- What is bad about ordinary water
- Coolant frost resistance
- Heat capacity reduction problem
- Protection of aluminum radiators
- Special additives and shelf life
- The issue of toxicity and disposal of the coolant
- Coolant preparation rules
In hydraulic heating systems, it is not necessary to use water as a heating medium. Depending on the mode of use and the type of system, liquids with special properties can be used, for example, low freezing point or chemical inertness.
What is bad about ordinary water
The established world practice of using water as a heat carrier for heating systems is explained by its cheapness and availability. At the same time, the modern chemical industry offers a number of alternative substances and compounds that, at a higher cost, are devoid of the key disadvantages of ordinary water..
Most often, the replacement of water with a special heat carrier is required due to the inconsistent heating mode. At negative temperatures, the water freezes and expands in volume, which in most cases causes the destruction of pipelines and the boiler heat exchanger. A number of coolants, called antifreezes, do not possess this property: even at temperatures below -30 ° C, their viscosity only increases, but without irreversible consequences for the system.
Destroyed cast iron radiator after freezing water
Additional disadvantages of water include its aggressiveness to metals and the ability to cause corrosion. Also, water dissolves oxygen well, which is why gas formation with the formation of air jams is possible in a closed heat supply system. Finally, water is capable of dissolving salts and minerals, which is reflected in the formation of scale on the inner surfaces of the heat exchanger..
Coolant frost resistance
One of the two largest groups of special heat transfer fluids is based on propylene glycol (PG), a colorless viscous liquid with a melting point of -60 ° C. Liquids based on this substance can freeze at different temperatures, the required threshold is determined by climatic and other operating conditions of the equipment.
Propylene glycol based heat transfer fluid
There is another class of compounds – based on ethylene glycol (EG). And although this substance has a rather high melting point, its mixture with water is able to maintain a liquid phase when cooled to -50 ° C. As in the case of SG, the freezing point of the coolant can vary depending on the ratio of the initial components of the mixture in accordance with the requirements for the quality of the coolant.
Ethylene glycol based heat carrier
If from the coolant only the ability to maintain fluidity at low temperatures is required, then the compositions based on GHG in this regard are much more profitable for economic and a number of other considerations, which will be considered below. In this case, the coolant does not have to correspond to the critical temperature mark. Instead of filling the system with an expensive concentrate, you can provide a device for maintaining an acceptable temperature, for example, an electric heating element, while pouring diluted antifreeze.
Heat capacity reduction problem
One of the first prerequisites for the introduction of special coolants was the idea of using an aqueous solution of glycerin as such. It was believed that due to the higher density, such a composition would provide increased heat removal from the heat generator, thereby reducing parasitic leaks with exhaust gases. However, the idea did not justify itself: from overheating, glycerin polymerizes, releasing a toxic gas, moreover, its thermophysical properties were not the most outstanding. The situation is similar with modern antifreezes: as it turned out, there is no more heat-capacious liquid than water in nature, except perhaps for a toxic and reactive ammonia hydrate.
Therefore, the opinion that modern special coolants increase the efficiency of a heat-generating unit is an absolute myth. Manufacturers’ statements about increased heat capacity should be considered from a subjective point of view, these are nothing more than attempts to eliminate the inherent lack of antifreeze.
One of the most advantageous in terms of heat capacity of antifreezes is considered to be an aqueous solution of potassium formate. Heat carriers on such a basis really have a higher heat capacity in comparison with SG and EG, but the scope of their application is limited to closed systems. The fact is that in the presence of oxygen, the formate gradually decomposes, in other words, in an open system the coolant loses its properties relatively quickly. At the same time, formate antifreezes have been used for a long time, and in addition to a low melting point, they also have the properties of a corrosion inhibitor..
Protection of aluminum radiators
If sectional aluminum radiators are used in the heating system, there is a high risk of gradual corrosion of their inner surface. This problem is well known to heating engineers: water reacts extremely actively with aluminum, especially when heated. Under normal conditions, the oxidation reaction gradually fades away due to the passivation of the metal surface with an oxide film, however, in the heating system, the liquid constantly moves, while the mechanical particles suspended in it peel off the resulting film, thus, the wall of the radiator housing is continuously thinning.
Aluminum radiator corrosion
An obvious way out of this situation is to replace water with an inactive liquid, which are the majority of special coolants. In addition to the fact that the base materials (PG and EG) do not show a tendency to chemical reactions with metals, special additives eliminate the risk of unbound water coming into contact with aluminum.
However, the decision to replace water with antifreeze only due to the problem of aluminum radiators is unjustified. The term of effective use of the coolant is limited, it has to be changed periodically. Therefore, from a purely economic point of view, it is more expedient either to replace aluminum radiators with bimetallic ones, or to equip the heating system with a water treatment station and a mechanical filtration unit to remove solid undissolved impurities..
Special additives and shelf life
By themselves, glycols do not lose their properties over time, at least during use inside the heating system. However, in addition to the base, the antifreeze composition also includes a package of additives that improve the chemical and sometimes thermophysical properties of the liquid..
The exact composition of the additive package is not announced by any of the manufacturers. On the one hand, this is due to a trade secret, on the other, with a prudent concern about incompatibility with other brands of antifreeze. Propylene glycol and ethylene glycol mix well with each other, the same is true for their aqueous solutions. However, it is precisely because of the presence of special additives when mixing different antifreezes that such phenomena as the formation of dense inclusions, coagulation and precipitation of sediment, as well as foaming, can occur, and the type of base of the coolant does not play a decisive role..
The presence of additives is also due to the limited service life of the coolant. Antifreeze can be stored in a closed container and under recommended conditions for a relatively long time, but in operation it retains its properties from 3 to 7 years. The cost of the composition is largely determined by the required frequency of its replacement: the less often, the more expensive.
The issue of toxicity and disposal of the coolant
Ethylene glycol is a toxic substance and antifreeze based on it is also extremely toxic. In this case, the pathways of entry of the poison into the body are completely different: through the digestive tract, skin, lungs and mucous membranes. The dangers of EG-based antifreeze are largely due to the likelihood of microleaks, which are difficult to detect: regular inhalation of vapors, even in minute doses, has a cumulative effect. Therefore, heat transfer fluids based on ethylene glycol should not be used in open heating systems, with insufficient confidence in the quality of the installation of pipes and radiators, as well as if there is a double-circuit boiler and an indirect heating boiler in the system, where poison may get from one circuit to another.
Propylene glycol belongs to the class of safe substances, it is used as a food additive. However, the used coolant is not allowed to be discharged into drainage channels and sewers. Dispose of special heat transfer fluids in accordance with environmental safety rules. One of the best ways out is to go to a car service station, where the car “Tosola” is recycled regularly.
Coolant preparation rules
Special heat transfer fluids are supplied in concentrated form, but can also be used diluted. The proportions of mixing with water are set by the manufacturer, the freezing point primarily depends on the ratio. At the same time, anti-corrosion and other properties are not lost much, but the saving effect is evident.
Diluting the coolant with tap water is not a good idea. Chlorate and fluoride impurities can cause an unpredictable chemical reaction cycle, as can ions and minerals dissolved in water. The most suitable for these purposes is boiled water, and also a fairly inexpensive option – drinking bottled water used in coolers. The use of rainwater is often impractical for a simple reason: a lot of active oxygen is dissolved in the liquid.
Water treatment for boiler room
In general, the very idea of preparing water for a heating system can serve as a good alternative to using a special coolant, provided that it does not require the properties of antifreeze directly. For about the same price, you can purchase the simplest drinking water treatment station with a reverse osmosis cycle, thus eliminating electrochemical corrosion and scale deposits. Mechanical impurities are easily removed by a mechanical filter of 30-50 microns, installed parallel to the return flow with forced circulation by an additional pump.