STONE ELECTRIC SERVICES

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Information provided by Answers.com:

An electric meter or energy meter is a device that measures the amount of electrical energy supplied to or produced by a residence, business or machine.

The most common type is a kilowatt hour meter. When used in electricity retailing, the utilities record the values measured by these meters to generate an invoice for the electricity. They may also record other variables including the time when the electricity was used.

Unit of measurement

Panel-mounted solid state electricity meter, connected to a 2MVA electricity substation. Remote current and voltage sensors can be read and programmed remotely by modem and locally by infra-red. The circle with two dots is the infra-red port. Tamper-evident seals can be seen.

The most common unit of measurement on the electricity meter is the kilowatt hour, which is equal to the amount of energy used by a load of one kilowatt over a period of one hour, or 3,600,000 joules. Some electricity companies use the SI megajoule instead.

Demand is normally measured in watts, but averaged over a period, most often a quarter or half hour.

Reactive power is measured in "Volt-amperes reactive", (varh) in kilovar-hours. A "lagging" or inductive load, such as a motor, will have negative reactive power. A "leading", or capacitive load, will have positive reactive power.

Volt-amperes measures all power passed through a distribution network, including reactive and actual. This is equal to the product of root-mean-square volts and amperes.

Distortion of the electric current by loads is measured in several ways. Power factor is the ratio of resistive (or real power) to volt-amperes. A capacitive load has a leading power factor, and an inductive load has a lagging power factor. A purely resistive load (such as a fillament lamp, heater or kettle) exhibits a power factor of 1. Current harmonics are a measure of distortion of the wave form. For example, electronic loads such as computer power supplies draw their current at the voltage peak to fill their internal storage elements. This can lead to a significant voltage drop near the supply voltage peak which shows as a flattening of the voltage waveform. This flattening causes odd harmonics which are not permissible if they exceed specific limits, as they are not only wasteful, but may interfere with the operation of other equipment. Harmonic emissions are mandated by law in EU and other countries to fall within specified limits.

Other units of measurement

In addition to metering based on the amount of energy used, other types of metering are available.

Meters which measured the amount of charge (coulombs) used, known as ampere-hour meters, were used in the early days of electrification. These were dependent upon the supply voltage remaining constant for accurate measurement of energy usage, which was not a likely circumstance with most supplies.

Some meters measured only the length of time for which current flowed, with no measurement of the magnitude of voltage or current being made. These were only suited for constant load applications.

Neither type is likely to be used today.

Types of meters

Mechanism of electromechanical induction meter. (1) - Voltage coil - many turns of fine wire encased in plastic, connected in parallel with load. (2) - Current coil - three turns of thick wire, connected in series with load. (3) - Stator - concentrates and confines magnetic field. (4) - Aluminium rotor disc. (5) - rotor brake magnets. (6) - spindle with worm gear. (7) - display dials - note that the 1/10, 10 and 1000 dials rotate clockwise while the 1, 100 and 10000 dials rotate counter-clockwise.

This mechanical electricity meter has every other dial rotating counter-clockwise.

Three-phase electromechanical induction meter, metering 100 A 230/400 V supply. Horizontal aluminium rotor disc is visible in centre of meter.

Modern electricity meters operate by continuously measuring the instantaneous voltage (volts) and current (amperes) and finding the product of these to give instantaneous electrical power (watts) which is then integrated against time to give energy used (joules, kilowatt-hours etc). The meters fall into two basic categories, electromechanical and electronic.

Electromechanical meters

The most common type of electricity meter is the Thomson or electromechanical induction watt-hour meter, invented by Elihu Thomson in 1888.^[1][2]

Technology

The electromechanical induction meter operates by counting the revolutions of an aluminium disc which is made to rotate at a speed proportional to the power. The number of revolutions is thus proportional to the energy usage. It consumes a small amount of power, typically around 2 watts.

The metallic disc is acted upon by two coils. One coil is connected in such a way that it produces a magnetic flux in proportion to the voltage and the other produces a magnetic flux in proportion to the current. The field of the voltage coil is delayed by 90 degrees using a lag coil. [1]This produces eddy currents in the disc and the effect is such that a force is exerted on the disc in proportion to the product of the instantaneous current and voltage. A permanent magnet exerts an opposing force proportional to the speed of rotation of the disc - this acts as a brake which causes the disc to stop spinning when power stops being drawn rather than allowing it to spin faster and faster. This causes the disc to rotate at a speed proportional to the power being used.

The type of meter described above is used on a single-phase AC supply. Different phase configurations use additional voltage and current coils.

Reading

The aluminium disc is supported by a spindle which has a worm gear which drives the register. The register is a series of dials which record the amount of energy used. The dials may be of the cyclometer type, an odometer-like display that is easy to read where for each dial a single digit is shown through a window in the face of the meter, or of the pointer type where a pointer indicates each digit. It should be noted that with the dial pointer type, adjacent pointers generally rotate in opposite directions due to the gearing mechanism.

The amount of energy represented by one revolution of the disc is denoted by the symbol Kh which is given in units of watt-hours per revolution. The value 7.2 is commonly seen. Using the value of Kh, one can determine their power consumption at any given time by timing the disc with a stopwatch. If the time in seconds taken by the disc to complete one revolution is t, then the power in watts is . For example, if Kh = 7.2, as above, and one revolution took place in 14.4 seconds, the power is 1800 watts. This method can be used to determine the power consumption of household devices by switching them on one by one.

Most domestic electricity meters must be read manually, whether by a representative of the power company or by the customer. Where the customer reads the meter, the reading may be supplied to the power company by telephone, post or over the internet. The electricity company will normally require a visit by a company representative at least annually in order to verify customer-supplied readings and to make a basic safety check of the meter.

Accuracy

In an induction type meter, creep is a phenomenon that can adversely affect accuracy, that occurs when the meter disc rotates continuously with potential applied and the load terminals open circuited. A test for error due to creep is called a creep test.

Solid state meters

Some newer electricity meters are solid state and display the power used on an LCD, while newer electronic meters can be read automatically.

In addition to measuring electricity used, solid state meters can also record other parameters of the load and supply such as maximum demand, power factor and reactive power used etc. They can also include electronic clock mechanisms to compute a value, rather than an amount of electricity consumed, with the pricing varying by the time of day, day of week, and seasonally.

Solid state electricity meter used in a home in Holland.

Technology

Most solid-state meters use a current transformer to measure the current. This means that the main current-carrying conductors need not pass through the meter itself and so the meter can be located remotely from the main current-carrying conductors, which is a particular advantage in large-power installations. It is also possible to use remote current transformers with electromechanical meters though this is less common.

Historically, rotating meters could report their power information remotely, using a pair of contact closures attached to a KYZ line. In this scheme, line "K" is attached to two single-pole single-throw switches "Y" and "Z". "Y" and "Z" open and close as the meter's disk rotates. As the meter rotates in one direction, Y closes, then Z closes, then Y opens, then Z opens. When it rotates in the opposite direction, showing export of power, the sequence reverses. KYZ outputs were historically attached to "totalizer relays" feeding a "totalizer" so that many meters could be read all at once in one place.

KYZ outputs are also the classic way of attaching electric meters to programmable logic controllers, HVACs or other control systems. Some modern meters also supply interfaces to PLCs, or a contact closure that warns when the meter detects a demand near a higher tariff.

Communication technologies

High end electronic meters may now be equipped with a range of communication technologies including Low Power Radio, GSM, GPRS, Bluetooth, IrDA apart from the now conventional RS-232 and RS-485 wired link. They now store the entire usage profiles with time stamps and relay them at a click of a button. The demand readings stored with the profiles accurately indicate the load requirements of the customer. This load profile data is processed at the utilities and renders itself to a variety of representations, all sorts of graphs, reports et el. Remote meter reading is an application of telemetry. Often, meters designed for semi-automated reading have a serial port on that communicates by infrared LED through the faceplate of the meter. In some apartment buildings, a similar protocol is used, but in a wired bus using a serial current loop to connect all the meters to a single plug. The plug is often near the mailboxes.

In the European Union, the most common infrared and protocol is "FLAG", a simplified subset of mode C of IEC 61107. In the U.S. and Canada, the favoured infrared protocol is ANSI C12.18. Some industrial meters use a protocol for programmable logic controllers (Modbus). The most modern protocol proposed for this purpose is DLM/COSEM which can operate over any medium, including serial ports. The data can be transmitted by Zigbee, WiFi, telephone lines or over the power lines themselves. Some meters can be read over the internet.

Some meters have an open collector S0 output that gives 32-100 ms pulses for a constant amount of used electrical energy. Usually 1000-10000 pulses per kWh. Output is limited to max 27 V DC and 27 mA DC. The output usually follows the DIN 43864 standard. ^{[3] [4]}

Automatic reading

AMR (Automatic Meter Reading) and RMR (Remote Meter Reading) describe various systems that allow meters to be checked by without the need to send a meter reader out. This can be effectively achieved using off-site metering, that is an electronic meter is placed at the junction point where all the connections originate, inaccessible to the end-user, and it relays the readings via the AMR technology to the utility.

Design

Basic Block Diagram of an Electronic Energy Meter

As in the block diagram, the meter has a power supply, a metering engine, A processing and communication engine i.e a microcontroller, other add-on modules such as RTC, LCD display, communication ports/modules etc.

Metering engine

The metering engine is given the voltage and current inputs and has a voltage reference, samplers and quantisers followed by an ADC section to yield the digitised equivalents of all the inputs. These inputs are then processed using a Digital Signal Processor to calculate the various metering parameters such as powers, energies etc.

The largest source of long-term errors in the meter is drift in the preamp, followed by the precision of the voltage reference. Both of these vary with temperature as well, and vary wildly because most meters are outdoors. Characterizing and compensating for these is a major part of meter design.

Processing and communication section

This section has the responsibility of calculating the various derived quantities from the digital values generated by the metering engine. This also has the responsibility of communication using various protocols and interface with other addon modules connected as slaves to it.

RTC and other add-on modules

These are attached as slaves to the processing and communication section for various input/output functions. On a modern meter most if not all of this will be implemented inside the microprocessor, such as the Real Time Clock (RTC), LCD controller, temperature sensor, memory and analog to digital converters.

Multiple tariff (variable rate) meters

Electricity retailers may wish to charge customers different tariffs at different times of the day to better reflect the costs of generation and transmission. Since it is not generally possible to store electricity during a period of low demand for use during a period of high demand, costs will vary significantly depending on the time of day. Low cost generation capacity (baseload) such as coal can take many hours to reach peak efficiency from a cold start, meaning a surplus in times of low demand, whereas high cost but flexible generating capacity (such as gas turbines) must be kept available to respond at a moment's notice (spinning reserve) to periods of peak demand, perhaps being used for a few minutes per day, or even year, which is very expensive.

Some multiple tariff meters use different tariffs for different amounts of demand. These are usually industrial meters.

Domestic usage

Domestic variable-rate meters generally permit two to three tariffs ("peak", "off-peak" and "shoulder") and in such installations a simple electromechanical time switch may be used. Historically, these have often been used in conjunction with electrical storage heaters or hot water storage systems.

Multiple tariffs are made easier by time of use (TOU) meters which incorporate or are connected to a time switch and which have multiple registers.

Switching between the tariffs may happen via a radio-activated switch rather than a time switch to prevent tampering with a sealed time switch to obtain cheaper electricity.

United Kingdom

Economy 7 Meter and Teleswitcher

Radio-activated switching is common in the UK, with a nightly data signal sent within the longwave carrier of BBC Radio 4, 198 kHz. The time of off-peak usage is between 12.30am - 7.30am, and this is designed to power storage heaters and immersion heaters. In the UK, such tariffs are branded Economy 7 or White Meter. The popularity of such tariffs has declined in recent years, at least in the domestic market, due to the (perceived or real) deficiencies of storage heaters and the low cost of natural gas.

Some meters using Economy 7 switch the entire electricity supply to the cheaper rate during the 7 hour night time period, not just the storage heater circuit. The downside of this is that the daytime rate will be a touch higher, and standing charges may be a little higher too. For instance, normal rate electricity may be 7p per kWh, whereas Economy 7's daytime rate might be 7.5p per kWh, but only 2.8p per kWh at night. Timer switches installed on washing machines, tumble dryers, dishwashers and immersion heaters may be set so that they switch on only when the rate is lower.

Commercial usage

Large commercial and industrial premises may use electronic meters which record power usage in blocks of half an hour or less. This is because most electricity grids have demand surges throughout the day, and the power company may wish to give price incentives to large customers to reduce demand at these times. These demand surges often corresponding to meal times or, famously, to advertisements in popular television programmes.

Appliance energy meters

Plug in electricity meters (or "Plug load" meters) measure energy used by individual appliances. The meter is plugged into an outlet, and the appliance to measured is plugged into the meter. Such meters can help in energy conservation by identifying major energy users, or devices that consume excessive standby power. Examples of plug in meters include various Kill A Watt, Plugwise[2], and Watts Up[3] Meters. A power meter can often be borrowed from the local power authorities[4] or a local public library[5][6].

In-home energy use displays

Main article: Home energy monitor

A potentially powerful means to reduce household energy consumption is to provide real-time feedback to homeowners so they can change their energy using behavior. Recently, low-cost energy feedback displays, such as The Energy Detective, Eco-eye[7], wattson,[8], PowerWatch[9], or Cent-a-meter, have become available. A study using the similar PowerCost Monitor[10] deployed in 500 Ontario homes by Hydro One showed an average 6.5% drop in total electricity use when compared with a similarly sized control group. Hydro One subsequently offered free power monitors to 30,000 customers based on the success of the pilot.[11]

Smart meters

Main article: Smart meter

Smart meters go a step further than simple AMR (automatic meter reading). They offer additional functionality including a real-time or near real-time reads, power outage notification, and power quality monitoring. They allow price setting agencies to introduce different prices for consumption based on the time of day and the season.

These price differences can be used to reduce peaks in demand (load shifting or peak lopping), reducing the need for additional power plants and in particular the higher polluting and costly to operate natural gas powered peaker plants. The feedback they provide to consumers has also been shown to cut overall energy consumption.[12]

Another type of smart meter uses nonintrusive load monitoring to automatically determine the number and type of appliances in a residence, how much energy each uses and when. This meter is used by electric utilities to do surveys of energy use. It eliminates the need to put timers on all of the appliances in a house to determine how much energy each uses.

Prepayment meters

Prepayment meter and magnetic stripe tokens, from a rented accommodation in the UK. The button labeled A displays information and statistics such as current tariff and remaining credit. The button labeled B activates a small amount of emergency credit should the customer run out.

The standard business model of electricity retailing involves the electricity company billing the customer for the amount of energy used in the previous month or quarter. In some countries, if the retailer believes that the customer may not pay the bill, a prepayment meter may be installed. This requires the customer to make advance payment before electricity can be used. If the available credit is exhausted then the supply of electricity is cut off by a relay.

In the UK, mechanical prepayment meters used to be common in rented accommodation. Disadvantages of these included the need for regular visits to remove cash, and risk of theft of the cash in the meter.

Modern solid-state electricity meters, in conjunction with smart card technology, have removed these disadvantages and such meters are commonly used for customers considered to be a poor credit risk. In the UK, one system is the PayPoint network, where rechargeable tokens (Quantum cards for natural gas, or plastic "keys" for electricity) can be loaded with whatever money the customer has available.

Prepayment key

A similar system, with 2 way communication smart cards, has been used for more than 1 million meters by Elektromed in Turkey.

In South Africa and Northern Ireland prepaid meters are recharged by entering a unique, encoded twenty digit number using a keypad. This makes the tokens, essentially a slip of paper, very cheap to produce.

Around the world, experiments are going on, especially in developing countries, to test pre-payment systems. In some cases, a lack of social acceptance has led to non-implementation of this technology. Utilities are finding it to depend on one supplier and multiple supplier systems demand their own system and network connectivity. There are various groups, such as the Standard Transfer Specification (STS) association, which promote common standards for prepayment metering systems across manufacturers. However in spite of these efforts prepayment meter market had not spread except in South Africa.

Time of day metering

Time of Day metering (TOD), also known as Time of Usage (TOU) or Seasonal Time of Day (SToD), metering involves dividing the day, month and year into tariff slots and with higher rates at peak load periods and low tariff rates at off-peak load periods. While this can be used to automatically control usage on the part of the customer (resulting in automatic load control), it is often simply the customers responsibility to control his own usage, or pay accordingly (voluntary load control). This also allows the utilities to plan their transmission infrastructure appropriately. See also Demand-side Management (DSM).

TOD metering normally splits rates into two segments, peak and off-peak, with peak typically occurring during the day (non-holiday days only), such as from 1 pm to 9 pm Monday through Friday during the summer and from 6:30 am to 12 noon and 5 pm to 9 pm during the winter. The times of peak demand/cost will vary in different markets around the world.

Large commercial users can purchase power by the hour using either forecast pricing or real time pricing. Prices range from we pay you to take it (negative) to $1000/MWh (100 cents/kWh).^[5]

Some utilities allow residential customers to pay hourly rates, such as Illinois, which uses day ahead pricing.^[6][7]

Power export metering

See also: Net metering

Many electricity customers are installing their own electricity generating equipment, whether for reasons of economy, redundancy or environmental reasons. When a customer is generating more electricity than required for his own use, the surplus may be exported back to the power grid. Customers that generate back into the "grid" usually must have special equipment and/or safety devices to protect the grid components (as well as the customer's own) in case of faults (electrical short circuits) or maintenance of the grid (say voltage potential on a downed line going into an exporting customers facility).

This exported energy may be accounted for in the simplest case by the meter running backwards during periods of net export, thus reducing the customer's recorded energy usage by the amount exported. This in effect results in the customer being paid for his/her exports at the full retail price of electricity. Unless equipped with a detent or equivalent, a standard meter will accurately record power flow in each direction by simply running backwards when power is exported. Such meters are no longer legal in the UK but instead a meter capable of separately measuring imported and exported energy is required. Suppliers offer different rates for imported and exported electricity while meters that go backwards provides a different area of risk for the industry.

Lately, upload sources typically originate from renewable sources (e.g., wind turbines, photovoltaic cells), or gas or steam turbines, which are often found in cogeneration systems. Another potential upload source that has been proposed is plug-in hybrid car batteries (vehicle-to-grid power systems). This requires a "smart grid," which includes meters that measure electricity via communication networks that require remote control and give customers timing and pricing options. Vehicle-to-grid systems could be installed at workplace parking lots and garages and at park and rides and could help drivers charge their batteries at home at night when off-peak power prices are cheaper, and receive bill crediting for selling excess electricity back to the grid during high-demand hours.

Ownership

Following the deregulation of electricity supply markets in many countries (e.g., UK), the company responsible for an electricity meter may not be obvious. Depending on the arrangements in place, the meter may be the property of the meter Operator, electricity distributor, the retailer or for some large users of electricity the meter may belong to the customer.

The company responsible for reading the meter may not always be the company which owns it. Meter reading is now sometimes subcontracted and in some areas the same person may read gas, water and electricity meters at the same time.

Location

Current transformers used as part of metering equipment for three-phase 400 A electricity supply. The fourth neutral wire does not require a current transformer because current cannot flow in this wire without also flowing in one of the three phase wires.

Commercial power meter

The location of an electricity meter varies with each installation. Possible locations include on a power pylon serving the property, in a street-side cabinet (meter box) or inside the premises adjacent to the consumer unit / distribution board. Electricity companies may prefer external locations as the meter can be read without gaining access to the premises but external meters may be more prone to vandalism.

Current transformers permit the meter to be located remotely from the current-carrying conductors. This is common in large installations. For example a substation serving a single large customer may have metering equipment installed in a cabinet, without bringing heavy cables into the cabinet.

Connection

In North America, it is common for smaller electricity meters to plug into a standardised socket. This allows the meter to be replaced without disturbing the wires to the socket. Some sockets may have a bypass while the meter is removed for service. The amount of electricity used without being recorded during this small time is considered insignificant when compared to the inconvenience which might be caused to the customer by cutting off the electricity supply.

In the UK, the supply and load terminals are normally provided in the meter housing itself, at least for smaller meters (up to around 100 A).

Tampering and security

A Duke Energy technician removes the tamper-proof seal from a electricity meter at a residence in Durham, North Carolina.

Meters can be manipulated to make them under-register, effectively allowing power use without paying for it. This may be dangerous and illegal.

In some markets, the enforcement actions enabled by modern anti-tampering meters may be inexpensive compared to the revenue losses and public inconveniences they prevent.^{[citation needed]} Power companies may install remote-reporting meters specifically to enable remote detection of tampering, and specifically to discover theft of energy.

When tampering is detected, the normal tactic, legal in most areas, is to switch the subscriber to a "tampering" tariff charged at the meter's maximum designed current. At US$ 0.095/kWh, a standard residential 50 A meter causes a legally collectible charge of about US$ 5,000.00 per month. Meter readers are trained to spot signs of tampering, and with crude mechanical meters, the maximum rate may be charged each billing period until the tamper is removed, or the service is disconnected.

A common method of tampering on older meters is to attach magnets to the outside of the meter. These act in addition to the braking magnets already installed in the meter, causing the meter to under-register. Rectified DC loads will not cause the meter to under-register the amount of power used to a significant degree, nor will a combination of capacitive and inductive load. An electricity meter registers real power (watts), not apparent power (VA); changing the reactive load has no effect on the meter. Similarly, a meter will not run backwards unless you are generating power and feeding it back on the grid from your house (and if detent equipped, will not run backward even then). This is called "net metering", and is commonly used where homeowners have photovoltaic or wind energy systems installed.

The owner of the meter normally secures the meter against tampering. Revenue meters mechanism and connections are sealed. Meters may also measure VAR-hours (the reflected load), neutral and DC currents (elevated by most electrical tampering), ambient magnetic fields, etc. Even simple mechanical meters can have mechanical flags that are dropped by magnetic tampering or large DC currents.

Newer computerized meters usually have counter-measures against tampering. AMR (Automated Meter Reading) meters often have sensors that can report opening of the meter cover, magnetic anomalies, extra clock setting, glued buttons, reversed or switched phases etc. These features are normally present in computerized meters.

Some fraud perpetrators bypass the meter, wholly or in part. This normally causes an increase in neutral current at the meter, which is detected and billed at normal rates by standard tamper-resistant meters.^{[citation needed]} However, most residential meters in use in the United States are single-phase 240 volt meters that are coupled only to the energized lines with the neutral bypassing the meter entirely. This common setup is unable to detect neutral currents.

Even if the meter's neutral connector is completely disconnected, and the building's neutral is grounded to the phantom loop, causing an unsafe house or building, metering at the substation can alert the operator to tampering. Substations, interties and transformers normally have a high-accuracy meter for the area served. Power companies normally investigate discrepancies between the total billed and the total generated, in order to find and fix power distribution problems. These investigations are an effective method of discovering tampering.

In North America power thefts are often connected with indoor marijuana grow operations. Narcotics detectives associate abnormally high power usage with the lighting such operations require. Indoor marijuana growers aware of this are particularly motivated to steal electricity simply to conceal their usage of it.

Privacy issues

The introduction of advanced meters in residential areas has produced additional privacy issues that may affect ordinary customers. These meters are often capable of recording energy usage very frequently, usually once every 15, 30 or 60 minutes. Readings of this sort can be used for surveillance, revealing information about people's possessions and behavior.^[8] For instance, it can show when the customer is away for extended periods. Nonintrusive load monitoring gives even more detail about what appliances people have and their living and use patterns.

A more detailed and recent analysis of this issue was performed by the Illinois Security Lab, as discussed on the Attested Metering project website.

History

Ottó Bláthy's electric Wattmeter (Budapest 1889)

The first specimen of the kilowatt-hour meter produced on the basis of Hungarian Ottó Bláthy's patent and named after him was presented by the Ganz Works at the Frankfurt Fair in the autumn of 1889, and the first induction kilowatt-hour meter was already marketed by the factory at the end of the same year. These were the first alternating-current wattmeters, known by the name of Bláthy-meters.

WATER HEATING SERVICES

Information provided by Answers.com

Water heating is a thermodynamic process using an energy source to heat water above its initial temperature. Typical domestic uses of hot water are for cooking, cleaning, bathing, and space heating. In industry, both hot water and water heated to steam have many uses.

Domestically, water is traditionally heated in vessels known as kettles, cauldrons, pots, or coppers. These vessels heat a batch of water but do not produce a continual supply. Appliances for providing a more-or-less constant supply of hot water are variously known as water heaters, boilers, heat exchangers, calorifiers, or geysers depending on whether they are heating potable or non-potable water, in domestic or industrial use, their energy source, and in which part of the world they are found. In domestic installations, potable water heated for uses other than space heating is sometimes known as domestic hot water (DHW).

In many countries the most common energy sources for heating water are fossil fuels: natural gas, liquefied petroleum gas, oil, or sometimes solid fuels. These fuels may be consumed directly or by the use of electricity (which may derive from any of the above fuels or from nuclear or renewable sources). Alternative energy such as solar energy, heat pumps, hot water heat recycling, and sometimes geothermal heating, may also be used as available, usually in combination with backup systems supplied by gas, oil or electricity.

In some countries district heating is a major source of water heating. This is especially the case in Scandinavia. District heating systems make it possible to supply all of the energy for water heating as well as space heating from waste heat from industries, power plants, incinerators, geothermal heating, and central solar heating. The actual heating of the tap water is performed in heat exchangers at the consumers premises. Generally the consumer needs no backup system due to the very high availability of district heating systems.

Contents [hide] 1 Types of water heating appliance 1.1 Gravity system 1.2 Instantaneous water heaters 1.3 Storage systems 2 Thermodynamics and economics 3 Tank-type water heaters 3.1 Insulation and other improvements 3.2 Electric water heating 4 Tankless heaters 4.1 Combination Boilers 4.2 Various types and their advantages 4.3 Advantages 4.4 Disadvantages 5 Solar water heaters 6 Geothermal heating 7 Water heater safety 8 See also 9 References 10 External links

Types of water heating appliance

Water for space heating can be heated by fossil fuels in a boiler. Potable water may be heated in a separate appliance: this is common practice in the USA where warm-air space heating is usually employed.

Gravity system

Where a space-heating water boiler is employed the traditional arrangement in the UK is to use boiler-heated ("primary") water to heat ("secondary") water in a cylindrical vessel (usually made of copper) containing potable water supplied from a cold water storage tank, usually in the roof space of the building. This produces a fairly steady supply of DHW at low static pressure head but usually with a good flow. Water heating appliances in most other parts of the world do not use cold water storage tanks but heat water at pressures close to that of the incoming mains water supply.

Instantaneous water heaters

Stand-alone appliances for instantaneously heating water for DHW (Domestic Hot Water) are known in North America as tankless heaters, elsewhere as multipoint heaters, geysers or Ascots. In Australia and New Zealand there was a similar wood fired appliance known as the chip heater.

A common arrangement where hot-water space heating is employed is for the boiler to also heat potable water giving a continuous supply of DHW without any extra equipment required. Appliances capable of supplying both space-heating and DHW are known as combination (or "combi") boilers.

Although instantaneous heaters can give a continuous supply of DHW the rate at which they can produce it is limited by the thermodynamics of heating water from the available fuel supplies.

Storage systems

Another popular arrangement where higher flow rates are required (although for limited periods) is to heat water in a pressure vessel capable of withstanding a hydrostatic pressure close to that of the incoming mains supply. (A pressure reducing valve is usually employed to limit the pressure to a safe level for the vessel.)

In North America these vessels are known as tanks and may incorporate a gas or oil burner heating the water directly.

Where hot-water space heating boilers are used DHW cylinders are usually heated indirectly by primary water from the boiler, or by an electric immersion heater (often as backup to the boiler). In the UK these vessels are known as unvented cylinders (or commonly as Megaflos after the brand name of a widely-used model). In the US, when connected to a boiler they are known as indirect-fired water heaters.

Thermodynamics and economics

Water enters residences in the US at about 10 °C (50 °F) (varies with latitude and season). Hot water temperatures of 40–49 °C (105–120 °F) are preferred for dish-washing, laundry and showering; requiring the water temperature to be raised about 30 °C (54 °F) or more, if the hot water is later mixed with cold water. The Uniform Plumbing Code reference shower flow rate is 2.5 gpm (gallons per minute); sink and dishwasher usages range from 1–3 gpm.

Natural gas in the U.S. is measured in CCF (100 cubic feet), which is converted to a standardized heat content unit called the therm, equal to 100,000 British thermal units. A BTU is the energy required to raise one pound of water by one degree Fahrenheit. A U.S. gallon of water weighs 8.3 pounds. So, to raise a 40-gallon tank of 55 °F water up to 105 °F would require 40 x 8.3 x (105 − 55) / 100,000 BTU, or approximately 0.17 CCF, at 100% efficiency. A 40,000 BTU (per hour) heater would take 25 minutes to do this, at 100% efficiency. At $1 per therm, the cost of the gas would be about 17 cents.

In comparison, a typical electric water heater has a 4500 watt heating element, which if 100% efficient results in a heating time of about 1.1 hours. Since 16,600 BTU is roughly 4.9 kWh, at 10 cents/kWh the electricity would cost $0.49. Operating a shower at 2.5 gpm and 104 degrees Fahrenheit is equivalent to operating a 13.2 kW appliance.^[1] In the UK, domestic electric immersion heaters are usually rated at 3 kilowatts.^[2]

Energy efficiencies of tank water heaters in residential use can vary greatly, particularly based on manufacturer and model. However, electric heaters tend to be slightly more efficient with recovery efficiency (how efficient energy is transferred to the water) reaching about 98%. Gas fired heaters have maximum recovery efficiencies of only about 86% (the remaining heat is lost with the flue gasses). Overall energy factors can be as low as 80% for electric and 50% for gas systems.^[3]

A tankless water heater operating at those same power levels (at 100% efficiency) would be able to supply 1.6 gpm continuously, raising the temperature by 50 °F. The same unit could supply 1.3 gpm while raising the temperature by 60 °F. To be able to handle a full house load of multiple uses (at least 5 gpm) with a centralized tankless water heater would require three to four times this power level — somewhat difficult to achieve with natural gas, and very difficult to achieve with electricity. Many tankless water heaters can use over 100,000 BTU/h during high flow, and so require especially large power supplies.

Unfortunately, it takes a great deal of energy to heat water, as one may experience when attempting to boil a gallon of water on a stove. For this reason, tankless on-demand water heaters need to have a very large energy source to be usable. A wall outlet, by comparison, can only source enough energy to warm a disappointingly small amount of water: about 0.17 gpm at 40 °C temperature elevation.

Tank-type water heaters

A storage water heater

In household and commercial usage, most water heaters in North America are of the tank type. Also called storage water heaters, these consist of a cylindrical tank in which water is kept continuously hot and ready for use. Typical sizes for household use range from 75 to 400 litres (20 to 100 U.S. gallons). These may use electricity, natural gas, propane, heating oil, solar, or other energy sources. Natural gas heaters are most popular in the United States and most European countries, since the gas is often conveniently piped throughout cities and towns and currently is the cheapest to use. Compared to tankless heaters, storage water heaters have the advantage of using energy (gas or electricity) at a relatively slow rate, storing the heat for later use. Larger tanks tend to provide hot water with less temperature fluctuation at moderate flow rates.

Storage water heaters in the United States and New Zealand are typically vertical, cylindrical tanks, usually standing on the floor or on a platform raised a short distance above the floor. Storage water heater tanks in Spain are typically horizontal. In India, they are mainly vertical. In apartments they can be mounted in the ceiling space over laundry-utility rooms.

In western countries, where ambient temperature is colder, tiny point-of-use electric storage water heaters with capacities ranging from 8 to 32 litres (2 to 6 gallons) are made for installation in kitchen and bath cabinets or on the wall above a sink. They typically use low power heating elements, about 1 kW to 1.5 kW, and can provide hot water long enough for hand washing, or, if plumbed into an existing hot water line, until hot water arrives from a remote high capacity water heater. They are sometimes used when retrofitting a pump and recirculating plumbing in a building is too costly or impractical. Since they maintain water temperature thermostatically, they will supply hot water at extremely low flow rates, unlike tankless heaters.

In tropical countries, like Singapore, India: An ideal storage water heater may vary from 10 L to 35 L Usage of 6 L tanks is not uncommon. Smaller tanks are sufficient as ambient weather and water temperature are moderate.

The inner tank of the Water heater is the single most important feature of a water heater. The best heaters have a copper container. The second most important feature may be the type of heating element. The cartridge elements score over tubular elements.

Insulation and other improvements

In general, the more tank insulation the better, since it reduces standby heat loss. Tanks are available with insulation ratings ranging from R-6 to R-24. It may be possible to add an extra insulating blanket or jacket on the outside of a poorly insulated tank to reduce heat loss.^[4] The most common type of water heater blanket is fiberglass insulation with a vinyl film on the outside. The insulation is wrapped around the tank and the ends are taped together. It is important that the blanket be the right size for the tank and not block air flow or cover safety and drainage valves, the controls, or block airflow through the exhaust vent, if any. In very humid locations, adding insulation to an already well-insulated tank may cause condensation problems, potentially causing rust, mold, or operational problems.

Modern water heaters have PUF (Polyurethane Foam) insulation. In countries where serviceability is very important, PUF capsules are kept between the inner tank and the outer body. Depending upon the insulation efficiency, star rating is given in India.

Other improvements include check valve devices at their inlet and outlet, cycle timers, electronic ignition in the case of fuel-using models, sealed air intake systems in the case of fuel-using models, and pipe insulation. The sealed air-intake system types are sometimes called "band-joist" intake units. "High efficiency" condensing units can convert up to 98% of the energy in the fuel to heating the water. The exhaust gases of combustion are cooled and are mechanically ventilated either through the roof or through an exterior wall. At high combustion efficiencies a drain must be supplied to handle the water condensed out of the combustion products which are primarily carbon dioxide and water vapor.

In traditional plumbing in the United Kingdom the space-heating boiler is set up to heat a separate hot water cylinder or hot water tank for potable hot water. Such tanks are often fitted with an auxiliary electrical immersion heater for a quick temperature boost. Heat from the space-heating boiler is transferred to the potable water tank by means of a heat exchanger, and the boiler operates at a higher temperature than the potable hot water supply. Most potable water heaters in North America are completely separate from the space heating units.

Residential combustion water heaters manufactured since 2003 in the United States have been redesigned to resist ignition of flammable vapors and incorporate a thermal cutoff switch, per ANSI Z21.10.1. The first feature attempts to prevent vapors from flammable liquids and gasses in the vicinity of the heater from being ignited and thus causing a house fire or explosion. The second feature prevents tank overheating due to unusual combustion conditions. These safety requirements were made based on homeowners storing, and sometimes spilling, gasoline or other flammable liquids near their water heaters and causing fires. Since most of the new designs incorporate some type of flame arrestor screen, they require monitoring to make sure they don't become clogged with lint or dust, reducing the availability of air for combustion. If the flame arrestor becomes clogged, the thermal cutoff may act to shut down the heater.

A wetback stove or wetback heater is the name (used in New Zealand at least) for a simple household secondary water-heater using incidental heat. It typically consists of a hot water pipe running behind a fireplace or stove (rather than hot water storage), and has no facility to limit the heating. In the UK, this is called a back boiler. Modern wetbacks may run the pipe in a more sophisticated design to assist heat-exchange.

Electric water heating

For small electric boilers, see electric water boiler.

In the UK, electric water heating is often done by an immersion heater fitted near the bottom of the hot water tank. The immersion heater is a metal tube containing an insulated electric resistance heater which is usually rated at 3 kilowatts.

Because tank-type water heaters store heat, electrical water heaters can be a good match for an intelligent electrical power distribution system, heating when the electrical grid load is low and turning off when the load is high. This could be implemented by allowing the power supplier to send load-shedding requests, or by the use of real-time energy pricing. See Economy 7.

Tankless heaters

Tankless water heaters, also called instantaneous, continuous flow, inline, flash, on-demand or instant-on water heaters, are also available and gaining in popularity. These water heaters instantly heat water as it flows through the device, and do not retain any water internally except for what is in the heat exchanger coil.

Tankless heaters are often installed throughout a household at more than one point-of-use (POU), far from the central water heater, or larger models may still be used to provide all the hot water requirements for an entire house. The main advantages of tankless water heaters are a continuous flow of hot water and energy savings (as compared to a limited flow of continuously heating hot water from conventional tank water heaters).

Combination Boilers

Combination or combi boilers, combine the CH with the domestic hot water (DHW) in one box. They are not merely infinitively continuous water heaters having the ability to heat a hydronic heating system in a large house. When DHW is run off, the combi stops pumping water to the hydronic circuit and diverts all the boilers power to instantly heating DHW. Some combis have small internal water storage vessels combining the energy of the stored water and the gas or oil burner to give faster DHW at the taps or increase the DHW flowrate.

Combi boilers are rated by the DHW flowrate. The kW ratings for domestic units are 24kW to 54kW, giving approximate flowrates of 9 litres per minute to 23 litres per minute. There are larger commercial units available. The high flowrate models will simultaneously supply two showers.

A further advantage is that more than one combi unit may be used to supply separate heating zones, giving greater time and temperature control, and multiple bathrooms. An example is one combi supplying the downstairs heating system and another the upstairs. One unit may supply one bathroom and one another. Having two units gives backup in case one combi is down.

Great saving are to be had in installation costs as water tanks and associated pipes and controls are not required. This also saves space in a home that may be given over to living space.

Combi boilers are highly popular in Europe, where in some countries market share is 70%.

Various types and their advantages

Point-of-use tankless water heaters are located right where the water is being used, so the water is almost instantly hot, which saves water. They also save even more energy than centrally installed tankless water heaters because no hot water is left in the pipes after the water is shut off. However, point-of-use tankless water heaters are usually used in combination with a central water heater since they are usually limited to under 6 litres/minute (1.5 U.S. gallons/minute), as the expense of buying a heater for every kitchen, laundry room, bathroom, or sink can outweigh the money saved in water and energy bills. In addition, point of use water heaters until recently were almost always electrical, and electricity is often substantially more expensive than natural gas or propane.

Tankless heaters can ideally be somewhat more efficient than storage water heaters. In both kinds of installation (centralized and POU) the absence of a tank saves energy as conventional water heaters have to reheat the water in the tank as it cools off, called standby loss. There is a misconception that the energy lost by a tanked heater stored inside a home merely helps to heat the home. This is true of an electric unit, but for a gas unit most of this wasted energy leaves through the exhaust vent. However, if the building needs to be cooled to maintain normal temperatures this results in a loss in efficiency With a central water heater of any type, water is wasted waiting for water to heat up because of the cold water in the pipes between the faucet and the water heater. This water waste can be avoided if a recirculating pump is installed, but at the cost of electricity to run the pump and wasted energy to heat the water circulation through the pipes.

Tankless water heaters can be divided into two categories: "full on/full off" and "modulated". Full on/full off units do not have a variable power output level; the unit is either on or off. Modulated tankless water heaters base the heat output on the flow of water running through the unit. This is usually done through the use of a 'flow sensor', modulating gas valve, inlet water temperature sensor and an outlet water temperature sensor-choke valve and means that the occupants should receive the same output temperature of water at differing velocities, usually within a close range of ±2 °C.

The high efficiency condensing combination boiler^[5] provides both space heating and water heating, an increasingly popular choice in UK houses. In fact, combination boilers now account for over half of all the new domestic boilers installed in Britain.^[6]

In certain parts of South America as well as Costa Rica and Puerto Rico, a point of use style water heater commonly referred to as the "Electric Shower Head" is used in many residential and some commercial installations. As the name implies, an electric heating element is incorporated into such shower heads to heat the water. However, many of these units are often poorly installed, often with exposed wiring in wet locations.

Under current North American conditions, the most cost effective configuration from an operating viewpoint is usually to use a central tankless water heater for most of the house, and install a point of use tankless water heater at any distant faucets or bathrooms. However, this may vary according to how much electricity, gas and water costs in the area, the layout of the house, and how much hot water is used. Only electric tankless water heaters were available at first and they are still used for almost all point of use heaters, but natural gas and propane heaters are now common. When consumers are considering a whole house gas tankless unit, they are advised to look at how the unit functions when raising the water temperature by about 42 °C (75–77 °F). Thus, if they live in a cold weather climate, they are advised to look at the unit's capacity with 3-10 °C (38–50 °F) inlet water temperatures, and find a size that produces approximately 15 litres/minute (4 gpm) even in winter if they have a typical-sized house and desire what is called a 2-appliance heater. This same unit may produce 25-30 litres/minute (6.3–6.9 gpm) in summer with higher inlet temperatures, but there is greater interest in year round production and usability.

Advantages

There are certain advantages to tankless water heaters :

• Long term energy savings: Although a tankless water heater might cost more initially it will result in both energy and cost savings in the long term. As water is heated only when it is needed there is no wasteful heating of water. With a tank water will be kept hot all day even if it never gets used and heat loss through the tank walls will result in a continual energy drain. Even in homes or buildings with a high demand for hot water a tankless water heater will provide some level of savings. In a typical home these savings are quite substantial. If instant hot water at the taps at limited hours is a priority, a recirculation system similar to those in the tank-type systems can be accommodated by using an aquastat and timer in order to decrease the added heat loss from the recirculation system.
• Unlimited hot water: As water is heated while passing through the system an unlimited supply of hot water is available with a tankless water heater. Although flow rate will determine the amount of hot water that can be generated at one time it can be generated indefinitely.
• Less physical space: Most tankless water heaters can be mounted on a wall or even internally in a building's structure. This means less physical space has to be dedicated to heating water. Even systems that can't be mounted on walls take up less space than a tank-type water heater.
• No risk of water damage: No stored water means there is no risk of water damage from a tank failure or rupture. Improper piping in either the hot or cold water lines to the tankless water heater can result in water damage though.^{[citation needed]}
• Temperature compensation A temperature compensating valve tends to eliminate the issue where the temperature and pressure from tankless heaters decrease during continuous use. Most new generation tankless water heaters, like the Takagi TK3, TK3 PRO, TM32, and the TM50 stabilize water pressure and temperature by a bypass valve and a mxing valve which is incorporated in the unit. Modern Tankless are not inversely proportional, because they will regulate the amount of water that is created and discharged, therefore stabilizing water temperature by utilizing a flow control valve. Flow speed is not the issue, but delta T is the important issue to address. The wider the temperature rise, the less flow you receive from the unit. The smaller the temperature rise, the more flow you receive. The flow control valve in conjunction with thermistors, maintains a stable temperature throughout the use of the unit.

Disadvantages

Tankless heaters also have several disadvantages:

• Installation cost: Installing a tankless system comes at an increased cost, particularly in retro-fit applications. They tend to be particularly expensive in areas such as the US where they are not dominant, compared to the established tank design. If a storage water heater is being replaced with a tankless one, the size of the electrical wiring or gas pipeline may have to be increased to handle the load and the existing vent pipe may have to be replaced, possibly adding expense to the retrofit installation. Many tankless units have fully modulating gas valves that can range from as low as 10,000 to over 1,000,000 BTUs. For electrical installations (non-gas), AWG 10 or 8 wire, corresponding to 10 or 6 mm², is required for most POU (point of use) heaters at North American voltages. Larger whole house electric units may require up to AWG 2 wire. In gas appliances, both pressure and volume requirements must be met for optimum operation.
• Heat source flexibility Tankless heaters are limited to a choice between expensive and CO₂ problematic energy sources: gas and electricity. This makes it impossible to include other heat sources, including renewable energy. Tank-type systems have a much wider choice of heat sources available, such as district heating, central heating, solar heating, geothermal heating, micro CHP and ground-coupled heat exchangers.
• Start-up delay: There is a longer wait to obtain hot water. A tankless water heater only heats water upon demand, so all idle water in the piping starts at room temperature. Thus there is a more apparent "flow delay" for hot water to reach a distant faucet.
• Intermittent use: There is a short delay between the time when the water begins flowing and when the heater's flow detector activates the heating elements or gas burner. In the case of continuous use applications (showers, baths, washing machine) this is not an issue. However, for intermittent use applications (for example when a hot water faucet is turned on and off repeatedly) this can result in periods of hot water, then some small amount of cold water as the heater activates, followed quickly by hot water again. The period between hot/cold/hot is the amount of water which has flowed though the heater before becoming active. This cold section of water takes some amount of time to reach the faucet and is dependent on the length of piping.
• Recirculation systems: Since a tankless water heater is inactive when hot water is not being used, they are incompatible with passive (convection -based) hot water recirculation systems. They may be incompatible with active hot water recirculation systems and will certainly use more energy to constantly heat water within the piping, defeating one of a tankless water heater's primary advantages.
• Achieving cooler temperatures: Tankless water heaters often have minimum flow requirements before the heater is activated, and this can result in a gap between the cold water temperature, and the coolest warm water temperature that can be achieved with a hot and cold water mix.
• Maintaining constant shower temperature: Similarly, unlike with a tank heater, the hot water temperature from a tankless heater is inversely proportional to the rate of the water flow—the faster the flow, the less time the water spends in the heating element being heated. Mixing hot and cold water to the "right" temperature from a single-lever faucet (say, when taking a shower) takes some practice. Also, when adjusting the mixture in mid-shower, the change in temperature will initially react as a tanked heater does, but this also will change the flow rate of hot water. Therefore some finite time later the temperature will change again very slightly and require readjustment. This is typically not noticeable in non-shower applications.
• Operation with low supply pressure: Tankless systems are reliant on the water pressure that is delivered to the property. In other words, if a tankless system is used to deliver water to a shower or water faucet, the pressure is the same as the pressure delivered to the property and cannot be increased, whereas in tanked systems the tanks can be positioned above the water outlets (in the loft/attic space for example) so the force of gravity can assist in delivering the water, and pumps can be added into the system to increase pressure. Power showers, for example, cannot be used with tankless systems because it cannot deliver the hot water at a fast enough flow-rate required by the pump.
• Time-of-use metering and peak electrical loads: Tankless electric heaters, if installed in a large percentage of homes within an area, can create demand management problems for electrical utilities. Because these are high-amperage devices, and hot water use tends to peak at certain times of the day, their use can cause short spikes in electricity demand, including during the daily peak electrical load periods, which increases utility operating costs. For households using time-of-use metering (where electricity costs more during peak periods such as daytime, and is cheaper at night), a tankless electric heater may actually increase operating costs if the hot water is used during peak times.^[7]

Solar water heaters

Main article: Solar hot water

Direct-gain solar heater panels with integral storage tank

In some locales, solar powered water heaters are used. Their solar collectors are installed outside dwellings, typically on the roof or nearby. Nearly all models are the direct-gain type, consisting of flat panels in which water circulates. Other types may use dish or trough mirrors to concentrate sunlight on a collector tube filled with water, brine or other heat transfer fluid. A storage tank is placed indoors or out. Circulation is caused by natural convection or by a small electric pump. At night, or when insufficient sunlight is present, circulation through the panel can be stopped by closing a valve and/or stopping the circulating pump, to keep hot water in the storage tank from cooling. Depending on the local climate, freeze protection, as well as prevention of overheating, must be addressed in their design, installation, and operation.

Another type of solar water heater is the evacuated tube collector. It is usually mounted on a roof, and has a row of glass tubes containing heat conducting rods, typically copper. The rods act as heating elements in a circulating loop of antifreeze. The captured heat is transferred into the domestic hot water system by a heat exchanger. This design is smaller and more efficient than traditional flat plate collectors, and works well in very cold climates. The evacuated description refers to air having been removed from the glass tubes to create a vacuum. This results in very low heat loss, once the inside coating has absorbed solar radiation.

Geothermal heating

In countries like Iceland and New Zealand, and other volcanic regions, water heating may be done using geothermal heating, rather than combustion.

Water heater safety

Water heaters potentially can explode and cause significant damage, injury, or death if certain safety devices are not installed. When the water temperature exceeds 100 °C (212 °F), the water will remain a liquid inside the tank, but when the pressure is released as the water comes out the tap the water will boil, potentially inflicting steam burns. Water above about 88°C (190 °F) will cause burns on contact. A safety device called a temperature and pressure relief (T&P or TPR) valve, is normally fitted on the top of the water heater to dump water if the temperature or pressure becomes too high. Most plumbing codes require that a discharge pipe be connected to the valve to direct the flow of discharged hot water to a drain, typically a nearby floor drain, or outside the living space. Some building codes will allow for the discharge pipe to terminate in the garage.

If a gas or propane fired water heater is installed in a garage, it is recommended, and many codes require, that it be elevated at least 18 inches (0.46 m) above the floor to reduce the potential for fire or explosion due to spillage or leakage of combustible liquids in the garage. Furthermore, some local codes mandate that tank-type heaters in new and retrofit installations be braced to an adjacent wall with a strap to prevent them from tipping over and breaking the water and gas pipes in the event of an earthquake.

For older houses where the water heater is part of the space heating boiler, and plumbing codes allow, some plumbers will install a "Watts 210" device in place of a TPR valve. When the device senses that the temperature reaches 99 °C (210 °F), it will shut off the gas supply and prevent further heating. In addition, an expansion tank or exterior pressure relief valve must be installed to prevent pressure buildup in the plumbing from rupturing pipes, valves, or the water heater.

Scalding is a serious concern with any water heater. Human skin burns quickly at high temperature, e.g., only 60 °C (140 °F), but also at lower temperatures, e.g., 50 °C (120 °F), if the exposure times are sufficient. Older people and children often receive the most serious scalds due to disabilities or slow reaction times. In Australia and elsewhere it is common practice to put a tempering valve on the outlet of the water heater. A tempering valve mixes enough cold water with the hot from the heater to keep the outgoing water temperature fixed, often set to 50 °C. Without a tempering valve, reduction of the water heater's setpoint temperature is the most direct way to reduce scalding. However, for sanitation, hot water is needed. Most residential dishwashing machines, for example, include an electric heating element for increasing the water temperature above that provided by water heaters. The result of mixing hot and cold water via a tempering valve is also referred to as tempered water.^[8]

There are two seemingly conflicting safety issues around water heater temperature — the risk of scalding from excessively hot water, and the risk of incubating bacteria colonies, particularly Legionella, in water that is not hot enough to kill them. Both risks are potentially life threatening and are balanced by setting the water heater's thermostat to at least 50 °C (120 °F). The European Guidelines for Control and Prevention of Travel Associated Legionnaires’ Disease recommend that hot water should be stored at 60°C (140 °F) and distributed such that a temperature of at least 50°C and preferably 55°C is achieved within one minute at outlets.^[9] If there is a dishwasher without a booster heater, it may require a water temperature within a range of 57 °C (134.6 °F) to 60 °C (140 °F) for optimum cleaning,^[10] in which case tempering valves set to no more than 55°C can be applied to faucets to avoid scalding. (Note: Tank temperatures above 60°C may produce calcium deposits, which could later harbor bacteria, in the water tank. Temperatures above 60°C may also cause gradual erosion of glassware in a dishwasher.)

HISTORY OF THE ELECTRIC CAR

Information Provided by Wikipedia.com:

The design of the electric car is one of the oldest for automobiles — small electric vehicles predate the Otto cycle upon which Diesel (diesel engine) and Benz (gasoline engine) based the automobile. Between 1832 and 1839 (the exact year is uncertain), Scottish businessman Robert Anderson invented the first crude electric carriage. Professor Sibrandus Stratingh of Groningen, the Netherlands, designed the small-scale electric car, built by his assistant Christopher Becker in 1835.^[2]

Practical and more successful electric road vehicles were invented by both Thomas Davenport, an American, and Robert Davidson, a Scotsman, in 1842. Both inventors were the first to use non-rechargeable electric cells.^[3]

Gaston Plante invented a better storage battery in France in 1865^[4], and his fellow countryman Camille Faure improved the storage battery in 1881.^[5] This improved-capacity storage battery paved the way for electric vehicles to flourish. An electric-powered two-wheel cycle was put on display at the World Exhibition 1867 in Paris by the Austrian inventor Franz Kravogl.^[6]

France and Great Britain were the first nations to support the widespread development of electric vehicles.^[7] In November 1881 French inventor Gustave Trouvé demonstrated a working three-wheeled automobile at the International Exhibition of Electricity in Paris.^[8] Thomas Parker claimed to have built a working electric car by 1884^[9]

Before the pre-eminence of internal combustion engines, electric automobiles held many speed and distance records.^[10] Among the most notable of these records was the breaking of the 100 km/h (62 mph) speed barrier, by Camille Jenatzy on April 29, 1899 in his 'rocket-shaped' vehicle Jamais Contente, which reached a top speed of 105.88 km/h (65.79 mph).

It was not until 1895 that Americans began to devote attention to electric vehicles after an electric tricycle was built by A. L. Ryker and William Morrison built a six-passenger wagon both in 1891. Many innovations followed and interest in motor vehicles increased greatly in the late 1890s and early 1900s. In 1897, the first commercial application was established as a fleet of New York City taxis built by the Electric Carriage and Wagon Company of Philadelphia. Electric cars, produced in the US by Anthony Electric, Baker, Detroit Electric (Anderson Electric Car Company), Edison, Studebaker, and others during the early 20th century for a time out-sold gasoline-powered vehicles.

These vehicles were successfully sold as city cars to upper-class customers and were often marketed as suitable vehicles for women drivers due to their clean, quiet and easy operation. Due to technological limitations and the lack of transistor-based electric technology, the top speed of these early electric vehicles was limited to about 32 km/h (20 mph).

By the turn of the century, America was prosperous, and cars, now available in steam, electric, or gasoline versions, were becoming more popular. The years 1899 and 1900 were the high point of electric cars in America, as they outsold all other types of cars. Electric vehicles had many advantages over their competitors in the early 1900s. They did not have the vibration, smell, and noise associated with gasoline cars. Changing gears on gasoline cars was the most difficult part of driving, and electric vehicles did not require gear changes.

While steam-powered cars also had no gear shifting, they suffered from long start-up times of up to 45 minutes on cold mornings. The steam cars had less range before needing water than an electric car's range on a single charge. The only good roads of the period were in town, causing most travel to be local commuting - a perfect situation for electric vehicles, since their range was limited.

The electric vehicle was the preferred choice of many because it did not require the manual effort to start, as with the hand crank on gasoline vehicles, and there was no wrestling wsalith a gear shifter. While basic electric cars cost under $1,000, most early electric vehicles were ornate, massive carriages designed for the upper class. They had fancy interiors, with expensive materials, and averaged $3,000 by 1910. Electric vehicles enjoyed success into the 1920s with production peaking in 1912.