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98_dewpoint: Consolidated and corrected formulas for dewpoint (Forum #78359)

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git-svn-id: https://svn.fhem.de/fhem/trunk@15476 2b470e98-0d58-463d-a4d8-8e2adae1ed80
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hotbso 2017-11-22 09:58:44 +00:00
parent c85dceb77e
commit fba07d1728
1 changed files with 68 additions and 33 deletions
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103
fhem/FHEM/98_dewpoint.pm
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@ -27,6 +27,8 @@ package main;
use strict;
use warnings;
sub Log($$);
# Debug this module? YES = 1, NO = 0
my $dewpoint_debug = 0;
# default maximum time_diff for dewpoint
@ -409,56 +411,89 @@ dewpoint_Notify($$)
}
# -----------------------------
# Dewpoint calculation.
# see http://www.faqs.org/faqs/meteorology/temp-dewpoint/ "5. EXAMPLE"
# 'Magnus formula'
#
# Parameters from https://de.wikipedia.org/wiki/Taupunkt#S.C3.A4ttigungsdampfdruck
# Good summary of formulas in http://www.wettermail.de/wetter/feuchte.html
my $E0 = 0.6112; # saturation pressure at T=0 °C
my @ab_gt0 = (17.62, 243.12); # T>0
my @ab_le0 = (22.46, 272.6); # T<=0 over ice
### ** Public interface ** keep stable
# vapour pressure in kPa
sub dewpoint_vp($$)
{
my ($T, $Hr) = @_;
my ($a, $b);
if ($T > 0) {
($a, $b) = @ab_gt0;
} else {
($a, $b) = @ab_le0;
}
return 0.01 * $Hr * $E0 * exp($a * $T / ($T + $b));
}
### ** Public interface ** keep stable
# dewpoint in °C
sub
dewpoint_dewpoint($$)
{
my ($temperature, $humidity) = @_;
my $dp;
my $A = 17.2694;
my $B = ($temperature > 0) ? 237.3 : 265.5;
my $es = 610.78 * exp( $A * $temperature / ($temperature + $B) );
my $e = $humidity/ 100 * $es;
if ($e == 0) {
Log 1, "Error: dewpoint() e==0: temp=$temperature, hum=$humidity";
return 0;
}
my $e1 = $e / 610.78;
my $f = log( $e1 ) / $A;
my $f1 = 1 - $f;
if ($f1 == 0) {
Log 1, "Error: dewpoint() (1-f)==0: temp=$temperature, hum=$humidity";
return 0;
}
$dp = $B * $f / $f1 ;
return($dp);
my ($T, $Hr) = @_;
if ($Hr == 0) {
Log 1, "Error: dewpoint() Hr==0 !: temp=$T, hum=$Hr";
return undef;
}
my ($a, $b);
if ($T > 0) {
($a, $b) = @ab_gt0;
} else {
($a, $b) = @ab_le0;
}
# solve vp($dp, 100) = vp($T,$Hr) for $dp
my $v = log(dewpoint_vp($T, $Hr) / $E0);
my $D = $a - $v;
# can this ever happen for valid input?
if ($D == 0) {
Log 1, "Error: dewpoint() D==0 !: temp=$T, hum=$Hr";
return undef;
}
return round($b * $v / $D, 1);
}
### ** Public interface ** keep stable
# absolute Feuchte in g Wasserdampf pro m3 Luft
sub
dewpoint_absFeuchte ($$)
{
# Formeln von http://kellerlueftung.blogspot.de/p/blog-page_9.html
# http://www.wettermail.de/wetter/feuchte.html
my ($T, $rh) = @_;
if (($rh < 0) || ($rh > 110)){
Log 1, "Error dewpoint: humidity invalid: $rh";
my ($T, $Hr) = @_;
# 110 ?
if (($Hr < 0) || ($Hr > 110)) {
Log 1, "Error dewpoint: humidity invalid: $Hr";
return "";
}
# a = 7.5, b = 237.3 für T >= 0
# a = 7.6, b = 240.7 für T < 0 über Wasser (Taupunkt)
my $a = ($T > 0) ? 7.5 : 7.6;
my $b = ($T > 0) ? 237.3 : 240.7;
my $SDD = 6.1078 * 10**(($a*$T)/($b+$T));
my $DD = $rh/100 * $SDD;
my $AF = (10**5) * (18.016 / 8314.3) * ($DD / (273.15 + $T));
my $af = sprintf( "%.1f",$AF);
return($af); # $aF = absolute Feuchte in g Wasserdampf pro m3 Luft
my $DD = dewpoint_vp($T, $Hr);
my $AF = 1.0E6 * (18.016 / 8314.3) * ($DD / (273.15 + $T));
return round($AF, 1);
}
1;
=pod
=item helper
=item summary compute dewpoint and/or generate events for starting a fan
=item summary_DE berechne Taupunkt und/oder erzeuge events zum starten eines Lüfters
=begin html
<a name="dewpoint"></a>