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Error Hard Sizing DX Cooling Coils

asked 2014-12-12 17:34:35 -0500

jdunn gravatar image

updated 2015-07-27 11:56:20 -0500

Simulation community -

So I'm in the proposed modeling phase of LEED energy simulation, and I'm having some problems hard sizing some cooling coils for some split dx heat pump units serving technology closets. See error below, it looks like I'm inputting what I think is the total cooling capacity, but its calculating something else for the "Design Size Gross Rated Total Cooling Capacity."

*** SizeDXCoil: Potential issue with equipment sizing for Coil:Cooling:DX:SingleSpeed DX-1 SYSTEM COOLING COIL * ~~~ * User-Specified Gross Rated Total Cooling Capacity [W] = 5274.00000 * ~~~ * differs from Design Size Gross Rated Total Cooling Capacity [W] = 3590.75955 * ~~~ * This may, or may not, indicate mismatched component sizes.

So I must be missing an input, but since I'm just using the template objects so I think its pretty straightforward: - HVACTemplate:System:UnitaryHeatPump:AirToAir - HVACTemplate:Zone:Unitary

I'm inputting a hard value for the Supply Air Maximum Flow Rate in the zone object, and I'm inputting a hard value for the "cooling supply air flow rate" and "Cooling Coil Capacity" fields in the system object. Upon checking out the coil:cooling:water object in the expanded .idf, it looks like everything is hardsized properly. Not sure what's going on here, but the slight reduction in capacity is causing unmet hours in the proposed case.

Here are the text objects in case anyone is interested:


 DX-1,                  !Zone Name 
 DX-1 system,           !Template Unitary System Name  
carver_admin_tstat,     !Template Thermostat Name  
0.22,                   !Supply Air Maximum Flow Rate {m3/s} 
,                       !Zone Heating Sizing Factor  
,                       !Zone Cooling Sizing Factor  
sum,                    !Outdoor Air Method  
,                       !Outdoor Air Flow Rate per Person {m3/s}  
0.0006096,              !Outdoor Air Flow Rate per Zone Floor Area {m3/s-m2}  
,                       !Outdoor Air Flow Rate per Zone {m3/s}  
,                       !Supply Plenum Name  
,                       !Return Plenum Name  
,                       !Baseboard Heating Type  
,                       !Baseboard Heating Availability Schedule Name  
,                       !Baseboard Heating Capacity {W} 
TEMPERATUREDIFFERENCE,  !Zone Cooling Design Supply Air Temperature Input Method  
,                       !Zone Cooling Design Supply Air Temperature {C} 
11.31,                  !Zone Cooling Design Supply Air Temperature Difference {deltaC} 
TEMPERATUREDIFFERENCE,  !Zone Heating Design Supply Air Temperature Input Method  
,                       !Zone Heating Design Supply Air Temperature {C} 
11.31;                  !Zone Heating Design Supply Air Temperature Difference {deltaC}


 DX-1 system,           !Name 
admin_outside_air_schedule_compact, !System Availability Schedule Name  
 DX-1,                  !Control Zone or Thermostat Location Name  
0.22,                   !Cooling Supply Air Flow Rate {m3/s} 
0.22,                   !Heating Supply Air Flow Rate {m3/s} 
0,                      !No Load Supply Air Flow Rate {m3/s} 
admin_outside_air_schedule_compact, !Supply Fan Operating Mode Schedule Name  
blowthrough,            !Supply Fan Placement  
0.7,                    !Supply Fan Total Efficiency  
117.0829616414,         !Supply Fan Delta Pressure {Pa} 
0.99,                   !Supply Fan Motor Efficiency  
1,                      !Supply Fan Motor in Air Stream Fraction  
singlespeeddx,          !Cooling Coil Type  
,                       !Cooling Coil Availability Schedule Name  
12.8,                   !Cooling Design Supply Air Temperature {C} 
5274,                   !Cooling Coil Capacity {W} 
autosize,               !Cooling Coil Rated Sensible Heat Ratio  
3.48,                   !Cooling Coil Rated COP  
Singlespeeddxheatpump,  !Heat Pump Heating Coil Type  
,                       !Heat Pump Heating Coil Availability Schedule Name  
50,                     !Heating Design ...
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answered 2014-12-13 12:31:48 -0500

Archmage gravatar image

It isn't clear that there is an error here. The program will run with the larger "User-Specified" capacity. The "Design Size" is what it would have used if you had not hard sized the capacity. It is just here for information. If the design size was larger, then that would be more important.

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Thanks for the information!

jdunn gravatar imagejdunn ( 2014-12-15 12:57:43 -0500 )edit

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Asked: 2014-12-12 17:34:35 -0500

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Last updated: Dec 13 '14