gledhill Torrent GreenHeat TGH140-OV Design, Installation & Servicing Instructions page 13

General
• All Torrent GreenHeat HP models covered by this manual, are only suitable for open
vented primary (heat pump and space heating) circuits. Therefore the pressure
in the primary circuit depends upon the height of the feed and expansion cistern
and could be as low as 0.20 bar. Therefore ensure that the heat pump selected
will operate at primary circuit pressures e.g. it is not fi tted with a non-adjustable
low system pressure switch.
• The heat pumps normally operate at lower temperature difference (5-10°C)
between fl ow and return than that for a gas boilers (10-20°C) resulting in higher fl ow
rates in the heat pump primary circuit. Therefore it is important that the primary
pipework connecting the heat pump to the thermal store and the circulating pump
are sized to achieve fl ow rates recommended by the heat pump manufacturer.
• The effi ciency (i.e. coeffi cient of performance, COP) of a heat pump depends
upon the primary fl ow and return temperatures and it is generally higher at lower
primary circuit temperatures. Also the heat pumps normally operate at lower fl ow
temperatures; typically 45-55°C compared with 75-80°C for gas boilers. Therefore if
traditional radiators are used then, these should be oversized in accordance with
the heat pump manufacturers recommendations.
• For optimum operational effi ciency and hence lower running costs, a low temperature
space heating (e.g. under-fl oor heating) system should be used where feasible.
Hot water performance of TGH210HP at 15 - 17 l/min draw off rate
60
50
40
30
20
10
0
HW Outlet (65) (°C)
HW Outlet(75) (°C)
The draw off volume fi gures shown above are for the TGH210 HP store. These are
increased accordingly as the cylinder capacity increases. The graph illustrates the
increase in volume that can be achieved by the use of the auxiliary heat source.
A 15 - 17 litre/min fl ow restrictor is fi tted to the Torrent GreenHeat HP hot water supply
outlet on commissioning. Check that the hot water fl ow does not exceed 17 litre/min.
Particular attention needs to be paid to the product size selection. If the
intention is for the majority of the hot water to be provided by the heat
pump with minimal use of the auxiliary immersion element then it may be
necessary to choose a larger store.
Draw-off volume (litres)
HW Outlet (55) (°C)
Page 13
Heat Pump Sizing
• The effi ciency (i.e. coeffi cient of performance,
COP) of an air source heat pump and hence
its heat output generally decreases as
the ambient air temperature decreases.
Therefore, this factor should be taken into
account when sizing and selecting the heat
pump.
• The design space heating load of a dwelling
should be calculated in accordance with
BS 5449. The allowance for domestic hot
water heating (shown in table below),
depends upon the operating mode. For
example, if the system is designed to operate
with priority for domestic hot water, then
no additional allowance for hot water is
required for sizing the heat pump.
Allowance for Domestic Hot Water
Torrent
Model
180 HP-SOL
180 HP
210 HP-SOL
210 HP
250 HP-SOL
250 HP
300 HP-SOL
350 HP
450 HP-SOL
450 HP-SOL
AVG CW Inlet Temp (°C)
DESIGN
Heating
Allowance for Domestic
Hot Water
Hot Water
Flow Share
Priority
Mode
Mode
0kW 1.5kW
0kW 2.5kW
0kW 3.0kW
0kW 3.5kW
0kW 4.0kW
0kW 5.0kW
SYSTEM DESIGN