condensing boiler technology · boiler stand-by and jacket loss< 1% flue gas loss < 1 %...

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Ashrae Presentation April 2010Foil 1

CONDENSING BOILER TECHNOLOGY

Presented by:Ted SchmellingMulcahy CompanyManufactures rep of:Viessmann Manufacturing Co. (US) Inc.45 Access Rd.Warwick, RI


What is condensing boiler TECHNOLOGYNon-condensing construction

Fin tube boiler Cast-iron sectional boiler

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Ashrae Presentation

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N

N

N

N

N

Natural gas CH4

Air

Oxygen

Nitrogen

Combustion

Nitrogen+

Nitrogen Oxides

Water vapor

Carbon Dioxide - CO2

�Light �Heat

NATURAL GAS COMBUSTION

Foil 3April 2010


ENERGY CONTENT OF NATURAL GAS

SENSIBLE HEAT89.8%

Heat that can be measured or felt by a change in temperature

LATENT HEAT10.2%

Latent – Definition:Latin for “hidden”

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Flue gas loss = 3 to 5 %

Boiler stand-by and jacket loss =3 to 5 %

Seasonal efficiency of conventional

Boilers=80%+

Fuel input = 100 %

Sensible heat =89.8%

Latent HeatHeat Loss = 10.2 %

Latent Heat10.2 %

CONVENTIONAL BOILER HEAT FLOW

Into mechanical room

Up chimneyUp chimney

Useful heat


10% LATENT HEAT RECOVERY

WATER VAPOR LIQUID

Energy released

� Water vapor turns to liquid when it is reduced in temperature.

� Energy is released when vapor turns to liquid (Condenses)

132 F degrees

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Boiler stand-byand jacket loss< 1%

Flue gas loss < 1 %Latent HeatHeat Loss < 2 %

Seasonal efficiency of conventional

boilers=82%+

Fuel input = 100 %

Sensible heat =89.8%

Latent Heat10.2 %

Seasonal efficiency

condensing

boilers= 96%+

CONDENSING BOILER HEAT FLOW


Condensing boiler

Sensible heat

CondensationLatentheat

Total heatingvalue

Useableheat

Heatingsystem

MORE USABLE HEAT THROUGH CONDENSATION

What influences What influences the the raterateof of condensation?condensation?

100%

10.2%

Eff. From 85% to 98%

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Heatingsystem

Emissions

FuelFuelBurnertype

Returnwater temp

Effective use of condensing

technology Pipinglayout

FACTORS INFLUENCING EFFECTIVENESS OF CONDENSING TECHNOLOGY

Combustionair


Heatingsystem

Returnwater temp


technology


Greatest Influence

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Boiler return water temperature determines condensing operation

RETURN WATER TEMPERATURE

Less then 132F

Ashrae Presentation Nov 2005Foil 12

TYPICAL HYDRONIC WATER TEMPERATURE REQUIREMENTS:

High-temperature RFHunder wood sub-floor

Low temperature:è High mass radiant floor

ie: concrete floors 80 - 120 oFè Snowmelting systems 80 - 120 oF

High temperature:è Finned tube baseboard 140 - 190 oFè Air heat fancoils 140 - 180 oFè Pool/spa heat exchangers 160 - 180 oFè DHW production 150 - 190 oF

Medium temperature:è Cast iron radiators 100 - 140 oFè Low mass radiant floor

ie: wood joist floors 100 -150 oF

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IMPACT OF SYSTEM TEMPERATURES ON CONDENSATIONExample 3: Supply/return temperature:

104/86oF

1559

1050

541

032

-523

-1014

-155

oCoF

Outside temperature

104oF

86oF

Dewpoint temperature (natural gas 132oF)

Condensation rangeCondensation range

20

30

40

50

Sys

tem

wa

ter

tem

per

atu

re

68

86

104

122

60

70

140

158

oCoF

2068

Radiant floor



180/160oF

1559

1050

541

032

-523

-1014

-155

oCoF


Dewpoint temp 132oF

180oF

160oF

25.5oF

20

Sys

tem

wa

ter

tem

per

atu

re

68

3086

40104

50122

60140

70158

oCoF

80176

90194

Outside temperature

2068

Fin tube

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ASHRAE weather data for Boston, MA

CONDENSING / NON CONDENSING RATIOS

yste

m w

ate

r te

mp

era

ture

75% Condensing

25% Non-condensing

Condensation Condensation rangerange

72

86

104

122

140

158

176oF

+68 +54 +41 +28 +14 0 -13 oF

Supply180oF

Return160oF

Design temperature

Boston: +7oF

Dewpoint temp135

Ashrae weather data, hours of occurrence: Sept -May

1497 hr24.3%

627 hr10% 11 hrs

0.2%

124 hrs2%

1675 hr27%

2258 hr36.5%



160/140oF

1559

1050

541

032

-523

-1014

-155

oCoF

160oF

140oFDewpoint temp 132oF

Condensation range

11.3oF

20

Sys

tem

wa

ter

tem

per

atu

re

68

3086

40104

50122

60140

70158

oCoF

80176

90194

Outside temperature

2068

�Hydro-Air�Radiators

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ASHRAE weather data for Boston, MA

CONDENSING / NON CONDENSING RATIO

97% Condensing

3% Non-condensing


72

86

104

122

140

158

176oF

+68 +54 +41 +28 +14 0 -13

Sys

tem

wa

ter

tem

per

atu

re

oF

Supply160oF

Return140oF

Design temperature

Boston: +7oF

1497 hr24.3%

627 hr10% 11 hrs

0.2%

124 hrs2%

Dewpoint temp135

2258 hr36.5%

1675 hr27%

Ashrae weather data, hours of occurrence: Sept -May


SYSTEM WATER TEMPERATURE DROP

Typical system 20oF Temperature drop

180oF

160oF

What about a higher temperature drop?30oF……40oF?

150oF

Benefits to this?

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Ashrae Presentation

Low-Temp technology

Evolution of the heat exchanger

Low-Temp heating elementThese can work very effectively at low water temper atures, as low as 90 F


Air flowAir flow

Air flowAir flow

180OF

160OF

140OF

120OF

Same BTU’s Same BTU’s delivereddelivered

TRUE SYSTEM EFFICIENCY System Components

Fan coil sizing

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technology

Pipinglayout



USE OF MIXING VALVES WITH CONDENSING BOILERS

3-way mixing valve

No boiler return water temperature elevation

CORRECT

4-way mixing valve

Boiler return water temperature elevation

INCORRECT

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INJECTION PUMPING WITH CONDENSING BOILERS

INCORRECT


High temp system

Lowtempsystem

CONDENSING BOILERS IN HIGH FLOW SYSTEMS

Hydraulic system decoupling

How many have heard of this before?

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Ashrae Presentation

COMMERCIAL LOW LOSS HEADER

Main Return

Main Supply

RADIANT FLOOR HYDRO AIR

1

OUTDOORSENSOR

SNOW MELT

HEATEXCHANGER

EXPANSIONTANK

FLOOR MOUNTED LOW LOSS HEADER

DEKAMATIK-M1

EXPANSIONTANK

DEKAMATIK-M2

Custom Control

M

Benefits of LLH:�Hydraulic separation�Protects boiler from debris�Air removal�Optimum boiler operation

For use with all commercial boilers

Foil 25April 2010

Ashrae Presentation

Low loss header

Principle of operation:T1 – Boiler supply temperature

T2 – Boiler return temperature

T3 – System supply temperature

T4 – System return temperature

Vprimary – Boiler circuit flow rate

Vsecondary – Heating circuit flow rate

Qprimary – Heat supplied by boiler

Qsecondary – Heat consumed by system

Vprimary < Vsecondary

T1 > T3T2 = T4Qprimary = Qsecondary

Vprimary Vsecondary

T1

T2

T3

T4

What is going to happen here?Temp Sensor needed

: ..: : .::::

. :.::.

.:

Debris can fall out

Air Bleed

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Ashrae Presentation

• Vp < Vs

• T1 > T3

• T2 =T4

T1 T3

T2 T4

Vp Vs

LOW LOSS HEADERSPrinciple of operation

Boiler supply 100 GPM

Boiler supply 100 GPM

System supply 125 GPM

System return 125 GPM

Bypass flow 25 GPM

Ashrae Presentation

COMMERCIAL LOW LOSS HEADERS

Maximum system flow rate

Model 400/200 – 250 gpmModel 400/400 – 528 gpm

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Ashrae Presentation

LOW LOSS HEADERFrom small to very big

Back to Piping

Foil 29April 2010


COMBINATION OF BOILERS

LAG BOILER LEAD BOILER

System Return

System Supply

Condensing boilerNon-Condensing boiler

Boiler

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MULTIPLE FUNCTION, MULTIPLE TEMPERATURE SYSTEM

3 way mixing valve

Boiler

System water fill

M M

M

Unique Germany piping and mixing system

Series ConnectionHot

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1

1


FuelFuelBurnertype


technology


Combustionair

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Ashrae Presentation

98%

EF

FIC

IEN

T

….can reach efficiencies of 98% - and more…..

MARKETING AND REALITY

Foil 33April 2010

Ashrae Presentation

…pending return watertemperature, can reach efficiencies of98% - and more.

April 2010Foil 34

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Ashrae Presentation

85% 85% 85%

April 2010Foil 35


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Ashrae Presentation

EFFICIENCYWhat does it all mean??What does it all mean??

• Combustion Efficiency

• Cycle Efficiency or turn down

• AFUE (Seasonal Efficiency)

• Thermal Efficiency

• System Efficiency

• Manufactures claimed Efficiency

April 2010Foil 37

Ashrae PresentationFoil 38

Fuel Input

Air Input

Tair

CO2%Tflue gas

Boiler Boiler

Constant load

180oF

80oF

ANSI Z21.13 / CSA 4.9-2000

Heat exchanger

Condensate measured for condensing boilers test

∆T=100°F

COMBUSTION EFFICIENCYTesting for non-condensing gas commercial boilers

April 2010

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Ashrae Presentation

CYCLE EFFICIENCY

Cycle Efficiency = Total useful heat output (Btu/h) of boiler over a period of time

Energy content of fuel (Btu/h) over same time perio d

Cyc

le E

ffici

ency

%

Run Fraction %

90

35

80

25

65

15

55

45

0

5

One Cycle

Steady State Steady State Efficiency = 90%Efficiency = 90%

0 1009040 8030 7020 605010

Time required to reach Steady State depends on appliance

April 2010Foil 39

Ashrae Presentation

AFUE EFFICIENCYAnnual Fuel Utilization Efficiency

Seasonal efficiency test for boilers up to 300,000 Btu/h

HeatHeatExchangerExchanger

Hot Water out

Cold Water in

Constant Load140 F

120 F

Vent Damper

Boiler Boiler

Fuel Input

Heated SpaceHeated Space

One cool down cycle evaluated

JacketLosses

Measured in test:CO2, O2%, Tgas , Troom

April 2010Foil 40

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Ashrae Presentation

BoilerBoilerHeat Heat

ExchangerExchanger

Thermal efficiency:Thermal efficiency:The ratio of the amount heat absorbed by the water to The ratio of the amount heat absorbed by the water to the higher heating value (HHV) in the fuel burnedthe higher heating value (HHV) in the fuel burned

Hot water outHot water out

Cool water inCool water in

Total fuel burnedTotal fuel burned

Thermal efficiency is sometimes confused with combustion efficiency

THERMAL EFFICIENCY TESTING

April 2010Foil 41

Ashrae Presentation

Condensate measured for condensing boilers test

Heat Exchanger

Constant Load

∆T=100°FBTS-2000

180oF

80oF

COMBUSTION EFFICIENCY TESTINGFor condensing gas commercial boilers >300 MBH

Boiler

Air Input

Fuel Input

………………

April 2010Foil 42

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Ashrae Presentation

CONDENSING BOILER EFFICIENCY

Measured rate of condensate (Boiler only!)

Heat gain from condensate = 8783 Btu / usg of conde nsate2320 Btu / ltr of condensate

[ Boiler input btu/hr (metered gas flow) x

Combustion eff. (measured) + Heat gain from

condensate (btu/hr)

Formula:

]Efficiency of condensing boiler (%) =

Boiler input btu/hr

BoilerCombustion efficiency from flue gas analysis

TOTAL HEAT OUTPUT OF CONDENSING BOILER

SENSIBLE HEAT CAPTURED

LATENT HEAT CAPTURED= +

………

April 2010Foil 43

Ashrae Presentation

Boiler efficiency (%)

=1,008,000 btu/hr

[ 1,008,000 btu/hr x 0.89 ] + [ 4.68 usg x 8783 btu/hr/gal ]

897,120 btu/hr + 41,104 btu/hr

1,008,000 btu/hr = = 93.1%

Boiler

Flue gas analysis:� Comb. Eff.=89%� Flue gas temp. = 118 oF

Condensate rate:� 4.68 gal/hr (60 g/KWh)

� CT3-89� Low fire rate:

1,008 MBH / 295 KWh

� Return water temp. – 113 oF

� Altitude – 2091’

CONDENSING BOILER EFFICIENCYSample project: Community College, Alberta

………

April 2010Foil 44

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Ashrae Presentation

HIGH EFFICIENCY BOILERSUnder what conditions??Under what conditions??

• Burner Efficiency (C02%) or excess air

– Sealed combustion?

– Turn down ratio?

• System water temperatures (return water)

• Boiler Controls

• Boiler Construction and Materials

April 2010Foil 45


Higher CO2

=Higher Dew point=More Condensation

Dew

po

int w

ater

vap

or

77

86

95

104

113

122

131

140

oF oC

25

30

35

40

45

50

55

60

CO2 in Vol %2 3 4 5 6 7 8 9 10 11 12

Natural Gas (95% CH4)

CO2% of flue gas influences dew point temperature

WATER VAPOR DEW POINT

Lower CO2

=Lower Dew point=Less Condensation

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DEW POINT AND ALTITUDE

120

122

124

126

128130

132

134

136

138140

0 1000 2000 3000 4000 5000 6000 7000 8000 9000

Altitude – Feet above sea level

Dew

Po

int T

emp

erat

ure

Dew Point of Natural Gas Based on 1000 btu/ft3, 50% RH and 60oF Room Air

Fo Co

60

50

52.2

54.4

56.6

58.8

53.3

55.5

57.7

51.1



What influences the CO 2% ?

THE BURNER!

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Ashrae Presentation

PERFECT (STOICHIOMETRIC) COMBUSTION

Each fuel has an Maximum CO 2 % ifStoichiometric Combustion is achieved:

�Natural gas : 11.9% CO2

�Propane gas : 13.7% CO2

When theoretical perfect air/fuel mixtures are applied, Stoichiometric Combustion is achieved.

Eg: 10 parts air to 1 part Natural gas,25 parts air to 1 part Propane.

April 2010Foil 49


THEORETICAL PERFECT NATURAL GAS COMBUSTION OR STOICHIOMETRIC

1 part gas

9.7 parts air by volume

Excess air0%

The CO2 = 11.9%The CO = 0 ppm

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Ashrae Presentation

SAFE AND EFFICIENT COMBUSTION

Acceptable range of CO 2%:

�Natural gas: 9.1 – 10 % CO 2

�Propane gas: 10.7 – 11.1% CO 2

Acceptable values for safe and efficient combustion:

Excess Air: 17 - 30%Oxygen: 3 – 5%

April 2010Foil 51


REAL WORLD NATURAL GAS COMBUSTION WITH GOOD BURNER TECHNOLOGY

1 part gas

9.7 parts air

Excess air20 to 25%

What can cause the amount of excess air to change after start-up?

The CO2 = 9.5 to 10%The CO = 0 to 20 ppm

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Ashrae Presentation

COMBUSTION ANALYSIS RESULTS

Boilers with good burner technology should be able to get very low CO!

New power fired boilers

April 2010Foil 53


NATURAL GAS COMBUSTION

Power-fired burner technology

GasAir

25% Excess Air 9.5% CO2

4% O2

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� Combustion with minimal excess air

�CO2: 9.5 to 10%

�Excess air: 20 – 25%

� Fully modulating input

� Precise calibration thru entire firing range (Linkage-less control)

� O2 trim

� Low NOx and CO emissions

BURNER REQUIREMENTS FOR CONDENSING BOILERS

Ashrae Presentation

Combustion air temperatures

Air temperature correction chart from an Analyzer Company

INLET AIR TEMPERATURECO2%

April 2010Foil 56

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Ashrae Presentation

0

87

84

85

86

90

89

88

92

91

93

100

95

94

96

98

97

99

100604030 50 8070 90

Partial Load in %

Boi

ler e

ffici

ency

in %

SUPPLY / RETURN at 100% Load (Design Conditions):

104oF/86oF40oC/30oC

140oF/120oF60oC/49oC



BOILER EFFICIENCY

April 2010Foil 57



Construction requirements of condensing boiler technology

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PHYSICAL REQUIREMENTS OF THE HEAT EXCHANGER SURFACES

Best material for condensing boilers: � Single wall� Highly conductive� Smooth surface

BoilerWater122oF

Heat Flow

158oF

194oF

131oF

122oF

Condensateformation

Dew PointNatural gas

Flue Gas

Ashrae Presentation

PYSICAL REQUIREMENTS OF THE FLUE GASAND CONDENSATE PASSAGE WAYS

Boi

ler W

ater

Boi

ler W

ater

Flue gas

Con

dens

ate

Con

dens

ate

Flue gas

Flue gas and condensate must flow in the same direction (parallel flow)

CORRECT INCORRECT April 2010Foil 60

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Condensing boiler requirements:

� Counterflow principle for flue gas and boiler water – optimal heat transfer

� Parallel flow direction for flue gas and condensate – uniform flow with self-cleaning effect of heat transfer surfaces

Condensing boiler

Hot Flue gas

Flue gas

HR

HR

HS

Normalheating boiler

HS

HR

CONDENSING BOILER CONSTRUCTION


Why is material construction of the boiler heat exchanger so important?

HEAT EXCHANGER CONSTRUCTION

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Oil Gas

Flue gas condensate

Typical householdsewage

pH-ValueBasicAcidic

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

AmmoniaLakewater

Tapwater

Distilledwater

(neutral)

Clean rainwater

Rainwater

Vinegar

Lemonjuice

Battery acidGastric acid

pH VALUES OF VARIOUS FLUIDS


� Highly corrosion resistant

� High strength with thin wall thickness

� Formable

� Long term reliability

MATERIAL REQUIREMENTS FOR CONDENSING BOILERS

condensing boiler technology · boiler stand-by and jacket loss< 1% flue gas loss < 1 %...

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