# Building heating

Heating cellar (gas) of an office building - 360 ° panorama
Display as spherical panorama

A building heating system (often called 'heating') is a device for heating buildings (so-called "central heating" or "collective heating") or individual rooms in buildings ("individual heating"). Are common gas heating and oil heating ; Renewable raw materials use pellet heating and wood heating . The night storage heating is considered out of date, as a refined form of energy - electricity - is used for heating purposes.

Heating technology is used to generate heat in closed rooms. It includes heating technology in the true sense ( heating technology) and the construction of the heat distribution system (as part of the building services ) as well as the supply of fuels . The article on heat technology gives a general overview .

## General

Under heating refers to:

A central heating system (out of date known as collective heating) has a central heating point and supplies one or more rooms or buildings with the generated heat via a carrier medium ( heat transfer medium ). The following are used as heat transfer media:

## history

The oldest known hot water heating system was developed by the Swede Marten Trifvald in 1716. It was used to heat a greenhouse in Newcastle, England. From around 1850, some princes and wealthy citizens had hot water heating systems installed in their castles and villas. Mention should be made here of the Palais Strousberg in Berlin , built by August Orth in 1867/68 .

Hot water heating has spread in private residential construction since around 1900.

Because the transport of energy sources used to be more complex than it is today, regional aspects played a greater role. For example, in the Ruhr area - a metropolitan area with relatively little forest - a lot of coal was used for heating; In wooded areas, heating was predominantly made with wood.

It was not until after the Second World War that central heating  - together with the switch from solid fuel to oil and gas - became widespread in western industrialized countries; previously they were a luxury and decentralized, selective and temporary heating of rooms during the heating season was common.

In 1973/74 there was a first oil crisis after delivery cuts in the OPEC countries ; In 1979/80 there was a second oil crisis. Since 1986, the Chernobyl disaster  - a core meltdown in a Ukrainian nuclear power plant , after which a radioactive cloud moved over large parts of Europe - has made it clear that electrical heating consumes a relatively large amount of energy because power plants have a relatively low average efficiency. (For the advantages and disadvantages of electrical heating of buildings, see electrical building heating )

Since the 1980s, the proportion of gas heating has increased and that of oil heating has decreased.

Oil and gas heating systems installed today often work with condensing technology . Wood pellets can also be burned in condensing boilers.

Central heating systems with logs as fuel now mostly have wood gas boilers .

Wood chip heaters are only available for heating very large buildings (e.g. farms, apartment buildings or public buildings) or for heating plants for local or district heating networks. They are mainly used in areas with a high proportion of forests. You chop up residual wood . This is not useful for the wood industry.

Heating costs have risen sharply since 1973: in 1973 and 1979/80 there were two oil crises , after which the oil price was much higher than before. The gas price and the electricity price also rose.

Since September 1, 2015, every newly installed heating system must be marked with an energy consumption label (a variant of the exhaust sticker that is issued by the chimney sweep).

## Energy sources or fuels

CO 2 emissions from selected heating systems (2008)
Energy source Heating system CO 2 equivalent g / kWh
electricity Electric storage heater 953
Heating oil Oil heating 375
natural gas Condensing boiler 256
Natural gas + solar Condensing boiler plus solar thermal 224
electricity Electric heat pump, air 187
electricity Electric heat pump, ground 167
natural gas Gas heat pump, engine 169
Wood Pellet heating 35

A distinction can be made between fossil fuels ( fossil energy ) and fuels from renewable raw materials ( biomass ).

Electrical energy can also be used for heating, but is not referred to as fuel because nothing is burned with electrical heating . The electric heating is electric heat in order to heat a building here. There are both electrical direct heating systems such as night storage heating systems and electrically operated heat pump heating systems , with the latter extracting thermal energy from the environment and therefore requiring only a fraction of the electrical energy as electrical direct heating systems. Furthermore, thermal energy from various sources can also be supplied via district and local heating networks or obtained using solar thermal energy .

Depending on the respective energy source, building heating systems produce different emissions. In the case of electric heaters and electric heat pumps, the emissions from the heater result primarily from the emission intensity when generating electricity.

The most important energy source in the EU in 2012 was natural gas, which provided 45% of heating energy in the EU. This was followed by heating oil products with 17%, renewable energies with 14%, district heating systems with 11% (primary energy not broken down), electricity with 9% and coal with 4%.

### Fossil and Biogenic Fuels

Fuel oil tank of an oil heater

The following fuels are used (depending on their physical state):

### Local or district heating

The four generations of district heating systems and their heat sources

If the heat is centrally located in a thermal power station (the principle cogeneration ) produced or the process waste heat from industrial installations used and distributed via pipelines to a plurality of spatially remote heat consumers, it is called, depending on the spatial size of the heat bond, by a local heating - or District heating supply . Such composite heat networks are used to supply heat to city districts and / or in industrial plants. To date, primarily crude oil, natural gas, coal, waste (→ waste-to-energy plant ) and, in individual cases, nuclear energy have been used to generate heat .

In the case of smaller heating networks in particular, waste heat from block-type thermal power stations (e.g. conversion of biogas , pellets, wood chips) or heat from wood chip heating plants is increasingly being used .

### Electrical current

Electrically heated storage heater

Electric power as an energy source in electric heating systems is often used for short-term needs in fan heaters . To heat apartments, night-time electricity storage heaters are sometimes used, which use the energy of the night-time electricity at the so-called low tariff (colloquially night tariff) at certain times - usually at night and in the afternoon - to heat a heat-insulated storage tank and by convection - and additionally at Need at any time of the day via an additional blower - deliver.

Oil-filled, fanless radiators with built-in heating rods and temperature controllers are also used for room heating.

### Geothermal energy

Surface collector for a heat pump heating when laying

To heat buildings with geothermal energy , heat pumps use the stable temperature level under the earth's surface to warm up the temperature-transferring medium in the heating circuit (see heat pump heating ). For a single-family house, one or two holes close to the surface are necessary.

The use of low-temperature heating such as B. the underfloor heating . One advantage of geothermal heating is that some of these systems can also be used to cool buildings in summer.

Only in some regions is it possible to use geothermal energy in geothermal warm water heating systems , in which the heating water is heated to the consumption temperature (up to over 40 ° C) directly via geothermal energy.

### Block-type thermal power station

Mini-CHP for multi-family houses

The thermal energy required to heat a building can also be generated in a block-type thermal power station. This is based on the principle of combined heat and power ; In addition to heat, it also generates electricity. The energy conversion can take place in very different ways (e.g. by an internal combustion engine , a steam turbine , a gas turbine , a Stirling engine or a fuel cell ). The waste heat from the system can then u. a. be used for room heating. In addition to the combination with a heat accumulator, it is also common to use a peak load heater to cover the maximum heat demand.

## Heating technology

### Bivalent heaters

Heating systems that use several heat sources are called polyvalent heating (bivalent = two-valued). Examples:

• All- burner (classic wood or coke boiler) are polyvalent
• Combined solar burner heating ( solar thermal and oil / wood / gas etc.), log wood combination systems (wood gasifier with pellet module), and others.

There are also systems for more than two forms of energy in power plant technology .

### Trivalent heaters

Heating systems that use three heat sources are called trivalent heating (trivalent = trivalent) or hybrid heating. Example:

### Individual heating

Electrically operated halogen infrared heater

A simple form of space heating is that of individual heating or individual stoves. Small individual heaters (e.g. fan heaters) only heat their immediate surroundings; Most individual heaters heat the entire room in which they are located. Examples:

Infrared emitters generate infrared-C radiation. These rays do not heat the air, but the surfaces they hit.

Open chimneys only heat to a limited extent: they have a poor degree of efficiency (depending on the design by 10%, i.e. 90% of the released heat escapes through the chimney) and use a lot of oxygen to operate, which then has to be replaced in the form of outside air.

### Central heating

Central heating (collective heating) has a central heating point and supplies one or more rooms or buildings using water (liquid or vapor) as a carrier medium.

#### Hot water heating

Hot water central heating for residential buildings with wood pellets as fuel. The round white container is the
membrane expansion vessel

A hot water heating system consists of a central heat generator ( boiler , combi boiler ), which heats the heat transfer medium water and with the help of a circulation pump or (rarely) through the density difference of the differently warm water ( gravity heating ; thermosiphon principle ) via pipes to the radiators ( radiators , heating strips ) pumps. These give off part of the thermal energy to the room air through convection . The cooled water flows back to the heat generator via the return lines . With a one- pipe heating system , which has a poorer thermal efficiency , there is no separate return - the radiators are arranged hydraulically in series.

The hot water heating works with flow temperatures between 30 ° C ( low temperature heating system ) and 90 ° C. By dimensioning the radiators larger or using underfloor or wall heating , the energy from the flue gas can also be used with a low flow temperature . One then speaks of condensing technology ( calorific value ), in contrast to the previously common heating value technology ( calorific value ). Since acidic water condenses from the exhaust air , the chimney must be of a suitable design.

To compensate for changes in volume due to the heating and cooling of the water in the system, a membrane expansion tank (MAG) is essential . In older heating systems, there are occasional open reservoirs at the highest point of the heating system.

To fill the heating system, tap water is usually used, which is fed into the heating circuit via a backflow preventer (filling valve that prevents backflow from the heating pipe network into the drinking water network).

Heating systems are also widespread being filled with treated heating water using cartridge desalinators in order to avoid corrosion in the system.

Air in the pipeline network must be removed from the water circuit via ventilators on the individual radiators and, in larger systems, on air bubble separators (automatic ventilators) so that all radiators can be supplied with hot water over the entire surface and there is no noise (flow noise) and corrosion in the network.

Hydraulic balancing is required for optimal operation of a hot water heating system. For this purpose, a pipe network calculation is carried out before the system is built . Hydraulic balancing is required both in VOB Part C and in the Energy Saving Ordinance and is carried out by heating engineers or (since 2003) system mechanics for sanitary, heating and air conditioning technology . Without hydraulic balancing, the radiators are u. U. differently warm and the circulation pump needs more electrical work ( kWh ) than necessary.

#### Steam heating

With hot water heating and steam heating , the water is heated to over 100 ° C. The water vapor generated is transported through pipes and condenses in the radiators, giving off heat. Then the condensate flows back to the boiler. The latent heat released during the condensation causes a very large heat output. The steam is sometimes taken directly from a district heating system and the condensate is discharged into the sewer system .

#### Warm air heating

The warm air heating uses the room air as a heat carrier. The warm air generated in an automatic heating system is fed into the rooms via air ducts.

Also designed as warm air heating, but a different structure in detail, which is hypocausts-air heating . It was made in the 1st century BC. Invented and can be seen today in excavation sites.

## Costs, amortization

The profitability of a heating system depends on the acquisition costs and the operating costs. The latter are strongly influenced by the usage behavior or the comfort needs of the residents. The public sector grants purchase grants for some heating systems ; which lower the acquisition costs. Taxpayers in Germany can claim the costs for the craftsman's services with a tax-reducing effect (details here ).

For the evaluation of the overall efficiency , the annual degree of utilization is more important than the degree of efficiency .

• The efficiency only indicates the losses when the burner is running.
• The annual degree of efficiency describes the relationship between the useful heat provided and the amount of fuel used. The specification of the annual degree of utilization or the standard degree of utilization also takes into account (in addition to the losses that occur while the burner is running) all losses that occur during the burner shutdown.

Since a burner run time of around 1,800 hours can only be achieved in one year and the burner is stationary for the rest of the time, an efficiency figure is always only a snapshot. In contrast, the degree of utilization considers the energetic efficiency over a certain period of time B. a year. The efficiency can be improved by installing a condensing boiler - provided the return temperature in the heating circuit is relatively low. They also use the heat of condensation from the water vapor produced during combustion.

### Calculation of space heating

In order to determine the power requirement of a heating system for a closed room, it is necessary to calculate the heat transfer of the room boundary surfaces (walls, ceiling, floor, doors, windows). The heat flowing off the surfaces must be supplied as heating power.

${\ displaystyle {\ dot {Q}} = U \ cdot A \ cdot \ left (T _ {\ mathrm {i}} -T _ {\ mathrm {a}} \ right)}$

With

${\ displaystyle {\ dot {Q}}}$ = Power in W (1 Nm / s = 1 J / s = 1 W)
${\ displaystyle U}$= Heat transfer coefficient in W / (K m²)
${\ displaystyle A}$ = Area in m²
${\ displaystyle T _ {\ mathrm {a}}}$ = Outside temperature in ° C
${\ displaystyle T _ {\ mathrm {i}}}$ = Room temperature in ° C

A performance surcharge of 10 to 15 percent is required for rooms with several external walls. The power requirement is calculated individually for all areas of the room and added up later.

Furthermore, when designing (dimensioning) heating systems, the ventilation heat losses (windows or mechanical ventilation ), night reduction , reheating factor , etc. must be taken into account within the framework of the recognized rules of technology . EN 12831 ( heating load ) defines the calculation. Until October 2004, the DIN 4701 for heat demand was valid , with which the so-called standard heat demand was calculated.

In addition to the physical calculation, the physiological effects of the radiators as convection heating and radiant heating and their position in the room must be taken into account in order to achieve thermal comfort . In the past, when windows were still significant cold bridges , architects positioned the radiators under windows to compensate for the cold falling air and to reduce air flows in the room. Thermal insulation glass has had a Uw value of 1.1 (double glazing) or 0.5-0.7 (triple glazing) since the end of the 1990s .

A passive house has such good thermal insulation that its residents can do without active room heating (energy supply only by residents, solar gains , ventilation preheating, etc.).

## Control and regulation

The desired temperature is maintained by controlling and regulating the heating.

The control of the heating behavior of the systems went with the state of the art. While the first large heating systems still had heaters to maintain and control the combustion process, this is now done by heating technology (automatic control and monitoring of the fuel supply). The type of control used depends on the size of the heating system. In one and two-family houses, the heating and hot water preparation is usually implemented completely by the control in the boiler .

In larger systems in which one heating network supplies several houses or residential areas, only the control for the heating network is implemented in the boiler house. This means that a constant or variable flow temperature is fed into the network. There are then two or more boilers in these systems. These are no longer controlled by the burner's own control, but by DDC-GA controls .

The heating and hot water preparation are then controlled separately in the house connection stations (HAST) of the individual houses. The house is then controlled via compact controllers or DDC-GA controls.

The control strategy for heaters is based on the outside temperature, i.e. the flow temperature of the heating network is parameterized via a heating curve . The flow temperature of the heating circuit increases the colder it gets. In the case of a control with a temperature sensor usually installed in the living room , the flow temperature of the heating circuit is also influenced by the room temperature, so that the external heat from solar radiation etc. is also taken into account. In addition, parameters such as night reduction and extended usage times of rooms are used via the party button to intervene in the control. This is most conveniently done using a remote control in the living area.

In apartments and rooms that are only used temporarily, such as holiday apartments or certain commercial spaces, remote controls using a mobile app are increasingly being used. In Switzerland, with its many second homes in the Alpine region, the installation of such controls as a means of saving energy is actively promoted by the authorities, in particular through the MakeHeatSimple program from EnergieSchweiz .

## Small heating system or large heating system

### Legal situation in Germany

The ordinance on small and medium-sized combustion systems defines small combustion systems as systems that do not require a permit under the Federal Immission Control Act, with the following limits:

• Firing systems for wood and coal below 1 megawatt (MW) thermal output,
• Systems for straw, grain and similar vegetable fuels with a thermal input of less than 0.1 MW,
• Oil and gas firing systems with a thermal input of less than 20 MW.

If owners by moving the heating costs to their tenants, it is the (introduced in 1981) heating regulation observed. It regulates the heating bill . Heat cost allocators are therefore attached to many radiators in rented apartments .

### Legal situation in Austria

The Combustion Plant Ordinance differentiates plants according to size without defining the term "small combustion plant". The approval of small combustion systems is regulated by the federal states. All nine federal states have agreed on uniform provisions with the “Agreement pursuant to Art. 15a B-VG on the placing on the market of small combustion systems”, but u. U. not yet implemented this contains the following definition: "Small combustion systems are technical equipment up to a fuel heat output of 400 kW, which are intended for the purpose of obtaining useful heat for space heating or hot water."

### Legal situation in Switzerland

The Swiss Clean Air Ordinance (LRV) regulates the approval of fireplaces for solid fuels with a thermal output of up to 350 kW.

## State funding

As part of the Market Incentive Program (MAP), the German Federal Environment Ministry awards financial grants for heating based on solar, environmental or bioenergy. The applications are submitted online to BAFA . The Kreditanstalt für Wiederaufbau (KfW) stopped funding for the renewal of heating systems on December 31, 2019.

## Useful life

The useful life for boilers is assumed to be around 20 years, for fan burners 15 to 20 years, and 25 to 30 years for fittings and tank (sheet steel). In addition to the technical service life, legal regulations can limit the service life of heating systems. In Germany, the Energy Saving Ordinance sets the permissible age and the ordinance on small and medium-sized combustion systems sets the maximum tolerated exhaust gas losses for heating systems. In Germany, these are determined or measured by the chimney sweep and, if necessary, reported to the competent authority.

## Overall market for heat generators in Germany in 2014

Domestic sales 2013 and 2014 in units
Heat generator Number 2013 Number 2014
Gas condensing technology 421,500 412,500
Low-temperature gas technology 110,000 107,000
Oil condensing technology 46,000 46,500
Air Water heatpump 40,000 39,500
Low-temperature oil technology 21,500 21,000
Firewood biomass boiler 9,500 15,500
Biomass boiler pellet 14,500 15,500
Brine-to-water heat pump 15,000 13,500
Biomass boiler wood chips 3,500 5,000
Water-water heat pump u. Others 5,000 5,000
total 686,500 681,000

Due to the expansion of the reporting circuit for biomass boilers, higher numbers are recorded compared to 2013.

## literature

• Jürgen Dispan: Analysis of the heating industry - structural change, development trends, challenges . Düsseldorf 2016, ISBN 978-3-86593-214-3 ( detailed display, imu-institut.de).
• Alfred Faber: Development stages of domestic heating. Oldenbourg 1957.
• Hermann Recknagel, Eberhard Sprenger, Ernst-Rudolf Schramek (eds.): Pocket book for heating + air conditioning. Including hot water and refrigeration technology . Oldenburg Industrieverlag, Munich (published annually), ISBN 978-3-8356-3200-4 .

## Web links

Wiktionary: heating  - explanations of meanings, word origins, synonyms, translations
Wikibooks: Optimization of small heating systems  - ... with a focus on small heating systems
• Full cost comparison of heating systems for single-family houses - comparison of the life cycle costs of heating oil, natural gas, pellet and log heating for old single-family houses in nine scenarios , Austrian Society for Environment and Technology [sic], Vienna December 2011; oegut.ati (PDF) accessed on May 30, 2019.
• Comparison of heating systems: save up to 30 percent on heating costs . test.de , May 24, 2012; accessed in April 2019

## Individual evidence

1. Federal Environment Agency 2008, cited. according to: Holger Rogall : 100% supply with renewable energies. Conditions for global, national and local implementation . Marburg 2014, p. 113.
2. Carvalho et al .: Ground source heat pump carbon emissions and primary energy reduction potential for heating in buildings in Europe - results of a case study in Portugal . In: Renewable and Sustainable Energy Reviews , 45, 2015, pp. 755–768, here p. 759, doi: 10.1016 / j.rser.2015.02.034 .
3. nuclear energy e.g. B. in Switzerland: www.fernwaerme-schweiz.ch (PDF January 2007)  ( page no longer available , search in web archivesInfo: The link was automatically marked as defective. Please check the link according to the instructions and then remove this notice.
4. Instructions for the remote control of a heater on the website of the MakeHeatSimple program (accessed on November 27, 2019).
5. Text of the ordinance on small and medium-sized combustion systems
6. Anja Behnke: Amendment of the ordinance on small and medium-sized combustion systems , Federal Environment Agency [Germany] (ed.), March 2010; Umweltbundesamt.de (PDF) p. 3; accessed in October 2012
7. Combustion Plant Ordinance . (PDF) Austria, at the legal information system of the Federal Chancellery
8. For more information on the implementation of the "Agreement pursuant to Art. 15a B-VG on the placing on the market of small combustion systems" see also emission limit values, comparison of the approval limit values ​​in Austria, Germany and Switzerland
9. Swiss Clean Air Ordinance (PDF; 829 kB)
10. Emission limit values, comparison of the approval limit values ​​in Austria, Germany and Switzerland
11. ^ BAFA funding programs for "Heating with Renewable Energies", In: BAFA.de
12. VDI 2067
13. ^ Daniel Wetzel: Heating industry - market for eco-heating collapses. In: welt.de . March 2, 2015, accessed October 7, 2018 .
14. Balance sheet heating industry 2013 ( Memento of March 8, 2014 in the Internet Archive ; PDF)