Sample distribution for planning boiler systems
The planning of heating and hot water boiler systems requires a structured approach to ensure that all technical, energy and economic aspects are covered. The essential planning principles were explained in the previous sections. Based on this, three examples of variants for covering the heat energy demand are presented below.
Two boilers, each with 50 % of the design output (identical units)
Annual load duration curve with 50 % of the design output in each case
For a period of 1,200 operating hours (14 % of the annual hours) [1], both boilers must be operated in parallel in order to cover the required load. This variant can cover ~ 7,560 operating hours (86 %) of the annual load in a fail-safe, i.e. redundant, manner. Depending on the control ratio of the burner/boiler combination, [2] the system cycles at minimum load for ~1,000 operating hours (11 %) when there is a demand for power on the consumer side.
Three boilers for 100 % reliability (identical units)
Annual load duration curve with three boilers of equal design output
Here, 100 % of the annual load for a boiler is covered redundantly. For a period of 1,200 operating hours (14 %), two of the boilers [1] must be operated in parallel in order to cover the required load. Depending on the control ratio of the burner/boiler combination, [2] the system cycles at minimum load for ~1,000 operating hours (11 %) when there is a demand for power on the consumer side. A third boiler acts as a back-up boiler to ensure that the heat supply is maintained at all times.
Two boilers with different design outputs
Annual load duration curve with two boilers of unequal design output
The distribution of the two boilers in the example is 33 % of the total load for the smaller boiler and 67 % for the larger boiler. With this variant, the lower output of the boiler covers the summer period [1] for ~ 6,350 operating hours (72 %) largely without burner cycles. Boiler 1 has a reliability rating of 8,000 operating hours (91 %) in the event of failure. Boiler 2 has a reliability rating of 6,350 operating hours (72 %) in the event of failure.