[TRNSYS-users] Type 123 Cooling Coil Psychometrics Problem

Hofmann, Daniel daniel.hofmann at dreso.com
Wed Jul 17 04:13:56 PDT 2019

Hello David,

I jumped over to a sensible heat exchanger. This solution works perfectly for me.
Many thanks for your help and the description of the problem

best regards,
Daniel Hofmann

From: David BRADLEY <d.bradley at tess-inc.com>
Sent: Tuesday, July 16, 2019 9:47 PM
To: TRNSYS users mailing list at OneBuilding.org <trnsys-users at lists.onebuilding.org>
Cc: Hofmann, Daniel <daniel.hofmann at dreso.com>
Subject: Re: [TRNSYS-users] Type 123 Cooling Coil Psychometrics Problem


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,


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.

[cid:image001.jpg at 01D53CA1.25AC0790]

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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