COP calculation fails for Na values in temperature timeseries

[pascal-vecsei]

Ugly fix:

  weather_data = weather_data[:len(sh_profile)]

  weather_data[pd.isna(weather_data)] = np.min(weather_data[pd.notna(weather_data)])

  temp_brine_ = temp_brine[:len(sh_profile)]

and

  low_temp = kelvin_offset+tech_instance._cop_source_constant_temperature_value if tech_instance._cop_source_temperature == 'constant_temperature' else kelvin_offset+weather_data
  low_temp[pd.isna(low_temp)] = np.min(low_temp[pd.notna(low_temp)])
  carnot_eff = hot_temp / (hot_temp - low_temp)

in COP calculation (may cause freezing temperatures in summer)