Thermal and Energy Modeling of PCM-Enhanced Building Envelopes

Abstract

Energy storage in building envelopes can be accomplished by means of sensible and latent heat accumulation. Latent heat storage using PCMs has been the focus of multiple building studies, due to its relatively high thermal energy storage capacity per volume, compared to sensible storage available in conventional construction materials. PCM-enhanced building envelopes are widely considered as a prospective building enclosure technology which can help in the near future in peak-hour load reductions and cutting of HVAC energy consumption. Currently, there is a great variety of commercially available PCM products that vary in PCM types (salts, paraffins, fatty acids, etc.) and in packaging and encapsulation options (i.e., PCM pouches, containers, macro-and microencapsulation). In addition, PCMs can be differentiated based on their melting temperatures, which together with PCM location and its quantity, are essential for designing of PCM building envelope applications.Most typically, PCMs used in building envelope applications, need to go through a complete phase transition during 24-h time periods in order to be fully effective. This is why it is critical that the temperature in the location where PCM is installed fluctuates (possibly daily) above and below the PCM functional temperature range. As depicted in Fig. 6.1, the PCM functional temperature range starts usually at the lowest temperature limit of the solidification process. Similarly, it ends at the highest temperature of the melting process.Ideally, the entire heat transported should be available at approximately the same temperature for both, melting and solidification processes. However, in real live, this situation only occurs for the paraffinic PCMs. That is why, for well-designed PCM systems, it is crucial that this temperature range be as narrow as possible. One of the complications is an existence of the temperature hysteresis between PCM melting and solidification. Figure 6.1 depicts a situation when the melting point of a PCM-enhanced material is well above its solidification point. In addition, in most of inorganic and some organic PCMs the supercooling effect can be observed.

PCM-Enhanced Building Components

“…Since, most often, PCMs used in building envelopes are difficult to analyze complex heterogeneous composites or structures with multidimensional heat transfer effects, Kośny et al (2007b) introduced a new test method utilizing a conventional ASTM C518 heat flow meter apparatus (HFMA). This method determines the amount of phase-change energy available in heterogeneous PCM-enhanced materials to provide thermal storage (Kośny et al 2009a;Shukla et al 2013).…”

“…The measured steady-state heatflux difference was about 20 %, which was caused by the additional thermal resistance provided by the PCM-foam-foil facing. Following the dynamic measurements described above, the ORNL research team performed a series of similar dynamic hot-box experiments where thermal performance of PCM-enhanced cellulose fiber, used as a wall cavity insulation, was measured (Kośny et al 2007b). A similar experimental procedure was used for testing of the wood frame wall assembly containing PCM-enhanced fiberglass .…”

“…In addition to dynamic wall testing, dynamic hot-box experiments were performed on a residential attic module insulated with PCM-enhanced cellulose (Kośny et al 2007b). The attic module was tested under periodic temperature changes in the ORNL LSCS (see Fig.…”

“…Table 6.2 summarizes major US references available for testing and modeling of PCM-enhanced thermal insulations. Kośny et al (2009a, c) 2 System-scale laboratory testing with the use of the dynamic hotbox experiments for walls Kośny et al (2007bKośny et al ( , 2008b) Kośny et al (2008bKośny et al ( , 2010b 3 System-scale laboratory testing with the use of the dynamic hot-box experiments for attics and roofs Fig. 6.8 Examples of system-scale test assemblies, constructed by the Oak Ridge National Laboratory, USA, containing PCM-enhanced insulations-Source Author's archive.…”

The potential of thermal energy storage as an energy retrofit measure for high-rise residential buildings in Canada

“…Another important factor is the data input for thermophysical properties of PCMs in the software. As stated by Kosny (2015b) often limited and unreliable information is available for PCM products. Data inputs rely on thermal and physical data of the products derived from DSC results, this leads to significant inaccuracies as tests conducted by DSC are on pure PCMs and on very small sample sizes.…”