gledhill Torrent GreenHeat TGH140-OV Design, Installation & Servicing Instructions page 37

Boost Immersion Heater
All Torrent GreenHeat HP models are fi tted 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 signifi cance 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 fi gures 3-5, page 5). However, the overall COP of
the system will reduce and so to maximise the benefi t of fi tting 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 the preferred 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 in fi gure 13.
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 fi tted.
WIRING DIAGRAM