Dimplex LA 9 MI - Selection of Heat Emitters and Flow Temperatures; Minimising Flow Temperature; Considerations for Fan Convectors

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Section 4: Selection of heat emitters and flow temperatures
Minimising the flow temperature
In most oil and gas boiler systems the efficiency doesn‟t
vary greatly with flow temperature, therefore the flow
temperature is set to around 70°C to 75°C. The high
temperatures are not always required as downstream
regulator such as mixing and thermostat valves, prevent
the building from overheating.
To design the most efficient heat pump system it is
essential to minimise the flow temperature. When using
low flow temperatures the choice of heat emitter is critical
to ensure enough heat can be emitted into the room. A
number of industry stakeholders have produced a guide to
selecting the correct heat emitter, an extract of which is
shown in Figure 5. The full guide is available for download
from HHIC website. The guide shows that systems with
lower flow temperature achieve the highest SPF‟s which
would reduce running costs and carbon emissions.
Green areas show suitable heat emitters
Example: a domestic fan convector such as a
SmartRad can be installed with a flow temperature of
45C.
Orange areas show that extra caution is advised
Example: standard radiators should not be installed
with a flow temperature of 60C as a flow
temperature of 50C would give the necessary output
without causing the radiator to become excessively
large.
Red areas show that this technology is not suitable
Example: under floor heating on a screed floor with a
wood covering would not emit enough heat into the
room with a flow temperature of 45C.
Figure 5: Extract from the HHIC's guide to heat emitter selection for a heat loss of 80W/m2
Considerations for fan convectors
The benefits of installing SmartRad with a heat pump
system are well known and explained in the SmartRad
planning manual. This selection deals with connecting
SmartRad with the LA MI range of heat pumps.
When connecting the SmartRad the same principles
should be followed as for any other heat emitter. The
minimum flow rate for the heat pump should be observed.
The heating circuit should be designed in such away to
maintain the flow to the heat pump even when the part of
the circuit is shut off by motorised valves or the heating
circulation pump is off.
For full details about connecting SmartRad
to an inverter air source heat pump see the
SmartRad planning manual.
The Heat Emitter Guide is widely available to
download on the internet. Hard copies are
available upon request by contacting the
MarComs team at Dimplex.
As a rule of thumb, by lowering the flow
temperature by one degree, the system
performance will improve by 2%.