uwg: documentation | urban microclimate

Urban Weather Generator

urban heat island effect modeling software

Model Parameter Documentation

Refer to this page for tips on how to customize your xml input file.


A note on the beta version

Please note that this beta version still requires users to input albedo and emissivity values in the template library before running the simulation. Thank you for trying it out!


construction

The building construction materials for wall, roof, and internal mass as well as urban road and rural site [these are in the advanced setting section] are defined by same parameter inputs in the <construction> tag. Glazing is also in this section.

Assembly

albedo

key design parameter: consider using green roof. A significant parameter determined by the sensitivity analysis [Boston], in conjunction with emissivity

definition Also known as reflection coefficient. It is the ratio of reflected radiation from the surface to incident radiation upon it. Affects sensible heat flux into boundary layer

unit [--]; ranges between 0 and 1

typical values concrete 0.1 [2], brick 0.2 [2], soil 0.05 [2], cool roof 0.55 [California Title 24] [3]

emissivity

key design parameter: consider using green roof. A significant parameter determined by the sensitivity analysis [Boston], in conjunction with emissivity

definition Relative ability of the surface to emit energy by radiation. It is the fraction of energy radiated by a particular material compared to a black body. Affects sensible heat flux into boundary layer. Note: Visual surface color is not significant to total emissivity [surface color affects spectral emissivity at visible wavelength, which is negligible]

unit [--]; ranges between 0 and 1

typical values concrete 0.71 [2], brick 0.9 [2], soil 0.98 [2], cool roof 0.75 [California Title 24] [3], for reference, polished silver 0.02

names

definition list construction layers; outer layers first

unit [--]

typical values see [1] for typical U.S. constructions

thermal conductivity [thermalConductivity]

definition intrinsic property of the material to conduct heat

unit W/m-K

typical values see [1] for typical U.S. constructions

volumetric heat capacity [volumetricHeatCapacity]

definition Also known as thermal mass. ability of a given volume of a substance to store internal energy while undergoing a given temperature change, but without undergoing a phase transition. It is density * specific heat

unit J/m3-K

typical values see [1] for typical U.S. constructions

thickness

definition

unit [--]; ranges between 0 and 1

typical values see [1] for typical U.S. constructions

							
  1. <materials>
  2. <names>
  3. <item>brick</item>
  4. <item>insulation</item>
  5. </names>
  6. <thermalConductivity>
  7. <item>1.15</item>
  8. <item>0.03</item>
  9. </thermalConductivity>
  10. <volumetricHeatCapacity>
  11. <item>1580000</item>
  12. <item>52000</item>
  13. </volumetricHeatCapacity>
  14. <thickness>[0.30,0.03]</thickness>
  15. </materials>
vegetation coverage [vegetationCoverage]

definition The amount of vegetation on surfaces, such as green roof, grassy lawn, and vine-covered wall.

unit [--]; ranges between 0 and 1

typical values green roof 1, concrete wall 0

inclination

definition Orientation of the element. 0o = vertical [i.e. wall] and 1o = horizontal [i.e. roof].

unit [--]; ranges between 0 and 1

typical values wall 0, roof 1, sloped roof 0.5

initial temperature [initialTemperature] advanced setting

definition The initial temperature of a model element at the start of the simulation. Since the UWG does not "warm up" as EnergyPlus would, this value is a user input

unit oC

typical values 20oC


Glazing

window to wall ratio [glazingRatio]

definition ratio of glazed area to total facade surface

unit [--]; ranges between 0 and 1

typical values 0.2 - 0.4

total U-value [windowUvalue]

definition thermal transmittance of windows, equal to 1/R-value. Good insulators have lower U-values

unit W/m2K

typical values single glazing with frames 4.5W/m2K, double glazed 3.3W/m2K, double glazed with low-e coating and frames 2.2W/m2K, triple glazing with low-e coating and frames 0.8W/m2K

total solar heat gain coefficient [SHGC] [windowSHGC]

definition fraction of incident total solar radiation that reaches the interior

unit [--]; ranges between 0 and 1

typical values single glazing [clear glass 6mm] 0.81, double glazing [clear glass 6mm, low-e Ar, 13mm clear glass] 0.57, double glazing with low-e spectrally selective Ar [13mm clear glass, Ar, 13mm clear glass] 0.42, triple glazing with low-e selective Ar [13mm clear glass, Ar, 13mm, low-e, 13mm clear glass] 0.47


building

daytime internal gain [dayInternalGains]

definition Typical total daytime internal heat gains per hour, including heat gains from people, lights, and equipment

unit W/m2

typical values 4 - 25W/m2

nighttime internal gain [nightInternalGains]

definition Typical total nighttime internal heat gains per hour, including heat gains from people, lights, and equipment

unit W/m2

typical values 4 - 7W/m2

infiltration

definition typical building infiltration

unit ACH [air changes per hour]

typical values 0.25 - 0.5 ACH

ventilation

definition typical building ventilation rate

unit ACH [air changes per hour]

typical values 0 - 0.65 ACH

floor height [floorHeight] advanced setting

definition Typical floor-to-floor height within the urban area

unit m

typical values 3m

radiant fraction of internal heat gains [radiantFraction] advanced setting

definition average of radiant fraction of the total building internal gains including people, light, and equipment, weighted by hourly internal load from each component. Internal gain can be split into sensible [radiant [mostly] and convective] and latent heat

unit [--]; ranges between 0 and 1

typical values 0.2 - 0.5. Individually people 0.3, lights 0.7, equipments 0.5 [1]

latent fraction of internal heat gains [latentFraction] advanced setting

definition average of latent fraction of the total building internal gains including people, light, and equipment, weighted by hourly internal load from each component. Internal gain can be split into sensible [radiant [mostly] and convective] and latent heat

unit [--]; ranges between 0 and 1

typical values 0.1 - 0.2. Individually people 0.3, lights 0, equipment 0 [1]

cooling system type [coolingSystemType] advanced setting

definition mechanical cooling system in the urban area. UWG can simulate air or water system

unit n/a

typical values 'air' or 'water'

cooling system COP [coolingCOP] advanced setting

definition mechanical cooling system coefficient of performance, described by the ratio of the heat removed from the typical building over the energy used by the cooling system

unit [--]

typical values 2.5 - 3.67[1]

cooling capacity of cooling system [coolingCapacity] advanced setting

definition cooling system's ability to remove heat

unit W/m2

typical values 3.67 [1]

efficiency of heating system [heatingEfficiency] advanced setting

definition effectiveness of a system in transforming the energy and power that is input to the device into an output. Efficiency is measured as a ratio of the measured performance to the performance of an ideal system

unit [--]; ranges between 0 and 1

typical values gas heating 0.8

daytime cooling setpoint [daytimeCoolingSetPoint] advanced setting

definition indoor setpoint for mechanical cooling system during the day

unit oC

typical values 24 - 27oC

nighttime cooling setpoint [nighttimeCoolingSetPoint] advanced setting

definition indoor setpoint for mechanical cooling system during the night

unit oC

typical values 24 - 27oC

daytime heating setpoint [daytimeHeatingSetPoint] advanced setting

definition indoor setpoint for heating system during the day

unit oC

typical values 15 - 21

nighttime heating setpoint [nighttimeHeatingSetPoint] advanced setting

definition indoor setpoint for heating system during the night

unit oC

typical values 15 - 21

daytime setpoint start time [nightSetEnd] advanced setting

definition characterizes the internal heat gain value for daytime

unit 1 - 24 hours

typical values 5

daytime setpoint end time [nightSetStart] advanced setting

definition indoor setpoint for heating system during the night

unit oC

typical values 19

amount of heat released to canyon [heatReleasedToCanyon] advanced setting

definition amount of the waste heat from the mechanical cooling system that is exhausted into the urban canyon above your neighborhood boundary layer

unit [--]; ranges between 0 and 1

typical values 0

initial temperature [initialT] advanced setting

definition The initial temperature of a model element at the start of the simulation. Since the UWG does not "warm up" as EnergyPlus would, this value is a user input

unit oC

typical values 20oC


urban area [urbanArea]

The geometric parameters such as average building height, site coverage ratio, and facade-to-site ratio can be extracted using this Rhino-plugin grasshopper file


average building height [averageBuildingHeight]

definition average building height in the urban area, normalized by building footprint

unit m

typical values Boston Financial District, MA, USA 50m; Punggol, Singapore 26; Basel, Switzerland 15; Toulouse, France 20m. Typical values are available in Stewart's Local Climate Zone studies [4]

site coverage ratio [siteCoverageRatio]

key design parameter: affects canyon width; important especially when the site has tall buildings. Consider decreasing this parameter. A significant parameter determined by the sensitivity analysis [Boston, Basel, and Toulouse]

definition describes how close buildings are built in the city. Defined by ΣAbldg / Asite , where Abldg = building footprint and Asite = site area. This value can be extracted from the Grasshopper file

unit [--]; ranges between 0 and 1

typical values Boston Financial District, MA, USA 0.68; Punggol, Singapore 0.38; Basel, Switzerland 0.54; Toulouse, France 0.68

facade-to-site ratio [facadeToSiteRatio]

key design parameter: Consider decreasing this parameter. A significant parameter determined by the sensitivity analysis [Boston, Basel, and Toulouse]

definition ratio of the vertical surface area [walls] to the urban plan area. Defined by ΣPhwtd / Asite, where P = building perimeter, hwtd = average building height, weighted by footprint, and Asite = total site area. Used to calculate canyon height and thus solar radiation received by building facade

unit [--]; ranges between 0 and 1

typical values Boston Financial District, MA, USA 1.05; Punggol, Singapore 1.55; Basel, Switzerland 0.48; Toulouse, France 1.10

tree coverage [treeCoverage]

definition amount of tree coverage in the urban area, includes those on the side streets

unit [--]; ranges between 0 and 1

typical values Boston Financial District, MA, USA 0.1; Punggol, Singapore 0.19; Basel, Switzerland 0.16; Toulouse, France 0.08

sensible anthropogenic heat, other than from buildings [nonBldgSensibleHeat]

key policy parameter: consider taking measures to decrease traffic level in the city. A significant parameter determined by the sensitivity analysis [Boston]

definition defines amount of heat released to urban canyon as sensible heat, mostly from traffic. Includes all sensible anthropogenic heat other than from buildings such as traffic, street lighting, and human metabolism

unit W/m2

typical values commercial area in Singapore 10, residential area in Singapore 4, Toulouse, France 8. Values are available for some cities by Sailor [5]

non-building latent heat [nonBldgLatentAnthropogenicHeat] advanced setting

definition latent anthropogenic heat other than from buildings in the urban area

unit W/m2

typical values 0

neighborhood characteristic length [radius] advanced setting

definition radius of the urban area being modeled

unit m

typical values Street showed that 500m radius works best for Cambridge, MA [6], but this parameter is not as relevant, compared to other variables


Vegetation Properties

latent fraction of trees [treeLatent] advanced setting

definition characterizes the amount of latent heat given off by trees. Affects the moisture balance in the urban area

unit [--]; ranges between 0 and 1

typical values 0.7

latent fraction of grass [grassLatent] advanced setting

definition characterizes the amount of latent heat given off by grass. Affects the moisture balance in the urban area

unit [--]; ranges between 0 and 1

typical values 0.6

albedo of vegetation [vegAlbedo] advanced setting

definition Ratio of reflected radiation from the vegetation surfaces to incident radiation upon them

unit [--]; ranges between 0 and 1

typical values 0.25

vegetation participation begin month [vegStart] advanced setting

definition beginning month for vegetation

unit month

typical values 1 - 12

vegetation participation end month [vegEnd] advanced setting

definition end month of vegetation

unit month

typical values 1- 12


Boundary Layer Parameters

daytime boundary layer height [daytimeBLHeight] advanced setting

definition height of the urban boundary layer during daytime. The height is increases with the height of the buildings

unit [m]

typical values 700

nighttime boundary layer height [nighttimeBLHeight] advanced setting

definition height of the urban boundary layer during nighttime. The height is increases with the height of the buildings

unit [m]

typical values 80

reference height [refHeight] advanced setting

definition Reference height at which the vertical profile of potential temperature is vertical. It is the height at which the profile of air temperature becomes stable. Can be determined by flying helium balloons equipped with temperature sensors and recording the air temperatures at different heights

unit [m]

typical values 150


reference site [referenceSite]

latitude

definition latitude of the reference site

unit [o]

typical values n/a

longitude

definition longitude of the reference site

unit [o]

typical values n/a

reference site obstacle height [averageObstacleHeight]

definition height of objects that obstruct views to the sky at the weather station site, such as trees and buildings

unit m

typical values n/a

temperature measurement height advanced setting

definition the height at which temperature is measured on the weather station

unit [m]

typical values 2

wind measurement height advanced setting

definition the height at which wind speed is measured on the weather station

unit [m]

typical values 10


simulation parameters

start month [simuStartMonth]

definition start month of the simulation. UWG will morph the weather file for only the selected period

unit month in number format

typical values 1 - 12

start day [simuStartDay]

definition start date of the simulation. UWG will morph the weather file for only the selected period

unit date in number format

typical values 1 - 31

duration [simuDuration]

definition duration of the simulation. UWG will morph the weather file for only the selected period

unit number of days

typical values 365 [annual], 7 [week]


other resources

The values above have been validated with these resources. Please refer to these documentations for further details and other recommended values.

  1. Commercial Reference Buildings. U.S. Department of Energy
  2. Oke, T.R. (1987). Boundary Layer Climates. London: Methuen and Company, Print.
  3. Cool Roof Rating Council
  4. Stewart I.D., T. Oke (2012). Local Climate Zones for Urban Temperature Studies. Bulletin of American Meteorological Society, 92, 1879 - 1900
  5. Sailor, D.J., (2011). A review of methods for estimating anthropogenic heat and moisture emissions in the urban environment. International Journal of Climatology, 31 (2), 189 - 199
  6. Street M , C F Reinhart, L Norford and J Ochsendorf (2013). Urban heat island in Boston – Evaluation of urban air-temperature models for predictive building energy use, Building Simulation 2013, Chambery, France

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