Utilities Infrastructure Cooling Distribution. Purpose of Today s Presentation. Agenda. GLHN Architects & Engineers, Inc.

Transcription

1 Utilities Infrastructure Cooling Distribution APPA Institute for Facilities Management Dallas Jan 2017 Bill Nelson PE 1 Purpose of Today s Presentation To provide a broad understanding of Chilled water distribution systems. How to teach old cooling coil new tricks. To share information about current technologies related to central plants To provide some useful handout material with sizing guides 2 Agenda Introduction What makes for a high performance Chilled Water System The Coil Story How many pumps do we need? The Fundamentals Water 3

2 Fundamentals: Water--Ideal Heat Transfer Fluid 75ºF 76ºF Specific Heat 32ºF 1 BTU/lb 212ºF Heat of Fusion 144 BTU/lb Heat of Vaporization 970 BTU/lb 4 chilled water plant design Provocation Are our rules of thumb 44 F chilled water supply 10 F T for chilled water system 3 gpm/ton condenser water flow in need of repair? chilled water plant design A Paradigm Shift New rules of thumb 41 F chilled water supply 16 F T across the evaporator that s at 1.5 gpm/ton 15 F T across the condenser that s at 2.0 gpm/ton (We won t change the coil, chiller or piping. CAN THE EXISTING PROVIDE 16 F T??

3 Plant Load Sum of Cooling Coils Basic GPM = BTUH/500xDelta T Bigger Delta T = Smaller Flow Rates Lower Send Out Temp Better?? Teaching Old Coils New Tricks Do Chillers like to make cold water? The Coil Story: System Equations System Heat Transfer Load (Tons) = 1/24 Q(gpm) (Tr - Ts) Coil Heat Transfer Heat Exchanged (BTUH) = Q Cp (log mean DT) System Head Loss H (ft) = k Q 2 (gpm) System Pump Work W(hp) = (H) (Q) 3960 eff W(hp) = k Q 3 (gpm) Chilled Water Coils 9

4 Sample Calculations: Cooling Coil Grains of Moisture Per Pound of Dry Air Dewpoint or 7 Saturation Temp. F Dry-Bulb temp. F % 25 60% 40% % % 70% 26 50% 30% % The Coil Story: Coil Heat Transfer (1) Temperature TEAT Q TLWT 1 Water Side Air Side TLAT dq TEWT Location The Coil Story: Coil Heat Transfer (2) Temperature TEAT TLWT 2 TLWT 1 Water Side Air Side 1 2 Location TLAT TEWT 1 TEWT 2

5 Solutions: Improve dt Cooling Coil Physics 85 EAT LAT 218 GPM 146 GPM LWT 57 LWT 45 EWT 41 EWT Entering Water Temp Effects When we lower the EWT in a fixed coil, the LWT goes up and the velocity of the water through the coils goes down in order to cool the air to the same state point. 10º ΔT to 17º ΔT 6 FPS to 3.5 FPS Can we maintain high ΔT at part load? 1. If the CFM and Face Velocity decrease, VAV Systems? 2. If the Leaving Air Dry Bulb temp (LADB) increases? 3. If the Entering Air Temp (EADB/EAWB) decreases? We can determine these by using very similar copperaluminum fixed cooling coils from Trane, Carrier & York at an elevation of 1500 ft, a fouling factor of , with 6 rows and no special coatings and a maximum air pressure drop of 1 inch. A fouling factor of hr-sq ft-deg F/Btu is considered very large while is a dirty coil.

6 Decreasing Face Velocity Effects When we lower the CFM & Face Velocity in a fixed coil, the LWT goes up and the velocity of the water through the coils goes down in order to cool the now decreased amount of air to the same state point. 17º ΔT to 20º ΔT 3.5 FPS to 1.25 FPS Increasing LADB Effects When we increase the Leaving Air Dry Bulb Temperature in a fixed coil, the LWT goes up and the velocity of the water through the coils goes down in order to cool the same volume of air to a higher state point. 17º ΔT to 22º ΔT 3.5 FPS to 2 FPS Changing Inlet Air Temperatures In a fixed coil, when the temperature of the outside entering air decreases, the LWT increases as the load decreases but then follows entering air temperature downwards. The velocity of the water through the coils drops rapidly at first, but then flattens out as the LWT decreases rapidly. No datawasreturnedifthevelocitywasbelow 1FPS

7 Fouled Coils Thermal Resistance on either Air or Water Side How to Maintain High DT Eliminate Mixing and Uncontrolled Loads Maintain Design Deck Set Point Solve Airside Problems on the Airside Clean Coils Minimize Plant DP Locate and Eliminate Poorest Performers The Chiller Story Evaporator Heat Exchanger (Case 1) Temperature Water Chillers TEWT 1 ( o ) Q Chilled Water Refrigerant 1 2 Location The fundamental heat transferbetween the boilingrefrigerantand chilled wateroccurs ina tube and shellheat exchanger. TLWT 1 (45 o ) T R (38 o )

8 The Chiller Story Evaporator Heat Exchanger (Case 1 & 2) 70 Temperature TEWT 2 (60 o ) TEWT 1 ( o ) Chilled Water TLWT 1 (45 o ) TLWT 2 (42 o ) Refrigerant TR 1,2 (38 o ) Location Central Plant Optimization Cooling Coil Selection Valve Distribution & Interface Building Tower Pumps Min GPM Max T Flow Ranges Chws Pumps Min GPM Max T VFD Towers Size Fan HP VFD Supply Temp Chillers kw/ton P Flow Ranges Minimum kw/ton Controls Staging Sequence Operations Schedule Facilities Organization Plant Chilled Water System Components Pumps/ Piping Primary/Secondary Direct Primary Parallel Pumping Series Pumping Variable Speed Pumping Reverse Return Piping System 24

9 Plant Configuration Primary/Secondary Pumping Variable Flow Direct Primary System Configurations Primary/Secondary (central plant secondary pumping) CHILLERS SECONDARY PUMP COIL COIL PRIMARY PUMPS DECOUPLER System Configurations Primary/Secondary (distributed secondary pumping)

10 System Flow Sequencing Primary Greater than Secondary Plant Side Distribution Side System Flow Sequencing Secondary Greater than Primary 42 Plant Side Distribution Side System Flow Sequencing Primary Synchronized with Secondary Plant Side Distribution Side

11 System Configurations Direct Primary CHILLERS COIL COIL PRIMARY PUMPS 31 Variable Flow Direct Primary Plant Configuration Why Primary/Secondary Pumping Save Pumps, Save Dollars, Save Energy Go To: Variable Flow Direct Primary

12 Legend Chilled Water Plants should NOT be run by Legend. Know when to Stop and Start your Chillers Preserve High Delta T Minimize Plant KW/Ton CHILLED WATER PIPING CAPACITY TONS (1000 ft 2 ) Capacity Area GPM swere selectedtomaintainwatervelocities (V) below10 fps,and pressuredrop (f) below1 /100 for largesizepipes. The GPMvaluesfor smallersize pipeswere selectedtomaintainwatervelocitiesbelow 7 fps, andpressuredropbelow4 /100.Thevelocities and friction drop values are according to Cameron. (C=100) s of gross sq. ft. of building are figured at 300 GSF/ton, I.e. (10,500) indicates that approximately 10,500,000 GSF can be air-conditioned with 35,000 tons. For heavy research areas use 220 GSF/ton. HP valuestopumpthewaterthrough1000 return calculated using: HP = GPM x TDH TDH = 2000 x f 3940 x This chart is intended to be used for obtaining an initial estimate of required pipe size and cost. Actual system design must be based on values obtained specifically for the project. Total installedcost per linear ft. of buriedsupply & return (2 pipes) piping. Price includes trenching,insulation, fittings, backfill & moderate amounts of surfacing repairs. For total projectcost add A-E fees, testing, escalations, contingencies, etc. 35 Questions? wnelson@glhn.com 36

13 example chilled water plant Base Design: 450 Tons 0.4% design wet bulb: 68 F Entering condenser water temperature (ECWT): 74 F Evaporator and condenser temperature differences: 10 F Coil, valve and chilled water piping pressure drop: 80 ft Condenser water piping pressure drop: 30 ft Pump efficiency: 75% Pump motor efficiency: 93% example chilled water plant dry climate System Energy Consumption With 2.4, 3.0 gpm/ton flows 2.4/3.0 Chiller Chilled Water Pump 29.6 Condenser Water Pump 31.1 Cooling Tower 24.1 Total kw example chilled water plant dry climate System Energy Consumption With 2.4, 3.0 gpm/ton flows 2.4/3.0 Chiller Chilled Water Pump 29.6 Condenser Water Pump 31.1 Cooling Tower 24.1 Total kw 281.7

14 example chilled water plant dry climate System Energy Consumption With 1.5, 3.0 gpm/ton flows 2.4/ /3.0 Chiller Chilled Water Pump Condenser Water Pump Cooling Tower Total kw example chilled water plant dry climate System Energy Consumption With 2.4, 2.0 gpm/ton flows 2.4/ / /2.0 Chiller Chilled Water Pump Condenser Water Pump Cooling Tower Total kw example chilled water plant dry climate kw with 1.5/2.0 Flows With 1.5, 2.0 gpm/ton flows 2.4/ / / /2.0 Chiller Chilled Water Pump Condenser Water Pump Cooling Tower Total kw

15 Plant Configuration Component Availability Chillers Thermal Storage -- Ice Plate and Frame Heat Exchanger?? Cooling Towers Pumps Combustion Turbines Waste Steam Electric, Gas & Water Cost Most Important -- Fuel Flexibility True Cost of Utilities??? Ton-Hr KW/Ton Chiller Only KW/Ton Plant (towers+pumps++) KW/Ton Campus Each Shift Must Know WIN What s Important Now

16 Dispatch Model Changes with Load Changes with Time of Day Changes with Fuel Cost Changes with Equipment Availability Large investment in Time and $ Large ROI!!! Implications for Operations Integrated concern for operating economics New operating paradigms require Education Cause/effect relationship between buildings/plant requires integrated attitude Hidden building problems will surface Operations become proactive rather than reactive