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Thermal end uses dominate building energy consumption and are a major driver of peak demand. As heating is electrified, peak electrical power required will surge, prompting a need for innovative HVAC system designs and controls.These designs must incorporate novel technologies at the component level and new integration techniques at the system level. One such possibility involves the addition of thermal energy storage (TES) in heating and cooling equipment using a phase change material (PCM) heat exchanger. Here, thermal energy storage via phase change can be used to shift the HVAC system loads to times of lower electricity cost, reduced carbon intensity, and greater energy efficiency. Most of the current utilization of PCM in buildings involves passive components. By actively controlling when heat is stored and released from PCM, we can optimize the building HVAC system to cost-effectively meet consumer needs with the flexibility to draw on renewable energy resources when they are abundant and available.While this combination of technologies is promising in theory, simulation-based evaluation of a prototype can be difficult due to the modeling requirements at the component level and the large number of possible configurations and operating modes at the system level. To conduct this evaluation, we use the Modelica language for modeling and simulation because it enables users to represent the important physics of the problem, interchange and rearrange components in an efficient manner, and implement a range of control configurations. In this work, we considered three case studies: a portable building, a large commercial retail store, and a multifamily residential apartment unit. Each of these employs a different system design, ranging from a single package vertical unit incorporating PCM to a central plant with independent heat pump, evaporative cooling, and thermal energy storage components. This paper describes the technologies in question, presents modeling at the component and system levels, and demonstrates building energy and demand charge cost savings with local time-of-use tariffs in a hot-dry climate.

As we continue to electrify space- and water-heating, the electricity demand profile of manybuildings will change significantly, and periods of high electricity demand will likely not alignwith renewable energy generation. We expect electricity demands will increase substantiallyin the winter, annual maximum electricity demands will increase, and more regions willexperience annual peak electrical demands – and higher wholesale electricity prices – in thewinter. This is especially important for cold climates where 60% of site energy use in buildingsis for heating, and where heat pumps perform least efficiently. This paper focuses on onepromising solution among the many paths to electrification: the use of phase change materials(PCM) for compact low-cost thermal energy storage (TES). We present the design andsimulation of a combi heat pump and phase change thermal storage system used for space- andwater-heating in a multifamily residence in a cold climate. To assess the benefits of thistechnology, we compare its annual performance to that of a current state-of-the-art air-to-airheat pump and separate heat pump water heater. Simulation results for IECC Climate Zone 6Areveal that the combi heat pump with phase change thermal storage can reduce the design sizefor heat pumps by 40-60%, reduce maximum electric demand by 30-50%, reduce electricityuse during 4-12-hour load shed periods by 50%, and avoid the need for auxiliary electricresistance for both space- and water-heating. Tariff structures are highly varied betweendifferent utilities and currently reflect higher wholesale market prices for electricity duringsummer days. Consequently, although this system design provides large electric demandreductions during hypothetical 4-12-hour load shed periods, it does not provide energy costreductions with current winter residential time-of-use tariffs.

Thermal end uses dominate building energy consumption and are a major driver of peak demand. As heating is electrified, peak electrical power required will surge, prompting a need for innovative HVAC system designs and controls.These designs must incorporate novel technologies at the component level and new integration techniques at the system level. One such possibility involves the addition of thermal energy storage (TES) in heating and cooling equipment using a phase change material (PCM) heat exchanger. Here, thermal energy storage via phase change can be used to shift the HVAC system loads to times of lower electricity cost, reduced carbon intensity, and greater energy efficiency. Most of the current utilization of PCM in buildings involves passive components. By actively controlling when heat is stored and released from PCM, we can optimize the building HVAC system to cost-effectively meet consumer needs with the flexibility to draw on renewable energy resources when they are abundant and available.While this combination of technologies is promising in theory, simulation-based evaluation of a prototype can be difficult due to the modeling requirements at the component level and the large number of possible configurations and operating modes at the system level. To conduct this evaluation, we use the Modelica language for modeling and simulation because it enables users to represent the important physics of the problem, interchange and rearrange components in an efficient manner, and implement a range of control configurations. In this work, we considered three case studies: a portable building, a large commercial retail store, and a multifamily residential apartment unit. Each of these employs a different system design, ranging from a single package vertical unit incorporating PCM to a central plant with independent heat pump, evaporative cooling, and thermal energy storage components. This paper describes the technologies in question, presents modeling at the component and system levels, and demonstrates building energy and demand charge cost savings with local time-of-use tariffs in a hot-dry climate.