- Device and purpose
- Selection of heating elements
- Choice of coverage
- Installation and operation
The more spacious the yard, the more time it takes to fight snow and ice, and it is this resource that is most appreciated by modern people. To solve such problems, anti-icing and snow melting systems are provided for the driveway and paths, which are gaining popularity despite the general trend of energy saving.
Device and purpose
Although the name of the systems we are reviewing seems quite obvious, their main function is not to melt drifts at all. The bulk of the inconvenience is not the snow cover at all, but the ice formed during its slow melting. Sometimes, due to the vicissitudes of the weather, the ice crust covers the pedestrian paths in just a few hours, it is in such cases that the ability to maintain a positive temperature of the road surface is invaluable.
Electric heaters or heaters connected to the heating unit serve as a source of heat in snowmelting systems. You should not think that heating outdoor areas is extremely energy-intensive, in fact, the power consumption is about 250-300 W / h per square meter, plus the heating is not constant, and the peak power can be reduced by organizing alternating operation of heating elements in different areas. The system automation and the use of temperature and humidity sensors also contribute to an increase in the efficiency of work. In the commercial segment, sidewalk heating is often cheaper than hiring workers with special equipment or using chemicals.
The snow removal system is not just a web of heating elements. Its installation with the already laid coating is impossible, therefore, such an option should be included in the project for the arrangement of the local area in compliance with a number of technical requirements. It should also be understood that heating elements are universal in their application and can be used, in addition to heating the main coating, also on steps and for thawing drainage channels..
Selection of heating elements
The most efficient and economical snow melting systems are those in which the heating element is a system of pipes through which the coolant circulates. Of course, water should not be used for these purposes; instead, propylene glycol or a special suspension with a low freezing point is used. Heating of the coolant is usually carried out from the heating system through a special circuit with a secondary heat exchanger, while forced circulation of the liquid is required.
Liquid snow melting systems are most widespread at municipal facilities; in everyday life they are less popular due to the complexity of the device and maintenance. In a civilian environment, a predominantly electric heating cable of variable resistance or similar to that used for floor heating in rooms is used. Such systems are reliable and easy to install, but at the same time not as economical due to the use of more expensive electricity..
The choice of the heating cable must be done taking into account the climatic features. For the middle band and southern regions, a power of 200 W / m will be enough2, for the northern ones, where the temperature can confidently stay at -25 ° C, it is recommended to increase the specific power to 350-400 W / m2. If there is insulation under the covering, the power can be reduced by about 20-25%. Each type of heating cable has an indicator of specific power, which must be selected based on the density of laying 3-4 m / m2. Other cable features such as number of cores, type of heating elements and insulation strength are determined by the installation and operating conditions.
It is possible to shield the heated layer from the ground with a heat-insulating screen under almost any operating load, it all depends on the correct choice of insulation. For these purposes, gas-filled polymeric materials are used, characterized by high compressive strength, mainly cheap non-pressed expanded polystyrene PSB with a thickness of 30 to 50 mm. The main task when choosing a heater is to correctly determine its density.
The density of expanded polystyrene determines its compressive strength at a maximum reversible deformation of 10% of the original size. Such material is suitable for such purposes as best as possible, it is it that is used to insulate foundations, where thermal insulation experiences very high loads. However, in open areas, the task is complicated by the fact that the nature of the loads is short-term and concentrated. It is not possible to distribute the load over the area, because the device of a full-fledged reinforced concrete screed is impractical due to its too high heat capacity.
The general rule is that the compressive strength of expanded polystyrene should be, on average, 3-4 times higher than the operational loads, taking into account the support area. For example, if a person weighs 70-80 kg and the average area of both soles is 500 cm2 the equivalent load will be about 1.5 t / m2, that is, the compressive strength of the EPS should be about 5 t / m2, accordingly, the material of the PSB-S-25 brand is guaranteed to be suitable for insulating pedestrian walkways. In parking areas for cars, the operating load is about 2.5 t / m2, small vans – up to 5 t / m2, what is considered an acceptable load for PSB-S-35 and PSB-S-50 grades, respectively.
The main task when installing thermal protection is to create a reliable reference plane. The soil on the site is removed to a depth of about 25 mm and filled with hygroscopic incompressible material, such as washed sand or stone chips. To prevent erosion of the cushion, it is separated from the ground by a geomembrane. The pillow must be rammed in layers and periodically spilled with water. After drying, the top layer is sprinkled with a mixture of dry cement M400 and sifted sand in a ratio of 1:10 with a compacted thickness of 20-25 mm, the alignment tolerance per meter in each direction is no more than 5% of the thickness of the insulation.
Choice of coverage
When the entire area of the heated area is paved with PPS plates, you immediately need to start installing the upper protective layer to protect the insulation from the weather. The choice of base material depends on the type of coating planned, there are also several options here.
For the reasons outlined above, materials such as paving stones or concrete slabs are not suitable for heated areas. To ensure a short time for the system to reach the operating thermal mode, it is required to reduce the coating layer above the heating elements to the minimum value at which the cable is protected from damage, and the expanded polystyrene – from punching.
The best option for pedestrian areas is to cover the heating elements with a dry mixture of cement and sand 30 mm thick with good compaction. On top, the protective layer is covered with 2-3 cm of asphalt concrete, which is compacted with a hand roller or rammer.
An option for parking lots is a reinforced screed over the insulation with a thickness of 6 cm or more made of lightweight concrete. This will slightly increase the inertia of heating, however, it will allow more evenly distributing the loads. Reinforcement is performed with a mesh of 8 mm reinforcement with a mesh size of up to 150 mm, screed material – expanded clay concrete of class B5-B7.5 on cement grade not lower than 400D0. Heating elements are laid on top of the screed, then any suitable type of coverage is arranged: eroded pebble screed, rubber crumb, asphalt, or a thin cement screed with joining.
The main task when installing a pavement is to ensure the correct slope and surface drainage system. After melting, the snow and ice should drain freely into the equipped receiver, otherwise, after turning off the heating, the water will freeze again, but this time with a smoother and slippery crust. A sufficient slope value is considered to be about 3 mm / m in the direction of the flow. If the site is extensive, it is divided into sections, the slope of which towards each other forms a kind of prefabricated gutters. These gutters should be directed towards the receiver of surface drains, while their total slope should be at least 5 mm / m.
Installation and operation
As for connecting the heating element system, any man in the street can handle this task. It is enough only when buying a cable to purchase everything you need: connectors, hermetic couplings, a temporary cable fixation system and other fittings specified in the instructions for the purchased heating system.
To begin with, a fixation system is laid on the prepared surface – perforated tapes or polymer mesh. Then the cable is laid out with a snake or a spiral with a step of about 25-30 cm. As the installation progresses, the heating elements are attached to the fixation system: the cable is tied to the mesh with nylon ties or wire ties, to the tapes it is attached by bending the perforated petals. After the heating elements are installed, they are connected and connected to the power cable according to the switching and load distribution scheme. In this case, it is imperative to use standard fittings and the appropriate tool for crimping them. The support system and heating elements are not attached to the base, they just need to be positioned in the same plane, and then pressed with the upper layers of the coating. Naturally, before installing protective layers, you should connect the heating system to the network and check its performance for several hours.
Power cables are connected to the home power grid immediately after the input switching device through a circuit breaker with a current-time characteristic “B” and a rating corresponding to the total power and operating voltage with a margin of about 10-15%. A switching device is installed in the break of the phase wire: a thermostat or a control unit, and if the power exceeds 2.5 kW, an intermediate contactor. Heating is usually turned on manually after precipitation falls, but the system can also work completely autonomously if an automation unit is available. In the event of a large amount of snow, it is recommended to remove the bulk of it manually, otherwise an ice crust may form under the snow cap on the road surface, since melt water cannot go into drainage channels covered with snow, heating will not be enough to warm up the entire thickness of the liquid.