Application of Phase Change Materials for Peak Load Shifting Through Price-Based Control Method

Abstract

This study proposed the application of phase change materials (PCM) in buildings in combination with a price-based control method for peak load-shifting application. A pricebased control method was proposed which would be able to use online real-time electricity price data to use electricity when it is cheap and to stop using it during high peak periods. The proposed method was first tested on a domestic freezer equipped with storage trays containing a eutectic solution of ammonium chloride. An electricity cost saving of up to 16.5% was achieved for the freezer experiment. Later, two identical test huts located at the Tamaki Campus, University of Auckland were used for the experimental studies. The experimental huts were constructed using standard lightweight materials and are referred to as Hut 1 and Hut 2. Hut 1 was used as the base case throughout the study, while various PCM applications were tested on Hut 2. In the first step, DuPont wallboards were installed in Hut 2 and were tested using the proposed price-based method, which resulted in a successful peak-load shifting and a cost saving of 26.7%. There was a corresponding energy saving of 21.5% achieved over a six-day period. In the next stage, the DuPont wallboards were removed from Hut 2 and a PCMimpregnated underfloor heating system was installed instead. The application of the underfloor heating system using the price-based method showed improvement during the morning peak, but it had almost no effect during the evening peak. To address this, the DuPont wallboards were installed once again to store energy for use during the evening peak period. A combination of PCM underfloor heating with DuPont wallboards resulted in up to 35% electricity saving per day. The underfloor heating system and the DuPont wallboards were removed from Hut 2 and were replaced with PT20-impregnated gypsum boards. The experimental huts then were tested in summer using an air conditioner unit in both. The results showed a successful peak load shifting, although no energy saving could be achieved. To solve this, night ventilation was used in Hut 2 in order to solidify the impregnated PCM at night instead of using the air conditioner unit. This resulted in an overall electricity saving of 73% over a period of one week. The same PT20-impregnated gypsum boards later were used for winter tests to study their heating performance. Winter tests showed a successful peak load shifting but only a little energy saving. In order to improve this, weather forecasts were used to reduce the electrical energy consumption and use solar energy more often. The application of weather forecasting resulted in an energy saving and a cost saving of up to 90% and 79% per day respectively.