Space heating solutions
With the considerable increase in prices of basic fuels, it must come as a priority the reduction of energy consumption.
Heat power decentralization is an advantageous solution which requires heating industrial plants to identify optimal solutions. For large spaces (surfaces and high altitudes) respectively for industrial warehouses, the beneficiary has the alternative:
1. Hot air heating:
- Heaters (hot water or steam)
- Air heaters (with gas burners)
- Distribution ducts.
2. Heating by radiation:
- Radiant tubes
- Ceramic radiants
And a comparative analysis must be made of these industrial heating systems in warehouses.
Factors contributing to the achievement of thermal comfort in industrial halls:
- Air temperature;
- Average temperature of radiation;
- Air speed;
- Air humidity.
These factors are influenced differently by each heating system. Technological processes taking place in industrial halls often require specific climate conditions. And not in last place, energy efficiency from implementing the heating system of industrial plants is implemented.
Manufacturers of heating systems do not produce both systems simultaneously (hot air and radiation) and have interest to argue the advantages without presenting the disadvantages.
On the other hand, each manufacturer sends commercial messages with appealing myths, but with a pertinent analysis, these may be removed.
Unfortunately, there is little neutral documentation sources to help the investor wisely to choose the optimal solution.
An important role in choosing the optimal solution for heating industrial plants should have the designers, but unfortunately, because of objective reasons, they merely provide known and verified solutions, or out of subjective reasons, they provide solutions that benefit through various agreements with equipment suppliers.
Equipment vendors are not always sufficiently trained to make a consultative sale or sell by priority in a way that brings greater benefit.
The selection of equipment, system design, installation, adjustment, exploitation are important factors influencing investment efficiency.
Determinants that have to take into account when analyzing the necessity and opportunity investment are:
1. Energy efficiency is influenced by combustion efficiency and how the produced heat is used. In large areas with a high degree of stratification leads to an inefficient use of heat produced by the equipment. High temperatures of the upper layers leads to the heat loss through skylights and roof area.
2. Layering is the phenomenon of the rise of hot air and intense heating to the upper layers of the enclosure.
Warming hot air stratification is normal
The heat emitted through radiation is 30-40% out of the convection heat, the equipment installation is done at the top of the spaces accordingly and in this case, a sufficiently intense stratification is established.
3. Burner modulation is the continuous adaptation of the power emitted by the burner related to heating and maintaining the prescribed temperature. Unlike the temperature of the burner all or nothing or two-stage system heating burner modulation has frequent stops and restarts, leading to fluctuating comfort parameters (air temperature and radiation temperature). It also makes a significant reduction in fuel consumption.
4. Setting comfort parameters - air temperature can be set relatively easily with room thermostats that start and stop (or modulate in some cases) the heating system. Radiation temperature and intensity of radiation are important factors that influence thermal comfort. Radiation temperature can be set by a thermostat with a round probe and the intensity of radiation is set by setting the maximum power of the burner.
5. The intensity of the radiation is enforced by the height of the installation, low height and high-intensity radiation can cause discomfort - effect of heatstroke.
6. Condensation - recovering heat from flue gases accompanied by the phenomenon of condensing water vapor from their content.
7. The degree of optimal thermal comfort is ensured by providing the following:
- Correct air temperature, evenly warming the surface of the room, fluctuations lack and thermal shock, short time in reaching operating temperatures.
- Optimum temperature and radiation intensity and uniform distribution
- Low air velocity and turbulence and lack of air drafts
- Optimal air humidity.
8. Turbulence and disturbing air drafts - phenomena that occur mainly while heating with hot air generators which use hot air from gas, with heaters or distribution piping in which hot air jets are strong in some areas, producing discomfort and raises dust.
9. Gas emissions and vapors from flue gas CO2, CO, NOx and water vapor remain in their compartment and it is implied the dilution and ventilation is required.
10. The possibility of air freshner – refers to feature equipment that introduces fresh air and is mixed with ambient air.
11. Mechanical ventilation – it is necessary to dilute the polluted air of pollutants that are in the flue gases (CO2, CO, NOx)
12. Heating time – refers to thermal inertia of the heating system, reaching (in the case of an unheated rooms) or to recapture (after opening doors or windows) thermal comfort parameters in a short time is essential
13. Equal general warming - refers to the uniformity of thermal comfort parameters in the entire room
14. Focused zonal heating – it mainly refers to heating of a certain area of the room, but achieving the prescribed comfort parameters.
15. Payback period - refers to the time in which from the savings made, by increasing the energy efficiency, covers the value of the investment.
Energy efficiency is influenced by the following factors:
a) The efficiency of combustion. In the case of radiant heating the yield is low and does not exceed 85%, better yield increases convective heat weigh of the transmission with a negative effect in terms of layering.
b) The way the heat produced is used for thermal comfort. In cases of large areas with a high degree of stratification leads to an inefficient use of heat produced by equipment. High temperatures of upper layers leads to heat loss through the surface of the roof and skylights. Layering is the phenomenon of the rise of hot air and intense heating to the upper layers of the enclosure.
- Warming hot air stratification is normal
- The heat emitted through radiation is 30-40% out of the convection heat, the equipment installation is done at the top of the spaces accordingly and in this case, a sufficiently intense stratification is established.
The degree of optimal thermal comfort is assured by the following:
- The correct air temperature. Warming with radiation may be 2-3 degrees lower than hot air heating as long as there is exposure to radiation source.
- Uniformity of room surface warming. Warming hot air unevenly may occur depending on distance from the source.
- Lack of fluctuation and thermal shock. Thermostatic lead to intermittent operation (all or nothing or two-stage) of all burners both for hot air generators and radiant or radiant tubes. In case the heating with radiation equipment malfunctions it leads to the sharp drop in temperature radiation which affects thermal comfort.
- Short time to reach operating temperature. Heating hot air cannot lead to increased temperature radiation for a long period of time and therefore thermal comfort is assured equally.
- Optimum temperature and radiation intensity. Correct radiation intensity is influenced by air temperature. At a high temperature the radiation intensity should decrease. Therefore, as the air temperature grows, in the case of radiation heating, thermal discomfort could appear (heatstroke effect). Also radiation intensity is influenced by the distance to the source a short distance can lead, in this case to thermal discomfort.
- Uniform radiation intensity on the surface of the room. In the case of radiants, focus radiation intensity is high.
- Low wind speed, lack of turbulence. In case of heating with warm air, in close proximity of generators, air drafts can form.
- Optimal air humidity. In the case of radiations, the combustion is realized within the interior of the water vapor space together with the other gases which lead to a significant increase of the humidity.
- NOx. Dust is dried when heating with warm air when the wind speed is too high. In the case of radiation heating, the combustion gases (CO2, CO, NOx, H2O) remain in the space. The dust may settle on the ceramic radiants, fact that lead to combustion modifications with dangerous CO releases.
Used for the heating of industrial halls with heating systems or mixed – radiation/convection
Radiant tubes and convection
Radiants with metallic fabric
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The advantages of radiant tubes in comparison to the classical heating system with hot air and to the classical heating system with ceramic panels:
- Use high yield
- The air is directly heated in a low percentage, and indirectly, through convection from the bodies heated by radiation
- Thermal radiation heats the work area
- It ensures thermal comfort at lower air temperature 2-4°C
- Lack of air currents don’t train dust particles or sediments
- Heating is evenly distributed over the entire space
- Combustion air can be extracted from the outside, so inside dust and humidity will not affect combustion
- Does not impose any mechanical ventilation to dilute pollutants
- Combustion is achieved inside the tube and the temperature is lower inside the radiant tube
- The waste gases are forcibly discharged outside
By using radiant tubes and convection, we combine, practically, the advantages of each type of heating system (with warm air and with radiation), we largely eliminate their disadvantages and highlight other advantages:
- high energy efficiency due to heat recovering condensing flue gases
- Ensure rapid and constant maintenance of both air temperature and radiation temperature
- Makes an efficient delamination
- Enables an efficient heating zones or in general
- Ensure uniform heating of large areas
- Enables setting maximum radiation intensity depending on the user's requirement
- Allows the setting of the warm air temperature, according to the users requirements
- Modulated operation - the heat emitted continuously adapts to the necessity heat
- Maintaining comfort parameters without disturbing fluctuations and shocks
- Security in operation
- Perfect combustion, sanitary with reduced pollutants (CO, NOx)