What I really meant was to add a return path to the VAV system like the CBVAV system.
Right now, the air volume has to be set farely high, if the AHU air temperature is set nearer to the required zone temperture.
With the by pass path, the fan volume can increase without increasing the zone air, as it is already at maximum for that condition which causes the ref set point to rise.
Changing the coil size does not help, becsuse the ref temperature is fixed.
The high added internal at the return air can not flow through the by-pass path and be cooled faster without increasing the zone air flow.
With the bypass, the AHU fan outlet temperature can be set to just below the zone temperature, and thus does not require the reheat.
Setting the fan temperature to 16 to 18°C would also meet the humidity control requirement, and does not require the reheat, if the air volume is allowed to go to a lower limit, using the damper control.
====================
You have shown many set point choices. I do not think many user can follow.
Dr. Li
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: RRaustad@xxxxxxxxxxxx
Date: Fri, 18 Nov 2011 13:37:35 -0500
Subject: Re: [EnergyPlus_Support] Problem with results of a simulation
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Primary EnergyPlus support is found at:
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Right now, the air volume has to be set farely high, if the AHU air temperature is set nearer to the required zone temperture.
With the by pass path, the fan volume can increase without increasing the zone air, as it is already at maximum for that condition which causes the ref set point to rise.
Changing the coil size does not help, becsuse the ref temperature is fixed.
The high added internal at the return air can not flow through the by-pass path and be cooled faster without increasing the zone air flow.
With the bypass, the AHU fan outlet temperature can be set to just below the zone temperature, and thus does not require the reheat.
Setting the fan temperature to 16 to 18°C would also meet the humidity control requirement, and does not require the reheat, if the air volume is allowed to go to a lower limit, using the damper control.
====================
You have shown many set point choices. I do not think many user can follow.
Dr. Li
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: RRaustad@xxxxxxxxxxxx
Date: Fri, 18 Nov 2011 13:37:35 -0500
Subject: Re: [EnergyPlus_Support] Problem with results of a simulation
That would defeat the purpose of the CBVAV system. It's not that the
reference node temperature can't be maintained at some set point,
it's that the zones could over-cool.
If users chose to use a SetpointManager:SingleZone:Cooling and SetpointManager:SingleZone:Heating to control the air loop cooling and heating coil instead of using a constant supply air temperature, at least there would be one zone at the set point. Or if they used a SetpointManager:MultiZone:Heating:Average or SetpointManager:MultiZone:Cooling:Average to control each coil then all zones would be near the thermostat set point temperature (assuming all zones used the same temperature set point). O fcourse some zones would be higher and lower than the set point based on zone load diversity.
On 11/10/2011 5:00 PM, YuanLu Li wrote:
If users chose to use a SetpointManager:SingleZone:Cooling and SetpointManager:SingleZone:Heating to control the air loop cooling and heating coil instead of using a constant supply air temperature, at least there would be one zone at the set point. Or if they used a SetpointManager:MultiZone:Heating:Average or SetpointManager:MultiZone:Cooling:Average to control each coil then all zones would be near the thermostat set point temperature (assuming all zones used the same temperature set point). O fcourse some zones would be higher and lower than the set point based on zone load diversity.
On 11/10/2011 5:00 PM, YuanLu Li wrote:
Richard,
Can you have a look whether you can modify the CBVAV to work with a variable fan. I find that the problem user are having with VAV without reheat is that the variable fan without a bypass of the return air to the OA mixer cannot keep the reference node temperature steady while the fan speed is waiting for the zone damper to move.
Without increase the fan flow volume the return air cannot be cooled to the reference node set point temperature. With the bypass path, the return air can be recycled through the cooling coil and be cooled independent of the zone air flow rate.
=======================
Setting the reference temperature at the zone setpoint temperature would drive all the dampers to fully open. Setting the reference lower, would over cool. Without the reheat, the zone thormstat must be set to zero as minimum. Then the zone temperature will just float to the low set point temperature.&nbYou are seeing the energy required to pull the zone temperature from setback to setup temp. The ideal loads air system provides the energy instantaneously. This is why you see the heating peaks. Increase the setback temperature in heating mode to reduce the peak. In V7, the ideal loads air system will have a maximum cooling/heating capacity input to better model correctly sized systems.
On 11/10/2011 9:34 AM, Ignacio wrote:Hi,
I'm having some strange results from a simulation in Energy+.
The building is composed by 2 zones,each one of 50X15(m)and a height of 5 meters.
//////////////////
/ / /
/ / /
/ 750m2 / 750m2 /
/ / /
/ / /
//////////////////
The results of "Ideal Loads Air Heating Rate" are very high,the peak is almost 750000W for each zone.The peak value occurs at 6:00am when the thermostat change the temperature target.(Almost all the days I have this peak).
The results of "Ideal Loads Air Cooling Rate" are normal, the peak is near 25000W for each zone.
I can send the files if someone needs it to help me.
Thanks
P.S.:The simulation is for Malaga(Spain)
-- Richard A. Raustad Senior Research Engineer Florida Solar Energy Center University of Central Florida 1679 Clearlake Road Cocoa, FL 32922-5703 Phone: (321) 638-1454 Fax: (321) 638-1439 or 1010 Visit our web site at: http://www.fsec.ucf.edu UCF - From Promise to Prominence: Celebrating 40 Years
-- Richard A. Raustad Senior Research Engineer Florida Solar Energy Center University of Central Florida 1679 Clearlake Road Cocoa, FL 32922-5703 Phone: (321) 638-1454 Fax: (321) 638-1439 or 1010 Visit our web site at: http://www.fsec.ucf.edu UCF - From Promise to Prominence: Celebrating 40 Years
__._,_.___
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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