Answer: Body Heat
The Mall of America at Bloomington, Minnesota, is the largest shopping center in the United States with over 4.8 million square feet of gross floor space in four floors. With so much square footage, you would expect it to have an absolutely massive heater to keep it warm in the cool Minnesota winters, right? While some retail stores in the mall have small heating systems to adjust their respective temperatures (for example, by making a spa warmer than in other rooms), the mall itself has no central heating.
The architects at Mall took into account the heat that comes from the building's numerous skylights, the waste heat from the lighting, and above all, the enormous amount of heat generated by the tens of thousands of buyers in the facility at all times. From the "About" page of the Mall of America:
MOA does not use central heating; instead, 70 ° C is maintained throughout the year with passive solar energy from 1
Buyers generate so much extra heat, in fact during peak purchases In the winter season (when temperatures in Bloomington can drop to the single-digit range), the mall operates the air conditioning to keep the facility pleasantly cool.