maximizing boiler plant efficiency - illinoisashrae.org · presenter: dan watkins, leed bd+c sales...

Maximizing Boiler Plant Efficiency

Presenter: Dan Watkins, LEED BD+C

Sales Engineer Bornquist, Inc.

Efficient Boiler Design

•  Boiler Types – Efficiency Definition – Non-Condensing – Condensing

•  Maximizing Efficiency – Understanding Efficiency – Outdoor Reset – Short Cycle Prevention – Hybrid Systems


•  Combustion Efficiency – 100 percent of efficiency minus the percentage of heat lost up the vent.

•  Thermal Efficiency – The combustion efficiency minus the jacket losses of the boiler. Based on ANSI Z21.13. For boilers 300,000 to 12.5 million Btu.

•  A.F.U.E. – The measure of annual efficiency of a boiler that takes into account the cyclic on\off operation and associated losses as it responds to changes in load. For boilers under 300,000 Btu


•  Non-Condensing – Cast Iron – Steel Tube – Copper Fin – Modulating

•  75-88% Efficiencies


•  Condensing – Cast Aluminum – Stainless Steel – Cast Iron – Dual Heat

Exchanger

•  85-99% Efficiencies depending on operating conditions

3/20/12 Condensing Boilers 6

98

% E

FF

ICIE

NT

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

Thermal efficiency

MARKETING AND REALITY


ENERGY CONTENT OF NATURAL GAS

SENSIBLE HEAT 89.8%

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

LATENT HEAT 10.2%

Latent – Definition: Latin for “hidden”


NON-CONDENSING BOILER HEAT FLOW


CONDENSING BOILER HEAT FLOW


What is a Condensing Boiler?

A condensing boiler is a boiler which has a heat exchanger that is made of materials which will withstand acidic condensate.


Materials on the market:

  Aluminum Alloy   SA 240 316Ti   316L   Cast Iron?

  Copper Tube w/ secondary heat exchanger

MATERIAL CHOICES FOR CONDENSING BOILERS


Oil Gas

Flue gas condensate

Typical household sewage

pH-Value Basic Acidic

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

Ammonia Lake water

Tap water

Distilled water

(neutral)

Clean rain water

Rain water

Vinegar

Lemon juice

Battery acid Gastric acid

CORROSIVE FLUE GAS CONDENSATE

pH Values of various fluids


What about Efficiency?

Condensing boilers are NOT 99% efficient all of the time.


 120oF return water  100% input  87% efficiency  Where is the

condensation?


With efficiencies like this . . .

. . . our customers have reduced their fuel bills by up to 80%.

Now you can, too!

140°F EWT

120°F EWT

100°F EWT

80°F EWT

Condensing/Modulating Boiler


LATENT HEAT RECOVERY

WATER VAPOUR LIQUID

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


  Simplified Chemical Combustion Formula: CH4 + 2 O2 CO2 +2 H2O

HEAT RECOVERY FROM FLUE GASES

Water vapor (steam) containing latent heat


LATENT HEAT RECOVERY 1 pound of water

144 Btus

Ice melting (Latent heat of fusion)

Water vaporizing (Latent heat of condensation)

Steam

Ice

970 Btus


WATER VAPOUR DEW POINT


NATURAL GAS COMBUSTION

1 part gas 10 parts air

+Excess air

More excess air = Lower CO2% Lower C02% = Lower dew point temperature Lower dew point temp. = Less condensation


Higher CO2 =Higher Dew point =More Condensation

Dew

poi

nt 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


Heat Exchanger Design:

 PRIMARY HEAT EXCHANGER DESIGN

 SECONDARY HEAT EXCHANGER DESIGN


PRIMARY HEAT EXCHANGER DESIGN


SECONDARY HEAT EXCHANGER

Efficient Boiler Design Condensing Boiler Design Guidelines

•  Design system for lower water temperatures – Use larger delta T’s – Radiant floor heat / snow melt – Water Loop Heat Pumps

•  Select boiler plant for small turndown capabilities

•  Save initial cost by using both condensing and non-condensing boilers when possible


•  Outdoor Reset – Designing a Reset Curve

•  Cycle Efficiency – How the cycle suffers – Adjusting the differential – Buffer Tanks

•  Piping Systems

Maximizing Efficiency

Efficient Boiler Design – Outdoor Reset

Boiler Plant Cycle Efficiency

28

29

CHICAGO, IL

Cycle Efficiency Curve Analysis

30

Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun

Energy Use Per Unit o

f Loa

d (e.g., HDDs)

Energy Use (T

herm

s, DecaThe

rms, etc.)

31


New

Ene

rgy Use Per Unit o

f Loa

d (e.g., HDDs)

Old Ene

rgy Use Per Unit o

f Loa

d (e.g., HDDs)

32

New

Ene

rgy Use Per Unit o

f Loa

d (e.g., HDDs)

Old Ene

rgy Use Per Unit o

f Loa

d (e.g., HDDs)

33


New

Ene

rgy Use Per Unit o

f Loa

d (e.g., HDDs)

Old Ene

rgy Use Per Unit o

f Loa

d (e.g., HDDs)

34



f Loa

d (e.g., HDDs)

Energy Use (T

herm

s, DecaThe

rms, etc.)

35



f Loa

d (e.g., HDDs)

Energy Use (T

herm

s, DecaThe

rms, etc.)

36


Total HDD x Best Therms/HDD = What’s Possible

Total Therms – What’s Possible = What Was Wasted

37

The E/L Curve Fast Calcula@on…

Billing Period Therms HDDs Therms/HDD

December

January

February

March

etc

Total Therms Total HDD

Best ?

1…track small fracPonal loads at high efficiency

39

To achieve HCE performance, you must…

2…make the efficiency rise as the load falls

3…size boilers so all loads fall within plant modulaPon range

4…use low mass boilers for jockey service

5…use modulaPng burners

6…opPmally match fuel input to real-‐Pme load

Piping Design Examples

40

Boiler Piping Examples

BOILER BOILER BOILER BOILER

42


Hybrid Boiler System

Buffer Tank Example

Using a buffer tank to add 200 gallons will increase firing to almost 3 minutes for a 20 °F delta T. Using reset on the system loop could allow for a 50 or 60 °F delta T. Using a 60 °F delta T would mean a minimum run time of over 8 minutes!

Buffer Tank Example

180

140

180

140

Buffer Tank Example

Condensing Boiler

Non-‐condensing Boilers

Buffer Tank Example

Non-‐condensing Boilers

BufferTank

Condensing Boiler

Buffer Tank Example

Design Guidelines

•  Utilize Buffer tanks and water temperature reset

•  Design for long on/off cycles •  Boilers do not need to be same size/style •  Use small, modulating boilers as a

“jockey” boiler •  Design for efficiency during light loads

Final Thoughts

•  System design is typically more important than individual equipment selections.

•  Energy retro-fits should be based potential savings and initial cost.

•  Every building and every system is different, so there is no one-size-fits-all approach to Energy Saving Design.

Thank You!

60

maximizing boiler plant efficiency - illinoisashrae.org · presenter: dan watkins, leed bd+c sales...

Documents