[TRNSYS-users] Working of the pump type 3

Alastair McDowell alastair.mcdowell at energyae.com
Sun Nov 15 13:52:37 PST 2015

Hi Benjamin,

TRNSYS is primarily a thermal analysis tool; the simulation does not automatically perform a hydraulic analysis as well, which is what you are asking for. (Although there are components to do this.)

If you review the TRNSYS documentation for the pump, you'll see the mass flow rate is set to the maximum mass flow rate when the control signal is 1. The power consumption is set by a polynomial in terms of the control signal, that you define with the power conversion coefficients. Since the power and mass flow rate are linked by the control signal, this allows you to define a power curve if you're operating at a range of mass flow rates. You must specify the power coefficients for your particular system.

If the system changes, i.e. you add another panel, you have increased the pressure drop for the pump to overcome, which will change the operating point of the pump (mass flow rate and pressure head). To calculate this new operation point, you need to know the pressure-flow rate characteristics of the pump, and the overall pressure loss in your hydraulic circuit (collector, valves, pipes, bends etc), and find the intersection of these. The power consumption is the mass flow rate multiplied by the pump pressure.

Kind regards,

Alastair McDowell
Engineering Consultant
Energy Analysis & Engineering - Enabling innovation for a sustainable future
T: +61 450 600 842
E: alastair.mcdowell at energyae.com
608 Harris St Sydney NSW 2007 Australia | http://www.energyae.com<http://www.energyae.com/>

From: TRNSYS-users <trnsys-users-bounces at lists.onebuilding.org> on behalf of Benjamin Stobbe <benjamin_stobbe at hotmail.com>
Sent: Sunday, 15 November 2015 12:52 AM
To: 'TRNSYS users mailing list at OneBuilding.org'
Subject: [TRNSYS-users] Working of the pump type 3

Dear people,

Still busy with my hybrid solar panel system on the side of facade and I'm now looking into the pump. My small system has now 4 panels connected to one pump and I was looking how the power consumption increased as function of connecting more panels to the pump, but the power does not increase, according to the model because this only takes into account the output flow and this is 90l/h only 4 or 5 times. You see in the input that it asks from the tank 360 o4 450l/h. Does someone have an idea to solve this, because I now believe the power consumption is not realistic. Or is the idea of scaling up not consuming more power of a pump?

Best regards,

Benjamin Stobbe
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