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C
L
OMBATTING
EGIONELLA
Water systems in buildings have been associated
with outbreaks of Legionnaires' Disease, particu-
larly in health care facilities where occupants are
signifi cantly more susceptible to infection.
In recognition of the risks in hospitals, a Code of
Practice for the Control of Legionella in Health
Care premises has been issued by the Department
of Health.
Codes of Practice applicable to other premises
have been published by other organisations,
principally the Health and Safety Executive (HS)
(G70) and the Chartered Institute of Building
Services Engineers (CIBSE, TM13).
All Codes of Practice draw attention to the design
and operation of water systems with reference to
avoidance of factors that favour colonisation by
Legionella bacteria. These factors include stagna-
tion, lukewarm conditions (20ºC to 45ºC) and the
accumulation of debris, scale and corrosion in the
base of tanks and calorifi ers.
An independent evaluation of our products was
commissioned to investigate their resistance to
the build-up of Legionella bacteria. Experiments
were conducted to determine whether, following a
substantial challenge by Legionella Pneumophilia,
after overnight and stagnation conditions, the
system was rendered free from viable recoverable
Legionella. It was found that at 61ºC, following a
challenge of approximately 107 organisms per litre,
within one hour, more than 99.999% of organisms
had been killed. After a subsequent stagnation pe-
riod, sampling did not reveal any residual contami-
nation. The design of the base of the integral water
tank precludes Legionella colonisation, even after
build-up of debris. The heating process ensures
that the water at the bottom of the tank reaches the
same temperature as in the rest.
In addition the controls of the appliance provide
anti-legionella routines to provide additional protec-
tion.
Based on data obtained through experiment, this
appliance can be described as Legionella resistant
as it is considered unlikely that, at the temperature
tested, the organism would colonise the water
heater and present a possible health risk.
iHE
DESCRIPTION OF APPLIANCE
The iHE is a gas fi red, low No×, multi-heat engine
cascading boiler system, with an integrated 5" Low
Loss Header for the supply of a low temperature hot
water heating system. The iHE range of boilers also
features an integrated stainless steel tank and plate
heat exchanger for the supply of hot water.
Fully automatic electronic controls are integrated
into the appliance, with a wide range of control and
sensor options available. The controls also provides
voltage free outputs for Enable, Burner On and
Fault, for remote BMS use.
Each heat engine module consists of a stainless
steel combustion chamber, premix burner, modulat-
ing fan, gas valve, ignition and fl ame detection elec-
trodes and an NTC sensor for management control.
Each heat engine module is equipped with NTC
sensors for precise temperature control on fl ow and
return manifolds. Fully premixed, radiating, modu-
lating burner, integrated with gas valve to deliver
precise gas/air mixture throughout the full modula-
tion range.
Common combustion air intake manifold, takes air
from boiler room (type B23 fl ue) or directly from
outside via a combined fl ue system (C13 & C33). An
air non-return valve is integrated into the air supply
of each heat engine, to ensure that fl ue products
cannot contaminate the air supply, when the heat
engine is not in use.
The safety and operation functions of each heat
engine are managed by micro processor control-
led circuit boards, one for each heat engine. The
upper controller also acts as the cascade controller,
switching/modulating the heat engines according to
the demand and readings from the systems sen-
sors. Control is performed using comparison param-
eters between the requested temperature and the
global fl ow temperature.
C
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:
ONTROL
OGIC
At full demand, each heat engine is ignited one at
a time, until all heat engines are operating at full
output.
As fl ow and return temperatures increase, all heat
engines will begin to modulate down together, until
all are operating at minimum input rate. As fl ow
temperatures begin to approach the calculated set
point, one of the heat engines will stop, leaving
the others operating at minimum input rate. This
will continue until all heat engines have stopped
and temperature fl ow requirements have been fully
satisfi ed.
5
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