Harnessing the Power of Heat

by | Oct 5, 2023 | Educational, Getting deeper | 0 comments

Heat energy is all around us. From our daily use of hot water for showers and washing dishes, to the industrial use of heat for various processes, thermal energy is an essential part of our lives. But have you ever wondered about the intricacies of storing this thermal energy efficiently? A buffer tank plays a vital role in such storage systems, making our heating systems more efficient and reliable. Let’s take a closer look at how this works, using a 1000L buffer tank as an example.

A buffer tank serves as an intermediary storage space for thermal energy. In a heating system, for instance, it stores excess heat produced by the boiler, solar thermal system or heat pump. This energy is then released when needed, such as when the demand for heat rises or when the main heat source is not operating. In a nutshell, it’s like a thermal battery that charges when there’s surplus energy and discharges when energy is required.

The Practical Benefits

The use of a buffer tank is particularly beneficial in scenarios where there is a mismatch between the supply and demand of heat. It ensures a smoother operation of your heating system, reduces the wear and tear on the heat source, and ultimately leads to energy and cost savings.

Buffer tanks are also important for the integration of renewable energy sources into heating systems. For instance, a solar thermal system may produce a lot of heat during sunny hours which can be stored in a buffer tank and used later in the evening or on cloudy days.

Doing the Math

Now, let’s dig into the mathematical part, which tells us how much energy a buffer tank can store. The energy content of a volume of water can be calculated using a straightforward formula:

E = V * p * c * ΔT


  • E is the energy stored in the buffer tank in joules.
  • V is the volume of water in the tank in cubic meters (m^3).
  • p is the density of water, approximately 1000 kg/m^3.
  • c is the specific heat capacity of water, approximately 4186 J/(kg·K).
  • ΔT is the temperature change in the tank in degrees Celsius or Kelvin.

Since 1 m^3 equals 1000 liters, a 1000L tank equals 1 m^3.

Let’s say we heat the water in the tank from 10°C to 90°C. The temperature change ΔT is therefore 90°C – 10°C = 80°C.

So the energy stored in the tank, E, can be calculated as:

E = 1 m^3 * 1000 kg/m^3 * 4186 J/(kg·K) * 80 K = 334,800,000 Joules

As we are aiming to express our result in kilowatts (kW), we need to convert Joules into kilowatt hours (kWh), and then divide by the number of hours the energy is used over.

1 kWh equals 3.6 million Joules, so our stored energy is approximately:

E = 334,800,000 J / 3,600,000 J/kWh = 93 kWh

If we use this energy evenly over a 24-hour period, the power provided by the tank is:

P = 93 kWh / 24 h = approximately 3.9 kW

Therefore, this 1000L buffer tank can deliver a power of around 3.9 kW over a day, with a temperature change of 80°C.

The simple math we’ve just walked through offers a glimpse into the remarkable potential of buffer tanks as thermal batteries. They are, indeed, a practical and effective means to store and dispatch heat energy, leading to efficient and economical heating systems. Understanding the science and mathematics behind buffer tanks helps us appreciate the critical role they play in our quest for more sustainable and reliable energy systems.


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