Re: [TRNSYS-users] Mass blance problem with flow diverter

[David BRADLEY <d.bradley@tess-inc.com>]

Santeri,
  Pumps in TRNSYS set the downstream flow rate according to their rated flow rate and the value of their current control signal. Apart from checking for mass balance problems, they ignore their inlet mass flow rate. When there are loops that have multiple pumped branches, you have to be particularly careful to make the flow splitting decisions based on the flow rate that is currently entering the flow diverter. I would recommend that you remove the connections from the diverter to the pumps. Then connect the outlet flow rate of every device in the loop to an online plotter and make sure that you understand the outlet flow at each component. Make sure that the mass balance is preserved. Next, reconnect the flow diverter to the pumps and see whether the mass balance is still preserved. If it is not, there may not be enough thermal capacitance in your loop. Controllers may be making decisions based on unconverged temperatures.
Best,
 David

On 9/19/2012 05:54, Santeri Siren wrote:

Dear all,

I have a problem with the mass balances of my system. In my proct a flow diverter divides the waterflow into two separate pipes. .After the flowdiverter both pipes go to their own pumps. The flow diverter is controlled according to the ratio of mass flows produced by the pumps. After the pumps comes heating loads. After that the waterflows are connected in a flow mixer and the water is being heated in a heatpump.

The problem is that Trnsys gives mass balance warnings for both pumps. When I check the mass flows of the pumps, they some times are even larger than the rated flow of the pump.I think the problem has something to do with the flow diverter...

Can someone give me advice how to fix this problem and make the mass flows balanced. I have attached a demonstrative picture of my project.

best regards.
Santeri Siren

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