water Age and Reservoir Pattern

Question

Dear Team, 
 In my model (Day1 + water ADD), i set a pattern for my reservoir ie. it will be active for 16 hours then from for 8 hrs inactive. Initial age is set for '0'. The system is , reservoir supplies to tank for 16 hrs and stop supply but distribution from tank is 24 hrs. While performing age analysis, i am getting age for the pipe between reservoir and tank is 8 hrs. reservoir and tank is next to each other. ( Say pipe lenght is10m). so this 8 hrs is added upon the downstream pipes also from the tank. Hence, i am getting more age but it should not be the case. I need the water age at tank outlet should be Zero. Need your suggestions please. for sure water age in potable water network (Suffix with PW-) is less than 24 hours only. I model for your reference (Model) uploaded in secure file transfer. 
 
 Thanks for the consistent support. 
 With Regards, 
 RSP

Tom Walski · Answer

If you only want to consider the system starting at the tank, eliminate the reservoir and pipe from the model and represent them as a negative demand with a pattern. Then the tank would be starting point for water age calculations.

Tom Walski · Answer

Once you start a day, the water in the tank ages both in the model and the real world.

Jesse Dringoli · Answer

Could you elaborate on what your concern is? 
 
You had mentioned "why model is considering the age for empty pipe." - the basic assumption is that pipes are pressurized with water, so if you close a pipe (or if it has zero flow), the pipe is still full of water, which will age accordingly. 
 
You also mentioned that you tried the negative demand but the age in all pipes was equal to the simulation duration. This indicates that no "new" water was getting into the system from the negative demand, which could be due to a number of different, likely real issues. For example maybe based on the tank mixing method, the "new" water (either from negative demand or reservoir) never gets out to the system. In your model I tried choosing LIFO as the tank mixing method and was able to see a reduction in water age in downstream nodes. However due to the large size of the tank, some "old" water still makes it out into the system. It could be that the tank is not allowed to fully "cycle" all it's fully fast enough.

Tom Walski · Answer

You are really talking about two different scenarios. In one you account for the tank and the age in the tank. You can use this for your hydraulic calculations. 
 
In the second scenario, you are dealing with a different active topology where you make the reservoir and pipe inactive and start the model from the tank. 
 
You can't handle both conditions in one model run.

Jesse Dringoli · Answer

Due to the assumption of full pipes, it seems that using a negative demand directly on the tank is your only choice (at least for the scenario you use for water age.)