Balance valves
- Ruben Gielen
- Dennis De Beuckeleer
Balance valves are used to balance the hydronic system. This is necessary when different end units are connected to the same pump. Without balance valves, every branch towards an end unit will have a different pressure drop. Within an unbalanced hydronic system, the flow will follow the path of the least resistance. This way, the actual flow rate towards the end systems will differ from the designed flow rate, and comfort issues can arise.
Example:
The system depicted below has two unbalanced end units with a different heat flow and a different pressure drop. The design flow rates of the end units are obtained by the design power and the temperature regime.
As can be seen, the actual flow rates(shown in red and orange) differ from the design flow rates (shown in red) as the flow will follow the path of the least resistance. This indicates that the end unit on the right - where the pressure drop is lower - will receive a larger flow rate than it was designed for, while the left end unit doesn’t receive enough flow rate. This will lead to comfort issues.
The system depicted below is the same as before, but this time, each end unit has a balance valve.
As can be seen, adding a balance valve to each end unit will ensure that the pressure drop over each branch to the pump will be equal by increasing to the total branch pressure drop until balance is achieved. This way, each path has the same pressure resistance, making the actual flow rates similar to the design flow rates.
Static balancing vs. dynamic balancing
Static balancing is done by commissioning balance valves based on designed peak load conditions. However, once the system works in partial load, flow rates change and therefore the hydronic balance also changes. Static balance valves can’t take this dynamic behavior into account, and comfort issues can once again arise.
Types of balance valves:
Balancer:
A balancer is a static balance valve with a fixed KV value. It can’t therefore account for dynamic imbalances in the system.
The balancer BC has three parameters:
Valve KV value: The KV value expresses the amount of flow for a pressure drop of 1 bar. It can be calculated by the Optimiser during the ‘Optimise components’ step in order to balance the system, as the software will calculate the optimal KV-value for every single balance valve placed in the system, also for those placed in other BC. If not calculated, the default value is set at 1 000 000 m³/h, meaning that there is no pressure drop over the BC.
When the user locks the KV value on 1 000 000, the valve minimal pressure drop must be set to 0 kPa. Otherwise, the Optimiser will generate an error.
The KV value can also be manually filled in by the user. Alternatively, if the actual KV value isn’t known, the user can click on the "pencil" icon which results in a calculation popup window. In the popup window, the user can calculate the KV value by entering the pressure drop and flow rate (and if needed, the brine, mixture and reference temperature). As a second alternative, the user can also let the software automatically calculate the KV value using the design flow rate and by entering the estimated pressure drop over the balancer.
Always press the “Save” button before closing the popup-window. If you click on another component before saving, your calculation will be canceled!
Always lock the KV value parameter after defining the KV value. If the parameter is not locked, the Optimiser will overwrite the value each time the ‘Optimise components’ step is run.
Valve minimal pressure drop: The minimal pressure drop that the optimiser must provide over the BC. By default, this value is set to 3 kPa. This is the value the optimiser will use in calculation.
Fully opened KV value: This is an optional value. By giving a number to the fully-open KV value, an upper limit is given to the range that the KV value can take during the ‘Optimise components’ step. In the case where certain valves are known to be placed, inserting this value can allow you to calculate the optimal setting for each valve, hence not requiring you to make substantial changes to the real life installation.
Flow regulator
A flow regulator is a dynamic balance valve and can account for both static and dynamic imbalances. In contrast to the balancer, it does not depend on a KV value for relating the pressure drop to the flow rate. Instead, a flow regulator opens and closes when the pressure decreases, respectively increases, keeping the flow rate constant, independent of the pressure drop.
The flow regulator BC has three parameters:
Minimal valve pressure loss: The minimal pressure drop that the optimiser must provide over the BC. By default, this value is set to 25 kPa. When this value is changed by the user, the parameter must be locked.
KVS-value: The KVS value expresses the amount of flow in a regulating valve at a fully-open valve position that creates a pressure drop of 1 bar. This parameter will be calculated by the Optimiser.
Target volume flow: The designed volume flow that is supposed to be kept constant by the flow regulator. This parameter can be manually filled or can be calculated by the Optimiser. If filled in manually, the parameter must be locked.
Pressure independent control valve
A PICV is a dynamic balance valve and can account for both static and dynamic imbalances. Similar as the flow regulator, it keeps the flow rate constant, independent of the pressure drop. In contrast to the previous balance valves, a PICV is also a control valve.