Coolant for heating, antifreeze for heating — how to choose what you need to know

The reliability of the heating system of a private house largely depends on the choice of coolant. But with all the richness of the choice of coolants or antifreezes on the market, it is simply impossible to find the ideal option “for all times and peoples”.

What is the difference between various antifreezes for heating, what are the limits of their application, what are the features of operation — all this will be discussed further.

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• Heat carrier for heating — basic information and characteristics

• The best coolant is water?

• Importance of Corrosion Control, Danger of Zinc Pipes

• Heat carriers of heat supply systems: types and features

• Design features of the heating system when using antifreeze

• Choosing a circulation pump

• Service life of antifreeze

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Heat carrier for heating — basic information and characteristics

First, let’s define what a coolant is. A heat carrier for a heating system is a liquid substance used to transfer heat energy from a heat source to heating appliances. Steam is sometimes used to transfer heat, but not in domestic heating systems.

Based on the definition, you can understand what qualities a coolant should have:

• transfer the maximum amount of heat from the heating boiler to the radiators;

• ensure the lowest possible heat loss during this transfer;

• have a low viscosity — otherwise the speed and temperature of the coolant in the system will drop, and the losses will increase accordingly;

• not cause corrosion of pipes and radiators through which it passes;

• do not leak and leak;

• be safe to use.

Important, especially in our time, is the cost of the coolant. But let’s make a reservation right away — a miser pays twice, and it’s better not to save on coolant.

Let’s also see how coolant and antifreeze differ. Antifreeze is the general name for liquids that do not freeze at low temperatures. Recall that among the requirements for the coolant is safety in operation. One of the main sources of danger in our latitudes is the freezing of the coolant due to a shutdown of gas or electricity and, as a result, a complete failure of the entire heating system at home. To prevent this, it is recommended to use antifreeze as a coolant. Although some believe that the best coolant is water.

The best coolant is water?

When it comes to choosing a coolant for heating a house, most often water is called the best option. Is it so? Let’s try to figure it out. Undoubtedly, water has many attractive properties, the main of which is its low price and availability. And this factor often outweighs all the others.

Water has excellent heat capacity (i.e., is able to carry the greatest amount of heat), low viscosity, it is non-toxic and fireproof in case of leaks. And if a leak did occur, then adding water to the heating system is not a great job.

But water also has disadvantages. First, tap water corrodes pipes and heating appliances. Secondly — and this is the main drawback, leveling all the positive properties — water freezes at only 0 ° C. And that’s not all — when freezing, water expands by about 9%, which inevitably leads to ruptures of pipes and radiators and failure of the entire heating system. If for some reason the temperature in the house drops to negative values, and water remains in the pipes, tragedy is inevitable. Thus, the risks in the operation of a system in which the coolant is water are very high.

Of course, there are ways to deal with shortcomings. For example, anti-corrosion additives are used to combat corrosion, and distilled water is used to reduce salt deposits on pipe walls. To lower the freezing point, special additives are also used.

It turns out that, despite its “watery” nature, most often it is not tap water that circulates in the heating system, but a certain solution. By the way, no one pours plain water into their car, only antifreeze, why should it be different in the heating system?

Importance of Corrosion Control, Danger of Zinc Pipes

Corrosion is dangerous because over time, violates the integrity of the system and causes leaks. But this is not all of its negative sides. The formation of rust in pipes and radiators reduces their efficiency, because. the corrosion layer has a thermal conductivity about 50 times lower than that of the metal.

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In other words, the heat transfer of radiators decreases with the same operating mode of the boiler. In addition, the speed of the coolant in the system decreases, which also reduces its overall efficiency. In general, corrosion in the system leads to the fact that part of the expensive fuel will go nowhere, and this proportion will only grow over time.

But that’s not all. Rust particles are separated from the pipe walls under the action of the coolant flow and negatively affect the circulation pump bearing, which can leak, clog the channels of the heat exchangers and the heating boiler.

Rust is often fought with galvanized pipes, which have good corrosion resistance. But, remember! In heating systems, elements containing zinc, in particular, pipes galvanized from the inside, cannot be used. The fact is that at operating temperatures (and this is + 70 ° C and above) of the coolant, the zinc coating will peel off and settle on the heating elements of the boiler, and the anti-corrosion properties of the coolant itself will be significantly weakened.

An exception is a glycerin-based coolant, but it is better not to risk it in this case either. Often, manufacturers of glycerin-based coolants sell mixed formulations that contain glycerin and propylene glycol.

Heat carriers of heat supply systems: types and features

The most effective coolants are antifreezes that do not lose fluidity at negative operating temperatures, and also practically do not expand when freezing. Today, water solutions of ethylene glycol, propylene glycol, other glycols, glycerin-based compounds, solutions of some inorganic and organic salts, transformer oils, and alcohol solutions are most often used as heat transfer fluids. Let’s analyze the capabilities and distinctive features of these antifreezes.

Aqueous ethylene glycol solution

One of the main characteristics of any coolant is its operating temperature range. Ethylene glycol solution is used at operating temperatures from -20°C to +130°C. Although these heat transfer fluids at certain concentrations can remain in the liquid phase up to temperatures of the order of -70°C, their use in this low temperature region becomes impossible due to excessively high viscosity.

But even if the temperature of the water-ethylene glycol solution falls below -20°C, the heating system will not fail due to pipe rupture. A heat carrier with an ethylene glycol concentration of 40% upon freezing (freezing point ~ -30°C) expands in volume by only 1.5%. Accordingly, its linear expansion will be only 0.5%, and this is safe for almost any structural material. In this case, ethylene glycol freezes gradually. Compare this to water freezing very quickly and expanding by 9%!

Most often, the upper temperature limit for ethylene glycol-based antifreezes is limited to 108 ° C — 110 ° C. If this threshold is crossed, the antifreeze begins to foam, the substance decomposes with the formation of acid and a solid precipitate, and the system becomes airy.

Speaking of an aqueous solution of ethylene glycol, one cannot fail to mention its toxicity. Ethylene glycol should not be allowed to enter food and drinking water in order to avoid poisoning. A life-threatening dose if it enters the stomach is 100 ml of ethylene glycol. Although if you accidentally get antifreeze on your hands or on clothes, it is easily washed off with water without causing any harm.

An aqueous solution of propylene glycol

Heat transfer fluids based on ethylene glycol and propylene glycol are quite similar in their characteristics. But there is also a significant difference — propylene glycol does not have a toxic effect, therefore it can be used even in double-circuit boilers. In addition, an aqueous solution of propylene glycol, unlike a solution based on ethylene glycol, has a lubricating effect, which facilitates the operation of the circulation pump.

But it is more expensive than ethylene glycol.

Aqueous solution based on glycerin

This solution is non-toxic. Its cost is lower than that of propylene glycol. Operating temperature range: from -30°С to +110°С. Solutions based on glycerin do not cause damage to pipes galvanized from the inside.

But this antifreeze also has its drawbacks. If an aqueous solution of glycerin is used, the requirements for sealing parts are increased: glycerin dissolves packing seals in threaded connections. And even with high heating, such a solution foams strongly, which leads to losses during heat removal, there is a risk of air locks in the heating system.

In addition, glycerin is heavier than ethylene and propylene glycols — this must be taken into account when designing a project.

Salt solutions

Most often, such solutions are used not in heating systems, but in the secondary circuits of refrigeration plants, which are operated at negative operating temperatures — mainly at temperatures below -20 ° C. This is due to their relatively low viscosity in these temperature conditions, compared with similar heat transfer fluids based on glycols.

The main disadvantage of salt-based antifreezes, which prevents their use in heating systems, is high corrosiveness, which, however, is significantly reduced at low temperatures.

Transformer oils

You can use as a coolant and special oils, for example, transformer. The main advantage of this solution is that the oil can operate at very high temperatures. Therefore, it has found application in industrial heating systems as an alternative to superheated steam. The main disadvantage of oil is flammability. Even a small leak in the system can lead to a fire. In addition, the oil is quite expensive.

Alcohol solutions

These solutions are of limited use and are currently used only in sealed heating systems that have forced circulation, since alcohol simply evaporates from open systems.

Also, water-alcohol solutions have the smallest operating temperature range, because. their boiling point is less than 100°C. But they are distinguished by a low price, low penetrating power and are not toxic.

Design features of the heating system when using antifreeze

Most manufacturers of household heating equipment produce models designed for operation using antifreeze as a coolant. And yet it is better to clarify this in the documentation for the equipment. To avoid unpleasant surprises. The fact is that the use of antifreeze in systems designed for water is impossible.

There are a number of design features that you should know before designing a heating system for a private house if you intend to use antifreeze:

• the increased viscosity of antifreezes leads to the fact that you need to install a powerful circulation pump that can ensure the movement of the coolant, even if it begins to thicken;

• since the heat capacity of any of the antifreezes is 15% or more lower than that of water, the amount of heat they carry will be less, which means you will need larger radiators;

• the high fluidity of antifreezes leads to the fact that you have to carefully seal the detachable connections. To seal these joints, it is better to use Teflon or paronite gaskets;

• due to the large volumetric thermal expansion of antifreezes, it is necessary to provide an expansion closed tank in the system;

• some antifreezes (ethylene glycol) are toxic, so it cannot be used in double-circuit boilers — only in single-circuit ones.

Choosing a circulation pump

To select the desired circulation pump, you can use a small cheat sheet. The performance of the pump is calculated based on the total volume of the heating system. The easiest way to determine it is to fill the system completely with water and bleed air, and then drain the water from the circuit into a measuring container with the air valves open.

The minimum coolant velocity in domestic heating systems is 0.5 m / s, this speed prevents the deposition of salts on the pipe walls. As a rule, the speed of movement of the coolant is chosen in the range from 0.7 to 1 m/s. If the coolant velocity exceeds 1 m/s, the pump will generate excessive noise during operation. The performance of the circulation pump depends on the speed.

Service life of antifreeze

Despite the fact that manufacturers often indicate the service life of antifreeze at the level of 7-8 years, practitioners believe that the coolant will not last more than 5 years without updating. And it seems that this assessment is fair. But 5 years is a pretty long time. So that you do not have problems, remember that in any case, the service life of antifreeze depends on its mode of operation.

It is not recommended to bring the coolant based on glycols or glycerin to a boiling state (boiling point at atmospheric pressure is 106°C-116°C, depending on the degree of dilution of antifreeze with water).

With local overheating of the coolant to temperatures exceeding +170°C, thermal decomposition of ethylene glycol, the formation of «soot» on the heating elements, the release of gaseous decomposition products and the destruction of anti-corrosion additives will occur.

Therefore, in heating boilers, proper circulation of the coolant must be ensured, and the heating elements must be completely immersed in the coolant during operation in order to prevent them from overheating and “burning” of the antifreeze.

Another factor affecting the suitability of antifreeze is the tightness of the heat exchange system. It is known that ethylene glycol is oxidized upon contact with atmospheric air, and the oxidation process is accelerated by an increase in temperature — approximately twice for every 10°C. Ethylene glycol oxidation products — glycolates destroy anti-corrosion additives and lead to increased corrosion. Therefore, it is necessary, if possible, to exclude the contact of the coolant with air, in particular, to use hermetic expansion tanks.

Finally, a few tips for those who decide to change the antifreeze in the heating system. Before filling in new antifreeze, it is best to flush the system. And to quickly remove air bubbles from the coolant, after filling the system, it is kept without pressure for 2-3 hours.

Source: TopClimat.ru