If you are using VAV with setpoint temperature control, you may need a return air bypass to increase the capacity. (from the fan output back to the OA return air input as in he CBVAV)
The added coil capacity can then be used to cool the return air without feeding it through the zone.
The capacity is partly determined by the difference between the sref. node set point and the zone thermostat values, when the damper is fully open. Fan speed has reached the maximum and cannot increase at this point, to provide more capacity.
Dr. Li
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx
Date: Tue, 15 Nov 2011 07:48:53 -0500
Subject: RE: [EnergyPlus_Support] increased sizing:parameter gives more hours not met - DX cooling
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The added coil capacity can then be used to cool the return air without feeding it through the zone.
The capacity is partly determined by the difference between the sref. node set point and the zone thermostat values, when the damper is fully open. Fan speed has reached the maximum and cannot increase at this point, to provide more capacity.
Dr. Li
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
From: jim@xxxxxxxxxxxxxxxxxxxxxxxxxxx
Date: Tue, 15 Nov 2011 07:48:53 -0500
Subject: RE: [EnergyPlus_Support] increased sizing:parameter gives more hours not met - DX cooling
Have you reviewed the output variables for both cases to see where they are different?
p.s., the typical coil curves should not affect you. They normally vary capacity only a few percent over the range of normal operation.
The Building Performance Team
James V. Dirkes II, P.E., BEMP , LEED AP
1631 Acacia Drive NW
Grand Rapids, MI 49504
616 450 8653
From: EnergyPlus_Support@xxxxxxxxxxxxxxx [mailto:EnergyPlus_Support@xxxxxxxxxxxxxxx] On Behalf Of Jean marais
Sent: Tuesday, November 15, 2011 6:51 AM
To: EnergyPlus_Support@xxxxxxxxxxxxxxx
Subject: [EnergyPlus_Support] increased sizing:parameter gives more hours not met - DX cooling
Dear Group,
Normally, upping the sizing factor should decrease unmet loads. I'm experiencing the OPPOSITE effect. I'm wondering if the curves describing the DX performance are mucking me about. They are default curves from design builder. Should I be adjusting these for a ASHRAE baseline case model?
Coil:Cooling:DX:SingleSpeed,
118451 AHU Cooling Coil, !- Name
SchCpct_LowTempClgOFF, !- Availability Schedule Name
autosize, !- Rated Total Cooling Capacity {W}
autosize, !- Rated Sensible Heat Ratio
3.81, !- Rated COP
autosize, !- Rated Air Flow Rate {m3/s}
, !- Rated Evaporator Fan Power Per Volume Flow Rate {W/(m3/s)}
118451 AHU Gas Heating Coil Outlet, !- Air Inlet Node Name
118451 Unitary Unit Outlet, !- Air Outlet Node Name
118451 AHU DX Coil Cap-FT, !- Total Cooling Capacity Function of Temperature Curve Name
118451 AHU DX Coil Cap-FF, !- Total Cooling Capacity Function of Flow Fraction Curve Name
118451 AHU DX Coil EIR-FT, !- Energy Input Ratio Function of Temperature Curve Name
118451 AHU DX Coil EIR-FF, !- Energy Input Ratio Function of Flow Fraction Curve Name
118451 AHU DX Coil PLF, !- Part Load Fraction Correlation Curve Name
0, !- Nominal Time for Condensate Removal to Begin {s}
0, !- Ratio of Initial Moisture Evaporation Rate an
Normally, upping the sizing factor should decrease unmet loads. I'm experiencing the OPPOSITE effect. I'm wondering if the curves describing the DX performance are mucking me about. They are default curves from design builder. Should I be adjusting these for a ASHRAE baseline case model?
Coil:Cooling:DX:SingleSpeed,
118451 AHU Cooling Coil, !- Name
SchCpct_LowTempClgOFF, !- Availability Schedule Name
autosize, !- Rated Total Cooling Capacity {W}
autosize, !- Rated Sensible Heat Ratio
3.81, !- Rated COP
autosize, !- Rated Air Flow Rate {m3/s}
, !- Rated Evaporator Fan Power Per Volume Flow Rate {W/(m3/s)}
118451 AHU Gas Heating Coil Outlet, !- Air Inlet Node Name
118451 Unitary Unit Outlet, !- Air Outlet Node Name
118451 AHU DX Coil Cap-FT, !- Total Cooling Capacity Function of Temperature Curve Name
118451 AHU DX Coil Cap-FF, !- Total Cooling Capacity Function of Flow Fraction Curve Name
118451 AHU DX Coil EIR-FT, !- Energy Input Ratio Function of Temperature Curve Name
118451 AHU DX Coil EIR-FF, !- Energy Input Ratio Function of Flow Fraction Curve Name
118451 AHU DX Coil PLF, !- Part Load Fraction Correlation Curve Name
0, !- Nominal Time for Condensate Removal to Begin {s}
0, !- Ratio of Initial Moisture Evaporation Rate an
__._,_.___
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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