Pipe Insulation

BACK TO BASICS: PIPE INSULATION INDUSTRIAL REFRIGERATION CONSORTIUM RESEARCH & TECHNOLOGY FORUM MAY 2-3, 2012

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

Overview 1

• Basics of insulation & insulation systems

2

• Industry insulation recommendations

3

• Annual energy simulation

4

• Conclusions

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 of low thermal conductivity blowing agents • Reduction of surface temperature relative to ambient further reduces convection & radiation and inhibits condensation & ice growth

Heat Transfer

TS,1

d2

TS,2

d1

k

• One-dimensional, steady-state, conduction heat transfer in cylindrical coordinates 2𝜋𝜋𝜋 ∙ 𝑇𝑠,1 − 𝑇𝑠,2 𝑄̇ = ln 𝑑2 ⁄𝑑1 • 𝑘 is a property of the insulation chosen • 𝑑2 = 𝑑1 + 2 ∙ 𝑡 • 𝑄̇ is a heat rate, i.e. units of Btu/hr, tons, kWt

TS,2

Heat Transfer, continued • Convection 𝑄𝑐̇ = ℎ ∙ 𝐴2 ∙ 𝑇𝑠,2 − 𝑇𝑜

k

h

– ℎ is a property of the orientation, diameter, velocity, and temperatures – 𝐴2 = 𝜋 ∙ 𝑑1 + 2 ∙ 𝑡 ∙ 𝐿 – 𝑄𝑐̇ is a heat rate, i.e. units of Btu/hr, tons, kWt

𝑄𝑐̇

Heat Transfer, continued • Radiation 𝑄𝑟̇ = 𝜀 ∙ 𝜎 ∙ 𝐴2 ∙ 𝑇𝑠,2 4 − 𝑇𝑜 4

– 𝑄𝑟̇ is a heat rate, i.e. units of Btu/hr, tons, kWt – 𝜀 is the surface emittance – 𝜎 is the Stefan Boltzmann constant – 𝐴2 = 𝜋 ∙ 𝑑1 + 2 ∙ 𝑡 ∙ 𝐿

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 𝑄̇ = 𝑄𝑐̇ + 𝑄𝑟̇

Design Analysis • Assumptions: – Ambient conditions: quiescent, 95°F, outdoors – Pipe at uniform temperature – Insulation 𝑘 = 0.0195 Btu/hr-ft2-°F – Aluminum jacket (weathered) 𝜀= 0.3 𝑇𝑜

𝑇𝑠,2

𝑄𝑟̇

𝑇𝑠,1 𝑑1

𝑑2

𝑄𝑐̇

𝑄̇

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

INDUSTRY RECOMMENDATIONS

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

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

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

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 data Month

Day

Hour

1 1 1 1 1 1

1 1 1 1 1 1

6 7 8 9 10 11

GHR Btu/hr-ft2 0.00 0.00 2.54 12.05 26.31 43.11

DB °F 34.0 33.6 33.4 33.1 33.4 33.6

DP °F 28.9 29.7 30.2 30.0 30.9 31.5

WS mph 13.87 13.20 12.30 11.63 10.74 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

𝐺𝐺𝐺

𝑇𝑠,𝑢

WS

̇ 𝑄𝑟,𝑢

𝑇𝑠,1 𝑑1

𝑑2

𝑇𝑠,𝑙

𝑄̇𝑙

̇ 𝑄𝑟,𝑙

̇ 𝑄𝑐,𝑢 𝑄𝑢̇ ̇ 𝑄𝑐,𝑙

𝑇𝑜

Refrigeration System Efficiency

Results for Piping @ -40°F Properly Maintained Insulation Estimate Pipe Size [in]

Insulation Thickness [in]

Annual Heat Annual Cost Gain [ton-hrs per 100 ft 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

Failed Insulation Estimate† Pipe Size [in]

8”

Insulation Thickness [in] 5”

Annual Heat Annual Cost Gain [ton-hrs per 100 ft per 100 ft] 3,730

$670

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

Results for Piping @ +20°F Properly Maintained Insulation Estimate Pipe Size [in]

Insulation Thickness [in]

Annual Heat Annual Cost Gain [ton-hrs per 100 ft 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

Failed Insulation Estimate† Pipe Size [in]

8”

Insulation Thickness [in] 3”

Annual Heat Annual Cost Gain [ton-hrs per 100 ft per 100 ft] 1,826

$120

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

Results for Piping @ -40°F Properly Maintained Insulation Estimate Pipe Size [in]

Insulation Thickness [in]

Annual Heat Annual Cost Gain [ton-hrs per 100 ft 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

Failed Insulation Estimate† Pipe Size [in]

8”

Insulation Thickness [in] 5”

Annual Heat Annual Cost Gain [ton-hrs per 100 ft per 100 ft] 4,900

$880

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

Results for Piping @ +20°F Properly Maintained Insulation Estimate Pipe Size [in]

Insulation Thickness [in]

Annual Heat Annual Cost Gain [ton-hrs per 100 ft 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

Failed Insulation Estimate† Pipe Size [in]

8”

Insulation Thickness [in] 3”

Annual Heat Annual Cost Gain [ton-hrs per 100 ft per 100 ft] 3,460

$230

† 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?