Re: [EnergyPlus_Support] Re: Simulation of a water pipe

The pipe does both conductive and convective heat losses. The significance of these will depend on your configuration. If you use insulation on your pipe, the conductive heat transfer resistance will be much higher than the convective resistance, and vice-versa. I took the example file for the pipe:outdoor object, change the insulation and pipe steel conductivity to both higher values, and noticed a significant change in the heat transfer rate. In the overall scheme of the plant, the chiller loads were not altered drastically, but the pipe heat transfer changed up to 10 fold. If you play around with your parameters, you should notice similar effects.

Edwin

On Tue, May 12, 2009 at 4:15 AM, Stefano Galli <ste_gallo82@xxxxxxxxx> wrote:

Hi, I'm still working on this simulation: I'm simulating with only water in the pipe and trying to model the real situation of the heat exchange by varying the waterflow, as you suggested.
I found out that the outdoor pipe simulates only a convective heat exchange: in the Engineering Reference (page 687) the equation that describes the model uses the film convective resistance, but ignores the pipe's material conductivity. In fact, if I change the material's lambda value, the heat loss value does not change.
Is this correct?
How can I simulate the pipe with both convective and conductive losses?

Thank you

Stefano

--- In EnergyPlus_Support@xxxxxxxxxxxxxxx, Edwin Lee <leeed2001@...> wrote:
>
> Not sure if you are still working with this issue or not. The pipe heat
> transfer object can definitely only handle one fluid running through it.
> You may be able to make a good estimate at the loss by running a custom
> fluid through the pipe using manually generated glycol data for density,
> specific heat, and conductivity. This could be a weighted average assuming
> the air and water are close to isothermal at each point along the length of
> the pipe. The work to generate this data may not be worth it, so you may
> also consider running the pipe with a large flow of water, and then with a
> very small flow of water. Look at the bounds of the heat loss and make an
> estimate. This neglects the air, but should get in the ballpark.
> Edwin
>
> On Fri, Apr 10, 2009 at 3:02 AM, Stefano Galli <ste_gallo82@...>wrote:

>
> >
> >
> > Hello, I am trying to calculate the thermal loss of an external pipe
> > installed in an aquatic amusement park.
> > The pipe is not totally filled with water: just a small amount of water
> > flows in it. The rest of the pipe's section is occupied by air: the water is
> > heated and has a fixed temperature. There is no control on the air
> > temperature in the pipe.
> > I need to calculate the thermal loss in order to size the heating plant and
> > to evaluate the option of installing some sort of thermal insulation on the
> > pipe.
> > Is it correct to simulate the pipe with a pipe:outdoor ? Is it possible to
> > simulate just the small waterflow or pipes can only be totally filled with
> > just one fluid?
> >
> > Thank you!
> >
> > Stefano
> >
> >
> >
>