Modeling heat loss in WaterGEMS and WaterCAD

 Product(s): WaterGEMS, WaterCAD Version(s): V8i, CONNECT Edition Area: Layout and Data Input

Problem

Is it possible to model heat loss in buried water pipe lines with WaterGEMS or WaterCAD? (generally in cold climates)

Background

Keeping water in liquid form throughout a distribution system is a problem confronting water supply engineers in cold areas.

Of all the schemes developed for this purpose, basically only two are used. Either enough heat is added to the water to prevent freezing or the system is designed in such a way that the water is removed from the system before it freezes. So, it is necessary to consider the heat loss in pipe lines in such cases.

Solution

Heat loss currently must be approximated using constituent concentration as a proxy for temperature. So, with the help of Constituent Analysis you can workaround this situation.

There is a certain temperature at the source of water and the driving force is trying to reach equilibrium with the surrounding environment. What you could do is uncheck the "Unlimited Concentration" box in the Constituents dialog and set the concentration limit to the equilibrium concentration that will be reached. For example, the temperature of the ground for a buried pipe in this case.

You would expect this to follow a first order reaction rate because heat diffusion through a pipe wall would be of first order. The difficult part is determining the first order "Bulk reaction rate" though. To overcome this, you may need to obtain some real data from your system as this will vary depending on the pipe wall material (plastic, iron, concrete, ductile iron, etc.)

Steps to be followed to set up constituent analysis:

• You would set the temperature at your source reservoir and name the constituent Temperature in the Constituent Alternative.
• If you don't set the Concentration (Initial) to a reasonable value, it will start from 0 which will lead to slow convergence (run the model long enough to reach equilibrium). So it is better to pick some value (between the value at the reservoir and at the equilibrium) and set in as the Concentration (initial) in the concentration (Initial).
• And then perform constituent analysis by setting other values like specifying concentration limit in constituents.

Unfortunately, there is no way at the time of writing this article to set the units on concentration to degrees C or F. So, you will get mg/L as the unit and you just need to keep in mind that you are dealing with temperature.

The above information is applicable for water pipes system only and not for HVAC system because the heat/cold fluid in the pipe will change the equilibrium temperature.