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Measuring energy for heating

When we are talking about steam we have a lot of irritating definition! Finally, it doesn’t matter if you want to heat water, air in a tumble dryer or steel at a flat work ironer. In all cases, you need only the energy of the steam and not the pressure or temperature.

However, there is a fixed relation between Steam Pressure, Temperature and Evaporating Heat (Energy). This is the reason why a lot of people talk about steam pressure or temperature, when they mean energy.

The boiling point of the water is always related to pressure. When you increase the pressure you automatically increase the boiling point of the water

The steam pressure results from the increase of volume during evaporation. One litre of water results in 1.7m3 of steam, without any pressure. This 1.7m3 has a weight of one kilogram and a boiling point of 100°C

When you heat one litre in a closed boiler at a pressure of 10 bar you will get a volume 0.177m3 steam but at a boiling point of 184°C. The weight of the steam is as well one kilogramme.

The total energy contains:

• The evaporating energy to reach the boiling point

• Heat of vaporization

• Pressure energy


To calculate the steam needed is not a question of steam volume or amount. It is mainly a question of energy. Depending on different steam pressures the steam contains different energy levels. These result in different temperatures reached with different steam pressure. The reason for different temperatures is the different energy levels.

If you know the steam pressure and the type of steam you use, you will know the energy level in kilojoules contains. Based on this energy level you can calculate how many kilojoules you will need to heat one litre of water from A-Z.

But this also depends on the water level being used – 1:4 or 1:5; the kind of linen being washed – towels will use more water which you have to head up as well; the kind of wash extractor being used; and the loading ratio of the machine.

With a required evaporating heat of around 2000 kilojoules / kilogram of steam you can calculate the energy savings. (Evaporating heat is not the total energy but only the energy to reach the boiling point. The boiling point depends on the pressure in the boiler and is calculated in this case at 10 bar).

Not all Ozone systems in market are really working well. So take care to get a performance and saving guarantee from the equipment supplier before you pay your invoice. (Three months test period before you pay in full). In addition talk to your detergent supplier to modify the wash application. With a well working ozone system you should save time, water and detergents as well.

Make sure to have a well working counting of your rewash level and measure the white level you have at the moment and in future. This is the only way to compare the performance of the system.

Klaus Menker
Managing Director Menker –
Laundry Management Consultants

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