Hot Water Distribution

Hot water is carried through the building by pipes arranged in distribution trees. When hot water flows through a single hot water distribution tree, it will cool off as it gets farther from the hot water heater. To get hot water at the end of the run, you have to waste the cooled-off water already in the pipes. With a looped hot water distribution tree, the water circulates constantly. There is still some heat loss in the pipes, but less water has to be run at the fixture before it gets hot. Hot water is always available at each tap in one to two seconds.

Hot water is circulated by use of the thermosiphon principle. This is the phenomenon where water expands and becomes lighter as it is heated. The warmed water rises to where it is used, then cools and drops back down to the water heater, leaving no cold water standing in pipes. Thermosiphon circulation works better the higher the system goes.

Forced circulation is used in long buildings that are too low for thermosiphon circulation, and where friction from long pipe runs slows down the flow. The water heater and a pump are turned on as needed to keep water at the desired temperature. It takes five to ten seconds for water to reach full temperature at the fixture. Forced circulation is common in large one-story residential, school, and factory buildings.

Computer controls can save energy in hotels, motels, apartment houses, and larger commercial buildings. The computer provides the hottest water temperatures at the busiest hours. When usage is lower, the supply temperature is lowered and more hot water is mixed with less cold water at showers, lavatories, and sinks. Distributing cooler water to the fixture results in less heat lost along the pipes. The computer stores and adjusts a memory of the building's typical daily use patterns.

Hot water pipes expand. Expansion bends are installed in long piping runs to accommodate the expansion of the pipes due to heat.

Where the pipes branch out to a fixture, capped lengths of vertical pipe about 0.6 meters (2 ft) long provide expansion chambers to dampen the shock of hot water expansion. Rechargeable air chambers on branch lines adjacent to groups of fixtures are designed to deal with the shock of water expansion. They require service access to be refilled with air.

Waste Plumbing f Each building has a sanitary plumbing system that channels all the waste downward through the building to the municipal sewer or a septic tank below. The sanitary system begins at the sink, bathtub, toilet, and shower drains. It carries wastewater downhill, joining pipes from other drains until it connects with the sewer buried beneath the building. The sanitary system has large pipes to avoid clogs. Since the system is drained by gravity, all pipes must run downhill. Underground pipes for sewage disposal are made out of vitrified clay tile, cast iron, copper, concrete pipe, polyvinyl chloride (PVC) or acrylonitrile-butadiene-styrene (ABS) plastic. The large size of waste pipes, their need to run at a downward angle, and the expense and difficulty of tying new plumbing fixtures into existing waste systems means that the interior designer must be careful in locating toilets.

Until the advent of indoor plumbing, wastes were removed from the building daily for recycling or disposal. Historically, table scraps were fed to animals or composted. Human wastes were thrown from windows into the gutters of the street, or deposited in holes below outhouses. Urban inhabitants continued to dump sewage and garbage in gutters until the 1890s. Rural people dumped wastes into lakes, rivers, or manmade holes in the ground called cesspools, which were fed by rainwater or spring water. These cesspools generated foul smells and created a health hazard.

In the 1700s, shallow wells, springs, or streams provided potable water for farms. Widely separated dry-pit privies (outhouses) produced only limited ground pollution. By the nineteenth century, natural streams were enclosed in pipes under paved city streets. Rain ran into storm sewers and then to waterways. When flush toilets were connected to the storm sewers later in the nineteenth century, the combined storm water and sanitary drainage was channeled to fast-flowing rivers, which kept pollution levels down. Some sewers continued to carry storm water only, and separate sanitary sewers were eventually installed that fed into sewage treatment plants. Older cities still may have a combination of storm sewers, sanitary sewers, and combined sewers, in a complex network that would be difficult and expensive to sort out and reroute.

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