Hydraulic Balancing Of Heating and Cooling Circuits


Published: 20 June 2016

Hydraulic balancing
Fig. 1 Hydraulic balancing of heating and cooling circuits in larger systems requires control valves as well as an option to monitor the actual flow rates.
​Changes in thermal and hydraulic conditions affect the hydraulics of heating and cooling distribution systems.

Among the most common causes for an oversupply or undersupply occurring at consumer installations in heating systems, or cooling distribution systems for air-conditioners, is the lack of hydraulic balancing.

​For this reason hydraulic balancing of existing systems (Figure 1) is crucial. Furthermore, when modernisation measures have been taken to improve the energy efficiency of a system, a different energy input changes considerably the thermal and hydraulic conditions.
​Existing distribution networks often lack the data required for hydraulic balancing. Some general guidance for optimising heat distribution is provided by the actual flow rates and temperatures in the supply and return pipes of heating or cooling circuits. For existing distribution networks, hydraulic balancing means setting defined, fixed resistances at the respective branches. This can only be achieved if the flow rate can be controlled and the actual flow rate can be verified at the same point in the branch.

Measuring flow rates per ultrasoun

BOA-ControlFig.2 The BOA-Control measurement and control valve (Figure 2) uses ultrasonic sensors, so it has no physical contact with the fluid flowing through the pipe.
Building services increasingly focus on the availability of data for consumption records, on energy management and controlling flow rates and temperatures. Depending on the application, the measured values can be read out via a mobile device or continuously monitored via data transmission. 

​The energy required to heat and cool buildings is influenced by many factors. Apart from heat losses through the building fabric, the type of use and periods of use together with the settings made at the hydraulic system play a significant role.

Simultaneous control and monitoring of the flow rate in a pipe section to meet the set point can be performed using a measurement and control valve developed by KSB. The BOA-Control measurement and control valve (Figure 2) uses ultrasonic sensors, so it has no physical contact with the fluid flowing through the pipe. The flow rate is determined by sensors measuring the transit time difference of the ultrasound waves. Because the sensors are located on the outside of the valve, neither dissolved substances nor impurities in the water can influence the accuracy of the measurement.

A BOATRONIC measuring computer, which is part of the system, calculates the flow rate directly via the ultrasonic sensors. With the ultrasound measurement method the flow rate can be determined regardless of valve positions and minimum differential pressures. During commissioning of the system the flow rate can be verified directly with the measuring computer to see if the valve was adjusted correctly to the set value.

Periodic or continuous measurement of flow rate and temperature

KSB offers two different versions of the BOA-Control measurement and control valve and the BOATRONIC  MS measuring computer in order to match the specific application, e.g. periodic or continuous measurement. These versions are the BOA-Control and the BOA Control IMS. The choice as to which is used is determined primarily by the valve, this having been designed either for attaching to mobile sensors, or fitted with permanently attached sensors for reading the measured data.

The BOA-Control version enables users to connect their BOATRONIC MS measuring computer to several valves of the same type to measure the respective flow rates. For this purpose the valve bodies are provided with two measurement contacts to which the sensor set can be attached via a magnetic connector. Optimum contact is achieved by applying coupling grease between the measurement contacts and the sensors. This valve version is perfectly suited to hydraulic balancing, followed by periodic monitoring of flow rates and fluid temperatures.

The BOA-Control IMS version is factory-fitted with permanently integrated ultrasonic sensors. The sensor cable of the ultrasonic sensors is permanently fixed to the valve body and therefore can be fed through the pipe insulation. This version is specifically designed for systems where the pipe insulation is either of high quality, or where it has to satisfy specific requirements on diffusion tightness and protection from condensation. 
For periodic short-term measurements of flow rate and fluid temperature the measured data by both valve models can be saved with the BOATRONIC MS measuring computer and read out via a USB interface. In addition, KSB provides the BOATRONIC S software, which offers further control functions. It also serves to create a measurement log as proof for hydraulic balancing.

If the operation of the heating and cooling circuit being controlled requires continuous monitoring of the flow rate, a BOA-Control IMS measurement and control valve can be used together with a BOATRONIC MS-420 measuring computer. This computer continuously transmits the flow rate and temperature values in real time to a higher-level building management system via a 4 - 20 mA signal.

The solution for automated set point control is a BOA-CVE Control IMS control valve, which forms an autonomous control loop together with an actuator. The valve position can be adjusted to the required set point for the corresponding pipe section. The valve automatically controls the set point when temperature or flow rate fluctuate.