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 2 3 4 Basics of insulation & insulation systems Industry insulation recommendations Annual energy simulation 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 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 1 + 2 t Q is a heat rate, i.e. units of Btu/hr, tons, kw t
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 1 + 2 t L k T S,2 h Q c Q c is a heat rate, i.e. units of Btu/hr, tons, kw t
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 1 + 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 Q = Q c + Q r
Design Analysis Assumptions: Ambient conditions: quiescent, 95 F, outdoors Pipe at uniform temperature Insulation k = 0.0195 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
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 GHR DB DP WS Btu/hr-ft 2 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-ft 2 -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 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
Refrigeration System Efficiency
Results for Piping @ -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 $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] 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
Results for Piping @ +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 3 540 $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] 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
Results for Piping @ -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 $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] 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
Results for Piping @ +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 $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] 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
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?