(57) The invention provides a heat exchange system wherein primary fluid (heated water)
is circulated by means of a pump (34) through a heat exchanger (33) through which
secondary fluid (water to be heated) is also circulated, and including sensing means
(42, 47) for controlling the rate of heat supplied to the heat exchanger (33) via
the primary fluid, characterised in that the sensing means (42, 47) comprises a temperature
sensor means (42, 47) which is arranged to sense the rate of change of temperature
of the primary and/or secondary fluid issuing from the heat exchanger (33). Preferably,
there are two temperature sensors (42, 47) which respectively sense the rate of change
of temperature of the secondary water and primary water such that in use, when a pre
set rate of change of temperature in the secondary water is detected (showing that
the secondary water is flowing), the pump (34) is switched on for the supply of hot
primary water, and the rate of change of temperature of the primary water is used
to control the pump (34) to control the temperature of the secondary water.
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