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Relative humidity now calculated (apparently) correctly.

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This commit is contained in:
Simon Brooke 2026-08-11 17:55:03 +01:00
parent d679bcf781
commit be68481d06
6 changed files with 52 additions and 24 deletions
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7
src/humidity/absolute.clj
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@ -31,8 +31,7 @@
;; AH=(RH × Ps)​​/(Rw ​× T × 100)
(defn abs-humidity [& {:keys [relative-humidity saturation-pressure temperature-kelvin]}]
(when (and relative-humidity saturation-pressure temperature-kelvin)
(defn abs-humidity [& {:keys [relative-humidity saturation-vapour-pressure temperature-kelvin]}]
(when (and relative-humidity saturation-vapour-pressure temperature-kelvin)
;; I don't know why I'm having to multiply by a thousand here...
(* (/ (* relative-humidity saturation-pressure) Rw temperature-kelvin) 1000))
)
(* (/ (* relative-humidity saturation-vapour-pressure) Rw temperature-kelvin) 1000)))

1
src/humidity/actual_vp.clj Normal file
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@ -0,0 +1 @@
(ns humidity.actual-vp)

2
src/humidity/core.clj
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@ -1,6 +1,7 @@
(ns humidity.core
(:require [humidity.absolute :refer [abs-humidity]]
[humidity.constants :refer [celsius-offset Pa]]
[humidity.relative :refer [rel-humidity]]
[humidity.saturation-vp :as saturation-vp]
[humidity.utils :refer [?assoc]]
[humidity.wet-bulb :refer [wet-bulb-temperature]]))
@ -28,6 +29,7 @@
(if pressure-millibars (* pressure-millibars 100) Pa))
:pressure-millibars (when-not pressure-millibars
(if pressure-pascals (/ pressure-pascals 100) (/ Pa 100)))
:relative-humidity (when-not relative-humidity (rel-humidity packet))
:saturation-vapour-pressure (saturation-vp/saturation-vp packet))))

53
src/humidity/relative.clj
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@ -1,7 +1,7 @@
(ns ^{:authority "https://journals.ametsoc.org/view/journals/apme/35/4/1520-0450_1996_035_0601_imfaos_2_0_co_2.xml/"
:author "simon"
:doc "Function to return relative humidity."} humidity.relative
(:require [humidity.constants :refer [celsius-offset e]]
(:require [humidity.constants :refer [celsius-offset e Rw]]
[humidity.utils :refer [expt]]))
(def ^:const magic-numbers
@ -13,22 +13,43 @@
(def C magic-numbers)
;; / / relative-humidity x saturation-pressure \ \
;; | | --------------------------------------- | |
;; 1000 * | \ Rw / | = absolute-humidity
;; | ------------------------------------------- |
;; \ temperature-kelvin /
;;
;; divide both sides by 1000 ==>
;; / / relative-humidity x saturation-pressure \ \
;; | | --------------------------------------- | | / absolute-humidity \
;; | \ Rw / | = | ----------------- |
;; | ------------------------------------------- | \ 1000 /
;; \ temperature-kelvin /
;;
;; multiply both sides by temperature-kelvin ==>
;; / relative-humidity x saturation-pressure \ / absolute-humidity x temperature-kelvin \
;; | --------------------------------------- | = | -------------------------------------- |
;; \ Rw / \ 1000 /
;;
;; Multiply both sides by Rw ==>
;; absolute-humidity x temperature-kelvin x Rw
;; relative-humidity x saturation-pressure = -------------------------------------------
;; 1000
;;
;; Divide both sides by saturation-pressure ==>
;;
;; absolute-humidity x temperature-kelvin x Rw
;; relative-humidity = -------------------------------------------
;; 1000 x saturation-pressure
(defn rel-humidity
"Returns relative humidity (as a percentage, 0...100) given values for dew
point and temperature in either Celsius or Kelvin."
[& {:keys [dew-point temperature-celsius temperature-kelvin]}]
(cond (and dew-point (or temperature-celsius temperature-kelvin))
(let [Tc (if temperature-celsius
temperature-celsius
(- temperature-kelvin celsius-offset))]
point and temperature in Celsius or for absolute humidity, saturation vapour pressure temperature Kelvin."
[& {:keys [absolute-humidity dew-point saturation-vapour-pressure temperature-ke temperature-kelvin] :as packet}]
(cond (and dew-point temperature-ke)
(* 100 (/ (expt e (/ (* (C 1) dew-point)
(+ (C 2) dew-point)))
(expt e (/ (* (C 1) Tc)
(+ (C 2) Tc))))))))
;; Absolute Humidity (grams/m3) = 6.112 × e^[(17.67 × T)/(T+243.5)] × rh × 2.1674
;; -----------------------------------------------
;; (273.15+T)
;;
;; => /
;;
(expt e (/ (* (C 1) temperature-ke)
(+ (C 2) temperature-ke)))))
(and absolute-humidity saturation-vapour-pressure temperature-kelvin)
(/ (* absolute-humidity temperature-kelvin Rw) (* 1000 saturation-vapour-pressure))))

2
test/humidity/absolute_test.clj
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@ -8,6 +8,6 @@
(let [min-expected 39.58
max-expected 39.59
actual (abs-humidity :relative-humidity 100
:saturation-pressure 56.29
:saturation-vapour-pressure 56.29
:temperature-kelvin (+ 35 celsius-offset))]
(is (< min-expected actual max-expected)))))

7
test/humidity/relative_test.clj
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@ -1,9 +1,14 @@
(ns humidity.relative-test
(:require [clojure.test :refer [deftest is testing]]
[humidity.constants :refer [celsius-offset]]
[humidity.relative :refer [rel-humidity]]))
[humidity.relative :refer [rel-humidity rel-humidity-2]]))
(deftest relative-humidity-test
(testing "definitional"
(let [min-expected 99
max-expected 101
actual (rel-humidity-2 :absolute-humidity 39.58 :saturation-vapour-pressure 5622.49 :temperature-kelvin (+ 35 celsius-offset))]
(is (< min-expected actual max-expected))))
(testing "Online examples"
(let [min-expected 99
max-expected 101