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All Topics | Topic "System flow balance"
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Author Message
Mr. Christopher Fischer

Subject: System flow balance   
Posted: 4/4/2018 Viewed: 9443 times
Dear all,

within my WEAP model I want to have an expression which is calculating with the flow balance of the whole system. Therefore I want to subtract the Outflows out of the area from the inflows into the area.

First I tried to achieve that through the following expression;

PrevTSValue(Supply and Resources:Total Node Inflow[m^3])-PrevTSValue(Supply and Resources:Total Node Outflow[m^3])

But since I realized that the branches "total node inflow" and "total node outflow" are something different from "Inflow into area" and "outflow from area", I'm running out of ideas how I can do that alternatively.
My preferred expression would be:

PrevTSValue(Supply and Resources:Inflow to area[m^3])-PrevTSValue(Supply and Resources:Outflow from area[m^3])

Unfortunately it is not possible to write the expression into the expression builder.

I'm really thankful for any help or idea, to solve my problem. Furthermore I would be satisfied, if someone can explain me what is meant by "Total Node Flow".

Many thanks for your answers

Ms. Stephanie Galaitsi

Subject: Re: System flow balance   
Posted: 4/16/2018 Viewed: 9411 times
Hi Christopher,

I'm trying to figure out how to help. For your equation, do you want:

1) All of the water coming into the system (rain, groundwater, other supply, plugged in streamflow) minus all the water leaving the system (evaporation, consumption, streamflow exiting the model)?
2) Water going to point sources withdrawing from the river (or other supplies) minus the water returned from those areas to the river or other supply?
3) Something else?

It's possible - depending on what you want - that WEAP already calculates this in the results. What do you need this data for? Does it need to be in the data view, or could it be in the results view, for your purpose?
Mr. Christopher Fischer

Subject: Re: System flow balance   
Posted: 4/17/2018 Viewed: 9404 times
Hi Stephanie,

in fact I only have a single source system, where all the accounted water is produced from three different desalination plants designated as "Other Supply".

Now I want to calculated with an expression the water balance of the system. Therefore the inflow into the system (only provided by desalination plants) shall be compared with the outflow of the system.
Whenever the amount of inflow (production) is greater than the outflow, there is still capacity in the system to store produced water. Whenever the inflow is equal or smaller as the outflow, there is a overproduction.

An other approach would be, to have a dimension for "System Requirement", where all water required (supply, filling reservoirs, system losses, etc.) is summarized, to be compared with the production.

I'm pretty sure this is already calculated in the results. But, since I want to have the expression as a term for further calculations, I need theses results (from the previous time steps) in the data view for building an expression.
While I can find the inflow under "Branches/Supply and resources:Inflow", my only problem is to find a expression for the flow out of the system.

In the hope that I could point out my problem, I really thank you for your patience and any advice or suggestion you can give to me.
Ms. Stephanie Galaitsi

Subject: Re: System flow balance   
Posted: 4/17/2018 Viewed: 9396 times
Hi Chris,

Now that I better understand your question, I think you can calculate this information as a Key Assumption that sums the Inflow from all the desal plans, sums the Supply Requirement, and subtracts the latter from the former. They would both have to be in previous time step, unless you want to do the math for Supply Requirement yourself (it is not so bad).

I assume if you're using Supply Requirement, you have losses, reuse or DSM savings in your system. Otherwise you can use Water Demand, which is even easier to calculate. Anyway, the equation would look something like this, although this just shows 1 desal plant and 1 demand site.

PrevTSValue(Supply and Resources\Other Supply\Desal Plant:Inflow[CMS])-PrevTSValue(Demand Sites and Catchments\Big City:Supply Requirement[m^3])

Mr. Christopher Fischer

Subject: Re: System flow balance   
Posted: 4/17/2018 Viewed: 9385 times
Hi Stephanie,

thanks for your immediate answer.

As far as I know "supply requirement" does not include the amount of water required for filling reservoirs. Since this is a major condition for running my model I'm looking for something like "system requirement", which should include the required water to satisfy the whole system including the reservoirs.

Right now im calculating this with the following schematic equation:

PreTSValue(Supply Requirement)+PreTSValue(StorageCapacity-StorageVolume)

Since there is a vulnerability to failures because of other characterizations in my model, I would like to replace that.
Mr. Christopher Fischer

Subject: Re: System flow balance   
Posted: 4/19/2018 Viewed: 9376 times
Can you maybe tell me, where to find "Outflow from area" in the KeysAssumtion branches? I can only find it in the results under Result/Supply and Resources/Outflow from area.
Ms. Stephanie Galaitsi

Subject: Re: System flow balance   
Posted: 4/23/2018 Viewed: 9366 times
Unfortunately WEAP does not have the ability add up the Outflow from System in the data view. You can do it yourself, using the results from the previous time step. To make sure that you incorporate all the outflows of your model, go into the Results view and look at Outflows from Area and then look at “All Outflow Points” under the variable dropdown menu on the right. This will show you all the outflows that you would have to add up in the data view.
Topic "System flow balance"