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place – provided the boiler connections were on the same level. If one pipe
were connected to the top and the other to the bottom of the boiler, a slow cir-
culation would be found to exist. If instead a pipe leaving the top of the boiler
were to be taken to the top of the room, allowed to circulate around the room
and return to the bottom of the boiler, a rapid circulation would be evident. This
principle should be borne in mind in the design of any heating system. Most
heating installations are a compromise between what is ideal and what is prac-
ticable, in consideration of possible pipe runs, radiator and boiler positions, and
the shape of any particular building.
There are a few rules, which should be observed:
l. The boiler must be big enough for the job it has to do.
2. The pipes should be of a size sufficient to convey the volume water re-
quired to give up the needed heat.
3. Pipe runs should be as direct as possible.
4. A system should be planned to provide enough heat. In the worst pos-
sible conditions.
5. The occupants of rooms should be given a means of controlling the
heat output in the room by means of valves.
From the point of view of heat control, one valve only is needed and
this can be fixed on either pipe although in practice it is usually fitted to the
return or lower pipe where it is out of the way. It is useful to fit a valve on
each pipe so that radiator can be taken out for repair without having to run off
the whole of the water in the system.
Cold water supply and distribution
All the water we use derives initially from the oceans and is made
available to us by the rain cycle. The heat of the sun, to rise and form clouds of
water vapour evaporates water at the surface of the ocean. These clouds are
swept towards the land by the incoming sea breezes. Where there are hills the
clouds are carried upwards into a cooler atmosphere and condensation takes
place in the form of rain. The cycle is completed when the water so falling on
the land drains away to streams and rivers and is carried back to the sea. Some
of the rainwater, of course, evaporates from the surface of the earth, from rivers
and lakes. Some of the rain-water soaks into the earth and is held in under-
ground basins of impervious rock strata, from where it can be raised by means
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