Page 108 - GRIHA Manual Volume III - Introduction to National Rating System
P. 108
Renewable energy application 101
Classiication of solar water heating systems
Solar water heaters can be classified into following main categories.
1. Closed-loop system and open-loop system: In a closed-loop system, the water when heated
never comes in contact with the atmosphere. These systems use a heat transfer fluid (water
or some other liquid with a much lower freezing point) that easily absorbs and releases
heat. This fluid runs in the copper tubing attached to the absorber plate. After getting
heated, it moves into a heat exchanger in the water tank to boil the water stored in the
tank. These heat exchangers are installed to protect the solar water heater from hard water
and to survive freezing temperatures in cold regions. In very cold regions, the heat transfer
fluid can contain an anti-freeze like non-toxic propylene glycol.
In open-loop systems there is no need for heat exchangers as the heated water
circulates directly through the solar collector. These systems do not use any heat transfer
fluid. Open loop systems are simple to design and construct, and require comparatively less
maintenance.
2. Active system and passive systems: Active solar water heating systems require external
energy to operate. They have a forced circulation system and generally use electrical pumps
to circulate water through the collector panel and storage tanks.
Passive systems do not require any external power to run. They utilize the thermo-
siphon effect, which is a simple system that uses the natural convection phenomenon
of hot water rising from the collector panel to carry the heat up to the storage tank. This
movement occurs due to different densities of hot and cold water. The water in the solar
collector gets heated and due to its comparatively lower density (than cold water), it
rises to replace the cold water in the storage tank. However, in this case the storage tank
should always be installed above the collector panel. These systems are apt for small-scale
applications where the water is of potable quality.
Design, operation, and maintenance of solar water heating system
1. Estimate the building’s hot water requirement: For designing system capacity, the first step is
to estimate the building’s hot water demand. Hot water requirement for the building can
be calculated as per the values given below for typical hot water consumption for different
activities. (Consumption figures may vary depending on lifestyle, age, habits, and weather
conditions).
Table 1 Typical hot water consumption for different activities
Bathing (using bucket water) 15 litres per person per bath (one bath)
Shower bath 25 litres per person per bath
Tub bath 35–50 litres per person per bath
Cooking 5 litres per person per day
Washing clothes 10 litres per person per day
Washing utensils 5 litres per person per meal
Making tea/coffee 150 ml per person per cup
Typically, the capacity for a solar water heater system is such that it can meet one day’s
requirement of hot water during winter season.
Classiication of solar water heating systems
Solar water heaters can be classified into following main categories.
1. Closed-loop system and open-loop system: In a closed-loop system, the water when heated
never comes in contact with the atmosphere. These systems use a heat transfer fluid (water
or some other liquid with a much lower freezing point) that easily absorbs and releases
heat. This fluid runs in the copper tubing attached to the absorber plate. After getting
heated, it moves into a heat exchanger in the water tank to boil the water stored in the
tank. These heat exchangers are installed to protect the solar water heater from hard water
and to survive freezing temperatures in cold regions. In very cold regions, the heat transfer
fluid can contain an anti-freeze like non-toxic propylene glycol.
In open-loop systems there is no need for heat exchangers as the heated water
circulates directly through the solar collector. These systems do not use any heat transfer
fluid. Open loop systems are simple to design and construct, and require comparatively less
maintenance.
2. Active system and passive systems: Active solar water heating systems require external
energy to operate. They have a forced circulation system and generally use electrical pumps
to circulate water through the collector panel and storage tanks.
Passive systems do not require any external power to run. They utilize the thermo-
siphon effect, which is a simple system that uses the natural convection phenomenon
of hot water rising from the collector panel to carry the heat up to the storage tank. This
movement occurs due to different densities of hot and cold water. The water in the solar
collector gets heated and due to its comparatively lower density (than cold water), it
rises to replace the cold water in the storage tank. However, in this case the storage tank
should always be installed above the collector panel. These systems are apt for small-scale
applications where the water is of potable quality.
Design, operation, and maintenance of solar water heating system
1. Estimate the building’s hot water requirement: For designing system capacity, the first step is
to estimate the building’s hot water demand. Hot water requirement for the building can
be calculated as per the values given below for typical hot water consumption for different
activities. (Consumption figures may vary depending on lifestyle, age, habits, and weather
conditions).
Table 1 Typical hot water consumption for different activities
Bathing (using bucket water) 15 litres per person per bath (one bath)
Shower bath 25 litres per person per bath
Tub bath 35–50 litres per person per bath
Cooking 5 litres per person per day
Washing clothes 10 litres per person per day
Washing utensils 5 litres per person per meal
Making tea/coffee 150 ml per person per cup
Typically, the capacity for a solar water heater system is such that it can meet one day’s
requirement of hot water during winter season.
