Use of PCM Enhanced Insulation in the Building Envelope David W. Yarbrough, PhD, PE Jan Kosny, PhD William A. Miller, PhD, PE Building Technology Center Oak Ridge National Laboratory Oak Ridge, Tennessee, USA
Limitations Standard method to reduce heat flow is to add R-value. Limits have been reached. Adding more R-Value is not practical when space is limited.
Basic Concepts A thin layer of Phase Change Material (PCM) that maintains a constant temperature is used to control the T across a layer of insulation. The PCM stores and releases heat as the surrounding temperatures change.
PCM CAN BE CONFIGURED TWO WAYS PCMs can be localized or distributed in an insulation or some other building material. Exterior temperatures must cycle across the phase change temperature for the PCM to be useful. Materials for use in a building envelope are selected with a phase change material near the occupied space temperature. PCMs include organic materials that melt in the temperature range 60 to 90 F. Inorganic salt solutions exhibiting large heats of solution or dilution can also be used.
Without PCM Layer R24 Attic + + + + + + Ceiling 120.0 F 112.3 F 106.6 F 100.0 F 93.30 F 86.60 F 80.00 F Thermocouples Typ. Temperature distribution is linear. Heat flow into ceiling is 1.666 BTU/ ft 2 h under these conditions.
With PCM Layer PCM layer Attic Thermocouples R 8 R16 Ceiling 120.0 F 100.5 F 81.00 F 80.75 F 80.50 F 80.25 F 80.00 F PCM layer is 0.125 inch thick and maintains 81 F throughout the diurnal cycle. Heat flow into ceiling is 0.0625 BTU/ft 2 h. (1.666 without PCM)
Low Space Requirements A 0.125 in. thick layer of PCM (0.5 lb) with thermal resistance on both sides will last a complete diurnal cycle.
Test Box 1/8 inch PCM Layer Diurnal T2 Cycle T1 Room Temp T3 R=6 foam board R=16 foam board
One Cycle Demonstration No PCM No PCM PCM PCM Heating Saved Heating Heating Cooling 93% 2.29 0.15 Cooling Reduction 13.30 4.36 67.2% 115 110 105 100 95 90 85 80 75 70
0.25 lb of Octadecane per sq. ft. Heating 2.63 63.64% Cooling 5.37 65.04% 110 Temperature (F) 90 70 50 1 49 97 145 193 241 289 337 One 24 Hour Cycle
Peak Load is Shifted Temperature (F) 120 100 80 60 4 hrs. PCM Peak Normal Peak 1 49 97 145 193 241 289 337 Time (10 min. increments)
Lower Heat Flow into Building. Reduction in heat flow into the conditioned space is demonstrated. These examples demonstrate the potential for heating and cooling load reductions.
Observations 1. A thin layer of phase change material can control the T difference across an inner layer of insulation for several hours. 2. The amount of Phase Change Material needed can be minimized by thermally protecting it with a second layer of insulation 3. Optimum amount and position is provided by simulation for a given site and location in the building envelope.
HFM CAN BE OPERATED IN TRANSIENT MODE TO TEST PCMs Test specimen is initially isothermal at a temperature below the phase change temperature. One plate is ramped quickly to a temperature above the phase change temperature. The heat fluxes in and out of the test specimen are monitored with time. A comparison of heat flux data for specimens with and without PCM is used to evaluate performance.
Test Configuration Top Plate cold Top layer of insulation R = 9 ft 2 h F/Btu Layer of PCM Bottom layer of insulation R=5 ft 2 h F/Btu Bottom Plate cold ramps to hot hot ramps to cold
TEMPERATURES ABOVE AND BELOW THE PHASE CHANGE TEMPERATURE ARE UTILIZED Test specimen is initially isothermal. bottom plate 69.8 F top plate 70 F Bottom plate temperature changed rapidly to a temperature above the phase change temperature. bottom plate 69.8 F to 120.2 F Result is a positive flux (into specimen) on the hot side and negative flux (out of specimen) on the cold side. (charging) Bottom plate temperature is returned to initial temperature when steady state is achieved. (discharging) This procedure can be carried out for specimens with and without PCM.
Hot-Side Flux During the Charge and Discharge Portions of the Cycle Cellulose with 0% PCM 20 Flux (Btu/ft^2.h) 10 0-10 hot side/flux in/out cold side/flux out -20 0 50 100 150 200 250 300 350 Time (minutes)
Hot-Side Flux During the Charge and Discharge Portions of the Cycle for Cellulose with 30 wt% PCM
Comparison of the Charging of Cellulose Insulation Materials with and without PCM
Comparison of the Flux out of the Cellulose Insulation Materials with and without PCM
Total Heat into Cold Plate as a Function of PCM Content
Heat Flux Data for Inorganic PCM Heat Flow into Conditioned Space 4 Flux 3 2 1 No PCM Chloride 1 Chloride 2 0 0 100 200 300 400 Time (minutes)
A COMPARISON OF FLUX DATA FOR SPECIMENS WITH AND WITHOUT PCM ALLOWS AN EVALUATION OF PERFORMANCE Heat Flow into Conditioned Space 4 Flux 3 2 1 No PCM PCM 0 0 100 200 300 400 Time (minutes)
HFM CAN BE USED TO MONITOR HEAT FLUX FOR INSULATION WITHOUT PCM Transient Heat Flow Meter Test flux into specimen is positive 10 5 Heat Flux 0-5 Hot Side Cold Side -10 0 36 72 108 144 180 216 Time (minutes)
Total Heat Discharged to Hot Plate as a Function of PCM Content
Wall Containing Cellulose-PCM Blend have been Tested in a Hot-Box (C 1363)
PCM Enhanced Cellulose Insulation has been Tested in Field Conditions In Two Full-Scale Demonstration Projects 2x6 Wood-Framed Walls were Used North-Western Wall South - Facing Wall
In Both Experiments, Walls Containing ~ 20% PCM were Instated Next to the Walls without PCM
Charging and Discharging PCM 90.0 PCM is absorbing heat and melting Discharging time about 6 hours PCM is releasing heat and solidifying Temp. inside the wall F 80.0 Charging time about 6 hours Temperatures inside the wall cavity: Thick line PCM Thin line No PCM 70.0 1 13 25 37 49 61 73 85 97 109 121 133 145 157 169 181 193 Cellulose W all East No PCM (of) CELL_E_TC5 Cellulose W all West W / PCM (of) CELL_W_TC5
Significant Difference in Energy Performance was Observed Example of Heat Flux Measurements Btu/hft2 2 Heating Load PCM wall is 1.5 significantly more thermally 1 stable than the other wall 0.5 0-0.5-1 1 49 97 145 193 241 289 337 385 433 481 529 577 625 673 PCM wall Peak-hour heat flux reduction by at least 1/3 in PCM wall Significantly lower heat flux amplitude in -2 PCM wall No PCM wall ~2 hours shifting of the -3 Cooling Load One week of data peak-hour load time [h/4] Sunny days by PCM wall Cool nights -1.5-2.5
Potential 40% Cooling Load Savings for 40 o F Temperature Excitation 2006 ORNL Dynamic Hot-box testing of 2x6 Wall with PCM-Enhanced Cellulose Insulation (22% PCM) Cluster of PCM pellets 0.5 42.00% Cellulose fiber Surface Load Reduction [%] 0.4 0.3 0.2 0.1 27.00% 19.00% 0 First 5 hours First 10 hours All 15 hours
Long-Term Energy Performance Monitoring Spring, Summer, Fall, Winter 2006 and Spring 2007 130 120 110 Example of Results from ORNL 2006 Measurements Exterior surfaces Temperatures [F] 100 90 80 Interior surfaces 70 One week data Sunny days 60 Cool nights Exterior air 50 1 49 97 145 193 241 289 337 385 433 481 529 577 625 673 Cellulose Wall East No PCM (of) CELL_E_TC1 Cellulose Wall West W/ PCM (of) CELL_W_TC1 ESRA OUTSIDE T/C (of) AMB_AIR Cellulose Wall East No PCM (of) CELL_E_TC8 Cellulose Wall West W/ PCM (of) CELL_W_TC8
PCM-Enhanced Cellulose in Test Walls 100.0 Temp. inside the wall F 90.0 PCM stabilizes the core of the wall by its heat storage capacity 85 o F PC action Warming and cooling down of the core in the PCM wall is significantly slower 80.0 78 o F Peak-hour temperature excitation is shifted in PCM wall Significantly lower Temperatures inside temperature 70.0 the wall cavities: amplitudes can be Thick lines PCM observed in PCM wall Thin lines No PCM cavities 60.0 1 13 25 37 49 61 73 85 97 109 121 133 145 157 169 181 193 Cellulose Wall East No PCM (of) CELL_E_TC3 Cellulose Wall East No PCM (of) CELL_E_TC5 Cellulose Wall West W/ PCM (of) CELL_W_TC4 Cellulose Wall East No PCM (of) CELL_E_TC4 Cellulose Wall West W/ PCM (of) CELL_W_TC3 Cellulose Wall West W/ PCM (of) CELL_W_TC5
% Cooling Load Reductions 100 90 80 Cooling-dominated loads 70 60 50 40 Average ~42% 30 20 10 April May June July August Sept. Oct. Nov. Dec. Jan. 0 0 5 10 15 20 25 30 35 40 Weeks
Summary Several applications of microencapsulated organic PCMs were tested. Applications with localized PCM have been tested. Laboratory and field work demonstrated good performance of PCM-enhanced insulation Thermal conductivity of the PCM-enhanced cellulose was not increased by the addition of PCM microcapsules Cellulose wall with dispersed PCM demonstrated potential for over 40% reduction of the peak thermal load during 5 hour thermal ramp Field tests confirmed hot-box test data on cooling load reduction potential of PCM-enhanced cellulose Field tests demonstrated potential for application of PCMs in mixed and heating-dominated climates for reduction of heating loads