Low Temperature Radiant tubing length

asked 2017-05-30 07:36:21 -0500

Ali Raad gravatar image

updated 2017-05-30 08:01:45 -0500

Hello everyone,

I am modeling a ZoneHVAC:LowTemperatureRadiant:VariableFlow, using the CFD algorithm. I have noticed that when I change the tubing length that does not show any significant effect on the air inside temperature. A 40m tubing length has the same effect as a 1m tubing length. Also when I change the circuit length I have the same results. May I know why is that happening?.Since changing the tube length should effect the temperature inside the room. And what is the different between the tubing length and the circuit length?

Thank you

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Comments

Have you autosized anything in the component such as capacity, flow rate etc... it might be that the autosized fields are trying to make up the capacity to meet the load. Also have you checked your temperature and flow rates through the pipes, ie delta T from one side of the component to the other to see if that is changed, have you checked the surface temperature on your ceiling/floor to see if that is changing, also it is worth checking these things against the manufacturers data. It is also worth checking the plant loop, temperatures from the boiler/chiller and flow rates from those.

Annie Marston gravatar imageAnnie Marston ( 2017-05-31 03:48:49 -0500 )edit

Thank you for your comment. actually I have autosized some component, I also thought that the autosized fields are trying to make up the capacity to meet the load. But after checking the capacity and the flow rate. I did not see any difference that could make up to the change in the tubing length. The flow rate inside the pipe does not change, however there is a change of few degrees in delta T from one side of the pipe to the other. I have also noticed the same thing happening in the IDf examples that come with E+ when changing the tubing length.

Ali Raad gravatar imageAli Raad ( 2017-05-31 09:05:36 -0500 )edit

I have the same problem as Ali Raad using low temperature radiant variable flow objects. My model is also autosized, the tubing length is near to 1000m. This value leads the outlet temperature node of the radiant system to be very close to the zone ambient temperature. If I manually size the length to very small values (1-10m), for system size capacity of around 4000W, the outlet temperatures seem to be reasonable and not very close to ambient temperature. Has someone play around with this objects and the tube length? Did you obtain reasonable results?

nachogo27 gravatar imagenachogo27 ( 2017-06-07 09:42:51 -0500 )edit

Have you tried to increase the system capacity to more than 4000W, Have you tried to set higher water temperature at the inlet of the radiant.

Ali Raad gravatar imageAli Raad ( 2017-06-07 15:17:00 -0500 )edit

Yes, I have increased the capacity to 10000W, I tested with higher inlet temperatures (I started with 45°C and finally tested with 60°C) and the outlet temperature always is close to the ambient temperature. I tried increasing the maximum flow rate and I have also used an EMS to try to force the system to set higher flows (in order to decrease the outlet temperature) but this temp always has the same behaviour. I only could reduce the outlet temperature by reducing the tubing length... The autosized length is 1066m and finally I reduced it to 1-2m to achieve reasonable outlet temperatures.

nachogo27 gravatar imagenachogo27 ( 2017-06-07 17:30:15 -0500 )edit