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Some Links to Information on Legionnaires' Disease
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Advantages and Benefits of Copper in Hot Water Systems Copper has been in widespread use in heating systems for many years. Over the last 30 years, a wide variety of competing materials have tried and failed to replace copper as the preferred plumbing and heating material. Listed below are some of the benefits of copper:- Resistance to corrosion : Copper has proved to be a reliable and economical non-ferrous metal for the construction of hot water storage vessels. It is used extensively throughout the world due to its long life and an ability to withstand most concentrations of corrosive elements found in domestic hot water. Resistance to Pressure : It can withstand pressure and stresses with no problems, side effects or long-term degradation. Resistance to Expansion : Copper has a low coefficient of linear expansion. Resistance to Fire : Copper offers excellent resistance to fire and does not generate toxic fumes. Biostatic Properties : Copper is well known as an inhibitor to bacterial growth, such as E coli, Legionella bacteria which cause Legionnaires Disease. Between 1982 and 1984, the Public Health Laboratory Service carried out a survey in England and Wales to establish the prevalence of Legionellae within the domestic water services of large buildings such as hospitals and hotels. The results indicated that the bacterium was less prevalent in copper system. Further research, at the Centre for Applied Microbiology and Research, under laboratory conditions, confirmed that copper suppressed the growth of legionellae whilst other materials did not.
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Rycroft Copper-lined Calorifiers & Maximisers The
Rycroft Maximiser has been developed to meet today’s need for a
compact calorifier which will respond to high peak loads with minimal
demand for boiler power. This high output semi-storage calorifier is the
ultimate solution to space limitations, power regulations, fluctuations
in demand and energy savings. The Rycroft Maximiser is a semi-storage calorifier equipped with an in-built non-storage heat exchanger. The baffled heat exchanger with a 2-pass shell provides an efficient compact unit which is considerably smaller than a conventional storage heater battery. An
integral pump circulates secondary water between the storage section and
the heat exchanger. The interconnecting pipes are so arranged that the
entire volume quickly reaches full storage temperature. This
not only assures a maximum reserve of hot water but also eliminates any
areas of cool water, which may promote the growth of Legionella
pneumophilia. The
maximum demand from the boiler can be regulated by adjusting the
circulation rate through the heat exchanger and offers a flexibility of
control not possible with a simple storage battery. Demands for hot
water are promptly sensed by the control system which immediately starts
the heat recovery process. Low draw off rates only require low demands
from the boiler service. High draw-off rates can only generate a demand
from the boiler equal to the limit by the Maximiser control. The
reserve of stored water provides the extra supply of hot water required
for peak flows and the heat exchanger continues to make up the loss
after the surge has ended. How
it Works The
Maximiser has a fixed speed centrifugal pump which circulates secondary
water through the heat exchanger and into the storage cylinder. The flow
rate through the heat exchanger is set above the calculated peak hourly
demand. The heat exchanger is sized to raise the temperature of the
secondary water from cold to design temperature in a single pass through
the exchanger. When
the unit is first commissioned the content is cold. The pump draws water
from the bottom and returns it hot through the spreader into the top
half of the cylinder. Here the hot water mixes with the cold storage,
gradually raising the entire contents to the design temperature. When
the demand for hot water is less than the peak hourly rate the cold feed
is drawn directly into the heat exchanger by the pump together with some
hot water from the bottom of the cylinder. The water passing through the
exchanger is already partially warmed and only sufficient heat is added
to reach the design temperature. When
the demand for hot water exceeds the pump rate, cold feed is still drawn
into the heat exchanger but the excess cold feed enters the bottom of
the cylinder without disturbing the layer of hot water above. The heat
exchanger now generates hot water at the maximum design rate and flow
from the cylinder outlet is supplemented by hot water from the storage
section. After
a heavy demand the heat exchanger continues to work at high output until
the storage temperature in the bottom of the cylinder is restored. In
order to make full use of the stored hot water it is advisable to fit a
non-return valve on the secondary return. This will prevent cold water
entering the secondary system via the return leg. It will be appreciated
that even under severe overload conditions the heat exchanger will
maintain full power output giving a moderate mix temperature until such
time as normality returns. •
The Maximiser is able to handle peak flow rates in excess of its
hourly rating without overloading the boiler. An advantage over the
various forms of instantaneous heaters available. •
The Maximiser offers an adjustable limit to the demand from a
boiler system that may have other priorities during the year. •
The Maximiser ensures maximum use of the stored volume with no
stagnant cold areas normally associated with storage calorifiers. • The Maximiser with its high output battery and quick response allows considerable saving in floor space over conventional domestic hot water storage systems. Storage Volume The
optimum storage capacity for the Maximiser is approximately 25% of the
peak hourly consumption. This capacity normally provided sufficient
buffer volume to cope with the fluctuations in demand while the heat
exchanger continues at a steady input. For some applications, the hourly
demand is concentrated into a few minutes. Under these conditions,
either the storage capacity must be increased to meet the full demand or
the heat exchanger sized accordingly. |
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Figure 1: When the draw off is less than the pump circulation rate, all the cold feed is fed straight to the heat exchanger. The pump also takes hot water from the bottom of the cylinder, maintaining a full reserve of hot water.
Figure 2: When the drawoff exceeds the pump circulation rate, the excess cold water collects in the bottom of the cylinder, ready to be passed through the heat exchanger when the peak demand ceases. |
Figure 3 : The pen trace is typical of a fluctuating demand for hot water; sometimes in excess and sometimes less than the hourly peak rate.
Figure 4 : The response to fluctuating demand by the Maximiser heater is restrained, due to the regulated throughput of the pump.
Figure 5 : Combining the two curves helps to illustrate the principle functions of the Maximiser. The BLUE areas indicate a period when the hot water is drawn from the store and replaced with cold water. The RED areas represent a period when the Maximiser is recharging the cylinder with hot water. |
