Hot water, like heating, is one of those “conveniences” without which the very notion of comfortable housing is unthinkable. In apartment buildings in the city it is perceived as a necessary condition. The hero of a well known joke would bathe in the river in summer, and when asked “And in winter??” answer the question “How much of this winter!”. A city dweller is uncomfortable even with a few weeks in the summer, during which the centralized hot water supply is stopped for the prophylaxis of the system. There are several ways out. It is possible to go to someone on a visit at the same time and to wash or to buy a small water heater, and if it is possible, to leave for the country, on a summer residence. The water heater, however, will certainly come in handy there as well.
Those who permanently live out of town, have to solve the problem of DHW and heating individually in each house. Sometimes the two tasks can be combined by installing a common boiler, but there are cases when it makes more sense to “separate” the systems. In small towns and villages one can also encounter the variant when heating is centralized and HTW is provided individually.
In general, we can say that the water heater – a device that can be useful to anyone, from city dwellers to the owner of a comfortable house.
Almost all modern water heaters run on either electricity or gas Other options, such as wood or coal-fired boilers, can be classified as exotic.
Electric water heaters
From the point of view of design simplicity, heating water with electricity is the most convenient solution. And, as is often the case, the most expensive. However, the advantages of electric water heating systems are more than disadvantages, and in many cases it is most convenient to use them. The first advantages are the compact size and low cost of devices. They are divided into two types – flow-through and storage.
Flow-through electric water heaters. The design of such models is simple: inside the housing is a heating unit one or more heating elements in a bulb or a heat-resistant fluoroplastic casing, inside which the heating elements of uninsulated wire , control and safety devices. According to the features they are divided into non-pressurized and pressurized.
The first tap to shut off the water is installed at the cold water inlet. These models are above all used at a single extraction point. Their capacity is relatively low, many come with a shower head or a tap.
For domestic use, such models are used in country houses or during scheduled outages of the centralized hot water supply. Alternatively, these heaters are suitable for supplying hot water to individual rooms e.g. washbasins and showers in businesses, e.g. where installing a separate domestic hot water pipe makes no sense.
High-pressure models are designed for permanent connection to a pressurised water mains They are generally larger heaters that can supply several extraction points at the same time or a current comparable with that of a centralised DHW installation, e.g. in a city. In principle, a pressure water heater can be used in unpressurized mode, but not vice versa: their internal capacity is not designed for high pressure.
Electric water heaters are divided into devices with mechanical hydraulic and electronic control The task of the control system is to ensure that the water heater turns on and off at the right time. The “mechanics” switches on the heating elements usually all together , based on the change of position of the membrane, which has a mechanical drive and a block of contacts.
More complex electronic control circuits include heating elements depending on the flow rate, temperature and water pressure. This results in energy and water savings and a stable outlet water temperature. These models are considerably more expensive. Basically, these are powerful devices, designed for several points of water withdrawal.
The control panel of the water heater can be mechanical having a direct drive on the power or flow control unit or electronic touch buttons and display . But here it is the same: “mechanics” is cheaper, “electronics” gives more options.
Pros and cons of flow-through heaters
First of all, the advantages of electric water heaters should include small size and weight, which simplifies installation. They are also convenient if the water extraction point is used only occasionally.
The energy is only consumed as the water passes through the heater. Almost everything that is heated, and immediately consumed the volume of unspent liquid in the pipes of the pressure water heater is small, heat loss of all types is also negligible .
The main limitation in their application is connected with the consumed electric power. Such models themselves are available in capacities from 2.5 to 8-10 kW for single-phase connection and up to 30 kW for three-phase, but it is usually very difficult to obtain such power in normal household conditions.
Electrical wiring in the house is unlikely to be designed for power over 5-6 kW in old houses and even less , and this for instantaneous heating of a large amount of water is clearly not enough.
So before choosing you have to clarify the maximum permissible power for your own conditions. The easiest way to clarify this with the power supply company. It will most likely be necessary to replace the wire or run a new one to the place where the heater is installed.
The second issue is usually associated with the same power, or rather the temperature difference between the inlet and outlet. Cold water coming from the water supply system in winter and summer has a different temperature, and the difference may well reach 10-15 ° C. This means that the heater, successfully working in summer, in winter can simply “not cope.
In brief descriptions of technology, many companies indicate an approximate capacity for hot water in l min, but for a more accurate selection must also take into account the value At delta te in the characteristics of heaters can be written with a capital AT and lowercase letters , t. e. the stated temperature difference at the inlet and outlet. This parameter is usually easy to find in the documentation of the device, although you can also calculate it yourself based on the power of the heating element and the consumption of water.
For example, to heat up 100 liters of water for 30 degrees in an hour, we need a water heater with a heating element with the power just over 3.5 kW heat loss is neglected, and to the same extent we assume that the voltage in the network corresponds to the declared one . Dependence is almost linear, you can “play around” with any parameter.
For example, per minute this is obtained at approximately 1.6 liters of water heated from 5 to 33 ° C winter conditions . To put it bluntly, not much, but if you want to heat up by 10 degrees for example, from 20 to 30 ° C, as it happens enough in the summer – it is 5 liters per minute.
It is quite clear, that in summer one can take a shower with such heater, but hardly ever in winter, you need to change something, most likely, to increase power. That is why the scope of application of small electric flow heaters up to 6-8 kW is primarily summer use. Larger models are also suitable for all-day operation and for simultaneous operation of several outlets.
Electric storage water heaters
They can provide a sufficiently large amount of hot water per unit of time, unlike the flow-through type.
No special need to redo the wiring for domestic models – they are quite capable of working from the usual power supply, only some of them can if desired connect to a three-phase network that will make it possible to use more power and respectively faster to heat water. But devices with these options are more expensive.
To connect a single-phase storage water heater, the minimum requirements. They can also be used with a relatively “Weak” wiring. The water in the tank is heated for some time, and is consumed as required.
The tank capacity of storage water heaters is from 5 to 500 and more liters.
The most common applications are in the 30 to 200 liter range. Smaller volume will not be enough for continuous use but enough, for example, for the kitchen sink , the larger will be too large for domestic conditions.
Most models are wall-mounted, only “large” heaters are mounted on the floor. Wall-mounted heaters are available in horizontal or vertical mounting, although some models allow for both.
Accumulation heaters, like electric heaters, can be non-pressurised, i.e.e. electric storage water heaters for the connection of single-phase storage water heaters of the open-type and pressure type, which can be built into a pressurised system.
In non-pressurized heaters, the water stop valve is mounted in front of the tank when it is opened, the cold water that enters the tank displaces the hot water, which drains through a special faucet. These models are suitable for one tap only and usually have a small tank volume. The more popular closed type water heaters are also suitable for DHW in several locations.
Materials
The most common material for the inner tank is steel with enamel or glass ceramic coating The enamel protects the inner steel tank from corrosion. Since the tanks are working under high thermal loads, the enamel must be flexible enough and have a close ideally the same coefficient of thermal expansion with the material of the tank to prevent the possibility of cracks.
Manufacturers can use different enamels and apply them using different methods. Stainless steel tanks are made somewhat less frequently, sometimes also with an additional protective coating. Even less common, in small volume water heaters use copper or plastic.
Of course, the material of the tank should be chemically inert, so as not to “spoil the water. Both enamel coating and “food grade” stainless steel meet these requirements, but there are nuances.
Appliances with an enameled tank can develop holes and defects in the enamel coating over time. But in spite of this, the water heater can serve for a very long time. But for this it is necessary to check and promptly replace the protective magnesium anode, which is in every enameled water heater and which neutralizes the corrosion oxidation process by applying an opposite current.
The ensuing surplus of electrons cathode voltage at the damaged place shifts the potential difference between the anode and the cathode tank and causes corrosion. The anode, which gives off electrons, is connected to the steel inner tank. A current flows from the anode to the possible defective areas This anode current, which results from the destruction of the more active material Mg , prevents corrosion in the defective area.
Leaks in stainless steel usually leak at the weld seams. During welding the composition of stainless steel in the places of welds changes and corrosion resistance decreases. It is impossible to visually check the condition of the stainless steel tank.
Without special analysis it is impossible to find out the quality of non-rusting steel used in the tank. In low-cost models the economy can be due to the cheapening of the material, breaking and simplification of welding technologies. The tank is “invisible” anyway, so the unscrupulous manufacturer is ready to save money on this.
Meanwhile the quality of stainless steel depends on the service life of the entire heater: to repair it in case of leakage makes no sense. Many leading manufacturers guarantee the tanks for 5 – 10 years other components of the water heaters are guaranteed for a shorter period .
As the heating elements are usually used heating elements of different shapes, sometimes placed in a special enameled bulb to reduce the flue build-up. The normal number is one or two.
For the normal economic mode, a single heating element is turned on, if accelerated heating is required – the second element is connected as well. If you use two different wattages you can have three heating stages.
Also inside the tank is located the aforementioned anode. In order to prevent the passage of anode current to the tank components such as the heating element and the heat exchanger, the latter are installed through insulators.
Also, to prevent the anode from being wasted, there is a technical solution that balances this protection: the compensation resistor. This resistance balances the potentials and enables the magnesium anode to protect only the inside of the tank
The anode should be replaced from time to time. How often depends on the size weight of the anode, the hardness of the water and the intensity of use. Most often it is recommended to check the condition of the anode and the walls of the tank once a year. The “active anode”, which requires a power supply but is not consumable, is rarely used for domestic models.
Heating elements, anode, thermostat sensor are usually mounted on a common flange, which is attached to the bottom of the tank in the vertical version . Pressure gauge tube – short. The intake takes the heated water from the top. In the horizontal design the inlet tube is bent so that its end is at the top of the tank. If both installation versions are permitted, the tube end is inserted in the “corner”.
Flat heaters have two reservoirs connected by several horizontal overflow tubes. Water is pumped from the bottom of the first tank and taken from the second tank at the top.
With a large flow rate comparable to the volume of the tank, the incoming cold water mixes with the remaining hot water more evenly.
Between the inner tank and the body is a layer of insulation – polyurethane foam, which fill all the space between the inner tank and the outer casing of the water heater.
A layer of a few centimeters thickness is basically enough to keep the heat for a long time.
The body of the heater is often made of steel with a powder coating also encountered housing made of plastic. Occasionally, “for beauty”, the casing is made of stainless steel. The cross section of the body shape can be square, straight carbon, round.
What’s inside?
Any water heater includes a thermostat, overheat sensor thermostat limiter , as well as an external very important node – safety group, sometimes – an additional pointer thermometer its purpose – more aesthetic than practical and, of course, the control panel. In simple models on the panel are a power button and temperature regulator – for operation it is enough. The more sophisticated models have a touch screen control panel with an LCD or LED display that allows you to control all the modes of operation of the device. Here are just a few of them:
– the setting of the desired temperature. Some models – with an accuracy of up to 1 ° C
– fast heating at full power at the touch of a button
– Setting various heating programs, including on a timer, day or not
– Reducing the water temperature when not in use for a long time in order to save energy and resources
– periodical switching on heating to high temperature for disinfection purposes
– mode of limiting the heating temperature in the range of 40-60 “Q
– child lock mode
Various other modes are available from different manufacturers. Some heaters are able to work with remote control and even remote control devices. Each of these functions, directly or indirectly, can increase the comfort of operation, most of them also allow you to reduce energy consumption this does not of course apply to the maximum heat mode . Currently, the “evolution” of water heaters is mainly in this direction: fundamentally new competitive technical solutions on the “mechanical part” can not be invented, but the potential of electronics is great enough.
So: flow-through or storage?
A reminder: both types of water heaters use the same amount of electricity to heat the same amount of water. Only a flow-through one will need a lot of it, and a storage one will need it gradually. “Disadvantages” of storage heaters – a higher price, large garaits, the impossibility of getting hot water quickly you have to wait until it heats up .
Heat loss of the storage heater will be more, if used infrequently, you will also have to put up with the fact that the heated water will aimlessly cool in the tank. A little caveat, though: when using multi-tariff meters, a storage water heater with a built-in timer can be set to heat water at night, and the cost of heating will be markedly reduced.
Actually the main operational difference is in this: for the periodic use it is more expedient flow-through model if the wiring will allow . In the case of permanent residence, the accumulation tank will be more convenient and cheaper. And the capacity and volume of the tank should be selected based on your own needs.
Gas water heaters
Like electric, they can be either flow-through or storage, but in any case – are built into a regular DHW system, t. e. are pressurized. Here we will not look at the many design features of such heaters. They are not much different from boilers used for space heating.
Most of the gas water heaters on the market, are equipped with an open combustion chamber and are “traditional” convection , in addition – flow. The reason.
Most of the potential market for such heaters are long designed and built homes that have central heating, gas supply, no general hot water system and a working chimney.
In fact, the new equipment is offered to replace previously installed gas heaters that also used an open combustion chamber. In general, it makes little sense to do nutritional alterations, and unnecessary space to install the storage tank is unlikely.
Of course, this does not mean that models with a closed combustion chamber or storage tanks are not available. There are just a lot fewer of them. As for condensing boilers, their use only for domestic water heating is unlikely to pay off – too expensive. There are such heaters, but they are designed for industrial applications.
Gas instantaneous water heaters
The usual range of maximum power in the domestic sector – from 15 to 30 kW. For several points of water use it is enough, t.e. These models cover the needs of an apartment or small home with plenty of room to spare.
Such heaters are categorized primarily by the way in which the heater is installed. The simplest – with piezo ignition from the button.
Slightly more expensive, but more convenient heaters with an electric ignition. It is automatic, the energy source is often a pair of batteries. There are also units that do not require batteries: they have a small hydrogen generator that generates the necessary electrical energy using the energy of the water flow.
It is noteworthy that all three of these types of heaters with an open combustion chamber are energy independent. Models with a closed chamber and built-in fan require a power connection from the network.
Accumulation gas water heaters
As usual, their most important parameter – the volume of the tank, which can be 50-300 liters, for smaller models the installation is usually wall-mounted, the larger – of course, floor standing. The maximum thermal capacity – in the region of 5-10 kW.
Flow-through heaters are mostly used in apartments, while the accumulators should be installed in detached houses, in the country.
Their comparatively low popularity can be explained by the fact that it is difficult to find a country house, in which heating and hot water have to be implemented separately. It is easier to organize a combined system with heating from a single boiler. Although the options may be different, and in the countryside you can sometimes find homes with a centralized heating system. Or, alternatively, if the water points are far away from the home boiler room, it would be easier to put such a heater closer to them.
Advantages and disadvantages of flowing and storage gas heaters are similar to electric heaters, only, of course, there is no question of the allocated electrical power.
Combined water heaters
Although such models are not covered in the reviews in this issue, they are worth mentioning. Such water heaters, also called indirect water heaters, receive their energy from outside sources. They are a tank with tubular coils installed inside, through which the heating medium flows.
Typically, the main heating of water is from a stationary heating system, t.e. any type of boiler or heat pump. Most of these boilers also have a heating element that comes on at a high flow rate of hot water, or when the system starts up after a break.
There are also more interesting solutions. We need energy to heat water, which means we have to pay for it eventually. The easiest way to save money is to use solar collectors.
Heating water from the sun is the cheapest, the costs here will only be for the circulation of the fluid between the boiler and collectors although in some schemes the pump is not needed and the operation of electronics.
We can assume that one panel of the solar collector with an area of about 2 m is enough to heat the house2 Half is not enough to get the required amount of hot water in an average room for one or two people. The rest can be obtained either from the heating system or from the heating. There are many options here.
With solar collectors are available as “solo” systems, not connected to the heating system, and combined. The main drawback is the relatively high initial cost of these systems, but they pay off later.
Personal water heater
Article content
Can you recommend a reliable and cost-effective personal water heater for daily use? I’m looking for something compact and easy to use in my small apartment.
What is the average cost and energy consumption of a personal water heater?