Pressure losses & valves

Overview

These components represent pressure losses and valves. They are hydraulically relevant but – with the exception of the fluid volume – exchange no heat with the surroundings.

Controlled valve

The controlled valve throttles the flow according to the assigned controller. It is the standard valve for flow-rate control at the consumer. Controllable quantities are:

• Mass flux – setpoint mass flux through the branch
• Temperature difference of the following element – e.g. a constant spread across the consumer’s heat exchanger
• Outlet temperature on the secondary side – control to the secondary-side outlet temperature of a transfer station

Parameter	Unit	Default	Meaning
Kvs value	m³/h	optional	Flow coefficient: volume flow at 1 bar pressure loss in the fully open state
Fluid volume	L	0.5	Fluid volume of the valve

If a Kvs value is set, the base pressure loss of the open valve results as

$\Delta p_0 = 1\,\text{bar} \cdot \left( \frac{\dot V}{K_{vs}} \right)^2$

The controller increases the pressure loss beyond this in order to meet the setpoint. Without a Kvs value the valve acts purely as an actuator with no base pressure loss.

Element, constant pressure loss

An element with a fixed pressure loss independent of the volume flow – for example for a differential pressure controller or a lump-sum built-in component.

Parameter	Unit	Default	Meaning
Pressure loss	bar	0.2	Constant pressure loss (sign follows the flow direction)
Fluid volume	L	0.5	Fluid volume

Element, quadratic pressure loss

The pressure loss scales quadratically with the volume flow, defined via a nominal point – the usual model for apparatus whose design pressure loss is known from the datasheet:

$\Delta p = \Delta p_{nom} \cdot \left( \frac{\dot V}{\dot V_{nom}} \right)^2$

Parameter	Unit	Default	Meaning
Nominal pressure loss	bar	0.2	Pressure loss at the nominal volume flow
Nominal volume flow	m³/h	10	Reference volume flow
Fluid volume	L	1	Fluid volume

Element, defined zeta

The pressure loss is computed from a resistance coefficient (zeta value) and the flow velocity – suitable for fittings and built-in components with tabulated zeta values:

$\Delta p = \zeta \cdot \frac{\rho}{2} \, v \, |v| \qquad \text{with} \qquad v = \frac{\dot m}{\rho \cdot A(d_{hyd})}$

Parameter	Unit	Default	Meaning
Pressure loss coefficient (zeta value)	–	150	Resistance coefficient of the element
Hydraulic diameter	mm	50	Reference diameter for the flow velocity
Fluid volume	L	1	Fluid volume

Non-return valve

The non-return valve prevents reverse flow: in the blocking direction the model applies a very high pressure loss, in the flow direction it is resistance-free. The transition is numerically smoothed so that the equation solver remains stable. The valve has no parameters.

Typical application: parallel generators or branches that must not be flowed through in reverse.

Building internal installation

This component represents the pressure loss of the pipe installation in the building – from the house connection to the transfer station – without the lines having to be drawn individually. The pressure loss is computed from the specified pipe length and the configured fittings (e.g. bends); the pipe dimension is automatically taken from the adjacent connection pipe of the network.

Parameter	Unit	Default	Meaning
Pipe length	m	20	Single line length in the building; it is internally doubled for supply and return
Fittings	–	–	Number and type of fittings (e.g. bends); the zeta values are summed and likewise applied for supply and return

The pipe length and fittings of the building internal installation can optionally be counted in the bill of materials.

Notes

• A controller is required only by the controlled valve; all other elements on this page are passive.
• None of these elements support a heat exchange type – they are adiabatic.

Related topics

• Controllers
• Fittings
• Component reference