A pipe filled with water is called by different names in EPlus. Pipe adibatic, pipe by-pass, radiator, raianant, coil, etc.
When you place two pumps at its two ends, the flow rate must be equal. Otherwise, the pipe would burst by pressure or crushed by vacuum. Therefore, one pump must have a by-pass.
If the system is a loop, there is no reason to use two pumps in cascade. The branch pump iacts as an actuator or control valve to control the flow. If a branch requires more water, the pipe size is adjusted rather than adding a pump. This branch pump is usually one with much smaller capacity than the main pump. By making the main pump variable speed, the by-pass branch is not needed in the simulation, but is not "not possible" to be included.
The by-pass pipe is not a short circuit equivalent of an electric circuit. It is actually a pressure valve.
Almost every real pupmp has a by-pass pipe installed for variaous puprposes. When a by-bass is not necessaruy in the EPlus simulation, when a variable speed pump is used, does not mean that any installation using a variable speed pump must not have by-pass. In fact, the safety valves and releive valves are alss still there.
Eplus user should not read different parts of the manuals and make up new rules.
What is the purpose of a pump? Why do you have two pumps one after the other, on a single pipe?
Are you using the pump as a flow control element in the simulation and do not have a real one in an installation? How are you conrolling the variable speed pump? If you ask yourself these questions, some of the questions raised in this forum are not valid.
The problem "Solution to constant branch pumps, when bypass is not possible," shoud not arise. By-pass is always possible, depends on how you use it or install it.
Dr. Li
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: brent.griffith@xxxxxxxx
Date: Mon, 18 Jun 2012 14:08:09 -0600
Subject: RE: [EnergyPlus_Support] Solution to constant branch pumps, when bypass is not possible
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Primary EnergyPlus support is found at:
http://energyplus.helpserve.com or send a message to energyplus-support@xxxxxxxx
The primary EnergyPlus web site is found at:
http://www.energyplus.gov
The group web site is:
http://groups.yahoo.com/group/EnergyPlus_Support/
Attachments are currently allowed but be mindful that not everyone has a high speed connection. Limit attachments to small files.
EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.
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When you place two pumps at its two ends, the flow rate must be equal. Otherwise, the pipe would burst by pressure or crushed by vacuum. Therefore, one pump must have a by-pass.
If the system is a loop, there is no reason to use two pumps in cascade. The branch pump iacts as an actuator or control valve to control the flow. If a branch requires more water, the pipe size is adjusted rather than adding a pump. This branch pump is usually one with much smaller capacity than the main pump. By making the main pump variable speed, the by-pass branch is not needed in the simulation, but is not "not possible" to be included.
The by-pass pipe is not a short circuit equivalent of an electric circuit. It is actually a pressure valve.
Almost every real pupmp has a by-pass pipe installed for variaous puprposes. When a by-bass is not necessaruy in the EPlus simulation, when a variable speed pump is used, does not mean that any installation using a variable speed pump must not have by-pass. In fact, the safety valves and releive valves are alss still there.
Eplus user should not read different parts of the manuals and make up new rules.
What is the purpose of a pump? Why do you have two pumps one after the other, on a single pipe?
Are you using the pump as a flow control element in the simulation and do not have a real one in an installation? How are you conrolling the variable speed pump? If you ask yourself these questions, some of the questions raised in this forum are not valid.
The problem "Solution to constant branch pumps, when bypass is not possible," shoud not arise. By-pass is always possible, depends on how you use it or install it.
Dr. Li
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: brent.griffith@xxxxxxxx
Date: Mon, 18 Jun 2012 14:08:09 -0600
Subject: RE: [EnergyPlus_Support] Solution to constant branch pumps, when bypass is not possible
Yes, this variable speed approach is a good solution.
The plant routines inside EnergyPlus have recently been completely reworked and now it is very likely that branch pumps on demand side are fully supported. (The same general solver is now used for both the demand side and supply side.) This and other expanded flexibility is not yet claimed in the documentation because more detailed testing is needed. As long as you are careful and check the results, it should be okay to push the model in this way.
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of ecoeficientees
Sent: Sunday, June 17, 2012 4:02 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] Solution to constant branch pumps, when bypass is not possible
I am using a configuration for branch pumps when in the real HVAC system they are constant flow pumps with bypass (through three-way valves).
I use variable speed pumps, setting the curve performance coefficients (1,0,0,0), so power consumption is constant although it can deliver variable flow.
I think it is a good solution to account for a constant pump with bypass, since it provides variable flow but constant power. It is the only way I have found to account for constant pumps as branch pumps, since bypass is not possible.
Do you see it right?
It seems to work ok even with branch pumps in demand side, which should not work according to E+ Reference but Energyplus is not complaining.
That's my second doubt, are branch pumps in demand side correct? As I've said, E+ seems to simulate them right, but Engineering Reference says that pumps in demand side can only be used in the first branch. Why is not Energyplus launching an error, then?
Regards,
Germán Campos.
I use variable speed pumps, setting the curve performance coefficients (1,0,0,0), so power consumption is constant although it can deliver variable flow.
I think it is a good solution to account for a constant pump with bypass, since it provides variable flow but constant power. It is the only way I have found to account for constant pumps as branch pumps, since bypass is not possible.
Do you see it right?
It seems to work ok even with branch pumps in demand side, which should not work according to E+ Reference but Energyplus is not complaining.
That's my second doubt, are branch pumps in demand side correct? As I've said, E+ seems to simulate them right, but Engineering Reference says that pumps in demand side can only be used in the first branch. Why is not Energyplus launching an error, then?
Regards,
Germán Campos.
__._,_.___
Primary EnergyPlus support is found at:
http://energyplus.helpserve.com or send a message to energyplus-support@xxxxxxxx
The primary EnergyPlus web site is found at:
http://www.energyplus.gov
The group web site is:
http://groups.yahoo.com/group/EnergyPlus_Support/
Attachments are currently allowed but be mindful that not everyone has a high speed connection. Limit attachments to small files.
EnergyPlus Documentation is searchable. Open EPlusMainMenu.pdf under the Documentation link and press the "search" button.
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