Night storage heating
The electric storage heating , also night storage heaters , night storage heaters , night storage heaters or low tariff storage heater called, is a electrically driven heater in which a heat storage in off-peak hours by as compared to the normal rate cheaper offered electrical energy is heated. This low-tariff electricity, offered by many electricity suppliers , is usually - not entirely accurate - referred to as night electricity .
In the low-load phases at night and occasionally in the afternoon, the electricity is used to heat the storage stoves. The heat is kept there for a few hours. In order to use low tariff electricity, special electricity meters with two counters for high tariff (HT, daytime or normal tariff ) and low tariff (NT or nighttime electricity ) as well as a device for tariff switching are required . The switchover is usually carried out by the energy supply company (EVU) using audio frequency ripple control technology or remote-controlled long-wave radio ( radio ripple control technology ), in some cases also using time switches in the customer's main distribution board.
history
Storage heaters were promoted in the 1950s and 1960s as an alternative to stoves for coal or heating oil . The main arguments were reduced dust and odor nuisance at the place of use, saved storage space for fuel and simpler building services. In contrast to hot water heating systems, power lines that could be easily retrofitted were required instead of pipes .
The main motive for the energy suppliers was the constant utilization of their base load power plants , initially coal-fired power plants , later also nuclear power plants . Therefore an attempt was made to create more demand at night. Storage heaters made it possible for electricity suppliers to largely determine for themselves when deliveries are made. Subsidy programs and electricity at lower tariffs promoted the use of storage heaters in apartments and houses.
After the first oil crisis in 1973 , energy costs rose and the subsidies for the NT tariffs were put into perspective; Storage heating lost its economic efficiency compared to conventional central heating . In addition, the overall efficiency, which is low compared to conventional heating, had a negative effect, as did the overall significantly higher environmental impact from the (still predominantly conventional) power generation. Equally negative from an environmental and health point of view is the fact that asbestos was used in night storage heaters for many years , the fibers of which can get into the air and pose considerable health risks.
In the meantime, night electricity tariffs are no longer available nationwide in Germany. In other countries such as Austria they still exist; New registrations with a state energy supplier or with private energy suppliers are possible.
Germany
By the end of the 1980s, night storage heaters with an electrical connection capacity of approx. 40,000 MW were installed in Germany.
The introduction of the electricity tax on April 1, 1999 increased the cost of this heating method. Until the end of 2006, the tax rate for electricity in the low tariff, with which the storage heaters are generally operated, was reduced compared to the standard tax rate; since 2007 the electricity tax rate for high and low tariff (day and night electricity) has been the same. The liberalization of the electricity market with the division of the previously integrated companies also deprives night storage heating of its livelihood. The power plant operators looking for capacity utilization at night are no longer necessarily the network operators via whose lines the special use of the control system must take place, and both are no longer necessarily the marketers for end customers who have to take into account the additional expense of double consumption recording and billing.
With regard to primary energy consumption and CO 2 pollution, the federal government decided in Section 10a of the Energy Saving Ordinance (EnEV) in the version of April 29, 2009 that after a transition period all night storage heaters may no longer be operated. This regulation was repealed in 2013 (see last paragraph).
The KfW bank paid until August 31, 2010, up to 200 euro subsidy per night storage heater for its disposal; Previously issued invoices were still taken into account until November 30, 2010.
In 2012, the energy suppliers RWE and EnBW started discussions about lifting the ban on night storage heaters in order to use them for the targeted storage of energy from renewable sources. During storm phases, wind power is occasionally available in large quantities, which means that conventional power plants have to be severely throttled or shut down, especially at night due to the priority of renewable energies. The Federal Ministry of Transport, Building and Urban Development initially denied this report. As of 2018, however, it became apparent that in practice night storage heaters are usually far too inflexible for the possible integration of renewable energies. As part of a European research project, it was shown that making German night storage heating systems more flexible would not necessarily lead to better integration of fluctuating renewable energies and would probably not be cost-efficient either.
On May 17, 2013, the Bundestag decided to repeal the ban on the operation of night storage heaters from 2019 by the Merkel I cabinet (2005–2009). These can now continue to be operated after December 31, 2019. While representatives of the coalition government, the energy companies as well as the home and landowners association Haus und Grund praised the decision, environmental associations expressed sharp criticism and described it as a clientele policy for energy companies. Due to their high electricity consumption, night storage heaters cause emissions that are three times as high as gas condensing boilers, and the justification that night storage heaters are a necessary storage technology for the energy transition is a farce. Night storage systems consumed 10–15 TWh of electrical energy annually, but only about 0.42 TWh of wind power would be curtailed per year. The use of night storage heaters in consumption-intensive, windless hours also leads to an additional load on the electricity system.
Due to the comparatively high costs, however, night storage heaters are still unattractive. Since, in addition, many devices installed in the 1960s and 70s have now reached the end of their service life, they are often no longer renewed, but replaced by other heating systems, especially when the property in question is generally renovated. Since the installation of new night storage heaters practically no longer takes place, the number of night storage heaters in Germany is continuously decreasing.
Storage types
Room stove (single storage device)
A night storage heater is a largely thermally insulated, electrically operated heater in which molded bricks with a high magnesite content serve as heat storage. The memory core can be up to temperatures of 650 ° C to achieve. At low tariff times, it is heated up with electrical heating elements that switch off with a thermostat in the core when the maximum temperature of the storage mass is reached. A charging control that is dependent on the outside temperature can ensure that the storage heater is charged according to the outside temperature - the heating elements are then switched off earlier if necessary.
In spite of the insulation, some of the heat is released into the room through thermal radiation and convection , but most of the heat is released by a fan . The fan conveys the room air through the heated stone package and is controlled by a thermostat .
Solid central storage for hot water central heating
The functional principle is the same as that of the room stove, but there is an air-water heat exchanger in the substructure of the central storage tank. The air heated in the air ducts is conducted via this heat exchanger in a closed air circuit. The air is blown by a fan through air ducts into the storage stone structure, thereby extracting heat from the storage stones and heating the water of the central heating as it passes through the heat exchanger. The heated heating water is fed by a circulation pump through the radiators inside the building and then returned to the heat exchanger.
Underfloor night storage heating (electric)
In addition to the hot water underfloor heating with water storage tank, there is the electric version:
The screed is heated with meandering resistance wires, which are fixed in welded plastic foils to form mats. The structure is as follows: On the subsurface (e.g. a concrete ceiling) there is a 2 to 4 cm thick layer of polystyrene , followed by a 2 cm thick hard-wearing mineral fiber board because of the heat given off by the heating wires. The heating mats are laid next to each other on the mineral fiber boards without crossing. A layer of plastic film follows on the heating mats, then the storage screed is applied, in which the heat sensor is located. The thicker the screed, the greater the storage effect. The heat sensor should be located in the swivel area of doors, as it is not covered by furniture there. Otherwise a higher temperature would be displayed than in the rest of the screed and the room would be insufficiently heated. Tiles, suitable carpeting, etc. can be laid on the screed.
In the area in front of large window areas, edge zone heating is usually installed close to the floor surface, which can be operated via room thermostat with daytime heating or household electricity (e.g. at lower outside temperatures).
Disadvantages of this type of heating:
- Only the charge can be influenced, but not the heat emission: the warmest in the morning, the coolest in the evening.
Advantages:
- no radiators, more free space.
- no dust whirling up as with night storage heaters with fans.
- no cleaning or regular maintenance required.
Backward control is best suited for operation; H. Depending on the outside temperature and residual heat, charging starts as late as possible until the end of the storage tank in the morning. As a result, "night heat", provided this low-tariff electricity is still offered, is available at low cost as long as possible into the daytime, and the use of afternoon recharging (more expensive) is reduced to a minimum. A charging end as late as possible, specified by the EVU, has a favorable effect here.
Set tiled night storage heaters
In the 1950s and 1960s, the stoves were mostly not delivered ready, but instead were installed as tiled stoves. A stove builder usually uses a rectangular tiled stove, other types of construction are also possible. This is filled with storage stones. An electrician installs the heating elements, connects them to the control unit and connects the furnace to the power supply. Finally, the stove builder closes the stove with tiles. Since the stoves are quite heavy, the load-bearing capacity of the subsurface must be taken into account. The heat is mainly emitted via radiation from the tiles ("tiled stove climate"), and a mostly thermostat-controlled fan is often attached to an opening on the underside, which emits additional heat when required. Due to the larger surface of the oven, the heat given off is perceived as more even than with smaller, ready-made devices. The heat given off for the most part by radiation avoids the constant turbulence of dust, dry air, etc. caused by the fan. With the appropriate construction, only one oven is required per apartment or per floor in a single-family house.
Types
- static: heat emission only through radiation
- dynamic: heat dissipation if required via a fan
- statically and dynamically combined: radiant heat and, if required, heat dissipation by fan (as described above). This is the most common type.
- Convection: There are closable openings on the top and bottom, the cooler air is heated in a space in the oven and rises to the top.
- more: There is a space between the storage core and the tiles, if necessary, hot air is blown from the storage stones onto the tiles by a fan. Advantage: the air is only circulated in the furnace. As a result, pure radiant heat and no dust whirling up and dust smoldering. The disadvantage is the lower heat transfer to the outside.
It is also possible to have heating elements (e.g. heating wires) installed directly on the inside of the tiles, which are operated with daytime electricity so that heat is quickly available in the event of a sudden cold snap.
water-tank
Water can also be used as a heat store.
- In the form of a hot water storage tank that
heats up at low tariff times. The usual volumes in single-family homes are 60–100 liters per person, sufficient for a family's daily needs. - Electrically heated heating hot water storage tank
In principle, any central heating system can be operated or supplemented with it. However, a low-temperature heating is to be preferred because of the greater usable temperature difference.
Operation of night storage heating
Determination of the daily requirement
In order to determine the amount of heat to be provided on the next day, the outside temperature is measured using an outside temperature sensor and the amount of heat required for the next day is estimated. This task is taken over by the charge control . The charge controller is located on the storage heaters, which switches off the charge when the device has stored the heat required for the next day.
Sudden temperature changes are not taken into account with a simple control. Night storage heaters with additional heating elements for daytime electricity are more convenient, so that after a sudden cold snap it can be reheated.
The charging times of a night storage system depend on the regulations of the energy supply company and the type of heating and are between eight and ten hours. Depending on the collective bargaining agreement and supply area, the energy supplier gives the approval for charging in a time range from around 8 p.m. to 6 a.m. the following day. This release time can also be split in order to equalize the network load, for example from 9 p.m. to 10 p.m. and from 11 p.m. to 6 a.m. Most heat electricity providers have a significantly cheaper low tariff (NT) compared to the high tariff (HT ) , which is colloquially referred to as "night electricity".
The utility companies usually offer several charging programs: over 8 hours, 8 + 2 hours, up to 10 hours or 10 + 6 hours, different variants are used. With the last-mentioned charging program, this means a ten-hour night-time charge and an additional release for six hours a day.
Static and dynamic heat emission
The part of the heat that is given off via the surface of the device is called static heat output, the part that is made available with the help of the fan is called dynamic.
A room thermostat compares the room temperature with a set target value. If the room temperature falls below the setpoint, the room temperature controller switches on the fan on the device , which means that the heat stored in the device core is blown into the room. When the setpoint is reached, the room thermostat switches the fan off.
Night storage heating compared with other types of heating
Operational risks
The dangers of falling over and high surface temperatures exist to the same extent as with incinerators. Accordingly, minimum distances to furniture and combustible materials must be observed and heat build-up due to objects placed directly in front of and on the stove must be prevented. The fall-over protection devices usually present on the devices must be correctly installed.
A night storage heater brings with it the electrical operating hazards like any other electrical device. In return, there are no risks of direct combustion with regard to the room air; Gas leakage, carbon monoxide enrichment, oxygen consumption.
advantages
General
Advantages of night storage heating:
- low wear, no maintenance costs
- Electricity is easy to transport
- no chimney, no chimney sweep costs
- no tanks or storage rooms for fuel required
Single ovens only
A single stove is cheaper to buy than retrofitting central heating. There is no risk of freezing with heating without a water circuit, for example in adjoining rooms outside a heated apartment or in buildings that are only used temporarily, such as B. Holiday homes.
The subsequent installation in a building without central heating is much easier than the installation of central heating with radiators , because no heating pipes have to be laid to the radiators, laying the necessary power cables is easier because it is just one cable that is also more flexible. This is why night storage heaters are often found in old buildings that were originally heated with individual stoves.
disadvantage
General
Compared to forms of heating that are operated directly with fuel (such as gas heating , oil heating or pellet heating ), electric heating systems are by far the most inefficient. Although 100% of the electrical energy arriving in the house is converted into thermal energy, the production of electricity in fossil power plants results in high losses that must also be taken into account in the overall system. While modern oil or gas-fired condensing boilers have efficiencies close to 100%, the efficiencies of power plants are between approx. 30 to 40% for average coal-fired power plants and up to 60% for the most modern gas and steam combined power plants . In addition, there are losses in power transmission.
The climate footprint of night storage heaters depends heavily on the fuel used. If the energy comes from fossil fuels, the CO 2 balance is significantly worse than with all other heating systems. This is especially true if the electrical energy is obtained from coal , which has higher emissions than the energy sources oil and gas used in building heating. Even with the current energy mix in Germany, night storage heaters emit significantly more climate-damaging CO 2 than fossil heaters. If, on the other hand, the electrical energy comes largely or entirely from carbon dioxide-free sources such as B. hydropower or wind energy , the emissions balance is better than with fossil-fueled heating systems. However, it must be taken into account that in this case, too, night storage heaters have a significantly worse environmental balance than the likewise electrically operated heat pump heaters , since night storage heaters require around 2.5 to 4 times as much electricity per kWh of heat as heat pumps.
Another disadvantage is that rooms that have not been heated cannot be heated spontaneously. Control devices with programmable reduction times are available so that, for example, holiday apartments do not have to be charged every night even if you are absent for a longer period of time.
A reinforced house connection is required for a heating and hot water system that is completely powered by electricity , as the connected load is very high.
Single ovens
Individual stoves take up a considerable amount of space in each room, especially more space than radiators powered by water . Usual storage heaters have a mass of 100 to 400 kg. In the case of old buildings, sufficient ceiling load-bearing capacity must be ensured.
If dust gets into the stove, it can smolder there during operation and cause pollutant emissions or unpleasant smells, especially on the first few days of a heating season. Older single stoves usually have no outside temperature-controlled storage tank loading. If the outside temperature suddenly rises or falls, the heat output of the radiators cannot be readjusted immediately.
In comparison to other forms of heating, many people find the room climate uncomfortable: night storage heaters heat up the room considerably at night when hardly any heat energy is actually required. Part of the costly charge is already dissipated as unwanted heat. Night storage heaters should not be planned for bedrooms only. Night storage heaters cause fluctuations in humidity due to the heating up / cooling down. In addition, cooling often occurs in the evening. To counteract this, some devices are equipped with controllable fan motors that generate a stronger air flow in the evening.
The sound of the fan can be annoying.
Problems
By heating with electricity from fossil fuels caused about three times more CO₂ - emissions than fossil fuels with the local combustion in central heating systems. The use of night storage heaters was nevertheless justified in the past and even promoted in the 1970s in particular in order to increase the nightly base load and thus improve the utilization and efficiency of base load power plants throughout the day. Today this buffering is generally no longer considered necessary; Any "holes" are compensated for by flexible medium-load power plants .
The fans can create air rolls in some rooms in which dust and dirt particles are constantly circulated. The surface temperatures on the exhaust grilles of the devices can be as high as those on incinerators, so that there is a similar risk of injury.
Older night storage heaters in particular can contain weakly bound asbestos , storage stones with high chromate contents and electrical components containing PCBs . A disposal on the bulky waste is not possible. For dismantling, specialist companies may therefore be required who must observe TRGS 519 ( technical rules for hazardous substances - asbestos / demolition , renovation or maintenance work ). It is therefore not advisable to install stoves purchased second-hand if it is not certain that they do not contain asbestos. The device manufacturers usually provide information on the devices in which asbestos was used.
Since new ovens are practically only sold as a replacement for defective devices, the sales figures have fallen sharply and the prices are therefore relatively high.
Change of electricity provider
According to research by Stiftung Warentest , many users of night storage heaters believe that they can only obtain electricity from the local energy provider , the basic supplier . In fact, numerous companies are now offering tariffs for night storage heaters with joint measurement. According to Stiftung Warentest, a change of provider can bring annual savings of several hundred euros.
Web links
- regional BUND page on the topic of night storage stoves
- Information on the topic of "night storage heating" from "co2online non-profit GmbH", funded by the Federal Environment Ministry
Individual evidence
- ↑ Thomas Herzig, Economic- historical aspects of the German electricity supply 1880 to 1990 , in: Wolfram Fischer (Ed.), The history of the power supply . Frankfurt am Main 1992, 123-166 p. 153.
- ↑ EnEV 2009: § 10a Decommissioning of electrical storage heating systems. on: www.gesetze-im-internet.de
- ↑ Energy-efficient renovation - special funding. on: kfw-foerderbank.de
- ↑ RWE wants the night storage system to make a comeback. ( Memento June 15, 2013 in the Internet Archive ) In: Financial Times. Germany, December 4, 2012.
- ↑ Power companies are planning the comeback of night storage. on: spiegel.de , December 3, 2012.
- ↑ Government removes ban on night storage heaters. In: WirtschaftsWoche . September 15, 2012, Retrieved November 5, 2012.
- ↑ Night storage heaters must be taken out of service www.haufe.de from September 17th, 2012.
- ↑ The most expensive way to heat . In: Süddeutsche Zeitung , March 15, 2018. Retrieved March 17, 2018.
- ↑ Wolf-Peter Schill, Alexander Zerrahn, Nils May and Karsten Neuhoff: Flexible use of night storage heaters can be a small building block for the energy transition . In: DIW weekly report No. 46/2018. Retrieved June 24, 2020 .
- ↑ Wolf-Peter Schill, Alexander Zerrahn: Flexible electricity use for heating in markets with renewable energy . In: Applied Energy . tape 266 , May 15, 2020, ISSN 0306-2619 , p. 114571 , doi : 10.1016 / j.apenergy.2020.114571 ( sciencedirect.com [accessed June 24, 2020]).
- ↑ Energy transition: Bundestag overturns ban on night storage heaters. on: Spiegel online. 17th May 2013.
- ↑ Bundestag lifts ban on night storage heating. ( Memento of the original from February 2, 2016 in the Internet Archive ) Info: The archive link was automatically inserted and not yet checked. Please check the original and archive link according to the instructions and then remove this notice. In: Thuringian General . May 17, 2013. Retrieved May 18, 2013.
- ↑ Runtime extension for power guzzlers: The night storage madness. In: Spiegel Online . May 17, 2013. Retrieved May 18, 2013.
- ↑ CDU / CSU and FDP are lobbying with RWE for the comeback of antediluvian night storage heaters in living rooms and bedrooms. Website of the German Environmental Aid. Retrieved May 18, 2013.
- ↑ a b electric heating . RP energy dictionary. Retrieved December 10, 2015.
- ↑ Night storage heating. In: thema-energie.de. Archived from the original on April 17, 2009 ; Retrieved April 7, 2016 .
- ↑ www.baua.de: TRGS asbestos work
- ↑ AEG building services; Do all heat accumulators contain asbestos?
- ↑ Stiebel-Eltron Asbestos Table
- ↑ Night storage heating and heat pump: change of electricity provider finally possible , test.de from February 24, 2015, accessed on February 24, 2015
