Full Title: Evaluation of Phase Change Thermal Storage in a Cascade Heat Pump
Author(s): Ransisi Huang, Allison Mahvi, Nelson James, Eric Kozubal, and Jason Woods
Publisher(s): Elsevier
Publication Date: October 20, 2023
Full Text: Download Resource
Description (excerpt):
This study proposes a low-global warming potential cascade heat pump system with integrated phase change material (PCM) for combined space heating and cooling. PCM is embedded in the intermediate heat exchanger that couples an outdoor R290 refrigerant circuit and an indoor CO2 circuit. They used a clustering method to develop seasonally representative load and ambient temperature profiles for residential buildings in Minneapolis, Minnesota. They simulated the system peak shaving performance on the selected representative days, assuming three different PCM options including ice (0 °C), tetradecane (5.6 °C), and a commercially available PCM, SP9 (10.5 °C). The baseline was the same cascade system without thermal storage. They investigated the effect of both thermal energy storage capacity (kWhth) and PCM transition temperature on system performance.
The results show that higher thermal energy storage capacity shaves more electric energy until it reaches a maximum value set by the load characteristics of the building. SP9, with the highest transition temperature, shaves the most electric energy, while ice shaves the least. Moreover, ice has the highest charging cost, especially in the cooling season when the outdoor circuit has to operate at an evaporating temperature lower than 0 °C to make ice. The results show that SP9 presents the lowest levelized cost of storage, closely followed by ice. A lower off-peak electricity rate benefits ice more than SP9 or tetradecane because ice has the largest charging cost penalty.