What is infrared heat?
In short: It is electromagnetic energy in the wavelength range of 780 nanometers to 1 millimeter.
What has infrared heat to do with human biology?
Generally speaking, a human in resting position at an ambient air temperature of about 20°C emits heat in several ways:
The majority of the heat, about 46%, is emitted as far-infrared heat,
about 33% as convective heat,
ca. 19% in the form of sweat,
and about 2% of the heat is emitted by breathing.
In order to compensate for the majority of human heat loss by far-infrared heat emission, far-infrared heaters can provide a proper solution to counterbalance that heat loss. Therefore, far-infrared heaters are by no means detrimental to humans, but very helpful during colder periods of the year to keep humans warm.
What is an electric infrared heater?
In short: An electric heating device with a nominal radiant efficiency of 50% or more.
What is nominal radiant efficiency, and how is that different from electrothermal efficiency?
This pertains to the conversion of “electric energy” to “heat energy” which is the sum of the three basic heat transfer modes of radiant heat, convection and heat conduction.
A simple explanation of electrothermal efficiency:
100 watt electric current is converted to 100 watt heat energy. That constitutes a ratio of 1: 1, or in other terms an electrothermal efficiency of 1 (=100%).
There are two reasons why electrothermal efficiency of direct space heaters is always close to 100%.
First, there are hardly any resistance or dissipation losses in the conversion from the input, which is electrical power, to the output, which is heat energy on the surface of the heater.
Secondly, the conversion takes place directly in the space to be heated, with no line losses and no heat storage losses as they occur in central heating systems.
However, electrothermal efficiency is not a suitable qualification criteria to compare different kinds of electric direct space heaters. After all, electric infrared heaters, electric radiators and even electric fan heaters (which only produces warm air), all of them achieve the same electrothermal efficiency of 100%.
Nonetheless, when comparing electric direct space heaters with common central room heating systems, electrothermal efficiency may be a suitable qualification criteria. Reason being, contrary to electric direct space heating systems, central heating systems have conversion-, storage- and conduction losses throughout the system.
Nominal radiant efficiency
Here, we have to distinguish between radiant efficiency and nominal radiant efficiency.
As mentioned in the article “Radiant power measurement for electric infrared heaters – Part 1” a widely accepted general definition of “radiant efficiency” is as follows:
The measured infrared heat output power from the frontal surfaces of the heater, in relation to the measured electrical input power of the heater under steady-state operating conditions.
In plain terms: When the electric heater reaches its operating temperature, the ratio of the measured electrical input power to the infrared heat output power is determined. This ratio is called the “radiant efficiency”. For example, a radiant efficiency of 52% means that 52% of the electrical input power was converted to infrared heat output on the frontal surfaces of the heater.
However, in the case of low-temperature heaters with a maximum heater surface temperature of up to 250°C, laws of physics limit the radiant efficiency to a theoretical maximum of 72% at 250, assuming ideal laboratory conditions. At a heater surface temperature of 100°C it is even less than that – only a theoretical maximum of ca. 60% radiant efficiency is achievable.
To take these theoretical maxima into account, stakeholders in the European electric infrared heating industry prefer another metric that is based on the measured radiant efficiency – the “nominal radiant efficiency“.
The definition of the nominal radiant efficiency is as follows:
The ratio of the measured radiant efficiency to the theoretical maximum radiant efficiency at a given operating temperature of the heater.
The following provides an example of how the nominal radiant efficiency is determined in practice:
An electric heater with a frontal surface temperature of i.e. 100°C has an actually measured radiant efficiency of i.e. 52%.
At 100°C heater surface temperature, the theoretical maximum for the radiant efficiency is 60%, which constitutes a 100% radiant efficiency rating.
To calculate the nominal radiant efficiency, 100% is divided by 60% and multiplied by the actually measured radiant efficiency, which is 52% in this example.
The calculation result for this electric heater is a nominal radiant efficiency of 86,67% which is more than 50%, and therefore constitutes an “infrared heater”.
What is the difference between "infrared heater" and "radiant heater"?
The difference is that an “infrared heater” carries a nominal radiant efficiency rating of 50% or more, whereas a “radiant heater” has a rating of less than 50%.
In other words, an electric infrared space heater generates more infrared heat from the electricity input than a radiant heater.
Why are some electric infrared and radiant heaters advertised with very high efficiency numbers of 100% or even more?
There are three main reasons for that.
Advertisements mentioning an efficiency rating of 100% relate to electrothermal efficiency of electric heaters. Electrothermal efficiency of all electric direct space heaters is the same – close to 100%. Therefore, electrothermal efficiency is not a relevant comparison metric between electric heaters. The correct comparison metric is nominal radiant efficiency as the results of this metric are very different between electric infrared heaters, electric radiators, electric fan heaters and electric storage heaters.
On the other hand, the radiant efficiency testing method for high-temperature electric space heaters may be mistakenly used on low-temperature electric space heaters. The difference is that with low-temperature space heaters the infrared heat absorption rate of air needs to be taken into account, which lowers their nominal radiant efficiency. This is not the case with electric high temperature space heaters. Hence, when using the wrong testing method low-temperature space heaters mistakenly receive a much higher efficiency rating.
On rare occasions, one might get across a statement that the efficiency of an electric infrared space heater is more than 100% due to the effects of quantum physics. A statement that claims to generate more than 100% heat from 100% electricity is not supported by current scientific understanding.
Why do many manufacturers not publish performance numbers?
The correct performance metric for electric infrared space heaters would be the nominal radiant efficiency, for which currently no widely accepted performance testing Standard exists.
To remedy this, an European Standards proposal for a new performance testing method of electric infrared space heaters is currently in preparation. This proposal will establish an official definition of what constitutes an electric infrared space heater, how performance is being measured, and hopefully also includes a rating system for electric space heaters.
After this Standard is officially established through the European Standard institution CENELEC, manufacturers will submit their electric space heaters for performance testing at certified testing facilities.
It is estimated that the first performance numbers for electric space heaters will be available at the earliest sometime in 2018.
What constitutes a good electric infrared heater?
There are several issues to consider.
Human safety and health:
– A certification from an accredited testing institution according to European Standards to be electrically safe to use;
– A certification from an accredited testing institution according to European Standards that the electromagnetic field of the heater fulfills safety standards for human use;
– When finally available, a certification from an accredited testing institution according to European Standard EN60675, showing a nominal radiant efficiency of equal or greater than 50%;
– Short heating-up and cooling-down periods, preferably below 5 minutes each;
– Uniform temperature distribution on the front-facing surfaces of the heater, ideally 5°C or less between the highest and lowest temperature points;
– High thermal emissivity (“epsilon value”) of the front-facing surfaces of the heater, ideally 0,9 (=90%) or more;
– Low temperature and heat dissipation (low thermal emissivity) on the wall- or ceiling-facing surfaces of the heater, ideally with a backside temperature of 30°C or less, and a thermal emissivity value of 0,2 or less;
– Long operating life of the heating device (currently no standardized tests available);
– Publication of a EU-national WEEE number (Waste and Electronic and Electrical Equipment) by the manufacturer or importer / distributor of electric infrared space heaters, as proof to participate in EU mandatory material recycling efforts;
– Publication by the manufacturer / distributor which control systems are used or recommended for a specific electric infrared heater type according to the EU Commission Regulation 2015/1188 – EU-EcoDesign requirements for local space heaters. This EU regulation will come into effect on January 1st 2018;
What are the most important technical features of an electric infrared heater?
For the application as direct space heater in a residential or light commercial building, the two single most important technical features of an electric infrared heater are a lightweight design and a uniform temperature distribution on the frontal heater surfaces.
A lightweight heater design enables a quick reaction to changes in occupants chosen thermal comfort levels.
A uniform temperature distribution on the frontal heater surfaces is important to achieve maximum heat efficiency.
A short reaction time has two advantages:
First, the heater is able to achieve occupants thermal comfort levels quickly. For example, during a cold winter day when the clouds begin to disappear and the sun starts shining into the rooms of a building, the installed electric infrared heater switches off quickly. It does not keep on heating because of a high thermal mass like electric storage heaters and semi-storage heaters. Conversely, when warming-up a room, a lightweight electric infrared heater quickly establishes the occupants chosen temperature level.
The second advantage of a short reaction time is heat efficiency. Electric infrared heaters have their maximum nominal radiant efficiency at their operating temperature. In other words: The longer an infrared heater takes to reach the operating temperature, the more energy it uses to heat-up the air in the room like a normal radiator, which is very energy inefficient.
Equally important is a uniform temperature distribution on the frontal surfaces of the far-infrared heater. Electric infrared heaters achieve their maximum nominal radiant efficiency when all areas of the frontal surface are nearly at the same operating temperature. However, this is usually not the case, as many areas of the frontal surfaces differ more or less in their temperature levels. The best electric infrared heaters get all areas of the frontal surfaces to as close to operating temperature as possible.
In connection with a uniform surface temperature, also a high thermal emissivity (epsilon value) of the frontal heater surface materials is important. Epsilon values of common surface materials, i.e. enamel, glass, powder coatings, etc., for electric infrared space heaters are between 0,82 (=82%) and 0,90 (=90%). These values were determined by using a Fourier Transformation Infrared Reflexion (FTIR) Spectrometer in the infrared wavelength spectrum of 2,5 micrometers to 35 micrometers at the operating temperature of the respective heaters.
The closer the material’s emissivity is to a value of 1 (=100%), and the more uniform the temperature distribution on the frontal heater surface, the higher their impact on the nominal radiant efficiency.
What about electric infrared heaters and electromagnetic radiation?
In general, all electric household devices generate more or less electromagnetic radiation, and so do electric infrared space heaters.
In order to limit their electromagnetic radiation levels and make them safe for humans to use, many manufacturers have their electric infrared space heaters tested according to the European Standard EN62233 “Measurement methods for electromagnetic fields of household appliances and similar apparatus with regard to human exposure.”
Also, unpublished experiments with various infrared space heaters carried out by the German electric infrared heater distributor “INFRApur GmbH” have shown, that ALL tested heaters have far lower electromagnetic radiation levels than the limits of 5.000 V/m or 100.000 nanoTesla imposed by German law (“Bundesimmisionsschutz Verordnung”).
Considering German building biology guidelines, bedrooms have especially low limits for electromagnetic radiation, which range from 1 to 5 V/m or 20 to 100 nanoTesla.
What made the distributor’s measurement results particularly interesting was the fact, that electric infrared space heaters with a glass-surface produced somewhat higher electromagnetic radiation levels than heaters with a metal surface substrate. This is due to the faraday effect of the grounded metal substrate.
Also, the distributor’s measurements showed, that heaters equipped with an onboard control system inevitably generated somewhat higher electromagnetic radiation levels due to their control systems electrical components.
Further, the distributors measurements could not determine a quality difference at a measurement distance of 10 centimeters and 1 meter based on the “country of origin” of the electric infrared heaters.