[TRNSYS-users] TRNSYS Message 114

[David BRADLEY]

Avishek,
   There are a number of issues with the project that you sent.

First, the absorption chiller that you specified has a 425 ton capacity 
while the collector has a 2m2 area. There is no pump in the hot water 
loop to set the flow rate so because the absorption chiller appears 
first in the component order, the flow rate in that loop is a constant 
58000 kg/h. There is no weather data reading component attached to the 
solar collector.

Second, the cooling water loop components (tower and pump) do not appear 
to be sized to match the absorption chiller. The pump's rated capacity 
is 1000 kg/h while the default cooling water flow rate for the chiller 
is 279000 kg/h. There is no weather data reading component attached to 
the cooling tower.

Third, I am not clear on the intent of the chilled water loop. The 
chilled water from the absorption chiller is passing across the source 
side of a liquid to liquid heat exchanger (which would cool down the 
liquid on the other side of the heat exchanger). However, the other side 
of the heat exchanger is connected to the air coming out of an 
electrically fired unit heater. Air presumably cooled down by the heat 
exchanger is then returned to the unit heater but the heater control 
signal is set so that the unit heater is not allowed to turn off.

Thermally I would guess that since there is no heat input into the air 
circulating through the unit heater and the absorption chiller is set to 
be constantly on the air is being driven to absolute zero, well beyond 
the range of applicability for the psychrometrics routine.

When working with TRNSYS simulations it is vitally important to 
construct systems one component at a time. The procedure that I follow 
is to select an appropriate model from the library then open it and make 
certain that its parameters are set appropriately for the size of 
equipment that I intend to model. It is also important to click on the 
"more" button for the parameters and for the input initial (and 
constant) values so that I understand what information they are asking 
me to provide. Once I have a component in place, I connect its inputs 
and then use an online plotter to watch whatever outputs are appropriate 
(usually temperatures and flow rates). I often make a guess as to what I 
think I should see at the output of a component, then run the simulation 
and test whether I was right or wrong. Once I understand the output then 
I add another component. Inputs that are not connected stay constant 
throughout your simulation.

I would recommend that you start by specifying only the absorption 
chiller in your system and send the temperature and flow rate of its 
three liquid streams to an online plotter. Set the chiller's control 
signal using a forcing function so that it is on or off only as a 
function of time. Once you understand the behavior of the model then you 
could add a solar collector with a constant flow rate and a weather 
file. However, do not yet connect the hot water output of the chiller to 
the input of the solar collector. Connect only the outlet of the solar 
collector to the input of the absorption chiller. Set a constant flow 
rate into the collector by specifying an input flow rate but do not 
connect the input. Change the size of the solar collector until it is 
providing you with the temperature and flow rate of water that is 
required by the absorption chiller that you selected.

Regards,
  David


On 2/3/2015 06:42, avishek ray wrote:
>  Hi All,
> I am a new user of TRNSYS. I have designed a solar hot water fired 
> vapour absorption cooling system of 1 TR size. The diagram is given 
> below. The error displayed is having the message TRNSYS Message 114 
> ---- The utility routine PSYCHOMETRICS which calculates the 
> thermodynamic properties of moist air has been calledwith wet bulb 
> temparature above the maximum wet bulb temparature for a given 
> pressure. please check the routine which calls the PSYCHOMETRICS 
> routine for possible sources of error. The .tpf file is also attached. 
> Please enlighten me to overcome this error
>
>
> Avishek Ray
>
> Research Fellow and Teaching Assistant
> Department of Energy Management
> Indian Institute Of Social Welfare and Business Management; Kolkata-700073
>
> M:9038707191
>
>
> _______________________________________________
> TRNSYS-users mailing list
> TRNSYS-users at lists.onebuilding.org
> http://lists.onebuilding.org/listinfo.cgi/trnsys-users-onebuilding.org

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

P:+1.608.274.2577
F:+1.608.278.1475
d.bradley at tess-inc.com

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

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