Manual 02 - Section 04

Non-Residential Solar Information Manual
SECTION 4: Hot Water Demand Calculation


The following table is a guide to determine the hot water demand for commercial or light industrial facilities.

 DEVICE              LOCATION                       WATER CONSUMED AT   

Shower              Aged Homes                     18 - per person      
                    Domestic Dwellings             15 - per person      
                    Caravan Parks                  18 - per person      
                    Hotels/Motels                  18 - per person      
                    Mining Towns                   25 - per person      

Baths               Domestic & Hotels              60 - per person per day 

Wash Basins         Domestic Dwellings              2 - per person per day
                    Offices                         1 - per person per day

Dish Washing Sinks  Domestic Dwellings              7 - per sink full  
                    Hotel/Motel                    10 - per sink full   

Dish Washers        Domestic Dwellings             10 - per meal        
                    Hotel/Motel                    90 - per hour        
                    One Meal Sitting                2 'hour' Operation   
                    Two Meal Sitting                4 'hour' Operation   

Glass Washers       Hotel Bars                                             
                    Weekdays 3 hours use/day       55 - per hour per unit   
                    Weekends 5-6 hours use/day                             

Restaurants                                         6 - 10   per hot meal    

Messes (Mining)     75'C required                  10 - per meal        

Full Laundry                                       27 - per person per day
Blocks (Mining)                                                            

Ring Main Losses    Good condition - Small         +(10%) of Total Demand
                    Good condition - Large         +(20%) of Total Demand
                    Long or Poorly Insulated       +(50%) of Total Demand


As some dish washers have their own water heating system, not all dish washers will require inclusion with the hot water demand calculations. The types to be used on the installation should be checked prior to calculating the hot water demand. Use manufacturers' recommendations wherever possible when considering the actual hot water usage of the dish washer.

When the project is to add a Non Residential Solar Hot Water System to an existing installation it is preferable to install a water meter in the existing system and accurately measure the hot water demand over a 2 or 3 month representative period. This method will ensure that the actual demand is known and can also provide hard facts to present to the customer during the selling process.

When connecting a Non Residential Solar Hot Water System to an existing hot water system, care should be taken to ensure that energy is not wasted.

The following points require particular attention:

i) Existing hot water pipe work insulation should be checked and up-graded where necessary.

ii) Heat loss up hot flow pipes and into header tanks should be checked and heat traps fitted where appropriate.

iii) When connecting into an existing oil or gas fired hot water boiler, care should be taken to ensure that the low operating efficiency of the boiler does not adversely affect the whole system.

Use by-pass valves to isolate the existing boiler during the summer months so that during these periods the boiler can be isolated from the circuit.

Low efficiency boilers can be deleted in favour of gas boosted Non Residential Solar Hot Water Systems.

iv) It is preferable to install several systems, strategically placed around the building or groups of buildings to avoid long ring main circuits. For low usage areas not economically connectable or economically suitable to the central Heat Store system, install standard Solahart roof top Residential Solar Hot Water systems.