What do the technical terms mean?


Heating and air-conditioning


  1. Burner ignition / Pollutants
  2. Burning efficiency
  3. Charging times, heat-up times
  4. Chimney, chimney remediation, wet chimney
  5. Circulation
  6. Circulating pump
  7. Corrosion
  8. Cycles
  9. Degree day
  10. Dew-Point
  11. Energy consumption characteristic value
  12. Fast heat-up
  13. Gross calorific value
  14. Heat capacity
  15. Heating curve
  16. Heating degree day
  17. Heating output
  18. Heating threshold
  19. Heating trigger
  20. Hydraulic balance
  21. k-number, U-number
  22. kv-number
  23. Legionella
  24. Map of climate zones
  25. Modulation
  26. Net calorific value
  27. Night-time reduction
  28. Passive house
  29. Pressure
  30. Self-regulating effect
  31. Undetected waste

Others



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Burner ignition / Pollutants
Unit: times per hour
Pollutants at ignition/shutdown of burner
Pollutants at ignition/shutdown of burner [Source:owi]
At startup a burner produces a level of pollutant which is many times the level produced during constant operation.

Test reports of the institute EST of the University of Aachen show that an (oil-)burner only reaches stable operation 3-6 minutes after ignition.
      Only taking account of the peak level for pollutant emission during the first 20 seconds, this will add up to approx. 280 operating hours during which over the year an increased proportion of unburned hydrocarbons go directly up the flue. Instead of delivering the normal quantity of warmth (approx. 1000 kWh), which under these conditions 100 liters of oil (or 100m³ of gas) should deliver, only 360 kWh, i.e. 36% of normal efficiency, is delivered. You might just say that 'Coitus interruptus' applies for most burners (normally run for 4 minutes): They stop just when they get going.
This is why we think longer running times are better - to find out more, look at:
  1. Annual heating work
  2. Burning efficiency
  3. Burner running times
  4. Optimization

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Charging times, heat-up times
Unit: s,m,h
This is the time it takes to charge (heat up) a hot water tank. Only in large systems is heating and charging up a tank possible (or necessary).
It is always a good idea only to have a tank fully charged at those times when you need hot water.

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Chimney, chimney remediation, wet chimney
Unit: euro ;-)
Bitter experience with oil heating systems has taught us that chimney remediaton using NiCr-steel or PP is not advisable. The durability of these materials is limited to 3-10 years (due to the formation of sulphuric acid). The ideal material for wet chimneys is Technaflon (PVDF), which is quasi-self-cleaning.
In Germany, if a chimney remediation becomes necessary, you need a 'Feuerungstechnische Berechnung nach DIN 4705', which is supplied by the manufacturer of the boiler. You hand this paper to the chimney sweeper next time he calls to measure. The tube is inserted into the old chimney and then connected. The air space between the tube and the chimney which is thus created acts as an ideal heat-exchanger for the air inlet to the burner. Why not make use of the easily achievable air/off-gas chimney?
Luft-Abgas-System The inlet air is preheated to approx. 24-30ºC (not beyond, because the volume of air is too low to create a turbulent flow) but this is enough to make approx. 63% of the sulphurous acid in the off-gas condense.
This gives you a heating system which is independent of the air environment in which the system is installed. You are thus able to close off the inlet opening through which your energy is normally wasted.

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Circulation
Here: circulation of water flows.
There is both intended and unintended circulation.
      Intended circulation occurs when you switch on the circulating pump, but the unintended kind is the more frequent and the more expensive.
      Unintended circulation always occurs when water of different temperature meets, i.e. also in pipes when the cool water inside the end of the pipe flows under the warm water in the boiler inlet, thus creating a vagabond flow which cools every kind of tank.
 
Honeywell-Centra has been recommending a heat stop U-bend since 1960(!) for use with its 3-way mixers:
To make sure there is no two-directional flow in the backflow pipe, in all systems with 3-way mixers, our advice is to install a heat stop U-bend in the backflow pipe which has a U-length of between three and six times the diameter of the pipe and a U-width between eight to ten times the diameter.

Convection stop What you can see is 'in-pipe circulation' occuring in horizontal pipes.
 
Wagner Solar offers a convection stop for tanks with horizontal outlets, which can be easily inserted later.
 
Thanks for the good graphic:
It is from Wagner & Co, slightly modified.
 
Circulation in a coaxial pipe To minimize circulation losses in multi-storey appartment buildings, a good solution was created: Viega offers couplings for inner circulation systems.
 
Graphic: Viega

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Circulating pump
In a system where the water is heated in a central location, hot water is pumped directly to all hot water outlets by the circulating pump. The boiler has to be boosted with heat very frequently, so this luxury doesn't come cheap. Not only does the circulation pump empty the boiler, but you lose heat (even in summer!) by radiation of heat through the pipes.
      Quote from Ansgar Schrode, energy consultant: '...even well-insulated and time-controlled circulation systems consume up to 100 liters of oil per year.'
      We can tell you about a lot of ways to limit losses due to the circulation pump by getting the pump to run only when you really need hot water at the outlets. Currently, no company is able to provide a controller able to achieve this 'self-learning strategy' function. Consider yourself lucky if you don't have a circulating pump. (PS: you can switch it off :-)

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Corrosion
Unit: none
The standard definition of corrosion of metals is as follows:
'The change which takes place on the surface of a material due to chemical or electrochemical attack.'

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Dew-Point
Unit: C
Dew-point does not refer to a local point, but that air temperature at which air can no longer hold water as vapor. Drops of water then form. This is to be seen on frozen water coolers or in damp corners. This principle is applied in humidity control of air-conditioning systems.
Off-gas temperature is important in keeping the chimney relatively dry. The dew-point of the off-gas depends on its CO2 content. The dew-point temperature for modern natural gas (95% CH4) burners is 57ºC and for oil-burners 47ºC. This results from the fact that the water content of gas (11%) and oil (6%) differs.

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Fast heat-up
Possibility of a controller to boost room temperature mornings to the required 20ºC in the shortest possible time. This normally involves all settings to be overridden and pumping into the heating and ventilation system continues until target room temperature is reached.
For heating systems, the easy solution is to install a minimum of 2 sensors to obtain a mean value.
Is fast heat-up reconcilable with the graph of personal thermal comfort?

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Gross calorific value (upper heating value)
Unit: kJ/kg
... is the amount of warmth set free when a combustible material burns completely. A distinction is made between the gross calorific value (g.c.v.) and the net calorific value (n.c.v.) for all combustible materials containing hydrogen (and therefore carrying water vapor in their off-gas).

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Heat capacity, Storage effect
Unit: Wh/KgºK
The heat capacity of water is a constant: 1.163 Wh/KgºK.
      The storage effect in houses is determined by the mass of the walls. The greater the storage effect of a house, the less extreme is the impact of the outside weather conditions on the climatic conditions inside. In autumn, when the temperature is falling, the storage effect crucially impacts the heating trigger and also, because cold peaks in northern Europe normally do not last long, what size the heating system needs to be.
 
The minimal outside air temperatures in the map of climate zones of Germany can be increased by the temperatures shown in the table below, according to the way the walls are built:
Construction of the walls dT [K] Typical materials
Light <600kg/m 0 Mineral fiber, cork, wood=600
Heavy 600...1400kg/m³ +2 Aerated cement blocks, plaster
Extra heavy >1400kg/m³ +4 Brick, chalk sandstone, heavy cement, stone=2800

Examples
  • The lower extreme is a tent.
  • The upper extreme is a cave, such as in Matmata/Tunesia or on the Seine/France.
  • At our latitudes, a wall would have to be approx. 2m thick to compensate seasonal temperature fluctuations. [Construction textbook]

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Heating curve
Unit: none
heating curve
Relationship between outside temperature and inlet temperature of the heating medium.
 
The broken lines will guide you to a steepness of 1.2, which is appropriate for radiator-type heating systems in northern Europe from 1983. Underfloor heating systems require values in the range 0.4 to 0.6. If you alter: Only when freezing and begin with the minor values!

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Heating output
Unit: Watt, kW
When do you really need the full output of a heating system?
heating output
[Source: E. Buscher, Wilo GmbH: Pumpen Spezial]
 
Sum curve of total heating energy requirement over a year:
  • The period over which you need more than 50% of the calculated heating output is only one month!
  • Approx. 85%...90% of the annual heating work is delivered at those times when the system is running below 50% of its full capacity.
  • The statistics of the annual heating work tell you when you will need a given output of your heating system.

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Heating threshold
Unit: ºC
The heating threshold is that outside temperature at which heating a house is not necessary. Historically, the conventional measurement period is one day. However, ist is imaginable and feasible to calibrate this threshold to a smaller data gathering period (e.g. 15 minutes). The threshold is thus calculated more exactly.
      Even though it sounds simple, the calculation is complicated, because the value varies according to which house you live in and what you do there. The threshold not only depends on the inside temperature (20ºC), but also on the wall insulation (heat loss) and het capacity of the wall (when the temperature drops quickly). Also, the users decide if a building is well-heated at an inside temperature of 18ºC, or if a lab produces so much interior heat that heating is only necessary at outside temperatures inferior to +5ºC.
      In Germany, the heating threshold is defined as 15ºC (the corresponding figure in Switzerland is 12ºC). There are combinations of 17/25C. Figures not defined in detail are therefore unhelpful.
The heating threshold is the basis of the calculation of heating days and the number of degree days.

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Heating trigger
Unit: ºC
The conventional wisdom is that you have to heat when on two consecutive days the mean outside temperature does not reach the heating threshold of 15ºC. (Since this temperature refers to a mean value over a day, you can only start heating the third day according to this directive. )
      This assumes that the house has a certain heat capacity which can act as a buffer for 2 days. This is only the case if the walls are fairly massive.
In practice, greater savings can be achieved by:
  • switching off at exactly the right second when the outside temperature is rising.
  • starting to heat again when the outside temperature is falling according to the time constant of the building.

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Hydraulic balance
Unit: =
... means balancing resistances:
In hydraulic networks, every circuit has its own resistance. However, this resistance determines the flow through a circuit. Resistance increases twice as fast as velocity of water flow, while an increase in flow volume results in a 32-fold increase in resistance (to the power of five). This is analogous to the situation in an electric circuit: I=U/R.
Balancing means adjusting the resistances of the circuits and other parts of the network so that the nominal flow volume obtains in each simultaneously, i.e. the water quantities required are distributed correctly. In most circuits, the constantly changing adjustment effected by the thermostatic valves results in a variation in water quantity. We thus have to install water flow controllers.
 
Operating without hydraulic balancing means:
  1. high pumping costs (increasing by a power of 3 in relation to volume)
  2. less use of gross calorific value
  3. reduced controlling ability
  4. noise in the system
  5. delayed heating-up of entire parts of the building
  6. non-achievement of desired interior temperatures
  7. unfair distribution of heating costs

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k-number (new name: u-number)
Unit: W/m²*K
Specific heat flow transmission value for building elements.
The k-number is that heat output (in watts) which flows through the dry(!!) surface of a building element of 1m² at a temperature difference of 1ºK. The k-number is (as in electronic engineering) a surface-related current density which describes heat flow. The lower the heat loss, the slower the loss of room heat.
 
The k-number for a complete building can be determined from heating energy consumption by a rule of thumb.
k-number * 10 = Liters oil per m² and year
Examples of building standards Consumption
[Liters/m²a]
Total k-number
[W/m²a]
Typical consumption in Germany in 1999 18 1.8
Energy-saving house 7 - 3 0.7 ... 0.3
Super energy-saving house 3 0.3
(1 Liter oil/gas approx. 10kWh)
 
Go to our optimization results. To obtain the correct k-numbers, subtract 30% from the heating consumption figures to compensate for system losses. Honest users must also include their annual electricity consumption in their heating energy requirements. (In 2000, the average German household consumed approx. 3420 kWh of electricity, and 20750 kWh in other forms of energy, not counting the use of a private car.)

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kv-number
Unit: m³/h or m³/sec
The characteristic number defines that volume of heat carrier (water) flowing through a partially opened valve per second, when a pressure of 1 bar applies across the valve.
That kv-value which applies to a fully opened valve is sometimes called the kvs value.

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Legionella
Unit: m
A bacterium can be present in fresh water and can be inhaled as droplets (aerosols). This is a health risk for humans - especially smokers and males (for whom the risk is 3 times higher than for females). The bacterium occurs in (man-made) water systems and reproduces rapidly in the 25...55ºC temperature range. Cold water does not kill them.
Where can you find them?
  • Hot water systems: Showers!
  • In air washers, e.g. in dew point-controlled air conditioning systems.
  • Cooling circuits: Cooling towers
  • Water features with spray effects
  • Outside sprinklers
What to do?
  • Legionella are the result from lack of maintenance - so always ask about this in hospitals or hotels! ;-)
  • Copper tubes inhibit reproduction, which means that the problem rarely occurs in domestic environments.
  • It is recommended to heat the hot water system periodically up to 70ºC or to use chlorine.
Many thanks to Jochen Alfery for the good information!

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Map of climate zones
Unit: C
This map shows Germany in 4 zones according to the lowest 2- day mean air temperature values reached 10 times over the last 20 years. These temperatures are taken into account when engineering the size of burners and boilers. A further factor is the heat capacity of the building.

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Modulation
Unit: %
describes the possibility of modifying burner output (via a controller) so that the generation of heat is adapted to your heating requirements at any given moment. Gas device manufacturers were quick to take up continuous adjustment of heat output because it is quite simple and was identified as the best way of combatting losses when the burner goes into pause mode. These losses always occur when the burner goes off and the boiler is hot.
Modulation When modulation of the burner is not provided for, or when the lower modulaton limit is reached, the burner has to be switched on and off. We talk about cycles, or, in general technical terms, pulse width modulation, which results in greater wear on parts and heat losses during the times the burner is off. These losses also occur when the burner has been oversized, meaning that the lower modulation limit is always reached, and the burner therefore can only go into cycle mode. This causes unnecessary fuel consumption: the annual Utilisation Ratio drops and drops....
      Nearly all gas device manufacturers can achieve 100-50% modulation, some manufacturers even 100-10%. This is much more difficult to achieve with oil burners, and even in 2002 experts have to live with 2-stage burners.

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Net calorific value (lower heating value)
Unit: kJ/kg, BTU
.. is the quantity of heat released when a combustible burns completely. In the case of fuels containing hydrogen (and thus water in the off-gas) a distinction is made between gross calorific value (formerly, upper combustion value) Ho and the net ? combustion value Hu (formerly, lower combustion value).

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Night-time reduction
Unit: h
This is the time when room heating is reduced. When heating stops completely, we talk about a night-time shut-down. With some controllers, it is possible to set a minimum night-time room temperature. In northern Europe the outside temperature is about 10ºC lower at night, so that minimum heating nevertheless continues. This is unnecessary.
A better option is to use heating controllers with automatic start-up (triggered by the outside temperature) and to set them correctly. Setting the night-time reduction to a level which is really low enough will stop the burner running at night and you are making sure that the system goes on early enough in the morning.
There is one exception at very low temperatures and small system capacities (happening once every ten years), in which case it is better to make no night-time reduction/shut-off, if you want your rooms to get warm next morning.

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Passive house
Unit: kWh/m²a = Kilowatt hours per square meter and year
"...is a frequently used term. The 'passive house' aims to achieve an energy consumption inferior to 3 liters, i.e. consumption in the range of approx. 1 to 2.5 liters (of oil or m³ of gas). Although this may be the correct goal, the term itself is incorrect and stands in contradiction to the definitions contained in the literature. According to definition, a passive house would have to be constructed exclusively by non-energy-consuming building techniques. However, the ventilation and heat recovery technologies applied in such a house are clearly active system elements, thus rendering the term incorrect."
[Quoted from Prof. Dr. Karl Gertis from his presentation at the velta congress in 2001.]
 
The correct term is 'zero heating energy house' or 'heating energy autonomous house'.

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Pressure
Unit: Pascal, bar, cm, at, N/m
Everybody knows what pressure is :-). In the world of heating and air-conditioning we speak about low pressures and an infinity of pressure units. (You will know how easy it is to convert to and from the imperial system ;-). Although Pascal is currently the correct SI unit, other units, in particular 'watercolumn cm', which has a good look-and-feel, are always cropping up.
1 mbar = 1hPa = 1 cm WS
1bar = 100KPa = 10m WS = 1 at = 1kp/cm
Rule of Thumb:
The pressure, acting on a thermostatic valve has to be in the range 40..100mbars, otherwise you will get hissing and a control malfunction.

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Self-regulating effect
Heat transfer from a surface only takes place if the temperature of the surface is higher than the surrounding environment. The hotter the heating surface, the bigger the temperature gradient: under-floor heating 2C, radiators ca. 15C.
Example:
When the flow temperature is correctly set, your under-floor heating will only heat you room up to 21ºC. All other sources of heat (Sonne=1000-3000W, Kochen=2000W, PC & Monitor=200W) increasing your room temperature are reducing the temperature gradient, so the underfloor heating will stop heating automatically. In strong sunlight, the floor will be colder than the room and will start to cool the room.

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Undetected waste
Unit: kWh
Current technology does not protect the user from wasting energy unknowingly (although he has to pay the bill!). Inadequate quality assurance in the domain of heating technology is the cause. Oversizing (especially following remedial measures) results in over-capacity, which the user ventilates away, unaware of the waste. Affordable counter-measures: getting the right output and hydraulic balance.

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page written 03.1.1999, last change 13:20 29.6.2014, Sonntag