Question #$1$

A condominium unit has a single exterior surface of $60m^2$ facing north in Ottawa. The window$-$to$-$wall ratio is $0\mathrm{.}5.$ The R$-$SI of the wall is $5m^2\frac{K}{W}.$ The thickness of the concrete floor slab is $0\mathrm{.}12m,$ and the floor area is $110m^2.$ Determine the window U$-$SI value that will ensure your building is resilient to a three$-$day power outage subject to the following conditions. The temperature of the building should not be less than $10C$ after a three$-$day power outage. Assume that the outdoor temperature is constant at $-15C$ for the entire period. Neglect solar and internal heat gains. Neglect infiltration and ventilation. Assume that the temperature of the unit is $21C$ at the onset of the power outage. Treat the unit as a single lumped thermal mass. Assume the density, specific heat, and thermal conductivity of the concrete slab as $2400k\frac{g}{m^3},0\mathrm{.}9k\frac{J}{k}g*K,$ and $2\mathrm{.}2\frac{W}{m}*K,$ respectively; the density and specific heat of air are $1\mathrm{.}2k\frac{g}{m^3}$ and $1k\frac{J}{k}g*K,$ respectively.