What are Heat Accumulator Tanks
A heat accumulator tank is a device that stores thermal energy in the form of hot water or other heat transfer fluid for later use. The main purpose of a heat accumulator tank is to bridge the gap between heat supply and demand, allowing for more efficient and flexible operation of heating systems. It is an essential component in many heating systems, particularly those that utilise renewable energy sources, have intermittent heat supply, or have intermittent heat demand. The physics behind heat storage in accumulator tanks involves the principles of thermodynamics and heat transfer.
Physics of heat storage in accumulator tanks
Sensible heat storage:
- Accumulator tanks primarily store heat in the form of sensible heat, which is the thermal energy that causes a change in the temperature of a substance without changing its phase.
- The amount of heat stored in an accumulator tank depends on the mass of the storage medium (usually water), its specific heat capacity, and the temperature difference between the stored water and the surrounding environment.
- The heat storage capacity of a tank can be calculated using the formula: Q = m × c × ΔT, where Q is the heat stored (in joules), m is the mass of the storage medium (in kilograms), c is the specific heat capacity of the medium (in joules per kilogram per kelvin), and ΔT is the temperature difference (in kelvins).
How Accumulator Tanks Optimise Heat Storage
Heat accumulator tanks play a crucial role in balancing the mismatch between heat supply and demand, enabling heating systems to operate more efficiently and effectively. This is particularly important in systems that rely on intermittent or variable heat sources, or have intermittent or variable heat demand. Here’s how accumulator tanks help to balance heat supply and demand:
Storing excess heat:
- When the heat supply exceeds the immediate demand, the excess heat is stored in the accumulator tank.
- For example, in a solar thermal system, the solar collectors may generate more heat during peak sunlight hours than is needed for immediate use.
- Instead of wasting this excess heat, it is transferred to the accumulator tank, where it is stored as hot water or heat transfer fluid.
- The stored heat can then be used later when the heat demand increases or when the heat source is unavailable.
Meeting peak demand:
- Accumulator tanks help to meet peak heat demand by providing a buffer of stored thermal energy.
- During periods of high heat demand, such as cold winter days or during peak occupancy hours in a building, the stored heat in the accumulator tank can be quickly released to supplement the heat supply.
- This reduces the strain on the primary heat source, such as a boiler or heat pump, allowing it to operate at a more steady and efficient rate.
Optimizing heat source operation:
- By decoupling the heat supply from the immediate demand, accumulator tanks allow heat sources to operate at their optimal efficiency points.
- For instance, heat pumps typically have higher coefficients of performance (COPs) when operating at lower temperatures and steady-state conditions.
- With an accumulator tank, the heat pump can charge the tank during off-peak hours or when ambient conditions are favourable, running at its most efficient settings.
- The stored heat is then used to meet the heat demand, while the heat pump can remain off or operate at a reduced capacity, improving its overall efficiency.
Reducing cycling and wear:
- Frequent on/off cycling of heat sources, such as boilers or heat pumps, can reduce their efficiency and increase wear and tear on the equipment.
- By storing heat in an accumulator tank, the heat source can operate for longer, more continuous periods, reducing the number of start/stop cycles.
- This not only improves the efficiency of the heat source but also extends its lifespan and reduces maintenance requirements.
Enabling flexibility in heat generation:
- Accumulator tanks provide flexibility in heat generation by allowing heat to be produced and stored when it is most convenient or cost-effective.
- For example, in a system with time-of-use electricity tariffs, a heat pump can be programmed to charge the accumulator tank during off-peak hours when electricity prices are lower.
- The stored heat can then be used during peak hours, reducing the overall operating costs of the heating system.
Integrating multiple heat sources:
- Accumulator tanks can facilitate the integration of multiple heat sources into a single heating system.
- For instance, a system may combine solar thermal collectors, a heat pump, and a backup boiler.
- The accumulator tank acts as a central hub, storing heat from all available sources and distributing it as needed.
- This allows for the optimal use of each heat source based on its availability, efficiency, and cost, resulting in a more reliable and cost-effective heating system.
Integrating multiple heat sources:
- Accumulator tanks can facilitate the integration of multiple heat sources into a single heating system.
- For instance, a system may combine solar thermal collectors, a heat pump, and a backup boiler.
- The accumulator tank acts as a central hub, storing heat from all available sources and distributing it as needed.
- This allows for the optimal use of each heat source based on its availability, efficiency, and cost, resulting in a more reliable and cost-effective heating system.