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 0.2m3 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 0.37m3 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@tess-inc.com]
Sent: 03 December 2012 17:56
To: Zhe Li
Cc: trnsys-users@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 0.3m3 to 1m3) 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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