14. Condensing System Design
THE IMPLICATIONS OF eco hometec VCOCONDENSING BOILERS
and
THE DESIGN OF OLD AND NEW CENTRAL HEATING AND HOT WATER SYSTEMS
eco hometec VCO condensing boilers are,
without doubt more efficient (up to 98%
efficient) than conventional balanced or
natural draught boilers and condensing
boilers without output control.
The principal design criterion for a
condensing boiler installation is controlling
the return water temperature. If the return
water temperature is allowed to rise in
excess of 55
O
C the potential for optimum
efficiencies will be lost. This simple fact
has design implications that must not be
ignored if we are to achieve the maximum
fuel savings and efficiencies from a
condensing boiler installation. In order to
achieve condensing mode the design of old
and new systems needs to be considered
carefully.
14.1
Design Considerations.
Under-floor Heating System Design.
Radiator sizing and their output.
Pipe sizing - the flow of water.
Controls - Thermostatic Radiator Valves.
Hot water and its control.
The following system temperatures are
generally the norm for the following.
14.2
Traditional
Flow temperature
80
O
C
Return temperature 70
O
C
System drop
10
O
C
14.3
Condensing
Flow temperature
70
O
C
Return temperature 50
O
C
System drop
20
O
C
14.4
Under-floor
Flow temperature
50
O
C
Return temperature 40
O
C
System drop
10
O
C
14.5
Under-floor Heating
Under-floor heating systems generally offer
the lowest return water temperatures and
will ensure the condensing boiler will
operate more efficiently. The EC25 may
be safely fitted to systems using a high
temperature thermal store however we bring
to your attention that any heating system
using constant high temperature circuits
(80
O
C) will inevitable lead to a reduction in
the potential efficiency of a true low
temperature design optimised for a
condensing boiler. Clearly, for the
purposes of condensing boiler efficiency,
these types of systems should be
considered carefully, ask your heating
engineer or call the eco hometec technical
department for further advice.
15. Under-floor heating
The EC25 HS (higher specification)
condensing boiler has two built in circuits.
The HS range provides 4 No. 22mm
connections offering a low temperature
circuit for under-floor heating and a high
temperature circuit for domestic hot water.
This low temperature heating circuit (50
O
C)
can be dedicated to an under-floor heating
system.
Boilers not configured for under-floor
designs will overcome the problem by
mixing their high temperature flow output
with the return heating water via a mixing
valve to achieve the required 50
O
C design
temperature.
Controlling the water temperature to 50
O
C
by modulating the burner uses less gas and
is obviously more efficient than lowering,
with mixing valves, the temperature from a
fixed 80
O
C start point.
The eco hometec range of VCO boilers has
been specifically designed to work with low
temperature under-floor heating.
15.1
Systems using radiators
Assuming the objective is to maximise the
condensing feature of the boiler, when
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ECO HOMETEC
(
UK
)
LTD
.
