Water Cylinders

Water cylinders are devices used for making domestic hot water (DHW). Heating the water in the cylinder can be done by using different types of energy – electricity, gas, wood, renewable sources or combined systems. The main principle of operation is convection – cold water from the lower part of the water cylinder is heated and rises to the top part. When the hot water tap the pressure applied by the entering in the water cylinder cold water makes the hot water exit it through a pipe. This way the volume of water is reduced and more cold water enters the cylinder. This makes the overall temperature of the water to drop and a thermal regulator turns on the heating element.

Main types of water cylinders:

Conventional storage tank water cylinder (water heater)

These are the most popular type of water cylinders used in homes. Water cylinders with storage tanks have an internal body which holds water kept at a preset temperature even when there is no water consumption. This is why in terms of efficiency these water cylinders have a larger electric power consumption and they need time in order to heat the water. Due to the good insulation, the water cylinder cools down very slowly and the water maintains its temperature for a long period. Time to heat the water depends on the volume of the water cylinder, the power of the electric heating element and the set temperature. The main parts of this type of water cylinder are:

• Water tank. The part that stores water and where it’s heated. Depending on the type and quality of the construction material (of the water tank) the operating life of the water cylinder can greatly vary. It can be made of:
• Stainless steel, which is the most reliable but also most expensive option. These water cylinders have very high corrosion and mechanical deformation protection. They don’t need anode protectors.
• These water tanks are made of cold-rolled steel with enamel coating up to 2mm thick.
• Thermal insulation layer that covers the outside of the water tank. The insulation is made of polyurethane foam or porous rubber and reduces heat loss.
• External layer (casing). The external layer of the water cylinder combined with the insulation is usually no less than 5cm thick which allows the water to be kept warm for up to 48 hours after the water heater is turned off.
• Heating element
• Cold water inlet. Usually located in the lower end of the water cylinder and has threaded connection for the water mains.
• Hot water outlet. The internal part is in the upper part of the water cylinder and the external is threaded.
• Thermal regulator (thermostat). This is the device that turns the water cylinder off when the set temperature is reached. The thermostat can be mechanical – bimetallic plate that opens the electric circuit when reaching a set temperature or an electronic one.

Depending on the mounting type the water cylinders can be:

• vertical water cylinder. This is the most common type that can completely cover the needs of a household.
• horizontal water cylinder. The operation principle is the same as the vertical water heater, the difference is only in the mounting direction. The horizontal water cylinder is more suitable for smaller rooms where space needs to be saved. They are usually mounted close to the ceiling
• low volume water cylinders for mounting above or below a kitchen sink. They have a maximum volume of 30 L, they heat water very quickly and that makes them very suitable for installing in kitchens when the main water cylinder is installed far away.
• free standing water heaters. This type of water cylinders have large volumes reaching more than 1000 L and electric heating elements with up to 12 kW of power. They are mainly used for providing DHW to hotels, large domestic and administrative buildings.

Instantaneous water heaters

These are tankless water heaters that heat the water instantly when it passes through them and they are characterized with higher electrical power. Instantaneous water heaters have compact sizes, no storage tanks and produce hot water only when needed. This makes them more energy efficient. The most common type of instantaneous water heaters are using gas as a power source.

Combined water heaters

Also known as indirect water cylinders, they are electrical water cylinders that have one or more heat exchanging coils and an electric heating element. Apart from electricity, they can use different power sources.

Solar water heaters

Water is heated from an external solar collector (panel or vacuum tubes). Some versions heat the water to a certain temperature and then it is sent to a larger water tank where it can be heated further. This type of water cylinders can be active (using pump) or passive (using the pressure of the water mains to circulate water).

Heat pump water heaters

These water cylinders extract heat from the air and use it to warm up water. They use very little electrical energy and have very high energy efficiency. They are usually equipped with a display used to adjust the working mode of the water cylinder.

Condensing water heaters (gas water heaters)

They are used in systems with constant water heating. The condensing water heater uses natural gas or propane from a central network or propane gas tanks. The fuel is burned in a combustion chamber which heats water in the heat exchanger.

Depending on the volume (capacity) there are models from 5 to more than 1000 L. Water cylinders with capacity up to 15 L are used in kitchens, mounted above or below the sink. The most commonly used water cylinders installed in bathrooms are with volumes with 50 to 100 L. For guest houses, villas, restaurants and similar establishments are used water cylinders with volumes of around 300 L. For large hotels and public buildings water cylinders with volumes of 1000 L and more are used.

Another way to separate water cylinders is according to the heating element power. Instantaneous water heaters use more power – models for kitchens usually consume about 3,5 kW, and bathroom versions about 7,5 kW. Water cylinders with tanks have lower power consumption - from 1,5 kW to 3 kW.

Water cylinder kits usually includes a non-return valve and mounting elements.

WATER CYLINDERS

Conventional storage tank water cylinder (water heater)

Instantaneous water heaters

Combined water heaters

Solar water heaters

Heat pump water heaters

Condensing water heaters (gas water heaters)