discomfort_index.js

import { round } from "../utilities/utilities.js";

/**
 * @typedef {Object} DiscomfortIndexReturnType - a result set containing the discomfort index and the classification of the
 * thermal comfort conditions
 * @property {number} di – Discomfort Index(DI)
 * @property {string} discomfort_condition Classification of the thermal comfort conditions according to the discomfort index
 * @public
 */

/**
 * Calculates the Discomfort Index (DI). The index is essentially an effective temperature based on air temperature and humidity.
 * The discomfort index is usuallly divided in 6 dicomfort categories and it only applies to warm environments. {@link #ref_24|[24]}
 *
 * - class 1 - DI < 21 °C - No discomfort
 * - class 2 - 21 <= DI < 24 °C - Less than 50% feels discomfort
 * - class 3 - 24 <= DI < 27 °C - More than 50% feels discomfort
 * - class 4 - 27 <= DI < 29 °C - Most of the population feels discomfort
 * - class 5 - 29 <= DI < 32 °C - Everyone feels severe stress
 * - class 6 - DI >= 32 °C - State of medical emergency
 *
 * @see {@link discomfort_index_array} for a version that supports arrays
 *
 * @public
 * @memberof models
 * @docname Discomfort Index (DI)
 *
 * @param {number} tdb - air temperature [C]
 * @param {number} rh - relative humidity [%]
 *
 * @returns {DiscomfortIndexReturnType} object with results of DI
 * @example
 * const DI = discomfort_index(25, 50); // returns { di: 22.1, discomfort_condition: 'Less than 50% feels discomfort' }
 */
export function discomfort_index(tdb, rh) {
  const di = calculate_di(tdb, rh);
  const condition = check_categories(di);

  return {
    di: round(di, 1),
    discomfort_condition: condition,
  };
}

/**
 * @typedef {Object} DiscomfortIndexArrayReturnType - a result set containing an array of discomfort index and an array
 * of classification of the thermal comfort conditions
 * @property {number[]} di – Discomfort Index(DI) Array
 * @property {string[]} discomfort_condition Classification of the thermal comfort conditions in array
 * @public
 */

/**
 * Calculates the Discomfort Index (DI). The index is essentially an effective temperature based on air temperature and humidity.
 * The discomfort index is usuallly divided in 6 dicomfort categories and it only applies to warm environments. {@link #ref_24|[24]}
 *
 * - class 1 - DI < 21 °C - No discomfort
 * - class 2 - 21 <= DI < 24 °C - Less than 50% feels discomfort
 * - class 3 - 24 <= DI < 27 °C - More than 50% feels discomfort
 * - class 4 - 27 <= DI < 29 °C - Most of the population feels discomfort
 * - class 5 - 29 <= DI < 32 °C - Everyone feels severe stress
 * - class 6 - DI >= 32 °C - State of medical emergency
 *
 * @see {@link discomfort_index} for a version that supports scalar arguments
 *
 * @public
 * @memberof models
 * @docname Discomfort Index (DI) (array version)
 *
 * @param {number[]} tdb - air temperature [C]
 * @param {number[]} rh - relative humidity [%]
 *
 * @returns {DiscomfortIndexArrayReturnType} object with results of DI
 */
export function discomfort_index_array(tdb, rh) {
  const di = tdb.map((temperature, index) =>
    calculate_di(temperature, rh[index]),
  );

  const discomfortCondition = di.map((value) => check_categories(value));

  return {
    di: di.map((value) => round(value, 1)),
    discomfort_condition: discomfortCondition,
  };
}

/**
 *
 * Determine the discomfort categories based on DI.
 *
 * @param {number} di - Discomfort Index (DI)
 * @returns {string} Discomfort condition
 */
function check_categories(di) {
  const threshold = [21, 24, 27, 29, 32, 99];
  const condition = [
    "No discomfort",
    "Less than 50% feels discomfort",
    "More than 50% feels discomfort",
    "Most of the population feels discomfort",
    "Everyone feels severe stress",
    "State of medical emergency",
  ];

  for (let index = 0; index < threshold.length; index++) {
    if (di <= threshold[index]) {
      return condition[index];
    }
  }
}

/**
 * Calculate Discomfort Index (DI) based on air temperature and relative humidity.
 *
 * @param {number} tdb - air temperature [C]
 * @param {number} rh - relative humidity [%]
 * @returns {number} Discomfort Index (DI)
 */
function calculate_di(tdb, rh) {
  return tdb - 0.55 * (1 - 0.01 * rh) * (tdb - 14.5);
}