[TRNSYS-users] Capacity of buffer tank

[David BRADLEY]

Dear Zhe,
   Would you mind sending me project? From your explanation, it 
certainly sounds as though everything is correct. I am curious as to 
which component is generating an error saying that the buffer tank is 
too small.
Kind regards,
  David


On 12/4/2012 05:03, Zhe Li wrote:
>
> Dear David,
>
> Thank you very much for your reply.
>
> I did a number of calculations followed by your recommendation in 
> designing the correct size of buffer tank. However, The answer I am 
> getting is far from the size of buffer tank that I am allowed to 
> simulate my model.
>
> The rated flow rate I am using is 1548kg/h and time step is 0.1h. For 
> one time step, the volume is 154.8kg. I would think the buffer tank 
> having a size of 0.2m^3 is sufficient to hold one step volume liquid. 
> However, I always get error when performing the simulation. The 
> minimum size of buffer tank that I have to use is 0.37m^3 in order to 
> carry out the simulation without error occurring.
>
> I have also worked out the total amount liquid is in the loop. I am 
> using a pipe inside diameter is 0.022m, the total length of pipe is 
> 60m, this gives me a total volume water is 22.8kg, I am not sure how 
> this is related to the size of the buffer tank.
>
> Hope you don't mind to explain to me a little more.
>
> Thank you very much.
>
> Zhe Li
>
> *From:*David BRADLEY [mailto:d.bradley at tess-inc.com]
> *Sent:* 03 December 2012 17:56
> *To:* Zhe Li
> *Cc:* trnsys-users at cae.wisc.edu
> *Subject:* Re: Capacity of buffer tank
>
> Dear Zhe,
>   In order for the simulation to be numerically stable, the buffer 
> tank must be large enough to hold at least one time step of liquid. So 
> the answer to your question depends upon the rated flow rate of the 
> pump in the loop and on the time step that you have chosen. In the 
> actual system, there is liquid volume contained in the piping network. 
> I would recommend that you determine how much liquid volume there is 
> (knowing the inside diameter and length of each pipe section), then 
> create a buffer tank of equivalent size and reduce your time step 
> accordingly.
> Kind regards,
>  David
>
> On 11/28/2012 11:07, Zhe Li wrote:
>
>     Dear David,
>
>     Thanks for your time.
>
>     As we discussed before, due to the fact that the current air-water
>      heat pump (Type 941) is a single stage heat pump, a buffer tank
>     is used to prevent overheating when a imposed thermal load is
>     employed. Even though the desired system is not working with a
>     buffer tank, this does solve the original problem I had. However,
>     I have discovered a new problem. What would be the right capacity
>     of this buffer tank to built into in order to simulate the actual
>     system (system without using buffer tank)? I have tried to
>     simulate using varies capacity tank ( from 0.3m^3 to 1m^3 ) as the
>     buffer tank, the electricity consumption can be different as much
>     as 5% which it is significant as far as I am concerned.
>
>     Also, I understand there is an auxiliary heater built into the
>     air-water heat pump component. Would you recommend to use this
>     auxiliary heater or use an external heater built into the circuit
>     where after the buffer tank which makes it more realistic?
>
>     Hope I have explained the problem clearly.
>
>     Thank you very much.
>
>     Zhe Li
>
>
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>
> -- 
> ***************************
> David BRADLEY
> Principal
> Thermal Energy Systems Specialists, LLC
> 22 North Carroll Street - suite 370
> Madison, WI  53703 USA
>   
> P:+1.608.274.2577
> F:+1.608.278.1475
> d.bradley at tess-inc.com  <mailto:d.bradley at tess-inc.com>
>   
> http://www.tess-inc.com
> http://www.trnsys.com
>
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-- 
***************************
David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
22 North Carroll Street - suite 370
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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