Valves and actuators are largely unseen elements of a building services system
Valves and actuators can have a significant impact on system performance, occupant comfort and energy efficiency.
Despite pressure independent control valves (PICVs) being in the market for almost 20 years, it is only in the last 5 to 10 years that we have seen a significant uptake in their use. As a result, there has been a relatively short period of time for specifiers and installers to gain and in-depth understanding of their use and function.
Hydronic systems, which use water as the medium for transferring heat, must be in balance. Any imbalance leads to overheating or over-cooling; causes discomfort for building occupants; and wastes energy. In the past, the main type of hydronic system contained a constant volume of water, with 3- or 4-port control valves with constant speed (low volume) pumps to control the heat output of the terminal.
The benefit of this approach is easy sizing of control valves. But the constant volume approach means that water is being pumped around a system even when there is no demand. And this in turn leads to areas of discomfort (temperatures too hot or too cold) for occupants as well as energy waste.
With the move to more energy-focused system design, variable volume systems have come very much to the fore. They deliver heat only when it’s needed. The challenge is that achieving and keeping balance in the system means using three pieces of equipment: a differential pressure control valve (DPCV); a 2-port control valve; and a balancing valve. This means the system is more complex to design and time-consuming to install.
However, the pressure independent control valve (PICV) is capable of making the variable volume system much easier to design and manage. It combines all three functions in a single technology. Design is much easier, and PICVs make installation and commissioning more straightforward. As their use has become more widespread, it is now acknowledged that PICVs greatly assist in the efficient and effective operation of heating and cooling systems.
There are a number of characteristics to consider when selecting and sizing a PICV for a project. Accuracy of control is vital for a balanced hydronic system, so flow control and flow rate are the first points to check. Flow setting is another important aspect. The valve should be easy to set by hand for commissioning purposes. The latest PICVs offer quick-fit actuator connection with no tools required.
Due to the wide range of flow rates available within PICVs it is often possible to select a valve at a smaller pipe size than requested, which is still capable of achieving the required flow rates in an efficient manner. This can subsequently help in reducing capital expenditure for the project
The minimum pressure required to activate the PICV can vary between sizes and setting so this is also something to think about. Pressure drop across the PICV can vary between valve sizes, about 15kPa for smaller sizes increasing to 30kPa for larger valves. An increased pressure drop in the least-favoured circuit could increase the whole-life operating costs of the system.