Boiler heat exchanger’s the bottom heated and the heat will be transferred to water at the bottom. This heated water will rise and cooler water above will descend to the bottom and heated. If a large pipe is taken from the top of the boiler to rise through the house and then returned to the bottom as in the diagram, the heated water will rise up and push the cooler down. It will enter the boiler at its bottom, heated and rise again. This is the basis of gravity system.
The gravity system consists a BOILER to heat the water, situated at lowest
position in the house (basement or cellar), FLOW pipe for the hot water to rise
directly up as high as possible in the house, RETURN pipe to bring the cooler
water back to the boiler. The other things are built on that.
The RADIATORS increase the heat emitting surfaces, where the heat is wanted, the
valves to control or divert the flow of water and the feed and expansion tank
maintains a reserve of water.
This is the simplest system. It has its limitations that only motive power to
circulate the water is the force of gravity. Although, this powerful force pulls
down the heavier cooler water, its effect is reduced by the need to raise the
same amount of hot water, which is only slightly lighter, so the net force
(effort) is very slight. This makes the system slow and unresponsive
.
Another limitation is that each liter of water can hold a limited amount of
heat. Therefore, many liters of water are needed to be heated and moved around
the house. This means large pipe work and longer heating time.
The biggest advantage with a gravity system is the fact a pump is not needed.
Hence eliminate the common single reason for breakdowns. This advantage is more
than out weighed by the disadvantages. The system is slow and unresponsive.
Large pipes are needed they are expensive to install and heat loss from them can
make the system more expensive to run, not installed in domestic properties.
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