Electric water heaters: storage or flow-through?

Hot water, like heating, is one of those “amenities” without which a comfortable home is unthinkable. In a multifamily house, it is perceived as a must. The hero of a well-known joke would bathe in the river in summer and answer the question “And in winter??In winter” he would answer “How much of a winter is this?!”. Even a few summer weeks during which the centralized hot water supply is stopped for system profiling are a source of discomfort for city dwellers. There are several ways out. You can visit someone and wash at the same time or buy a small water heater, and if possible go out of town, to the cottage. However, a water heater will definitely come in handy there as well.

Those who live permanently out of town, however, have to deal with the challenges of DHW and heating individually in each home. Sometimes both tasks can be combined by installing a common boiler, but there are cases when it makes more sense to “separate” these systems. In small towns and villages there is also a variant, in which heating is centralized, and DHW 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 operate either with electricity or gas Other options, such as wood or coal-fired boilers, can be treated as exotic.

ELECTRIC WATER HEATERS

In terms 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 have more advantages than disadvantages, and in many cases they are the most convenient to use. First of all, the advantages include the compactness and low cost of the devices. They are divided into two types – flow-through and storage.

Electric instantaneous water heaters. The design of these 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 their features they are divided into non-pressurised and pressurised.

The first tap, shut off the water, installed at the inlet cold water. These models are used primarily for a single point of water extraction. Their power is comparatively low and many are supplied with a shower head or a tap.

In domestic conditions, such models are used in villas, or in moments of planned outage of 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 it makes no sense to lay a separate domestic hot water pipe.

High-pressure models are designed for permanent connection to a pressurised mains water supply network These are usually larger heaters that can supply several taps at the same time, or a flow rate comparable to that of a centralised DHW supply, e.g. in a city. They can in principle be used without pressure, but not vice versa: Their internal pressure capacity is not designed for high pressure.

Electric water heaters are divided into devices with mechanical hydraulic and electronic control – to ensure that the system turns on and off at the right time. “Mechanics” switch on the heating elements usually all together , based on the change of position of the membrane, which has a mechanical drive of the contact block.

More complex electronic control circuits switch the heating elements on gradually, depending on the flow rate, temperature and water pressure. It saves energy and water, and also gives you a stable outlet water temperature. Such models are much more expensive. Most 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 it’s the same here: “mechanics” is cheaper, “electronica” gives more possibilities

PROS AND CONS OF FLOW-THROUGH HEATERS

First of all, the advantages of cylinders should include small size and weight, which simplifies installation and mounting. They are also convenient if the water extraction point is used only occasionally.

The energy is consumed only while the water passes through the heater. Practically everything that is heated is immediately consumed the volume of non-dissolved liquid in pipes of the pressure heater is small, heat losses of all types are also negligibly small .

The main limitation in their application is related to 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 difficult to get such power in normal household conditions.

Electric wiring in the house is unlikely to be designed for power over 5-6 kW in old houses 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 allowable power for your own conditions. The easiest way to do this is to ask the power supply company. It is likely that the wire must be replaced or a new one brought to the place where the heater is installed.

The second issue is usually related to the same power, or more precisely, to the difference between the inlet and outlet temperatures. 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 give an approximate hot water capacity in l min, but for a more accurate selection must also take into account the value of At delta te in the characteristics of heaters can be written with a capital AT and a small letter , ie. e. Declared inlet and outlet temperature difference. This parameter is usually easy to find in the documentation for the device, although you can calculate yourself based on the capacity of the heating element and water consumption.

For example, to heat up 100 liters of water at 30 degrees for an hour, we need a water heater with a heating element capacity of just over 3.5 kW heat loss is neglected, and in addition we assume that the voltage in the network corresponds to the declared . Dependence is practically 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 10 degrees for example, from 20 to 30 ° C, as it happens quite a lot in summer – it is 5 l min.

It is quite clear that in summer you can take a shower with such heater, but in winter you can hardly take a shower, you should change something, most likely, increase the power. That is why the application area of small electric flow heaters up to 6-8 kW is primarily summer use. Models with higher output are also suitable for circular operation and for simultaneous operation of several outlets.

ELECTRIC STORAGE HEATERS

Unlike flow-through, such devices are capable of providing a sufficiently large volume of hot water at a time.

Especially redistribution of wiring for domestic models does not need – they are quite capable of working from the usual power supply, only some of them can if desired connect to a three-phase network, which will make it possible to use more power and therefore faster to heat water. However, the devices with such options are more expensive.

To connect a single-phase storage water heater, the requirements are minimal. They can also be used with relatively “Weak” wiring. The water in the tank is heated for a certain time and is consumed as required.

Tank capacity of storage water heaters ranges from 5 to 500 and more liters.

The most commonly used tanks have a capacity of 30 to 200 liters. A smaller capacity will not be sufficient for continuous use but will suffice, for example, for the kitchen sink , the larger will be too large for domestic conditions.

Most models are wall-mounted, only “heavy duty” heaters are mounted on the floor. Wall heaters differ in the way of installation: horizontal or vertical, although some models allow both types of installation.

Hot water heaters, just like electric water heaters, can be non-pressurized, i.e.e. Open-type, and pressure, which can be built into the system under pressure.

Non-pressurized heaters have a stopcock installed in front of the tank when it is opened, the cold water flowing into the tank displaces the hot water which drains through a special faucet. Such models are suitable for one tap only and usually have a small tank volume. More popular closed-type water heaters are also suitable for the organization of DHW in several places.

WHAT THE TANKS ARE MADE OF?

The most common material for the inner tank – steel with enamel or glass ceramic coating Enamel protects the inner steel tank from corrosion. Since the tanks work in conditions of high thermal loads, the enamel must be sufficiently elastic and have a similar ideally the same coefficient of thermal expansion with the tank material to avoid the possibility of cracks.

Manufacturers can use different composition of enamels and apply them using different methods. Slightly less often the tanks are made of stainless steel, sometimes also with a protective coating. Even less often, in small water heaters, copper or plastic is used.

Of course, the tank material must 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 enameled tanks over time can develop pitting and enamel coating defects. Despite this the heater can serve for a very long time. For this purpose, however, it is necessary to check and promptly replace the protective magnesium anode, which is included in every enamelled water heater and which neutralizes the corrosion oxidation process by imposing an opposite current.

The resulting 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. From the anode a current flows to the possible damaged areas This anode current, resulting from the destruction of the more active material Mg , prevents corrosion in the damaged area.

Leaks in stainless steel usually occur at welds. Welding changes the composition of stainless steel at welds and reduces corrosion resistance. And visually assess the condition of the stainless steel tank is unlikely.

How to find out the quality of non-rusting steel used in the tank without a special analysis. Inexpensive models can save money by reducing the price of the material, disrupting and simplifying welding procedures. The tank is “invisible” anyway, so that the unscrupulous manufacturer is willing to save just on this.

Meanwhile the quality of stainless steel determines the service life of the whole heater: to repair it in case of a leakage is pointless. Many leading manufacturers provide a 5-10 year warranty on the tanks other components of the water heater have a shorter warranty .

Heating elements are usually made of variously shaped heating elements, sometimes placed in a special enameled bulb to reduce nakedness. Their usual number – one or two.

For normal economy mode one heating element is used, if accelerated heating is required – a second element is connected as well. If two different wattages are used, it is possible to have three heating stages.

The above-mentioned anode is also located inside the tank. To prevent the passage of anode current to the tank components such as the heating element and heat exchanger, the latter are installed through the insulators.

To keep the anode from being wasted, there is also a technical solution to counterbalance this protection: A compensation resistance. This resistance balances the potential and allows the magnesium anode to protect only the inside of the tank

The anode must be changed from time to time. How often – depends on the size weight of the anode, the amount of hardness salts in the water and the intensity of use. Most often it is recommended to check the condition of the tank and the walls once a year. “Active anode”, which requires a power supply, but is not consumable, for domestic models is used quite rarely.

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 . The feeding tube is short. The intake takes the heated water from the top. In the horizontal version, the inlet tube is bent so that its end is near the top of the tank. If both types of installation are allowed, the end of the tube is inserted “in the corner”.

Flat-panel heaters have two reservoirs connected by a series of horizontal overflow pipes. Water goes down the first tank and comes out of the second tank from above.

At a large flow rate, comparable to the volume of the tank, the incoming cold water mixes with the remaining hot water more evenly.

There is a layer of polyurethane foam between the inner tank and the outer casing to fill all the space between the inner tank and the outer casing of the water heater.

a few centimeters thick layer is basically enough to keep the heat for a long time.

The heater casing is most often made of powder-coated steel. Sometimes, for “beauty”, the housing is made of stainless steel. The cross section of the body shape can be square, rectangular, round

WHAT’S INTO THE INVESTMENT?

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 – rather aesthetic than practical and, of course, the control panel. In simple models on the panel are the power button and the temperature regulator – for work 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. Let’s list just a few of them:

– setting the desired temperature. In some models – with an accuracy of 1 ° C

– rapid heating at full power at the touch of a button

– setting of different heating programs, including a timer, day or night timer

– reduction of the water temperature when not in use for a long time in order to save energy and resources

– Intermittent high-temperature heating for disinfection

– temperature limitation mode in the range of 40-60

°C

– child lock mode

Different manufacturers have different modes. Some heaters can be controlled remotely or even remotely. Each of these functions can directly or indirectly increase operating comfort, most of them also reduce energy consumption this does not apply to maximum heat mode of course . 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?

To begin with, it should be recalled: electric power to heat the same amount of water, both types of heaters also use the same. Only the flow-through one will need it a lot and immediately, and the accumulation one – gradually. “Disadvantages” of storage heaters – higher price, large gary, 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 also have to put up with the fact that the heated water will aimlessly cool in the tank. True, it is worth making a small reservation: when using a multi-tariff meters storage water heater with a built-in timer can be set to heat water at night, and the cost of heating will be significantly reduced.

Actually, the main operational difference is just that: for periodic use, the flow-through model is more appropriate if the wiring will allow . If you live in a permanent flat, the accumulator is more convenient and cheaper. And the capacity and size of the tank should be chosen according to your own needs.