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
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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David BRADLEY
Principal
Thermal Energy Systems Specialists, LLC
22 North Carroll Street - suite 370
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d.bradley@tess-inc.com
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