TYPES OF WATER HEATERS
STORAGE WATER HEATERS (tank type, most common).
In household and commercial usage, most water heaters are the tank type, also called storage water heaters. These consist of a cylindrical vessel or container that keeps water continuously hot and ready to use. Typical sizes for household use range from 20 to 100 gallons. These may use electricity, natural gas, propane, heating oil, solar, or other energy sources. Natural gas heaters between 40 and 50 gallons are the most popular, with a burner rated at 34,000 to 40,000 BTU/power. Some models offer high efficiency and ultra-low NOX emissions
TANKLESS WATER HEATERS.
Also call instantaneous, continuous flow, in-line, flash, on-demand, or instant-on water heaters. These high power 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. Cooper heat exchangers are preferred in these units because of their high thermal conductivity and ease of fabrication. The mail advantages of tankless water heaters are a plentiful continuous flow of hot water and potential energy savings under some conditions. The mail disadvantage is a much higher initial cost.
POINT OF USE WATER HEATERS.
Small point of use electric storage water heaters with capacities ranging from 2 to 6 gallons are made for installation in kitchen and bath cabinets or on the wall above/below a sink. They typically us low power heating elements, about 1KW to 1.5KW, and can provide hot water long enough for hand washing. They may be used when retrofitting a building when hot water plumbing is too costly or impractical.
WATER HEATER IMPROVENTS.
Other improvements to water heaters include check valve devices, cycle timers, electronic ignition, high-efficiency condensing units can convert up to 98% of the energy in the fuel to heating the water. Residential combustion water heaters manufactured since 2003, have been redesigned to resist ignition of flammable vapors and incorporate a thermal cutoff switch, per ANSI. Z21.10.1. These safety requirements were made in response to home owners storing, or 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 do not became 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.
WATER HEATER SAFETY
Water heaters potentially can explode and cause significant damage, injury, or death if certain safety devices are not installed. A safety device called a temperature a pressure relief valve (T&P), is normally fitted on the water heater to dump water if the temperature or pressure becomes to 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 or outside the living space. Some building codes allow the discharge pipe to terminate in the garage. In addition, an expansion tank can be installed to prevent pressure buildup in the plumbing for rupturing pipes, valves, or the water heater.
BACTERIAL CONTAMINATION
Two conflicting safety issues affect water heater temperature. The risk of scalding from excessively hot water greater than 131°F (55°C), and the risk of incubating bacteria colonies, particularly legionella, in water that is not hot enough to kill them. Both risks are life-threating potentially and are balanced by setting the water heater’s thermostat to 131°F (55°C) and distributed so that a temperature of a list 122°F (50°C) is achieved within 1 minute at points of use.
However legionella can be safely and easily control with good design and engineering protocols. For instance, raising the temperature of water heaters once a day or even once every few days to 131°F (55°C) for 30 minutes effectively controls legionella. This process is done automatically by the gas control valve/thermostat.
In all cases and in particular energy efficient applications, legionnaires’ disease is more often than not the result of engineering design issues that do not take into consideration the impact of stratification or low flow. It is also possible to control legionella risks by chemical treatment of the water, this technique allows lower water temperatures to be maintain in the pipework without the associated legionella risk.
