A very important and crucial part of a central heating system are the radiators because they transfer the heat from the source (boiler, heat pump etc.) to the rooms. Their working principle is based on fluid circulation in the radiator. Heated fluid enters the radiator from a piping system and when it cools it gives off the heat in the room. There are two main types of radiators: those that radiate heat (the water flowing through the radiator is with a high temperature), and those that use convection (accelerated heating with a fan-coil unit).
Main classification of radiators is based on the material they are made of.
Steel radiators keep warm and give off heat for long periods of time. They are made using cold rolled steel that is highly durable and corrosion resistant. This makes steel radiators reliable and with long working life. They work both on the radiation and convection principle and can have thermal regulators installed to automatically set desired temperature in the separate rooms. Their main disadvantage is that even with small mechanical impacts the protective layer can be damaged. They are recommended for local closed systems where the heat carrier quality is controlled.
Made completely out of aluminium which is light and pliable material that allows fast and cheap manufacturing as well as easy transport and installation. Aluminium reacts quickly to temperature changes which means that it has very high thermal conductivity. Aluminium radiators are heated fast but they also cool down fast. The material allows them to be covered with a protective layer and powder coated in different colours (even though white is the most commonly used colour). This type of radiator has very high heating capacity even in small size. They are not recommended for large central heating systems due to the bad quality of the heat carrier (high acidity, rust and particles). This can lead to electrochemical corrosion.
The most popular radiator type, known for decades and mainly used in old buildings. Their main disadvantage is the very high weight and large size which makes them difficult to transport and install. They are not resistant to hydraulic impact – cast iron is a relatively fragile metal. Due to the high inertia of cast iron, traditional cast iron radiators are characterized with a prolonged heating time, but they also keep the heat and radiate it for extended period. This, coupled with the long operation life are the main advantages of cast iron radiators.
They are also made in sections and they are made of combination of steel and aluminium. Due to this fact they have the advantages of both radiator types. For the base details (the ones coming in contact with water) steel is used, and the role of heat exchanger is taken by aluminium parts, i.e. internally they are made of steel and the external cover is made of aluminium fins. They are beautifully designed and have long operation life. Bimetallic radiators withstand pressures of about 50 bar and hydraulic impact and they don’t have any special requirements regarding the heat carrier fluid. Higher quality models have external and internal layer of corrosion resistant primer which also makes them relatively expensive.