Designing skyscrapers is an extremely complicated art that integrates several different logistic operations, utilities and systems. Plumbing is one of the more challenging problems to solve due to the loss in pressure as water travels up a vertical pipe.
Plumbing engineers found out that as you lift water above a datum, you lose 1 pound per square inch for every 2.3 feet of elevation. This small but incremental loss makes achieving high water pressure at the top of a water column very difficult. Most water fixtures require at least 25 psi to operate or flush properly, so measures to insure consistent water pressure throughout the building must be implemented. As the building get taller, another problem arises as the water pressure at the bottom of a vertical pipe becomes too great for safe operation and building codes.
The early solution to this problem was a water tank mounted on the top of a building with fill pumps at the bottom of the building. Water is supplied to occupants through a simple gravity down feed system.
Today, a system of pressure-reducing valves and sub-risers are used to manage the inconsistent water pressure throughout a skyscraper. Pressure-reducing valves reduce the pressure at the bottom of the building, while sub-risers increase the pressure for the skyscrapers upper floors. Today’s systems lack a main tank, but rather integrate the whole system within a buildings walls and basement.
Water pressure controlling devices are constantly evolving as new concerns about the environment arise and the publics awareness about green building practices increases.
Drainage is another common issue in skyscrapers, and is often just as difficult to solve as water pressure problems. When water falls vertically down a pipe, the water will adhere to the pipe’s walls until the pipe’s cross sectional area is about one-fourth full. Once the gravity propelled water hits a horizontal bend in the pipe, the flow velocity drops dramatically, and fills the pipe considerably more due to the lost speed. It is common practice to use relief or yoke vents to slow the water before it encounters a horizontal flow change. The piping at the base of a vertical drainage column must be secured, as to reduce the risk of breaking joints.
For water to travel down a vertical pipe, air is necessary. Air ventilation must be controlled so that low pressure zones can be created, and the flow of water can continue. The low pressure zones should not be placed near a fixture, or else poor drainage could occur (often recognized by a gulping sound and poor flow performance). However, it is fine to place air vents in the fixtures themselves to increase water flow.
Most high-rise plumbing systems use Type-L copper. On some very tall buildings, stainless steel must be used because of the extra pressure.