Tall ceilings can add a really nice spacial design aspect. They make a space, any space, feel larger. Raise the ceiling and instantly you feel as if metaphorical and sensual weight has been lifted off your head.
Buildings and houses built in the late 18th and early 19th century before the advent of air conditioning often incorporated tall ceilings as a natural design element to help keep people cool. This was especially true in areas prone to warm weather.
People have generally understood that warm air rises and tall ceilings kept people cool in warm weather for centuries before the invention of air conditioning, through a process called thermal or air stratification. Air stratification is a natural process wherein the air forms bands of different temperatures in a space with the hottest air rising to form the highest band. The size, height, and number of bands depend on the height of the space, size of the windows, location of HVAC grills and units. Ceiling heights in new construction started shrinking in the 1930’s after air conditioning was invented.
Unfortunately today, tall ceilings can often pose a problem for the same reason—air stratification.
Building codes today commonly call for ceilings with a minimum height of 7′-0″ to 8′-0″ with no specified maximum, this is mostly so tall people won’t smack their heads on everything hanging from the ceiling. new residential construction customarily includes rooms with ceilings at 10′-0″ to 15′-0″ feet high. In commercial and institutional construction you can easily find ceiling heights that exceed 20′-0″ feet. In these tall spaces air can easily stratify in bands that exceed the height of a person. This means that if the space is not properly engineered, you can have the heat on full-blast in winter and still be cold in the room.
Ceiling fans, when properly sized, do a good job of preventing air stratification by keeping the air moving around the room. In the absence of ceiling fans the mechanical system must be powerful enough to overcome the distance to the floor.
I remember working with a general contractor on a project in Chicago. The architect had designed a space with a 25-foot ceiling height and ceiling-flush HVAC grilles. Three of the building’s exterior walls were not insulated at all, and I realized there would be a terrible thermal stratification problem. In order to make sure that the contractor wouldn’t be blamed for the problem I wrote both the architect and the owner a letter describing the problem. I even did the calculations and in doing so I found that the supply air had to be moving at 25 miles per hour when leaving the grill in order to reach the ground. No one listened. I visited the restaurant recently, some 28 months later, and there are significant changes. Additional duct work was installed from the ceiling to within 10 feet of the floor. At the time that I wrote the letter I could have stood on my head and no one would have heard me. Instead, the owner spent more money and time correcting the problem AFTER the fact.
Tip: Deal with issues as early as possible to prevent them from gaining momentum and snowballing into serious problems.
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