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Practical illustration of the increase in water-side efficiency

A boiler system with the following design data is assumed:

1,700 kW boiler output
110 °C safety temperature limiter
Boiler supply flow temperature: 90 °C
Boiler return flow temperature:
A 20 K temperature difference: 70 °C
B 30 K temperature difference: 60 °C

Hydraulics for increased water-side efficiency

	Hot water boiler
	Low loss header
	Network flow temperature
	Boiler return flow temperature
	Boiler supply flow temperature
	Eco intake temperature
	Chimney
	Shut-off valve

Figure showing load ranges for a heating system with a maximum load requirement of 1,700 kW

	Scenario A 1,700 kW boiler capacity Flow 90 °C Return 70 °C Variant A: 20 K temperature difference	Scenario B 1,700 kW boiler capacity Flow 90 °C Return 60 °C Variant B: 30 K temperature difference
Volume flow through boiler	75 m³/h	50 m³/h
Boiler circuit pump rated output	1.5 kW	1.1 kW
Boiler system efficiency	96 %	96.3 %

Scenario A: ΔT 20 K
Pump output: 1.5 kW
System load range	1	2	3	4	5	Total
Boiler load range [%]	100–80	80–60	60–40	40–20	20–0
Operating hours [h]	125	600	1,850	3,500	2,685	8,760
Pump with frequency converter [kWh]	221	447	408	167	128	1,370
Pump without frequency converter [kWh]	188	900	2,775	5,250	4,028	13,140
Boiler system efficiency [%]	96	96.4	96.8	96.5	96.5
Fuel consumption of natural gas H [m³N]	19,248	71,562	156,955	179,650	137,103	564,518



	Power consumption [kWh]	Electricity costs [€/kWh]	Total [€]
Power consumption of boiler circuit pump without frequency converter	13,140	0.2	2,628
Power consumption of boiler circuit pump with frequency converter	1,370	0.2	274
		Savings	2,354



	Fuel consumption [m³N/h]	Gas costs [€/m³N]	Gas costs [€/kWh]	Total [€]
Fuel consumption	564,518	0.5175	0.05	292,138

Scenario B: ΔT 30 K
Pump output: 1.1 kW
System load range	1	2	3	4	5	Total
Boiler load range [%]	100 – 80	80 – 60	60 – 40	40 – 20	20 – 0
Operating hours [h]	125	600	1,850	3,500	2,685	8,760
Pump with frequency converter [kWh]	150	303	277	113	87	930
Pump without frequency converter [kWh]	138	660	2,035	3,850	2,954	9,636
Boiler system efficiency [%]	96	97	97	97	97
Fuel consumption of natural gas H [m³N]	19,188	71,266	156,470	177,798	136,396	561,118



	Power consumption [kWh]	Electricity costs [€/kWh]	Total [€]
Power consumption of boiler circuit pump without frequency converter	9,636	0.2	1,927
Power consumption of boiler circuit pump with frequency converter	930	0.2	186
		Savings	1,741



	Fuel consumption [m³N/h]	Gas costs [€/m³N]	Gas costs [€/kWh]	Total [€]
Fuel consumption	561,118	0.5175	0.05	290,379

This means that the energy costs of the boiler circuit pump are reduced by up to 90 % annually when using a frequency converter, as shown in the annual curve above. The additional costs for this frequency converter on the pump pay for themselves within a year. Due to the increased efficiency, fuel consumption and therefore CO₂ emissions at the system are reduced.

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