Let’s take a look at how they work and the difference between Manual vs PICV systems. Water in a system takes the path of least resistance. Units closest to the pump receive excess water flow whereas units further away from the pump receive insufficient flow. So, the system needs to be balanced to ensure all circuits receive the required flow. When the system is balanced, water flow can be delivered at design requirements to all parts of the circuit, resulting in the required ambient temperature and greater occupant comfort. Unnecessary energy consumption is prevented.
Where manual balancing valves can be installed
Manual balancing valves which are set and then left can be installed within PICV-controlled zones. Each terminal unit within the PICV-controlled zone is fitted with a static balancing valve so that water is distributed proportionally to all terminal units within the zone. They can also be used in the mains off the riser to distribute flow in Chilled Beam or particularly in Radiator systems, where the system is designed with particularly low pump head.
Manual vs PICV systems
The control valve acts like a normal valve. It has a cone which moves up and down to decrease or increase the area available for a fluid to pass through. This is attached to the spindle and the control knob. When we turn the control knob by hand or use an actuator to manoeuvre it remotely, it will force the shaft up or down to open or close the valve. As the valve closes, the amount of fluid flowing decreases. As the valve opens, the volume flow rate increases. So as long as we can maintain the same pressure difference across the valve, we can accurately tell how much water will flow through the valve at a given position. We can lock the maximum flow rate through the valve to balance the system.
Why should Pressure Independent Control Valves be Used?
Most hydronic systems these days are designed as variable flow systems to reduce the cost of ownership, utilising pressure independent or electronic control valves. In a hydronic heating or cooling system, pumps boost the pressure and circulate the water. Some cooling and heating systems use variable speed pumps that change the flow rate and therefore the system pressure. There are also control valves which open and close to control the water flow in the heat exchangers. With these varying water pressures, system inefficiencies are embedded. The use of pressure independent control valves maintains constant pressure in the system.
How do pressure independent control valves work?
This PICV uses a small cup, known as a shutter, which rises and falls to compensate for fluctuations in pressure within the system. The shutter sits concentrically within a guide to ensure it slides up and down correctly. A downward force acts on the shutter by use of an internal spring, the spring is held in place by a support frame. Underneath the shutter is a flexible membrane which acts as a physical barrier between the high-pressure inlet and the lower pressure outlet. A small passage connects the cavity on the underside of the membrane to the inlet. This way when water flows through the valve, some of it will flow into this small hole and the pressure of the incoming fluid will force the membrane to move upwards. That pushes the shutter up to maintain the pressure difference across the valve.
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