Saving power while heating: It’s the control mode that matters

Hidden power munchers in the boiler room

Almost every building is fitted with radiators these days. The heat radiated is usually generated in a boiler. To transport the heated water to the radiators you need circulators. And circulators need energy, and quite a bit of it. In an average single-family house the circulator is easily responsible for one fifth of the entire household’s energy consumption – exceeding the power used by the washing machine or fridge.

Energy consumption at the example of Germany:

In Germany alone about 30 million circulators consume up to 15.6 billion kilowatt hours per year, according to the German Environment Agency. This corresponds approximately to the annual power input for the country’s entire rail traffic, including urban and underground trains.

Decisive are a pump’s input power and control mode

In principle, two factors are responsible for the power consumption of a circulator: First of all, its input power in Watt (W) and secondly the accuracy of its control mode in adjusting the output to the actual heating requirements. As a rule of thumb, the lower the pump input power, the less electricity the pump consumes. The more accurate the control system's response to heating demand, the less frequent an operation with high or excessive input power, which saves energy and costs.

With this in mind, you would think that demand-driven pump operation is standard these days. However, that is not the case: About a quarter of all circulators used in Germany is more than 20 years old. Half of these pumps are still operated at a fixed speed. Such fixed speed pumps are true power munchers. They can either not be adjusted at all or they can only be set to one speed level at which they are then operated. Since these circulators usually produce a continuously high output, they consume a large amount of power.

Not only do fixed speed pumps generate a high power bill, they have also got a negative impact on the environment. For this reason the EU Commission decided to successively phase out the placing on the market of fixed speed circulators from 2013. Future-oriented circulators have to be state of the art and meet stringent requirements regarding energy efficiency. One of the conditions is for the circulators to be speed-controlled.

High-efficiency pumps with variable speed system cut power costs

Unlike fixed speed circulators, whose power consumption remains the same even when heat consumption is low, modern high-efficiency pumps are run at variable speeds, adjusting the output to the actual heat demand and only circulating hot water in the quantities necessary. Sensors measure the required value (e.g. pressure, flow rate or temperature) and transmit it to the heating control system that adjusts the frequency inverter of the pump accordingly.

This may sound good, except for one weakness. Most variable speed circulators adjust their flow rate or head based on an algorithm causing their operating point to move along a programmed control curve. The minimum system curve describes the friction loss when all thermostatic valves are fully open. As the minimum system curve is usually unknown, the control curve of conventional systems is often well above the minimum system curve. As a consequence, a lot of valuable energy is still going to waste despite variable speed operation. In addition, hot water circulating too fast in the piping can cause annoying noises at the thermostatic valves of the radiators.

It’s better with Dynamic Control

Dynamic Control is KSB's response: an intelligent system enabling the power input of circulators to be lowered by up to 20 percent compared to conventionally controlled pump sets. 

Dynamic Control moves the operating point of the circulator down from the currently selected control curve until the minimum system curve is reached.

Should the minimum system curve be undercut, the Dynamic Control algorithm re-sets the pump immediately to its original control curve, thus ensuring sufficient supply. This not only saves power, it also helps protect the environment as the CO2 emission of the heating system is lowered significantly thanks to the dynamic control process.

By the way, Dynamic Control does not mean extra work for installation contractors and operators of heating systems. The intelligent program determines the necessary information itself based on the pump’s internal signals. No additional settings need to be made. Also, reliable recognition of the minimum system curve by means of a flow rate signal rules out undersupply.

Dynamic Control is fitted as standard in KSB’s current Calio and Calio S circulator type series. As firmware update Dynamic Control can also be easily installed in pumps of the third Calio generation.

Benefits of Dynamic Control at a glance:

• The implementation of the algorithm is based on software; it does not require any additional sensors or actuators and does not incur any additional costs.
• As the Q_tolerance limits are continuously monitored no undersupply will occur.
• At a steady operating state, the pump input power can be substantially reduced (by 20 % on average).