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| Hot Water Systems Design | The design of a hot water system may be put into effect reasoning from the following course of actions:
1. Determine the requirement of hot water - amount and temperature
2. Selecting the type, heating area and capacity of the calorifier - or heat-transfer device
3. Selecting the boiler
4. Design pipe scheme and size pipes
The Demand of Hot Water - quantity and temperature
Consumers of hot water commonly have it at 50 - 60oC. Temperature of 65oC is needed to suit most sanitary regulations for canteens and professional kitchen. With the intention of legionellosis prevention, hot water should be provided at above 60oC (140oF) temperatures.
In some houses lower temperatures are required for safety reasons (akin to centers for disabled or kindergartens for example), that's why the hot water temperature should not exceed 40 - 50oC there.
Note! The hot water can be stored at higher temperatures and reduced to maintain temperature by mixing with cold water in blender valves. Overall capacity of the system is increased and the need of storage volume reduced when storing hot water at a higher temperature.
The quantity of hot water is determined by number of dwellers and consumer habits.
The type, heating area and capacity of calorifier - or heat-transfer device
A hot water accumulator unit will reduce the necessary maximum heat supply. The heat supply capacity to a system with an accumulator can be calculated as:
H = 4.19 V (q1 - q2) / t (1)
where
H = heat supply capacity (kW)
V = accumulator volume stored (liter)
q1 = temperature of the cold feed water (oC)
q2 = temperature of the hot water (oC)
t = available time for the accumulated volume to be heated (sec)
(1) can be modified to express heated accumulated volume if heat supply capacity and available time for heating is known:
V = Ha ta / 4.19 (q1 - q2) (1b)
where
Ha = heat supply available (kW)
ta = heating time available (sec)
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