hello all , Im modeling chilled water system ( closed loop) on watercad,I am studying the losses (from valves, fittings ..etc) through the hall system.
*I need to control the flow from exceeding 14m3/h by placing FCV on incoming pipe of the cooling skids,
1- the losses on FCV can be calculated by the system without the value of K(minor loss coefficient) ?? its important to me to know the losses occur on the valve ??
2- sitting the initial flow as 14m3/h will control the outlet flow 14m3/h?
*What is the meaning of Demand on the junctions is it flow rate ??
Appreciate your support
Hello A.S.,
What are trying to model with this? This might help to ultimately find the best setup for the system.
One item of note is how WaterCAD works in a closed system. WaterCAD and WaterGEMS are demand-based programs, meaning the demands will always be satisfied. The demand at a location is the flow rate coming out of the system at that point.
With a closed system and only one source of flow, like a reservoir or tank, the flow that you will see out of that will be equal to the demands in the system. If you have 14 m^3/hr of demand in the system, the flow out of the source will be 14 m^3/hr as well.
Based on this, with a closed system, an FCV may not be necessary or may actually cause issues with the results balancing. Instead, if your concern is introducing some sort of minor loss, you can include a minor loss on a pipe though the pipe properties. There is minor loss engineering library available that has some common values you can use. The following link has information on this: Adding Minor Losses to Pipes.
Regards,
Scott
It sounds as if what you have is a true closed loop with no inflow or outflow. In this case the flow is controlled by the pump and the pipe and valve losses. There are no Demands in a closed loop.
Exactly how will you control the flow? Will there be a throttling valve that is controlled by a PLC; will it be controlled by the pump and valve selection with no real time control (The usual setup) or will the pump be a variable speed pump? Don't use an FCV unless you really have one.
For a model to run, you need at least one constant head node to set the Hydraulic grade. This depend on how the system is initially charged and how makeup water is provided to offset any leakage. This can be modeling by connecting a reservoir node to the loop with a tiny pipe such that there is negligible flow inflow/outflow. The elevation of the reservoir determines the pressure.
Hi Tom
you said that i shouldn't use FCV unless i have it, what i have is PICV it control the flow, ∆P constant let say its like balancing valve how can i represent this type of valve on WaterCAD ???
You can model a constant headloss using a Pressure Breaker Valve (PBV): Modeling a Constant Headloss
Jesse DringoliTechnical Support Manager, OpenFlowsBentley Communities Site AdministratorBentley Systems, Inc.