Energy-Saving Designs for Existing Buildings

Presented by:

Dan Watkins, LEED AP

Bornquist, Inc.

Topics to Cover

• Designing for Efficiency• System Design Examples

– Variable Speed Pumping– Hot Water Boiler Systems

• Final Tips

Designing for Efficiency

• Equipment Efficiency• System Efficiency• Payback Considerations

Equipment Efficiency

• Equipment efficiency does play a role in increasing the overall efficiency of the system. The efficiency of some types of equipment are directly related to the system in which they are installed. Equipment efficiency can also be affected by the geographic area in which it is installed.

System Efficiency

• System Efficiency plays the biggest role in determining the overall affect of the replacement equipment. Designs should be based on overall system efficiency and not only based on individual equipment efficiency ratings.

Payback Considerations

• Payback is also a very big consideration, especially in retrofit projects. Sometimes the payback time period can dictate the design chosen. A good payback analysis blends initial cost with system efficiency, not just equipment efficiency.

System Design Examples

• Variable Speed Pumping• Boiler Systems

Variable Speed Pumping Applications

• Easy Pump Balancing• Variable Flow Systems

– Hot Water Pumps– Chilled Water Pumps– Condenser Water Pumps– Zone Pumps

• Pressure Booster Packages

Variable Speed Pumping

• VFD turns down the speed of the pump to match demand.

• HP requirements drop significantly compared to flow rate reduction.

GPM2 GPM1

HEAD2

RPM2

RPM1

HEAD1

HP2 HP1

=

= =

=

=

RPM2

RPM1

RPM2

RPM1

HP2 HP1

GPM2

GPM1

GPM2

GPM1

HEAD2 HEAD1

22

33

Variable Speed Pumping

Variable Speed PumpingEasy Pump Balancing

Pump Selected at:1000 GPM @ 100’40 HP required.Duty Point: 30 HP

Oversized by 15%15’ head on TDV

X

Variable Speed PumpingEasy Pump Balancing

Variable Speed PumpingConstant Volume Primary - Variable Volume Secondary

Variable Speed Pumping Example

Pump Selected at:1000 GPM @ 100’40 HP required.Duty Point: 30 HP

Constant Volume Primary - Variable Volume Secondary

Variable Speed Pumping Example

SENSOR ACROSS COILSENSOR ACROSS COIL

Coil

10 - 15’ P.D.

Control Valve

10 - 15’ P.D.

Typical Total P.D. 20 -30’

Typical Setting Equals

Design Pressure Drop

Across the Coil, Control Valve, and

Circuit Setter.

Constant Volume Primary - Variable Volume Secondary

Variable Speed Pumping ExamplePump Selected at:1000 GPM @ 100’

Variable Speed andSystem curves shown

20’ Control Head

725 RPM Minimum

Constant Volume Primary - Variable Volume Secondary

Variable Speed Pumping Example

PE Motor

Constant Volume Primary - Variable Volume Secondary

Variable Speed Pumping Example

• Savings not as great as compared to closed loop systems

• Still should utilize hydro-pneumatic tanks

• Better for pump life cycle• Does not require booster

pump PRV’s

Variable Speed Domestic Pressure Boosting

Variable Speed Pumping Example

• Height of building – 12 stories• 150 ft. static lift• 30 PSI City pressure• 30 PSI required at the top• 50’ piping pressure drop at

design flow

Variable Speed Domestic Pressure Boosting

Variable Speed Pumping Example

Pump Selected at:300 GPM @ 200’30 HP required.Duty Point: 25 HP

2950 RPMMinimum Speed

Variable Speed Domestic Pressure Boosting

Variable Speed Pumping ExampleVariable Speed Domestic Pressure Boosting

Efficient Boiler Design

• Boiler Types– What is Efficiency?– Non-Condensing – Condensing

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

Efficient Boiler Design

• 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

Efficient Boiler Design

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

• 75-88% Efficiencies

Efficient Boiler Design

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

• 85-99% Efficiencies depending on operating conditions

Efficient Boiler Design

120oF return water

100% input 87% efficiency Where is the

condensation?

Efficient Boiler Design

80

82

84

86

88

90

92

94

96

2001801601401201008060

130oF Dew Point of Natural Gas

Condensingmode

Non-Condensingmode

Ste

ady

stat

e boile

r effi

cien

cy %

Boiler returnwater temp oF

98

80

82

84

86

88

90

92

94

96

2001801601401201008060

130oF Dew Point of Natural Gas

Condensingmode

Non-Condensingmode

Ste

ady

stat

e boile

r effi

cien

cy %

Boiler returnwater temp oF

9898

Efficient Boiler DesignCondensing 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

Efficient Boiler Design

• Outdoor Reset– Designing a Reset Curve

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

• Hybrid Systems

Maximizing Efficiency

Efficient Boiler Design – Outdoor Reset

Efficient Boiler DesignCycle Efficiency

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65 64 66 54 53 73 43 3 0 0 0 1 14 27 51 269 4.34 4.34 2.78

63 62 64 39 54 47 55 3 0 0 0 8 18 34 38 259 4.18 8.51 5.56

61 60 62 26 26 45 34 3 0 0 0 6 26 60 48 227 3.66 12.17 8.33

59 58 60 11 9 19 21 3 0 0 0 2 17 21 12 104 1.68 13.85 11.11

57 56 58 7 14 49 42 11 0 0 0 3 35 45 29 207 3.34 17.19 13.89

55 54 56 6 16 32 41 23 0 0 0 3 28 47 41 197 3.18 20.36 16.67

53 52 54 1 9 37 44 29 1 3 1 4 36 54 17 220 3.55 23.91 19.44

51 50 52 0 0 30 56 11 10 4 1 9 46 62 7 230 3.71 27.62 22.22

49 48 50 0 0 29 64 46 23 7 9 27 63 66 7 335 5.40 33.02 25.00

47 46 48 0 0 8 41 27 3 9 18 17 83 40 1 247 3.98 37.00 27.78

45 44 46 0 0 4 39 42 4 17 29 15 79 31 4 261 4.21 41.21 30.56

43 42 44 0 0 1 34 54 9 9 24 36 42 16 0 226 3.64 44.86 33.33

41 40 42 0 0 2 15 18 9 2 9 31 20 3 0 110 1.77 46.63 36.11

39 38 40 0 0 0 30 43 24 7 28 34 63 6 0 236 3.81 50.44 38.89

37 36 38 0 0 0 38 74 54 32 35 68 43 5 0 350 5.64 56.08 41.67

35 34 36 0 0 0 16 54 70 62 36 97 30 2 0 368 5.93 62.01 44.44

33 32 34 0 0 0 6 64 63 42 21 85 30 0 0 312 5.03 67.04 47.22

31 30 32 0 0 0 15 107 88 87 87 67 26 0 0 478 7.71 74.75 50.00

29 28 30 0 0 0 8 46 40 43 44 67 2 0 0 251 4.05 78.80 52.78

27 26 28 0 0 0 0 22 42 63 48 48 0 0 0 224 3.61 82.41 55.56

25 24 26 0 0 0 0 18 44 29 72 31 0 0 0 195 3.14 85.55 58.33

23 22 24 0 0 0 0 5 20 23 29 20 0 0 0 98 1.58 87.13 61.11

21 20 22 0 0 0 0 0 44 27 34 27 0 0 0 133 2.14 89.28 63.89

19 18 20 0 0 0 0 0 45 46 29 23 0 0 0 144 2.32 91.60 66.67

17 16 18 0 0 0 0 0 48 36 21 6 0 0 0 112 1.81 93.41 69.44

15 14 16 0 0 0 0 0 31 30 17 2 0 0 0 81 1.31 94.71 72.22

13 12 14 0 0 0 0 0 26 36 27 0 0 0 0 90 1.45 96.16 75.00

11 10 12 0 0 0 0 0 7 14 17 0 0 0 0 39 0.63 96.79 77.78

9 8 10 0 0 0 0 0 3 12 13 0 0 0 0 29 0.47 97.26 80.56

7 6 8 0 0 0 0 0 4 21 14 0 0 0 0 40 0.64 97.90 83.33

5 4 6 0 0 0 0 0 1 6 1 0 0 0 0 9 0.15 98.05 86.11

3 2 4 0 0 0 0 0 4 11 7 0 0 0 0 23 0.37 98.42 88.89

1 0 2 0 0 0 0 0 4 21 1 0 0 0 0 27 0.44 98.86 91.67

-1 -2 0 0 0 0 0 0 5 12 0 0 0 0 0 18 0.29 99.15 94.44

-3 -4 -2 0 0 0 0 0 4 9 0 0 0 0 0 14 0.23 99.37 97.22

-5 -6 -4 0 0 0 0 0 14 24 0 0 0 0 0 39 0.63 100.00 100.00

Efficient Boiler DesignCycle Efficiency

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

Ener

gy U

se P

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nit o

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.g.,

HD

Ds)

Ener

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Efficient Boiler DesignCycle Efficiency

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

New

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(e.g

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Old

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Efficient Boiler DesignCycle Efficiency

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Old

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

Efficient Boiler DesignCycle Efficiency

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Old

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Use

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

Efficient Boiler DesignCycle Efficiency

Ener

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

Efficient Boiler DesignCycle Efficiency

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

Total Therms – What’s Possible = What Was Wasted

The E/L Curve Fast Calculation…

Billing Period Therms HDDs Therms/HDD

December

January

February

March

etc

Total Therms Total HDD

Best ?

Efficient Boiler DesignCycle Efficiency

Se

aso

n

Mo

nth

Th

erm

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ow

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OCT 12,614.86 399 31.62 28.30 13.71 5,469.29 12.20 4,867.67

NOV 38,831.88 940 41.31 66.67 32.29 30,355.75 28.74 27,016.62

DEC 63,143.90 1148 55.00 81.42 39.44 45,276.10 37.07 42,559.54

JAN 68,300.44 1410 48.44 100.00 48.44 68,300.44 45.53 64,202.41

FEB 52,692.62 1003 52.54 71.13 34.46 34,561.07 32.39 32,487.40

MAR 41,710.14 832 50.13 59.01 28.58 23,781.10 25.44 21,165.18

APR 25,161.45 587 42.86 41.63 20.17 11,837.54 17.95 10,535.41

302,455.29 219,581.29 202,834.23

82,874.00 99,621.06

27.4 32.9

83.2 16.8Percent of savings due to each measure

Winter '96 - '97

TOTAL FUEL USE (THERMS)

HISTORICAL DATA

Measure #1: IMPROVE LOAD

MATCHING PLUS FIX CYCLE

Measure #2: IMPLEMENT

MEASURE #1 PLUS IMPROVE BOILER

EFFICIENCY

TOTAL FUEL SAVINGS (THERMS)

Total fuel savings as percent of current fuel use

Efficient Boiler DesignHow the Cycle Suffers

BOILER 800 MBH Output

10 GPM 10 GPM 60 GPM

20 Gallons in boiler at 170 °F. At 10 GPM and 100 MBH loadAt 800 MBH firing, boiler will hit 190 °F in about 20 seconds.

Efficient Boiler DesignHow the Cycle Suffers

Added piping increases boiler volume…but to what extent?Adding 20 Ft. of 3” pipe adds 7.6 gallonsFiring increases from 20 seconds to 25 seconds!

Efficient Boiler DesignHow the Cycle Suffers

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!

Efficient Boiler DesignHow the Cycle Suffers

180

140

Efficient Boiler DesignHow the Cycle Suffers

180

140

Efficient Boiler DesignHybrid Systems

Condensing Boiler

Non-condensing Boilers

Efficient Boiler DesignHybrid Systems

Non-condensing Boilers

BufferTank

Condensing Boiler

Efficient Boiler Design

• 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

General Guidelines

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.

Questions?