Dear Dr. Li,
I respectfully disagree regarding how commonly a bypass is used in real systems. Other than primary ? secondary piping systems, I almost never have seen a bypass. For primary ? secondary systems (which use a bypass), EnergyPlus uses the ?CommonPipe? for the bypass function.
The use of a bypass in real systems is not the primary issue here, though, so it?s probably not worth going into great detail in the forum, but I would welcome discussion it further privately.
Now that I am thinking about this in more detail, I believe that I had some input from one of the Help Desk wizards that an upcoming release may make bypasses unnecessary (but I am not sure about that and cannot find the message).
Finally, I have a feeling that Vaibhav is using DesignBuilder or something similar. The bypass does not appear accidentally, someone has to put it there! As hinted / mentioned earlier, I think the use of a bypass has been the recommended practice.
James V Dirkes II, PE, BEMP, LEED AP
The Building Performance Team Inc
1631 Acacia Drive, Grand Rapids, MI 49504
616 450 8653
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of YuanLu Li
Sent: Tuesday, August 14, 2012 1:35 PM
To: EnergyPlus_Support
Subject: RE: [EnergyPlus_Support] What ByPass component means?
"A bypass is an EnergyPlus idiosyncrasy that helps E+ balance mass flows in a loop."
I disagree. I bypass path is in most real water systems.
Air can be compressed and a fan will not fully blocking the flow. Therefore, a bypass is not generally provided.
A variable balanced flow system cannot be implemented without some dedicated controller or computer control. For safety and other reasons, bypass are still provided in a real system.
For your SVG diagram, the constant speed pupmp has a constrant flow rate. The zone demand is addusted by varying the flow rate. The excess flow must go somewhere. Therefore, a by-pass path is provided. If there is only one branch in the loop, the system can use the on/off mode to control the supply capacity, because there is no other demand in the loop.
For the supply side by-pass, I visualize it as the link to the heating or cooling source. When the pump is off, the water can still be maintained at the set point temperature by cycling the source.
For a coal furnace, it cannot be shut off quickly. The pump is usuallby fitted with a bypass so that the demand is not completely disconnected. The furnace air intake is reduced, and the file will then be slowly extinguished.
The tower has a by-pass, because it also have a setpoint temperature to meet, even when the condenser loop pump is turned off from the demand side.
"By-pass" is not a redudent element for EPlus simulation purose only. It is also a reminder that they are in a real system.
Dr. Li
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx
Date: Tue, 14 Aug 2012 09:36:54 -0500
Subject: RE: [EnergyPlus_Support] What ByPass component means?
Vaibhav,
A bypass is an EnergyPlus idiosyncrasy that helps E+ balance mass flows in a loop. They are not always needed, but also, they don?t get used or affect results in a balanced loop. I think of them as a way to avoid certain problems in the simulation while I am solving other problems. I review the flows in the bypass after a simulation, and if there is flow when I don?t expect it, I investigate to determine its cause.
James V Dirkes II, PE, BEMP, LEED AP
The Building Performance Team Inc
1631 Acacia Drive, Grand Rapids, MI 49504
616 450 8653
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Vaibhav Jain
Sent: Tuesday, August 14, 2012 10:08 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] What ByPass component means?
Hello Group!
As I am not a mechanical engineer that's why I am curious to know - what does ByPass component means, which I see in both demand and supply side, and what is its function in real world systems, if any? I am attaching a picture (in line with text) to explain what exactly I mean. I somehow couldn't understand it very intuitively from documentation. Thank you!
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