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Research Papers

Energy Impacts of Nonlinear Behavior of Phase Change Materials When Applied to Opaque Building Envelopes

[+] Author and Article Information

National Renewable Energy Laboratory,
15013 Denver West Parkway,
Golden, CO 80123

Contributed by the Solar Energy Division of ASME for publication in the Journal of Solar Energy Engineering. Manuscript received August 8, 2012; final manuscript received May 14, 2013; published online August 5, 2013. Assoc. Editor: Gregor P. Henze.

J. Sol. Energy Eng 136(1), 011013 (Aug 05, 2013) (7 pages) Paper No: SOL-12-1196; doi: 10.1115/1.4024926 History: Received August 08, 2012; Revised May 14, 2013

Research on phase change materials (PCM) as a potential technology to reduce peak loads and heating, ventilation and air conditioning (HVAC) energy use in buildings has been conducted for several decades, resulting in a great deal of literature on PCM properties, temperature, and peak reduction potential. However, there are few building energy simulation programs that include PCM modeling features, and very few of these have been validated. Additionally, there is no previous research that indicates the level of accuracy when modeling PCMs from a building energy simulation perspective. This study analyzes the effects a nonlinear enthalpy profile has on thermal performance and expected energy benefits for PCM-enhanced insulation. The impact of accurately modeling realistic, nonlinear enthalpy profiles for PCMs versus simpler profiles is analyzed based on peak load reduction and energy savings using the conduction finite difference (CondFD) algorithm in EnergyPlus. The PCM and CondFD models used in this study have been previously validated after intensive verification and validation done at the National Renewable Energy Laboratory. Overall, the results of this study show annual energy savings are not very sensitive to the linearization of enthalpy curve. However, hourly analysis shows that if simpler linear profiles are used, users should try to specify a melting range covering roughly 80% of the latent heat; otherwise, hourly results can differ by up to 20%.

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References

Figures

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Fig. 6

ASHRAE Standard 140 Case 600 construction

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Fig. 5

Calculated inside surface heat flux for the different PCMs distributed in insulation for all walls with and without PCMs

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Fig. 4

Calculated temperature at the middle of the insulation layer containing distributed PCM for all walls with and without PCMs

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Fig. 3

Calculated outside surface heat flux for the different PCMs distributed in insulation for all walls with and without PCMs

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Fig. 2

Calculated outside surface heat flux for the different PCMs distributed in insulation for all walls with and without PCMs

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Fig. 1

Enthalpy curves for PCMs analyzed as shown in Table 1

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Fig. 7

Predicted monthly peak and cooling energy for Case 600 building with (PeakCool, CoolEner) and without PCMs (PeakCoolPCM, CoolEnerPCM)

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Fig. 8

Predicted monthly cooling energy savings (kWh and percentage) for different PCM linearization

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Fig. 9

Predicted peak cooling reduction (kW and percentage) for different PCM linearization

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Fig. 10

Predicted hourly cooling energy savings for all PCMs on Aug. 22

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Fig. 11

Predicted hourly cooling energy savings for all PCMs on Mar. 2

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Fig. 12

Predicted hourly cooling energy savings for all PCMs on Dec. 21

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Fig. 13

Predicted hourly heating energy savings for all PCMs on Dec. 21

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Fig. 14

Predicted heating energy savings (kWh) for different PCM linear curves

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Fig. 15

Normalized RMSE for the six linear enthalpy profiles (Table 1) versus the heat flux RMSE for the simple wall and the hourly RMSE cooling energy

Tables

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