District Heating/Cooling System Optimization: Principles and Examples from US Army Studies

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1 District Heating/Cooling System Optimization: Principles and Examples from US Army Studies Szenarienvorschläge für die sanfte Energiewende Strukturoptimierung in Flächengebieten, SWM September 20, 2009 Dr. Stephan Richter GEF Ingenieur AG Ferdinand-Porsche-Str. 4a Leimen Germany 1

2 Agenda 1. Overview and Technical Description of a Central Energy System 2. Operation Modes with Variable Temperature-Variable Flow Systems 3. Contributions and Outcomes from Energy Assessments I. Conceptual Ideas II. Searching for ECMs I. Examples from the Fort Bragg Heating and Cooling Master Plan Study II. Experiences from about 25 On-Site Assessments 2

3 Overview on Central Energy Systems Purpose of Central Energy Systems - Provide heating and/or cooling to a group of buildings generated in a Central Energy Plant (CEP) - Heat can be used for space heating, Domestic Hot Water (DHW) preparation and for technical purposes (e.g. pressing units, dehumidification, sterilization, technical shaping etc.) - Cooling can be used for air conditioning, dehumidification and heat removal from processes Basic Principles - The CEP generates thermal energy at a certain temperature. The thermal energy is then transported in pipelines from the CEP to the location of use. Mostly the transport medium is water or steam. At the location of use a part of the energy content is taken from the water and the temperature is reduced (= heating) or raised (cooling). The water is then transported back to the CEP and used again. - The temperature of the transported water depends on the requirements of the users: Requirements are the temperatures itself and the energy capacity. 3

4 Central Energy Systems at a Glance Combined Heat and Power Generation for District Heating Turbine and Generator Boiler Transformer Power Line Heat Users and Substations Return Pipe Central Heat Exchanger Supply Pipe 4

5 Central Energy Systems at a Glance Distribution Pumps Supply Pipe Bypass Building Substation Δp DHW Space Heating Boiler Return Pipe Water Treatment 5

6 Central Energy Systems at a Glance Distribution Pumps Supply Pipe Bypass Building Substation Δp DHW Boiler Space Heating Return Pipe Water Treatment 6

7 Pressure Diagram Pressure Drop Pump CEP Heat Users Problem: horizontal distance between CEP and User As distance to heat users increases the result is a greater pressure drop. A increase of sea level high results into a greater pressure drop, too. Differential pressure at the critical building needs to be higher than 10 to 14 psi 7

8 Agenda 1. Overview and Technical Description of a Central Energy System 2. Operation Modes with Variable Temperature-Variable Flow Systems 3. Contributions and Outcomes from Energy Assessments I. Conceptual Ideas II. Searching for ECMs I. Examples from the Fort Bragg Heating and Cooling Master Plan Study II. Experiences from about 25 On-Site Assessments 8

9 Heat Demand Depends on the Ambient Temperature 105 MW 20 F 40 F 60 F 80 F 100 F 3.5x10 8 BTU 90 MW correlation factor ~ 0.75 to x10 8 BTU Total Sum of Heat Demand 75 MW 60 MW 45 MW 30 MW 15 MW 2.5x10 8 BTU 2.0x10 8 BTU 1.5x10 8 BTU 1.0x10 8 BTU 5.0x10 7 BTU 0 MW 0.0 BTU -15 C 0 C 15 C 30 C 45 C Outdoor Temperature 9

10 Satisfying the Heat Demand by Adapting the Flow and the Supply Temperature Power P Central Energy System = Flow Heat Capacity = Q& = m& c ΔT p of Water Temperature difference Variable Parameter: Supply and Return Temperature Water Flow (= Water Velocity) Approach Keep the flow dm / dt and the return temperature T R constant and vary the supply temperature T S 10

11 Central Heating System Supply Temperature Curve 150 C 0 F 20 F 40 F 60 F 80 F 100 F 120 F 300 F 135 C 280 F Supply Temperature 120 C 105 C 90 C 75 C 260 F 240 F 220 F 200 F 180 F 160 F 60 C 140 F -20 C -10 C 0 C 10 C 20 C 30 C 40 C 50 C Outdoor Temperature 11

12 Why Shall the Supply Temperatures be as Low as Possible? Efficiency of Plant Type 100 C = 215 F Efficiency 1990 Design Hard Cole 530 C = 990 F Waste Incineration 390 C = 735 F Biomass 450 C = 840 F = T Warm T T Cold Warm T Combined Cycle 1100 C = 2010 F 2035 Design Hard Cole 700 C = 1290 F Energy can be used not be used T cold in C = Return Temp from Distribution System T Warm Cold In an existing system a reduction of the return temperature (= a better use of provided temperature) can increase the distribution system s capacity. More users can be supplied by the same diameters and installation costs. In case of new network constructions one can use smaller diameters and, thus, save costs. Flow, pressure drop and electricity for pumps can be reduced. The ratio of power to heat generation increases if less heat/steam is taken from the turbine (e.g. in Munich a additional power generation of 100 GWh el per year can be achieved). 12

13 Agenda 1. Overview and Technical Description of a Central Energy System 2. Operation Modes with Variable Temperature-Variable Flow Systems 3. Contributions and Outcomes from Energy Assessments I. Conceptual Ideas: Examples from the Fort Bragg Heating and Cooling Master Plan Study II. Experiences from about 25 On-Site Assessments 13

14 Current Conditions: Overview on the Central Plants and Distribution System Heating 14

15 Overview Heating Systems 82 nd Heating 96x10 6 BTU/h icl. DUCT Burner: 140x10 6 BTU/h C-Area Faith Barracks Peak load 12x10 6 BTU/h COSCOM 50x10 6 BTU/h C-Area Peak load 40x10 6 BTU/h Steam and Hot Water M-Area Peak load 5x10 6 BTU/h D-Area Zone 1 Peak load 4x10 6 BTU/h E-Area Zone 1 Peak load 4x10 6 BTU/h CMA 109.5x10 6 BTU/h D-Area Zone 2+3 Peak load 8x10 6 BTU/h 4x10 6 BTU/h H-Area Peak load 12x10 6 BTU/h E-Area Zone 2 Peak load 5x10 6 BTU/h SOCOM 40x10 6 BTU/h 15

16 SOCOM (Heating Zone 1) Log Data 175 C SOCOM Hot Water Zone 1 HW Zone 1 Supply HW Zone 1 Return 120m³/h 500gpm 300 F 150 C 100m³/h 250 F 125 C 80m³/h 400gpm 200 F 100 C 60m³/h 300gpm 150 F 75 C 50 C 40m³/h 200gpm 100 F 25 C 20m³/h 100gpm 50 F 0 C 0m³/h gpm Hours since October 05 16

17 SOCOM (Heating Zone 1) Model Parameter Total building heat load (from PNNL FEDS model): Btu/h = 1,306 kw Peak load taken from log data Btu/h = 1,200 kw Load factor ( peak load / total load ) 84% Peak temperatures T supply /T return 340 F/250 F = 170 C/120 C Water mass flow calculated by flow model 84.5 gpm = 19.2 m³/h CEP calculated by flow model 33.4 psi = 2.3 atm 17

18 SOCOM (Heating Zone 1) Results of Flow Model Line colors critical building Rectangle colors CEP 18

19 Operating a Modern Variable Flow Hot Water System Hydraulic Flow Analysis in Peak Load Case supply return Pump CEP 19

20 Current Conditions: Overview on the Central Plants and Distribution System Cooling 20

21 Overview Cooling Systems 82 nd Heating 1820 tons C-Area Faith Barracks Peak load 800 tons COSCOM 1344 tons C-Area Peak load 2600 tons 82 nd Cooling 4400 tons M-Area Peak load 1000 tons D-Area Zone 1 Peak load 600 tons H-Platons H-Plant 2000 tons 2000 tons E-Area Zone 1 Peak load 1000 tons CMA D-Area Zone 2 H-Area E-Area Zone 2 SOCOM 3413 tons Peak load 480 tons Peak load 1100 tons Peak load 740 tons 2100 tons 21

22 H-Plant (Cooling) Log Data 100 F 40 C H-Plant Chilled Water CW Supply CW Return 1200m³/h 5000gpm 80 F 30 C 1000m³/h 800m³/h 4000gpm 20 C 600m³/h 3000gpm 60 F 400m³/h 2000gpm 10 C 40 F 200m³/h 1000gpm 0 C 0m³/h Hours since October Oktober 05 0gpm 22

23 H-Plant (Cooling) Model Parameters Total building cooling load (from PNNL FEDS model): 1581 tons = 5,554 kw Peak load taken from log data 1110 tons = 3,900 kw Load factor ( peak load / total load ) 70% Peak temperatures T supply /T return 43 F/52 F = 6 C/11 C Water mass flow calculated by flow model CEP calculated by flow model 2947 gpm = m³/h psi = 8.6 atm 23

24 H-Plant (Cooling) Results of Flow Model CEP critical building Line colors Rectangle colors 24

25 Interconnection of the Central Plant and Distribution System Cooling 25

26 Connected Cooling Net in the Central Cooling System critical buildings CEP CEP CEP CEP critical buildings 26

27 New Cooling Pipes Required to add Bldg. to the Central Cooling System and Locations where larger Pipe Diameters are Needed To interconnect the heating systems, the green pipes are additionally required The pipes in blue must have larger diameters to interconnect the systems Pipes that need to have larger sizes are required due to the growth of the system in red 27

28 New Cooling Pipes Required to add Bldg. to the Central Cooling System and Locations where larger Pipe Diameters are Needed 28

29 Heat Generation incl. Heat for Absorption Chillers Heating Load 60 MW 50 MW 40 MW 30 MW 20 MW 10 MW 0 MW Boiler: peak: 118.2x10 6 BTU/Hr annual: 1.5x10 9 BTU p.a. Duct-Bruner: peak: 44x10 6 BTU/Hr annual: 15.3x10 9 BTU p.a. Gas Turbine Heat from 82nd Heating GT for 82nd Heating Absorption Chiller Heat from CMA New GT Heat from New CMA GT for NEW CMA 1-Stage-Absorption Chiller Duct Burner Boiler Demand New CMA Gas Turbine: peak: 34x10 6 BTU/Hr annual: 79.9x10 9 BTU p.a. Gas Turbine: peak: 36x10 6 BTU/Hr annual: 263.9x10 9 BTU p.a. Potential of additional heat for absorption chiller for 365 days per year chilled water supply New CMA Gas Turbine: peak: 34x10 6 BTU/Hr annual: 154.7x10 9 BTU p.a. 82nd Heating Gas Turbine: peak: 10x10 6 BTU/Hr annual: 32.0x10 9 BTU p.a x10 6 BTU/Hr 180x10 6 BTU/Hr 160x10 6 BTU/Hr 140x10 6 BTU/Hr 120x10 6 BTU/Hr 100x10 6 BTU/Hr 80x10 6 BTU/Hr 60x10 6 BTU/Hr 40x10 6 BTU/Hr 20x10 6 BTU/Hr 0x10 6 BTU/Hr Hours 29

30 Suggestion: Using Pre-Insulated Bonded Pipe Components of pre-insulated bounded pipe system: Water carrying pipe made from steel. Bonding insulation made from PUR foam having a leak detection system. Jacket pipe made from polyethylene (PE). It is recommended to engage a quality control and management system during the installation of the pipes to ensure the proper installation. Sensible issues are the bevel seams, the bushings and the adding of insulating foam at field welded connections, the sand bed, the proper connection of the leak 30 detection system and the expansion cushions.

31 Comparison between Reality and Drawings 31

32 Schematic of Pre-Insulated Bonded Pipes Buried Valve Anchor T-Junktion Elbow Expansion Cushion Bushing 32 32

33 Cost Savings by Using European Type Standard Pre- Insulated Bonded Pipes Compared to Steel-Jacket Pipes 75.0 Mil. EURO Total 5-Years Costs for replacing Steel-Jacket Steam Pipes by Kind Total 5-Years Costs for replacing Steel-Jacket Steam Pipes by Pre-Ins. Bounded Pipes Total 5-Years Savings 62.5 Mil. EURO 50.0 Mil. EURO 37.5 Mil. EURO 25.0 Mil. EURO 12.5 Mil. EURO 0.0 Mil. EURO Mil. EURO Mil. EURO Years Phase 33

34 Agenda 1. Overview and Technical Description of a Central Energy System 2. Operation Modes with Variable Temperature-Variable Flow Systems 3. Contributions and Outcomes from Energy Assessments I. Conceptual Ideas: Examples from the Fort Bragg Heating and Cooling Master Plan Study II. Experiences from about 25 On-Site Assessments 34

35 Central Energy Systems at a Glance Combined Heat and Power Generation for District Heating Turbine and Generator Boiler Transformer Power Line Heat Users and Substations Return Pipe Central Heat Exchanger Supply Pipe 35

36 Potentials for ECMs in Distribution Piping System 1. Central Plant 2. Piping and related Construction 3. Man Holes 4. Operation Modes 36

37 1. Central Plants Oversized or undersized pumps Wrong/missing controls for VF-pumps High return temperatures from field (e.g. cavitation of pumps) Poor water treatment Missing deaerator Wrong sized expansion tank Poor piping insulation Leakages on fittings, valves, pipes, Oversized or undersized boilers All problems with boilers/chillers (Presentation Al Woody/Scot Duncan) 37

38 2. Piping System Oversized or undersized pumps (pressure drops) Poor insulation Improper junctions (welding, bushings, ) Wrong connection of leak detection system wires or missing leak detection system Missing corrosion protection if steel pipes Missing/undersized stress/expansion compensation Temperature too high regarding the demand (e.g. steam for space heating and DHW) Too high differential pressure at critical bldg. Leakages Missing/unadjusted expansion compensation and anchors If concrete ducts: missing down-grade in ducts If steam: condensate losses and problems with steam traps (steam flashes) Missing venting at high points 38

39 3. Man Holes (if needed or existing) Flooded man holes by groundwater, rain, ) Uninsulated valves, fittings, Leaky or missing covers Missing pump/drainage in man holes Oversized man holes 39

40 4. Operation Modes Too high supply water temperatures regarding usage and demand Constant supply temperatures Constant flow Steam distribution for space heating and DHW Unadjusted codensate pumps in Bldg. Too high return temperatures while flow is constant 40

41 Variable Speed Pumps do not Work Proper Solution The variable speed pumps, frequency drivers, isolation valves and valve actuators must be replaced with new variable flow equipment. This enables the adaptation of the mass flow in the central system to meet the cooling load of the building served by central chilled water. 41

42 Flooded Trenches and Man Holes Savings Normally pipes found in flooded pits require replacement after 15 years rather than after 30 years at a total cost estimated to be $ 360,000. This investment can be postponed by 15 years. Averaging this cost over 15 years results in an annual saving of about $ 24,000. Payback The resulting payback period is years or one month. 42

43 Stop Leaks Fix Broken Release Valve Savings A 465 gal/hr leak equals about 4,000 kgal/yr while the costs for 1 kgal of city water are $ 4. Thus, the annual savings are about $ 16,000. Investment The cost for a 1 valve including a full day of labor is about $ 500. Payback The resulting payback period is 0.03 years or 11 days. 43

44 Problems with Pipe Installation Requires Quality Management and Control of this type of Construction 44

45 2 Systems within a few Feet Distence # Boilers 4,580 MMBH total HW 180 F psi seasonal 4 Bldg. peak: 1,371 MMBH annual: 1,921 mmbtu # Bldg. 1 Chiller 240 tons total peak: 94 tons annual: 1,128 mmbtu # Boilers 4,580 MMBH total HW 180 F psi seasonal 4 Bldg. peak: 1,371 MMBH annual: 1,921 mmbtu # Bldg. 2 Chillers 250 tons total peak: 94 tons annual: 1,128 mmbtu 45

46 Poor Piping Insulation in CEP 46

47 Uninsulated Fittings 47

48 Brocken Insulation in Overgound Piping 48

49 Fibre Glas Condensate Pipe after Steam Flusehes 49

50 Man Holes Without Cover and Pumps 50

51 Man Holes Without Cover and Pumps 51

52 Leakages in Pipes without Leakges Control and Detection System 52

53 Unsealed Foam Opening 53

54 Poorly Installed Bushing 54

55 Highly Corroted Equipment 55

56 Steam Leakages 56

57 Uninsulated Flange 57

58 Flooded Man Hole 58

59 Leaky Valve in Man Hole 59

60 Swimming Pool in Man Hole 60

61 61

62 Who is GEF Ingenieur AG? GEF is a engineering and energy economic consulting and design company for energy supply, focused on district heating. We are developing economic solutions in the field of energy supply, media transport and environment related technologies for our customers since almost 25 years. GEF Office in Leimen, Germany GEF Office in Chemnitz, Germany Our neighborship in Leimen 62