Phase Change Materials for Quick Service Restaurants

The purpose of this study is to determine the effectiveness of passive phase change materials (PCMs) for controlling room temperatures in buildings and reducing the need for mechanical cooling. The PCM technology is designed to absorb heat during the daytime, and release heat overnight. This function is expected to help reduce the cooling requirements of the facility by mitigating heat gain into the conditioned spaces. This product is becoming more popular in building and refrigeration applications, and this report is necessary to help determine if the technology is resulting in a significant energy savings. Currently, PCM use in Southern California is limited to a few pilot installations. There is no incumbent technology equivalent to this product installed. By installing the PCM in the attic, heat is expected to be absorbed when the temperature rises above the melting point, preventing it from reaching the occupied space. This, in theory, will require less energy for the Heating, Ventilation, and Air Conditioning (HVAC) system to cool the building in the proposed case as opposed to the base case. While PCMs are relatively new, the concept of passively storing heat in a building has been around for centuries. Early iterations of passive heat transfer are not very functional in the summer when cooling is required. PCMs however have both heating and cooling applications, and are far more versatile as they can be integrated into the building envelope during new construction or placed in plenum/attic space in retrofit applications. In addition, the PCMs can be designed to an ideal melting/freezing temperature for most applications. The purpose of this demonstration project is to evaluate the energy saving capabilities of the PCM used in the attic space in a fast food restaurant located in Irvine, California. The technical approach for this field test ensured that any environmental or loading differences between the two cases, baseline and retrofit, be identified and accounted for in order to effectively compare the performance data of the two cases on an equitable basis. The field test for this study monitored the impact of the PCM on a fast food restaurant’s HVAC related electrical load. This location is served by two rooftop package units serving the kitchen (7.5 ton unit) and dining areas (10 ton unit). The store operates from 10:00 AM to 10:30 PM every day of the week, and is typically occupied by employees for an hour or two before and after closing for prep and clean up. The test site is estimated at 2,176 square feet. The technology reduced the cooling loads of the dining room as expected. There was a definite temperature shift within the attic space after the installation of the PCM that caused the space to remain significantly cooler on hot days for a longer period of time than it did without the PCM installed. However, only minimal energy savings were seen at the kitchen HVAC units. Analysis shows the location may not have been the optimal testing facility for this technology, as the heat loads in the attic space were less significant overall when compared to the heat loads from the excessive windows in the dining room and the internal gains from the kitchen food preparation. PCM placement needs to be strategic in order to optimally leverage the thermal capacity of the material. The PCM was installed over approximately 60% of the attic space above the ceiling tiles in both the dining room and the kitchen. In order to determine the efficiency of the PCM with respect to the heat load reduction, the PCM properties are referenced and used to calculate the quantity of energy that the PCM is designed to remove from the attic through the phase change process. The dining room installation delivered the expected energy reduction to the space. The kitchen did not have as much of an impact since there was much internal heat gain from cooking. The kitchen ventilation system may have also limited PCM efficiency in the kitchen. More understanding is needed on how infiltration, internal heat gains and exhaust hoods impact PCM efficiency. Based on the results of this assessment, the product can be recommended for customized utility energy efficiency programs. The PCM demonstrated that it was able to affect the overall space temperature of the attic area and reduce energy consumption for the dining room. However, since there was no significant reduction in the kitchen area, future installations are cautioned to consider their applications, the internal gains as well as how those internal gains will work in conjunction with PCM.