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Where Conventional Equipment Falls Short
The oldest boiler designs had only one level of power - 100%. They were either on or off. This creates cycling losses each time the unit shuts down; the heat exchanger cools off and must be fully "re-heated" before heat transfer can begin. (See "The Impact of Heat Soak")
Once the unit re-starts, the 100% firing rate may be far more than what is required to meet the building's load.
While newer burners and boiler designs incorporate 5:1 or 3:1 turndown ratios, limited firing rates still result in some wasteful overshooting or cycling losses.
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The Importance of Modulation
In general, modulation refers to the ability to adjust a boiler or water heater's firing rate (input) to meet the heating demand (output) of the system.
AERCO equipment utilizes a fully-modulating design which precisely matches firing rate to actual building demand. A 2.0 million BTU/hr. capacity Benchmark boiler can run with as little as 100,000 BTU/hr., or 5% input. Likewise, the 1.0 million BTU/hr. KC1000 line maintains steady combustion with only 50,000 BTU/hr. input. Drawing only enough fuel to meet actual load changes, each unit will gradually increase its capacity - in precise 1% increments - up to 100% full capacity.
Not only is less fuel burned as a result of modulating input, but heat transfer is also enhanced when the AERCO units operate at "part-load." Constant operation maintains temperatures within the heat exchanger, yet the reduced input increases the time these combustion gases are in contact with the heat exchanger surface to promote greater energy transfer and cooler exhaust gases. AERCO equipment features an inverse efficiency curve performing best at lowest loads.
Since the majority of a boiler's operating hours will be under "part load conditions," modulating units promise greater seasonal efficiency.
BMS & Modulation
AERCO's inverse efficiency profile can be fully leveraged by carefully coordinating the operation of multiple units using the AERCO Boiler Management System. Put simply, it requires less energy for a group of modulating boilers, each firing at a lower-load, to heat a building, than if a single boiler, operated at full or high fire, to carry the entire workload.
AERCO's BMS regulates the operation of multiple Benchmark or KC1000 installations, giving each unit firing instructions to maximize the efficiency of the plant as a whole as loads change throughout the day. Operating hours are also distributed evenly across all units, always alternating the lead boiler so that no particular unit receives more work over time than the others.
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