FOR THOSE OF YOU WHO DO NOT WISH TO
SLOG THROUGH THE MATHEMATICS BELOW, THE BOTTOM LINE OF THE CALCULATION
IS:
The Mall of America has an area of about 2.8 million square
feet
Lighting requirements are generally in the range of 3
W/sq. ft.
(Cf. ASHRAE standards: American Society of Heating, Refrigerating,
and Air Condtioning Engineers, Section 90.1)
A/C requirements are generally in the range of about 3
W/sq. ft.
This is based on the commonly used requirement of 1200
sq. ft./ton of cooling capacity. 12,000BTU/hr. = 1 ton, and 1 Watt =
3.41 BTU/hr. Thus,
1200 sq. ft. requires about 3500 W. (12,000 BTU/hr/3.41BTU//hr./Watt).
Thus, 3 W. will cool one square foot of building space.
(Note: I have seen values as low as 1.6 W and as high
as 9 W. This obviouslydepends on efficiency of the units and other factors
such as insulation. It is probable that with the “open air”
idea of malls, surrounding yourself with much glass that absorbs a tremendous
amount of heat, the requirements will exceed the 3 W/sq. ft. that is
used here.)
Heating requirements are generally in the range of about
10 W/ sq. ft.
Since heating and A/C are probably needed more or less
equally throughout the year, a good working average for both together
would be about 6 W/sq. ft.
Thus, just for heating, A/C, and lighting, a building
would require about 9 W/sq. ft.
Naturally, individual businesses would require additional
amounts of power. For instance, an electronics store displaying 50 TVs
would require about 15,000W additionally just to power these sets.
Nonetheless, just taking 9 W/ sq. ft. as the basic consumption,
our Mall of America would require about 25,000,000 W. of power, or 25
MW.
Thus, if we have 1.5 MW turbines, operating at 33% efficiency
(definitely an overestimate), each would produce about .5 MW.
Thus, we need 50 turbines just to provide the basic needs
of ONE SHOPPING MALL!!
