[TRNSYS-users] Problem with active layer in type 56b

[David BRADLEY]

Amirreza,

  I would try three things.

  One is to set the mass flow rate and inlet temperature to the active 
layer as INPUTS to Type56 (they may already be set that way) and then 
run some cases where you use a forcing function or an equation to switch 
between a high inlet temperature and a low inlet temperature and between 
flow on and flow off. If the flow rate and inlet temperature are 
constant then sometimes it can be hard to see what their effect is 
because everything is steady state. In doing this, make sure that your 
weather conditions are cold; if the building's ambient condition is 
close to 26C then putting 26C water into the active layer is not going 
to have much of a visible effect

  The second thing I would recommend is to put a layer of insulation on 
the side of the concrete that you are NOT trying to condition with the 
active layer. We ran into this same situation where there was a 
mezzanine that had a radiant floor. It was impossible to control the 
temperature of the mezzanine area without insulating the underside of 
that floor (which was also the exposed ceiling below). It may be that a 
lot of your energy is going up instead of down.

   Lastly, instead of watching the air temperature, look at the surface 
temperature of the concrete. It should be quite close to the temperature 
of the active layer. That surface temperature should be more directly 
impacted by the active layer than the air temperature is

best,

  David


On 1/6/2023 3:56 PM, Amirreza Heidari via TRNSYS-users wrote:
> Hello,
>
> I am trying to model a ceiling heating system in type 56b. The actual 
> heating system is actually some hot water heating panels that are 
> located in the ceiling. The actual sizes or thickness of layers are 
> not important, and I only expect the model to reflect a realistic 
> behavior. To model the ceiling heating system, I putted an active 
> layer between two layers of common concrete. The specifications of 
> active layer, common concrete, and the ceiling structure are shown 
> below. However, the model does not show a reasonable behavior because:
>
> 1- The temperature increment of the zone is very small (with 11000 L/H 
> flowrate and 26 C inlet water for a 50 m2 zone)
> 2- The temperature increment of zone does not change with the change 
> of inlet flowrate
> 3- When I change the specifications of active layer (for example by 
> reducing the pipe spacing), the minimum required flowrate of water 
> reaches to unreasonable high values
>
> I tried to get a reasonable behavior by trying following actions:
> 1- *Reducing the thermal capacity of common cement:* It did not work 
> because when I have a big surface with very low thermal capacity, the 
> solar radiation from windows increases the zone temperature to very 
> high values (e.g. 30 C). The same happens with the use of 
> low-capacitance layers like hollow brick.
> 2- *Trying the chilled ceiling: *Although it is not exactly what I 
> need, I tried it to see if it can have a reasonable behavior. But it 
> does not do any change of indoor air temperature (maybe it is only 
> coded for cooling!)
> 3- *Huge increase in inlet flowrate: *Does not change anything !!!
>
> I have attached the .b18 file as well. The inlet temperature and flow 
> to the active layers are as inputs (from other components). The 
> simulation timestep is 30 minuts. Would you please let me know why the 
> zone temperature variation versus the inlet water temperature is 
> extremely low and how I can fix it?
>
> image.png
>
> image.png
>
> image.png
>
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-- 
***************************
David BRADLEY
Principal
Thermal Energy System Specialists, LLC
3 North Pinckney Street - suite 202
Madison, WI  53703 USA

P:+1.608.274.2577
d.bradley at tess-inc.com

http://www.tess-inc.com
http://www.trnsys.com
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