Page 8
DESIGN
SY
STEM DESIGN
General
• All Torrent 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 efficiency and hence lower running costs, a low
temperature space heating (e.g. under-fl oor heating) system should be used where
feasible.
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 Heating
Model
Allowance for Domestic Hot Water
Hot Water Priority Mode
Flow Share Mode
THP150
THP180-SOL
0kW
1.5kW
THP180
THP210-SOL
0kW
2.5kW
THP210
THP250-SOL
0kW
3.0kW
THP250
THP300-SOL
0kW
3.5kW
THP300
THP450-SOL
0kW
4.0kW
THP450-SOL
0kW
5.0kW
Heating System Arrangement
The Torrent HP models are designed to be
heated directly by an air or a ground source
heat pump and the space heating can be
supplied directly from the heat pump circuit
as shown in fi gures 6 and 8 or from the thermal
store as shown in fi gures 7 and 9. The selection
between the two options will depend upon the
operating characteristics of the heat pump,
type of heating system and control strategy.
For general guidance: -
• If the heat pump requires a buffer for
operation; for example to reduce rapid
cycling etc, then the system would benefi t
if the heating system is supplied from
the thermal store (figures 7 and 9). In
this configuration, the operation of the
heat pump Is only controlled by the store
thermostat(s).
• If the heat pump is multi-stage or modulating
type or has weather compensating controls,
then the space heating circuit should be
supplied directly from the heat pump as
shown in figures 6 and 8. In this system
confi guration, the thermal store is only used
for producing hot water.
• A hybrid system arrangement can also
be used (not shown). For example; a low
temperature weather compensated heating
circuit e.g. under floor heating can be
supplied directly from the heat pump circuit
and constant temperature e.g. towel rails can
be supplied from the thermal store.
Ballvalve/overfl ow - All Models
Where the whole of the heating system is
supplied from the thermal store, fi gures 7 and
9, then a ballvalve and overfl ow should be fi tted
in the feed and expansion tank.
Where the heat pump supplies the heating
circuit directly, fi gures 6 and 8, then fi tting a
ballvalve and overfl ow is optional if it is practical
on occasions to manually fi ll the store. However,
fi tting a ballvalve and overfl ow will eliminate the
need for the householder to undertake this task
and is therefore preferable. If the siting of the
Torrent HP makes it diffi cult to fi t an overfl ow
then the ‘manual fi ll’ option can be used. In all
cases, if a ballvalve is fi tted, then an overfl ow/
warning pipe must always be fi tted.
Содержание THP180 sol
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