Hot water is needed for bathing and washing in domestic uses. Higher temperatures melt oil and grease from the human body, pots and pans, making the clean-up easy. Bathing with hot water opens the body pores, washing dirt and sweat easily and giving a sense of freshness.
In its rudimentary form, water in Indian homes is heated in pots on local stoves and heaters. However only a small quantity required for immediate use is heated. Fuel used varies from solid fuels, like wood and coal to kerosene, liquefied petroleum gas (LPG) and electricity.
Except for very local use, this method of water heating is inefficient and dangerous. Open flames, apart from creating harmful gases, can also cause burn injuries which might lead to death.
HAMAM, a traditional displacement-type hot-water heater, which consists of a copper sheet, a chimney and a grating and uses, solid fuels, like coal, and wood. Hamam serves its purpose safely if installed in the correct manner.
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Ambient air temperature in India varies widely form near Arctic conditions in Leh, (Jammu and Kashmir state) (-20° C or lower in winter) to 40-45°C in Southern India. Hot water usage is, thus dictated by the weather conditions, bathing habits and economics. The requirement of hot water is calculated according to these conditions.
Hot Water Requirement:
Hot water is used in kitchens and bathrooms in residential areas.
Hot water may also be required as heating medium for space heating and air conditioning. The water is not consumed directly but the boiler capacity has to be increased to provide for the heat lord.
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It is required for laundries and industrial kitchens and in buildings like hotels hospitals, schools, hostels, industrial canteens, etc.
Hot water generated in a central boiler must be supplied to point of use efficiently without excessive loss of temperature and pressure.
If the length of the pipe from the boiler to the point of supply is long, the heat in the water will dissipate even when the pipes are insulated. On opening a tap hot water will come out of it only after delivering the cold water in it taking a time of one to five minutes.
If the rate of flow at the tap is about 8-10 lit/min, the user will waste about 8-50lit. of water before getting the hot water. He would also have wasted the energy used for heating the water initially.
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Recirculation –
To overcome this wastage of heat, a return pipe is installed from the remotest section of the hot water main which is connected back to the vessel supplying hot water to the building. In case there are a number of risers, each one is provided with a return line, connected to a common return heater to the boiler.
Thermo-siphonic action
(a) Circulation of hot water from the main pipe connected to the boiler and the return line can occur without the aid of a pump by thermos phonic action which takes place due to the difference in the density of water at different temperature.
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Reverse Circulation System:
Reverse circulation is similar to the up feed system, except that the return flow occurs in the same direction as that of the main flow pipe (i) till the end of the remotest circuit from where it returns to the clarifier through a separate reverse return line (ii) This system is suitable where the circuits are long and where there is a likelihood of the least favorably placed fixtures not receiving adequate flow or pressure. A reverse return-line enables closer balancing of pressure in the system.
Many a time the main hot water flow and return lines are laid on the terrace of the building and supply pipes dropped to lower floors in pipe shafts.