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Calculate the demand for domestic hot waterIl best before date of hot water is not distributed evenly in the course of a day, but is concentrated in the time intervals of limited duration, defined "peak periods".
The diagram shows the typical performance of consumption daily of water in a single house.

In peak periods occur the maximum consumption contemporary of hot water for which the installation of preparation of ACS must be able to meet these needs.

Le habits of determine the duration of the peak period, which is known can determine the power required for the production of ACS.

 In the following table are reported durations of peak periods of hot water as a function of the type of user.

Time period
peak (h)
Home to 4 rooms 2-2,5
Home over 4 rooms 3,0
Hotels and pensions * 2,5-4
Offices 1,0
Hospitals and clinics 3-4
Sports ** 1,0
Changing rooms and facilities ** 1,0

* In case of receipt of the groups there during peak times can drop to 1-1,5h
** To be checked case by case 

To determine the total consumption of hot water in the peak period should also take account of sanitary appliances installed and the frequency of their use.

The following table shows the consumption of hot water at 40°C normal sanitary fixtures:

Apparatus Consumption for single use (s)
Bath 120 - 160
Shower 50 - 60
Washbasin 10 - 12
Bidet 8 - 10
Kitchen sink 15 - 20

Table consumption of equipment for individual use

For the determination of the maximum simultaneous use of hot water at 40 ° C to the UNI 9182 offers the following formula:

Qm = Σ * ((qi*Ni) / Di) = (L / m)
  • qi : Consumption of each device in liters (l);
  • Ni : Number of units corresponding to the consumption qi;
  • di: Duration equivalent to the consumption qi in hours (h).

Durations corresponding to the consumption depend on the particular type of users for which in relation to 'intensity of use should determine how many times each unit is used during the peak period.

In applications of type residential one can reasonably assume that each unit is used once per hour.

For dwellings account should be taken of some correction factors taking into account the number of dwellings: increase of users reduces the likelihood of contemporary uses of sanitary appliances.

multiplication Fall
1 1,2
2 0,9
3 0,7
3 - 8 0,92(N-3) * 0,73
9 - 25 0,985(N-9) * 0,48

* N = number of dwellings
Table multiplication factors for the max. contemporary

 La hourly flow Contemporary residential applications is:

Qmall = Qm * Fall * 1,2 * 0,8 * 1,06(M-1) = (L / h)

m with the average number of rooms per apartment.


  • Residential building with n = 15 accommodation
  • Number of rooms for accommodation m = 4
  • Domestic hot water appliances for accommodation:
    2 1 bidet washbasin + bathtub + + 1 1 shower + sink 1
  • Total number of units:
    30 basins bidet + + 15 15 baths + showers + 15 15 sinks;
  • Duration of the tip (see table): 2h;
  • Number of Uses for now: 1 (so 2 use during peak times);

Hourly flow simultaneously:

Qm =((2*10*30)/2)+((2*8*15)/2)+((2*160*15)/2)+((2*60*15)/2)+((2*15*15)/2)= 3.945l / h

Correction based on the number of number of dwellings and number of rooms:

Fall = 0,985(15-9) * = 0,48 0,44

with m = 4

The maximum range of contemporary result is:

Qmall Qm * = * 0,44 1,2 * 0,8 * 1,06(4-1) 1985 = (l / h)

If you want to do the insights on the products suitable for the production of domestic hot water , You can find information at the following links:

Rossato Group Srl
Via del Murillo, km 3.500, 04013 Sermoneta LT - Italy
Share capital € 200.000,00 fully paid up - no. REA LT-107494
VAT-CF IT01745300598

Working Time
From Monday to Friday
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