Use of PCM Enhanced Insulation in the Building Envelope

Transcription

1 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

2 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.

3 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.

4 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.

5 Without PCM Layer R24 Attic Ceiling F F F F F F F Thermocouples Typ. Temperature distribution is linear. Heat flow into ceiling is BTU/ ft 2 h under these conditions.

6 With PCM Layer PCM layer Attic Thermocouples R 8 R16 Ceiling F F F F F F F PCM layer is inch thick and maintains 81 F throughout the diurnal cycle. Heat flow into ceiling is BTU/ft 2 h. (1.666 without PCM)

7 Low Space Requirements A in. thick layer of PCM (0.5 lb) with thermal resistance on both sides will last a complete diurnal cycle.

8 Test Box 1/8 inch PCM Layer Diurnal T2 Cycle T1 Room Temp T3 R=6 foam board R=16 foam board

9 One Cycle Demonstration No PCM No PCM PCM PCM Heating Saved Heating Heating Cooling 93% Cooling Reduction %

10 0.25 lb of Octadecane per sq. ft. Heating % Cooling % 110 Temperature (F) One 24 Hour Cycle

11 Peak Load is Shifted Temperature (F) hrs. PCM Peak Normal Peak Time (10 min. increments)

12 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.

13 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.

14 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.

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16 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

17 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 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.

18 Hot-Side Flux During the Charge and Discharge Portions of the Cycle Cellulose with 0% PCM 20 Flux (Btu/ft^2.h) hot side/flux in/out cold side/flux out Time (minutes)

19 Hot-Side Flux During the Charge and Discharge Portions of the Cycle for Cellulose with 30 wt% PCM

20 Comparison of the Charging of Cellulose Insulation Materials with and without PCM

21 Comparison of the Flux out of the Cellulose Insulation Materials with and without PCM

22 Total Heat into Cold Plate as a Function of PCM Content

23 Heat Flux Data for Inorganic PCM Heat Flow into Conditioned Space 4 Flux No PCM Chloride 1 Chloride Time (minutes)

24 A COMPARISON OF FLUX DATA FOR SPECIMENS WITH AND WITHOUT PCM ALLOWS AN EVALUATION OF PERFORMANCE Heat Flow into Conditioned Space 4 Flux No PCM PCM Time (minutes)

25 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 Time (minutes)

26 Total Heat Discharged to Hot Plate as a Function of PCM Content

27 Wall Containing Cellulose-PCM Blend have been Tested in a Hot-Box (C 1363)

28 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

29 In Both Experiments, Walls Containing ~ 20% PCM were Instated Next to the Walls without PCM

30 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 Cellulose W all East No PCM (of) CELL_E_TC5 Cellulose W all West W / PCM (of) CELL_W_TC5

31 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 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

32 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 % Cellulose fiber Surface Load Reduction [%] % 19.00% 0 First 5 hours First 10 hours All 15 hours

33 Long-Term Energy Performance Monitoring Spring, Summer, Fall, Winter 2006 and Spring Example of Results from ORNL 2006 Measurements Exterior surfaces Temperatures [F] Interior surfaces 70 One week data Sunny days 60 Cool nights Exterior air 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

34 PCM-Enhanced Cellulose in Test Walls 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 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 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

35 % Cooling Load Reductions Cooling-dominated loads Average ~42% April May June July August Sept. Oct. Nov. Dec. Jan Weeks

36 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