Condensing boiler

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Condensing boiler

A condensing boiler is a boiler for hot water heating that uses almost all of the energy ( calorific value ) of the fuel used. With condensing boilers, the flue gas is cooled down as far as possible and the condensation heat (= latent heat ) of the water vapor contained in the flue gas is used to provide heat.

Depending on the type of fuel, combustion temperature, oxygen content and other factors, different substances are produced during combustion. If the exhaust gas is cooled below the dew point , its condensable substances begin to condense.

Origin of the water vapor

The water vapor in the exhaust gas has two sources:

The higher the hydrogen content of a fuel, the higher the amount of water vapor that is contained in the exhaust gas after the fuel has burned. Condensing boilers are able to use a greater or lesser proportion of the condensation heat according to their quality and depending on the operating conditions.

When methane is burned, one molecule of CH 4 results in one molecule of CO 2 and 2 molecules of H 2 O, so one mole (around 16 g) of CH 4 produces two moles (around 36 g) of H 2 O, i.e. roughly the 2, 25 times the mass of water (steam). The conversion of C to CO 2 and of H to H 2 O releases energy. The low humidity in natural gas is negligible, the humidity in solid fuels is not. Most of the water is produced by the oxidation of the hydrogen atoms in the fuel. When burning longer-chain (mostly liquid) hydrocarbons (shown in the example of octane C 8 H 18 ), the ratio of the carbon atoms supplying thermal energy to the hydrogen atoms producing water vapor is increased, so that correspondingly less water vapor (per mass) is produced.

This has the following effects:

  • The water vapor dew point in flue gas when burning natural gas is approx. 59 ° C and when burning heating oil is approx. 48 ° C (precise information is not possible because natural gases and heating oils have variable compositions). The dew point when burning wood is between 20 and 60 ° C, depending on the moisture content.
  • With natural gas condensing boilers, it is possible to use the condensing technology at higher flow temperatures than with heating oil condensing boilers.
  • Natural gas condensing boilers generate more condensate than heating oil condensing boilers (if the exhaust gas is cooled to 40 ° C, for example).
  • Natural gas condensing boilers provide more condensing effects in relation to the calorific value than heating oil condensing boilers.
  • The loss of latent heat in conventional boilers when burning fuel gas is a maximum of around 11 percent of the calorific value, and when burning fuel oil EL is a maximum of around 6 percent.
  • Sulfur compounds present in the fuel burn to SO 2 and SO 3 , which react with the water vapor in the exhaust gas to form sulphurous acid and sulfuric acid . The acid dew point of fuels containing sulfur is in the range of 120 to 150 ° C. The further the dew point is lowered, the more the acidic condensate is diluted by condensation from the flue gas. Depending on the corrosion behavior of the condensates, different materials can be used in heat exchangers depending on the condensation zone. If the service water temperature ("flow") is set too high (in order to use outdated radiators for heating the building), the acid condensation zone shifts to the area where, at a (correct) lower flow temperature, more dilute acid would condense and corrosion problems can occur .

history

The first condensing boilers were developed by Richard Vetter (ready for series production in 1982 for gas, 1984 for oil) and are now standard when a new boiler is to be installed.

Full gas condensing boiler technology has been state of the art since the early 1990s . The oil condensing technology has prevailed since the mid-90s. Initially, smaller companies such as Bomat or ROTEX relied on condensing technology. The big names in the industry like Viessmann and Buderus only followed suit when the market demanded more and more oil condensing technology. The first mass-produced gas condensing boiler series FSM-RK was approved in 1978. The power range was 130-1000 kW. The first condensing boiler "with gas burner without fan" was presented in 1980 by the gas appliance company (GGG) from Bochum at the international sanitary and heating fair (Frankfurt am Main). The power range was 8-20 kW.

The problem with the approval of the Vetter boiler by the TÜV was the outdated " state of the art " (due to its invention) , for condensing boilers the DIN 4702 part 6. Vetter cooled the flue gases so far that thermoplastic plastics were used for discharge and in the waste heat exchanger were suitable. However, the previous regulation required heat-resistant materials.

In 1978 the Froling company registered its DIN-DVGW registration number. 86.01. up to 10.dB for the first gas condensing boiler type FSM-RK on this basis. The head of development, Robert Kremer in Leverkusen, was registered as the inventor of the FSM-RK condensing boiler when applying for a patent.

Oil condensing boilers have been standardized in accordance with DIN 4708 Part 7 since 1996. According to the last Energy Saving Ordinance of 2015, 30-year-old boilers (with the exception of low-temperature boilers or condensing boilers) are now to be replaced by condensing boilers in Germany.

Basics

When naming the specific energy content of fuels, a distinction is made between the terms calorific value and calorific value . The calorific value Hi (formerly Hu) relates to the heat that can be obtained from complete combustion; In addition, the calorific value Hs (previously Ho) also includes the heat of condensation ( latent energy ) of the exhaust gas. The efficiency of boilers is based on the calorific value Hi. As a result, condensing appliances i. d. Usually an efficiency over 100%.

The maximum achievable efficiency related to the calorific value Hi depends on the fuel. Natural gas enables a theoretical efficiency of 111% based on Hi, while heating oil enables a relatively lower (theoretical) increase to 106%, which is why changes to the design of the burner in oil heating systems ( blue burner , increased air supply makes the combustion more complete compared to conventional yellow burners) offer higher savings in the low-temperature boiler.

Separately from the boiler or permanently installed behind the burner, the exhaust gas is passed through an exhaust gas heat exchanger , which cools the exhaust gases completely or partially below the dew point . As a result, both the combustion product water, which is mainly produced in addition to carbon dioxide, and other substances condense ( see also the article Condensate (heating technology) ). For example, vapors of acids from the exhaust gas, especially nitric acid / nitrous acid from combustion ( nitrogen oxides NO x ) and sulfuric acid / sulphurous acid from the proportions of sulfur contained in the fuel . Desulphurised heating oil is therefore recommended when using condensing technology.

The use of the condensation heat of the condensable substances in the exhaust gas improves the combustion efficiency . This reduces the consumption of fuels (keyword: energy saving ) and thus the emission of CO 2 , but also the emission of acid-forming gases and other condensable compounds (see below). In addition to using the calorific value, this also prevents condensable compounds and dust that can be separated with the condensate from polluting the air and the acidic components from entering the atmosphere and falling down as acid rain .

Condensate that is discharged directly into the sewage system must be in accordance with the provisions of the German Association for Water Management, Sewage and Waste e. V. (DWA). With heating oil and on discharge to small sewage treatment plants , neutralization is always necessary with natural gas or liquefied petroleum gas until a minimum size of the boiler; an acid-sensitive sewage installation in the house can also make neutralization necessary. For this purpose, the condensate is passed through granules in a neutralization box; the remaining water is neutralized, used granules can be disposed of with the garbage.

The actually achievable efficiency of a condensing system depends on the lowest possible temperature of the heat exchanger media (heating return water or cold drinking water or supply air); the lower this is, the higher the efficiency of the flue gas heat exchanger.

Block-type thermal power station

In addition to conventional boilers, combined heat and power plants that generate electricity via a motor / generator and its waste heat ( combined heat and power ) can also be operated with downstream exhaust gas heat exchangers using condensing technology.

The manufacturer of a frequently installed mini-CHP system gives the following values:

natural gas

Gasoline engine, electrical 5.5 kW (27%), thermal 12.5 kW (61%), calorific value 20.5 kW - overall efficiency 88%

Assumptions: exhaust gas temperature 150 ° C, natural gas consumption 2 m³ / h, M exhaust gas emissions 40.8 kg / h.

Return temperature Exhaust gas temperature (approx.) Degree of condensation Heat gain (approx.) Efficiency
20 ° C 40 ° C 80% 3.0 kW 102.4%
35 ° C 55 ° C 50% 2.3 kW 99%
50 ° C 75 ° C 5% 0.9 kW 92.2%
60 ° C 85 ° C 0% 0.8 kW 91.7%

With complete condensation, approx. 1.5 liters of condensed water per m³ of natural gas are created (approx. 3 l / h per heating and power system (HKA)).

Heating oil

Diesel engine electrical 5.3 kW (30%), thermal 10.5 kW (59%), calorific value 17.9 kW - overall efficiency 89%

Assumptions: exhaust gas temperature 150 ° C, heating oil consumption 1.9 l / h, exhaust gas emissions 42.9 kg / h.

Return temperature Exhaust gas temperature (approx.) Degree of condensation Heat gain (approx.) Efficiency
20 ° C 40 ° C 60% 2.0 kW 99.4%
35 ° C 55 ° C 20% 1.4 kW 96%
50 ° C 75 ° C 0% 0.8 kW 92.7%
60 ° C 85 ° C 0% 0.7 kW 92.2%

With complete condensation, approx. 0.8 liters of condensed water per liter of heating oil are created (with 1 HKA approx. 1.5 l / h).

With a running time of the HKA (heating and power plant) of 5000 hours, approx. 3000 kg of CO 2 emissions are also avoided with the condenser . For the heat gain from the exhaust gas - the heat would otherwise be released into the environment without a condenser - around 20 m² of solar collectors would have to be installed. If the return temperature is high, an exhaust gas heat exchanger is only of interest in order to cool the exhaust gas and thus to be able to use exhaust gas ducts designed for lower temperatures.

technology

Scheme

The condensate that arises during combustion is acidic and therefore attacks base materials. The boiler materials and chimney pipes used in the past were not corrosion-resistant enough. The boiler design therefore intentionally prevented condensation in the boiler, which was only possible with high boiler water temperatures (> 70 ° C). Subsequent condensation in long chimneys would have caused sooting , which is why efforts were made to keep the exhaust gas temperature below 120 ° C.

Since the cooled flue gases from condensing boilers no longer heat the chimney, but their condensable components condense on the "cold" chimney (which acts like a flow cooler), an old chimney must be converted when a condensing boiler is installed. To do this, an acid-resistant pipe with a non-absorbent, non-porous surface (made of temperature-resistant polypropylene -S up to 120 ° C, PTFE up to 160 ° C or a pressure-tight stainless steel pipe) is pulled into the chimney through which the exhaust gases are directed to the outside. Chimney pipes with an acid-resistant ceramic coating are also used in new buildings . If this pipe is not installed in old chimneys, the chimney will become damp. This can cause serious damage to the masonry.

The condensates of the exhaust gas flow back down the inner wall of the tight pipe and are drained from the heat exchanger together with the condensate . The acid contained can be neutralized by suitable equipment. The entire condensate can then be discharged into the sewer system in accordance with legal regulations .

If the condensing effect of an installed condensing boiler is not used in heating systems with a higher return temperature (radiator systems) because the heating return does not cool the flue gases deep enough, various solutions can be used:

  • With an air-exhaust system (also called LAS pipe or LAS chimney system), the fresh air required for combustion is heated in countercurrent by the outflowing flue gases. The warm exhaust gases are discharged through the inner tube of a tube-in-tube system, while heat is transferred to the colder supply air that is routed through the outer tube of the LAS system to the burner. Energy is extracted from the exhaust gases through heat exchange or after condensation of the water vapor. As a result, condensation heat can still be used at return temperatures above the flue gas dew point of the respective fuel and calorific value operation can be enabled.

The exhaust gas can with the o. G. Process can be cooled down to the maximum that corresponds to the temperature of the coldest medium in the entire heat exchange process:

  • At low flow temperatures, for example with low-temperature heating systems or in the transition period (spring and autumn), when the heating is operated with little power or low flow temperatures in partial load, either the heating return or the fresh air is the coldest medium.
  • At high return temperatures, the cold fresh air is the colder medium in quantitative terms, and the cold drinking water supply is less (because of the lower hot water consumption compared to the heating expenditure). Above all, high return temperatures occur
    • in high-temperature heating systems (radiators),
    • in cold winter at high flow temperatures, in order to quickly bring heat into the rooms that cool down more quickly,
    • with closed radiator valves,
    • in the event of insufficient hydraulic balancing of the radiator system.
    • When heating a hot water storage tank: If a cooled-down storage tank is reheated too frequently (with a small temperature difference ), the circulating boiler water can have a higher temperature.

Accordingly, the calorific value effect cannot be used to the maximum at all times of the year, so advertised optimal savings effects must be put into perspective.

Low-temperature heating systems ( underfloor heating , wall heating , heating strips, etc.) cause a lower return temperature from the outset, below the possible dew point. The energy gain when upgrading from a normal condensing boiler to a full condensing boiler or LAS system is therefore lower with these heating systems, since only the low energy content of the exhaust gas that has already cooled down can be used. The economy of the upgrade should therefore be proven by the manufacturer for such applications.

Exhaust system

Flue system of a condensing boiler

Because of the low flue gas temperatures, the chimney effect in the fume cupboard is only weak. That is why many condensing boilers have built-in fans. This should ensure the safe extraction of the exhaust gas.

Load and return temperature independent condensing boiler

Vetter had the idea of ​​having the water vapor contained in the exhaust gas condense in a separate plastic heat exchanger. The prerequisite for this is that the exhaust gases have already been cooled to around 65 ° C (otherwise the plastic will deform).

The exhaust gases are then cooled further in the plastic heat exchanger and the temperatures required for condensation are thus fallen below.

The fresh air required for the combustion process cools the heat exchanger on its way to the burner and warms up. In this way, the thermal energy is retained in the system and is not lost with the exhaust gas. The colder the incoming fresh air is (e.g. in winter), the better the efficiency, because then the exhaust gases are cooled down more.

Since the plastic heat exchanger is insensitive to the sulfuric acid contained in the condensate, the sulfur content in the fuel is irrelevant. Oil condensing boilers can therefore burn fuel oils containing sulfur.

With this arrangement, the calorific value of these boilers is neither dependent on the load nor the return temperature. Such boilers can be used where flow and return temperatures must be between 90 ° C and 60 ° C. They are called high-temperature condensing boilers or "full condensing boilers".

Load and return temperature dependent condensing boiler

Other designers have taken up the idea, but are using other options. With them, the fresh air required for combustion is not heated with the exhaust gases. Instead, the energy available from condensation is transferred directly to the heating water.

The utilization of the calorific value is achieved by lowering the return temperature (= the temperature of the heating water entering the boiler) to such an extent that the dew point of the flue gas on the heat exchanger surfaces is not reached.

Depending on the design, this can be done in the boiler itself or in a separate, downstream heat exchanger . The boiler (with internal condensation) or the heat exchanger (with downstream condensation) must be acid-resistant because of the resulting condensate.

With this arrangement, the calorific value depends on the load and return temperature. These devices should therefore be used in systems where return temperatures are low, e.g. B. with underfloor heating (<30 ° C) or the permanent condensation temperature is high. As a rule, only partial condensation takes place here, since the return temperature is below the dew point, but the exhaust gas temperature is above it. One speaks here of a low-temperature condensing boiler.

Necessary changes / requirements to heating systems

In principle, condensing boilers can be used in any heating system. However, the drainage of the condensate must be ensured, i. H. the boiler must be connected to the waste water drain. Manual emptying is not practical due to the amount of water that occurs. In most cases, the condensate can be discharged into the drain without neutralization. Whether the calorific value effect is actually being used can be checked by checking the amount of condensate (with comparison to fuel consumption).

With high-temperature condensing boilers (see above), the calorific value is not dependent on the load or return temperature. There are therefore no restrictions here, neither for underfloor heating nor for other heating systems.

In the case of the low-temperature condensing boilers, the calorific value depends on the load and return temperature; Excessively high return temperatures destroy the calorific value effect. In this way, low return temperatures increase the effectiveness. A combination with appropriately large heating surfaces, e.g. B. underfloor heating is therefore useful, but not mandatory. As a rule, following modernization measures on the building (e.g. window replacement) , the existing radiators are large enough that they have sufficiently low return temperatures. The heat output that a radiator has to give the room also drops drastically when the outside temperature rises. The less heat that has to be given off by the radiator, the higher the return temperature of the radiator.

That is why the installation of differential pressure-controlled circulation pumps is a must for condensing boilers: only then can it be ensured that the volume flow of the heating circuit is always adapted to the requested heating output and that the return temperature is optimally low. However, this also requires the (one-off) adjustment of the differential pressure of the circulation pump to the conditions of the respective heating system. With pumps of this type, this is usually possible using a potentiometer attached to the pump.

Influences on the return temperature

So-called overflow valves , often just after the circulation pump between pre - and return (integrated wall units in the unit) are installed, open at part load to reduce the pressure. This happens when too little water is pumped through the heating system due to the closing thermostat valves and as a result too little heat is dissipated in the boiler and the boiler overheats (the boiler volume flow is less than the design volume flow). These overflow valves then open to relieve the pump or to ensure a minimum amount of circulating water required by the boiler, and raise the return temperature ( return increase ). The latter also applies to 4-way mixers.

Both overflow valves and 4-way mixers should be shut down or removed when using condensing boilers so that the return temperature at the boiler is as low as possible. However, wall-mounted units in particular often have such low boiler water contents that a certain minimum amount of circulating water must be ensured by overflow valves to protect the heat exchanger surfaces from thermal overload. The minimum amount of water circulating should be as small as possible.

Some manufacturers understand by raising the return temperature that only the temperature of the boiler water in the hottest part of the heat exchanger is raised so that (if the water-flowing heat exchanger is cooled down to the too cold return temperature after a burner shutdown) no water vapor condensation takes place in this section (which can lead to corrosion, considerable soot formation on the exchanger surfaces and total damage to the heat exchanger) and in this part of the heat exchanger only cooling above the dew point takes place, for cooling below the dew point, a "downstream" more corrosion-resistant section of the heat exchanger is provided.

The problems with overflow valves do not apply when the boiler is connected via a hydraulic switch . When using a hydraulic separator, make sure that the volume flow on the boiler side does not exceed the volume flow on the heating circuit side in the hydraulic separator. Otherwise, hot feed water would be added to the return to the boiler again and raise its temperature, which would reduce or even destroy the calorific value effect. The volume flow on the boiler side should therefore be set 10 to 30% lower than the volume flow on the heating circuit side. The hydraulic switch often increases consumption costs.

Damage can occur if a condensing boiler is "operated improperly" (for example by connecting it to a non-low temperature heating system or if the return temperature is always too high). In pellet condensing boilers, the fine dust consists of soot and mineral salts that are deposited in the heat exchanger and washed off by the steam condensate that occurs at the same time; if steam condensation does not occur due to excessively high return temperatures, these salts clog, reduce the heat transfer in the heat exchanger and clog the exhaust gas ducts.

Condensing boiler with output modulation

Modern condensing boilers adapt the burner and pump output to the required heating load. This reduces clocking of the device. Switching on and off wear out the boiler and lead to cooling losses in the breaks between the operating phases.

Efficiency and degree of utilization of the condensing boiler

The efficiency of a device indicates which part of the power used can be used. Efficiencies always represent a snapshot (e.g. measurement in steady state at 70 ° C boiler water temperature and nominal output) and relate to the ratio of input to output. However, this is not sufficient for the energetic evaluation of a boiler, since the standby heat losses are not taken into account. In other words, only the losses that occur while the burner is running are taken into account.

The firing efficiency, which is shown in the chimney sweep protocol, indicates what proportion of the power supplied to the boiler in the form of fuel remains after deducting the dry (or sensitive) exhaust gas losses. The latent exhaust gas loss that arises due to the condensation heat of the exhaust gas that is not used or is not fully used should now be correctly deducted from this portion.

A complete energetic evaluation of boilers can only be made with the help of the boiler utilization rate. The boiler utilization rate is the ratio of the amount of energy supplied in the form of fuel in a certain period of time and the useful energy given by the boiler to the downstream heating network or to the hot water storage tank. In contrast to the boiler efficiency specification, the specification of the boiler efficiency also takes into account the standby heat losses of the boiler that occur, for example, through the emission of radiant heat to the installation room during the burner shutdown.

In the case of efficiency and degree of utilization, it must always be stated whether these refer to the calorific value H i (formerly H u ) of the fuel used or to the calorific value H s (formerly H o ). In order to be able to compare the efficiency and efficiency of boilers that are operated with different fuels, only calorific value-related information is suitable, since only these state the total energy contained in the fuel. The theoretically achievable degrees of efficiency and utilization for oil condensing boilers are 100% if H s was used and 106% if H i was used. For gas condensing boilers, a maximum of 100% calculated with H s and a maximum of 111% calculated with H i are achieved.

The consideration of the calorific value ignores the latent heat losses (condensation heat).

The electricity consumption of a heating system must also be taken into account.

Only gas-powered heat pumps and gas-powered combined heat and power units, which are only offered for heating larger houses, offer better efficiency than condensing boilers.

In the assessment of a condensing boiler should in addition to the efficiency in heat generation and supply losses are taken into account, which are caused by heat dissipation of the equipment (boilers, storage, pipes) with poor thermal insulation. Supply losses are given in data sheets as a percentage (of the maximum boiler output, not the annual energy consumption) and are in the order of magnitude of around 0.5–1% for modern devices. Reductions in supply losses can be achieved, for example, by switching off at night (heating target temperature 3 ° C) instead of lowering the temperature by two degrees and by additional thermal insulation of buffer storage tanks and pipelines. The standby losses only occur when the device is in operation or cools down afterwards; an extrapolation to 365 × 24 = 8760 hours of standby still results from times when small pilot lights were "ready" and leads to excessive values. The cycling of a boiler during heating and the resulting cooling losses can cause considerable heat losses that by far exceed the one percent mark of the standby losses (see also Recording and Avoiding Unnecessarily High Energy Consumption in Boilers ).

With a condensing boiler, when the supply air is sucked in from the boiler room (in the basement), other bound latent heat (from the drying out of the building moisture when the boiler room is used to dry clothes, bathroom and sauna exhaust air from the controlled living room ventilation ) can be used by saving condensation (see plus flue gas condensation # energy efficiency ).

Hints

50% of the maximum heating output according to DIN 4701 would often be sufficient to cover 90% of the heating energy requirement. In order to cover the remaining 10%, many (condensing) boilers are oversized and thus lead to high standby losses.

Determination of the calorific value utilization

The amount of condensate can be used to control how well the condensing boiler uses the energy of the fuel used. Under certain conditions, conclusions can even be drawn about the overall degree of system utilization. The measurement method using the amount of condensate is integrative and avoids errors in instantaneous values ​​and the formation of differences from much larger numbers.

As part of a (limited) field study, the consumer advice center examined how efficiently condensing technology actually works in practice. The condensate was the most important measured variable. 88% of the condensing boilers were fired with natural gas, 9% with EL heating oil and 3% with liquid gas. The inspection of 996 condensing boilers in private residential buildings showed that "the potential of the device technology in the implemented overall systems is often wasted". The calorific value benefit was acceptable in around a third of the devices, in a further third there was a need for optimization and in the last third the calorific value benefit was inadequate. The investigation also found weak points in the thermal insulation of heating pipes (25% had no thermal insulation), 25% of the systems were equipped with an overflow valve that was counterproductive for the utilization of the condensing technology, and 78% of the systems lacked hydraulic balancing, which in these systems worsened the Results contributed.

According to research report 601 of the DGMK from 2002, oil condensing boilers produce one liter of condensate per liter of heating oil burned (i.e. 0.1 l / kWh), whereby technically and practically only a condensation rate of 50 to 70% is possible. With equally efficient gas condensing boilers (i.e. the same condensing related boiler efficiency) approx. 1.5 liters per m³ of natural gas. The different amount of condensate in oil and gas results from the different fuel composition. Natural gas contains more hydrogen, which means that more water vapor is produced during combustion. If the water vapor contained in the flue gas is not fully condensed in practical operation due to higher flow / return temperatures (e.g. during hot water preparation), gas condensing boilers have a lower efficiency (calorific value reference) due to the higher latent heat losses (max. 11 percent) as an oil condensing boiler (max. 6 percent latent heat loss).

Check by the chimney sweep (Germany) / cost advantages

The test interval for gas-fired condensing boilers is two years in Germany (the test interval for most calorific boilers is one year). In the case of a condensing boiler, there is no activity according to BImSchV (exhaust gas loss determination), but a recurring activity according to the sweeping and inspection regulations. This check includes the determination of the CO content in the exhaust gas ( exhaust gas measurement ) and an exhaust gas path test.

This means a not inconsiderable cost advantage for condensing boilers.

Condensing boiler and thermostatic valves on the radiators

The use of thermostatic valves on radiators or wall-mounted condensing boilers with a lower water content can lead to the return water flowing back too hot and therefore not using the calorific value or the burner clocking (and thus increasing standby losses). To remedy this

Assistance through home automation

Some home automation systems can record and evaluate states and measured values. This enables a significant optimization of the heating operation. This is especially true when certain operating modes are to be achieved. Examples:

Setting the characteristic curve of the outdoor thermometer
With access to the positions of the actuators on the radiators, you can easily optimize the basic level and gradient of this characteristic curve. So z. B. minimize the return temperature. A few years ago, a study showed that the majority of condensing boilers had this characteristic in the delivery condition. In practice, the heating technician will only turn this when the customer complains about temperatures that are too low: The technician has no criteria for a sensible setting.
Switching off the entire heating system when no heat is required
Here, too, the states of the actuators are decisive: If the actuators in the main rooms (living room, kitchen, toilet, bedroom) are more or less closed, the heating can also be switched off completely. Even with temperatures around freezing point and a 40 year old house without full thermal insulation, you can get by without heating for 3–5 hours a night. Mind you, only the side rooms cool down that are not used in the morning anyway: As soon as it gets too cool in the main rooms, the heating starts again immediately.

The home automation market is not yet mature. There are a large number of different systems that can often only be used effectively with sufficient knowledge of physics, IT and electronics.

Condensing boiler or low temperature boiler?

When buying a new or replacing an old heating system, what is initially impressive is the higher standard utilization rate of condensing technology compared to heating technology. However, there are restrictions to be observed:

  • The condensing technology is more expensive to buy. This applies to the boiler / thermal bath itself, possibly larger radiators and the necessary changes to the chimney (pipe insertion). If there is no sewage connection nearby, it must be created.
  • In practical use, a condensing device can quickly and unintentionally fall back into quasi-calorific value mode, so that the efficiency drops. The reason for this is usually too high a return temperature of the heating water, B. by regulated thermostatic valves on the space radiators or by space radiators with too little surface, d. H. Oversizing of the boiler or undersizing of the heat consumers. However, this is not a problem if the heating system has a differential pressure-controlled circulation pump, since the volume flow of the heating circuit is reduced accordingly when the thermostat valves are closed or when the heating output is less requested. However, even if a condensing boiler does not always use the calorific value, the flue gases come out of the boiler at lower temperatures (in the range 60–80 ° C) than with conventional low-temperature boilers (120 ° C)
  • When using the same high-efficiency pumps, condensing systems consume approx. 30-40% more electricity than heating value systems because the relatively cool exhaust gases do not passively rise in the chimney and therefore have to be actively blown off. However, in a study, electricity consumption was measured at 3% in relation to fuel consumption, of which two thirds were used by the circulation pump and one third by the burner, fan and control system. The additional electricity consumption, caused by the pressure drop in the exhaust gas volume flow due to additional heat exchanger surfaces, was just under 0.3% and the ratio of additional yield to expenditure - at the primary energy level - was just under 7. When considering the energy costs, the electricity price comes into play.
  • The residual heat contained in the exhaust gases is usually recorded as a total loss. This is only true for the relatively cool flue gases from condensing technology, which are actively blown off through the chimney in a separate acid-proof pipe with little further heat exchange. This only partially applies to the warmer exhaust gases from a calorific value system because they cool down as they rise in the chimney and heat is transferred to the masonry (although the masonry is a poor conductor of heat and the heat transfer is therefore lower than with a heat exchanger made of a metallic material). This heat contributes to the heating of the adjacent rooms and is not to be regarded as a loss.

Web links

Wikibooks: Optimization of small heating systems  - including condensing technology

Individual evidence

  1. ↑ Hans Hartmann, Paul Roßmann, Heiner Link, Alexander Marks: Testing the condensing technology in domestic woodchip firing with secondary heat exchangers. (PDF; 1003 kB) Technology and Promotion Center in the Competence Center for Renewable Raw Materials and the Bavarian State Office for Environmental Protection, Straubing, 2004; Retrieved February 7, 2012.
  2. ↑ neutral company web presentation (PDF)
  3. ↑ Helmut Effenberger: Steam generation . Springer, Berlin Heidelberg New York 2000, ISBN 3-540-64175-0 ( limited preview in the Google book search).
  4. ↑ The Vetter story .
  5. ↑ Robert Kremer: The use of condensing technology is state of the art. Gas heat international volume 30 (1981), issue 11, page 558, Vulkan-Verlag, Essen 1.
  6. ↑ Robert Kremer, Jürgen Selbach: Condensing boiler after 30 years of state of the art. Part 1 in HLH , Volume 60, 2009, No. 1, pp. 19-25, Part 2 in HLH , Volume 60, 2009, No. 2, Springer VDI Verlag, Düsseldorf.
  7. ↑ Worksheet DWA-A 251 "Condensates from condensing boilers", ISBN 978-3-941897-89-2
  8. ↑ Frank Sprenger: Condensation water from boilers and its neutralization (PDF) buderus
  9. ↑ senertec-service.de ( Memento from March 28, 2016 in the Internet Archive ; PDF)
  10. ↑ Basics of chimney technology - schiedel.de (PDF)
  11. ↑ Quality assurance measures for heat generators (PDF; 127 kB)
  12. ↑ Condensing boiler heating systems : "Most municipalities comply with leaflet 251 of the Abwassertechnischen Vereinigung ATV. For gas condensing boilers with an output of up to 25 kW, neutralization is not required. The heating specialist knows which requirements apply in the respective municipality."
  13. ↑ According to which criteria do you choose a condensing boiler? At: heiz-tipp.de.
  14. ↑ Nicolas Bukowiecki: Fine dust emissions from wood furnaces: Investigations into the behavior of pollutants in the atmosphere. Paul Scherrer Institute PSI, FOEN-Cercl'Air symposium, 8 and 9 November 2011, Ittigen near Bern, can be downloaded from bafu.admin.ch.
  15. ^ Gerhard Hausladen: Lecture script for heating technology , University of Kassel, 1992; delta-q.de (PDF) accessed in October 2012.
  16. ^ Action calorific value check of the consumer advice center for energy advice ( memento of the original from July 18, 2011 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. . @1@ 2Template: Webachiv / IABot / www.verbüberszentrale-energieberatung.de
  17. ↑ Final report on the “Calorific Value Check Campaign” by the consumer centers, July 2011, verbüberszentrale-energieberatung.de ( Memento of the original from March 10, 2014 in the Internet Archive ; PDF) 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. . @1@ 2Template: Webachiv / IABot / www.verbüberszentrale-energieberatung.de
  18. ^ Heike Stock, Dieter Wolff: Development tendencies in the control engineering of heating systems . (PDF; 168 kB)
  19. ↑ Kati Jagnow, Dieter Wolff: Calorific value is added value - what you should pay attention to when choosing a boiler . (PDF) accessed in October 2012.
  20. ↑ Markus Erb: Field analysis of condensing gas and oil combustion systems in the renovation area . ( Memento of November 10, 2013 in the Internet Archive ; PDF) Liestal (CH), 2004.