In EnergyPlus simulations using hysteresis data, the integration of PureTemp phase change materials in a building's suspended ceiling tiles showed potential savings in cooling energy ranging from 5.5 percent to 37.4 percent.
The PCM modeling research, conducted at University of Manitoba, also found a reduction in "discomfort hours" from 10 percent to 29 percent, depending on the zone and PCM type.
The researchers set out to investigate the feasibility of integrating PCMs within a suspended ceiling using the hysteresis method in EnergyPlus 8.9. The hysteresis effect, wherein a PCM has different melting/freezing temperature curves, complicates the simulation of PCM use in buildings. The EnergyPlus modeling software was updated in 2017 to include the effect of hysteresis.
Minneapolis-based PureTemp LLC provided the researchers with the thermo-physical properties of PCMs required for modeling in EnergyPlus. Five types of PCMs, namely PCM20 (PureTemp 20), PCM21, PCM22, PCM23 (PureTemp 23), and PCM24, were tested and analyzed. The melting and freezing temperatures of the five PCMs fall within the thermal comfort range and operation of the HVAC system of the building the researchers chose as a case study: the University of Manitoba's new Stanley Pauley Engineering Building.
The number of each PCM represents the material's peak melting temperature in degrees Celsius. The theoretical properties of PCM21, PCM22 and PCM24 were derived from the actual properties of PureTemp 20, PureTemp 23 and PureTemp 25.
One of the study's authors, Dr. Miroslava Kavgic, right, is an assistant professor of civil engineering at the university. She answered questions about the research by email.
Q: What do you think is the most important finding, as far as impact on manufacturers of PCMs and PCM products?
A: "The findings of our research study suggest a promising future for the applications of PCMs in buildings located in cold climates. Furthermore, our study showed that in addition to already proven cooling energy-saving potential, PCMs can be very efficient in reducing heating energy demand. As a result, the findings from our study can increase application of PCMs in buildings located in the dominant heating climates, and therefore increase the demand for these unique building materials. We also hope that higher demand for PCMs will bring down their price which currently hinders the more extensive application of PCMs in areas with the lower energy prices such as Manitoba."
Q: Why did you choose to use PureTemp data? Was there a preference to use a biobased PCM? Or was data on other products hard to obtain?
|EnergyPlus PCM model, enthalpy-temperature method|
Q: Given the impact of a PCMs hysteresis the final simulation results, is there a standard you’d like the industry to establish for consistent data from the PCM manufacturers?
|EnergyPlus PCM model, hysteresis method|
A: "Consistent data from the PCM manufacturers would increase confidence in the modeling results, and this applies to both hysteresis and temperature-enthalpy methods. Moreover, the consistent PCM properties could also be beneficial for the manufacturers as they will allow the end-user to test multiple PCMs and purchase several different materials for real-world implementation. This is particularly important considering the need for numerical analysis before the real-world implementation due to both complex behavior of PCMs and their relatively high price. The sensitivity analysis of the hysteresis input parameters suggests that manufacturers should pay partial attention to the parameters that have high impact on the simulation results."
Q: For future work, is there interest in comparing the same PCM measured with different methods, such as T-history and DSC?
A: "The t-history method is relatively inexpensive and straightforward to measure the phase-change enthalpy of PCM products using considerably larger sample sizes compared to DSC, and therefore for non-uniform PCMs it is a good testing alternative to DSC."
Table 3. Thermo-physical properties of the tested PCM:
|Latent heat during the entire phase change process (J/kg)||171,000||189,000||208,000||227,000||207,000|
|Peak melting temperature (°C)||20||21||22||23||24|
|Peak freezing temperature (°C)||18||19||20||21||22|
|Liquid-state thermal conductivity (W/(m∙K))||0.14||0.143||0.146||0.15||0.15|
|Solid-state thermal conductivity (W/(m∙K))||0.23||0.236||0.243||0.25||0.25|
|Liquid-state density (kg/m3)||680||730||780||830||840|
|Solid-state density (kg/m3)||950||936||923||910||930|
|Liquid-state specific heat (J/(kg∙K))||2150||2096||2043||1990||2140|
|Solid-state specific heat (J/(kg∙K))||2070||1993||1916||1840||1915|
The full version of the paper is available here through the end of September 2019: