[TRNSYS-users] Flow of water thru Type927 when it is off

[Jeff Thornton]

For reference, our default time step when running heat pump simulations is usually in the 1-5 minute range.  Large time steps (>15 minutes) often cause unrealistic results and very often lead to non-convergence issues.  Try running your simulation at a smaller time step and see if you get different results - if not then the larger time step can be used.

Jeff



On Jan 8, 2013, at 6:41 AM, Richard Thygesen <richard.thygesen at mdh.se> wrote:

> Thank you for your reply. I added some volume to my buffer tank and that helped with the convergence problem.
>  
> Best regards
> Richard Thygesen
>  
> Från: Amdi Worm [mailto:amdiworm at gmail.com] 
> Skickat: den 8 januari 2013 11:00
> Till: Richard Thygesen
> Kopia: TRNSYS-users at engr.wisc.edu
> Ämne: Re: [TRNSYS-users] Flow of water thru Type927 when it is off
>  
> HI.
>  
> Yes it is indeed possible. I have attached a screen dump of a system I have made where the pump is running between the storagetank and the heatpump (927) and is running constantly. My heatpump is controlled by the temperature in the returning fluid from the tank to the heatpump ( as it is done in many cases in real-life). The heat demand is simulated in another program and imported by type 9a. 
>  
> I dont know your system, but the convergens problems could be caused by large timesteps compared to the inertia of your system ( often a buffertank / pipe system that is not capable of "consumeing" the energy produced i one time step). My heatpump has a rated performance at 8kW ( 0/35 ) and a buffer tank with a capacity of 200 liters + 20 meters of pipeing. I am running my simulation at 0.5h pr timestep.
>  
> I hope this is a help for you.
> Best regards.
> Amdi Worm
>  
> Esbensen Consulting Engineers
> Aarhus, Denmark
>          
>  
> 2013/1/8 Richard Thygesen <richard.thygesen at mdh.se>
> Hi.
>  
> Is it possible to have  water flow thru type 927 when the heat pump is off? In real heat pumps the circulation pump is on constantly to provide heat to the heating system above an outdoor set point temperature for example 17°C (62.6 °F).
> When I control the circulation pump to only be on during heat pump operation it works perfectly but when I set it to work constantly above a certain outdoor temperature I get convergence errors.
>  
> Any suggestions on how to solve this?
>  
> Best regards
> Richard Thygesen
>  
> 
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