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flow tEmpEratUrES of HEatIng SUrfacES
Heating surface temperature
the flow temperature of the heating
system is decisive for the application
options and the operating mode of
the heat pump. Heating systems that
require a flow temperature in excess
of +60 °C can only be operated in
dual-mode together with a second
heat source. the changeover point
of the heat pump is determined not
only by the heating output of the heat
pump, but also by the sizing of the
heating surfaces. radiator heating
systems used to be sized around a
flow temperature of +90 °C. today,
retrofitting thermal insulation or
oversizing generally means, that a
flow temperature of only +70 °C or
less is generally required. the heating
surfaces of new systems should be
sized around a flow temperature of no
more than +55 °C to enable a mono-
mode operation.
Example:
Up to what outside temperature
can a heating system with a flow
temperature of +75 °C (heating
curve b) be operated with a heat
pump operating with a flow
temperature of up to +60 °C? in this
example, the point of intersection
between heating curve b and the max.
heat pump flow temperature of +60 °C
arrives at an outside temperature
of –4 °C. the application limit of
this heat pump therefore lies at an
outside temperature of – 4 °C because
of the heat distribution system. it is
often noted in practice that, through
external and internal energy recovery,
the heating limits can be extended to
meet lower temperatures. this means
that the heat pump covers a higher
percentage of the annual heating
load.
Rule of thumb:
the lower the flow temperature of the
heating system, the higher the output
of the heat pump.
According to the above diagram the following flow temperatures produce the
following changeover points to start the second heat source:
Curve A: Flow temperature 90 °C changeover point – 0 °C ot
Curve b: Flow temperature 75 °C changeover point – 4 °C ot
Curve C: the flow temperature is lower than +60 °C, enabling the heat pump
to operate in mono-mode.
Curve D: the flow temperature is lower than +60 °C, enabling the heat pump
to operate in mono-mode.
Flow temperatures for the corresponding outside temperatures
Heating flow temperature
external temp
Heat pump
flow temp.
Summary of Contents for Heat pumps
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