Re: [EnergyPlus_Support] Re: Pipe:Indoor Pipe Fluid against Ambient Heat Transfer Rate

["Jean Marais jeannieboef@xxxxxxxxx [EnergyPlus_Support]" <EnergyPlus_Support@xxxxxxxxxxxxxxx>]

This looks like a numerical problem.

2 things to check:

1) that the length of pipe is long enough to capture at least one finite element of water going through it, i.e. make your timestep so small that the fluid cannot manage to pass through the pipe section within a timestep (ideally you'd like the water particle to stay in the pipe for 3 timesteps), or make your pipe artificially longer (pressure drop is not being simulated) and live with the drawbacks.

2) the engineering reference on limits to the thermal diffusivity, if any exist and try and rectify...again small timesteps may help.

2015-05-19 12:54 GMT+02:00 robertogrilloait@xxxxxxxxx [EnergyPlus_Support] <EnergyPlus_Support@xxxxxxxxxxxxxxx>:

 

Hello Jean,

Thank you for your answer!

The pipe is a distribution pipe between a constant temperature boiler and several baseboard objects, situated on the inlet branch of the demand half loop. The pipe inlet temperature is practically fixed at 70 °C, so a situation with cold water filling a hot wall does not happen.

In the period where the heating system is always active, the pipe outlet temperature does not fall below 68°C, while the environment temperature is around 20°C.

In this period, the pipe fluid heat transfer rate is always significantly higher than the pipe ambient heat transfer rate.

I do have some isolated HVAC equipment convergence warnings, but the unequality also holds true for long periods without convergence problems.

Reporting at the zone timestep (1/6 and 1/12 hour) yields less smooth curves, but does not help me to understand the results!

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Posted by: Jean Marais <jeannieboef@xxxxxxxxx>

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