Useful information about radiators

The purpose of any heating system is to create a comfortable temperature in the environment where people stay, that is, to heat the air in a room to a temperature of 18–20 °C and maintain it at this level. Walls, of course, will transfer part of the heat to the external environment, so heat in the room must be continuously replenished, i.e. a heat balance must be maintained — as much heat as goes outside, the same amount must be added. A person, as needed, creates local heating of certain objects (a frying pan on a stove) or their cooling (beer in a refrigerator).

A space heating system consists of heat generators (stoves, boilers) and heating devices (batteries, radiators). A stove (fireplace) that directly heats the air in a room belongs to local heating. A system in which the heat generator (boiler) is located in a separate room and the heating of rooms is carried out by batteries is called central heating. A stove is one of the simplest heating devices and does not allow quick temperature regulation in a room. The stove must be fired continuously or periodically. It accumulates heat in its mass and then gradually releases it by radiation through its external surfaces. Part of the heat is transferred to the air by convection. The efficiency of even the best stoves does not exceed 50%, meaning that half of the energy of the burned fuel literally goes up the chimney.

The central heating system consists of three parts, which we will consider separately:

  1. Batteries or radiators of various designs;
  2. Pipelines that transfer heat using a heat carrier (water, steam);
  3. Boilers for various types of fuel.

The boiler must quickly heat the water in the system and switch off when the required temperature is reached in order to save fuel. The pipeline must deliver heated water to the radiators as quickly as possible and lose as little heat as possible along the way. The radiator must quickly heat the air in the room to the set temperature and, using a thermostatic valve, stop taking hot water from the system.

CAST-IRON SECTIONAL RADIATORS — heating devices well known to everyone since childhood. They belong to outdated heating systems and are not used abroad. They have a small heat-emitting surface and low thermal conductivity of the metal, transfer heat mainly by radiation and only about 20% by convection. A common domestic cast-iron radiator section MS-140 weighs 7.5 kg, holds 4 liters of water, and has only 0.23 m2 of heating surface area. Each room in an apartment requires a battery of 8–10 cast-iron sections or even more. In a large apartment or a private house, the total weight of all cast-iron batteries and the water in them amounts to tons, which makes it necessary to use large-diameter pipes that cannot be hidden in walls. The movement of the heat carrier in the system occurs by gravity, which greatly slows down heat transfer.

Reference books state the thermal radiation power of a cast-iron section MS-140 as 160–180 watts at a heat carrier temperature of 90 °C. However, this radiation power is achieved only under ideal (laboratory) conditions that are unattainable in real life. Since radiation power strongly depends on temperature, the actual heat output of a cast-iron section at 60 °C will not exceed 80 watts. The supply of heated water from the boiler to a cast-iron battery occurs slowly; to ensure an average temperature of the entire battery of 60 °C, the supplied water temperature must be at least 75 °C, while the return flow will be about 45 °C. Calculate what power the boiler must have to heat a ton of water to 75 °C. It should also be taken into account that several degrees are lost in thick metal supply pipes, so the boiler must deliver 85–90 °C and operate at its limit. Ensuring a cast-iron battery temperature of 90 °C with conventional (non-steam) boilers is impossible and also dangerous — burns can occur even at 70 °C.

In order to slightly increase the convective heat output of cast-iron radiators, they are recommended to be installed only under windows, so that cold air descending from the glass surface is forced to pass through the radiator. The aesthetics of cast-iron radiators, to put it mildly, are imperfect and spoil the interior, so they are hidden behind decorative screens. Such screens completely isolate thermal radiation inside the room, leaving only a weak flow of convective air for heating. The cast-iron radiator then has no choice but to intensively heat the wall on which it is installed by radiation. The wall, naturally, successfully transfers this heat to the external environment. There are even reflective screens sold that must be glued to the wall.

STEEL PANEL RADIATORS — an attempt to combine the properties of sectional radiators with convective ones. Such a radiator consists of two steel plates between which the heat carrier circulates. The plates are 1.2 mm thick, connected by spot electric welding, and contain stamped channels through which water flows. A panel the size of a typical cast-iron radiator has a thickness of 30 mm, but only half the heat output. To increase thermal power, two or even three panels are installed in parallel. With two or three panels, the radiator transfers heat by radiation only from the outer surfaces, so rows of U-shaped plates are welded to all inner surfaces, significantly increasing the heat-transfer area — that is, the inner surfaces function as a convector.

All these modifications did not go unnoticed in the design — the weight of a three-panel steel radiator with a set of plates is not much less than that of a cast-iron battery of the same size, it also holds a significant amount of water, which greatly reduces the efficiency of temperature regulation. The overall thickness of such a radiator is even greater than that of a cast-iron one and is about 160 mm.

The thermal characteristics are not much better than those of cast-iron radiators. The thermal output stated in technical documentation is given for a water temperature of 90 °C, but with such volumes of water in the system and such radiator weight, an ordinary boiler cannot provide this temperature. Technical materials necessarily include reduction coefficients for radiator heat output at lower temperatures; for example, at a typical system water temperature of 60 °C, the power drops threefold.

The main disadvantage is the same as that of aluminum radiators — accelerated corrosion. The difference is that this unpleasant effect is even more pronounced. Steel corrodes in water at a rate of about 1 mm per year even under favorable conditions. Hot central heating water can hardly be considered favorable, so steel pipelines with a wall thickness of 3–4 mm do not last more than 30–40 years. Panel radiator plates with a thickness of 1.2 mm will not last more than 12 years even theoretically. The fact is that the plates are welded together by spot welding, so the steel in the welding zones is annealed, loses all anti-corrosion properties, and deteriorates much faster.

Unfortunately, other types of radiators were previously unknown in our country, so panel radiators looked modern compared to poor cast-iron batteries and became widespread, aided by aggressive advertising from exporting companies. Even now, advertisements continue to claim good anti-corrosion protection of these radiators — indeed, they are well painted on the outside, but rot from the inside.

ALUMINUM SECTIONAL RADIATORS — a more advanced design using a material with a high heat transfer coefficient in the form of an aluminum alloy. Aluminum radiator sections have a depth of only 80–110 mm (cast iron — 140 mm), a water volume of about 0.5 liters, a heating surface area of 0.4 m2, and a wall thickness of 2–3 mm. Aluminum sectional radiators transfer more than half of their heat by radiation, and the rest by convection.

Some types of aluminum radiators have a highly developed surface in the form of additional thin fins placed inside the section, increasing the heating surface area of one section to 0.5 m2 and raising convective heat transfer to 60%. The thermal power of one section is declared by manufacturers to be up to 180 watts.

Externally, aluminum sectional radiators look quite aesthetic, have low weight, and are convenient for wall installation. Due to the reduced volume of water in the sections, aluminum radiators are well suited for regulation using thermostatic shut-off valves and thermostatic heads. Heat-regulating elements, which must be installed on all aluminum radiators, allow limiting the flow of hot water through the radiator when the set room temperature is reached. The thermal inertia of an aluminum radiator is low, so the thermostatic valve reacts to temperature changes in the room literally within 5–7 minutes — opening or closing the access of hot water to the radiator, achieving fuel savings of up to 30%. Cast-iron radiators have much higher thermal inertia — more than one hour — making regulation and fuel savings practically impossible.

However, aluminum radiators have disadvantages that limit their application:

  1. The main and most significant drawback is susceptibility to electrochemical corrosion. Some materials form so-called electrolytic pairs — when connected in an electrolyte environment, an electrochemical reaction occurs in which one of the metals undergoes electrochemical corrosion and rapidly deteriorates. Aluminum alloys are generally resistant to corrosion, but when paired with copper in a liquid non-distilled environment (a weak electrolyte), they corrode intensively — aluminum turns into white powder. This phenomenon can be observed in old flashlight batteries. If an aluminum radiator is connected to copper pipelines or to a boiler with a copper heat exchanger (all modern wall-mounted gas and electric boilers have copper heat exchangers), this can lead to rapid electrochemical corrosion of the radiator.
  2. Aluminum radiators are made thinner to improve heat transfer, making them insufficiently strong. Damage often occurs during installation — excessive force when tightening a nipple or valve leads to destruction. Pressure die casting is used in manufacturing, which creates a risk of hidden defects in the form of internal cavities that only appear during operation.

BIMETALLIC SECTIONAL RADIATORS — the most advanced design, allowing all the advantages of aluminum radiators to be used while avoiding their disadvantages.

The originality of the bimetallic radiator design lies in the fact that it consists of a strong and electrochemically corrosion-resistant steel tubular frame, with external fins made of high-quality aluminum alloy using high-pressure casting. This forms a monolithic connection that eliminates contact between aluminum and water, and therefore corrosion. The design guarantees resistance to sudden overpressure spikes up to 25 atm throughout its entire service life — something neither aluminum nor cast-iron radiators can withstand. Since the heat carrier moves inside the radiator through the steel frame, hidden defects in the form of internal cavities in the aluminum shell do not affect the overall strength of the structure. The radiators are adapted for any heating systems of residential and industrial premises with a working pressure of up to 18 atm. They do not require special water preparation (purification, acidity or alkalinity reduction), unlike aluminum radiators. The radiator housing has no sharp corners, and the surface temperature is twice as low as inside, which allows their use, even under very strict standards, in children’s and medical institutions. During operation, the radiator creates an air thermal fan effect and mixes air layers in the room very effectively. In Ukraine, the only patented manufacturer of bimetallic radiators is LLC “PRES”, although imported bimetallic radiators can also be found on the market. However, imported radiators are inferior in some parameters to those produced by LLC “PRES”:

  1. the nominal bore of the vertical internal pipe in PRES radiators is 3/4 inch, while foreign analogs have 1/2 inch, which leads to faster clogging;
  2. the wall thickness of the steel pipe in PRES radiators is 2.8 mm, while foreign analogs have 1.2 mm, meaning higher reliability and durability;
  3. the use of pipes with an internal diameter of 22 mm in PRES radiators reduces hydraulic resistance compared to foreign analogs (internal diameter 13–17 mm).

Considering all the above qualities, PRES radiators have a price approximately equal to imported aluminum radiators, and sometimes even lower, and are significantly cheaper than comparable bimetallic ones.

We wish you success in equipping your home with a modern, comfortable, and reliable heating system.