Control valves are used to control the hydronic system. They regulate the flow in function of the load. Therefore, control valves must always be connected with an actuator. Without control valves, only the static designed (peak) flow rates could be provided.

In the Hysopt Optimiser, the controlling ports of control valves are symbolised with a black triangle. In essence, there are two different types of control valve mechanisms: 2 & 3-way control valves.

2 & 3-way control valves

2-way control valves vary the secondary flow rate while keeping the flow temperature constant. In contrast, 3-way control valves keep the secondary flow rate constant while varying the flow temperature. Using this difference in behavior, both valves will be the cornerstone for a large variety of distribution circuits that can be created.

Both control valves have the following parameters:

Valve type: a list containing three types of valves: 'Equi-percentile, ‘linear’ and ‘mixed’. More information on the importance of the valve type can be found below.

Control valve 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 or can be filled in & locked manually. Typically, the KVS value of a control valve is linked with the (DN) size of the valve.

KVS-value on the bypass gate: This is an optional parameter only found on a 3-way valve. It can be used when you wish to use a different KVS value than the one on the primary gate.

Continuous KVS-range: By default, the Optimiser uses a list of discrete variables when calculating the KVS value. If preferred, flipping the node allows you to use a continuous rage.

Control valve rangeability: KVS/KV0. The theoretical range between the maximal (KVS) and minimal (KV0) controllable flows. By default, the parameter is set at 100.

Control valve real rangability: KVS/KVr. The real controllable range between the maximal (KVS) and minimal (KVr) controllable flows. This value is always smaller than the theoretical range. By default, the parameter is set at 95.

The greater the rangability values, the better the control action of the valve. When you notice in the software that the lift of a control valve is cycling continuously (usually between small values), it might be useful to further increase the rangeabilities 100 & 95 to 500 & 495. This usually leads to a more stable control output, which can drastically reduce simulation times. The downside of this action is possibly a too perfect, theoretical simulation.

Minimal authority: The lower limit that is imposed to the Optimiser while running the ‘Optimise components’ step. By default, the parameter is set at 0.3. More information on a valve’s authority can be found here: Control valve authorityarchived.

Actual authority: The computed authority of the valve after running the ‘Optimise components' step. This value cannot be changed manually.

Full load valve position: The computed maximal opening position of the main gate on a 3-way valve. This restriction is used to protect the flow downstream against too high temperatures. An example can be found here: Active mixing circuitarchived. This value cannot be changed manually.

Special types of control valves

On-off valve

A 2 way on-off valve is a 2 way control valve that only has two operationg positions: ‘fully open' and ‘fully closed’. It’s therefore usually not used to control the end units, but rather the production units. Whenever a boiler or heatpump is activated/deactivated, the on-off valve will be opened/closed.

A 3 way on-off valve behaves similarly. If one of the control ports is ‘fully open’, the complementary port is ‘fully closed’. It can be used to switch between production units or between consumption units.

Radiator valve

A (thermostatic) radiator valve is a 2 way control valve typically used to control the flow going to a ‘radiator/convector’ end unit BC. The ‘radiator valve’ BC models the pressure drops over the valve much more in detail. This block is therefore mainly used in a technical/detail study. For conceptual studies, it's rather adviced to use a ‘throttle circuit’ BC. This is especially true whenever the ‘radiator/convector’ BC is used to represent a larger group of radiator end units, as the ‘radiator valve’ BC will generate very large pressure drops. It has the following parameters:

KVS-value: Expresses the amount of flow for a pressure drop of 1 bar whenever the valve is fully open. This value must be manually filled in by the user.

KV2-value: Expresses the amount of flow for a pressure drop of 1 bar whenever the TRV is commissioned. This value is related to the setting value of the valve put on the radiator and must be manually filled in by the user. Note that the KV2-value must always be smaller than the KVS value. When calculating the pressure drop, the Optimiser will use the KV2-value rather than the KVS-value.

Minimal authority: The minimal required authority over the control valve. This value will act as a lower limit during the ‘Optimise components’ calculation step. The Optimiser then iteratively tries to optimise the system components until all actual authorities over the control valves are higher than their given minimal authorities. Whenever the Optimiser cannot find a solution where the actual authority is higher than the minimal required authority, it will give a warning message on the BC.

A more detailed explanation of control valve authorities can be found here: Control valve authorityarchived

KV curve: A curve mapping the KV value on the valve position. Similar to a pump curve, the KV curve can be used to simulate the TRV’s characteristics more in detail. This is only advised during technical/detail studies whenever the type of TRV and its corresponding setting values are known.

Don’t forget to lock the parameter after filling in the curve. If not, the Optimiser will override this value when performing the ‘Optimise components’ step.

Minimal pressure drop: This is an optional value. It will act as a lower limit during the ‘Optimise components’ step when calculating the pressure drops throughout the system.

Design KV value: The KV value for which the TRV is designed. When this variable isn’t locked, the Optimiser will take it as a variable in its search to create an actual authority higher than the minimal required authority.

Effective proportional band: The range around the setpoint for which the TRV is allowed to let the temperature run free before control action has to be taken. When this variable isn’t locked, the Optimiser will take it as a variable in its search to create an actual authority higher than the minimal required authority.

Differential pressure regulator

A differential pressure control valve (DPCV) is a 2 way control valve that is used to keep the differential pressure (the pressure drop at the secondary side of the BC) constant. If the differential pressure during partial load conditions drops, the DPCV closes, increasing the differential pressure again. This way, the pressure drop over the primary side of the BC remains constant.

In a way, the DPCV disconnects its riser from the remainder of the upstream circuit. This can be extremely useful to maintain valve authority within large systems.

The differential pressure regulator component has the following parameters:

Differential pressure proportional band: The range around the setpoint pressure drop for which the differential pressure regulator is allowed to let the pressure drop run free before control action has to be taken. By default, this value is set to 5 kPa.

Pressure target: The designed differential pressure target at the secondary side of the BC. By default, this value is set to 20 kPa.

Design primary pressure: The designed differential pressure target at the primary side of the BC. It propagates the expected pressure increase that a pump further upstream of the system must deliver. By default, this value is set to 22 kPa.

KVS-value for differential pressure valve part: Expresses the amount of flow for a pressure drop of 1 bar whenever the valve is fully open. This value must be manually filled in by the user & locked.