It's the flooding problem most of all. I'm in one of the few Manhattan co-ops that still allows washing machines and dryers and it's a wonderful thing to have it in my apartment. But many landlords, co-op board and condos don't permit them because of the flooding.
Sodium acetate or hot ice is an amazing chemical you can prepare yourself from baking soda and vinegar. You can cool a solution of sodium acetate below its melting point and then cause the liquid to crystallize. The crystallization is an exothermic process, so the resulting ice is hot. Solidification occurs so quickly you can form sculptures as you pour the hot ice.
To melt, the ice, the heat pump takes heat from the house to heat the outdoor coils. This reduces average heat pump efficiency. Supplemental Heat. As it gets colder outside, the heat pump provides less heat. Yet the house needs more heat to keep comfortable. At some outdoor temperature it will be too cold for the heat pump to provide all the heat the house needs.