Two identical models, only difference is the SizingPeriod:DesignDay objects for heating design day, "Maximum Dry-Bulb Temperature" and "Wetbulb or DewPoint at Maximum DryBulb." In one model I've hard-inputted these cooling sizing temperatures to be about 3degC higher. 4degC higher to approximate a 2050 climate scenario.
In the model with higher dry- and wet-bulb temperatures for my cooling design days, the HVACTemplate:Zone:PTAC cooling coils autosized to LOWER capacities by about 4%. That is, the autosized "Cooling Coil Gross Rated Total Capacity {W}."
This certainly goes against intuition... does the model take into account other factors when autosizing PTAC cooling coils? What am I missing?
Model 1 cooling design day:
SizingPeriod:DesignDay,
Boston Logan IntL Arpt Ann Clg .4% Condns DB=>MWB, !- Name
7, !- Month
21, !- Day of Month
SummerDesignDay, !- Day Type
32.7, !- Maximum Dry-Bulb Temperature {C}
8.4, !- Daily Dry-Bulb Temperature Range {deltaC}
, !- Dry-Bulb Temperature Range Modifier Type
, !- Dry-Bulb Temperature Range Modifier Day Schedule Name
Wetbulb, !- Humidity Condition Type
22.9, !- Wetbulb or DewPoint at Maximum Dry-Bulb {C}
, !- Humidity Condition Day Schedule Name
, !- Humidity Ratio at Maximum Dry-Bulb {kgWater/kgDryAir}
, !- Enthalpy at Maximum Dry-Bulb {J/kg}
, !- Daily Wet-Bulb Temperature Range {deltaC}
101253, !- Barometric Pressure {Pa}
6.3, !- Wind Speed {m/s}
270, !- Wind Direction {deg}
No, !- Rain Indicator
No, !- Snow Indicator
No, !- Daylight Saving Time Indicator
ASHRAEClearSky, !- Solar Model Indicator
, !- Beam Solar Day Schedule Name
, !- Diffuse Solar Day Schedule Name
, !- ASHRAE Clear Sky Optical Depth for Beam Irradiance (taub) {dimensionless}
, !- ASHRAE Clear Sky Optical Depth for Diffuse Irradiance (taud) {dimensionless}
1; !- Sky Clearness
Model 2 cooling design day:
SizingPeriod:DesignDay,
Boston Logan IntL Arpt Ann Clg .4% Condns DB=>MWB, !- Name
7, !- Month
21, !- Day of Month
SummerDesignDay, !- Day Type
36.63, !- Maximum Dry-Bulb Temperature {C}
8.4, !- Daily Dry-Bulb Temperature Range {deltaC}
, !- Dry-Bulb Temperature Range Modifier Type
, !- Dry-Bulb Temperature Range Modifier Day Schedule Name
Wetbulb, !- Humidity Condition Type
26.12, !- Wetbulb or DewPoint at Maximum Dry-Bulb {C}
, !- Humidity Condition Day Schedule Name
, !- Humidity Ratio at Maximum Dry-Bulb {kgWater/kgDryAir}
, !- Enthalpy at Maximum Dry-Bulb {J/kg}
, !- Daily Wet-Bulb Temperature Range {deltaC}
101253, !- Barometric Pressure {Pa}
6.3, !- Wind Speed {m/s}
270, !- Wind Direction {deg}
No, !- Rain Indicator
No, !- Snow Indicator
No, !- Daylight Saving Time Indicator
ASHRAEClearSky, !- Solar Model Indicator
, !- Beam Solar Day Schedule Name
, !- Diffuse Solar Day Schedule Name
, !- ASHRAE Clear Sky Optical Depth for Beam Irradiance (taub) {dimensionless}
, !- ASHRAE Clear Sky Optical Depth for Diffuse Irradiance (taud) {dimensionless}
1; !- Sky Clearness
Both models are set for system sizing:
SimulationControl,
Yes, !- Do Zone Sizing Calculation
Yes, !- Do System Sizing Calculation
Yes, !- Do Plant Sizing Calculation
Yes, !- Run Simulation for Sizing Periods
Yes, !- Run Simulation for Weather File Run Periods
Yes; !- Do HVAC Sizing Simulation for Sizing Periods
Thanks all!
