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Reading an EPW file starts with function read_epw(), which parses an EPW
file and returns an Epw object. The parsing process is extremely inspired
by OpenStudio utilities library
with some simplifications.
epw <- read_epw(path) epw$city epw$city <- "city" epw$state_province epw$state_province <- "state_province" epw$country epw$country <- "country" epw$data_source epw$data_source <- "data_source" epw$wmo_number epw$wmo_number <- "wmo_number" epw$latitude epw$latitude <- "latitude" epw$longitute epw$longitute <- "longitute" epw$time_zone epw$time_zone <- "time_zone" epw$elevation epw$elevation <- "elevation" epw$time_step epw$time_step <- "time_step" epw$start_day_of_week epw$start_day_of_week <- "start_day_of_week" epw$path() epw$get_data(year = NULL, unit = FALSE, tz = Sys.timezone(), update = FALSE) epw$set_data(data) epw$save(path, overwrite = FALSE) epw$print() print(epw)
epw <- read_epw(path)
Arguments
path: Path of an EnergyPlus EPW file.
epw$save(path, overwrite = FALSE)
Arguments
path: A path where to save the weather file. If NULL, the path of the
weather file itself is used.
overwrite: Whether to overwrite the file if it already exists. Default is
FALSE.
epw$city epw$city <- "city" epw$state_province epw$state_province <- "state_province" epw$country epw$country <- "country" epw$data_source epw$data_source <- "data_source" epw$wmo_number epw$wmo_number <- "wmo_number" epw$latitude epw$latitude <- "latitude" epw$longitute epw$longitute <- "longitute" epw$time_zone epw$time_zone <- "time_zone" epw$elevation epw$elevation <- "elevation" epw$time_step epw$time_step <- "time_step" epw$start_day_of_week epw$start_day_of_week <- "start_day_of_week"
$city, $state_province, $country, $data_source, $wmo_number,
$latitude, $longitute, $time_zone, $elevation, $time_step and
$start_day_of_week are all active bindings, which means that you can get
the value and also set new value to it.
NOTE: Please be super careful when trying to modify those data. Some of them must be consistent with weather data in order to make the weather file successfully parsed by EnergyPlus and eplusr.
epw$path() epw$get_data(year = NULL, unit = FALSE, tz = Sys.timezone(), update = FALSE) epw$set_data(data)
$path() returns the path of EPW file. NULL if Epw is not created from
local file.
$get_data() returns the core weather data in a data.table.
$set_data() replaces core weather data with input data. NOTE: This feature is
experimental. There is no validation when replacing.
Arguments
year: A integer to indicate the year value in the return datetime column.
If NULL, which is the default, the year is left as it is in EPW file.
tz: The time zone of Date and Time in datetime column. Default:
value of Sys.timezone().
unit: If TRUE, units are set to all numeric columns using
units::set_units(). Default: FALSE.
update: If TRUE, not only datetime column, but also year, month,
day, hour and minute are also updated according to the input
year value. Default: FALSE
data: A data.frame which has all required columns.
An EPW file can be divided into two parts, headers and weather data. The first eight lines of a standard EPW file are normally headers which contains data of location, design conditions, typical/extreme periods, ground temperatures, holidays/daylight savings, data periods and other comments. For now, eplusr only parses headers of location, holidays/daylight savings and data periods. All other headers are left as they were when parsing and saving. For details on the data structure of EPW file, please see "Chapter 2 - Weather Converter Program" in EnergyPlus "Auxiliary Programs" documentation. An online version can be found here.
There are about 35 variables in the core weather data. However, not all of them are used by EnergyPlus. Actually, despite of date and time columns, only 14 columns are used:
dry bulb temperature
dew point temperature
relative humidity
atmospheric pressure
horizontal infrared radiation intensity from sky
direct normal radiation
diffuse horizontal radiation
wind direction
wind speed
present weather observation
present weather codes
snow depth
liquid precipitation depth
liquid precipitation rate
NOTE: Even though Epw class provides methods to replace core weather data,
it is still not recommended.
# NOT RUN {
# read an EPW file from EnergyPlus website
path_base <- "https://energyplus.net/weather-download"
path_region <- "north_and_central_america_wmo_region_4/USA/CA"
path_file <- "USA_CA_San.Francisco.Intl.AP.724940_TMY3/USA_CA_San.Francisco.Intl.AP.724940_TMY3.epw"
path_epw <- file.path(path_base, path_region, path_file)
epw <- read_epw(path_epw)
# read an EPW file distributed with EnergyPlus
if (is_avail_eplus(8.8)) {
epw_path <- file.path(
eplus_config(8.8)$dir,
"WeatherData",
"USA_CA_San.Francisco.Intl.AP.724940_TMY3.epw"
)
epw <- read_epw(path_epw)
}
# get file path
epw$path()
# get basic info
epw$city
epw$state_province
epw$country
epw$data_source
epw$wmo_number
epw$latitude
epw$longitude
epw$time_zone
epw$elevation
epw$time_step
epw$start_day_of_week
# set basic info
# NOTE: Use with caution. May mess up your weather data
epw$city <- "Chongqing"
epw$city
epw$state_province <- "Chongqing"
epw$state_province
epw$country <- "China"
epw$country
epw$data_source <- "TMY"
epw$data_source
epw$wmo_number <- "724944"
epw$wmo_number
epw$latitude <- 20.0
epw$latitude
epw$longitude <- -120.0
epw$longitude
epw$time_zone <- 8
epw$time_zone
epw$elevation <- 100
epw$elevation
epw$time_step <- 2
epw$time_step
epw$start_day_of_week <- "Monday"
epw$start_day_of_week
# get weather data
str(epw$get_data())
# get weather data but change the year to 2018
# the year column is not changed by default, only the returned datetime column
str(epw$get_data(year = 2018)$datetime)
str(epw$get_data(year = 2018)$year)
# you can force to update the year column
str(epw$get_data(year = 2018, update = TRUE)$year)
# get weather data with units
str(epw$get_data(unit = TRUE))
# with units specified, you can easily perform unit conversion using units
# package
t_dry_bulb <- epw$get_data(unit = TRUE)$dry_bulb_temperature
units(t_dry_bulb) <- with(units::ud_units, "kelvin")
str(t_dry_bulb)
# change the time zone of datetime column in the returned weather data
attributes(epw$get_data()$datetime)
attributes(epw$get_data(tz = "America/Chicago")$datetime)
# change the weather data
# NOTE: This feature is experimental. There is no validation when replacing.
epw$set_data(epw$get_data())
# save the weather file
epw$save(file.path(tempdir(), "weather.epw"))
# }
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