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ARCH 2614/5614 Lecture notes

Jonathan Ochshorn

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Electrical and plumbing systems

The following is based largely on Plumbing, electricity, acoustics: sustainable design methods for architects / Norbert Lechner [electronic resource for Cornell students].

Electrical systems

image of Franklin and kite
Benjamin West's painting of "Benjamin Franklin Drawing Electricity from the Sky" (do not attempt this experiment yourself!).

Water analogy. By analogy to water, electricity is said to "flow," from negative to positive charge. The difference in charge is measured in volts (V = electromotive force). The amount of current is measured in amperes or "amps" (A = current) which is constrained by the resistance of the wire (Ω = resistance measured in ohms — using the Greek letter "omega").

Ohm's law. The fundamental relationship between these terms is Ohm's Law, which states that the current is proportional to the force divided by the resistance (I = E / R) where the current, I, has amp (A) units; the electromotive force, E, has volt (V) units; and the resistance, R, has ohm (Ω) units.

Impedance. Most electrical devices are not quite this efficient, losing a bit more power due to something called "inductive resistance." The total of the resistance and this inductive resistance is called the impedance (Z), which is also measured in ohms. The equation thus becomes: (I = E / Z) where the current, I, has amp (A) units; the electromotive force, E, has volt (V) units; and the impedance, Z, has ohm (Ω) units.

Appliances are not generally placed in series.* Appliances are not placed in series (one after the other) but rather in parallel. In series, one blown-out lightbulb would kill power throughout the whole series. That's why a fuse or circuit breaker is always wired in series.

* An exception occurs where strings of small lights are placed in series; when one goes out, the whole string of lights goes out.

Appliances are placed in parallel. Placing appliances in parallel leaves the voltage intact, while increasing the needed current (amperage), since the total resistance actually decreases compared to the individual resistances of each appliance: For parallel circuits, the total resistance, RT = 1 / (1/R1 + 1/R2 + ... 1/Rn). The current differs for each appliance, depending on its resistance, since the voltage is constant for all appliances, with the total current equal to the sum of the individual currents. A fuse or circuit breaker, placed in series in such a parallel circuit, is designed to limit the total current (amperage), and will shut down the circuit if the maximum amperage (current) is exceeded. Typical household circuits are rated at 15 or 20 amps.

parallel vs series
Appliances in series (top) would lose voltage due to increased total resistance, and one appliance failure would cripple the entire circuit; appliances in parallel (bottom) have increased amperage because total resistance decreases, no loss of voltage, and no failure of the whole circuit in the event of one appliance failure..

Alternating current. Most commonly encountered electricity uses alternating current (AC) rather than direct current (DC). In the US, the direction of the current cycles at a rate of 60 changes per second, or 60 hertz (Hz). This creates some inefficiencies when used to power low-voltage direct current devices such as computers, which require some sort of integral power supply to handle the conversion.

apply power supply
Apple's power supply is part of the power cord..

Voltage measurement. The voltage is determined by the differential between the electromotive force at the two ends of the "battery": typical electric service, at least at the residential or small building scale, supplies three wires: two "hot" wires (black and red) are at 120 V. The third "neutral" wire (white) is at 0 V (because it is connected directly to the earth). When we combine either of the hot wires with the neutral wire, we get a difference of 120 V. This is the normal voltage in the US. However, since the two "hot" wires are 180 degrees out of phase (on purpose), they can be combined to create 120 + 120 = 240 V. service. This is useful for things that need lots of juice, like clothes dryers. A typical panel box alternates the "red" and "black" hot wires so that a double circuit breaker can be easily connected to the red and black wires for 240 volts.

panel box with 120 V and 240 V circuit breakers
This panel box contains mainly 120 volt breakers, but also a 240 volt circuit breaker..

Big buildings may have higher voltages to run things with big motors or large electric needs (e.g., elevators, water heaters).

120 and 240 volts
Circuits can have 120 V. by combining either of the "hot" wires (red or black) with the neutral (white) wire; 240 V. is achieved by combining the two out-of-phase hot wires (red and black).

Power and energy. The unit of electric power is the Watt (W) or, more commonly, the kW = 1000 W.

The power is equal to the force times the current, so that:

Power (watts) = rate at which energy is used = energy / time.

So the measure of electrical energy = power x time = kWh.

Example: How much current is drawn by a 100 W light bulb at 120 V? Since power = force x current, we get:

Circuits/ wiring. Most household circuits are rated at 15 or 20 amps. Some appliances (kitchen, bathroom, air conditioners) require their own circuit, since they draw so much current.

US wire sizes get smaller as the numbers get bigger: 12 AWG (american wire gauge) is common; 14 AWG was often used for smaller loads; the size of circuit breakers corresponds to the size of wire.

Protecting the copper wire is commonly a plastic or rubber casings (nonmetallic sheathed cable, or "Romex").

Romex wire

In most larger buildings, such wire is placed in conduits.

wiring diagrams
The abstract concept of wiring shows a circuit with electricity "traveling" from the positive cathode to the negative anode (left); in reality, the circular nature of such circuits is obscured by the way in which the pathway is squeezed into sheathed cables (right).

Switches are always placed in the "hot" wire, so that off really (mostly) means off. This only works consistently if the plugs are "polarized" so that they only fit into the outlets one way— this is why modern plugs have two different sizes for the two prongs.

polarized plug
Polarized plug (with one prong wider than the other) keeps the hot wire where it belongs.

switch wiring diagrams
In a switch box, the hot wire is cut (joined together by the operation of the switch) while the neutral wire remains continuous.

Grounding. An appliance ground (that extra unsheathed wire) guards against unintended shorts within the appliance that could direct current through the human touching the appliance. Three-prong plugs connect any conductive material on the appliance to the ground wire, which prevents the metal cover from maintaining a charge.

ground wire missing
ground wire
Without a ground wire, an appliance fault that connects the hot wire to the metal case could cause the human holding the appliance to become part of the circuit, especially if he is standing on a wet grounded floor or touching something that is equally well grounded (top). The ground wire, connected to the appliance cover, causes a short circuit which trips the circuit breaker, protecting the human (bottom).

Ground fault interrupters (GFI or GFCI) have an added precautionary device that measures whether any current is moving where it shouldn't—these are mandated where wet conditions (kitchens, bathrooms) could create a serious ground path through a defective appliance.

Distribution. Electricity starts with production of power by generators at 5,000 volts, stepped up to as much as 1,000,000 volts where distances are great; stepped down to 10,000 volts for overhead lines in streets; stepped down to building voltage in "service transformers." Goes to meter; then into the building where it is connected to a panel box with a main circuit breaker. Within the panel box are numerous smaller-amp circuit breakers; each circuit supplies power to a series of plugs or lights. Usually, plugs and lights are not combined on a single circuit so if a power surge from a plugged appliance trips a circuit, the lights stay on.

In larger buildings, the same general arrangement occurs, but on a larger scale. A service transformer may be placed outside or inside the structure in a ventilated vault. It supplies the regular 120 volts, but also various other voltages for things like large motors (elevators), lighting, etc. to an electrical room or closet. There, switchgear controls and distributes the power to various panel boxes placed around the building.

switchgear
Switchgear in a large building (image source).

Images showing a typical distribution network follow:

coal-fired electric plant
1. Electricity is mainly produced in coal-fired plants. (image source).

high-voltage transmission lines
2. It travels great distances through high-voltage transmission lines. (image source).

transformer transformer
3. Transformers reduce the voltage within cities (left image source) and generate revenue as live-action film stars (right image source).

transformer
4. Service transformers, either on the ground or perched up on telephone poles, bring down the voltage to what is used in buildings..

electric meter
5. Electricity is brought down to a meter, and then goes into the house—often into a basement circuit breaker panel pox (image source).


video link

Hopper, Adams House, 1928 watercolor
Edward Hopper's Adams House, 1928 watercolor (image source).

Placing outlets in a room. In general, outlets in a typical room are placed 12 feet apart. See National Electric Code for details.

required outlets in a room
Required distribution of outlets in a typical room, per 2009 IRC: no more than 12 feet apart.

typical electrical plan
Typical residential electrical plan (image source).

Lincoln Hall, Cornell partial electrical plan
Lincoln Hall, Cornell, partial electrical/lighting plan.

Lincoln Hall, Cornell partial electrical plan
Lincoln Hall, Cornell, partial electrical plan.

Plumbing systems

There are two main components of a building's plumbing system:
  1. Water supply

    • public system with water main
    • private well
    • harvesting rainwater

    Potable (rhymes with coat-uh-bull) water = safe to drink (treated; chlorinated)

    Water is often a scarce resource; nevertheless, almost 3/4 of potable water in the US is used for irrigation and flushing toilets—where potable water is not generally required.

    Graywater can be used (water recovered from bathroom sinks, for example), in theory, for flushing toilets; but is not permitted under some building codes.

  2. Sanitary drainage (waste)

    • public sewer system
    • private septic tank
    • composting toilets

    Air gap: Required between water and waste to prevent the waste from back-flowing into the potable water. Vacuum devices can sometimes be used where an air gap is not possible.

    air gap air gap
    Air gap between water supply and sanitary drainage.

    Water.

    Water was traditionally placed in pipes that used gravity to reach all locations in buildings. Where buildings are too high, pumps are used (filling tanks at the top of the building (downfeed), which then use gravity—or pumping from storage tanks at the bottom of the building (upfeed).

    Water can also be pumped into water towers, which then feed communities using gravity.

    water tower
    Water tower.

    Modern filtration systems require pressure (pumps) to force water through hi-tech filters, even when gravity would otherwise be sufficient.

    The Energy Policy Act of 1992 required low-flow toilets, showers, etc.
    • toilets = 1.6 gpf
    • urinals = 1.0 gpf
    • showerheads = 2.5 gpm

    See this classic article by Pulitzer Prize-winning humorist Dave Barry.

    Domestic hot water (versus water heated for hydronic heating systems). US = central hot water heaters in tanks; rest of world = tankless heaters where used.

    hot water heater
    Hot water heater (image source).

    Sanitary drainage.

    Water-borne (sanitary) waste from toilets, sinks, showers, etc. is piped to sewage treatment plants or septic fields, almost always using gravity (i.e., from high points to low points, e.g., to lakes and rivers). Sounds simple, but there is a big problem that needs to be overcome.

    To put it bluntly, that shit stinks (listen to official Outkast sanitary drainage theme song). To prevent sewer gases from entering buildings through open drains, some sort of "trap" is needed.

    trap for sanitary drainage trap for sanitary drainage
    (a) To create a trap, bend a waste pipe so that it traps water—the sewer gas can't come back up from below. But the siphoning action of water heading down the drain draws the trap water with it, and so the trap, configured simply like that, doesn't work. (b) To prevent that siphoning action, the vacuum that would pull the trap water must be broken. This is accomplished by connecting the drain with a so-called "vent," which heads up and out of the building, typically at the roof.

    plumbing diagram
    Typical plumbing diagram showing drains and vent (adapted from Lechner)

    In buildings, water pipes are generally small and can often be threaded through walls. Waste pipes are often larger; 3 or 4 in. pipes may be inserted in stud or CMU walls, but often a plumbing chase is created—two walls with the pipes between them.

    plumbing diagram
    Typical multistory apartment building plumbing chase, adapted from NY Times real estate article.

    Plumbing schematic diagrams are often drawn as isometrics, showing fixtures, drains, and vents, along with required minimum sizes for all the pipes. Examples of acceptable configurations can be found in the 2000 IRC:

    plumbing isometric
    Plumbing isometric showing typical "double-bath-wet-vent arrangements" from the 2000 IRC—Figure P3108.1(2).

    Lincoln Hall, Cornell partial plumbing diagram
    Lincoln Hall, Cornell, partial plumbing riser diagram.

    And here is my own adventure with plumbing: figuring out how to connect new fixtures in an addition to my home to the existing cast-iron waste line in the basement, and to the existing cast-iron vent in the attic.

    plumbing for Ochshorn addition
    Plans show how second-floor addition fixtures connect to existing vent and existing waste pipe.

    plumbing for Ochshorn addition
    Section shows how addition fixtures connect to existing vent and existing waste pipe.

    plumbing for Ochshorn addition plumbing for Ochshorn addition

    plumbing for Ochshorn addition plumbing for Ochshorn addition
    Inserting new waste line into old cast iron pipe (top, left); inserting new vent into old cast iron vent (top, right). Waste line hits floor and runs at low slope until it can join old cast iron pipe (bottom, left); waste lines join 4 inch PVC waste (bottom, right). Images from ochshornDesign.com