A Carnot heat pump is used to maintain the temperature inside a building at 20 $^\circ$C. Significantly, the colder it gets outside, the more heat is lost through the walls and windows of the building. Assume that 55 kW of heat are lost for each degree difference between the outside and the inside temperature. That means that the colder it gets, the harder the heat pump will need to work. However, for safety reasons, the controller circuit for the heat pump limits its electrical power consumption to 205 kW. What's the coldest it can get outside before the heat pump can't maintain the building temperature adequately?

$^\circ$C