Who needs a flow meter that reads zero?

The heating, ventilation and air-conditioning retrofitting specialist ‘Retrofit Service’ relies on Katronic’s non-invasive clamp-on flow meters for demanding sequencing and variable flow applications, where energy costs can be reduced by up to 60–65 per cent in various instantaneous water heater and air-conditioning systems.

If a system with constant flow rates of 100 per cent and continuously running pumps is replaced by a variable-flow design, the system’s flow rates can vary between 15 per cent and 100 per cent as required. The ability to control pump speeds so that they precisely match system demand can result in significant savings, particularly in large, multi-storey environments with multiple users.

In standard primary and secondary heating systems, hot water is continuously pumped through the network, with the flow to individual consumers within the network controlled by three-way valves. Regardless of the position of these valves, the system flow rate remains constant at 100 per cent; the pumps run at full capacity regardless of demand, leading to a waste of energy. Retrofit’s technical approach is to replace fixed-speed pumps with variable-speed pumps and variable-flow valves to regulate the flow to the various zones of a building. If the system is precisely balanced, the ‘waste’ of hot water that merely circulates within the circuit rather than flowing through one of the heating zones should be as close to zero as possible.

Any automated system relies on feedback from sensors within the process to a central control unit. The most important control elements are the feedback on flow rates in the secondary heating circuit and the flow rates of the decoupling system. Retrofit had previously tried various approaches, including several technologies – a turbine flow meter had excessive hysteresis, a paddle wheel flow meter could not measure in both directions, and a magnetic-inductive flow meter did not have the required accuracy at low flow rates.

Katronic’s clamp-on ultrasonic flow meter has proved to be the ideal solution. As the flow meter also records flow rates down to 0.01 metres per second (and up to 25 metres per second) and measures in both directions with the same sensitivity and accuracy, it delivered exactly what Retrofit needed: a ‘reliable zero point’. The flow readings from the decoupling pipe are used to control the speed of the primary pumps and, ultimately, the combustion rate in the boilers, ensuring that it always matches the flow rate of the secondary pumps (distribution pumps). The savings achieved by the Retrofit system are, in some cases, considerable: a large Irish installation serving 350 users generated savings of €500,000.00 in the first year alone.

Katronic’s product range includes both portable and permanently installed flow measurement systems, all of which are characterised by simple installation, visual and audible commissioning aids, and accurate performance. A system can be tested using a portable unit before a permanent monitoring system is installed. The ability to provide potential users with dual-channel meters – effectively two flow meters in a single housing – makes them exceptionally cost-effective.

Steve Chadwick, a director at Retrofit Services, comments: “We’ve been using Katronic devices for some time now (our oldest meter is over 15 years old); we have several flow meters in use and they’ve never failed. It’s a rather unusual requirement for a flow meter – to measure zero flow – but this need is driven by the customer, as the pressure to achieve greater energy savings increases. We are very satisfied with everything Katronic has supplied us with so far, and their technical support is excellent.”