Introductions John Calcagno-Formosa Account Manager –Sales Engineer/Account Manager-Carrier Corporation –BSME Rutgers University –Over 27 Years HVAC Industry Experience
This presentation applies to typical chiller plants. The type of building or process the plant serves will affect the design. Different criteria for different applications. This presentation will focus on chillers. Chiller Plant Design
Type of application ProcessReliability, durability, life cycle cost Data CenterReliability, life cycle cost, cold condenser water. Health CareReliability, first cost, efficiency Higher Education First cost, life cycle cost OfficeFirst cost District CoolingReliability, life cycle cost
Multiple Chillers Parallel Part Load Flow Reduction Shut down one chiller/pump at part LOAD. But what about the flow?
Multiple Chillers Parallel Part Load Flow Reduction Advantages Redundancy Ability to match load by staging chillers Saves pump energy at part load Disadvantages Significant reduction of flow at part load Chiller production loop is hydraulically tied to chiller consumption loop
Multiple Chillers In Series- Constant Flow Advantages Eliminates temperature mixing and flow problems Full flow at all loads Series/counterflow arrangement-efficiency Disadvantages Flow rate through each chiller is entire system flow- double the flow for parallel chillers Pressure drop is additive-bigger pumps and more energy Part load-pumping water around building not needed Limited to two chillers
Multiple Chillers In Parallel Primary/Secondary System Decoupler pipe
Multiple Chillers in Parallel- Primary/Secondary System Advantages Decouples or separates the chilled water production piping from the chiller water consumption piping Eliminates temperature mixing and flow reduction Part load-match chiller capacity to load Part load-reduced flow Disadvantages More pumps required Moderately complicated controls required Water balancing important
Multiple Chillers In Parallel- Variable Primary System
Multiple Chillers In Parellel- Variable Primary System Advantages Eliminates set of pumps Efficient Disadvantages Must coordinate minimum flow and rate of change with chiller manufacturer Moderately complicated controls
Variable Primary Flow Principles to follow: Confirm chiller vendors minimum acceptable flow rate (may require higher initial design cooler pressure drop) Specify flow meters or DP transmitters to measure/ maintain chiller minimum flows Design bypass for flow rates below minimum Find out what rate of change in flow is acceptable from chiller vendor(s) and put this in sequence of operation Provide ton-hr metering to measure machine capacity for sequencing logic (note, 23XRV speed is directly proportional to capacity, so speed can be used to sequence machines)
Variable Primary Flow – Rate of Change CarrierOther Model23XRV Single Centrifugal Multiple Compressors Rate of Change (%/min) 70%30%10% Minimum Loop Volume (gal)* 4509001,800 Industry Best! * = 300 Tons Comfort Cooling Application
In VPF applications, select a machine with high acceptable rate of flow change and specify rate (in % change/Minute). Compressor response time in VPF system If the evaporator flow to the chiller is halved, the load is halved. If the chiller does not unload quickly enough (VFD, IGV staging), the chilled water temperature will drop and either result in: 1.Recycle (LCWT too far below set point) or 2.Worst Cases, Freeze Trip (LCWT below freeze protection value) or Surge Trip (at least for a centrifugal compressor).
28 System Decisions 0.587 0.560 0.517 0.498 0.520
Summary No right configuration for all plants Must evaluate the design criteria Take advantage of chiller’s modern controls
Helical Rotary/Screw Compressor 2 or 3 Use variable frequency drive to slow down the compressor
Carrier 23XRV – Simple Simple: 3 moving parts No surge No purge No shaft seals No guide vanes No slide valves No EXV’s No chlorine No phase-out No refrigerant pumps No pressurization systems No bearing capacitors to change No pumps, hoses or clamps for VFD No glycol cooling required for VFD No motor heat rejection to the room Given the choice, aren’t fewer worries better?
Centrifugal Compressor Use inlet guide vanes and variable frequency drive for unloading
Semi-hermetic: Motor and Compressor are one sealed assembly. Motor is cooled by refrigerant. Open Drive: Motor and Compressor are separate assemblies. Compressor has shaft seal to contain refrigerant in compressor.
Replacement of open drive shaft seals costs $3000 to $5000 every 3 to 5 Years. “Open drive seals lose 2% of total refrigerant charge annually.” ARI Report 11/98 Shaft Seals-Leakage Source
Motor Cooling From Ambient Air Ventilation vents let contaminants in! (dirt, salt, production debris etc)
Open Drive Design Airborne dirt and contaminants in
Open Drive design Only ONE Major Manufacturer makes an open drive chiller. If a design is used so that it is easy to repair, shouldn’t this cause some concern?
Motor Health Open MotorHermetic Motor Heat – most common cause of premature failure. “Each 10C rise above the rating may reduce the motor lifetime by one half” - NEMA “Class B Rise” results in 120C (248 F) operating temperature. Motors can operate cool enough that insulation is applied to prevent sweating. Dirt – abrasion can cause insulation failure, buildup increases operating temperature Motor completely exposed to dirt, dust and debris in mechanical room as it actively pulls air through the motor internal vents to cool itself. Motor completely isolated inside clean, cool refrigerant boundary, unexposed to mechanical room dirt, dust or debris.
Motor Health Open MotorHermetic Motor Moisture – reduces motor insulation resistance, can cause catastrophic failure. Open motors must be equipped with internal heaters to prevent condensation. Condensation on motor windings is not possible – it is sealed in refrigerant circuit. Vibration – can cause bearing fatigue and failure, or cracks in insulation system and failure. Compressor and motor balanced separately. Coupling can increase balance issues. Compressor and motor dynamically balanced together – no coupling.
Mechanical Room Renovation When you need to install equipment, move a pipe, paint or do some sort of renovation in mechanical room … should you turn your chillers off? No … Run risk that dirt, dust or debris in air will cause motor failure or shorten motor life. Yes … Turn chillers off and cover motor intakes. Provide temporary cooling or no cooling at all.
Semi-Hermetic vs. Open Motors Condensation on motor windings is normal. Moisture degrades insulation resistance. Starting a motor with moisture on its winding can cause insulation failure and require a rewind. To prevent condensation, motor winding heaters are energized any time motors are off. If power to motor and motor winding heaters is lost, a megger test should be performed to confirm insulation strength before starting. All of this costs money. Is your customer willing to pay?
Competitor Open Motor Drive Open motors reject heat to the facility space, which must be tempered (air conditioned) or ventilated to a maximum of 104F indoor ambient to assure design motor and starter life Carrier Confidential Motor Heat Rejection
Competitor Open Motor Drive Open motors require no moisture intrusion at start up. Moisture in windings at start up/after power loss can cause motor failure. Motor Anti-Condensation Heaters Megger motor test required $ for insulation checks by technician after idle periods Strip Winding Heater required to prevent moisture intrusion $ in motor heater equipment costs $$ yearly heater wattage costs
Water Cooled Oil Cooler Requires regular maintenance (scaling/cleaning with acid solution) Additional failure modes created –Oil in water (EH&S safety issue) –Water in oil (catastrophic failure)
Additional Costs for Purchasing Open Drive Design Maintenance and Operating Costs – Weekly – check the shaft seal oil bottle – 3-5 Year - Shaft Seal maintenance cost – Yearly – Motor Air Filter maintenance cost – As Necessary – Top off refrigerant charge – As Necessary – Winding cleaning maintenance cost – As Necessary – Possible Megger Motor maintenance check – Yearly - Mechanical Room Cooling operating cost – Yearly – Strip Heater operating cost Efficiency Comparison –3% for open motor –4% for harmonic filter –1-3% refrigerant loss DID YOU FACTOR AN ADDITIONAL $ IN COSTS FOR YOUR CHILLER Additional Unanticipated Costs –Air Conditioner for Mechanical Room –TEWAC Motor –Harmonic Filter –Storage Tank –Sound Blanket –Motor Heaters
Open Drive vs. Hermetic Home refrigerator is a hermetic design Automobile is an open design Which design requires more refrigerant to be added?
Semi-Hermetic Motor Refrigerant cooled motor keeps motor heat out of the mechanical room Saves $ to cool mechanical room Minimizes alignment, vibration and shaft seal maintenance of open motors Saves $ in maintenance and shaft seal replacement costs Refrigerant cooled motors operate in a clean, cool environment. Saves $ in motor repair costs Hermetic Motor vs. Open Drive Motor
Carrier Corporation announces refrigerant warranty for all new centrifugal chillers sold in USA at Engineering Green Building Conference July 20, 2004. Warranty applicable for all Evergreen centrifugal chillers shipped after October 1, 2004. Carrier will cover refrigerant leaks above 0.1% for the first five years of operation and for the life of the chiller if the owner has a service contract with Carrier Commercial Service. R134a Refrigerant Warranty
Part load performance can be… Part load capacity 90%, 80%, 70%… OR Lower condensing temperature Condenser water off the tower (80, 75, 70 degrees…) Lower outdoor air temp (90, 85, 80 degrees…) Full load is defined as 100% load on design day! All other conditions are part load. What is Part Load?
IPLVORNPLV = 0.01 + 0.42 + 0.45 + 0.12 A B C D A B C D1 1% 42% 45% 12% ECWT 85 75 65 65 ECWT 85 75 65 65 WEIGHT % LOAD 100% 75% 50% 25% ARI Part Load Weighting Factors 99 % ARI 550-590
Compressor Input kW ~ Mass Flow X Lift Load Chiller Cooling Tower Compressor/Cycle Efficiency Like pumps, chiller energy consumption is a function of mass flow and differential pressure. KW = Tons x Lift Chiller Energy
Imagine carrying a backpack of bricks up 55 flights of stairs. Lift Requires Energy 97 F Saturated Condensing Temperature 55 42 F Saturated Suction Temperature
Refrigerant Temperature For refrigerant to condense, it must be warmer than leaving condenser water. 95 F + 2F approach = 97F To boil, refrigerant must be colder than leaving chilled water. 44F – 2F approach = 42F 95F 44F 85F 54F Refrigerant temperatures are based on leaving water temperatures! Lift = 97F-42F = 55F
42 F / 40 PSI 95F /97 F / 120 PSI 80F /82F SAT. LIQUID SAT. VAPOR Refrigerant Effect (Capacity) Compression Heat Rejection Enthalpy SCT Reduced Lift Pressure 42 82 97 SST Lower Lift = Less Work = Lower kW Pressure Enthalpy Chart-LIFT Lift = Sat Condensing Temp – Sat Suction Temp Lift 1 = 97 – 42 = 55 deg F Lift 2 = 82 – 42 = 40 deg F BETTER!!
42 F / 40 PSI 95F /97 F / 120 PSI 80F /82F / 90 PSI 59F /61F /60 PSI SAT. LIQUID SAT. VAPOR Refrigerant Effect (Capacity) Compression Heat Rejection Enthalpy SCT Reduced Lift Pressure 42 82 97 SST Lower Lift = Less Work = Lower kW Pressure Enthalpy Chart-PRESSURE 60 PSI-40 PSI = 20 PSI. Sufficient differential to provide proper refrigerant flow, oil return, and efficient consistent operation.
How centrifugals change speed Flow ~ V, A To increase flow, increase rotor speed (with fixed flow area) Lift ~ V 2 To increase lift, increase speed Power ~ Flow x Lift ~ V 3 Without LIFT reduction, speed can not reduce A reduction in LIFT allows a speed reduction. Lift is a function of the speed squared. Power is related to the speed cubed! V Diameter Flow Area Ideal Fan Laws Dictate the relationship between speed, flow and lift All centrifugal chillers are subject to Ideal Fan Law – Minimum speed approximately 65%, IGV for remainder
SAVINGS FROM COLD CONDENSER WATER Three 1400 ton Carrier 19XRV variable speed chillers Data Center Analyze savings operating chillers with 55 deg F versus 65 deg F and 75 deg F 0.13 $/kwh simple rate Net Present Worth Savings from 55 F vs… ECWT65F75F 20 year life cycle$217,550$468,880
Entering Condenser Water Temperature 570 600 630 643 630 Tons 85 o F 75 o F 70 o F <65 o F 80 o F 550 Carrier Carrier capacity increases as condenser water temperature decreases Additional Capacity
Chiller Heat Recovery Instead of rejecting heat to the condenser water loop, why not use this heat?
79 Heat Recovery Benefits Chillers can transfer heat for as little as 25% of the cost required to create heat with a boiler.
Hot Water Systems How can we capture sufficient heat for useful purposes? Building Heat Service Hot Water Process Heat
Why Heat Recovery? ASHRAE 90.1-2004 Heat Recovery for Service Water Heating, Section § 22.214.171.124 Operates 24 hours a day Total heat rejection exceeds about 400 tons of chiller capacity Service water-heating load exceeds 1,000,000 Btu/h –1,000 bed nursing home or 75 room full service hotel Provide the smaller of: 60% of the peak heat rejection load at design conditions or preheat of the peak service hot water draw to 85°F. Exceptions: Minimum 30% recovery from condenser water heat for space heating or 60% or more of service water heating from site solar or cogeneration, condensate subcooling, or solar panels.
Condenser Water Heat Recovery HEX Captures Condenser Water Heat “Wasted” Heat for Service Hot Water Make-up 85°F Make-up Water Caution: Higher LCWT Increases Chiller Lift, Reduces Efficiency Heat Out Heat In Heat Out
83 Confirming Savings Real World Example i-Vu® Controls on 30XW Heat Machine at Charlotte Factory 30XW