Break tanks are used to help boost pressure within a water system, where the current water pressure is not strong enough to supply the requirements of the building. Typically, break tanks are fitted with an air gap between the inlet and maximum water level to prevent backflow into the mains water supply.
To determine the size of the break tank required, there are a few things to consider.
Occupancy of the building
This is a big factor, as you need to understand how much water is required within the property. For example a hotel requires more water storage per bed space than a hostel.
Below are some examples of recommended minimum storage levels for each type of premises.
Hotel – 200 Litres per bed space
Office without Canteen – 40 Litres per employee
Office with Canteen – 45 Litres per employee
Restaurant – 7 litres per meal
Primary School – 15 litres per pupil
Secondary School – 20 Litres per pupil
Nursing Home – 120 Litres per bed space
(Source: BS EN 806 Part 2)
Please consider when using this calculation, the peak occupancy of the building.
When sizing for a domestic building, a rough guide of 90 litres per bed space should be sufficient, however high-end properties may require additional storage.
Another consideration would be the expected peak flow of the premises. This is calculated when sizing a booster set. In determining the peak flow rate, we must consider how much water storage must be provided to facilitate this flow rate.
Tanks Direct recommend that a minimum of 15 minutes’ storage, according to the peak flow rate of the booster set, should be provided in a booster set break tank within a commercial installation. For example, a booster set with a peak design flow rate of 1.1 litres/second, or 66 litres/minute, requires a break tank with a capacity of at least 990 litres.
Other factors such as the tank inlet flow rate and the usage patterns of the building should also be taken into account – buildings with a poor rate of mains water supply will require greater storage. This will also be influenced by the siting of the break tank – a tank on the ground floor of a building will fill at a higher rate than a tank on an upper floor or in the roof space. Siting a tank in the roof space of a building is likely to necessitate a larger storage volume.