GNOMY

A Python package for weather data gathering for further use.

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Quick Start

Info

The name "Gnomy" (while a working name) comes from the initial name of the effort to create a "NOAA-based AMY file". After being said repeatedly, "NOAA AMY" began to mumble together into "no-my" or gnomy.

Gnomy began with my personal need to collect actual measured weather data rather than typical meteorological year data in order to fit home energy models to measured data. Having worked with the Herbie python package, this package has the goal to make parallelized collection of weather data and export in the required format more accessible.

AMY Parameters

An epw file consists of 8 rows of header information followed by the body of the data with 34 columns

epw Header Information

Each line contains contextual information about the location and weather. See Climate Analytics for more information on each field specifically.

1. Location
2. Design conditions
3. Typical and extreme periods
4. ground temperatures
5. Holidays and daylight savings
6. Comments 1
7. Comments 2
8. Data Periods

epw Data Body

The columns of an AMY file are not labeled within the file itself. The energy plus documentation identifies many if the fields of interest.

Below is a table of the values used, their limits, conventions for missing data, and the source of the data using gnomy. Values in bold are used by EnergyPlus

Field	Name	Units	Min.	Max.	Missing	Used in Energy Plus	gnomy source
1	Year
2	Month
3	Hour
4	Minute
5	Data Source and Uncertainty
6	Dry Bulb Temerature	C	-70	70	99.9	Yes	NOAA analysis air temperature 2m above ground
7	Dew Point Temerature	C	-70	70	99.9	Yes	NOAA analysis dew point 2m above ground
8	Relative Humidity		0	110	999	Yes	NOAA analysis relative humidity 2m above ground
9	Atmospheric Station Pressure	Pa	31,000	120,000	999,999	Yes	NOAA Analysis surface pressure
10	Extraterrestrial Horizontal Radiation	Wh/m$^2$	0		9,999		Calculated from Solar Zenith Angle and the solar constant. See [1]
11	Extraterrestrial Direct Normal Radiation	Wh/m$^2$	0		9,999		Calculated from the day of year and the solar constant. See: [2]
12	Horizontal Infrared Radiation Intensity	Wh/m$^2$	0		9,999	Yes	Calculated from Sky Emissivity and dry bulb temperature. See [3]
13	Global Horizontal Radiation	Wh/m$^2$	0		9,999		Calculated from DNI, DHI, and Solar Zenith Angle. See [4]
14	Direct Normal Radiation	Wh/m$^2$	0		9,999	Yes	NOAA Analysis Visible Beam Downward Solar Flux
15	Diffuse Horizontal Radiation	Wh/m$^2$	0		9,999	Yes	NOAA Analysis Visible Diffuse Downward Solar Flux
16	Global Horizontal Illuminance	lux			>=999,900		Estimated using Irradiance. See [5]
17	Direct Normal Illuminance	lux			>=999,900		Estimated using Irradiance. See [5]
18	Diffuse Horizontal Illuminance	lux			>=999,900		Estimated using Irradiance. See [5]
19	Zenith Luminance	Cd/m$^2$			>=9999		Estimated using Irradiance. See [5]
20	Wind Direction	Degrees	0	360	999	Yes	NOAA Analysis Wind Speed in U and V directions converted to compass directions. See [6]
21	Wind Speed	m/s	0	40	999	Yes	NOAA Analysis Wind Speeds in U and V components used for total wind speed
22	Total Sky Cover		0	10	99		NOAA Analysis Total Sky Cover
23	Opaque Sky Cover		0	10	99	Used if horizontal IR intensity is missing	Calculated by estimating sky cover that is only Low or Medium Cloud Cover or 50% high cloud cover. See [7]
24	Visibility	km				9,999	NOAA Analysis Visibility
25	Ceiling Height	m				99,999	NOAA Analysis Geopotential Height
26	Present Weather Observation	Boolean				Yes, primarily to know if exterior surfaces are wet or frozen.
27	Present Weather Codes	str				Yes, primarily to know if exterior surfaces are wet or frozen	Estimated using precipitation forecasts. See [8]
28	Precipitable Water	mm			999	Yes	NOAA Analysis Precipitable Water
29	Aerosol Optical Depth	thousandths			0.999		NOAA Analysis Aeorosol Optical Thickness
30	Snow Depth	cm			999	Yes	NOAA Analysis Snow Depth
31	Days Since Last Snowfall				99		Calculated after collecting precipitation data
32	Albedo				999		Estimated using the land use category. See [9]
33	Liquid Precipitation Depth	mm			999		NOAA 1 hour forecast Total Precipitation. See [9]
34	Liquid Precipitation Quantity	hr			99		Calculated. The interval 33 accumulates over, which is 1 hour.

In summary, the following values are used by EnergyPlus:

The following variables are provided directly by NOAA analysis:

The following variables are estimated using NOAA 1h forecasts:

The following variables are calculated or estimated:

Notes

1) Calculating Extraterrestrial Horizontal Radiation