Technical data

4
Reduced Boiler Weight
Purewell VariHeat boilers have been reduced in weight significantly,
in comparison to traditional atmospheric cast iron boilers, with weights as
low as 1.3 Kg/kW output. The new casting designs are extremely efficient
therefore fewer sections are required to produce the given boiler outputs.
Purewell VariHeat - heat exchanger arrangement, PV 180c
Primary Heat Exchanger
Each boiler has a cast iron primary heat
exchanger arranged with horizontal sections,
connected at one end only to allow expansion
and contraction, retaining a proven
horizontal series water flow for even
hydraulic distribution.
The primary heat exchanger is fitted
on top of the base assembly, which
encloses the secondary heat exchanger
on the condensing models.
The high efficiency non condensing
models are designed for a traditional
11°C ∆t temperature rise and have a
minimum return temperature of 50°C.
Secondary Heat Exchanger
Condensing performance is achieved
by returning the system water through a
copper/aluminium composite construction
secondary heat exchanger and extracting
the latent heat from the flue gases in
the base of the boiler. In keeping with
most modern high efficiency boilers, the
condensing heat exchanger is designed for
20°C ∆t temperature rise, with minimum
flow temperature of 40°C, maximizing the
opportunity for condensing performance.
Burner
The Purewell VariHeat features a fully
modulating pre-mix burner control system.
An electronic thermostat monitors the boiler
operating conditions and automatically
adjusts the output to suit.
The gas/air ratio control system ensures that
clean and efficient combustion is maintained
throughout the maximum modulation range,
down to a minimum of 20% capacity.
The plaque burner is positioned centrally
above the primary heat exchanger and is
constructed using a FeCrAl Aconit woven
mesh. This design of burner allows for
good flame stability at low turndown rates.
The woven fibre construction of the burner
also results in lower flame temperatures
being achieved and lowering NOx emissions.
Specification
Purewell VariHeat
Natural Gas
Gas Valve
Fan
Pre-mix down
firing burner
Primary heat
exchanger -
cast iron
sections
Base assembly
Secondary heat exchanger
- condensing models only