.Buildings.Fluid.HydronicConfigurations.PassiveNetworks.DualMixing .Buildings.Fluid.HydronicConfigurations.PassiveNetworks.DualMixingThis configuration (see schematic below) is used instead of Buildings.Fluid.HydronicConfigurations.PassiveNetworks.SingleMixing when the primary and secondary circuits have a different design supply temperature. Contrary to the single mixing circuit, the use of this configuration is restricted to constant flow secondary circuits due to the constraint on the fixed bypass pressure differential that must remain sufficiently high.
The following table presents the main characteristics of this configuration.
| Primary circuit | Variable flow |
| Secondary (consumer) circuit | Constant flow |
| Typical applications | Consumer circuit supply temperature different from primary circuit such as underfloor heating systems |
| Non-recommended applications | Applications where primary and secondary supply temperature must be equal as secondary flow recirculation cannot be avoided. |
| Built-in valve control options | Supply temperature |
|
Control valve selection (See the nomenclature in the schematic.) |
β = ΔpA-AB / ΔpK-L =
ΔpA-AB /
(Δp1 + ΔpA-AB) The control valve is sized with a pressure drop equal to the maximum of Δp1 and 3e3 Pa at ṁ1, design (see below). |
| Balancing requirement |
The three-way valve should be fully open at design conditions. |
|
Lumped flow resistance includes (With the setting use_lumFloRes=true.)
|
Control valve val only(So the option has no effect here: the balancing valves are always modeled as distinct flow resistances.) |
The bypass balancing valve works together with the secondary pump to generate the pressure differential differential at the boundaries of the control valve. So it is paramount for proper operation of the consumer circuit that the bypass balancing valve generates enough pressure drop at its design flow rate ṁ3, design otherwise the consumer circuit is starved with primary flow rate despite the control valve being fully open. So oversizing the bypass balancing valve (yielding a lower pressure drop) is detrimental to the consumer circuit operation. Undersizing the bypass balancing valve (yielding a lower pressure drop) does not disturb the secondary circuit operation as the control valve then compensates for the elevated pressure differential by working at a lower opening on average. However, the secondary pump head is increased and so is the electricity consumption. See Buildings.Fluid.HydronicConfigurations.PassiveNetworks.Examples.DualMixing for a numerical illustration of those effects.
The parameter dp1_nominal stands for the potential
primary back pressure and must be provided as an absolute value.
By default the secondary pump is parameterized with a design pressure rise
equal to dp2_nominal + dpBal2_nominal + dpBal3_nominal.