[TRNSYS-users] Load calculation for radiant floor system

David BRADLEY d.bradley at tess-inc.com
Thu Jun 5 12:29:27 PDT 2014

   I think that you are mixing aspects of "energy rate control" and 
"temperature level control" and I would suggest that you get the 
tutorial called "Temperature Level Control from Energy Rate Control" 
available at 
as it will show you the steps necessary to take a "loads" based 
simulation and turn it into a simulation that uses thermostats and real 

   The reason that your simulation is giving you such low (and probably 
high) outlet water temperatures is that you have a constant capacity 
heat pump connected to a controller. If the capacity of the heat pump is 
very large (and it probably is if you have sized it to the peak load of 
the zone) then during times when there is only a little bit of load on 
the heat pump, it is still turning on at basically full capacity. Since 
you have a very tiny flow rate during those periods, you are getting a 
very big temperature change across the heat pump. In most systems like 
this the flow rate is not changed during low demand periods so the 
temperature change does not increase. If you do want to investigate the 
impact of a variable flow rate system then you probably also need to 
look at the use of a variable capacity heat pump that does not always 
run at or near its rated capacity.
Kind regards,

On 6/3/2014 04:17, Eleftherios Bourdakis wrote:
> Dear All,
> I'm trying to simulate a radiant cooling floor for an office room. 
> Firstly I simulated the model I made in TRNBuild by using the 
> 'heating' and 'cooling' options of it in order to find the maximum 
> cooling demand of my room.
> Then I implemented the active layer in the floor and altered my model 
> in Simulation Studio in the following way:
> 1. I entered in an excel file the cooling demand I got from the first 
> simulation.
> 2. I'm calling this excel file in order to define the hourly flow rate 
> by this formula
> 'Hourly_flow_rate=Max_flow_rate*(Hourly_cooling_demand/Max_cooling_demand)
> and I use this value as an input in the Type941 Air-Water Heat Pump.
> 3. I use a Type2 AquastatC for the cooling control signal of the Heat 
> Pump. The 'Temperature to watch' of the Type2 is the Operative 
> temperature output from my Type56 model and the setpoint for the Type2 
> is 27oC, while the deadband is ±0.5oC.
> 4. In the Heat Pump I use as 'Inlet liquid temperature' a constant 
> value of 15oC and I defined the 'Rated cooling power' as the maximum 
> cooling demand I got from the 1st simulation (Is this correct?)
> 5. Since in my heat gains I also have occupants, I included a 
> ventilation system consisting of a Type112b fan, a Type92, a Type 121b 
> and Type108 as it was described in the 'Temperature Level Control 
> Tutorial' in order mainly to remove the latent load.
> My problem is that in my annual simulation while the 'Inlet liquid 
> temperature' is 15oC suddenly it is reduced to values such as -50oC or 
> -100oC and then back at 15oC! Instead of using an equation for 
> defining the 'Inlet liquid temperature' I used the output of the 
> Type56 'fluid outlet temperature of active layer' but I got similar 
> results.
> Do you know why this is happening? Should I use a component to define 
> the 'Inlet liquid temperature'?
> Thank you in advance for answering my question.
> Best regards,
> Eleftherios
> _______________________________________________
> TRNSYS-users mailing list
> TRNSYS-users at cae.wisc.edu
> https://mailman.cae.wisc.edu/listinfo/trnsys-users

Thermal Energy Systems Specialists, LLC
22 North Carroll Street - suite 370
Madison, WI  53703 USA

d.bradley at tess-inc.com


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