Radiator

Radiators are parts of heating systems in rooms and buildings. This usually metallic hollow bodies are referred to as radiators, convectors or baseboard heating and give a portion of the heating medium (usually water, in electric radiators oil) transported thermal energy to the environment (usually air ), in order to increase the room temperature.

Heat distribution in the radiator

Each radiator is close to the inlet valve at its warmest, because there flows into the heated medium in the radiator. Since the entrained in the heat transfer medium is discharged from the heater through radiation and convection to the room, the temperature decreases up to the outlet where the cooled medium is recirculated through the return line to the heat generator. Stay areas of the radiator permanently cold while achieving other heating temperature has collected in the cold areas most likely air which lessens the circulation. The required ventilation is carried out by a vent valve.

It is often mistakenly believed, a radiator must be heated evenly from top to bottom. Ever since the oil crisis in the 1970s, the flow temperature of the heater (and thus also the radiator ) is adjusted depending on the outside temperature in most cases. In some older systems, the flow temperature is kept constant high, for example at 90 or 70 ° C. This leads to unnecessary heat losses - particularly when the outside temperatures are not so low.

The directed into the room, radiant surface plays a crucial role for the comfort. Most heaters work in heat transfer at the same time according to the principle of convection and radiation heating. The amount of heat radiated increases physical reasons with about the fourth power of the temperature and is higher for electric radiant heaters or even with steam-powered heaters. A higher proportion of radiation at lower temperatures is achieved by greater radiation areas. So there are times in workshops under the ceiling -mounted heating pipes that hold additional downward sheet metal reflectors to increase the amount of radiant heat. In most radiators a water-bearing front for maximum radiant power ensures by the the room facing surfaces are heated directly by the fresh hot water through optimal heat conduction nearly to the height of the water temperature. An aesthetic reasons before the water-bearing areas such as stuck- front with designer radiators with poor heat conduction causes a significant reduction in the surface temperature and hence the radiation power. Following the English term for radiator ( radiator ) are often referred to as radiators in Germany radiator, although the radiation ( Radiation) is low.

Radiator exponent

The radiator exponent describes the influence compared to the standard values ​​changed temperature differences of a particular type on the radiator heat output.

Examples of radiators

Previously, especially radiators made ​​of cast iron were in use; they had - compared to the used nowadays modern panel radiators - a lower surface and a very high net mass, but were in favor of highly corrosion-resistant. During the period of National Socialism radiators were to deprive the defense industry no ferrous materials, offered in porcelain. However, these could not prevail. In the GDR, the idea was taken up again, and from the mid- 1950s radiator from china in 3, 4 or 5 ribs blocks were manufactured. There were basically two versions: flanged and spindled. Here, the method of assembling of the blocks is meant the finished radiator. The use of porcelain radiator was preferred in public buildings such as hospitals, boarding schools, etc., occasionally also in residential construction. From various farms, including mobile electric radiator radiators were made ​​of the porcelain blocks. From the early 1960s, the production of porcelain radiators has been set.

Characteristic of the currently most common design is the ribbed construction since the 1960s from cold formed and welded rolling steel sheets; by large surfaces are achieved. The radiator so produced are painted or powder coated.

In addition, steel radiator pipe are increasingly used; especially in the sanitary area, this design is preferred for practical (towel dryer) and aesthetic reasons.

Current radiators are in different versions ( type of connections, length, width) and also colors available and ready for use immediately after installation. Their design has been over the decades constantly optimized. The installation of the convector fins on the hot water channels and primarily by increasing the convection heat output could be increased in the course of developments. So today's panel radiators have about a much higher efficiency than material such as older fin radiator and function because of the significant increase in the convection at low flow temperatures. This is achieved through multi-layer water pockets and convection standing, folded sheets. Thanks to reduced heat transfer media volumes to faster response times can be realized against external heat gains or losses. This allows low-temperature radiators can already provide with 55 ° C warm water for heat in the house, while older radiators for the same heat output with the same installation space partially still need up to 90 ° C warm water.

Special shapes provide floor and wall heating and radiant ceiling panels dar. Here the surfaces of the tubes or electric heating elements equipped with walls, floors or ceiling tiles serve as a large radiator. Another special form represent Hygiene radiators, which are particularly easy to clean and are used, for example, in hospitals or in food productions.

Radiator size

To calculate the radiator size the heating load of the building and the heat output of the heating are the most important factors. The size of the radiator also depends on the window width and height of the parapet.

The heat load or the standard heat demand of a building is listed in the Energy Performance Certificate of the house. Various structural factors affect the calculation of the heating load. Factors are in addition to the thermal insulation, the surface of the outer components, the number of joints, the size of the rooms and the difference between outdoor and indoor temperature. Accordingly, the heating load is greater than that in a well-insulated building in an old building.

The heat output of the heater is the total heat output, which has to provide a heater for heating a room to a desired temperature. According to DIN 4701, the indoor temperature 20 ° C in the rooms, 15 ° C degrees in the corridor and 24 ° C should be in the bathroom. The first step in calculating the heat output is the room size. It is determined by multiplying the length of the space with the width of the room. The room size is multiplied by a base value again. As a core value, you can expect 80 watts per square meter. At 80 watts, one starts from a well- insulated house / apartment. For a room 6 m × 8 m which gives 3840 watts. You need a heater with 3.6 kW. In a poor or non- insulated building, the benchmark is 150 watts per square meter of floor area.

Passive

The vast embodiment has no fan. The heat is transferred mainly by natural convection as well as by heat radiation into the room. advantages:

• Noise and vibration free, does not disperse dust
• No additional energy required for fans

Disadvantage

• The maximum heat output is relatively low for a given area and inlet temperature.

Active

In an active radiator (see heater ), a fan is mounted in addition to increase the amount of heat transferred. This forced convection increases the amount of heat dissipation. This smaller radiators are necessary for the same amount of heat, which is why this type is mostly used in tight spaces or under windows. In many cases, the radiators are provided with additional laminations to the ambient air to increase the contact surface. advantage:

• Active radiators can be smaller for the same heat dissipation.

Cons:

• Noise and vibration due to fan
• No-cost acquisition with heat cost allocators possible because the heat output varies. The detection is possible via calorimeter in the heating circuit. The additional cost of a single calorimeter into perspective, if all heat cost allocators accounts with their individual costs.