Savings Potential
If
it were possible to have perfect combustion, the amount of oxygen in the flue
gas stream would be at, or close to, zero.
Because perfect combustion is not practically possible, combustion
equipment is set up to have a small percentage of excess O2 present. The
lower the temperature for a given O2
(or CO2) reading, the higher is your combustion efficiency as less
heat is lost up the stack.
Fine
tuning a boiler’s combustion air and fuel input has a direct impact on the
amount of fuel consumed by a boiler. Unfortunately,
there are too many factors involved to be able to calculate exact savings
which can be achieved. However,
there are several 'rules of thumb' which can roughly estimate savings
potentials.
For each 1% decrease in excess air levels introduced into
the combustion process, the boiler’s efficiency increases by 1/4 to 1 of a
percent. While some excess air is
necessary to insure complete combustion, flue gas analysis will verify that
excess air is within the manufacturer’s specifications and optimize
efficient operation.
In
a Stoichiometric Mix or “perfect” combustion, all of the fuel and oxygen
introduced into the flame combine to generate only heat, water and
carbon dioxide (CO2).
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In
gas fired appliances, CO is the usual indicator of incomplete combustion.
CO is well known to be a health threat, but also represents unburned
fuel exhausting the appliance.
In oil fired appliances, both CO and smoke indicate incomplete combustion. In addition to poor combustion, smoke can deposit soot on heat exchange surfaces which will further reduce efficiency. Also, smoke coming out of the stack can be cause for an air quality violation and potential public relations concerns.
Another
method to quantify potential savings is to determine the change in Steady
State Efficiency and use the
following table to calculate fuel savings.
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SAVINGS FOR EVERY $100 FUEL COSTS BY
INCREASE OF COMBUSTION EFFICIENCY Assuming constant radiation and other unaccounted-for losses From an
original
To an increased efficiency
Combustion efficiency of:
of: |
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|
|
55% |
60% |
65% |
70% |
75% |
80% |
85% |
90% |
95% |
|
50% |
$9.10 |
$16.70 |
$23.10 |
$28.60 |
$33.30 |
$37.50 |
$41.20 |
$44.40 |
$47.40 |
|
55% |
--- |
8.30 |
15.14 |
21.50 |
26.70 |
31.20 |
35.30 |
38.90 |
42.10 |
|
60% |
--- |
--- |
7.70 |
14.30 |
20.00 |
25.00 |
29.40 |
33.30 |
37.80 |
|
65% |
--- |
--- |
--- |
7.10 |
13.30 |
18.80 |
23.50 |
27.80 |
31.60 |
|
70% |
--- |
--- |
--- |
--- |
6.70 |
12.50 |
17.60 |
22.20 |
26.30
|
|
75% |
--- |
--- |
--- |
--- |
--- |
6.30 |
11.80 |
16.70 |
21.10 |
|
80% |
--- |
--- |
--- |
--- |
--- |
--- |
5.90 |
11.10 |
15.60 |
|
85% |
--- |
--- |
--- |
--- |
--- |
--- |
--- |
5.60 |
10.50 |
|
90% |
--- |
--- |
--- |
--- |
--- |
--- |
--- |
--- |
5.30 |
Draft measurements verify sufficient stack draft to allow
for the introduction of additional fuel air mix. Excess draft will likely pull in too much combustion air
and/or excess air possibly causing the production of CO while removing hot flue
gases before complete heat transfer occurs.
A commonly accepted rule
of thumb states that for every .01 WC” the excess draft rate can be
reduced, fuel consumption will decrease 1%.
All
energy conservation savings, installation costs and payback periods are
estimates. Actual results may
differ depending on variations in weather, usage patterns of the occupants and
material and installation costs. BACHARACH
and its agents, employees, contractors and subcontractors do not guarantee the
savings, contractor costs, installation costs or payback periods.