thermal storage tanks , hot water storage units , < b> hot storage tanks and hot water cylinders ) are water tanks used to store hot water for heating or domestic use.
Water is a convenient heat storage medium because it has a high specific heat capacity. This means, compared to other substances, it can store more heat per unit of weight. Water is non-toxic and low cost.
Efficient insulated tanks can store stored heat for days, reducing fuel costs. The hot water tank may have a built-in gas or oil burner system, electric immersion heater. Some types use external heat exchangers such as central heating systems, or hot water from other energy sources. Most typical, in the domestic context, are fossil fuel burners, electric immersion elements, or district heating schemes.
The water heater for washing, bathing, or laundry has a thermostat control to regulate the temperature, in the range of 40 to 60 Â ° C (104 to 140 Â ° F), and connected to a domestic cold water supply.
Where local water supplies have high soluble minerals such as limestone, heating water causes minerals to settle in the tank (scaling). The tank may experience leakage due to corrosion after several years, a problem compounded by dissolved oxygen in the water that accelerates the corrosion of the tank and fittings.
Video Hot water storage tank
Isolation
Usually the hot water storage tank is wrapped with heat insulation to reduce energy consumption, speed up the heating process, and maintain the desired operating temperature. Thicker thermal insulation reduces the heat loss. The water heater is available with various isolation ratings but it is possible to add an additional insulating layer outside the water heater to reduce heat loss. Under extreme conditions, the heater itself may be completely enclosed in a specially constructed isolated space.
The most common type of water heater insulation available is fiberglass, mounted in place with tape or rope or an outdoor water heater jacket. Isolation does not have to block airflow or gas out of combustion, where the burner is used.
In very humid locations, the addition of insulation to well-insulated tanks may lead to condensation leading to rust, fungi, or other operational problems such that some airflow must be maintained, usually by convection caused by exhaust heat, but under very conditions humid as ventilation fans may have helped.
Most modern water heaters have applied polyurethane foam insulation (PUF). If access to the inner tanks is a priority (in the case of highly aggressive minerals or oxygen levels in local water supplies), PUF can be applied in encapsulated form, allowing the removal of the insulating layer for regular integrity checks and, if necessary, the repair of the water tank.
Maps Hot water storage tank
Solar hot water storage tank
In solar water heating systems, solar storage tanks save heat from solar thermal collectors. The tank has an internal heat exchanger to heat the domestic cold water. In relatively mild climates, such as the Mediterranean, storage tanks (which are very isolated but encased in metal) are often installed on the roof. All such tanks have the same problems as artificially heated tanks including limestone and corrosion deposits, and suffer the same reduction in overall efficiency unless properly maintained.
water tank leak
The water heater tank can be made of enamelled carbon steel coated with vitreous, stainless steel, or copper.
While domestic hot water tanks of steel and carbon steel are more common in Europe, carbon steel tanks are more common in the United States, where usually periodic checks are ignored, tanks develop leaks so that all equipment is replaced. Even when ignored, carbon steel tanks tend to persist for several years more than their factory warranty, which is usually 3 to 12 years in the US.
Vitreous coated tanks are much lower in initial costs, and often include one or more rod-shaft anodes designed to protect the tanks from perforation caused by the corrosion that is made necessary because chlorinated water is highly corrosive to carbon steel. Since it is virtually impossible to apply any protective layer perfectly (without microscopic cracking or pinhole defect in the protective layer), the manufacturer may recommend periodic checks of any sacrificial anodes, replacing them if necessary.
Some manufacturers offer an extended warranty kit that includes an anode replacement rod. Since conventional hot water storage tanks can leak every 5 to 15 years, high-quality installations will cover, and most building codes/pipes in the US now require a shallow metal or plastic pan to collect seepage when it occurs.
Hot water storage tank with closed water circuit
This method stores heat in the tank by using an external heat exchanger (coil) that can be tapped directly or used to power other (external) heat exchangers.
The main benefit is that by avoiding the direct withdrawal of domestic hot water, the tank is not constantly fed with cold water, which in the 'hard' water area reduces the limescale deposits to whatever is dissolved in the original water charge plus the relatively trivial amount added to compensate for seepage.
An added benefit is to reduce oxygen levels in such closed systems, allowing for some relaxation in requirements for materials used in hot water storage tanks and closed water circuits, external heat exchangers, and related pipeworking.
While an external heat exchanger system used for domestic hot water will have a mineral deposit, the crust agent extends the life of the system.
Hot water storage tank with closed water circuit
- For illustrations - see references
Other methods of storing heat in a hot water storage tank have many names: Stratified hot water storage tank with closed water circuit , thermally plated storage , thermoclin tank > and storage of multilevel water tanks but in all cases the significant difference is that the pain is taken to maintain the vertical stratification of the water column, in other words to keep the hot water at the top of the tank while the water at the bottom is at temperatures are clearly lower.
It is desirable in places with a wide range of climates where summer cooling is as important as warming in the winter, and requires one or more of the following steps:
- Different heating and cooling loops must send hot or cold water at the lowest possible speed. (This would necessarily require heating and cooling loops that have speed-controlled pumps and tube ports with a reasonable maximum diameter.)
- For cooling applications, cold water is sent out from the bottom and warm water (back) is inserted at the top.
- The heater application gets hot water at the top and returns cold water down.
- "Increased stratification" of devices in a hot water storage tank (but if the lowest possible water velocity is unnecessary).
- More sophisticated heat control systems are required.
When a tiered hot water storage tank has a closed water circuit, the water temperature can reach 90 to 95 ° C at the top and 20 to 40 ° C at the bottom. Quiet and uninterrupted water is a relatively poor conductor of heat compared to glass, bricks and soil.
(Illustrated by a calm lake, where the water level can be warm to swim, but the deeper layers become very cold to represent a danger to the swimmer, the same effect as giving notice in the city Docks warns of 'Cold Water Hazard').
Thus, the volume of arbitrary hot water can be stored, as long as the stratification remains intact. In this case there should be no vertical metal plates or tubes because they will heat through the water layer, defeating the purpose of stratification. When used effectively this technique can maintain water as high as 95 ° C (ie just below the boiling point) which results in higher energy densities, and this energy can be stored for long periods as long as hot water remains pure.
Depending on the purpose of installation, the exchange of water tapping at different levels allows the water temperature to correspond to the required use to be selected.
In many solar heating systems the energy parameters can be read as a function of time, from the time of 'stay' required to convert sunlight to heat, at its maximum hot water temperature near the top of the tank.
Duplicate electric elements
When the flow starts from the top outlet, the cold water enters the tank at the bottom. This temperature drop causes the thermostat to turn on the electric heating element at the bottom of the tank. When the water at the top of the tank is drawn from the hot water at the top moved by a relatively cooler water, the top thermostat activates the top element. When the stream stops, the element remains active until the settings are met.
While it is common to have different top and bottom thermostats to conserve energy, the fact that hot water goes up means that the thermostat that controls the upper elements should feed the hottest supply, while the lower element is the warmest one.
If the thermostat in such a system is reversed - warm bait from the top, the heat from the center - may not only affect the energy efficiency of the system, feeding hot water into domestic hot waterways may be dangerous, or if directed to a warm food washing machine damaging those who can not repaired.
Security issues
Hot water can cause painful and harmful wounds, especially in children and the elderly. Water in the outlet should not exceed 49 degrees Celsius. Some jurisdictions set a limit of 49 degrees at the temperature of the tank setpoint. On the other hand, water stored below 60 degrees Celsius can allow bacterial growth, as it causes Legionnaire disease, which is a particular danger for those whose immune systems are compromised. One technical solution is the use of blending valves at outlets used for sinks, baths or showers, which will automatically mix cold water to maintain a maximum of below 49C. A proposal to add this to the Canadian building code was unsuccessful.
References
Source of the article : Wikipedia
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