Hi, qutianfei
What ever your name meant. Flying in the Autumn sky?
I do not understand why you have an OAU, an AHU and an exhaust fan in the same zone. You can split the office into zones, so that the air can be better distributed and controlled even if you do not have physical partition walls. (open office concept.)
You may have heard me saying VAV and reheat is not commonly used, and it is not new. What I really meant is referring to people using VAV rehet per room.
I have used VAV at the AHU main duct so that the East and West zone would get different amount of cooling supply during the morning and afternoon hours. (stepper motor controlled dampers, a timer and a couple of theremostat switches.)
We (the University engineering team) design the system to fit the different requirement of the building demand, with minimum capital and
running cost. In tropical countries, the insulation requiements are not the same as the ASHRAE standard.
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If your AHU feeds many diffusers, and the return air is normally via the false ceiling space, you should model the ceiling space as a plenum mixer for the air loop. You can channel lighting heat to the plenum and get better cooling efficiency.
If the AHU is the main cooling and heating source, then the thermostat of the zone should be assigned to this system.
The exhaust fan is not required, unless it is for the toilet or printing room, etc. It that case, they should have a separate zone defined and use zone mixing to control the air flow.
If the OAU is for providing the so called 100% fresh air, it can be part of the air loop, unless the quantity is so high that the flow must be separately heated or cooled. If the AHU air is
ducted for distribution, the fresh air can be conditioned by the same sets of coils.
The zone thermostat can be used for either system, because you only have one zone.
I.e., one system, OAU or AHU has the use of the thermostat control. The other system can be uncontrolled or setpoint controlled. The outlet temperature will not follow the zone temperature value. This type of OAU is usually referred to as DOAS, which is not commonly used to feed a zone.
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I have no hands on experience in running the absorption chiller. I assume it behave the same way as a heat pump, with the compressor replace by the heat source.
In that case, the component may need to be repeated in the separate cooling and heating plant loopss with the heating and cooling side properly connected.
When it is used as a chiller, the other hot side is connected to the
condenser loop.
When used as a heater, the other cold side is the environment or auxiliary heat source.
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When you use the Controller:MixedAir there are two setpoints for cooling and one for heating, and one reference node. Two system would need six setpoint nodes. and two reference nodes.
These will not be required, if you use the AHU to feed the fresh air and save one fan.
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I have already mentioned the branch ordering in the plant loops.
The absorption chiller is the on the supply side of the CW loop, the hot end is the demand side of the condenser loop, which is connected to the tower.
When it is used as a heating source, the hot end is the source of the HW loop, the cold end is to be exposed to a warm environment.
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The above covers all those errors mentioned in the error
file.
Because the file has been sorted, the branches are listed according to the object ty pe and ot by the system group. This is not so easy to sort out.
That is why I asked you whether you used the template in DesignBuilder. If you did, export the IDF without sorting if possible. It will then be easier to correct. In fact, if the chiller is entered in two places, all the branches will be in correct order.
The zone setpoint problem can be solved by moving the OA mixer to the AHU and delete the OAU. 100% fresh air can be injected with a Ventilation object with a schedule to control the quantity required.
Dr. Li
To: EnergyPlus_Support@xxxxxxxxxxxxxxx; yli006@xxxxxxxxxxx
CC: leebye2008@xxxxxxxxx
From: leebye2008@xxxxxxxxx
Date: Tue, 16 Aug 2011 19:53:58 -0700
Subject: [EnergyPlus_Support] an idf model question
Dr.Li,
I am working with a two floor office building, but always cannot pass the simulation compiling. Together with some of my understanding of EP, I attached this model dxf scheme file and idf file to this mail. It's really great help to get some right knowledge on EP. Hope that you could spent a few minutes on my problem. Thank you very much.
qutianfei