A storage water heater, or a hot water system (HWS), is a domestic water heating appliance that uses a hot water storage tank to maximize water heating capacity and provide instantaneous delivery of hot water. [1] Conventional storage water heaters use a variety of fuels, including natural gas, propane, fuel oil, and electricity. Less conventional water heating technologies, such as heat pump water heaters and solar water heaters, can also be categorized as storage water heaters.
The primary difference between a storage heater and an instant heater is that a storage system can deliver hot water instantly, and an instant heater takes an amount of time to heat the water first.
Instant water heaters, as the name suggests, provide hot water almost instantaneously. There is hardly 1 or 2 minutes of heating time after which hot water can be accessed. But given the low storage capacity (max 5–6 liters (1.3–1.6 U.S. gal) at a given point of time) of these types of heaters, you cannot expect a bucket or a barrel full at the same speed. They are priced significantly higher than storage heaters but have a longer life period. This stands at an average of 15-20 years. Instant water heater provides water as you need. There are no heat losses and cheaper than the storage water heater. [2]
Storage heaters, are not as fast as the instant versions, as they are required heat a large tank of water that is then stored for later usage. Storage tank water heaters are ideal for large volume water usage (large tanks can store about 75 U.S. gallons (280 L)) and are popular due to their low upfront costs and long average life-span of 10-15 years. But these systems are the least energy efficient, making them expensive to run long-term. They also require more space for installation.[ citation needed ]
Solar heat is clean and renewable. This is the most modern system. Increasingly, solar powered water heaters are being used. Their solar thermal collectors are installed outside dwellings, typically on the roof or walls or nearby, and the potable hot water storage tank is typically a pre-existing or new conventional water heater, or a water heater specifically designed for solar thermal.
The most basic solar thermal models are the direct-gain type, in which the potable water is directly sent into the collector. Many such systems are said to use integrated collector storage (ICS), as direct-gain systems typically have storage integrated within the collector. Heating water directly is inherently more efficient than heating it indirectly via heat exchangers, but such systems offer very limited freeze protection, if any, can easily heat water to temperatures unsafe for domestic use, and ICS systems suffer from severe heat loss on cold nights and cold, cloudy days.
By contrast, indirect or closed-loop systems do not allow potable water through the solar panels, but rather pump a heat transfer fluid (either water or a water/antifreeze mix) through the panels. After collecting heat in the panels, the heat transfer fluid flows through a heat exchanger, transferring its heat to the potable hot water. When the panels are cooler than the storage tank or when the storage tank has already reached its maximum temperature, the controller in closed-loop systems will stop the circulator pumps. In a drainback system, the water drains into a storage tank contained in conditioned or semi-conditioned space, protected from freezing temperatures. With antifreeze systems, however, the pump must be run if the panel temperature gets too hot (to prevent degradation of the antifreeze) or too cold (to prevent the water/antifreeze mixture from freezing.)
Flat panel collectors are typically used in closed-loop systems. Flat panels, which often resemble skylights, are the most durable type of collector, and they also have the best performance for systems designed for temperatures within 100 °F (38 °C) of ambient temperature. Flat panels are regularly used in both pure water and antifreeze systems.
Another type of solar collector is the evacuated tube collector, which are intended for cold climates that do not experience severe hail and/or applications where high temperatures are needed (i.e., over 200 °F (93 °C)). Placed in a rack, evacuated tube collectors form a row of glass tubes, each containing absorption fins attached to a central heat-conducting rod (copper or condensation-driven). The evacuated description refers to the vacuum created in the glass tubes during the manufacturing process, which results in very low heat loss and lets evacuated tube systems achieve extreme temperatures, far in excess of water's boiling point.
Natural gas and propane storage water heaters operate identically with a gas or propane burner located at the bottom of the storage tank heating the water. Fuel oil fired storage water heaters are configured similarly by igniting a vaporizing mist of oil and air with an electric spark. [3]
Emissions from fossil fuel fired water heaters are expelled using a variety of venting technologies. Atmospheric vented systems use room air as combustion air and exhaust air. The exhaust air is expelled through the exhaust flue by buoyancy forces resulting from the combustion. Power vent models operate similarly to atmospheric vent systems, but an exhaust fan is added to aid in the expulsion of combustion gases. Direct vent systems do not use room air for combustion; instead, buoyancy forces air from the outside through the water heater combustion system and finally exhausts the combustion gases to the outside. Powered direct-vent systems include an exhaust fan to aid in the expulsion of combustion gasses. [4]
Most electric water heaters use electric resistance elements to heat the water in the storage tank. A two-element electric water heater has one element at the top of the storage tank, and one element at the bottom. Each element is controlled by an independent thermostat. The lower element provides recovery from standby losses, and the upper element provides extra heating when a lot of hot water is being used. Some heaters contain only a lower element. [3]
Electrical water heaters that store hot water can be a good match for a smart grid, so that it heats when the electrical grid load is low and turns off when the load is high. This could be implemented by allowing the power supplier to send loadshedding requests, or by the use of real-time energy pricing. See Economy 7.
Heat pump water heaters use an air source heat pump to transfer thermal energy from the air around the unit into the storage tank. Electric resistance element(s) are typically included to provide backup heating if the heat pump cannot provide sufficient heating capacity. [5] [6]
As with fossil fuels, burning wood causes greenhouse effect gases. However, wood is a renewable source of energy. A sustainable heat system would be to use solar heat in the summer, and the minimum of wood in the winter.
The storage tanks of water heaters are usually made out of steel with a lining of glass inside them. Water will corrode exposed steel, so the glass lining prevents or delays corrosion.
The tanks also have magnesium anode rods. The anode rod will slow down corrosion of the steel tank by corroding in its place. [7] When the anode rod is completely corroded, the steel tank will corrode much faster.
Given the constant contact of water, corrosion eventually happens anyway. If corrosion of the tank creates holes in it, there are some temporary fixes to try to patch it, but the long-term solution is to replace the tank altogether.
Water with a lower pH value will corrode the anode rods and steel tank faster. For proper maintenance of the tank, know the pH level of the water stored, watch for corrosion of the anode rod, and replace the anode when it becomes too corroded.
An autonomous building is a building designed to be operated independently from infrastructural support services such as the electric power grid, gas grid, municipal water systems, sewage treatment systems, storm drains, communication services, and in some cases, public roads.
Solar energy is radiant light and heat from the Sun that is harnessed using a range of technologies such as solar power to generate electricity, solar thermal energy, and solar architecture. It is an essential source of renewable energy, and its technologies are broadly characterized as either passive solar or active solar depending on how they capture and distribute solar energy or convert it into solar power. Active solar techniques include the use of photovoltaic systems, concentrated solar power, and solar water heating to harness the energy. Passive solar techniques include orienting a building to the Sun, selecting materials with favorable thermal mass or light-dispersing properties, and designing spaces that naturally circulate air.
Heating, ventilation, and air conditioning (HVAC) is the use of various technologies to control the temperature, humidity, and purity of the air in an enclosed space. Its goal is to provide thermal comfort and acceptable indoor air quality. HVAC system design is a subdiscipline of mechanical engineering, based on the principles of thermodynamics, fluid mechanics, and heat transfer. "Refrigeration" is sometimes added to the field's abbreviation as HVAC&R or HVACR, or "ventilation" is dropped, as in HACR.
A boiler is a closed vessel in which fluid is heated. The fluid does not necessarily boil. The heated or vaporized fluid exits the boiler for use in various processes or heating applications, including water heating, central heating, boiler-based power generation, cooking, and sanitation.
A furnace, referred to as a heater or boiler in British English, is an appliance used to generate heat for all or part of a building. Furnaces are mostly used as a major component of a central heating system. Furnaces are permanently installed to provide heat to an interior space through intermediary fluid movement, which may be air, steam, or hot water. Heating appliances that use steam or hot water as the fluid are normally referred to as a residential steam boilers or residential hot water boilers. The most common fuel source for modern furnaces in North America and much of Europe is natural gas; other common fuel sources include LPG, fuel oil, wood and in rare cases coal. In some areas electrical resistance heating is used, especially where the cost of electricity is low or the primary purpose is for air conditioning. Modern high-efficiency furnaces can be up to 98% efficient and operate without a chimney, with a typical gas furnace being about 80% efficient. Waste gas and heat are mechanically ventilated through either metal flue pipes or polyvinyl chloride (PVC) pipes that can be vented through the side or roof of the structure. Fuel efficiency in a gas furnace is measured in AFUE.
Solar thermal energy (STE) is a form of energy and a technology for harnessing solar energy to generate thermal energy for use in industry, and in the residential and commercial sectors.
Water heating is a heat transfer process that uses an energy source to heat water above its initial temperature. Typical domestic uses of hot water include cooking, cleaning, bathing, and space heating. In industry, hot water and water heated to steam have many uses.
Solar water heating (SWH) is heating water by sunlight, using a solar thermal collector. A variety of configurations are available at varying cost to provide solutions in different climates and latitudes. SWHs are widely used for residential and some industrial applications.
A solar thermal collector collects heat by absorbing sunlight. The term "solar collector" commonly refers to a device for solar hot water heating, but may refer to large power generating installations such as solar parabolic troughs and solar towers or non water heating devices such as solar cooker, solar air heaters.
A central heating system provides warmth to a number of spaces within a building from one main source of heat. It is a component of heating, ventilation, and air conditioning systems, which can both cool and warm interior spaces.
Thermal energy storage (TES) is achieved with widely different technologies. Depending on the specific technology, it allows excess thermal energy to be stored and used hours, days, months later, at scales ranging from the individual process, building, multiuser-building, district, town, or region. Usage examples are the balancing of energy demand between daytime and nighttime, storing summer heat for winter heating, or winter cold for summer air conditioning. Storage media include water or ice-slush tanks, masses of native earth or bedrock accessed with heat exchangers by means of boreholes, deep aquifers contained between impermeable strata; shallow, lined pits filled with gravel and water and insulated at the top, as well as eutectic solutions and phase-change materials.
Electric heating is a process in which electrical energy is converted directly to heat energy. Common applications include space heating, cooking, water heating and industrial processes. An electric heater is an electrical device that converts an electric current into heat. The heating element inside every electric heater is an electrical resistor, and works on the principle of Joule heating: an electric current passing through a resistor will convert that electrical energy into heat energy. Most modern electric heating devices use nichrome wire as the active element; the heating element, depicted on the right, uses nichrome wire supported by ceramic insulators.
Condensing boilers are water heaters typically used for heating systems that are fueled by gas or oil. When operated in the correct circumstances, a heating system can achieve high efficiency by condensing water vapour found in the exhaust gases in a heat exchanger to preheat the circulating water. This recovers the latent heat of vaporisation, which would otherwise have been wasted. The condensate is sent to a drain. In many countries, the use of condensing boilers is compulsory or encouraged with financial incentives.
Renewable heat is an application of renewable energy referring to the generation of heat from renewable sources; for example, feeding radiators with water warmed by focused solar radiation rather than by a fossil fuel boiler. Renewable heat technologies include renewable biofuels, solar heating, geothermal heating, heat pumps and heat exchangers. Insulation is almost always an important factor in how renewable heating is implemented.
A heater core is a radiator-like device used in heating the cabin of a vehicle. Hot coolant from the vehicle's engine is passed through a winding tube of the core, a heat exchanger between coolant and cabin air. Fins attached to the core tubes serve to increase surface area for heat transfer to air that is forced past them by a fan, thereby heating the passenger compartment.
A solar combisystem provides both solar space heating and cooling as well as hot water from a common array of solar thermal collectors, usually backed up by an auxiliary non-solar heat source.
Solar hot water is water that is heated using energy from the sun. Solar energy heats up large panels called thermal collectors, commonly known as solar panels. The energy is transferred through a fluid to a reservoir tank for storage and subsequent use. It is then used to heat water for commercial or domestic use and also as an energy input for heating and cooling devices and for industrial "process heat" applications.
Photovoltaic thermal collectors, typically abbreviated as PVT collectors and also known as hybrid solar collectors, photovoltaic thermal solar collectors, PV/T collectors or solar cogeneration systems, are power generation technologies that convert solar radiation into usable thermal and electrical energy. PVT collectors combine photovoltaic solar cells, which convert sunlight into electricity, with a solar thermal collector, which transfers the otherwise unused waste heat from the PV module to a heat transfer fluid. By combining electricity and heat generation within the same component, these technologies can reach a higher overall efficiency than solar photovoltaic (PV) or solar thermal (T) alone.
A hot water storage tank is a water tank used for storing hot water for space heating or domestic use.
Tankless water heaters — also called instantaneous, continuous flow, inline, flash, on-demand, or instant-on water heaters — are water heaters that 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 unless the unit is equipped with an internal buffer tank. Copper heat exchangers are preferred in these units because of their high thermal conductivity and ease of fabrication. However, copper heat exchangers are more susceptible to scale buildup than stainless steel heat exchangers.