[TRNSYS-users] Air-Water Heat Pump (Type 941) doesn't converge
David BRADLEY
d.bradley at tess-inc.com
Wed Jul 8 06:27:20 PDT 2020
Adrian,
When a simulation doesn't converge it just keeps the values that it
calculated for the outputs of its most recent iteration and goes on to
the next timestep. You are very likely to see outputs that don't match
each other (a controller might calculate an "off" output while the heat
pump might have last calculated its "on" state). The mathematics of the
models are not likely the problem.
Make sure that you are using a small time step (1-3 minutes) and that
you have thermal capacitance in all of your flow loops.
kind regards,
David
On 07/07/2020 18:15, Adrian Riebel Brummer via TRNSYS-users wrote:
>
> Hello Jeff,
>
> thanks very much for your answer. Maybe I didn't explain myself very well.
>
> The waterflow of the heat pump is zero because the pump which controls
> the flow is turned off. The control signals of the heat pump (heating
> and cooling control signals) are zero too, so the heat pump should be
> turned off and nothing should happen. The problem is, the outlet
> temperature of the heat pump is unstable. I think the reason is that
> the heat pump is not completely turned off and is trying to solve this
> equation:
>
> image.png
>
> Obviously the equation can't be solved because m_dot_liq is zero, but
> the heat pump shouldn't be trying to solve it either.
>
> As I said before, the documentation says something about a "Fan
> Control Signal" which should be set to zero, in order that the heat
> pump doesn't make any calculations. The problem is, I can't find that
> input when I look for it in the Simulation Studio.
>
> I hope that I managed to explain myself well (English is not my native
> language). I would be very grateful if you can tell me if I'm wrong or
> what should I do.
>
> Thanks very much,
>
> Adrian Riebel
>
>
>
>
>
>
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>
>
> El mar., 7 jul. 2020 a las 13:40, Jeff Thornton via TRNSYS-users
> (<trnsys-users at lists.onebuilding.org
> <mailto:trnsys-users at lists.onebuilding.org>>) escribió:
>
> Adrian,
>
> Any flow convergence issues you are having is likely due to
> something beyond the AWHP. This type does not set the water flow
> rate - it simply passes it through the device; heating or cooling
> it of the device is on or simply just passing it through if the
> device is off. Pumps are the devices in TRNSYS that typically set
> the flow rates for your loops. I would suggest you use the TRACE
> feature and watch to see what is happening when you are getting
> convergence issues.
>
> Jeff
>
> ---
> Jeff Thornton
> President - TESS LLC
> 3 N. Pinckney Street, Suite 202, Madison WI USA 53703
> Office: (608) 274-2577 Fax: (608) 278-1475
> www.tess-inc.com <http://www.tess-inc.com>
> E-Mail:thornton at tess-inc.com <mailto:thornton at tess-inc.com>
>
> On 07/05/2020 7:36 pm, Adrian Riebel Brummer via TRNSYS-users wrote:
>
>> Dear TRNSYS users,
>> I have a problem with Type 941 (Air-Water Heat Pump). My problem
>> is that the simulation doesn't converge when the waterflow in the
>> heat pump is zero, despite the heat pump is also in off mode
>> (heating and cooling control signals are both set to zero).
>> I have read the mathematical reference of this Type and it says
>> something about a "Fan control signal", which functions, as I
>> understand, as the master on-off switch of the heat pump. The
>> problem is that I can't find that Input in the TRNSYS programm.
>> I would like to know why I can't find that Input, and why the
>> model doesn't converge despite the heat pump shouldn't be doing
>> anything.
>> I send you a picture of all the inputs that I can see for this
>> Type. I have TRNSYS18 and TessLibs17.
>> Regards,
>> Adrian Riebel
>> image.png
>>
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>>
>>
>>
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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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