'Calculate the dewpoint for the indoor air.'

def _calc_dewpoint(self):

    alpha = ((MAGNUS_K2 * self._indoor_temp) / (MAGNUS_K3 + self._indoor_temp))
    beta = ((MAGNUS_K2 * MAGNUS_K3) / (MAGNUS_K3 + self._indoor_temp))
    if (self._indoor_hum == 0):
        self._dewpoint = (-50)
    else:
        self._dewpoint = ((MAGNUS_K3 * (alpha + math.log((self._indoor_hum / 100.0)))) / (beta - math.log((self._indoor_hum / 100.0))))
    _LOGGER.debug(('Dewpoint:    %f    ' + TEMP_CELSIUS), self._dewpoint)
