BACK TO BASICS: PIPE INSULATION

Transcription

1 BACK TO BASICS: PIPE INSULATION INDUSTRIAL REFRIGERATION CONSORTIUM RESEARCH & TECHNOLOGY FORUM MAY 2-3, 2012 Todd Jekel, Ph.D., P.E. Assistant Director, IRC

2 Overview Basics of insulation & insulation systems Industry insulation recommendations Annual energy simulation Conclusions

3 INSULATION BASICS

4 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)

5 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

6 Heat Transfer T S,1 d 2 T S,2 d 1 k One-dimensional, steady-state, conduction heat transfer in cylindrical coordinates Q = 2πππ T s,1 T s,2 ln d 2 d 1 k is a property of the insulation chosen d 2 = d t Q is a heat rate, i.e. units of Btu/hr, tons, kw t

7 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 A 2 = π d t L k T S,2 h Q c Q c is a heat rate, i.e. units of Btu/hr, tons, kw t

8 Heat Transfer, continued Radiation Q r = ε σ A 2 T s,2 4 T o 4 Q r is a heat rate, i.e. units of Btu/hr, tons, kw t ε is the surface emittance σ is the Stefan Boltzmann constant A 2 = π d t L

9 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 = Q c + Q r

10 Design Analysis Assumptions: Ambient conditions: quiescent, 95 F, outdoors Pipe at uniform temperature Insulation k = Btu/hr-ft 2 - F Aluminum jacket (weathered) ε= 0.3 T o Q r Q c T s,2 T s,1 d 1 Q d 2

11 Analysis (Load v. 8 Pipe Temperature)

12 Analysis (Load v. 4 Pipe Temperature)

13 Analysis (Load v. Pipe -40 F)

14 Analysis (Surface Temperature)

15 Analysis

16 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

17 INDUSTRY RECOMMENDATIONS

18 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

19 IIAR Recommended Thickness Table 7-3 IIAR Ammonia Refrigeration Piping Handbook Extruded Polystyrene insulation on outdoor piping Nominal Pipe Size (in) Service Temperature ( F) ½

20 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) ½

21 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) ½

22 SIMULATION

23 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

24 Weather Values Data excerpt for Madison, WI TMY2 data Month Day Hour GHR DB DP WS Btu/hr-ft 2 F F mph Descriptions GHR = Global Horizontal Radiation (solar), Btu/hr-ft 2 -F DB = Dry bulb temperature, deg F DP = Dewpoint temperature, deg F WS = Wind speed, mph

25 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

26 Model GGG Q r,u Q c,u T o T s,u WS T s,1 d 1 d 2 Q l Q u Q c,l T s,l Q r,l

27 Refrigeration System Efficiency

28 Results for -40 F Properly Maintained Insulation Estimate Pipe Size [in] Insulation Thickness [in] Annual Heat Gain [ton-hrs per 100 ft] Annual Cost per 100 ft 8 5 1,014 $ ,456 $ $ $ $ $110 Assumptions Madison, WI 2.4 HP/ton $0.10/kWh Failed Insulation Estimate Pipe Size [in] Insulation Thickness [in] Annual Heat Gain [ton-hrs per 100 ft] Annual Cost per 100 ft 8 5 3,730 $670 Factor of 2 loss of insulation thermal conductivity on top, factor of 6 on the bottom

29 Results for +20 F Properly Maintained Insulation Estimate Pipe Size [in] Insulation Thickness [in] Annual Heat Gain [ton-hrs per 100 ft] Annual Cost per 100 ft $ $ $16 Assumptions Madison, WI 0.9 HP/ton $0.10/kWh Failed Insulation Estimate Pipe Size [in] Insulation Thickness [in] Annual Heat Gain [ton-hrs per 100 ft] Annual Cost per 100 ft 8 3 1,826 $120 Factor of 2 loss of insulation thermal conductivity on top, factor of 6 on the bottom

30 Results for -40 F Properly Maintained Insulation Estimate Pipe Size [in] Insulation Thickness [in] Annual Heat Gain [ton-hrs per 100 ft] Annual Cost per 100 ft 8 5 1,340 $ ,920 $ $ ,200 $ $ $145 Assumptions Tampa, FL 2.4 HP/ton $0.10/kWh Failed Insulation Estimate Pipe Size [in] Insulation Thickness [in] Annual Heat Gain [ton-hrs per 100 ft] Annual Cost per 100 ft 8 5 4,900 $880 Factor of 2 loss of insulation thermal conductivity on top, factor of 6 on the bottom

31 Results for +20 F Properly Maintained Insulation Estimate Pipe Size [in] Insulation Thickness [in] Annual Heat Gain [ton-hrs per 100 ft] Annual Cost per 100 ft 8 3 1,010 $ $ $31 Assumptions Tampa, FL 0.9 HP/ton $0.10/kWh Failed Insulation Estimate Pipe Size [in] Insulation Thickness [in] Annual Heat Gain [ton-hrs per 100 ft] Annual Cost per 100 ft 8 3 3,460 $230 Factor of 2 loss of insulation thermal conductivity on top, factor of 6 on the bottom

32 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

33 Resources IIAR Ammonia Refrigeration Piping Handbook, Chapter 7 ASHRAE 2010 Refrigeration Handbook, Chapter 10 NAIMA 3EPlus (

34 QUESTIONS?