Efficiency and Environmental Comparisons Combined Heat & Power (CHP) Separate Heat & Power (SHP) Combined Heating & Cooling (CHC)

Transcription

1 Efficiency and Environmental Comparisons Combined Heat & Power (CHP) Separate Heat & Power (SHP) Combined Heating & Cooling (CHC)

2 Introduction The enclosed information is provided to explain and illustrate some of the differences between Cogeneration and Trigeneration; Combined Heat & Power (CHP) and Separate Heat & Power (SHP); and to introduce Combined Heat & Cooling (CHC) as a (re)emerging technology for providing heat, power, and cooling in district energy systems. For these illustrations it is necessary to select a common fuel type for calculation and comparison of overall system efficiencies. Whereas natural gas is the fossil fuel of choice for many new base load grid power plants as well as distributed cogeneration plants it is the fuel selected for the comparisons herein. Although the figures for Stanford University energy loads and system comparisons are real, the comparisons of efficiency in the initial Examples are for simplicity based on balanced heat, power, and cooling loads. The Examples also represent overall average system performance and in reality heat, power, and cooling loads are rarely balanced and change regularly through the day and year. While these Examples can be used for indicative high level comparisons of efficiency and environmental performance of these technologies, specific calculations on much more discrete intervals (e.g. hourly loads) using actual equipment performance data will provide more accurate comparisons of any energy systems being compared. Nevertheless as the Examples indicate, for a wide range of heat & power loads in cogeneration settings; or heat, power, and cooling loads in trigeneration settings; the calculations suggest that the use of SHP with modest amounts of heat recovery and/or renewable power will quickly eclipse the overall efficiency and environmental performance of even the best 100% gas fired cogeneration systems. The comparative economics of the Example systems herein are dependent on site specific energy, capital, and O&M costs. At Stanford local economics favored SHP with Heat Recovery and Renewable Power, even with state mandates for 33% renewable power, due to the substantial amount of heat recovery possible. Substantial amounts of heat recovery and/or the use of ground source heat exchange may also be possible in many other district energy systems and yield surprising results when considering long term life cycle costs. For complimentary assistance in evaluating the potential for heat recovery in your system please contact: Joseph Stagner, P.E. Executive Director Department of Sustainability and Energy Management Stanford University 327 Bonair Siding Stanford, CA (work) jstagner@stanford.edu More information on SESI may be found at: A copy of this document may be found at:

3 Definitions: CHP vs. SHP vs. CHC

4 Cogeneration: Heat & Power Combined Heat & Power (CHP) Separate Heat & Power (SHP) HEAT Steam Boiler or Hot Water Generator Cogeneration Unit POWER On-site or Off-site Power Generation

5 Trigeneration: Heat, Power, & Cooling Combined Heat & Power (CHP) Separate Heat & Power (SHP) HEAT Steam Boiler or Hot Water Generator Cogeneration Unit Steam or Electric Powered Chillers COOLING Steam or Electric Powered Chillers POWER On-site or Off-site Power Generation

6 Trigeneration: Heat, Power, & Cooling Combined Heat & Power (CHP) Combined Heat & Cooling (CHC) Cogeneration Unit Steam or Electric Powered Chillers HEAT COOLING Heat Recovery Chiller POWER On-site or Off-site Power Generation

7 Efficiency (Natural Gas fuel basis) Combined Heat & Power (CHP) Separate Heat & Power (SHP) HEAT Steam Boiler or Hot Water Generator Gas In Cogeneration Efficiency = Heat + Power Total Gas In Gas In Cogeneration Unit Note that for SHP the Total Gas In may be reduced by the use of Renewable power generation POWER On-site or Off-site Power Generation Gas In HEAT Steam Boiler or Hot Water Generator Gas In Trigeneration Efficiency = Heat + Power + Cooling Total Gas In Note that for SHP the Total Gas In may be reduced by the use of Renewable power generation Gas In Cogeneration Unit Steam or Electric Powered Chillers COOLING POWER Steam or Electric Powered Chillers On-site or Off-site Power Generation Gas In

8 Comparative Efficiency (Example) CHP vs. SHP vs. CHC

9 Example Energy Diagrams Combined Heat & Power (CHP aka Cogeneration) Separate Heat & Power (SHP) Combined Heat & Cooling (CHC aka SHP + heat recovery) Natural gas selected as comparative base fuel All figures based on gas High Heating Value (HHV) Example figures based on balanced electricity, heating, and cooling loads but conclusions hold for other typical district energy system load balances too Respective line losses for delivery of gas and electricity from production sources to final point of use are excluded but may be included for your site if you know the centroid of the respective production sources serving you

10 Example Calculations- Perfectly Balanced Cogeneration Plant CHP Efficiency Prime Mover (Cogen) Efficiency = [Useful H + P Work] / Gas In to hot water HEAT Trigeneration Efficiency = [Net useful H + P + C ] / Gas In Example: Cogeneration work (usable CHP unit output) = 31, ,849 = 66,849 btu Trigeneration work (usable overall system output) = 31, , ,000 = 93,000 btu.55 kw/ton *2.58 ton hr = 1.42 kwh to chiller & CT 35,846 btu to (incl. machine heat) waste heat to chiller 1.42 kwh COOLING (= 2.58 ton-hr) (70% prime mover cogeneration unit; maximum efficiency using high efficiency electric chillers and no steam chillers) If total gas in to CHP = 95,650 btu: Prime Mover efficiency = 66,849/95,650 = 70% Cogen unit Power out: 35,849 btu (=10.50 kwh) Trigeneration Efficiency = 93,000/95,650 = 97% 9.08 kwh POWER (=9.08 kwh)

11 Example Calculations- Separate Heat & Power + Heat Recovery (without renewable power) (Combined Heat & Cooling Plant with 30% Heat Recovery and 51% Grid Gas Power Plant) HEAT COOLING (= 2.58 ton-hr) 18,219 btu hot water 9,300 btu (30%) waste heat to HRC 21,700 btu (70%) waste heat to chiller.55 kw/ton *1.81 ton hr =.99 kwh to chiller & ct 18,219 efficiency = 21,434 btu gas in to hot water generator 12,781 btu hot water (incl. machine heat) 1.32 kw/ton *.77 ton-hr = 1.02 kwh to heat recovery chiller 25,079 btu to (incl. machine heat) SHP + HR Efficiency Prime Mover (Grid Power Plant) Efficiency = Power Out / Gas In Trigeneration Efficiency = [Net useful H + P + C ] / Gas In Example: Prime Mover work = kwh * 3,413 btu/kwh = 37,850 btu Trigeneration work (usable overall system output) = 31, , ,000 = 93,000 btu If gas to grid plant = 74,216 btu Prime Mover efficiency = 37,850/74,216 = 51% POWER (=9.08 kwh) 9.08 kwh.99 kwh 1.02 kwh kwh = 37,850 51% efficiency = 74,216 btu gas in to grid power plant If total gas to system = 74, ,434 = 95,650 btu Trigeneration Efficiency = 93,000/95,650 = 97%

12 Example Calculations- Relative Trigeneration Efficiency (without renewable power) CHP Efficiency Prime Mover (Cogen) Efficiency = [Useful H + P Work] / Gas In Trigeneration Efficiency = [Net useful H + P + C ] / Gas In Example: Cogeneration work (usable CHP unit output) = 31, ,849 = 66,849 btu Trigeneration work (usable overall system output) = 31, , ,000 = 93,000 btu If total gas in to CHP = 95,650 btu: Prime Mover efficiency = 66,849/95,650 = 70% Trigeneration Efficiency = 93,000/95,650 = 97% to hot water.55 kw/ton *2.58 ton hr = 1.42 kwh to chiller & CT 35,846 btu to (incl. machine heat) waste heat to chiller 1.42 kwh Cogen unit Power out: 35,849 btu (=10.50 kwh) 9.08 kwh HEAT COOLING (= 2.58 ton-hr) POWER (=9.08 kwh) 18,219 btu hot water 9,300 btu (30%) waste heat to HRC 21,700 btu (70%) waste heat to chiller.55 kw/ton *1.81 ton hr =.99 kwh to chiller & ct 9.08 kwh 18,219 efficiency = 21,434 btu gas in to hot water generator 12,781 btu hot water (incl. machine heat).99 kwh 1.32 kw/ton *.77 ton-hr = 1.02 kwh to heat recovery chiller 25,079 btu to (incl. machine heat) 1.02 kwh kwh = 37,850 51% efficiency = 74,216 btu gas in to grid power plant SHP + HR Efficiency Prime Mover (Grid Power Plant) Efficiency = Power Out / Gas In Trigeneration Efficiency = [Net useful H + P + C ] / Gas In Example: Prime Mover work = kwh * 3,413 btu/kwh = 37,850 btu Trigeneration work (usable overall system output) = 31, , ,000 = 93,000 btu If gas to grid plant = 74,216 btu Prime Mover efficiency = 37,850/74,216 = 51% If total gas to system = 74, ,434 = 95,650 btu Trigeneration Efficiency = 93,000/95,650 = 97%

13 Example Calculations- Relative Trigeneration Efficiency (with renewable power) If 33% power comes from renewables and 67% from a new 51% HHV efficient gas fueled grid power plant then total gas used to operate the system = (74,216*.67) = 49,725 btu (power) + 21,434 btu (hot water generators) = 71,159 btu gas in Trigeneration Efficiency (gas basis) = 93,000/71,159 = 131% (vs 97% for very high efficiency perfectly balanced and optimized cogen plant or SHP + HR alone...34% less gas used, 34% less GHG, and lower water use) See Comparative Trigeneration Efficiency chart for example comparisons of relative gas trigeneration efficiency for perfectly balanced CHP; SHP; and SHP plants with heat recovery and/or renewable power (example for balanced loads; all gas fuel source; and new equipment in all cases- calculations for each specific energy system are required based on local loads and equipment mixes) HEAT COOLING (= 2.58 ton-hr) POWER (=9.08 kwh) 18,219 btu hot water 9,300 btu (30%) waste heat to HRC 21,700 btu (70%) waste heat to chiller.55 kw/ton *1.81 ton hr =.99 kwh to chiller & ct 9.08 kwh 18,219 5% efficiency = 21,434 btu gas in to hot water generator 12,781 btu hot water (incl. machine heat).99 kwh 1.32 kw/ton *.77 ton-hr = 1.02 kwh to heat recovery chiller 25,079 btu to (incl. machine heat) 1.02 kwh kwh = 37,850 51% efficiency = 74,216 btu gas in to grid power plant SHP + HR Efficiency Prime Mover (Grid Power Plant) Efficiency = Power Out / Gas In Trigeneration Efficiency = [Net useful H + P + C ] / Gas In Example: Prime Mover work = kwh * 3,413 btu/kwh = 37,850 btu Trigeneration work (usable overall system output) = 31, , ,000 = 93,000 btu If gas to grid plant = 74,216 btu Prime Mover efficiency = 37,850/74,216 = 51% If total gas to system = 74, ,434 = 95,650 btu Trigeneration Efficiency = 93,000/95,650 = 97%

14 Comparative Trigeneration Efficiency Relative Natural Gas Trigeneration Efficiency in District Energy Systems with both Heating & Cooling Combined Heat & Power (CHP) vs. Separate Heat & Power (SHP) vs. Combined Heat & Cooling (CHC) Systems (Balanced Electricity, Heating, & Cooling Loads) 220% 220% 200% 200% 70% minimum CHC + 33% minimum renewable power 180% 180% Relative Natural Gas Trigeneration Efficiency (HHV) 160% 140% 120% Current Average Existing CA Grid Gas Plant Efficiency 1 Current Nominal New Grid Baseload Gas Power Plant Efficiency 2 Practical Maximum Efficiency of New Grid Baseload Gas Power Plant? 1 CHC with 30% Heat Recovery 1. ref: THERMAL EFFICIENCY OF GAS FIRED GENERATION IN CALIFORNIA, Michael Nyberg, California Energy Commission, August ref: Oakley Generating Station, Ca, et. al. 160% 140% 120% CHC 70%; 33% RE CHC 30%; 30% RE CHC 30%; 0% RE SHP; 30% RE SHP; 0% RE CHP; 0% RE 100% SHP 100% Perfectly Balanced Cogeneration Plant 80% 80% CHC = Combined Heat & Cooling (SHP with Heat Recovery) SHP = Separate Heat & Power (on-site boilers + grid power) 60% CHP = Combined Heat & Power 60% 45% 50% 55% 60% 65% 70% 75% Prime Mover Natural Gas Efficiency (HHV)(Cogen CHP unit or Grid Power Plant)

15 Comparative Efficiency (Stanford System) CHP vs. SHP vs. CHC

16 Energy Diagrams- Stanford System Energy System Options Considered A. 100% Gas Fueled Options Business As Usual: Maintain Existing Cogeneration System Hygeneration: Maximum Efficiency Gas Fired Cogeneration using Internal Combustion Engines with Partial Heat Recovery and Steam to Hot Water Conversion B. Grid Electricity Options (shown with and without Renewable Power included) Separate Heat & Power and Steam to Hot Water Conversion Combined Heat & Cooling (CHC): SHP + Heat Recovery and Steam to Hot Water Conversion CHC + Ground Source Heat Exchange (GSHE)

17 Total natural gas 100% fossil power = 3,860,868 mmbtu BAU- Cardinal Cogeneration All figures based on gas HHV 1,756,225 mmbtu 1,225,753 mmbtu 1,316,255 mmbtu Gas in 4,400,000 mmbtu Total = 2,643,775 mmbtu 1,327,520 mmbtu 388,960,000 kwh Cogeneration Efficiency (electricity + heating) 2,643,775 mmbtu 4,400,000 mmbtu = 60.0% 254,000 mmbtu 9,378 mmbtu 2,747,778 kwh 106,773 mmbtu 31,285,190 kwh 1,062,255 mmbtu Gas in 169,856 mmbtu Steam lb/ton Electric kw/ton Cogen Heating Boiler Heating 249,333 mmbtu 20,777,778 ton-hr 572,295 mmbtu 47,691,222 ton-hr 1,062,255 mmbtu 135,885 mmbtu environment (distribution line loss) 147,140 mmbtu Total usable chilling out = 821,628 mmbtu Total usable heat out = 1,051,000 mmbtu -347,404 mmbtu 248,983,788 kwh Electricity 849,782 mmbtu 248,983,788 kwh Total usable electricity out = 849,782 mmbtu Gas saved -708,988 mmbtu -361,584 mmbtu -105,943,244 kwh New Grid Gas Power Plant Efficiency 361,584 mmbtu 708,988 mmbtu = 51.0% Total usable heat & power (cogeneration work) out = Cogeneration Efficiency (electricity + heating ) 3,860,868 mmbtu = 49.2% Total usable heat, power, & chilling (trigeneration work) out = 2,722,410 mmbtu Trigeneration Efficiency (electricity + heating + cooling) 2,722,410 mmbtu 3,860,868 mmbtu = 70.5%

18 Total natural gas consumed = 2,615,621 mmbtu Hygeneration (IC) with Hot Water All figures based on gas HHV 733,412 mmbtu 5,207 0 mmbtu 762,479 mmbtu 823,324 mmbtu Gas in 2,564,378 mmbtu Total = 1,830,966 mmbtu 1,007,642 mmbtu 295,236,427 kwh Cogeneration Efficiency (electricity + heating) 1,830,966 mmbtu 2,564,378 mmbtu = 71.4% 18,659,174 kwh 92,338 mmbtu Heat Recovery Chiller (COP = 5.66) (1.51 kw/ton) 27,054,774 kwh Electric kw/ton HRC 1.51 kw/ton HRC Heating 661,692 mmbtu 55,141,018 ton-hr 159,936 mmbtu 13,327,982 ton-hr 223,620 mmbtu Total usable chilling out = 821,628 mmbtu 42,040 mmbtu environment (distribution line loss) Gas saved -2,988 mmbtu -1,464 mmbtu -1,524 mmbtu -446,499 kwh 823,324 mmbtu Gas in 54,231 mmbtu 315 mmbtu 92,192 kwh Cogen Heating Boiler Heating 823,324mmbtu 46,096 mmbtu Total usable heat out = 1,051,000 mmbtu Gas Power Plant Efficiency 248,983,788 kwh Electricity 849,782 mmbtu 248,983,788 kwh Total usable electricity out = 849,782 mmbtu 1,524 mmbtu 2,988 mmbtu = 51.0% Total usable heat & power (cogeneration work) out = Total usable heat, power, & chilling (trigeneration work) out = 2,722,410 mmbtu Cogeneration Efficiency (HW) (electricity + heating) Trigeneration Efficiency (HW) (electricity + heating + cooling) 2,615,621 mmbtu = 72.7% 2,722,410 mmbtu 2,615,621 mmbtu = 104.1%

19 Separate Heat & Power with Hot Water All figures based on gas HHV Total natural gas 100% fossil power = 3,186,552 mmbtu; 2,553,011 mmbtu w 33% RPS 1,134,053 mmbtu environment (distribution line loss) 931,305 mmbtu Gas in 1,285,929 mmtu 7,461 mmbtu 2,186,080 kwh Boiler Heating 1,093,040 mmbtu 42,040 mmbtu Total usable heat out = 1,051,000 mmbtu Gas in 1,900,623 mmtu 969,318 mmbtu 284,007,654 kwh 36.7 lb 112,075 mmbtu 32,837,786 kwh Electric kw/ton 821,628 mmbtu 68,469,000 ton-hr Total usable chilling out = 821,628 mmbtu 248,983,788 kwh Electricity 849,782 mmbtu 248,983,788 kwh Total usable electricity out = 849,782 mmbtu New Grid Gas Power Plant Efficiency 969,318 mmbtu 1,900,623 mmbtu = 51.0% Total usable heat & power (cogeneration work) out = Cogeneration Efficiency (HW) (electricity + heating) 3,186,552 mmbtu = 59.7% Relative Gas Cogeneration Efficiency (HW) with 33% Renewable Electricity (electricity + heating ) 2,553,011 mmbtu = 74.5% Total usable heat, power, & chilling (trigeneration work) out = 2,722,410 mmbtu Trigeneration Efficiency (HW) (electricity + heating + cooling) 2,722,410 mmbtu 3,186,552 mmbtu 2,722,410 mmbtu 2,553,011 mmbtu = 85.4% Relative Gas Trigeneration Efficiency (HW) with 33% Renewable Electricity (electricity + heating + cooling) = 106.6%

20 Total natural gas 100% fossil power = 2,539,552 mmbtu; 1,822,548 33% RPS Combined Heat & Cooling (CHC) with Hot Water 364,362mmbtu All figures based on gas HHV Gas in 388,540 mmtu 2,254 mmbtu 660,518 kwh Boiler Heating 330,259 mmbtu 42,040 mmbtu environment (distribution line loss) Total usable heat out = 1,051,000 mmbtu Gas in 2,151,012 mmtu 1,053,996 mmbtu 1,097,016 mmbtu 321,422,769 kwh 36.7 lb 61,238,537 kwh Heat Recovery Chiller (COP = 6.30) (1.327 kw/ton) 35,973 mmbtu 10,539,926 kwh Heating HRC kw/ton Electric kw/ton 762,781 mmbtu 553,777 mmbtu 46,148,106 ton-hr 267,851 mmbtu 22,320,894 ton-hr Total usable chilling out = 821,628 mmbtu 248,983,788 kwh Electricity 849,782 mmbtu 248,983,788 kwh Total usable electricity out = 849,782 mmbtu Gas Power Plant Efficiency 1,097,016 mmbtu 2,151,012 mmbtu = 51.0% Total usable heat & power (cogeneration work) out = Cogeneration Efficiency (electricity + heating) Total usable heat, power, & chilling (trigeneration work) out = 2,722,410 mmbtu Trigeneration Efficiency (electricity + heating + cooling) 2,539,552 mmbtu = 74.8% 2,722,410 mmbtu 2,539,552 mmbtu = 107.2% Relative Gas Cogeneration Efficiency with 33% Renewable Electricity (electricity + heating) 1,822,548 mmbtu = 104.3% Relative Gas Trigeneration Efficiency with 33% Renewable Electricity (electricity + heating + cooling) 2,722,410 mmbtu 1,822,548 mmbtu = 149.4%

21 Total natural gas 100% fossil power = 2,282,359 mmbtu; 33% RPS Combined Heat & Cooling with GSHE and Hot Water Gas in 21,061 mmtu 104 mmbtu 30,433 kwh 53,129 mmbtu Boiler Heating environment 17,902 mmbtu All figures based on gas HHV GSHE Pumps = 900,000 kwh (3,072 mmbtu) 226,770 mmbtu Heat Extracted from Open Loop Ground Source Heat Exchange System environment (distribution line loss) Gas in 2,261,298 mmtu 1,105,084 mmbtu 1,153,262 mmbtu 337,902,706 kwh 36.7 lb 87,215,445 kwh Heat Recovery Chiller (COP = 6.30) (1.327 kw/ton) 5,710 mmbtu 1,673,040 kwh Heating HRC kw/ton Electric kw/ton 1,075,138 mmbtu 780,547 mmbtu 65,045,550 ton-hr 41,081 mmbtu 3,423,450 ton-hr 42,040 mmbtu Waste Heat to Open Loop Ground Source Heat Exchange System instead of Cooling Towers Total usable heat out = 1,051,000 mmbtu Total usable chilling out = 821,628 mmbtu Gas Power Plant Efficiency 248,983,788 kwh Electricity 849,782 mmbtu 248,983,788 kwh Total usable electricity out = 849,782 mmbtu 1,108,036 mmbtu 2,261,298 mmbtu = 51.0% Total usable heat & power (cogeneration work) out = Total usable heat, power, & chilling (trigeneration work) out = 2,722,410 mmbtu Cogeneration Efficiency (HW) (electricity + heating) Trigeneration Efficiency (HW) (electricity + heating + cooling) 2,282,359 mmbtu = 83.3% 2,722,410 mmbtu 2,282,359 mmbtu = 119.3% Relative Gas Cogeneration Efficiency (HW) with 33% Renewable Electricity (electricity + heating) 1,528,593 mmbtu = 124.3% Relative Gas Trigeneration Efficiency (HW) with 33% Renewable Electricity (electricity + heating + cooling) 2,722,410 mmbtu 1,528,593 mmbtu = 178.1%

22 4,500,000 Stanford Energy Supply Options Natural Gas Use (2020) 4,000,000 3,500,000 3,000,000 2,500,000 mmbtu 2,000,000 1,500,000 1,000, ,000 - Cardinal Cogen Gas HW Generators & Electric Chillers Gas IC Engine Cogen + Heat Recovery Heat Recovery Heat Recovery + GSHE Gas HW Generators & Electric Chillers w 33% RPS Heat Recovery w 33% RPS Heat Recovery + GSHE w 33% RPS