Quick Start

The HEM help guide

Once HEM is installed, we can view the help guide of the hem.py module using -h or --help argument.

Use one of the following command prompts (they do the same thing):

• python [PATH_TO_HEM_ROOT_DIRECTORY]\src\hem.py -h

• python [PATH_TO_HEM_ROOT_DIRECTORY]\src\hem.py --help

This prints the following help text:

usage: hem.py [-h] [--epw-file EPW_FILE] [--CIBSE-weather-file CIBSE_WEATHER_FILE] [--tariff-file TARIFF_FILE] [--parallel PARALLEL] [--preprocess-only]
            [--future-homes-standard | --future-homes-standard-FEE | --future-homes-standard-notA | --future-homes-standard-notB | --future-homes-standard-FEE-notA | --future-homes-standard-FEE-notB]
            [--heat-balance] [--detailed-output-heating-cooling] [--no-fast-solver] [--display-progress] [--no-validate-json]
            input_file [input_file ...]

Home Energy Model (HEM)

positional arguments:
input_file            path(s) to file(s) containing building specifications to run

options:
-h, --help            show this help message and exit
--epw-file EPW_FILE, -w EPW_FILE
                        path to weather file in .epw format
--CIBSE-weather-file CIBSE_WEATHER_FILE
                        path to CIBSE weather file in .csv format
--tariff-file TARIFF_FILE
                        path to tariff data file in .csv format
--parallel PARALLEL, -p PARALLEL
                        run calculations for different input files in parallel(specify no of files to run simultaneously)
--preprocess-only     run prepocessing step only
--future-homes-standard
                        use Future Homes Standard calculation assumptions
--future-homes-standard-FEE
                        use Future Homes Standard Fabric Energy Efficiency assumptions
--future-homes-standard-notA
                        use Future Homes Standard calculation assumptions for notional option A
--future-homes-standard-notB
                        use Future Homes Standard calculation assumptions for notional option B
--future-homes-standard-FEE-notA
                        use Future Homes Standard Fabric Energy Efficiency assumptions for notional option A
--future-homes-standard-FEE-notB
                        use Future Homes Standard Fabric Energy Efficiency assumptions for notional option B
--heat-balance        output heat balance for each zone
--detailed-output-heating-cooling
                        output detailed calculation results for heating and cooling system objects (including HeatSourceWet objects) where the relevant objects have this functionality
--no-fast-solver      disable optimised solver (results may differ slightly due to reordering of floating-point ops); this option is provided to facilitate verification and debugging of the
                        optimised version
--display-progress    display progress for the json input file currently running
--no-validate-json    disable JSON schema validation (useful during development)

This tells us that when calling the hem.py module, we should provide the input_file argument (as it is a ‘positional argument’) and we can also supply many different options arguments (-h, --epw-file, --CIBSE-weather-file etc.).

What do all these arguments do? This doesn’t seem to be documentented anywhere but we can make reasonable guesses given the descriptions above.

An example simulation

This simulation uses:

• the demo.json input file from the HEM repository.

• the London_weather_CIBSE_format.csv weather data file from the HEM repository.

The steps are:

1. Save the demo.json and London_weather_CIBSE_format.csv files in the same folder on your local computer.

2. Open the Command Prompt.

3. Change the directory of the Command Prompt to where the files are stored using cd [PATH_TO_MY_DIRECTORY].

4. Run the prompt: python [PATH_TO_HEM_ROOT_DIRECTORY]\src\hem.py --CIBSE-weather-file London_weather_CIBSE_format.csv demo.json.

• python calls the Python interpreter.

• [PATH_TO_HEM_ROOT_DIRECTORY] is the directory where the HEM repository is stored on your computer. Please replace this text with the local path you have used.

• src\hem.py is the path to Python module hem.py which provides the point of access to the HEM calculations.

• --CIBSE-weather-file is the CIBSE weather data flag as described in the help text above.

• London_weather_CIBSE_format.csv is the filepath to the CIBSE weather file (this must follow directly after --CIBSE-weather-file).

• demo.json is the filepath to the input file.

This results in the following text printed in the Command Prompt.

Running 1 cases in series

This also creates a new subfolder named demo__results (the name of the input file plus ‘__results’) which contains the following results files:

• demo.json

• demo__core__results.csv

• demo__core__results_static.csv

• demo__core__results_summary.csv