Eco Hometec EC 25 COMPACT Technical Manual - page 25
designing a system using radiators, the
ECHS and S Combi model offers the
designer two options.
Option 1. Design the system using a
variable flow temperature decided by
outside air temperature. Maximum flow
temperature 85
O
C system differential 2O
O
C.
Maximum flow temperature would only be
required when the outside air temperature is
-1
O
C. For this period (typically no more
than 3-4 weeks per year) the return water
temperature would be too high to maximise
condensing mode. However for the
remainder of the year the boiler would
adjust the flow temperature (typically
7O
O
C/5O
O
C) providing the correct
temperature for condensing.
Option
2.
Controlling the maximum
heating flow temperature to 7O
O
C with
system differential of 2O
O
C.
15.2
Sizing Radiators and Output
The heat loss for the room should be
calculated accurately. Then, the radiators
mean water temperature should be used.
70 +50 = 60
O
C
2
or
85 + 65 = 75
O
C
2
15.3
Pipe Sizing and Flow Rates
It can be calculated, that a 15mm pipe with
an adequate flow rate is able to carry 8kw of
sensible heat a 22mm pipe 16kW.
Due to the higher flow and return
temperature differentials in a system
designed for condensing boilers
(approximately twice that of traditional
systems) an equivalent size pipe would
carry the sameamount of heat.
Therefore it can be calculated that a 15mm
pipe is able to carry 16kW, a 22mm pipe
32kW.
When designing installations using
eco hometec VCO condensing boiler with
radiators sized for a flow temperature of
7O
O
C with a return differential of 2O
O
C you
may permit the use of smaller pipe
diameters for the heating circuits.
This will result in lower heat losses, due to
smaller diameter pipework, and should
result in installation savings with reduced
costs for pipe, fittings, pipe insulation and
installation costs.
15.4
Control of Circuits
The relevant new Building Regulation
relating to the control of heat input to rooms
and houses requires something other than a
single room thermostat, Thermostatic
Radiator Valves (TRV's) should be used on
all new installations.
TRV's on condensing systems offer the
ideal solution as they will match exactly the
flow of water through the radiator to give the
current required heat output taking into
account any heat gains from secondary
sources such as cooking or solar gain.
We are all aware that TRV's on every
radiator were not a good idea because of
the above problem and it was usual to leave
one radiator without or to install a system
by-pass to maintain a flow across the boiler.
If this practice were to be continued then
the return temperature would rise as room
temperatures were achieved. This rise in
return water temperatures is counter
productive to the condensing mode of the
boiler.
The eco hometec super condensing VCO
boilers take boiler design and efficiencies to
new levels. If you have any queries or
points you would like to see discussed
and/or included in this guide then please
write or e.mail them – address is on the
back outside cover.
Finally something, for YOU, to consider.
Have you ever bought a gas cooker or a
gas fire that you couldn’t turn up or down?
The answer is of course no! No one would
consider, for even a minute, buying a fire or
cooker that could not be turned up or down!
Yet every day hundreds of people buy
boilers without automatic output and system
water temperature control.
As heating our homes accounts for 70% of
our annual fuel bills.
WHY?
EC 25 Compact Technical Manual page
25