About heat accumulators


Heat accumulator without an isolation	Heat accumulator with an isolation in tarpaulin mantle

Most of us know what the accumulator is but usually this device is associated with electric energy (batteries that can be charged or car batteries). But not everyone is acquainted with heat accumulators, the demand for which increases with every year, in Western Europe they have already become a norm.

Taking into consideration the rise in the usage of regenerating power sources many European producers admitted the necessity of combining several heat power sources in the unified heat supply system. Such a system may include gaseous-fuel and liquid-fuel boilers, electric heaters (eg, HEs) and alternative sources - heat pumps, solar collectors, wood-burning boilers and heat reclaiming devices. Combined heating system allows using heat sources that are temporarily available maximally effectively.

The solar energy comes only when the sun shines, the heat from burning wood or briquettes is available only when the fire burns. The income of heat energy from heat pump or electric heater can be profitable only during the periods of days when the rates for public utilities are reduced. There is a fact that can make the situation even more difficult: the water temperature which is provided by such sources of thermal energy may vary significantly. The use of heat accumulator that can simultaneously serve as a battery, hydraulic control valve and also continuous cooker for preparing sanitary hot water for household needs can solve the bulk of the problems that arise when implementing such systems.

Each source of heat energy during its functioning provides heat accumulator with heat, which, as appropriate, gives it back to the heating system to maintain proper temperature in the lodging that is heated. The most common and easy for usage are the capacitive type of accumulators that use thermal capacity of substance that is heated without changing its aggregate state. In most cases water is used (cheap and convenient), rarely - aqueous solutions of salts, and also stone, pebble. The thermal receiver capability or power (W) that can be accumulated in heat accumulator of capacitive type can be determined by the formula:

The most common is the use of accumulator tanks of 300-2000 l volume that are used in systems with natural and forced circulation. The heat accumulator in the simplest conformation is a vertical steel tank; its height is 3-5 times more than the diameter for the water temperature stratification. There are branch pipes placed throughout the tank height for water supply and drainage, as well as for assembling electric HEs.

High-temperature water accumulates at the top of the tank and can be drainaged through the upper branch pipes for radiator heating; less heated water (middle part of the tank) can be drainaged by middle level branch pipe for heating with the help of warm floor. The inner surface of the tank does not require protection from corrosion, because the same water is constantly used in the heating systems, it eventually becomes «neutral». To reduce heat loss through the tank wall you should isolate it, for example, with heat-resistant foam rubber, its thickness should be to 100 mm (Fig. 2).

There can be provided horizontal partitions in the tank, they divide it into sections with different levels of temperature according to the height. In some way, it improves the efficiency of heat accumulation. It can also be completed with audit flange.

The steel heat exchanger is placed at the bottom of the tank for connection to solar collector’s heat supply system. Its location provides the possibility of the collector circuit functioning at the lowest possible temperature with maximum efficiency.

A small tank (50-100 l) is traditionally placed at the top part of the tank for the preparation of drinking hot water. This reservoir is completely surrounded by hot water which causes rapid heat transfer to the drinking water. Here appears the possibility of legionella reproduction; it requires additional expenses for technical means of protection. The alternative option is the use of heat exchanger made of stainless esculent steel. The accumulator works as a running water heater in this case. There is the minimum amount of water in the heat exchanger; it reduces the likelihood of the legionella appearance. The small capacity does not mean low efficiency. The large area of heating and heat reserve in the accumulator instantly allow heating the cold water flow to the necessary temperature.

The maximum temperature of heat accumulators does not exceed 90 °C. The technical requirements for heating boilers also determine that the highest temperature is 95 ° C. The size and temperature conditions of heating elements provided for use in heating system is a very important factor when you install heat accumulator in your house. The experience shows that the most effect from accumulator will be achieved in low temperature system. The heat accumulator system will operate in the best way in a building heated with the help of warm floors.

It should be noted that the heat accumulator in many cases for complex heat supply systems is not an option which makes the system comfortable and economical, but an essential element – “the heart” of the system. For example, in Western Europe the installation of heat accumulator with fuel-wood boiler is an obligatory requirement. In this case the heat accumulator is not only economically profitable but also due to complete combustion of fuel it prevents clogging chimney with tar deposits. The firewood contains many different substances, including tar, acids and others that are evolved from incandescent firewood. The boiler should constantly function at full capacity to ensure the quality burning of all these substances, and this can be achieved by creating the heating system with heat accumulators. The principle of regulation the capacity of many solid-fuels boilers is focused on the incomplete fuel combustion or smouldering. This operation is performed in conventional boilers by damper controller - air valve which opens with a chain and close itself at a certain temperature. In this way oxygen is not supplied to the fuel, but it is incandescent and it evolves different volatile substances that would burn in other conditions.

We get 20 percentage firewood saving after installing the heat accumulator with thermal pyrolytic boiler.

Therefore, the installation of heat accumulator is recommended to plan at the stage of designing the building. Otherwise, the desire to install it may not coincide with the technical capabilities of the fuel due to lack of space.