Considering a diesel heater? Tubular fan heater or a safe infrared heater?
The energy contained in diesel or fuel oil can be used for heating by burning the oil. Simple traditional auxiliary heaters consist only of an oil burner and a fan that is used to direct the heat from the oil burner to the desired spot in the form of hot airflow. Airrex infrared heaters also include an oil burner, but instead of a naked flame, the heat is formed in a heat generator doubling as the exhaust system. From the heat generator, the heat is radiated to the surrounding atmosphere in the form of infrared waves. The heat radiation can be directed using the heat reflector structures in the heater. Single- or multi-stage combustion diesel heaters The forced airflow of traditional oil heaters with a burner and fan transfers all particles of the burned oil, including exhaust gases and unburned particles, directly through the heater into the heated space. Even with an efficient burner, the exhaust gas will contain small amounts of unburnt hydrocarbons and any contamination in the fuel. This will cause different kinds of smoke and odour emissions. Basic tubular heaters simply use the fan to circulate the air in the heated space pass the oil burner. This means that unburnt hydrocarbons from the oil burner “supplement” any impurities already in the heated space air. The amount of unburnt hydrocarbons increases significantly if the diesel or fuel oil does not burn efficiently. This is usually the case during the starting or stopping of the heater or if there is a problem with the fuel supply to the burner. Airrex infrared heaters burn the diesel or fuel oil very efficiently because, after the oil has been burned in the burner, practically all the remaining hydrocarbons are burned in the 3-stage exhaust system that doubles as the heat generator. In practice, the exhaust is left with only harmless carbon dioxide and water without any unburnt hydrocarbons causing unpleasant odours and/or health hazards. Airrex auxiliary heaters utilise practically all the energy contained in the fuel, meaning that they are highly efficient and consume very little fuel. Exposed or protected oil burner? Basic fan-equipped diesel and fuel oil heaters have their oil burners in direct contact with the outside air, exposing them to any impurities and humidity in the air. This can result in corrosion or dirt build-up in the burner structures, decreasing the performance and reliability of the burner. If you use a fan-equipped auxiliary heater with an oil burner as the heat source, you must always make sure that the air going inside the heater does not contain any combustible material, such as dust, straws of hay or any combustible material that can be carried by the airflow. Another thing to remember when using this kind of a heater is that you also must consider the fire hazard caused by the hot air coming from the heater and any smouldering particles carried in it. In Airrex infrared heaters, the oil burner is enclosed inside the device and has its own separate air intake channel. All air coming to the burner is burnt, and the resulting exhaust gases are directed to a long exhaust system that doubles as the heat generator. The flame of the burner is not in contact with the surrounding space, and exhaust gases and any sparks cool down and die out harmlessly in the exhaust system. The long exhaust system also protects the burner against damages due to any impurities and humidity in the air. Difference between heating by airflow and heating by radiation In case of a traditional oil burner, the hot naked flame heats the air directed past it by the fan. This means that the air in front of the auxiliary heater may be very hot. The heating effect becomes more even when the hot air mixes with ambient air. The heating effect of the heated air circulated by the fan can only be felt in places where the air can reach. In a large space with obstacles or structures blocking the airflow, there will be “nooks and crannies” where the heat cannot get. Heat energy radiated by an infrared heater does not heat the air but the objects with which it comes in contact. Therefore, you can be close to the heater without feeling uncomfortably hot. Heat radiation spreads evenly in the space, literally warming up the objects in its path from the inside out. Once the objects and structures in the heated space warm-up, they also warm up the space evenly. Do you want to circulate dust and air contaminants? Fan-boosted air circulation always circulates contaminants, dust and other impurities in the space as well. This spreads air contaminants everywhere, including people’s skin and lungs and from there further in the body. Heat radiation from an infrared heater does not cause any superfluous air movement that would cause dust or any contaminants in the heated space to migrate to the workspaces or supplies or in the bodies of people there. Humming fan and buzzing burner – or not? The humming sound of an efficient oil burner is familiar to all who have been around one. Traditional auxiliary heaters only have sound damping structures on the sides of the burner. And to ensure safe heater operation, the heated air must be made to move efficiently. This requires a fan that inevitably produces noise. Today, some high-end traditional auxiliary diesel heaters already have reasonably silent fans. In case of the fully enclosed Airrex infrared heaters, the air to the oil burner is conveyed via a separate sound dampening channel. The exhaust system located downstream the burner utilises any energy left from the burned oil and also dampens the “exhaust noise” down to a very moderate level. Airrex infrared heater’s noise level is 48 dB, corresponding with that of a quiet speaking voice. Burner requires electricity – a fan easily doubles the need for power Traditional auxiliary oil heaters have some components that require electric power: fuel pump, oil burner with the associated control electronics and the fan that
Fuel-fired large space heater – how much supply air is needed, and other questions.
How is it possible to have a large space heater without an exhaust pipe? It is made possible by using pure high-quality fuel that ensures perfect combustion. Of the exhaust, more than 99% is carbon dioxide and water vapour that are parts of the air that we breathe. There is practically no soot or other fine particles, not even carbon monoxide. Exhaust from clean-burning high-quality fuel contains very low nitrogen oxide levels that do not constitute a health risk. To learn more, read this article. Water vapour is in no way hazardous to health, and the moisture in the exhaust gas of Airrex infrared heaters does not harm the structures of the heated space. Oil heater and carbon dioxide load There are two stages in warming up enclosed spaces, such as halls and warehouses: initial heating and continuous heating. During the initial heating, the fuel heater blows or radiates heat at maximum power, producing the maximum amount of exhaust gases. Once the space is heated, continuous heating only requires a fraction of the heater’s heating capacity. In this stage, Airrex infrared heaters typically use only a small amount of fuel per hour. Due to the two heating stages, the exhaust load in the heated space also varies greatly. Therefore, the ventilation performance required to ensure an appropriate amount of supply air and a level of carbon dioxide suitable for people to breathe varies. Load on full heating capacity Airrex infrared heaters are offered in three capacity classes. The heating capacity of the smallest Airrex AH-200 is 13 kWh, the heating capacity of the medium Airrex AH-300 is 15 kWh, and the capacity of the largest AH-800 is up to 22 kWh. The capacity is achieved by burning approximately 1.0–2.5 litres of fuel per hour. Burning 1.5 litres of fuel or diesel oil produces approximately four kilograms, or 4,000 grams, of carbon dioxide. The burning process requires approximately 22 cubic metres of air. Correspondingly, to burn 2.5 litres requires approximately 36 m3 of air and produces approximately 6,600 grams of carbon dioxide as a combustion product. The carbon dioxide produced by the heating makes working in the heated space more stressing. But when does it become a health risk? Carbon dioxide is not dangerous as such, but large concentrations are considered harmful Carbon dioxide is one of the normal gases in the air and, as such, not dangerous at all. On the contrary, the human body needs carbon dioxide to work. If the level of carbon dioxide in the air increases, we feel like we are “running out of breath” and the body reacts by automatically increasing the rate of breathing. A high level of carbon dioxide in the air is reported to cause headache, fatigue and a feeling of stuffy air. The amount of carbon dioxide in the air is expressed in ppm, or parts per million. The amount of carbon dioxide in the open air is approximately 380 ppm. According to the Decree of the Ministry of Social Affairs and Health on concentrations known to be harmful (HTP) and the Ministry of the Environment procedure on carbon dioxide levels in indoor air, the maximum allowed concentration of carbon dioxide during normal weather conditions and while the room is occupied is 1,200 ppm. The acceptable exposure limit at workplaces during an 8-hour workday is 5,000 ppm. This translates into carbon dioxide concentrations of half a per cent (0.5%) mixed in the air. Something about the level of stress caused by carbon dioxide on the human body can be deduced from the fact that submarine crews work and live in an atmosphere that contains approximately one per cent (10,000 ppm) of carbon dioxide. Even a concentration of 2%, or 20,000 ppm, has not been found to cause adverse health effects during short-term exposure. How much does an auxiliary oil heater increase the carbon dioxide concentration in a hall space? The specific weight of air varies according to the temperature and humidity of the air, the average used in these calculations being 1.225 kg/cubic metre (at sea level). Of this figure, the amount of carbon dioxide is 0.038% = 0.0004655 kg, or approximately 0.47 grams. The 5,000 ppm carbon dioxide exposure limit allowed at workplaces translates into approximately 6.125 grams of carbon dioxide per cubic metre of air. Considering the amount of carbon dioxide already in the air (0.47 grams/m3), the amount of extra carbon dioxide allowed to be mixed in the air is 5.655 grams. If we now presume that there is no ventilation whatsoever in a heated space with Airrex AH-300 infrared heater blasting away at full capacity, how big must the space be in order to avoid any health hazard due to the exhaust? The four kilos, or 4,000 grams, of carbon dioxide produced per hour requires a space of approximately 710 m3to dilute below the 5,000 ppm concentration level. The area of a hall space that is four (4) metres high should, then, be approximately 180 square metres. Using the more powerful Airrex AH-800 for an hour at full capacity would require a hall space of approximately 1,150 cubic metres to keep the increase in the carbon dioxide level below the recommended 5,000 ppm limit. Continuous heating requires only one-third or significantly less fuel compared to full capacity heating. This means that carbon dioxide emissions are only one-third or less by comparison. Subsequently, the volume of the heated space only needs to be 230–380 m3 to keep the carbon dioxide level below the recommended workplace exposure limit. The floor area of a 2.70-metre high hall space with a volume of 230–380 m3 is 85–140 square metres. The significance of ventilation The above examples are theoretical in nature because there are not that many heated spaces that are completely sealed. On the other hand, a combination of a particularly low ventilation setting and use of a fuel-fired heater will result in continuously increasing indoor air carbon dioxide levels, something that should be considered. If the heated space is ventilated in a normal manner in compliance with the regulations, meaning a