gledhill TEC140-OV Installation & Servicing Instructions Manual page 37

Boost Immersion Heater
All Torrent ECO HP models are fitted with a 3kW immersion heater so that the store can be
heated to a temperature above the heat pump delivery temperature to increase the hot
water performance of the unit if necessary. Because the TorrentHP is a primary thermal
store it is not necessary to heat the store above 60°C for hygienic protection against
growth of 'legionella' . This is because the domestic hot water is heated instantaneously via
a heat exchanger and so there are no legionella problems associated with stored water.
This is of great significance for the heat pump application where the heat pump will
not normally be able to raise stored water to above 60°C which is necessary to sterilise
a cylinder.
By using the immersion element to boost the water temperature (not needed for
legionella protection as described above), this will provide a greater volume of hot
water from a given size of cylinder (see figures 3-5, page 5). However, the overall
COP of the system will reduce and so to maximise the benefit of fitting a heat pump,
minimal use should be made of the immersion heater.
The immersion heater should not be left permanently switched on as this will drastically
reduce the contribution of heat pump to hot water heating and hence increase the
running costs.
If the use of the immersion heater is necessary to meet the hot water requirements of
a dwelling, then please consult your heat pump manufacturers instructions regarding
the wiring and control of the immersion heater operation.
If these instructions aren't included in the heat pump manual, then a suggested method
of controlling it is described below.
Typical schematic wiring diagram for the boost immersion heater
using programmable immersion heater timer.
Page 37
INSTALLATION
Control By Programmer
The operation of the boost immersion heater
can be controlled by means of an independent
time switch as shown schematically. The on time
settings on the immersion heater should be
between 30 – 60 minutes later than the on times
set for the hot water programmer channel.
For example if the hot water is programmed to
come on between say 0600 – 0900 and 1700 –
2200 then the immersion heater timer setting
should be 0640 – 0900 and 1740 – 2200. This will
make maximum use of the heat pump allowing
it to charge the store to the maximum potential
temperature before any use of the immersion
element.
Additional top and bottom thermostat pockets
can be provided in case a more sophisticated
control system is required to be fitted.
Control By Heat Pump Control System
Where more sophisticated control systems
are used to control the immersion heater, the
immersion heater may be programmed to only
achieve 60°C. Please consult the heat pump
manufacturer's instructions/help desk for
further information on their control systems to
ensure that the required operation is achieved.
WIRING DIAGRAM