technical series: condensing technology
TRANSCRIPT
Condensing technology for improved economy and lower emissions
Technical Series
Condensing Technology
2
Whether gas or oil fired,freestanding or wall mounted –Viessmann offers a comprehensiveselection of condensing boilersfrom 4.5 to 6600 kW
1 Vitodens 300 Gas fired wall mounted condensing boiler
2 Vitolaplus 300Oil fired Unit condensing boiler
3 Vitodens 333 Gas fired condensing boiler with integral DHW loading cylinder
4 Vitocrossal 300Gas fired condensing boiler
1
2
3
Index
1 Basics
2 Significant variables for theutilisation of condensingtechnology
2.1 Efficiency ηK of condensingboilers
2.2 Standard efficiency
3 Condensing technology inexisting buildings
4 Significant variables and criteriafor optimum gain
4.1 Boiler design4.2 Utilising oil fired condensing
technology4.3 CO2 content, burner design4.4 Water connections
5 Condensate treatment
6 Emissions and flue gas system
6.1 Emissions6.2 Flue gas system
7 Selection guide
7.1 Gas fired wall mountedcondensing boilers
7.2 Oil fired wall mountedcondensing boiler
7.3 Oil fired Unit condensing boiler7.4 Gas fired condensing boiler
(freestanding)7.5 Flue gas/water heat exchanger7.6 Selection table for combination
boilers/boiler with focus onDHW heating
7.7 Modular design fromViessmann
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5 Vitocrossal 300Gas fired condensing boiler
6 Vitodens 300Gas fired wall mounted condensing boiler
7 Vitoplex 300 Low temperature oil fired boiler with Vitotrans 333 flue gas/water heat exchanger
8 Vitotrans 333Flue gas/water heat exchanger
3
5
6
7
84
1 Basics
4
2%
11%
98%
109%
Fig. 2: Condensing boilers achieve a standardefficiency of up to 109% by gaining additionalenergy from flue gas (natural gas)
100% 111%
100%
110%
109%
100%
96%
Energy inwater vapour
Flue gasloss 3%
Surfaceloss 1%
Gross calorific valueNet calorific value
Gross calorific value
Net calorific value
97%
Low-temperatureboiler
Gas fired condensingboiler
1%
1%
106%
100%
105%
104%
Gross calorific value
Net calorific value
Oil fired condensingboiler
1%
1%
Fig. 1: Comparison of the losses for low-temperature and condensing boilers (natural gas, fuel oil EL)
Fig. 3: Energy gain from hot gases (natural gas)
Condensing technology provides an efficient method of convertingnatural gas or fuel oil into usefulenergy by combustion (Fig. 1). Aswith low temperature technology, it follows the principle of operatingthe boiler only with that temperaturewhich is required to cover the currentheating demand.
Utilisation of latent heat
Whilst with low temperature boilers,the condensing of hot gases and subsequent wetting of theheating surfaces must be avoided,condensing technology operates to quite different rules: here,condensing hot gases is actuallyhighly desirable and is needed toturn the latent (hidden) energycontained in water vapour, inaddition to the sensible (tangible)flue gas energy, into useful heat.Also, the residual heat exhausted viathe flue will be substantially reduced,since, compared to low temperatureboilers, the flue gas temperature canbe substantially reduced (Fig. 2).
Through the reaction with the aircomponent (O2), the combustion offuel oil or natural gas, both of whichprimarily consist of carbon (C) andhydrogen (H) compounds, creates carbon dioxide (CO2) and water (H2O)(Fig. 3).
For natural gas (methane CH4), thefollowing simplified combustionequation applies:
CH4 + 2 O2 -> 2 H2O + CO2 + heat
Gaining energy from condensation
Condensate will be formed from thewater vapour contained in the hotgas, if the temperature on the wallsof the heating surfaces on the hotgas side falls below the water vapourdew point.
CH4
O2
O2
CO2
H2O
H2O
Heat
5
Basics
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
25
30
35
40
45
50
55
60
CO2 content [vol. %]
Wat
er v
apou
r de
w p
oint
[°C
]
Natural gas(95% CH4)
Fuel oil EL
47
57
Fig. 4: Water vapour dew point temperature
The various chemical consistenciesof natural gas and fuel oil result indifferent water vapour temperatures,at which the hot gas water vapourcondenses. In the near stoichiometricrange, the water vapour dew pointfor natural gas is approx. 57 °C, forfuel oil EL approx. 47 °C (Fig. 4).
The theoretical energy gain fornatural gas, compared to lowtemperature technology, is 11%. With fuel oil, the maximum gainthrough the use of condensingtechnology is 6%.
Net and gross calorific value
The net calorific value (Hi) describesthe energy released during completecombustion, if the water created inthe process is removed as vapour.
The gross calorific value (Hs) definesthe energy released during complete combustion including the evaporation energy containedwithin the hot gas water vapour.Table 1 provides an overview of the fuel characteristics which are relevant to the utilisation of condensing technology.
In the past, the evaporation energycould not be utilised because therelevant technical prerequisites were not yet available. Therefore, the net calorific value (Hi) was used as reference for all efficiencycalculations. Referring to Hi andutilising the additional evaporationheat can thus lead to standardefficiencies above 100%.
Because of guidelines, standardefficiencies in heating technologycontinue to refer to the net calorificvalue (Hi).
Gross Net Hs/Hi Hs – Hi Condensatecal. value cal. value volumeHs Hi (theoretical)kWh/m3 kWh/m3 kWh/m3 kg/m3 1)
Town gas 5.48 4.87 1.13 0.61 0.89Natural gas LL 9.78 8.83 1.11 0.95 1.53Natural gas E 11.46 10.35 1.11 1.11 1.63Propane 28.02 25.80 1.09 2.22 3.37Fuel oil EL2) 10.68 10.08 1.06 0.60 0.881) relative to the fuel volume2) for fuel oil EL, details refer to the unit ”litre”
Table 1: Energy content of different fuels
6
2 Significant variables for theutilisation of condensing technology
Fig. 5: Vitodens 300 gas fired wall mountedcondensing boiler with Inox-Radial heatingsurfaces and MatriX-compact burner, rated output: 4.5 to 35.0 kW
The energy advantage between acondensing boiler and a lowtemperature boiler is not just theresult of the condensing energy gain, but is, to a large extent, aconsequence of the low flue gas loss resulting from low flue gastemperatures.
A basic energy assessment can bemade using the boiler efficiency.
2.1 Efficiency ηK of condensingboilers
Significant variables
ϑA -> Flue gas temperature forcondensing boilers:unlimited
CO2 -> CO2 concentration: combustion quality subject to burner design
α -> Condensate value subject to boiler design and system(layout)
qA – qS Hs – HiηK = 1 – ––––––– + ––––––– • α
100 Hi
SensibleLatent(condensationpart)
A1qA = ( ϑA – ϑL ) • ( –––– + B )CO2
V Condensate volume (actual)α = ––––––––––––––––––––––––––
V Condensate volume (theor.) (see Table 1)
•
Fuel oil EL Nat. gas Town gas Coking gas LPG and LPG-air mixtures
A1 0.5 0.37 0.35 0.29 0.42A2 0.68 0.66 0.63 0.60 0.63B 0.007 0.009 0.011 0.011 0.008
Table 2: Fuel correction value acc. to the 1st BImSchV
Key
ηK = boiler efficiency [%]ϑA = flue gas temperature [°C]ϑL = air temperature [°C]A1 = fuel correction factor
according to 1st BImSchVB = fuel correction factor
according to 1st BImSchVCO2 = carbon dioxide content [%]qA = flue gas loss [%]qS = radiation loss [%]α = condensate valueHs = gross calorific valueHi = net calorific value
Compared with a conventionalboiler, the boiler efficiency formula isextended by the condensation part.The condensation part is defined bythe fuel-specific constant values Hsand Hi, as well as the variablecondensate value α. It provides theratio between the actual volume ofcondensate in a condensing boilerand the theoretically possiblevolume of condensate.
The higher the actual volume ofcondensate, the more effective thecondensing boiler.
The lower the flue gas temperature,the greater the volume of condensateand therefore the condensate valueα. At the same time, the lower fluegas temperature, for examplecompared to a low temperatureboiler, also reduces the flue gas loss. This means thatcondensing boilers (Fig. 5) achieve afurther improved energy utilisationthrough lowering the flue gas losses,as well as gaining condensationenergy.
•
7
Significant variables for the utilisationof condensing technology
00
10
20
30
40
50
60
70
80
90
100
20 40 60 80 100 120 140 160 180 200 220 240 260 280
–15
–12
–9
–6
–3
0
3
6
9
12
15Rel
ativ
e bo
iler
load
[%]
Heating days
Out
side
tem
pera
ture
[°C
]
63
48
39
30
13
24.5 32.2 39.5 50.5 119.7
Fig. 6: Calculating the standard efficiency acc. to DIN 4702, pt.8
20 15 10 5 0 – 5 – 10 – 15
20
30
40
50
60
70
Hea
ting
sys
tem
tem
pera
ture
[°C
]
Outside temperature [°C]
80
90
Flow temperature
Return temperature
Hea
ting
load
[%]
20
30
40
50
60
70
80
90
10
0
10
0
Ope
rati
ng d
atum
7%
22% 21%
9% 6%
35%
Heating system 75/60 °C
Fig. 7: Proportion of heating load subject to outside temperature
2.2 Standard efficiency
The standard efficiency defined inDIN 4702, pt. 8, is used to calculatethe energy efficiency of modernboilers. It is defined as the ratiobetween the heat available p.a. andthe combustion heat supplied to theboiler (relative to the net calorificvalue of the fuel). A process wasdetermined by DIN 4702, pt. 8, whichwill lead to comparable details basedon standardised teststandmeasurements.For Germany, five work load levelswere determined relative to thedefined annual heating output; theseare illustrated in Fig. 6. The sameheating output (area) is calculated foreach load stage. Two temperaturepairs result for each of the five levelsdefined by DIN 4702, pt. 8, (one pairbased on radiator central heating:design basis 75/60 °C; one pair basedon an underfloor heating system:design basis 40/30 °C to EN 677). For each, a part-load efficiency is determined on the teststand.
To calculate the standard efficiency,the five actual part-load efficiencylevels are averaged out. This results in comparable values, which generally reflect a realisticboiler operation in Germany.
Sizing the rated output
The boiler design should ensure that at the lowest likely outsidetemperature, the heat demand canbe fully covered. For Germany, these design temperatures are -10 to -16 °C. However, such lowtemperatures are only rarely reachedduring average daytime operation,hence the boiler must only provideits full output for a few days eachyear. For the rest of the time, only a fraction of its rated output isrequired. Looking at a year as awhole, the greatest part of therequired heating energy, therefore,relates to temperatures abovefreezing (0 to 5 °C) (Fig. 7).
8
Significant variables for the utilisationof condensing technology
110
100
90
80
70
60
50
40
30
20
10
10 20 30 40 50 60 70 80 90 10000
Boiler load [%]
Part
load
eff
icie
ncy
[%]
Increased gainlow temperature boiler
Increased gaingas fired condensing boiler
Gainconstant temperature boilermade in 1975
15 10 5 0 -5 -10 -1520Outside temperature [°C]
Fig. 8: Part-load efficiency levels for various boilers, subject to boiler load for low temperature andcondensing boilers
Fig. 9: Standard efficiency levels for variousboiler designs
A Gas fired condensing boilers 40/30°CB Gas fired condensing boilers 75/60 °CC Low temperature boiler
(without lower temperature limit)D Boiler made in 1987
(lower temperature limit: 40 °C)E Boiler made in 1975
(constant boiler water temperature: 75 °C)
75
80
85
90
95
100
105
10 20 30 40 50 60 70 80 90 100Specific combustion load [%]
Part
-load
eff
icie
ncy
[%]
110
A
B
C
D
E
015 10 5 -5 -10 -15Outside temperature [°C]
109106
96
90
84
Sta
ndar
d ef
ficie
ncy
[%]
This results in the average boilerload over a period of twelve months,being less than 30% of rated output.Fig. 8 shows a comparison of part-load levels, particularly for lowaverage loads.
Advantages of condensingtechnology
The advantages offered bycondensing technology areparticularly obvious at low loadlevels: boilers operating at a constant temperature suffersubstantial losses with reducing load levels, since the boilertemperature must be maintained at a high level, even if the heatingsystem temperature only demands a low output. One result is asubstantially higher proportion ofradiation loss as part of the overallenergy requirement, hence reducedefficiency.
Condensing boilers, on the otherhand, provide an especially highlevel of efficiency at low load levels,because the condensing effect isparticularly successful due to the lowtemperature of the heating water.
Fig. 9 demonstrates a comparison ofthe efficiency levels for various typesof boiler.
9
3 Condensing technology in existingbuildings
Fig. 10: Flow/return temperature, subject to outside temperature, condensing gain
20 15 10 5 0 –5 –10 –1520
30
40
50
60
70
Hea
ting
sys
tem
tem
pera
ture
[° C
]
Outside temperature [° C]
Dew point(natural gas approx. 57 °C)
Theoretical condensing range for gas (heating system 75/60 °C)80
90
75°C
60°C
(–11,5°C)
Dew point (fuel oil approx. 47 °C)
Theoretical condensing range for fuel oil (heating system 75/60 °C)
Fig. 11: Vitocrossal 300 gas fired condensingboiler with Inox-Crossal heating surfaces andMatriX-compact gas burner, up to 66 kW
Condensation energy can be utilisednot only with reduced load levels, i.e.low heating system temperatures.Even with heating systems designedfor 75/60 °C, the actual temperaturein the return falls below the dewpoint when operating at load levelsin excess of 90% or outsidetemperatures as low as -11.5 °C, so that hot gas water vapour cancondense. This enables the system tofunction inside the condensing rangefor more than 90% of its operation,even with a high design temperatureof 75/60 °C as shown in Fig.10. Evenbetter are the conditions for lowtemperature heating systems such asunderfloor heating (40/30 °C), where condensingoperation is achieved all the yearround.
Oversized older systems allow areduction in temperature
Experience shows that olderbuildings are frequently equippedwith oversized radiators. Thisoversizing is partly due to an over-generous design during initialinstallation and also to subsequentthermal insulation measures:retrofitted doubled glazed windows,cladding and roof insulationsubstantially reduce the heatingdemand, whilst the original radiatorsize remains unchanged. Thisenables the flow and returntemperatures to be significantlyreduced from their original design(e.g. 90/70 °C).
How much a system, originallydesigned for 90/70 °C, needs to bereduced or exactly how oversized itis, can be estimated in situ: for this, a simple test is carried out andassessed using Fig. 12.
10
Condensing technology in existingbuildings
Fig. 12: Calculating the oversizing of the heating surfaces (system 90/70 °C)
5-15
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.9
1.0
Condensationlimit
Heatingwater flowtemperature
Averageheating watertemperature
Heating water returntemperatureQ/QN
0.8
1.0
1.1
1.21.31.41.51.61.71.82.02.5
3.0
4.0
-10
-12.5
-5 0 10 15 20 30 40 50 60 70 80 90
Heating water temperature [°C]Outside temperature [°C]
Ove
rsiz
ing
fact
or
1
3
2
4
Boilerload level
6
7 5
In winter, and at cold outsidetemperatures, open all radiatorvalves in the evening and read offthe flow and return temperatures thefollowing afternoon. Preconditionsare that the boiler and mixer are setso that room temperatures reach thedesired range (20 to 23 °C) when theradiator valves are fully opened.
The average value, comprising theflow and return temperatures (mean heating water temperature,e.g. (54 + 46) / 2 = 50 °C) is the inputsize (1) for the diagram. At the sametime, the current outsidetemperature should be known (in this example: 0 °C) (2).
Bringing the vertical of (1) with thecurve of the average heating water
temperature to the intersectionresults in (3). Proceeding horizontallyfrom (3) to the intersection with thevertical of (2), the so-calledoversizing factor (6) results at theintersection with the outsidetemperature (4) (in this example 1.4).In other words, the heating surfacesare 40% oversized. This means thatwith the lowest expected outsidetemperature (e.g. -15 °C), the averageheating water temperature would nothave to be 80 °C, as intended, butonly 65 °C.
The condensation limit for hot gasescreated by the combustion of naturalgas is approx. 57 °C (5). The returntemperature must fall below thisvalue to achieve partial condensation
of the hot gases and thereby toachieve the condensing benefit.
In the example shown, whichindicates oversizing by a factor of 1.4 (6), the actual temperature fallsbelow this return temperature atoutside temperatures as low as -12.5 °C (7).
The utilisation of condensingtechnology in the illustrated examplewill not be fully achieved/notachieved at all only on days wherethe outside temperature falls below -12.5 °C. However, on such days, acondensing boiler will still be moreefficient than a low temperatureboiler because of its substantiallylower flue gas temperatures.
11
4 Significant variables and criteria foroptimum gain
Fig. 13: Boiler design features
Fig. 14: pH value of different substances
Return
Return
Flueoutlet
Flow
FlowReturn
Low temperature boiler Condensing boiler
0 1 2 3 4 5 6 7 8 9 10 11 12
0 1 2 3 4 5 6 7 8 9 10 11 12
Condensate fromcondensing boilers
Oil (EL) Gas
Domesticwaste water
alkalineacidicpH value
Battery acidStomach acid
Domesticvinegar
Lemon juice
Cleanrain water
Sea waterRain water Distilled
water(neutral)
Tap water
Ammonia
For some years now, stainless steelhas proved to be the ideal materialfor this purpose. For fuel oil andnatural gas, different stainless steelalloys are available (alloyingelements are, amongst others,chromium, nickel, molybdenum,titanium), which have been matchedto the characteristics of condensate.This enables these materials towithstand the corrosive attack ofcondensate without furthertreatment.
Carbon dioxide can form from theCO2 created during combustion, andthe nitrogen N2 contained within theair reacts to become nitric acid.Using standard fuel oil forcombustion can create particularlyaggressive condensate, as thesulphur content of fuel oil createssulphurous and sulphuric acid.Therefore, all heat exchangersurfaces which come into contactwith condensate must be made frommaterials which remain unaffectedby the chemical attack of thecondensate constituents.
4.1 Boiler design
Utilisation of condensing technologyimproves with increasingcondensation of the hot gas watervapour. Only this enables the latentenergy in hot gas to be convertedinto useable heating energy.Conventional boiler designs areunsuitable for this task, see Fig.13.
Flow paths
In conventional low temperatureboilers, the heating surfaces aredesigned to prevent condensation of hot gases inside the boiler.Condensing boiler design is quitedifferent: the Inox-Crossal heatingsurface was designed so that hotgases and condensate flow in thesame direction, i.e. down. Thiscreates a permanent self-cleaningeffect, which also preventscondensate concentrations.
Hot gas and heating water inside theheat exchanger should flow in acountercurrent pattern to utilise thelow temperature of the return waterinflux, in order to provide maximumcooling of the outflowing hot gases.At the same time, modulatingburners with suitably intelligentcontrols should be utilised, to enableautomatic matching of the output tothe current heating demand.
Material and fuel
The selection of suitable materialsshould ensure that the condensatecreated will not cause the boiler tosuffer corrosion damage. Duringcombustion, constituents of the fuel(fuel oil or natural gas) and of thecombustion air create compoundswhich shift the pH value (degrees ofalkalinity or acidity) of thecondensate up to acid levels (Fig. 14).
12
Significant variables and criteria foroptimum gain
Core flow
Range where condensate iscreated
ϑ Dew
Hot gas Hot gas
Wide, smoothhot gas cross-section
Condensation heating surfacesuitable for condensing technology
Fig. 15: Physical requirements for hot gas flues with a larger cross-section – Inox-Crossal heatingsurface
Fig. 16: Hot gas and condensate flow
Boi
ler
wat
er
Hot gas
Con
dens
ate
Hot gas paths
The use of stainless steel allows foran optimum geometric design of the heat exchanger surfaces.To transfer the hot gas energyefficiently to the heating water, it isessential that hot gases are inintensive contact with the heatingsurface. To achieve this, two optionsare generally available:
The heating surfaces may bedesigned so that the hot gas isconstantly swirled, avoiding theformation of core flows with highertemperatures (Fig. 15). Smooth pipes are unsuitable for thispurpose; instead deviations andchanges in the cross-section must be created (Inox-Crossal heatingsurface).
An alternative to the intensivelyswirling hot gas flow achieved by theInox-Crossal heating surface, is thelaminar heat transfer method (Inox-Radial heating surface).
Inox-Crossal heating surface
Fig. 16 shows the Inox-Crossalheating surface, which offersexcellent heat transfer properties.Deviations are achieved throughopposing pressings. The changingcross-sections created by theconstrictions reliably prevent thecreation of core flows.
To prevent concentration ofcondensate and its return into thecombustion chamber, hot gas andcondensate should flow in the samedirection, i.e. down. This allowscondensate droplets to flowdownward, supported by gravity andfollowing hot gases. Therefore, thehot gas exit of heat exchangers isgenerally arranged at the bottom.
13
Significant variables and criteria foroptimum gain
Constant gap width = 0.8 mm
Gap
hei
ght
= 36
mm
Hot gases900 °C
Flue gas40 °C
Fig. 17: Inox-Radial heating surface Fig. 18: Inox-Radial heating surface
Fig. 19: Laminar heat transfer of the Inox-Radial heating surfaces: individual windings are 0.8 mmapart
Inox-Radial heating surface
The Inox-Radial heating surface (Fig. 17 & 18) was developed toachieve this laminar heat transferprinciple; it comprises a stainlesssteel, spiral-shaped, rectangularhollow section. Special pressingscreate individual windings precisely0.8 mm apart. These centres, whichare matched to the special flowcharacteristics of hot gases, ensurethat a laminar flow without aboundary layer is created inside thegap, which provides an excellentheat transfer. Over a gap length ofonly 36 mm, the hot gases can becooled down from 900 °C (Fig. 19).
Under the most favourableconditions, the hot gas will reach atemperature level at the boiler outlet,which is only 3.5 K above the boilerwater return temperature.
14
Significant variables and criteria foroptimum gain
Basically a distinction is drawnbetween two types of oil firedcondensing systems (Table 3):
– Condensation on an integral boilerheat exchanger or on one installeddownstream and heat transfer to theheating water
or
– Condensation inside the flue gassystem and transfer of the energy tothe ventilation air (preheating the airsupply).
Integral boiler Downstream Neutralisingheat exchanger heat exchanger system
Standard fuel oil Problematic Permissible Compulsory(≤ 2000 ppm) high deposit levels moderate deposit levels
Sulphur Permissible, Permissible, Compulsoryreduced moderate low deposit levelsfuel oil deposit levels(≤ 500 ppm)
Low Permissible, Permissible, Notsulphur low deposits levels no deposits requiredfuel oil(≤ 50 ppm)
Table 3: Framework conditions for condensing boilers with integral or downstream heat exchanger
4.2 Utilising oil fired condensingtechnology
Fuel oil, itself, has been the mainobstacle for an early deployment ofoil fired condensing systems in thepast. According to DIN 51603-1,standard fuel oil EL can contain up to2000 ppm sulphur, i.e. 2000 mg/kg.At such levels, combustion createssubstantial quantities of sulphuroxide (SO2 and SO3). These formsubstantial quantities of sulphurousand sulphuric acid when the watervapour contained in hot gascondenses on the heating surface ofthe condensing boiler.
Now that fuel oil EL with a sulphurcontent of 50 ppm, which equates to50 mg/kg, is generally available inGermany, the way is finally clear foroil fired condensing technology. TheDIN committee on ”Mineral oil andfuel standardisation” has settled onthis new fuel oil quality and adoptedit into DIN 51603-1. It was alsoimportant to ensure that this newfuel oil quality was adopted into thethird ordinance regarding theimplementation of the FederalImmissions Act (3rd BImSchV). Thisstipulates that fuel oil EL may only bedescribed as ”low sulphur”, if itcontains less than 50 ppm sulphur. In addition to standard fuel oil ELwith a sulphur content of up to 2000ppm and low sulphur oil, both ofwhich are still available, ”sulphur-reduced” fuel oil with up to 500 ppmsulphur is also available.
Heat exchanger inside the boiler orinstalled downstream
Oil fired condensing boilers aredesigned, so that the condensationenergy is transferred directly to theheating water, either inside the boileror inside a heat exchanger installeddownstream of the boiler.
In systems only equipped with oneheat exchanger, condensation energyis gained immediately inside theboiler. Such boilers correspond tothe gas fired condensing boilers,which have been established formany years.
As an alternative, a separate heatexchanger for the utilisation ofcondensing technology, can also beinstalled downstream of the boiler. In such cases, the condensing boilercomprises of two heat exchangers:Inside the combustion chamber, thehot gas is cooled down by the firstheat exchanger to temperaturesabove the dew point. The cooled hotgas then flows through a secondheat exchanger, which is designed to condensate the hot gas. Both heatexchangers are connected to theheating circuit.
15
Significant variables and criteria foroptimum gain
Fig. 20: Vitolaplus 300 oil fired Unit condensing boiler and Vitoplus 300 oil fired wall mountedcondensing boiler
Preheating the air supply
This version of utilising oil firedcondensing technology is based onthe principle that condensationenergy is not transferred directly tothe heating water, but is used forheating the air supply. For this, heatexchanger and waterways inside theboiler are designed so, that theformation of condensate isprevented.
For that reason, flue gases enteringthe flue gas system are still at atemperature of approx. 100 °C. Forsystems like these, the flue gas/airsupply system is designed as coaxialsystem, enabling the flue gas
streaming downward to transfer itsenergy in a countercurrent to theinrushing air supply. The flue gascondensates, if the actualtemperature drops below the dewpoint, making it possible to alsotransfer latent heat to the ventilationair and thereby achieve the grosscalorific value.
The extent of achieving the grosscalorific value with these systems isnot only subject to the boiler, butalso to the framework conditions ofthe flue gas/air supply system. Itwould therefore be appropriate torefer to condensing systems insteadof condensing boilers.
Heat exchangers inside the boiler,where condensation takes place, aresubject not only to high flametemperatures but also to theunavoidable deposits which stemfrom the sulphur content of fuel oil.For this it is essential to design theheat exchanger for condensing, i.e.to use corrosion-resistant materials,such as stainless steel.
To reduce deposits, low sulphur (< 50 ppm) or sulphur-reduced (< 500 ppm) fuel oil EL should beused. This ensures a long service life,energetic quality and high efficiency,even if systems are cleaned onlyonce a year. Also, in accordance withthe new ATV Code of Practice[Germany], there is no longer anycompulsion to employ a neutralisingsystem when burning low sulphurfuel oil EL (< 50 ppm).
With downstream condensation heatexchangers, standard fuel oil canalso be used (up to 2000 ppm), ascombustion and condensation takeplace in physically separatelocations. The resulting combustionresidues, which also contain sulphurreaction products, are mainlydeposited on the heat exchangersurfaces inside the combustionchamber. However, the matchedtemperature control inside the boilerprevents any condensation formingthere. A practically deposit-freecondensation process only takesplace in the downstream heatexchanger.
It should be remembered, though,that condensate must be neutralisedwhen using standard or sulphur-reduced fuel oil EL. This obligation isonly waived for low sulphur fuel oil.
16
Significant variables and criteria foroptimum gain
Fig. 21: Oil fired wall mounted condensing boiler Vitoplus 300
Fig. 22: Vitoplus 300 with Vitocell-W 100 Fig. 23: Adjustable Inox-Radial spiral heatexchanger
Wall mounted oil fired condensingtechnology:Vitoplus 300
The Vitoplus 300 oil fired wallmounted condensing boiler (Fig. 21)is equipped with a stainless steelInox-Radial heating surface designedspecifically with oil fired condensingtechnology in mind. Together with theuse of low sulphur fuel oil, thisspecial material (1.4539) ensuresreliable operation and a long servicelife.
Vitoplus 300 (Fig. 22) is based on thesame modular design as the range ofVitotec gas fired wall mountedboilers.
The two stage Compact blue flameburner is characterised by its cleancombustion and its reliable,environmentally responsibleoperation. When using low sulphurfuel oil, the flue gas sulphur contentis comparable with that created bynatural gas. This makes neutralisingunnecessary.
Its practical usefulness is furtherenhanced by the ease with which itcan be cleaned. The adjustable spiralof the Inox-Radial heating surfacemakes annual maintenance very easy– indeed it can be relaxed to providean 8 mm cleaning gap –. This enablesunavoidable combustion residuesproduced by fuel oil to be quickly and thoroughly removed. (Fig. 23).
17
Significant variables and criteria foroptimum gain
Fig. 24: Oil fired Unit condensing boiler Vitolaplus 300
Fig. 26: Downstream Inox-Radial heat exchangerFig. 25: Vitoflame 300 in maintenance position
Freestanding oil fired condensingboiler:Vitolaplus 300
Vitolaplus 300 (Fig. 24) is afreestanding oil fired condensingboiler with an attractive cost:benefitratio. Apart from a high degree ofoperational reliability, particularly itscompact design offers benefits, asVitolaplus 300 can be installed evenin the tightest of spaces. For theoutput range 19.4 to 29.2 kW,Vitolaplus 300 therefore offers anideal solution for utilising oil firedcondensing technology inmodernisation projects.
Three components in the Vitolaplus300 oil fired Unit condensing boilerlead to our goal: The proven Vitola200 with its biferral heating surface,together with the new cleancombustion Vitoflame 300 blue flameburner (Fig. 25) and the downstreamInox-Radial heat exchanger result inthis reliable, economical andenvironmentally responsible oil firedUnit condensing boiler.
Vitolaplus 300 is particularly suitablefor modernising heating systems, asthe wide water galleries inside theheat exchangers are less sensitive tocontamination and sludge from olderheating systems. The combination of the proven biferral compositeheating surface inside thecombustion chamber and thecorrosion-resistant Inox-Radial heatexchanger in the condensation stageensures high levels of reliability anda long service life (Fig. 26).
Vitolaplus 300 can be operated withall commercially available types offuel oil. According to the [German]ATV-DVWK Code of Practice A 251, a neutralising system is superfluouswhen using low sulphur fuel oil (upto 50 ppm).
18
Significant variables and criteria foroptimum gain
Fig. 27: Vitoplex 300 with downstream Vitotrans 333 flue gas/water heat exchanger
Fig. 28: Vitotrans 333 with Inox-Crossal heatingsurfaces for boilers from 80 to 500 kW
Vitotrans 333 flue gas/water heatexchanger for condensing boilers upto 6600 kW
The Vitotrans 333 flue gas/water heatexchanger installed downstream ofthe boiler ensures, that condensingtechnology can also be used inmedium and large boilers. Their useleads to a substantial reduction inoperating costs (Fig. 27).
By installing a downstream Vitotrans333 flue gas/water heat exchangerwhen using natural gas, the standardefficiency can increase by up to 12%, and when using fuel oil by upto 7%.
Vitotrans 333 is available in twoversions for different output ranges.Up to 1750 kW, it is equipped withthe Inox-Crossal heating surfaces(Fig. 28), and from 1860 to 6600 kW itis equipped with the Inox-Tubal heatexchanger pipes.
Both flue gas/water heat exchangersare highly efficient and are madefrom stainless steel. This prevents therisk of corrosion through acidiccondensate. The countercurrentprinciple of flowing boiler water andhot gases in opposite directionscreates a particularly highcondensation rate. The vertical layoutsupports the self-cleaning effect: anycondensate can drain off freelydownward. In doing so, it flushes theheating surfaces and keeps themclean.
19
Significant variables and criteria foroptimum gain
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15
25
30
35
40
45
50
55
60
CO2 content [vol. %]
Wat
er v
apou
r de
w p
oint
tem
pera
ture
[°C
]
Natural gas (95% CH4)
Fuel oil EL
16
Fig. 29: Water vapour dew point subject to CO2content
Fig. 30: Modulating, pressure-jet MatriX-compact gas burner up to 66.0 kW
Fig. 31: MatriX radiant burner, rated output: 87 and 187 kW
4.3 CO2 content, burner design
For the efficient utilisation ofcondensing technology it isimportant, that combustion takesplace with a low level of excess air or a high CO2 content, since thisinfluences the water vapour dewpoint (Fig. 29).
The water vapour dew point shouldbe kept as high as possible, to allowcondensation to be achieved even inheating systems with high returntemperatures. Therefore, a high CO2content – in other words little excessair – in hot gas is desirable. Theactual CO2 content achieved dependsprimarily on the burner design.
For this reason, atmospheric burnersshould not be used, as these – due to their high level of excess air – tend to operate with low CO2 values, which lead to low hot gas dew point temperatures. At flue gastemperatures of 50 °C or below, thethermal flue gas current is generallyinsufficient to ensure the function ofthe chimney or flue gas system bynatural draught. In this context it isimportant that fans for modulatingboilers are speed-controlled toenable the air volume to be matchedto the gas volume flow. Only thisway can the high CO2 content beensured in modulating operation,too.
For wall mounted gas firedcondensing boilers, the powerconsumption of such fans amountsto approx. 50 kWh/p.a., leading toannual running costs of approx. € 6.
20
Significant variables and criteria foroptimum gain
Return temperatureraising facility
Three-waymixer
No return temperature raising
Correct
Four-waymixer
Incorrect
M M
Fig. 32: Hydraulic requirements for condensing technology
Radiator valvesTwo-way version
Correct
Radiator valvesThree-way version
Incorrect
MM
Fig. 33: Hydraulic requirements for condensing technology
loss header. This avoids raising thereturn temperature.
The capacity of boiler circuit orheating circuit pumps must beselected, so that the higher volumeflow is circulated in the heatingcircuit, to reliably prevent a mixing ofwarm flow water with the return. Theflow temperature sensor must beinstalled downstream of the low loss
header, to record the temperature,which is relevant to the system, afterthe colder return water has beenmixed into the flow.Careful design and adjustment arerequired, if the use of a low lossheader cannot be avoided to achievethe best possible condensing effect.
4.4 Water connections
The design of the hydraulic systemmust ensure, that returntemperatures significantly below the hot gas dew point are achieved,to ensure that the hot gas willcondense.
One essential measure to achievethis is to avoid raising the returntemperature by direct connectionwith the flow. For that reason,hydraulic systems using a four-waymixer should be avoided incondensing boiler systems. Instead,three-way mixers could be used.These channel the return water fromthe heating circuits directly to thecondensing boiler, i.e. withoutraising the temperature (Fig. 32).
Also, thermostatic three-way valvesshould be avoided, since they causethe flow and return to be directlyconnected and will therefore raisethe return temperature (Fig. 33).
Modulating circulation pumpsautomatically match their capacity tothe system requirements, and thusprevent any unnecessary raising ofthe return temperature. This supportsthe utilisation of condensingtechnology.
Low loss header
In some cases, a distributor withoutdifferential pressure or a low lossheader cannot be avoided (Fig. 34).Previously, low loss headers wereused to ensure the presence of aminimum circulation volume insidethe boiler. Modern condensingboilers no longer require this.
However, it may be the case that themaximum permissible boiler flowrate is less than the circulatingvolume inside the heating circuit, e.g.in underfloor heating systems. Herethe higher heating circuit volumeflow should be balanced with theboiler circuit volume flow via a low
21
Significant variables and criteria foroptimum gain
Key
Vprimary heating water volume boiler circuit
Vsecondary heating water volume heating circuit
ϑ1 Flow temperature boiler circuit
ϑ2 Return temperature boiler circuit
ϑ3 Flow temperature heating circuitϑ4 Return temperature heating circuit
Qprimary Heat volume supplied by the boilerQsecondary Heat volume dissipated by the
heating circuit
Vprimary < Vsecondaryϑ1 > ϑ3ϑ2 ≈ ϑ4
Qprimary = Qsecondary
ϑ1 ϑ3
ϑ2ϑ4
VsecondaryVprimary
Fig. 34: Low loss header function
·
·
··
· ·
· ·
Rules for designing with wallmounted boilers:
– A low loss header is generally required for cascades of several boilers.
– When balancing the low loss header, the volume flow on the boiler side should be adjusted approx. 10 to 30% lower than the volume flow on the system side (lower return temperature).
– The low loss header should be sized for the max. volume flowwhich may occur in the overall system.
Connection of DHW cylinders
Any DHW cylinder, which may beintegrated into the system, should beconnected upstream of the low lossheader, since that is where thehighest system temperatures occurthus enabling a reduction of theloading time. Connection downstream of the lowloss header would, if no mixer wasinstalled, also lead to theunregulated heating of the heatingcircuits.
The achievable gross calorific valueis also influenced by the sizing of thepump capacity or spread. Fig. 35illustrates this influence: halving, inan existing system (Q = const.), thecapacity (V) increases the spread(Δϑ). However, the average radiatortemperature will initially drop.
V = Q / Δϑ
If the flow is raised so that, whenheat is transferred to the room, theoriginal temperature conditions arereinstated, the spread doubles if theaverage temperature is identical; thereturn temperature dropscorrespondingly. This significantlyimproves the condensing effect.In reverse it follows that highcapacities reduce the spread and cantherefore potentially reduce thecondensing effect (Fig. 36).
M
Fig. 35: Hydraulic requirements for condensingtechnology
Capacity100 %
ϑin = 50 °C
ϑout = 40 °C
ϑave. = 45 °CRL
VL
40 °C
Capacity50 %
ϑin = 55 °C
ϑout = 35 °C
ϑave. = 45 °CRL
VL
35 °C
50 °C
55 °C
Fig. 36: Influence of sizing on capacity (spread)
·
· ·
22
5 Condensate treatment
Fig. 37: Condensate
20
40
60
80
20
40
60
0 0.2 0.4 0.6 0.8
80
1
100
Hea
ting
wat
er t
emp.
ϑV/ϑ
R [˚
C]
Flue
gas
tem
pera
ture
ϑA [˚
C]
Load ϕ
0
ϑV
ϑR
0 0.2 0.4 0.6 0.8 1
0
0.2
0.4
0.6
0.8
1
Con
dens
ate
valu
e α
Load ϕ
α modulating burner
ϑA modulating
ϑV
ϑR
α modulating burner
ϑA modulating
Heating system 75/60 ˚C Heating system 40/30 ˚C
Rated Neutralisation for combustion Limitationsoutput systems is required for
Gas Fuel oil to Fuel oil Neutralisation isDIN 51603-1 DIN 51603-1 still requiredlow sulphur 1) when draining domestic
waste water into smallsewerage treatment plants2) for buildings, thedrainage pipes of whichare not resistant to acidiccondensate (e.g. galvanised or other material containing copper).3) if required mixing ratio isnot achieved.
Up to 25 kW no1), 2) yes no1), 2)
25 to 200 kW no1), 2), 3) yes no1), 2), 3)
> 200 kW yes yes yes
According to ATV-DVWK-A 251 Codeof Practice, these materials include:– Vitrified clay– Hard PVC pipes– PVC pipes– PE HD pipes– PP pipes– ABS/ASA pipes– Corrosion-resistant steel pipes– Borosilicate pipes.
Materials for condensate lines
Select special materials if one pipe isused exclusively for condensate fromthe point of insertion to a collectionarea, and condensate is neverdiluted, not even occasionally.
Table 4: Compulsory neutralisation subject to boiler output (source: ATV-DVWK)
Condensate created in the boiler and in the flue pipe during heatingmust be discharged. With a gasconsumption of 3000 m3/p.a. for theaverage detached home, approx.3000 to 3500 l/p.a. of condensatemay be created (Fig. 37).
Subject to the return temperature, a certain flue gas temperature ϑAresults, which in turn influences thecondensate value α. α becomes 1, if the total theoretical condensatevolume (Table 1) is created (completecondensation). As the pH value hasbeen shifted towards ”acidic”, and thecondensate may contain substances,the Abwassertechnische Vereinigung[Germany] has published their Codeof Practice ATV-DVWK-A 251, onwhich the waste water regulations ofmost water authorities [in Germany]are based.
Direct introduction of condensateinto the sewer system
For gas fired condensing boilersbelow 25 kW, condensate may bedirectly drained into the public sewer(table 4). The proportion ofcondensate of the total waste wateris so small, that domestic wastewater provides sufficient dilution. Thesame applies to oil fired condensingboilers which are operatedexclusively with low sulphur fuel oil.Even with a higher rated output up to200 kW, condensate from gas/oilfired condensing boilers may besafely drained into the public sewer(condition: use of low sulphur fueloil) without prior neutralisation,provided the framework conditionsaccording to table 5 are being met.These conditions have beendetermined, so that condensate isdiluted with ordinary waste water ina ratio of 1:20.
Permits in connection with drainingcondensate from all condensingboilers are obtainable from the lowerwater authority [in Germany], whichmakes decisions based on localcircumstances.
23
Condensate treatment
Fig. 40: Neutralising system for oil firedcondensing boilers (compulsory for standardfuel oil)
Key:A Inlet (DN 20)B Outlet (DN 20)C Active charcoal filterD Coloured indicatorE Neutralising granulate
Table 4: Conditions for introducing condensate into the sewer system for condensing boilers inaccordance with ATV-DVWK-A 251
Fig. 38: Granulate neutralisation for condensatevolumes from gas fired combustion equipmentup to 70 l/h, which equals approx. 500 kWoutput
Fig. 39: Granulate neutralisation withcondensate lifting pump – applicable forcondensate volumes up to 210 l/h, whichequals approx.1500 kW output
Combustion output [kW] 25 50 100 150 <200
Domestic Maximum annualhouses condensate volume
for natural gas [m3/p.a.] 7 14 28 42 56for low sulphurfuel oil EL [m3/p.a.] 4 8 16 24 32
Minimum number ofapartments 1 2 4 6 8
Commercial Maximum annual buildings condensate volume 6 12 24 36 48
for natural gas [m3/p.a.]for low sulphurfuel oil EL [m3/p.a.] 3.4 6.8 13.6 22.4 27.2
Minimum number ofemployees (office) 10 20 40 60 80
Condensate drains running to thepublic sewer should be equippedwith an inspection port and a stenchtrap.
Use of neutralising systems
The pH value of the condensate willbe shifted towards ”neutral” if aneutralising system is prescribed.For this, the condensate is routedthrough the neutralising system (Fig. 38 & 39). This essentiallycomprises a tank filled withgranulate. Some of the granulate(magnesium hydroxide) dissolves in the condensate, reacts primarilywith the carbon dioxide whilstforming a salt, and so shifts the pH value to between 6.5 and 9.
It is important that this system isalways operated on a continuousbasis to prevent too much granulatebeing dissolved in idle periods. Thetank volume should be matched tothe expected condensate volume,and should be sized so that onefilling is sufficient for at least oneheating season. However, occasionalchecks should be made within thefirst few months after installation.The system should also be servicedannually.
In future, oil fired condensingboilers, which are not exclusivelyoperated with low sulphur fuel oil (≤ 50 ppm), must still be equippedwith a neutralising system. Thiscomprises a decantation chamberupstream of the neutralisation tank,as well as a charcoal filter to bind oilderivates. The granulate filling forraising the pH value consists ofmagnesium hydroxide (Fig. 40).
24
6 Emissions and flue gas system
Prior to work on the flue gas system,the heating contractor should conferwith the responsible flue gasinspector [where applicable].
Basically, a differentiation is drawndepending on whether thecondensing boiler is to be installed– inside the living space (where
people congregate) or– outside the living space (boiler
room).
Installation inside the living space isonly permitted up to 50 kW. Thesystem may also be installed insidethe living space if the flue pipe,inside the area where peoplecongregate, is run inside a protectivepipe and is surrounded by air (fan-assisted system, balanced flueoperation). Using a connector, whichprovides secondary ventilation up tothe duct (operation withinterconnected room air supply), acondensing boiler may, inexceptional cases, also be installedinside the living space, when it isoperated as open flue system.
Outside the living space, the fluepipe may also be installed inside theboiler room without secondaryventilation. In that case, however, theboiler room would require anadequately sized ventilation apertureto the outside (acc. to TGI ’86/96).Rated output up to 50 kW:150 cm2 or 2 x 75 cm2
Rated output above 50 kW(e.g.Vitodens 300, 66.0 kW or multi-boiler systems):150 cm2 and an additional 2 cm2 foreach kW output above 50 kW.
If an open-flue boiler (boiler type B)is selected, the combustion air willbe drawn from the room where theboiler is installed. Special measuresneed to be taken so that the livingspace can make adequate volumesof air available for combustionwithout sacrificing the ambientclimate (interconnected room airsupply). The flue pipe should becoaxial until it enters the duct, thusthe combustion air supply is effectedvia the outer pipe casing. Anyescaping flue gas is, therefore,directly piped back to the boiler (Fig. 42).Generally, the following conditionsapply:
Permissible:
– Gas fired boilers may be installedon the same floor
– Occupied rooms withinterconnected air supply
– Adjoining rooms withinterconnected air supply
– Adjoining rooms withinterconnected air supply (larders,basements, utility rooms, etc.)
Fig. 41: Emissions characteristics of Vitodens 300/333 and Vitocrossal 300 gas fired condensingboilers (type CU3 and CM3) compared to various regulations and designations
0
20
40
60
80
100
120
140
160
180
200
DIN 4702,pt 6
Swissvalues
Blue AngelRAL-UZ 61
Hamburgvalues
Vitodens 300/333Vitocrossal 300(type CU3 and CM3)
NOx
CO
Emis
sion
lim
its
in m
g/kW
h
6.1 Emissions
The particularly clean combustionachieved by modern MatriX radiantburners ensures that Viessmanncondensing boilers realisesubstantially better results than thelimits prescribed by all knownregulations (Fig. 41). In some casesemissions already fall belowtechnically verifiable levels.The extremely low emissionsachieved by the MatriX radiantburner are the result of the completepremixing of gas and air, as well asthe low combustion temperature,which results from the large semi-circular reaction surface.A high proportion of the releasedenergy is dissipated through infraredradiation from the reaction zone. Thissignificantly reduces NOx formation.Blue flame burners should be usedfor oil fired condensing boilers, sincethese offer particularly cleancombustion.
6.2 Flue gas system
The low flue gas temperature (< 85 °C) and the risk of residualhumidity condensing in the flue gassystem, make a conventionalchimney unsuitable for theinstallation of condensing boilers.The low flue gas temperature is notalways adequate to ensure a thermalcurrent within the flue gas system.Therefore, condensing boilers arefrequently equipped with a fan andare operated with positive pressure.Compared to conventional chimneys,these conditions lead to quitedifferent requirements:– During operation, there is no
requirement for resistance against soot combustion, etc.
– The chimney will be subjected to only minor temperature loads.
– The system may operate with positive or negative pressure.
– Corrosive condensate must beexpected.
These conditions can be met bysimple flue pipes which are madefrom plastic, stainless steel, ceramicsor glass.
25
Emissions and flue gas system
Fig. 42: Flue gas systems for Vitodens 200 and 300 for open flue operation
Open flue operation:
1 Coaxial pipe connection, combustion air supply with interconnected room supply2 Multiple connections to a moisture-resistant chimney3 Connection to a conventional chimney
3
1 2
2
Fig. 43: Flue gas systems for Vitodens 200 and 300 for balanced flue operation
Balanced flue operation:
4 Vertical roof terminal5 Outside wall terminal6 Sealed balanced flue
(multiple connections)7 Outside wall terminal8 Vertical roof terminal (flat roof)9 Existing sealed
balanced flue10 Horizontal roof terminal11 Separate air supply
and flue pipe
9
5
4
4
86
7
10
11
6
Pipes must be routed through a ductif the flue pipe passes throughseveral floors. This duct must beimplemented acc. to fire protectionclass F90; for low duct heights (< 7 m), F30 will be sufficient.
The boiler room must be providedwith a condensate drain as well asthe safety valve blow-off line.
Electrical interlocks for extract fans(extractor hoods, etc.) are notrequired for balanced flue operation.
– Adjoining rooms with outside wallapertures (ventilation air/exhaustair 150 cm2 or 2 x 75 cm2 each atthe top or bottom of the same wallup to QN ≤ 50 kW)
– Attic rooms, but only withadequate minimum chimneyheight, (acc. to DIN 18160 – 4 mabove inlet).
Not permissible:
– Stairwells and common hallways.Exception: detached houses andtwo-family homes of low height(top edge of the floor in the topfloor < 7 m above ground level)
– Bathrooms and toilets withoutoutside windows with ductventilation
– Rooms in which explosive or flammable materials are stored
– Rooms ventilated mechanically orvia individual duct systems to DIN18117-1.
Balanced flue boilers (boiler type C)draw combustion air from outsidethe building shell. For this purpose,either the available cross-section ofthe duct will be used, inside of whichthe flue pipe is installed, or a coaxialpipe, through the inside of which theflue gas flow is exhausted, whilstcombustion air is drawn in throughthe outer pipe casing. In either case,the flue pipe installed inside theboiler room (flue connector) issurrounded by an outer casing,inside of which the flue pipe issurrounded by secondary ventilation(Fig. 43).
In principle it is possible to connectseveral condensing boilers to oneflue pipe.
Options are, for example, installationin residential or living rooms, in non-ventilated adjoining rooms, insidecupboards and niches withoutclearance to combustible materials,as well as in attic rooms (pitched atticand long pane of the roof) with directoutlet of the flue pipe/ventilationpipe through the roof.
26
7 Selection guide
Fig. 45: Vitodens 333 – compact gas fired condensing boiler, 4.5 to 26.0 kW with integral loading cylinder (86 litres capacity)
Fig. 44: Vitodens 200 and 300 gas fired wall mounted condensing boilers from 4.5 to 66.0 kW;Vitodens 300 may also be supplied as cascade system up to 264 kW
Vitodens 300
Vitodens 300 (Fig. 44) offers powerfulgas fired condensing technology,packed into a compact attractivedesign. This represents high centralheating and DHW convenience, andeasy to integrate into the livingspace. The top combination: themodulating MatriX-compact gasburner and the stainless steel Inox-Radial heating surface for reducedheating costs and environmentalresponsibility. The emissions fallsubstantially below the limits set forthe ”Blue Angel” certificate ofenvironmental excellence. Thevariable speed AC fan and heatingcircuit pump are also economical torun.
Control is made easy with theconvenient Vitotronic energymanagement system. Vitodens 300up to 66 kW as single boiler, and upto 264 kW as multi-boiler cascade,offers a cost-effective and space-saving solution for multi-occupancyblocks and public buildings too.
7.1 Gas fired wall mountedcondensing boilers
Viessmann offers the rightcondensing solution for everydemand. In detached houses, a wallmounted boiler with DHW cylinder orintegrated standby instantaneouswater heater may be used. Such aboiler may be operated as open flueor as balanced flue system. Suchsystems can be installed in the attic,in the living space or in a cellar.Alternatively, a freestanding gas firedcondensing boiler with separateDHW cylinder may be installed in thebasement. A decentralised or centralsolution may be selected for multi-occupancy houses.
Usually, wall mounted boilers arelocated in every apartment whereheat is generated on a decentralisedbasis. Domestic hot water is thenproduced in a cylinder, which may behung alongside the boiler, or whichmay be freestanding below oradjacent to the boiler. Alternatively, a plate-type heat exchanger may beintegrated inside the condensingboiler to act as instantaneous waterheater.
Vitodens 200
Vitodens 200 (Fig. 44) offers highquality condensing technology forcentral and DHW heating using Inox-Radial heat exchangers and offeringa sound cost:benefit ratio. Itscompact dimensions and timelessmodern design furthermore make ita perfect match for any modernliving space. The Inox-Radial heatingsurface is responsible for itsadvanced condensing technology.The modulating stainless steelcylinder burner handles energy withthe greatest economy. And it reducesemissions, which lie below the limitsset for the ”Blue Angel” certificate ofenvironmental excellence.
Vitodens 333
The compact boiler Vitodens 333combines the Vitodens 300condensing boiler with a high-output86 l DHW loading cylinder.Innovative heating technology withan Inox-Radial heating surface and aMatriX-compact burner plus a spaceefficient modular design ensure highDHW convenience, which isgenerally only available with DHWcylinders twice the size. Thedimensions of Vitodens 333 havebeen designed to match those ofstandard kitchen units and whitegoods, thereby enabling easy andharmonious integration into theliving space. A height of just under140 cm allows it to fit equally wellunder the eaves and in niches.
27
Selection guide
7.3 Oil fired Unit condensing boiler(freestanding)
Vitolaplus 300
Vitolaplus 300 (Fig.47) is afreestanding oil fired Unitcondensing boiler with an attractivecost:benefit ratio, high operationalreliability and compact dimensions. For the output range 19.4 to 29.2 kW,Vitolaplus 300 offers an idealsolution for utilising oil firedcondensing technology, particularlyin modernisation projects. Theparticular advantage offered byVitolaplus 300 is its two-stage heatrecovery and the combination ofproven biferral composite heatingsurface and the corrosion-resistantInox-Radial heat exchanger installeddownstream of the boiler.
This principle ensures thatcombustion and condensation occurin physically separate locations.Inevitable combustion residuesremain in the easily accessiblecombustion chamber, leaving thedownstream Inox-Radial heatexchanger to effect condensation in aspace which is practically free fromresidues.
Fig. 46: Vitoplus 300 oil fired wall mountedcondensing boiler with Inox-Radial heatingsurfaces and compact blue flame burner, 12.9 to 23.5 kW
Fig. 47: Vitolaplus 300 oil fired Unit condensingboiler with downstream stainless steel Inox-Radial heat exchanger, 19.4 to 29.2 kW
In addition, the Vitoflame 300 blueflame Unit burner ensures soot-free,clean and efficient combustion in anenvironmentally responsible manner.Consequently, Vitolaplus 300performs better than the limits set forthe ”Blue Angel” certificate ofenvironmental excellence.
Vitolaplus 300 can be operated withall commercially available EL fueloils. A neutralising system is notrequired when using low sulphurfuel oil.
7.2 Oil fired wall mountedcondensing boiler
Vitoplus 300
The Vitoplus 300 oil fired condensingboiler (Fig. 46) now brings thebenefits of condensing technology tooil fired boilers. As genuine oil firedwall mounted condensing boiler,Vitoplus 300 is as universally andflexibly useful as any gas fired wallmounted condensing boiler. Vitoplus300 is offered with two outputratings: 12.9/19.3 kW and 16.1/23.5 kW.This enables Vitoplus 300 to coverfurther applications, mainly for modernisation projects and inlarger buildings.
The two stage Compact blue flameburner is characterised by its cleancombustion and its reliable,environmentally responsibleoperation. When using low sulphurfuel oil, the sulphur content of thecondensate is comparable with thatproduced when using natural gas.This makes neutralisingunnecessary.
The following operating conditionsapply to the whole Vitoplus 300range:– Fuel oil with sulphur content up to
500 ppm can be used,– During the initial fill, optional
mixing of low sulphur (50 ppm)with standard fuel oil at a ratio of3:1,
– One service per year is sufficient.
Its practical usefulness is furtherenhanced by the ease with which itcan be cleaned. The adjustable spiralof the Inox-Radial heating surfacemakes annual maintenance veryeasy – indeed it can be relaxed toprovide an 8 mm cleaning gap –.This enables unavoidablecombustion residues produced byfuel oil to be quickly and thoroughlyremoved.
28
Selection guide
7.4 Gas fired condensing boiler (freestanding)
Vitocrossal 300
Vitocrossal 300 is a top productamongst freestanding gas firedcondensing boilers. From 9 to 978 kW, this range offers the rightsolution for any demand – fordetached homes and apartmentbuildings, as well as local heatingnetworks or public/commercialbuildings. Vitocrossal 300 wascombined with another milestone of Viessmann heating technology:the vertically arranged Inox-Crossalheating surface. The smoothstainless steel heating surface allows condensate to simply run off downward. Combined with thesmooth stainless steel surfaces, thiscreates a permanent self-cleaningeffect, ensuring the long-term, highutilisation of condensing technology,whilst reducing maintenancerequirements and extending itsservice life. The highly efficient heattransfer and the high condensationrate, enable this boiler to achieve astandard efficiency of up to 109%.This is the result of the countercurrentflow of hot gas and boiler water, aswell as the intensive turbulence ofthe hot gases through the heatingsurface.
Balanced flue operation is feasible up to 66 kW (Fig. 48). This enablesVitocrossal 300 to be installed in-side the thermally insulated buildingenvelope. This is especiallyadvantageous for the EnEV[Germany] calculation. The Inox-Crossal heating surface in Vitocrossal300 was combined with anothermilestone of Viessmann heatingtechnology, the MatriX burner up to142 kW. This reduces heating costsand ensures minimised emissionswithout compromise. These are solow that Vitocrossal 300 performssignificantly better than the limits set for the ”Blue Angel”certificate of environmentalexcellence. Two return connectors on Vitocrossal 300 (187 to 978 kW)(Fig. 49) enable the separateconnection of heating returns withlower temperatures. This improveshot gas condensation.
Fig. 49: Freestanding Vitocrossal 300 gas fired condensing boiler with Inox-Crossal heating surface,187 to 978 kW
Fig. 48: Freestanding Vitocrossal 300 gas fired condensing boiler with MatriX gas burner
29
Selection guide
7.5 Flue gas/water heat exchanger
Vitotrans 333
The Vitotec range of freestandingcondensing boilers is supplementedby the stainless steel Vitotrans 333flue gas/water heat exchanger, forsystems with 80 to 6600 kW output.Flue gas/water heat exchangers areinstalled downstream of the boiler,particularly in the higher outputranges, to utilise condensingtechnology (Fig. 50).
The flue gas temperature isdramatically reduced in the Vitotrans333 flue gas/water heat exchangers(Fig. 51) and reaches levels only 10 to 25 K higher than the heatingwater return temperature. This aloneraises the efficiency by approx. 5%. The further energy savings and thereal advantage of condensing fluegas heat exchangers lies in theutilisation of that energy, which isreleased when hot gases condenseon the cold heating surfaces. Subjectto the heating water temperatureinside the flue gas/water heatexchanger, the additional energy gainthrough condensation can reach 7%.
Installing a downstream Vitotrans333 flue gas/water heat exchangerwhen using natural gas can raise thestandard efficiency by up to 12%,and when using fuel oil by up to 7%.
Vitotrans 333 is available in twoversions for different output ranges.Up to 1750 kW, it is equipped withthe Inox-Crossal heating surfaces(Fig. 28), and from 1860 to 6600 kW itis equipped with the Inox-Tubal heatexchanger pipes.
Both flue gas/water heat exchangersare highly efficient and are madefrom stainless steel. This prevents therisk of corrosion through acidiccondensate. The countercurrentprinciple of flowing boiler water andhot gases in opposite directionscreates a particularly highcondensation rate. The vertical layoutsupports the self-cleaning effect: anycondensate can drain off freelydownward. In doing so, it flushes theheating surfaces and keeps themclean.
Fig. 50: Vitoplex 300 with downstream Vitotrans 333 flue gas/water heat exchanger for the utilisationof condensing technology with boilers from 80 to 6600 kW
Fig. 51: Vitotrans 333 flue gas/water heat exchangers with Inox-Crossal heating surfaces and Inox-Tubal heat exchanger pipes
Selection guide
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Combination boiler with Boiler withstandby instantaneous separatewater heater DHW cylinder
Hot water demand, DHW demand for an apartment/flat + +convenience DHW demand for a detached house 0 +
Central DHW demand for an apartment block – +Decentralised DHW demand for a multi-occupancy house + +
Utilising One draw-off point + 0several Multiple draw-off points, no simultaneous use + 0 / +connected Several draw-off points, simultaneous use – + draw-off points
Distance of the Up to 7 m (without DHW circulation line) + –draw-off point With DHW circulation line – +from the boiler
Modernisation Existing DHW cylinder – +Replacement of an existing combination boiler + – / 0
Space requirement Low space requirement (installation in a niche) + 0Sufficient space (boiler room) + +
+ = recommended0 = qualified recommendation– = not recommended
associated connection sets makeinstallation quick and easy.
Table 6 provides some assistance inselecting either a wall mountedcombination boiler (incl. standbyinstantaneous water heater) or aboiler with separate DHW cylinderwith special focus on DHW heating.
Condensing technology offersparticular advantages for buildingrenovation, as simple and cost-effective solutions can be found forthe flue gas side of the system.Extensive chimney work involvingbrickwork is not required; instead thesimple insertion of plastic flue pipesinto existing ducts will normallysuffice. Alternatively direct access tooutside air will be created throughsmall wall apertures.
7.6 Selection table for wall mountedcombination/conventional boilerswith focus on DHW heating
The operation of Viessmann wallmounted boilers is particularly user-friendly, both through uncomplicatedcontrols and convenient DHWloading, utilising the integral QuickDHW heating system. Plate heatexchangers provide hot water incombination boilers – withoutwasting unnecessary energy or waterconsumption.
The extensive Vitocell range ofcylinders covers higher waterdemands, i.e. from 80 to 300 litres.Whether DHW cylinders are installedas wall mounted devices, orbelow/adjacent to the boiler, theirshape or colour always matchesViessmann wall mounted boilers. The
Table 6: Selection table to assist in selectingeither a combination boiler with integral standbyinstantaneous water heater or a boiler withseparate DHW cylinder
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Fig. 52:The consistent application of Viessmann's modular design philosophy ensures that thechassis can be combined with various function modules to create different boiler versions. Thisenables the use of many standardised components and uniform, easy to learn installation steps.
7.7 Modular design from Viessmann
Installation, service and maintenanceare made easy by the platform-basedmodular design from Viessmann.This enables the coming together ofthe basic chassis and variousfunction modules to create individualboiler types.
This is genuine system design:saving you time and money
Every element of the Vitotec range isrigorously designed for soundfunction – that goes for the new wallmounted boilers, too. Modulardesign, with its clear structure anduniformity, creates the basis for highefficiency – from initial design to finaloperation. Different boiler versionscan be assembled from a total of fourenergy cells, three aqua plates andtwo types of control unit. This createsa comprehensive product range witha high degree of componentuniformity (Fig. 52).
Less means more:harmonisation of components
Viessmann continues to harmonisethe components utilised in differentboiler versions. Identical elementsare used everywhere. The few typesof different boilers can bring manybenefits:
■ Time savings through uniforminstallation steps
■ Quicker and more economicalcommissioning
■ Easy service, simplifiedmaintenance
■ Fewer spare parts■ Modular design means fewer
sources for potential faults andless training required.
Viessmann offersyou a diverserange of products,which are uniformin quality andadaptable enoughto be able to meetany demand andany requirement
Wall mounted oil and gas firedcondensing boilers
The Viessmann Group
The Viessmann Group employsapproximately 6800 staff worldwide andis one of the foremost manufacturers ofheating equipment. For freestandingboilers, Viessmann is the mostsuccessful brand in Europe. TheViessmann brand stands for competenceand innovation. The Viessmann Groupoffers a comprehensive range of top-quality, high-tech products, along withperfectly matched modular components. For all their diversity, our products haveone thing in common: a consistentlyhigh standard of quality that is reflectedin operational reliability, energy savings,environmental compatibility and user-friendliness.
Many of our developments point theway forward for the heating sector, bothin terms of conventional heatingtechnologies and in the field ofrenewable forms of energy, such as solarand heat pump technology.
In all our developments we pursue our philosophy of always achieving the greatest possible benefit: for our customers, the environment and ourpartners, the heating contractors.
The Viessmann Group:Viessmann WerkeD-35107 Allendorf (Eder)Tel: + 49 6452 70 - 0Fax: + 49 6452 70 - 2780www.viessmann.com
Viessmann UK Office:Viessmann LimitedHortonwood 30,TelfordShropshire,TF1 7YP, GBTel: + 44 1952 675000Fax: + 44 1952 675040E-Mail: [email protected]
Subject to technical modifications 9446 803 - 1 GB 11/2004