Modern valve technologies have the potential to address many of the challenges facing variable volume chilled and hot water systems, says Martin Lowe of Marflow Hydronics.
It’s probably true to say that building services can be quite a conservative industry, with familiar methods often being selected simply because that’s what always been done. But while there are some benefits to the ‘tried and tested’ approach, we also have to ensure we keep pace with changes if we are to deliver best value to end clients.
Unfortunately, design, installation and commissioning practices for variable volume chilled and hot water systems are already lagging behind key developments in many projects. These developments include the growth of design and build, skills shortages and the increased use of multi-national labour forces, as well as the opportunities provided by modern valve technologies.
For example, with the growth of design and build there has also been an increase in the use of pre-fabrication. Crucially, at the same time, pre-fabrication is evolving from being just a way of transferring site work to another location. It is now becoming an engineered solution where assemblies are produced under controlled conditions bringing many trades together under one roof to produce something that is far more effective when installed on site.
Plus everything required is delivered to site at the same time ready for installation, so skilled operatives waste less time waiting for everything they need to arrive. If assemblies are supplied complete with pictorial instructions, this also eliminates any language issues.
In parallel with the increasing popularity of pre-fabrication, there is now wider use of manifold systems, where each manifold houses all of the valves for a group of, typically, up to six terminal units in a single, pre-insulated box. This allows the commissioning engineer to access up to six terminal units from a single location, saving a great deal of time. In addition, with a properly considered control solution the need to revisit each manifold more than once is unnecessary, often reducing the commissioning process to a ‘read and record’ exercise.
A further advantage is that a centralised manifold box provides the ideal location for information about the local system that can be accessed by the building operator beyond commissioning.
It also means that all valve information and hydronic performance data can be collated within a single location, for sharing by all relevant parties. To that end, our company has developed a spreadsheet-based software package to manage all of this information.
All of these developments set the scene for taking full advantage of the latest valve technologies. We’ve already seen increased use of pressure independent two-port valves in variable volume circuits – though all-too-often they are used with traditional proportional balancing techniques that really aren’t appropriate for variable volume systems.
Now, though, these valves can also be used in conjunction with programmable controllers to limit the maximum flow rate of a pressure independent control valve. The valve is linked to a BMS fan coil or chilled beam controller, and an actuator that can be set from a remote location to the required position to give design flow rates.
The controller provides two 0-10V analogue outputs to control the valve actuators while also communicating with other controllers via a BACnet MS/TP network. This enables communications with a PC, so that system software can be configured and updated without directly accessing the controller.
To reduce installation time and the risk of connection errors, the BMS controller, housed in its own case, can be wired to the actuator via pluggable leads and socket. Pluggable connections are also used for the cable from the controller to the fan coil unit supplying power and the temperature sensor and the communication cable to the BMS.
This ‘remote commissioning’ concept takes full advantage of the benefits offered by pressure independent two-port valves – adopting what we have dubbed a ‘single station balancing’ (SSB) method of commissioning. This eliminates the common problem of a commissioning engineer needing to balance the entire system before problem circuits can be identified – and then repeating the whole process if any problems are encountered.
Instead, SSB uses a subtraction technique to identify problem valves. Essentially, if the design flow rates for each individual valve are known, then the total flow rate for that group of terminal units is also known. Consequently, isolating one valve will have a predictable effect on the total flow rate for the remaining valves. If the result is not as expected, there is clearly a problem with that valve, so the commissioning engineer knows where to look in more detail.
This approach, combined with the remote control possibilities outlined above, means that it is only necessary to enter the ceiling void to connect a manometer. All adjustments can then be carried out from a PC. And if more affordable electronic measurement devices are developed in the future it may not be necessary to enter the ceiling void at all, unless problems are encountered.
As a result of the changes outlined in this article, this is an ideal time to take advantage of the opportunities that are now available to streamline the design, installation and commissioning of hydronic systems – to the benefit of all concerned.