[TRNSYS-users] Type 966 and Type 954 air heat pumps related problems.

Fri Aug 27 08:11:20 PDT 2021

Dear Bradley,

I tried what you said but with not much success. My timestep is 5 min,I added internal conditioning to the other zones and the heat pump is of logical size i think, because before introducing the heat pump I calculated the max loads of the zones through the internal calculation of the building. I still have the convergence problem and my simulation is still very slow (7,5 minutes for one run). I am attaching the new files including the .b18, if you could find the time to take a look.

Kind regards,
Jim Soukoulis
National Technical University of Athens

________________________________
From: David BRADLEY <d.bradley at tess-inc.com>
Sent: Friday, August 27, 2021 5:13 PM
To: TRNSYS users mailing list at OneBuilding.org <trnsys-users at lists.onebuilding.org>
Cc: dimitris soukoulis <saintdimi at hotmail.com>
Subject: Re: [TRNSYS-users] Type 966 and Type 954 air heat pumps related problems.

Jim,

 Your project connections are correct. I think your description of the building sounds reasonable too. I can't be 100% sure that the implementation is correct as I would need the look in the *.b18 file as well.

 The issues that you are running into with the heat pump and building are almost always caused by using too long a timestep (this should be on the order of 1 to 5 minutes) and/or a heat pump that is not sized correctly for the zone that it is serving. I'm not sure how you have handled the conditioning in the zones that are not served by the heat pump but I would recommend putting them into energy rate control while you are adding heat pumps. Each time you add a heat pump to a zone you'll want to turn off that zone's automatic/idealized heating and cooling. The problem is that if all but one zone is unconditioned, the additional load on the one conditioned zone (from all of its unconditioned neighbors) causes the heat pump to be undersized until the neighboring zones are also conditioned.

kind regards,

 David

On 08/26/2021 15:47, dimitris soukoulis via TRNSYS-users wrote:
Greetings community.
I am modelling a multizone building and I have two questions.
First, I would like to know if I am modelling the geometry correctly (through the TRNbuild wizard). It is a two floor apartment building with two apartments in each floor, so in the floorplan window, I model it as two separate floors (three zones each, with the middle zones representing the hallways)-as shown in the picture- and then connecting the floors  with adjacent floors ( or ceilings). Is that the right way ?
Secondly, I am constantly running into problems with the air pump system I am using. I have tried both approaches -DOE coefficient and catalog data- type 966 and 954 respectively, but I cant seem to solve the warnings and errors of the simulation. Some common problems i get are: Error 118  (SAT subroutine was called with a temperature below absolute zero), fail of input convergence, controller (Type 166) sticks for a considerable amount of timesteps. I also experience a very slow simulation even with a timestep of 1 hour. I have tried many things like short timestep, calibrating the heat pumps capacity, increasing the zone's thermal capacitance, using the absolute instead of the relative humidity etc.  but when I manage to erase one problem the other appears.
If anyone has some idea about what might be going wrong in my case I would be reaally grateful, considering the time I have consumed trying to get it right. I attached the .tpf of the simulation for better a understanding of my project. Looking forward for your ideas.

Thanks in advance,

Jim Soukoulis
National Technical University of Athens.

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David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
3 North Pinckney Street - suite 202
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