Moisture and diesel infrared heaters

When heating cold spaces, the moisture tends to condensate on windows, metal structures or other structures in the heated space.

From where does this moisture actually come?

As a rule, air contains humidity in the form of water vapour: the hotter the air, the more humidity there is in it. Cold air cannot hold as much moisture as warm air.

Air that contains water vapour heats up quicker than solid structures. Warmer air gathers more water vapour, but the solid structures in the heated space remain cool. The air close to the structures cools down, and the amount of water vapour in the air exceeds 100% RH.

When the relative humidity of air exceeds 100%, water vapour in the air starts to condensate into droplets visible particularly on windows and metal surfaces in the heated space. You can also witness the same phenomena on a frosty pint of beer on a terrace in the summer.

Two measurement units for humidity

The amount of water vapour in the air, or humidity, is described by two different concepts. One expresses the amount of water in the water vapour found in a cubic metre of air. This is referred to as absolute humidity. The other, relative humidity, expresses the percentage of water vapour contained in the air.

Relative humidity may vary from totally dry air (0%) to saturated air (100%) that contains the maximum amount of water vapour possible.

Oil heaters produce carbon dioxide and water vapour 

Airrex infrared heaters burn diesel or fuel oil extremely efficiently, using almost 100% of the energy contained in the oil for the heating of the space. In practical terms, this means that all of the 10 kW of (heat) energy contained in a litre of fuel is utilised.

10-kW heating capacity is enough to significantly raise the indoor temperature in most heated spaces. Once the desired working temperature has been achieved, Airrex heater’s thermostat steps in to control the heater, reducing fuel consumption and emissions.

A litre of fuel or diesel oil burnt creates 2.7 kg of carbon dioxide and 560 grams of water.

Heating dries the air

The capacity of air to hold water vapour is almost directly proportional to the temperature of the air. The colder the air, the smaller the amount of water vapour it can contain.

This explains why heating is the most effective way to dry out spaces. Even then, formation or entry of humidity from outside the heated space must be prevented.

If the relative humidity in a largish hall space is 40% at 0 degrees Celsius, each cubic metre of air in the space contains 1.9 grams of water vapour (water).

If additional humidity is prevented from entering the space, raising the temperature in the space from zero to +20 degrees Celsius reduces relative humidity to five (5) per cent. 

It does not take much to heat air

The average heat capacity of air is 1.01 kJ/kg/°C, based on which it is possible to calculate the output needed to heat it. To raise the temperature of one cubic metre of air by one degree, you need approximately 0.00035 kWh of heating power.

If the heated space is, for example, 300 m3 in size, the power required to heat the air in it from zero degrees to +20 degrees is just 2.1 kWh.

In reality, however, the above figure is not enough because of the significant effect the structures and objects in the heated space have on the required heating capacity, not to mention any heat loss due to structural leaks and ventilation in the space in question.

Humidity created by an oil heater is not a risk

The fact of the matter is as follows: to heat a 300-cubic-metre space from zero to +20 degrees, you require about 10 kWh of power, or one litre of oil, at maximum.

This translates into 560 grams of water vapour that is mixed with 300 cubic metres of air. The amount of water in each cubic metre of air is, then, increased by about 1.9 grams.

If the initial amount of water vapour per cubic metre of air in the heated space was 1.9 grams, the figure after the heating would be approximately 3.8 grams.

At +20 degrees Celsius, this translates into about 30% relative humidity, which will not cause a moisture damage risk to any structure whatsoever.

Unique benefits of oil-fired Airrex infrared heaters

Radiation heaters do not heat the air as such, but the objects in the way of the infrared waves. Thus, the structures and objects in the heated space will become warm quicker than the air. This efficiently prevents condensation of humidity in the air on the surfaces, minimising the risk of damage due to moisture.

Another factor that reduces the moisture risk is fuel. Many infrared heaters use liquefied petroleum gas, or LPG, which, when burnt, produces carbon dioxide and water. It is, therefore, a very clean fuel.

Airrex heaters are in practice just as clean, but they produce considerably less water than LPG heaters.

One (1) kg of LPG produces approx. 12.8 kWh of energy when burnt. At the same time, 2.99 kg of carbon dioxide and 1.63 kg (1,630 grams) of water vapour are produced.

Using diesel oil, the amount of water vapour produced to achieve the equivalent heating power is approx. 720 grams – less than half of that with LPG.

This is a significant difference, at least for anyone wishing to minimise the risk of moisture damage.

Infrared heat dries out structures

As described above, infrared heating increases the temperature of the structures and objects in the heated space rather than the air. This prevents condensation of moisture on the surfaces of the structures.

Infrared heaters can also be used to remove humidity in applications such as the drying of moisture damage from concrete structures, for example.

If there is moisture in the structures of the heated space from the time of construction or for some other reason, infrared heaters can be used to dry out the structures. The moisture that evaporates from the structures turns into water vapour mixed in the air, and this can increase the relative humidity of the air in the heated space significantly.

If there is a lot of moisture in the structures and no ventilation out of the heated space, relative humidity may rise almost up to 100%. At this point, the condensation will occur on cooler surfaces, typically on windows and metal structures.

Airrex infrared heaters can, then, also be used to dry out structures. Adequate heating using an infrared heater in a newly built building or one that has suffered moisture damage combined with as efficient ventilation as possible will dry out any residual construction moisture in just a few days.

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