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Hello.
I am planning to model a building using TRNBuild, Active Layer, and I have a question regarding the Active Layer settings (Active Layer Specificaton).
What is the difference between inlet mass flow rate (top right) and Min. Inlet Mass Flowlate (middle)? Also, what is the difference between the "desired" and "allowed" values?" What should I put in the "desired" value?
I would also appreciate it if you could tell me how to use Divide Surface. When is it necessary to divide a layer?
It would probably be helpful to refer to the 05-MultizoneBuilding manual for context about the capabilities and limitations of the active layer model that is built into Type56. Essentially though, the model is only valid over certain parameter ranges (such as the liquid flow rate and the ratio of the tube spacing to the thickness of the material in which the active layer is embedded). In the case of the liquid flow rate, it is also important to keep the flow turbulent and not let it go laminar. If the specific liquid flow rate (kg/h.m2) that you want to use in your floor is below the minimum value for which the model is valid then you can divide the surface into a series of surface "segments."
The inlet mass flow rate (top right) is the actual flow rate that will go through your surface.
The min inlet mass flow rate (middle) is the minimum (non zero) flow rate that can pass through the surface and have the model still give valid results.
The "desired" value is the minimum flow rate that you want to use. The "allowed" value is the minimum that the model (given the tube spacing, layer thicknesses, tube diameters, etc.) will support. If you do not have variable flow rates and the desired and allowed flow rates are already above the minimum then you don't need to concern yourself with these settings. If the flow rate that you want to pass through the surface is below the minimum allowed then you will need to set the desired minimum and the surface will need to be segmented. Segmenting the surface is an automated process (click the button) but in order for it to be available, you have to change the zone's geometry mode to "manual."
kind regards,
David
Manaya_ Topic starter
17/10/2023 9:00 am
@davidbradley
Thank you very much for your kind reply. Thanks to your answers, I understand that if the flow rate is sufficient, there is no need to divide the active layer.
Even if the flow rate is sufficient, is it ok to divide the active layer in case the flow rate is very low?
Is there a problem with dividing the active layer too much? Is it undesirable to divide a layer when it is unnecessary?
DavidBradley 23/10/2023 4:15 pm
>> Even if the flow rate is sufficient, is it ok to divide the active layer in case the flow rate is very low?
You'll need to segment the active layer to accommodate whatever the smallest non-zero flow rate that the floor will see during the course of the simulation. Be careful with very low flowrates! You need to make sure that the flow stays turbulent in order to get decent heat transfer between the fluid and the walls of the tubes in the active layer.
>> Is there a problem with dividing the active layer too much? Is it undesirable to divide a layer when it is unnecessary?
I have not seen any studies that look at the impact of dividing/segmenting a layer when it is not strictly necessary to do so. Segmenting basically puts smaller pieces of floor in thermal series with one another. I would imagine that to cause the outlet liquid temperature to be lower than if the circuits were more in parallel. In real-world radiant surface systems you don't want too big a delta T across the surface. I would definitely recommend looking in the literature to find out what kind of inlet/outlet temperature differences are common for the kind of system that you are trying to model and then to watch those in your simulation and make sure that they are reasonable.
kind regards,
David
Manaya_ Topic starter
18/11/2023 6:28 am
@davidbradley
Thank you for the detailed explanation.
・In a floor with Layer before being divided, the pipes are arranged in parallel.
(Water enters the pipes in such a way that it spreads uniformly over the entire floor)
・In a floor with Layer after being divided, several segments are arranged in series.
(Water passes through the pipe in one segment and then enters the pipe in the next segment. The water repeats this until it has passed through all the segments)
Is this interpretation correct?
I would like to apologize for my poor English.
