8.0 Technical Data
Formulae for calculating efficiency are detailed as follows;
where
ql
is the
heat
of the
dry
products
of
combustion
(% of
heat
released
per
unit
volume
of gas)
q2
is the heat of
the
water
vapour
contained in the
products
of combustion (% of heat released
per
unit
volume
of
gas
Cl
is the
mean
specific heat
of
the
dry
products
of
combustion (in
MJ
/ (m
3
.
K)
)
tl
is the average combustion air
temperature
(in D
C)
t2
is the average
temperature
of the
products
of combustion (in D
C)
Hi
is the
net
calorific value of the gas at 1013
mbar
and
15
°C,
dry
(in
MJ
/ m
3
)
Hs
is the gross calorific value of the gas at 1013
mbar
and
15
°C
dry
(in
MJ
/ m')
Vf
is the
volume
of
dry
products
of combustion
per
unit
volume
of gas (in m
'
)
Vf
is calculated from the
volume
of C02
(V
C02)
produced
by
the combustion of 1m
3
of gas (see
table below),
and
from the C02 content of the
products
of combustion
(V
C02.
M)
x 100
Ref Gas
I
G110
G120 G20 G25
G30
G31
V
CO
2
,I
0.26 0.32 1 0.86
4
3
The
net
efficiency, E (net) (in %) is given by;
where
and
H -
H·
x
100
q2
=
0.077
5 I
H·
I
Note
The required net efficiency
must
not be less
than
84
%
On
heaters that are fitted
with
a
modulating
or
high/low
burner
the
testing is carried
out
with
the
appliance
adjusted
to give the
minimum
rate,
and
the following formula is
used
.
E . ? E _
10
(Qrz
- Qmirz)
in
%
mm
rz
Qrz
Qrz
is the nominal heat
input
Qmin is
the
minimum
obtainable
heat
input
En
is the
net
efficiency
determined
by
the Notified Body
Note
The
minimum
net
efficiency for appliances fitted
with
modulating
or
high/low
burners
must
not be less
than
79
%.
34
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