[TRNSYS-users] Type 123 Cooling Coil Psychometrics Problem

[David BRADLEY]

Daniel,

Type123 does a computation to find the maximum possible heat transfer at 
the given rated conditions (air and water inlet temperature, air inlet 
humidity, air and water flow rates). It then compares the stated 
capacity to the calculated maximum. In the case of the parameters that 
you have specified below, the maximum possible heat transfer is being 
calculated as 234. kJ/h. However! if you reduce the total and sensible 
heat transfer rates to that value you will run into another error.

Fundamentally, the problem is that while Type123 assumes that the coil 
is either totally dry or totally wet during operation its basic UA 
calculation method is invalid if the coil's rated conditions are for 
sensible-only heat transfer. We will certainly work on making some 
better error handling for Type123. I think the workaround for your case 
would be one of two things. You can either give the model some rated 
conditions in which the total capacity is greater than the sensible 
capacity or you could simply use a sensible-only heat exchanger model 
for your cooling coil.

kind regards,

  David


On 07/16/2019 06:19, Hofmann, Daniel via TRNSYS-users wrote:
>
> Hello everyone,
>
> I currently try to use Type 123 Cooling Coil with TRNSYS18. Type 123 
> is directly connected to the TRY2017 weather data reader. All other 
> inputs to Type 123 are considered to be constant.
>
> The rated parameter values are measured values and do not include any 
> dehumidification.
>
> No matter whether I use humidity mode 1 or 2 and no matter whether I 
> reduce the total cooling capacity to e.g. 400 kJ/hr I always get the 
> following error: “The referenced Unit has a bad parameter value. 
> Reported information: Parameter #7, Reported Problem: The total 
> cooling capacity of the coil is impossible at the given conditions.”
>
> And an additional warning message is shown: “The referenced Unit has 
> called the PSYCHOMETRICS routine one or more times during the 
> simulation with a humidity ratio above the saturation humidity ratio 
> for the given dry bulb temperature. The air was assumed saturated at 
> the given dry bulb temperature and the humidity ratio set for this 
> condition.”
>
> I already checked the connection between the weather data reader and 
> Type 123. I also tried a simulation with constant input values…..there 
> is still not difference.
>
> Thus I think it is a bug in Type 123 or the psych subroutine.
>
> Does anyone have a solution or an idea what could cause the errors? 
> Thanks a lot for any help!
>
> Best regards
>
> Daniel Hofmann
>
>
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-- 
***************************
David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
3 North Pinckney Street - suite 202
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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