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Linkage to Linkageless Controls Savings Calculator

Estimate what parallel positioning, oxygen trim, and a variable speed fan save over a jackshaft linkage, in gas, electricity, and CO2. From the engineers at McKenna Boiler Works, Inc., a boiler manufacturer in California.

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McKenna Boiler Works, Inc.’s controls calculator estimates the savings from replacing a jackshaft linkage with linkageless (parallel positioning) combustion controls, with optional oxygen trim and a variable speed drive on the combustion air fan. A linkage moves the fuel valve and air damper from one shaft, so wear and slop force extra air across the firing range; field measurements published by ACEEE found 32 to 45% excess air at high fire and 88 to 115% at low fire on linkage boilers. McKenna is a factory-authorized Autoflame Tech Center and installs controls from other manufacturers. Call (323) 987-1816 or email info@mckennaboiler.com.

Calculator

Estimate the savings.

Four steps. Results update as you type. Use the numbers from your last combustion report and gas bills for the most accurate answer.

1The boiler and how it runs

HP
MMBtu/hr
Leave the input blank to use boiler HP × 33,475 ÷ 80%. Use the nameplate if you have it.
psig
°F
PeriodLoad, % of capacityHours per year
%
%
%
Most boilers spend most of their hours at mid and low fire, not high fire. The results show how many hours fall at each firing rate.
$/therm
therms
Optional but recommended. Enter this boiler's gas use from last year's bills and the loads above are adjusted until the model matches your bills.

2

High fire
%
Mid fire (50%)
%
Low fire
%
°F
°F

3

High fire
%
Mid fire (50%)
%
Low fire
%
High fire
%
Mid fire
%
Low fire
%
HP
$/kWh

4Project cost and payback

$
$
$/yr
%/yr
years
Simple payback uses today's prices. The lifetime figures apply the energy price change each year. Set it to 0 to stay with today's prices. Only enter maintenance savings you can document, like repairs on worn linkages or an old burner.

Results

$0saved per year
0therms of gas saved per year
0points of seasonal efficiency gained
0tons of CO2 avoided per year
Payback

Where the burner runs today
Efficiency across the load range

Estimates for planning, not a guarantee. Combustion efficiency comes from the U.S. DOE natural gas table (Steam Tip Sheet #4), interpolated on excess air, with O2 interpolated between your high, mid, and low fire readings. Purge loss per start uses a published pre-purge loss formula (Bosch Industrial). Shell loss follows DOE Steam Tip Sheet #16. Fan power uses the EnergyPlus inlet vane damper and variable speed curves. Stack temperatures are held the same before and after, which is conservative. CO2 uses EPA's 53.06 kg per MMBtu of natural gas. McKenna confirms savings from a site survey and a combustion analysis.