Technical data

10
Volt Free Contacts
All Purewell VariHeat modules are fitted with a multi-function clip-in module
to provide volt free contacts as standard. Remote alarm signalling is provided
for a general fault alarm and bolier normal run indication.
0-10 Volt DC Analog Input
The standard multi-function clip-in module also provides a 0-10 volt DC
analog signal interface to control the modulation level of the burner, or to
set the flow temperature set point. The 0-10 volt signal can be used for
remote connection of the boilers to a Building Management System,
(BMS) to enable modulating control remotely.
LPB Bus Communications Module
The optional LPB bus communication clip-in kit is used to connect the boiler
LMU control unit to the optional Cascade sequence control module.
Each boiler in a modular installation requires a clip-in LPB bus
communications module to communicate with the Cascade controller.
Outside Air Temperature Sensor
Purewell VariHeat boilers can be supplied with an optional outside
temperature sensor to exploit the full functionality of the boiler controls
and enable direct temperature compensation on the boiler, maximising the
condensing operating conditions. The outside temperature sensor is to be
used in conjunction with the optional Cascade control module.
When fitted with an outside temperature sensor, the boiler’s own thermostat
is overridden and the flow temperature is controlled as a function of external
temperature conditions. The flow temperature is adjusted according to a
preset heating curve built into the standard boiler controls. This slope can be
adjusted to suit the needs of individual systems by for example using
a steeper slope on underfloor heating systems.
Programmable Room Sensor
An optional combined room sensor and digital programmer can be connected
to the boiler to provide both temperature control of ambient conditions
and to programme up to three daily periods for heating or hot water.
Note: An outside sensor must be used when using the room sensor and
programmer. Separate ambient temperatures can be set for each time period
with an override facility, enabling the user to switch the system either on or
off at their request. The programmer will display the current system operating
parameters and also indicate any boiler fault conditions that might occur.
Frost Protection
The boiler control system features a two stage frost protection system.
When the boiler is not operating, the frost protection system fires
the boiler to maintain a minimum water temperature, to prevent
freezing of the heating system water.
Additionally, if an external temperature sensor is connected, the circulation
pump will be run intermittently when the outside temperature falls below 1.5°C.
Cascade Control Module
For use with multiple boilers, the optional Cascade controller can sequence
up to 12 modules. The controller is supplied with two clip-in LPB bus
communications modules as part of the standard Cascade kit, and for
each additional boiler in the modular installation, further clip-in LPB bus
communications modules must be ordered separately. (IE: A four module
installation with a Cascade control kit requires two additional LPB modules).
Purewell VariHeat boilers can be installed
in a wide variety of configurations, from
single boiler stand alone units to multiple
boilers controlled locally or by a building
management system. The controls package
is extremely versatile and can be tailored to
meet the exact needs of the heating system.
Integrated Systems
The full benefits of installing high efficiency
boilers can only be realised if the heating
system is equipped with appropriate controls,
that integrate the boiler and the other system
components, to create a cohesive solution.
For that reason, the Purewell VariHeat range
of boilers incorporate a control system that
is easy to integrate and communicates with
the leading building management system
protocols. The microprocessor based boiler
control system (LMU) accommodates clip-in
modules providing relay contacts for remote
alarm and signalling, for external control
and LPB bus communications, for use with
the boiler Cascade controller for multiple
boiler installations.
Clip in modules on the LMU
The Purewell VariHeat boiler incorporates
a number of inbuilt and optional controls
features that enable the end user to achieve
desired operational mode whilst maintaining
the optimum efficiency of the system.
The controls are housed within a fabricated
steel enclosure, and each module fascia
features a visual display allowing the user to
monitor the current operating status of the
boiler. The panel also displays comprehensive
fault code information in the unlikely event
of a boiler lockout.
Controls Overview
Purewell VariHeat