Tuesday, 19 January 2021

Clamp-on ultrasonic measurement for sophisticated HVAC systems – Or, who needs a flowmeter that reads zero?

HVAC systems innovators Retrofit Services choose Katronic clamp-on, non-invasive flowmeters for sophisticated sequencing and variable flow applications that can save as much as 60 – 65 % of the energy costs in multiple boiler/chiller applications

Key to the success of the application is the exceptional turn-down performance of Katronic flowmeters, giving a reliable indication of zero flow through the decoupler pipe when the Primary and Secondary flow circuits are equalised.

By replacing a system with constant 100 % flow rates and pumps working all the time with a variable flow approach, the system flow rates can be allowed to vary between 15 % and 100 % depending on demand. By allowing pump speeds to modulate to exactly match system demand, substantial savings can be made, especially in large multi-level, multiple user environments.

In a 'standard' heating Primary/Secondary system, hot water is continually pumped around the network, with flow to individual users within the network being controlled by three-port valves. Whatever the position of these valves, system flow remains constant at 100 % and pumps run at full power regardless of demand, wasting energy. Retrofit's approach replaces fixed speed pumps with variable speed, and variable flow valves to modulate the flow to the various zones of a building. When the system is balanced accurately, the 'waste' hot water that merely circulates in the loop rather than passing through one of the heating zones should be as close as possible to zero.

Any automated system depends on feedback to a central controller from sensors in the process, and in this process the most important control elements are the feedback of secondary & system decoupler flow rates. Retrofit had tried a number of different approaches, including several technologies – a turbine flowmeter had too much hysteresis, a paddle meter didn't measure in both directions, and an electromagnetic flowmeter didn't have the accuracy required at a low flow rate.

The Katronic clamp-on, non-invasive ultrasonic flowmeter approach has proved to be the ideal answer. Because the flowmeter will register flow readings right down to 0.01 metres/second (and right up to 25 metres/second), and will measure with the same sensitivity and accuracy in either direction, it provided exactly what Retrofit needed, a 'reliable zero'. The decoupler pipe flow readings are used to control the speed of the primary pumps and ultimately the firing rate in the boilers so that it always matches the flow through the Secondary (distribution) pumps thereby minimising any wasted pump energy. Some of the savings are made from the Retrofit system are substantial, with one large Irish installation with 350 users delivering €500,000 savings in the first year alone. 

Katronic's range includes both portable and fixed flowmeters, all of which share the same ease of installation, visual and audible commissioning aids and accuracy of performance, so an installation can be tested with a portable unit before installing a permanent system. The ability to provide a dual-channel meter, essentially two flowmeters in the same box, also makes them very cost-effective.

Steve Chadwick, a Director at Retrofit Services, commented, 'We have been using Katronic equipment for a while now (our oldest meter is over 15 years old), we have several flowmeters in place and they've never missed a beat. It's a strange request for a flowmeter – measure zero flow but this need is customer driven as pressure increases for greater energy reductions – we've been very pleased with everything that Katronic have supplied to us and their technical support is exceptional.'