It's also true with an A/C - the faster you are trying to cool the larger temperature gradient you need, and therefor you lose efficiency.
I'm not sure that's always correct. The Coefficient of Performance (heat moved/work done, higher COP is better) of an A/C is:
COP = T_hot / (T_hot - T_cold).
T_cold is the inside temp, T_hot is outside of the heat exchanger. The narrow the temperature range, the better the COP. Thus the A/C will actually be more efficient in terms of heat moved per watt while it's cooling a warm house down than when it's already cool.
There's one other factor that applies. The rate of heat transferring into the house is proportional to the temperature difference. Once the house has warmed up, you reach equilibrium. The net heat flow stops, so the total amount of energy you need to remove later stops rising. If you run the A/C all the time, heat is transferring in all the time. So the total amount of heat you need to move back outside in a day increases significantly if you leave the A/C on.
I'm not sure that's always correct. The Coefficient of Performance (heat moved/work done, higher COP is better) of an A/C is:
COP = T_hot / (T_hot - T_cold).
T_cold is the inside temp, T_hot is outside of the heat exchanger. The narrow the temperature range, the better the COP. Thus the A/C will actually be more efficient in terms of heat moved per watt while it's cooling a warm house down than when it's already cool.
There's one other factor that applies. The rate of heat transferring into the house is proportional to the temperature difference. Once the house has warmed up, you reach equilibrium. The net heat flow stops, so the total amount of energy you need to remove later stops rising. If you run the A/C all the time, heat is transferring in all the time. So the total amount of heat you need to move back outside in a day increases significantly if you leave the A/C on.