Heat pump water heaters are great for commercial buildings seeking to lower energy costs and minimize their carbon footprint. Installing these systems can be complicated due to the need for large water tanks, extensive plumbing, and limited space. This is where Phase Change Material (PCM) comes into play, offering a more effective way to store thermal energy. Integrating PCM into heat pump water heaters, such as the Pyroclast™ simplifies installation.*
*A product from Nyle Water Heating Systems, designed in partnership with Htec Packaged Systems & Controls.
What Is Phase Change Material (PCM)?
Phase Change Material (PCM) is a substance that absorbs and releases thermal energy during the process of melting and solidifying. When a PCM reaches its melting point (phase change), it absorbs heat without increasing in temperature, storing large amounts of thermal energy as latent heat. As it cools down and solidifies, it releases this stored heat back.
This characteristic makes PCM an ideal thermal energy storage (TES) media for hot water systems. It provides a compact solution that maintains a stable temperature during energy storage and release, unlike water or glycol based systems that require large volumes for similar storage capacity.
History of Phase Change Materials (PCM)
The concept of latent heat, which is essential to phase change materials, was first introduced by British chemist Joseph Black in the 18th century. He discovered that heating ice at its melting point or water at its boiling point doesn’t cause a temperature rise, but instead adds energy that becomes "latent," or hidden. This principle laid the groundwork for understanding how PCM can store and release thermal energy without major temperature fluctuations.
In the mid-20th century, Dr. Maria Telkes, known as the “Sun Queen,” advanced PCM applications by using solar energy and PCM for thermal storage in solar-heated buildings and other practical devices. Her innovations, including solar desalination kits, showed PCM’s potential in energy storage and survival tools. The University of Edinburgh, in collaboration with companies like Sunamp, later advanced PCM by creating materials like Plentigrade P58, designed for high-density, compact thermal energy storage.
Types of PCM and How They Work
PCMs can be categorized into two main types: organic and inorganic, with any mix of the two being called eutectic materials:
Organic PCMs
These include paraffins (such as alkanes) and fatty acids. Organic materials are stable, non-corrosive, and safe to handle, making them a popular choice for building applications. However, they tend to have a lower thermal conductivity, which can require heat exchangers for efficient energy transfer. Paraffins behave like candle wax. They are flammable, they possess less energy density, and are quite expensive.
Inorganic PCMs
These include salts and salt hydrates. Inorganic PCMs have higher latent heat capacity and better thermal conductivity than organic PCMs, enabling efficient heat transfer. For example, Plentigrade material, used in systems like the Pyroclast™, is based on inorganic PCM. These materials are particularly effective in commercial applications where robust thermal performance is required.
Sodium acetate trihydrate (SAT) is superior to paraffins as a phase change material (PCM) for several reasons:
- Thermal Energy Density: SAT has a higher thermal energy density (45-120 kWh/m³) compared to paraffins (45-60 kWh/m³). This means SAT can store more energy per unit volume, making it more efficient.
- Material Cost: SAT generally has a lower material cost ($1-20/kWh) than paraffins ($20-30/kWh), making it more cost-effective for large-scale applications.
- Environmental Impact: SAT is less harmful to the environment compared to paraffin, which is derived from petroleum.
These advantages make sodium acetate trihydrate a more desirable option for thermal energy storage in various applications.
Source: osti.gov
Eutectic PCMs
Eutectic mixtures are tailored combinations of organic and inorganic phase change materials (PCMs) designed for a specific melting point. Eutectics offer a balance between the properties of organic and inorganic PCMs, making them suitable for specialized applications where precise temperature control is needed.
How PCM Enhances Thermal Energy Storage
In the context of heat pump water heaters, PCM serves as an efficient heat energy storage medium. PCM can store thermal energy at densities up to four times greater than water due to its latent heat capacity. This means that PCM can provide the equivalent of hundreds of gallons of stored water in a compact form-factor—significantly reducing the need for large storage tanks. Plentigrade P58, for example, can have 4x the thermal energy density of water during phase change.
How PCM is Used in Thermal Storage
- Charging Phase: During periods of heat pump operation, the heat generated is transferred into the PCM modules. As the PCM absorbs heat, it changes from solid to liquid, storing thermal energy without a significant change in temperature. This makes it ideal for stable, controlled heating applications.
- Discharging Phase: When there is demand for hot water, but the heat pump is not actively running, the PCM releases the stored thermal energy as it solidifies, maintaining a consistent hot water supply.
This ability to charge and discharge thermal energy enables commercial hot water systems to efficiently handle varying demand levels without needing the heat pump to provide output to match the maximum thermal demand. This reduces the capital expenditure on the heat pump by enabling a longer recovery time and enabling time of use charging strategies aka load shifting.
In commercial water heating applications, PCM is leveraged in Thermal Batteries to store heat instead of heating external water tanks. This creates an instantaneous-style water heater and removes the need for complicated plumbing and water storage designs while significantly reducing space requirements and installation cost.
PCM Thermal Batteries vs. Traditional Water Storage
PCM thermal battery systems offer distinct advantages over traditional water-based storage for plumbing contractors, plumbing engineers, and MEP engineers:
Reduced Footprint
Traditional hot water systems need large tanks for thermal energy storage, which can occupy significant space in mechanical rooms or on rooftops. PCM systems, like those used in the Pyroclast™, offer a smaller footprint than water comparable water tanks by storing the same amount of thermal energy in a much smaller volume. This makes it easier to retrofit existing buildings or incorporate efficient hot water solutions into new designs with limited space.
Simplified Installation
PCM-based systems like the Pyroclast™ eliminate the need for multiple water storage tanks, leading to a streamlined installation process with only two water tappings required for connection. This results in a faster installation time, which could reduce labor costs and minimize installation errors.
Energy Efficiency
PCM can store energy more efficiently, releasing it when demand is high. This efficiency is vital for commercial settings such as multifamily housing, universities, and hospitals, where there is a constant and high demand for hot water. PCM’s ability to provide energy on demand means less strain on the heat pump and lower overall operating costs.
Key Applications for PCM in Commercial Heat Pump Water Heaters
PCM technology is particularly beneficial in environments with varying hot water demand and space constraints. Some common applications include:
Universities
Campus facilities and student housing need a reliable supply of hot water for showers, dining services, and heating systems. PCM-based solutions provide compact, energy-efficient options that help universities maximize space and energy performance.
Multifamily Housing
Urban multifamily buildings often face space limitations. PCM-based systems like the Pyroclast™ offer robust performance without taking up valuable floor space. With stable temperature control and efficient energy use, these systems meet resident needs while reducing the building’s energy footprint.
Hospitals and Extended Care Facilities
These facilities require a continuous supply of hot water for patient care, sanitation, and other critical functions. The thermal stability and quick energy discharge of PCM make it an ideal choice for maintaining consistent temperatures, ensuring hot water availability even during peak demand, while the absence of stored water reduces the risk of waterborne pathogen growth.
Systems like the Pyroclast™ operate in a “return to primary” configuration, effectively using the primary storage system (PCM thermal energy storage) to manage recirculation losses in the building. This setup ensures a continuous flow from the recirculation pump to the heat pump, eliminating any risk of stagnant water.
By utilizing PCM batteries for thermal energy storage instead of conventional hot water tanks, the system avoids large volumes of water. These features provide optimal legionella mitigation, making it an excellent choice for end users, particularly in healthcare facilities where risk management is critical.
The Role of PCM in Simplifying Hot Water Systems
Using Phase Change Material as a thermal energy storage application in commercial heat pump water heaters offers a powerful solution for simplifying installation, saving space, and cutting down on operational costs. PCM systems provide plumbing contractors, engineers, and facility managers with a reliable, efficient, and compact alternative to traditional water storage.
By storing energy at a stable temperature and releasing it when needed, PCM technology helps reduce energy consumption and streamline the installation process—making it a key innovation in the future of commercial water heating. The Pyroclast™ exemplifies how advanced PCM integration can transform the way thermal energy is stored and used, providing a compact, efficient solution that meets the needs of modern commercial applications.
As commercial buildings focus more on energy efficiency and sustainability, understanding the capabilities of Phase Change Material can unlock new possibilities for hot water systems. With its ability to provide efficient thermal storage in a compact form, PCM technology is redefining the future of heat pump water heaters. Systems like the Pyroclast™ not only simplify the installation process but also offer significant long-term savings, positioning PCM as a critical component in next-generation thermal energy storage solutions.
