To restate the 'knowns' and 'unknowns' to establish a formula, we have:
Knowns:
• HWT (i.e., 85deg)
• CWT (i.e., 15deg)
• TWT (i.e., 60deg)
• TWF (i.e. 100l/s)
Unknowns
• HWF
• CWF
Thus we have two unknowns, and we need two formulae to determine the values:
• HWF+CWF=TWF
• HWT*HWF+CWT*CWF=TWT*TWF
To solve for the flows, you can rewrite the formulae:
• HWF=(TWT*TWF - CWT*TWF) / (HWT-CWT)
• CWF=TWF-HWF
Plugging in for this example
• HWF = 64.3l/s
• CWF=35.7l/s
If we imagine a mixing valve to represent the mixing process, with ports named 'HW in', 'CW in', and ‘TW out', and you have assigned Systems to your supply piping (HW in and CW in), Revit knows the HWT and CWT because these are properties of their respective systems.
Revit also 'knows' TWF because it computes from the connectors at the 'points of utilization', and knows the TWT because you'd also create this system, and assign the temperature. We need to find ways to access the ‘known’ information, run the computation, then assign the values to the mixing valve’s connectors.
The problem is that there is no 'built-in' way to get the Systems' temperatures via parameters on the connectors of the valve. You could add your own params to the valve, and manually populate the values. You could use the API to extract the values and assign them to the params. Or, if you're using the API anyway, you could compute the values for the flows and assign to the connectors, and not necessarily use a param as a storage mechanism for the temperatures.
HTH,
Martin Schmid, PE
Martin Schmid
Product Line Manager
Mechanical Detailing and Electrical Design
Architecture, Engineering, and Construction
Autodesk, Inc.