Numerical and Experimental Analysis of Building Envelopes Containing Blown Fiberglass Insulation Thermally Enhanced with Phase Change Material ( PCM )

Different types of Phase Change Materials (PCMs) have been tested as dynamic components in buildings for at least 4 decades. Most of historical studies have found that PCMs enhance building energy performance. The PCMs store energy and alter the temperature gradient through the insulated cavity because they remain at a nearly constant temperature during the melting and solidifying stages. The use of organic PCMs to enhance the performance of thermal insulation in the building envelope was studied at the Oak Ridge National Laboratory during 2000–2009. PCMs reduce heat flow across an insulated region by absorbing and desorbing heat (charging and discharging) in response to ambient temperature cycles. The amount of heat that can be stored in PCMs is directly related to the heat of fusion of the material, which is between 116 J/g to 163 J/g (or 50 to 70 Btu/lb) for the most-popular microencapsulated paraffinic PCMs, or fatty acid materials used in this research. This paper presents experimental and numerical results from the long-term thermal performance study focused on blown fiber glass insulation modified with a novel spray-applied microencapsulated PCM. Experimental results are reported for both laboratory-scale and full-size building elements tested in the field. Test work was followed by detailed whole building Energy Plus simulations in order to generate energy performance data for different US climates. was utilized for dynamic hot-box testing. The test wall was constructed with nominal 14-cm. (2x6) studs installed on 40-cm. (16-inch) spacing. Three wall cavities were insulated with conventional blown fiber glass at a density of about 29-kg/m3 (1.8lb/ft3). The other three wall cavities were insulated with a multilayered fiber glass-PCM mixture. 2.1 Encouraging results of dynamic hot-box measurements The dynamic hot-box experiment was performed using the same testing procedure as in earlier ORNL tests with use of PCM-impregnated foams and blends of blown cellulose insulation with microencapsulated PCM [Kośny 2008, Kossecka and Kośny 2008]. At the beginning of the measurement, temperatures were stabilized at about 18.3 oC (65 oF) on the cold side and 22.2 oC (72 oF) on the warm side. Next, the temperature of the warm side was rapidly increased to 43.3 oC (110 oF) – on the side of the wall cavity containing PCM. It was observed that PCM content in the wall stabilized thermally the PCM section of the wall. It was associated with significantly lower local temperatures in the wall part containing PCM during the rapid heating process. Thermal lag time for that heating process was between 7 to 8 hours for the PCM part of the wall. Figure 1. Instrumentation of the test wall cavity. As shown in the Figure 1 test wall cavity was instrumented with temperature sensors installed at 2.5cm. (1-in.) intervals. The first 2/3 of the wall thickness (counting from the interior surface) was filled with conventional blown fiber glass of the same density as in the other non-PCM section of the wall. The remaining part of the wall cavity was filled with several layers of proprietary PCM blend with adhesive and blown fiber glass. The test wall contained approximately 20 wt. % PCM. It is estimated that about 13.6-kg (30-lb) of PCM-enhanced fiber glass insulation (containing 0.79-kg/m 3 or 0.16-lb/ft 2 of PCM) was used for this dynamic experiment. The PCM melting temperature was about 29 oC (84 oF). The PCM sub-cooling effect was about 6 C (11 F) wide with freezing temperature close to 23 C (73 F). The phase change enthalpy was about 170 J/g (73 BTU/lb). Test-generated heat flux results are shown in Figure 2 for the wall surfaces of constant temperatures. It took about 8-1/2 hours to fully charge the PCM material within the wall. Heat fluxes on both PCM and non-PCM sides of the wall were measured and compared. For 2-hour and 8-1/2-hour time intervals, heat fluxes were integrated for each surface. Comparisons of measured heat flow rates on the wall surface opposite to the thermal excitation enabled estimation of the potential thermal load reduction generated by the PCM. On average, the PCM part of the wall demonstrated over 27% of the cooling effect (total reduction of the heat flow) during 8-1/2 hours, and over 50% during the first two hours of the rapid heating process. Figure 2. Heat flows measured during dynamic hot-box ex-