PHP Script to update Nest thermostat target humidity based on outside temperature

update_nest_target_humidity.php

<?php

require_once dirname(__FILE__) . '/../includes/nest.class.php';

// Your Nest username and password.
define('USERNAME', 'YOUR_NEST_USERNAME');
define('PASSWORD', 'YOUR_NEST_PASSWORD');

define("MAX_HUMIDITY", 45);
define("MIN_HUMIDITY", 15);
define("LOG_FILENAME", "/tmp/humidity.log");

$nest = new Nest();

// Get the device information:
$nest_info = $nest->getDeviceInfo();
$current_target_humidity = $nest_info->target->humidity;
$inside_hum = $nest_info->current_state->humidity;
$is_heating = $nest_info->current_state->heat;

//print_r($nest_info);
//print "Current Nest target humidity = $current_target_humidity%, actual humidity = $inside_hum%\n";

if (!isset($argv[1])) {
        throw new Exception("Missing input for outside temperature");
}

$outside_temp = $argv[1];
$outside_hum = $argv[2];


// set target humidity based on outside temperature (in Fahrenheit)
if ($outside_temp >= 40) {
        $target_hum = 45;
} else if ($outside_temp >= 30) {
        $target_hum = 40;
} else if ($outside_temp >= 20) {
        $target_hum = 35;
} else if ($outside_temp >= 10) {
        $target_hum = 30;
} else if ($outside_temp >= 0) {
        $target_hum = 25;
} else if ($outside_temp >= -10) {
        $target_hum = 20;
} else if ($outside_temp >= -20) {
        $target_hum = 15;
}

$log_string = '';
$humidity_difference = $inside_hum - $target_hum;
//debug_log("humidity difference = $humidity_difference");

if ($is_heating && $humidity_difference < 4) {
        // Nest likes to get the humidity up to 5% more than what you set it to.  So, if you set it to 30%, it will humidify up to 35%.  It tends to run the heat for a while, then after the heat shuts off start humidifying.  It's more efficient to humidify while the heat is running since it doesn't consume any extra electricity because the fan is already running.  So, if the heat is currently running, we'll bump up the target humidity temporarily to preemptively start humidifying, so that once the heat shuts off, we hopefully won't need to run the humidifier on its own
        $log_string .= "Bumping target humidity up by 5% because heat is on. ";
        $target_hum += 5;
}

// safety check
$target_hum = max($target_hum, MIN_HUMIDITY);
$target_hum = min($target_hum, MAX_HUMIDITY);

// only make the call to Nest if we are changing the target humidity from what it is set to now
$should_change = $target_hum != $current_target_humidity;

if ($should_change) {
        $log_string .= "Setting Nest target humidity to $target_hum% for outside temp $outside_temp (current humidity inside = $inside_hum%, outside = $outside_hum%)";
} else {
        $log_string .= "Maintaining Nest target humidity of $target_hum% for outside temp $outside_temp (current humidity inside = $inside_hum%, outside = $outside_hum%)";
}


debug_log($log_string);

if ($should_change) {
        $return = $nest->setHumidity($target_hum);
        if ($return != 1) {
                debug_log("ERROR: Nest returned: $return\n");
        }
}

function debug_log($message) {
        $date = date('m-d-Y H:i:s');

        $message .= "\n";
        file_put_contents(LOG_FILENAME, "$date $message", FILE_APPEND);
        print $message;
}