Technical data

11
Options for a single Boiler only
Programmable room sensor (QAA73)
Outside air sensor (QAC34)
2nd Heating Circuit Clip-in relay kit (AGU2.500)
DHW Cylinder Sensor Kit (QAZ21)
Outside Air Sensor
An optional outside air temperature sensor may be wired directly to the boiler
to exploit the direct weather compensation functionality of the boiler controls.
This sensor may be connected to the control scheme and should ideally be
positioned on an external wall with northerly aspect.
2nd Heating Circuit Clip-in Relay Kit
To control a second heating circuit, an additional clip-in relay kit is required
for fitting directly to LMU. The kit comprises a relay and water temperature
sensor complete with pocket.
This kit provides outputs for a pump and mixing valve.
n Mixing valve allows second heating circuit to operate at a different
temperature set-point to heating circuit 1.
n Second heating circuit should operate at the same or lower temperature
than circuit 1, e.g. underfloor heating.
n Programmed via QAA73 programmable room sensor
n Compensated flow based on outside air temp and using a curve separate
to that of heating circuit 1 owing to mixing valve
n Optimised start/stop based on outside air temp
n Frost protection based on water temperature in second heating circuit
For the second heating circuit, the boiler will manage the circuit pump and/
or mixing valve via contactors, according to the program requirements of
the programmable room sensor and the water temperature sensor. Only one
programmable room sensor may be connected, therefore the second
heating circuit management is derived from time control and external air
temperature measurement.
DHW Cylinder Sensor Kit
This kit is for a domestic hot water (DHW) circuit directly controlled from the
boiler, but programmed via the QAA73 programmable room sensor, and
features:
n Immersion sensor complete with pocket
n DHW cylinder sensor and pump output directly from boiler LMU
n Frost protection based on stored water temperature
n Reduced storage temperature for non-occupancy hours
n Anti-Legionella function
For the DHW cylinder circuit, the boiler will manage the primary coil pump
according to the program requirements of the programmable room unit and
the DHW cylinder sensor.
On Purewell VariHeat boilers, the control
options for single boilers are different to
those for multiple boilers.
Please refer to page 12 for controls on
multiple boilers.
All controls functions are managed via the
‘boiler management unit’ Siemens LMU64.
Using a combination of options, the level
of control is expandable for up to 2 heating
circuits and 1 domestic hot water cylinder.
A circulation pump overrun timer is
incorporated within the boiler LMU.
Programmable Room Sensor
A single boiler Purewell VariHeat system
can be fitted with a single programmable
room sensor, which should be located in
the first heating zone. This room thermostat
allows heating circuit management to be
based on both the internal and external
air temperature. The boiler will manage
the heating circuit pump via a contactor
according to the program requirements
of the programmable room unit.
Features:
n Individual 7 day program with auto
summer / winter hour change for heating
circuit 1, heating circuit 2 and DHW
n 3 periods per day per time program
n Constant or variable temperature flow
n Compensated flow temperature based on
external and room air temperatures
n Optimised start / stop based on external
and room air temperatures
n Building frost protection based on
room air temperature
n Summer shutdown based on
outside air temperature
n Holiday period with frost protection
n Reduced temperature, night set back
for non occupancy hours
n Pump kick for pumps controlled
from boiler
n Programme lock to prevent tampering
n Individual temperature settings
for each zone
To achieve full functionality an outside air
sensor must be fitted.
Control Details
Purewell VariHeat Single Boiler Installations