Chapter 2 - Energy, Energy Transfer, and General Energy Analysis - Problems - Page 100: 2-44

$n_{units}=2$

First we calculate the total heat produced: $Q_{t}=Q_{people}+Q_{lightbulbs}+Q_{walls and windows}$ $Q_{people}=40*(360\frac{kJ}{h}*\frac{1h}{3600s})=4kW$ $Q_{lightbulbs}=10*100W=1kW$ $Q_{walls and windows}=15000\frac{kJ}{h}*\frac{1h}{3600s}=4.17kW$ $Q_{t}=4kW+1kW+4.17kW=9.17kW$ Now the number of units will be: $n_{units}=\frac{9.17kW}{5kW}=2$