Understanding Head Pressure Control Walter H Langille, M.A.Sc., P.Eng Sales Engineer KeepRite Refrigeration
WE WILL LOOK AT: 1. Why We Need Head Pressure Control? 2. How Do We Control Head Pressure - Methods? 3. EC Electronically Commutated Motors What is an EC Motor? Why use an EC Motor in a Commercial Refrigeration Application? 4. Examine Head Pressure Control Methods In Terms Of: Energy Consumption Sounds Levels Performance & Reliability 5. Compare Methods and Quantify Energy Savings 6. Floating Head Pressure Design/Concepts
WHY WE NEED HEAD PRESSURE CONTROL Constant Head Pressure Is Needed To Ensure: Proper TXV Operation Good Oil Return Optimized System Performance
2. HOW DO WE CONTROL HEAD PRESSURE? 1. Fan Cycling 2. Variable Fan Seed Control (Lead Fan with Fan Cycling or Speed Control ALL Fans) 3. Condenser Flooding 1 Flooding Valve 2 (ORI/ORD) Flooding Valves 4. Condenser Splitting
FAN CYCLING SOURCE: PARKER HANNIFIN Virtually eliminates Heat transfer in off cycled cells There is a lower ambient T limit ( works in warmer regions) Many flare fittings Shock to system when bank cycles off/on Still requires Variable Speed on last Fan (Low Ambient) closest to header
CONDENSER FLOODING 1 (Fixed) or 2 (ORI/ORD-Variable) Flooding Valves Liquid is backed up in the condenser eliminating effective heat transfer area. Section of condenser filled with liquid does not act as a condenser. Provides constant Head Pressure Fan Motors run @ 100% speed Requires More Refrigerant and Larger Receivers Obvious choice for 1 fan condensers Should NOT Cycle Lead Fan Thermal Shock to Header
Condenser Splittting Eliminates Half the tubes and the Secondary Surface SOURCE: PARKER HANNIFIN Slightly more money than fan cycling (Piping & Valves) Saves some refrigerant when only having to flood half the condenser Can be combined with fan cycling
Variable Fan Speed Control Reduced Air flow reduces coil heat transfer effectiveness Benefits are: Reduced Watt consumption ( Energy saving ) Sound reduction ( Lower Sound Power Levels ) Less refrigerant ( Cost Saving ) Technology has limited the confidence in this method Triac controls, VFDs, and now ECM
3. ECM ELECTRONICALLY COMMUTATED MOTORS What is an EC Motor? EC Motors are DC Motors that connect direct to AC mains, EC = Electronically Commutated Integrated AC to DC Conversion and Motor Commutation within the motor body The ECM (Electronically Commutated Motor) is: Programmable - Connect to Controller / BMS Ultra High Efficiency Brushless DC motor which uses a permanent magnet rotor and a built in inverter. DC motors are significantly more energy efficient than AC motors and much easier to control. Typically 0 to 10v DC Signal
AC Motor Construction Rotor Rotor conductors Air gap Stator Stator windings
DC Motor Construction Permanent magnet Rotor Commutation Stator Stator windings
Electronically Commutatted ( EC) Motor AC to DC conversion Rotor Permanent magnet Stator AC mains input Commutation
Efficiency Why use an EC Motor in a Commercial Refrigeration Application? 1. Regulatory Compliance Effective January 1, 2008, California Energy Commission (CEC) Title 20 will require all new unit coolers used in walk-in coolers and freezers to be equipped with EC motors. Other states are also considering this legislation and will likely adopt similar language within the next few years.. 2. Energy Efficiency EC motors are much more efficient than PSC or Shaded Pole motor offerings. EC motors are up to 75% to 80 % efficient that s a 51-59% increase over shaded-pole motors and a 30-35% increase over permanent split-capacitor (PSC) motors. Additionally, these motors run cooler than PSC or shaded pole motors, introducing less heat into the refrigerated space and further increasing energy savings. Typical motor efficiency for a 50 W motor 100 80 60 40 20 0 Shaded pole single phase capacitor three phase EC Motor type
Features and Benefits of EC motors > Efficiency > Noise (Low Sound Power Level) > Straight Forward Speed Control (DC) > Energy Savings
4. Head Pressure Control Methods In Terms Of: Energy Consumption Sounds Levels Performance & Reliability
ENERGY CONSUMPTION SOURCE: EBM PAPST
SOUND LEVELS SOURCE: EBM PAPST
PERFORMANCE & RELIABILITY
TRIAC (P-66) CONTROL & FAN CYCLING Condenser Mains (230V or 460V or 575) Most cost ( capital ) effective Poorest performance (High heat generation at low speeds) Capillary tube leak potential issues
AC INVERTER SYSTEM (VFD s) Motor Filter Fan Motor Condenser inverter 0-10V / 4..20mA Pressure Sensor Line Filter EMC filter Most complex Good Energy savings Can be very labour intensive on the jobsite, higher installation cost Motor reliability (Especially for 575V) an issue mains
EC MOTOR SYSTEM (Factory Controls) Condenser mains 0-10V 0-10V 0-10V pressure sensor 0-10V / 4..20mA No Filters Easier to understand & setup More reliable Best energy savings
EC MOTOR SYSTEM (Controls by others) Condenser mains 0-10V 0-10V 0-10V 0-10V / 4..20mA From Rack Controller
LETS INVESTIGATE FURTHER MOST COMMON APPLICATIONS AIR COOLED CONDENSERS FAN CYCLING vs. EC MOTORS AIR COOLED CONDENSING UNITS FLOODED SYSTEM vs. EC MOTORS
Payback on 8 EC Fan Condenser < 1 Year 66 dba 65 dba 4.5 X less energy or 80% Savings 59 dba 52 dba SOURCE: KEEPRITE REFRIGERATION ENGINEERING
Let s Quantify -85% vs. 1140-70% vs. 850-50% vs. 550 @ Typical Op Range 76 dba 68 dba 60 dba 56 dba SOURCE: KEEPRITE REFRIGERATION ENGINEERING
5. Let s Quantity Further ENERGY SAVINGS (BIN ANALYSIS) VS. AC Motors with Fan Cycling EC Fan Motors with Fan Speed Control ( All Fans )
Philadelphia, PA 67% LESS ENERGY = 58,307 kwh @ $0.10/kWh = $5,831 Payback 2 years*** ***Depending on location
Let s Quantity Further ENERGY SAVINGS (BIN ANALYSIS) AIR COOLED CONDENSING UNITS 2 HP System - Cooler VS. Flooded System for HPC Variable Speed EC Fan Motor for HPC
ENERGY SAVINGS (BIN ANALYSIS) 2 HP COOLER w/ FLOODED VALVE
SAME ENERGY BIN SAVINGS ANALYSIS (BIN ANALYSIS) AS BEFORE 2 HP COOLER w/ Variable Speed EC -2934 -$235 +32%
WHAT MAKES EC MOTOR SO SPECIAL HIGHEST EFFICIENCY AT REDUCED SPEED LOW HEAT GENERATION AT LOW SPEEDS ABILITY TO REDUCE TO LOWER SPEEDS SOFT STARTS AND NO START UP TORQUES ABILITY TO BE CONTROLLED BY LOW VOLTAGE SIGNAL HIGHEST RELIABILITY IN LOW AMBIENTS GIVES MORE ENERGY SAVINGS AND MORE RELIABILITY SIMPLE TO INSTALL AND UNDERSTAND CONVENIENCE OF SETTING ADJUSTABLE HEAD PRESSURE
Capacity TONS Power input kw 6. Floating Head Pressure Design / Concepts Allowing Head Pressure ( Condensing Temperature ) in Refrigeration Systems to operate at reduced levels ( Float Down ) during periods of Low Ambient can result in: Increased Compressor Efficiency 13.5 13 12.5 Capacity / Power Input at +40 F Evap T Q P 14 13 12 11 12 10 Lower Compressor Motor Amperage (Power Input ) 11.5 11 10 85 105 125 Condensing T F 9 8 7 6 NEEDED TO MEET ENERGY AND GREEN DEMANDS NEED TO MEET CURRENT AND FUTURE LEGISLATION (CALIFORNIA TILTE 20 & 24, EISA 2007 etc)
Floating Head Pressure Design / Concepts WHAT NEEDS TO BE DONE? ELIMINATE FLOODING VALVE FOCUS ON CONDENSER FIND WAY TO OPERATE AS LOW AS POSS. REFRIGERANT SAVINGS X ENSURE 100% LIQUID @ TXV ENSURE PROPER APPLICATION / BALANCE AT EVAP OPTIMIZE BTUH/W ADEQUATE SUPERHEAT AT COMP
Floating Head Pressure Design Concepts When Ambient T is below the design Ambient T we can take advantage of the greater condenser capacity. We can benefit by lowering the head pressure ( Float Down ) and get more compressor capacity To a point! IF Head Pressure is allowed to fall below certain Minimum Values System Performance can be adversely affected in the following areas: 1. Starving Evaps by Underfeeding TXV s 2. Oil Return / Oil Logging 3. Compressor Efficiency and Higher Discharge T s / Super Heat
Floating Head Pressure Design/Concepts 1. Starving Evaps by Underfeeding TXV s Lowering Head Pressure (Cond T) results in a ΔP reduction which will DECREASE TXV Capacity Lower Condensing T ( Lower Liquid T) will INCREASE TXV Capacity The effect of LowerΔP - (Reduced Valve Capacity) and Lower Liquid Temperature ( Increased Valve Capacity) Will tend to offset each other without any significant change in TXV Capacity Lower Head Pressure requires less motor current and increases compressor efficiency. There is a Limit If Lowered Too Far the TXV Capacity will not be able to meet Evaporator load Starving the Evap of Liquid Refrigerant Reducing Evap Capacity.
Floating Head Pressure Design/Concepts 2. Oil Return / Oil Logging Refrigerant and Oil do not mix completely For all the Oil to return properly to the compressor requires a minimum refrigerant velocity in the suction line (particularly the riser). If the Evap is starved ( from lower head pressure, available ΔP) the refrigerant mass flow in the evaporator will start decreasing. If the velocity is too low refrigerant will not return to the suction riser It will LOG in the Evaporator. Oil logged in the evaporator will coat the inner wall of the coil and reduce heat transfer through the walls. This will cause a loss of capacity and poor performance and may rob the compressor of oil for lubrication.
Floating Head Pressure Design/Concepts 3. Reduced Compressor Efficiency and Higher Discharge T s Specific Volume of the refrigerant vapour will decrease as the T rises. Compressor will pump the same volume of refrigerant but the mass flow will decrease reducing the effective pumping capacity Increasing the suction vapour T will result in higher Discharge T s Suction vapour entering the compressor Will be warmer as well. High superheats @ Evap outlet Means If TXV is underfed high Evap superheats can result Underfeeding the TXV will reduce the Load on the Compressor HOWEVER It will cause the Compressor to operate Less Efficiently at the Higher Discharge Temperatures
FLOATING HEAD CONSIDERATIONS Reducing Head Pressure Lowers the Operating Expense of the Compressor Potential For Lots Of Savings (Up to Approx. 30%) The determining factor for deciding what the minimum allowable Head Pressure should be is the minimum TXV ΔP required for it s capacity to meet the demands of it s Evaporator Load System Head Pressure Controls then adjusted to maintain that minimum. Standard JCI Controls A SYSTEM CONFIGURATION THAT CAN OPERATE IN A WIDE RANGE OF AMBIENTS AND SAVE ENERGY AND REFRIGERANT
FLOATING HEAD CONSIDERATIONS / FINDINGS Potential for Reduced Amount Of Refrigerant EC Fans + Condenser Splitting Low Ambient T s May Need To Still Consider Use of Flooding Valve(s) Balanced Port TXV Will Work Many Locations & Applications HOWEVER EEV Is Recommended for System Optimization & Especially For Proper Operation in Low Ambient T Be Aware Of Your Ambient T and Compressor Limitations Lowest condensing temp is not necessary optimal Liquid -Suction Heat Xer Needed To Ensure Pure (100%) Liquid at Evap
Standard fixed port valve does not cut it, balance port is better Additional hpc needed for lower ambient (EC as variable) Lowest condensing temp is not necessary optimal Too much capacity leads to high TD s and low humidity levels High TD s will effect product integrity and amount of condensate on the coil (icing issues) SLHX needed to ensure 100% liquid EEV s increase operating envelope of operation but does not resolve the issue of too much capacity! More system modification needed to allow to operate in lower ambient...ori/ord? 40
Thank You For Your Attention NOW Questions / Discussion / Input