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Calculation and selection of a water heater tank

The water is heated in the tank to a temperature [°C]
The hot water coming from the heat source (boiler) is cooled down [°C]
Option 1 — Priority - Water reserve
A water reserve is necessary
Option 2 — Priority - Accumulation of heat input
Thermal load of the heat source (boiler)
Operating time of the heat source (boiler) per day/cycle

Calculation of Water heater tanks

Calculation of the water heater tank depending on the priority, it can be performed in two ways. In one case, the stored volume of water is given and the power of the source and heat exchanger is calculated, and in the other – the volume of the storage water heater is calculated for the accumulation of heat produced by a source of a certain power for a certain time.

Regardless of the calculation methods, it should be understood that the ability of water to accumulate characterizes its heat capacity, which is equal to 4.187 kJ kg/°C, which means that to heat one kilogram of water by 1 degree, it is necessary to add the amount of heat equivalent to 4.187 kJ or that too exactly = 1 kcal = 1.163 W. For example, if we have a storage water heater with a volume of 1000 liters (further on, the mass of 1 liter of water is assumed to be 1 kg) and we heat it to 50 degrees, then for this we will need to supply such an amount of heat energy 1000*50 = 50,000 kcal = 0.05 Gcal = 58 kWh.

The power of the heat exchanger depends on the heat transfer coefficient and the temperature difference between the heated water and the heated water. The heat transfer coefficient is individual for each heat exchanger, therefore there is no universal calculation formula and it is recommended to choose a heat exchanger according to the diagrams presented in the technical characteristics of storage water heaters.

Selection of Water heater tanks

Selection of the water heater tank depending on the application scheme, it is performed using different techniques, but in general, it should be taken into account during selection.

  • The greater the peak heat consumption differs from the average hourly and the longer its duration, the larger the volume of the storage water heater should be.
  • The greater the peak heat input and the shorter its duration, the greater the power of the heat exchange device should be, regardless of whether it is external, integrated or an electric heater.
  • Over time, scale formed on the heat exchanger will increase the heating time of the storage tank. The rate of scale formation will be the higher the higher the water temperature.
  • The power of the heat source (boiler) must be greater than or equal to the power of the heat exchanger installed in the storage water heater.
  • A storage water heater connected to a solid fuel boiler must accumulate the heat generated by at least one loading of the boiler.
  • For houses with a low heat demand for heating, the power of the boiler is determined by the heating time of the tank, which is recommended to take from 30 to 45 minutes.
  • In schemes using one boiler to cover the heating load and water heating in the hot water supply system, it is recommended to choose the surface area of the storage heating element in such a way as to minimize the frequency of boiler operation and interruption in the operation of the heating system.

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