Controlling thermal energy storage
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Solution Overview
Problem
Conventional thermal energy storage systems, such as 'ice-on-coil' and 'encapsulated ice' systems, face inefficiencies due to inconsistent ice nucleation, limited contact between storage fluid and heat transfer fluid, and degradation over time, leading to reduced efficiency and reliability in storing and discharging thermal energy.
Innovation Solution
A method and system for thermal energy storage that includes a controller to manage the flow of refrigerant fluid through a Thermal Energy Storage (TES) system, using Phase Change Material (PCM) freezing during off-peak hours and discharging during peak hours, with a modular arrangement of ice bricks and capsules designed for efficient heat transfer and ice nucleation, allowing for high discharge rates and improved insulation efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If ice-on-coil storage systems are used to store thermal energy, then thermal energy can be stored during off-peak hours, but the system suffers from significant efficiency loss due to ice build-up on the coil forming a thermal insulator
Solution Approach 1:
The storage tank is divided into multiple compartments with separate coils in each compartment. This segmentation prevents ice build-up from completely isolating a single coil, as ice forms in different locations in each compartment and doesn't create a continuous insulating barrier around one coil throughout the entire storage period.
Solution Approach 2:
The system alternates between charging modes by switching between different compartments. During charging, one compartment is active while another charges, and they periodically swap roles. This periodic action prevents continuous ice build-up on a single coil by giving it time to thaw and be cleared before the next charging cycle.
2Quantity of substance
If very low temperatures are used to cool the coil to freeze water, then thermal energy storage capacity increases, but the chiller's coefficient of performance (COP) decreases making the process inefficient
Solution Approach 1:
Multiple compartments allow the system to distribute the freezing load across several smaller coils rather than one large coil requiring extremely low temperatures. Each compartment can operate at less extreme temperatures, improving chiller efficiency while achieving the same total storage capacity.
Solution Approach 2:
The system uses multiple compartments with smaller coils instead of one large coil, applying partial freezing action across multiple zones. This allows the chiller to operate at higher, more efficient temperatures while still achieving complete freezing capacity through the combined effect of all compartments.
3Reliability
If encapsulated ice storage systems are used, then thermal energy can be stored in containers, but the system suffers from slow or inconsistent ice nucleation resulting in inefficient thermal energy storage and discharge
Solution Approach 1:
Ice nucleation promoters or seeds are introduced as intermediaries to initiate and guide ice crystal formation in the encapsulated water. These promoters ensure consistent and reliable nucleation by providing a template for ice crystal growth, eliminating the randomness of spontaneous nucleation and ensuring predictable freezing behavior.
4Quantity of substance
If a large volume of water is used as phase change medium to increase storage capacity, then thermal energy storage capacity increases, but the contact between storage fluid and heat transfer fluid is limited reducing efficiency
Solution Approach 1:
The large volume of phase change medium is divided into multiple smaller compartments, each with its own heat transfer coil. This segmentation increases the surface area to volume ratio, allowing better contact between the heat transfer fluid and phase change medium throughout the entire storage tank, thereby improving heat transfer efficiency while maintaining large storage capacity.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system achieves high discharge rates, with over 50% to 90% of heat capacity discharged within 4 hours, enhancing energy storage efficiency and reliability, and mitigates peak demand on the electric grid by optimizing energy usage and reducing costs.
Implementation Method 1
using Phase Change Material (PCM) freezing during off-peak hours and discharging during peak hours
Implementation Method 2
a coil that is placed inside the tank in the water in order to exchange heat with the water/ice
Data Source
AI summary
A method of flattening electric energy demand from an electric grid including during less-than-peak electricity demand periods, freezing Phase Change Material (PCM) in a Thermal Energy Storage (TES) system, and during peak electricity demand periods, using the TES to cool air conditioning refrigerant fluid. A system of flattening electric energy demand of an air-conditioner from an electric grid including an air conditioner, a Thermal Energy Storage system, and a controller, wherein the controller is programmed to implement the above method. A method of freezing Phase Change Material (PCM) in a Thermal Energy Storage (TES) system including setting a temperature of heat exchange fluid at a temperature higher than −10 degrees Celsius when directed to ice bricks containing water and an ice nucleation agent. A Thermal Energy Storage (TES) system controller programmed to discharge more than 50% of a heat capacity of the TES. Related apparatus and methods are also described.