

Btu/hr-ft2 °F °F mph1 1 6 0.00 34.0 28.9 13.871 1 7 0.00 33.6 29.7 13.201 1 8 2.54 33.4 30.2 12.301 1 9 12.05 33.1 30.0 11.631 1 10 26.31 33.4 30.9 10.741 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– WS = Wind speed, mph

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

Model

𝑄𝑄𝑟𝑟,𝑢𝑢 𝑄𝑄𝑐𝑐,𝑢𝑢

𝑄𝑄𝑢𝑢

𝑇𝑇𝑜𝑜

𝑇𝑇𝑠𝑠,1

𝑇𝑇𝑠𝑠,𝑢𝑢

𝑑𝑑2

𝑑𝑑1

��𝑄𝑙𝑙

𝑄𝑄𝑟𝑟,𝑙𝑙

𝑄𝑄𝑐𝑐,𝑙𝑙

𝑇𝑇𝑠𝑠,𝑙𝑙

𝐺𝐺𝐺𝐺𝐺𝐺

WS

Refrigeration System Efficiency

Results for Piping @ -40°FPipe Size [in] Insulation

Thickness[in]

Annual HeatGain [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 HeatGain [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

Results for Piping @ +20°FPipe Size [in] Insulation

Thickness[in]

Annual HeatGain [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

Pipe Size [in] Insulation Thickness

[in]

Annual HeatGain [ton-hrs

per 100 ft]

Annual Cost per 100 ft

8” 3” 1,826 $120

Failed Insulation Estimate†

Properly Maintained Insulation Estimate

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

Results for Piping @ -40°FPipe Size [in] Insulation

Thickness[in]

Annual HeatGain [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

Pipe Size [in] Insulation Thickness

[in]

Annual HeatGain [ton-hrs

per 100 ft]

Annual Cost per 100 ft

8” 5” 4,900 $880

Failed Insulation Estimate†

Properly Maintained Insulation Estimate

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

Results for Piping @ +20°FPipe Size [in] Insulation

Thickness[in]

Annual HeatGain [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

Pipe Size [in] Insulation Thickness

[in]

Annual HeatGain [ton-hrs

per 100 ft]

Annual Cost per 100 ft

8” 3” 3,460 $230

Failed Insulation Estimate†

Properly Maintained Insulation Estimate

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

Conclusions

• IF insulation system is properly maintained the parasitic load is relatively low

• Failed insulation systems NOT ONLY effect the heat load, BUT ALSO put the underlying piping at increased risk for corrosion

Resources

• IIAR Ammonia Refrigeration Piping Handbook, Chapter 7

• ASHRAE 2010 Refrigeration Handbook, Chapter 10

• NAIMA 3EPlus (http://www.pipeinsulation.org/)

QUESTIONS?