50Low- and. No-Cost Tips for Saving Energy INDUSTRIAL REFRIGERATION ENERGY EFFICIENCY

Transcription

1 50Low- and No-Cost Tips for Saving Energy INDUSTRIAL REFRIGERATION ENERGY EFFICIENCY

2 LOW- AND NO-COST SOLUTIONS THAT INCREASE ENERGY EFFICIENCY If you pay the power bill at an industrial cold storage or food distribution center, you know that refrigeration systems never stop CONSUMING ENERGY. As the largest electrical energy consumers in cold storage or distribution facilities, REFRIGERATION SYSTEMS should be a major savings target for spend-weary corporations. Yet, in today's economic climate where budgets for capital projects are small or non-existent, finding ways to reduce your energy spend can be a challenge. THE SOLUTION? Driving energy savings through low- or no-cost operations and maintenance activities. This ebook offers FIFTY of the best opportunities for CONTENTS 1 Evaporator Opportunities 2 Compressor Opportunities 3 Evaporative Condenser Opportunities 4 Control System Opportunities 5 System Opportunities 6 Systems Influencing Refrigeration Load achieving savings at little or no capital cost. SAFETY ALERT The improper execution of the activities outlined in this ebook could result in poor system performance, property damage, product quality issues, and serious bodily harm. Put safety first. Get qualified third-party contractors or certified refrigeration operators to implement the O&M actions in this guide, if your staff does not have the expertise LOW- AND NO-COST TIPS FOR SAVING ENERGY: REFRIGERATION SYSTEM

3 EVAPORATOR OPPORTUNITIES Cleaning Coils Evaporator coils should be regularly inspected and cleaned, particularly in docks or production areas where dirt, cardboard dust, rubber tire particulate, and other contaminants are common. Dirty coils may prevent a space from achieving temperature, force the system to run at lower suction pressure, or hinder evaporator fan cycling or variable frequency drive (VFD) control effectiveness. Dirty coils may not defrost well. Tune Overfeed Rates Systems with liquid recirculation (also called overfeed) design utilize hand expansion valves to meter liquid refrigerant at a 3:1 or 4:1 overfeed rate. If the valve is throttled too low, the coil will starve. If the valve is too open, the evaporator will brine. Adjust the valve to provide the maximum air temperature drop across the coil. Adjust Defrost Relief Regulators Hot gas defrost is often managed with a gas relief regulator at the coil exit to maintain a target pressure within the coil during the hot gas phase of the cycle. If this regulator is set too low, the defrost will be too long (due to low refrigerant temperature) and the regulator will freely allow gas to pass and load the engine room. If the regulator is set too high, this may force the system s minimum condensing pressure to be set higher, or cause steaming during defrost. A reasonable target is pounds per square inch gauge (psig) for ammonia systems. 4 Adjust Master Hot Gas Regulator Some systems utilize a master hot gas pressure regulator to maintain consistent pressure in the main hot gas header serving the coils. Pressure that is too high in the main header, results in excessive coil temperature and increased false loading in the engine room. The minimum system condensing pressure must be set at least 5-10 psig above the master regulator set point. A reasonable target pressure for the master regulator is psig for ammonia systems. A service provider should ensure coils are clean and clear of heavy frost before tuning LOW- AND NO-COST TIPS FOR SAVING ENERGY: REFRIGERATION SYSTEM

4 EVAPORATOR OPPORTUNITIES Remove Oil In most systems, any oil that migrates from the compressor eventually ends up in low-pressure receivers or evaporator coils. Oil in evaporator coils hinders cooling, and makes it extremely difficult to achieve a complete defrost at the bottom of the coil. Ice builds up and may eventually bridge to the defrost pan. It is important to remove this oil. Repair Valves and Regulators It is important that hot gas solenoids fully close and do not leak hot gas into the liquid or suction line. Also, regulators should fully close, as well as smoothly and consistently maintain target pressures. Remove Aging Ductwork Older system designs included wooden or metal ductwork to distribute air flow throughout a space. Unfortunately, this ductwork cannot be cleaned and may also prevent cleaning the evaporator coil fans (usually centrifugal) and coil surface. Modifying or removing this legacy ductwork can dramatically improve zone temperature management and system efficiency. Tuning Pressure Regulators Some evaporator coils or process heat exchangers (e.g., water or glycol chillers) are equipped with fixed or dual-pressure regulators. Ensure that the regulators are set for the greatest temperature difference allowed by system limitations (such as freeze protection, high humidity, etc.). Consult the original design engineer or contractor to determine the limits of the application. Differing frost patterns on valves during a given mode of operation indicates inefficiency LOW- AND NO-COST TIPS FOR SAVING ENERGY: REFRIGERATION SYSTEM

5 COMPRESSOR OPPORTUNITIES Solve Current Limiting / Forced Unloading Screw compressor microprocessor panels usually include settings to prevent overloading of the motor. If the panel sees motor current driving above nameplate or the service factor, the compressor will stop loading or even unload. This causes the compressor to lose efficiency by running in an unloaded condition. This may force the control system or operators to fire off another compressor to supply capacity. Use a clamp-on current meter to ensure that the current reading of the compressor microprocessor is correct. Also ensure that the current limiting parameters in the panel correctly match factory recommendations for stop-load or force-unload settings. It is not uncommon for current transformer (CT) multipliers to be in error or for the incorrect current limiting parameters to be entered into the controller. Most modern screw compressors have a microprocessor panel and control sensors, both of which must be calibrated correctly or else compressor performance can suffer. Ensure Economizer Operation Ensure that economizer ports function properly. The economizer pipe should be cold to the touch when the system is operating. Most economizers have a pressure regulator; ensure that the regulator is set to its factory recommended level. Most microprocessor panels will disable economizer function below a prescribed slide valve position (e.g., 75%) since economizer port gas is open to main suction pressure as the compressor unloads. Ensure that this setting is correct. It is not uncommon for a failure on the microprocessor board, or a failed economizer solenoid to prevent function altogether. Auto VI Feature Some screw compressors have automatic volume ratio controls. This matches the compressor internal compression ratio to the external system pressures to prevent over or under compression and loss of efficiency. Ensure the auto VI system is calibrated and operating correctly. If an external control system is managing compressor VI, ensure the system is calibrated and functioning properly LOW- AND NO-COST TIPS FOR SAVING ENERGY: REFRIGERATION SYSTEM

6 COMPRESSOR OPPORTUNITIES Manual VI Feature Other screw compressors may be equipped with a manually-adjustable volume ratio feature. Read the factory operating manual to determine the proper VI setting. Repair Shaft Seals Repair any leaking compressor shaft seals, ESPECIALLY systems operating in a vacuum. Air entering the system will impact condensing pressure, place a burden on the purging system, and introduce water into the refrigerant charge. Avoid Excessively Low Cut-Out If compressor cut-out suction pressure is set too low, a compressor may not turn off under extremely low-load conditions. The compressor will simply pull down to extremely low suction pressure and draw fully-unloaded power. If the compressor is set up this way on purpose (e.g., it has problems starting, see below), resolve this issue. Solve Starting Issues If a compressor cannot reliably start and stop, it may be tempting to operate it in an unloaded state to avoid the problem. Instead, resolve the issue that prevents reliable starting, whether the issue is with the motor starter or controls. If the concern is excessive motor restarts, consult with the compressor or motor manufacturer to determine the minimum allowable anti-recycle time to allow the compressor to restart promptly and avoid system disruption. Critical set points for compressors include economizers, pressure sensors, VFD settings, current transducers, and compression ration settings LOW- AND NO-COST TIPS FOR SAVING ENERGY: REFRIGERATION SYSTEM

7 EVAPORATIVE CONDENSER OPPORTUNITIES 16 Unplug Spray Nozzles Regularly inspect evaporative condenser spray nozzles to ensure nozzles are not plugged. 17 Water Treatment It is critical that water be treated for solids and biological content. It only takes a small amount of buildup on condenser tubes to dramatically reduce capacity (e.g., 1/16 of calcium carbonate can reduce condenser capacity by nearly 50%). Hold your water treatment contractor accountable for system performance. This will require regular inspection of condenser tubes. Good water treatment is critical to avoiding scaling on the tubes that causes a reduction in performance Water Pressure Although tempting, increased water pressure does not improve evaporative condenser performance. Most condensers are designed with modest water pressure at the header, perhaps 3-6 psi. Install a glycerin-filled 0-15 psig gauge in the condenser water distribution header and throttle the condenser pump to deliver the correct pressure. If substantial throttling is required, have the pump impeller trimmed to provide the proper amount of pressure for the application. Clean Strainers Regularly inspect and clean the condenser sump pump inlet strainer. A plugged strainer will reduce condenser capacity and waste pump energy. Adjust Sump Water Level Ensure that condenser sump float level is correct and that water level is not too low. Low water level can result in poor pump performance and water flow. Plugged Fill or Drift Eliminators Regularly clean fill material on induced draft condensers and drift eliminators on most condensers. Otherwise, reduced air flow will impact condenser performance. Address Non-Condensables Ensure the purger is working properly and that air is being eliminated from the condenser. Do this by measuring pressure and temperature at the condenser to verify the values correspond LOW- AND NO-COST TIPS FOR SAVING ENERGY: REFRIGERATION SYSTEM

8 EVAPORATIVE CONDENSER OPPORTUNITIES Tension Belts Check condenser fan belt tension to ensure there is no slip. Slip will reduce air flow and waste fan energy through the slip itself. Address Recirculation or Bad Environment Poor condenser configuration may result in warm, moist exhaust air from one condenser being drawn into a neighboring condenser. Poor rooftop layout may result in a boiler blow-down stack or process exhaust air stream placed near the inlet to a condenser. In all cases, address the issue to relocate, raise, or otherwise reduce moist or warm air entering the condenser. Correct Poor Drift Eliminator Strap Configuration To properly inspect condenser performance, hold-down straps must be loosened to allow drift eliminators to be removed. In some cases, these straps are configured so that they re difficult or impossible to remove. Reorient, or otherwise modify the strapping system to correct this issue. Wet vs. Dry Operation Evaporative condensers are inefficient when operated dry, particularly when ambient temperatures are above F. Ensure that condensers are properly winterized (sump heaters, heat trace, etc.) so they safely operate wet down to F ambient. Sump Heaters Ensure any electric sump heaters (often 10 kw, 20 kw or more) are functioning properly. Failed or incorrectly adjusted thermostats can result in inappropriate energy use by the heaters, and heating of the water that elevates discharge pressure. Proper maintenance helps avoid the top threats to condenser performance: non-condensable gases, scale on the tube bundle, and poor spray-water dispersion LOW- AND NO-COST TIPS FOR SAVING ENERGY: REFRIGERATION SYSTEM

9 CONTROL SYSTEM OPPORTUNITIES Zone or Process Temperatures Warehouse cooler or freezer temperatures should be set at an appropriate value as determined by product or customer requirements. Product, glycol, or other process temperatures should not be set lower than required. This may seem obvious, but systems are often set to maintain lower temperatures than necessary. Suction Pressure Raise system suction pressure to the highest allowable value (which is usually dictated by the worst-case temperature zone or process load). Note that this will affect evaporator fan cycling or VFD control, so some optimization may be in order. Condensing Pressure Operate the system at the lowest allowable minimum condensing pressure set point. If a system can be operated as low as psig (for ammonia) without problems, this is a reasonable target. Note that Fine-tuning control systems and using them to take advantage of demandresponse programs or varying utility rate schedules can be a considerable source of energy and cost savings. defrost, freezer floor heat, liquid injection performance, and compressor oil carryover are potential barriers to reduced minimum condensing pressure. Discuss possible limitations with the equipment manufacturer, refrigeration contractor, and system operators. Condenser Wet Bulb Approach If the control system offers a condenser wet bulb approach control feature, activate it and target an approach in the degree range. The optimum value may require experimentation. This feature ensures an appropriate balance of condenser capacity relative to refrigeration load and compressor operation. Evaporator Fan Cycling If the control system offers an evaporator fan cycling feature, activate it. In some cases, a swirl feature will operate the fans a minimum duty cycle to mix room air. Set up the swirl feature for the minimum required. If the control system has separate cut out and cut in set points for liquid solenoids and fans, energy savings is maximized when the cut in and cut out set point is the same for the solenoid and fan control LOW- AND NO-COST TIPS FOR SAVING ENERGY: REFRIGERATION SYSTEM

10 CONTROL SYSTEM OPPORTUNITIES 33 Condenser Staging Operate the most efficient condenser in the lead list first. Generally, the most efficient condensers are axial fan units with integral sumps. Centrifugals are less efficient, as are those with remote sump pumps or limitations to operation during frigid weather. Evaporative condensers are most efficient when wet with air flow at mid-range fan speeds. Avoid turning all system pumps on first, and then starting to add fans. Turn on a condenser pump, then the fans, then the next condenser pump, then fans, etc. The goal is wet with air movement for the greatest efficiency. 34 Defrost Schedule If the control system only offers a fixed defrost schedule, experiment with the number of defrosts per day to minimize defrost count. Do not let frost build up so much that it becomes difficult to achieve a full, clean defrost. There is no rule of thumb for defrost interval many coils can operate 8-16 hours or more between defrosts. In dry climates, it is not uncommon for evaporators to be defrosted only once or twice a week. Make sure the winterizing heat trace and sump heaters are functioning so the system performs well in frigid weather Defrost Initiation If the control system offers a liquid run-time feature or frost sensors, use this feature to initiate defrost only when necessary. Defrost Pump Down Ensure that all liquid is fully boiled out of the evaporator coil before hot gas is introduced. Watch a coil closely during a test pump down and measure fin temperature with a laser thermometer, or watch air temperature drop to determine when a coil is completely dry. This may require minutes for a frosted coil or one with VFD control operating at reduced speed. Defrost Hot Gas Duration Most evaporator coils should be able to clear all frost with minutes of hot gas. If you find a coil needing 45-60, or more minutes of hot gas to clear all frost, there is probably something wrong that should be addressed (e.g., hot gas regulator pressure, inadequate pump down, etc.). Transducer & Sensor Calibration Use an ice bath to calibrate key zone or process temperature sensors. Calibration pressure gauges ensure that the pressure transducers, used by a central control system, are properly calibrated. You may need to adjust offsets in the control system or even replace a failed pressure transducer. For compressors operating off their local microprocessor panels, calibrating control pressure transducers is critical (particularly suction) LOW- AND NO-COST TIPS FOR SAVING ENERGY: REFRIGERATION SYSTEM

11 CONTROL SYSTEM OPPORTUNITIES Poor Ambient Probe Location If a control system ambient temperature probe is located in direct sun, the probe will not read properly. This is particularly important when utilizing a condenser wet bulb strategy. Frigid Weather Condenser Strategies Many central control systems can turn off condenser water pumps (or drain condenser sumps) during frigid weather for freeze protection. It is important that these set points be set at reasonable values to minimize dry operation of the condensers. 41 Tune Internal VFD Parameters For evaporator and condenser fans, the most efficient VFD configuration is typically a low carrier frequency and a square or variable torque curve. There may also be energy-saving features or settings that can improve efficiency. The best method is to measure VFD input power with an appropriate power meter and experiment with these parameters to obtain the minimum power. All VFDs have internal parameters such as carrier frequency, torque curves, minimum and maximum speeds. It is vital that VFDs do exactly what the control system tells them to Optimum Evaporator VFD Strategies In general, evaporator fan VFDs can be operated with a minimum speed in the range of 40-50%. There is little additional savings from going slower. Limiting evaporator maximum speed to 90 or 95% can add savings with very little impact on net evaporator capacity. Liquid feed or pressure regulators should stay at full capacity until the fan VFDs are at minimum speed. Simultaneous speed control will save more energy than sequential ramping of speed when there are multiple coils in the zone. Optimum Compressor VFD Strategies Compressor minimum speed is dictated by compressor or motor limitations, typically in the range of 20-50%. Consult the manufacturer for proper settings. In nearly all cases, the compressor micro-processor manages the VFD and slide valve. Speed should be reduced first. Once at minimum speed, then the slide valve can be closed. Avoid simultaneous adjustment of speed and slide. Optimum Condenser VFD Strategies Implement pump and fan staging, minimum and maximum fan speeds to target the general strategy of wet with air at mid-range speeds. Mid-range can be defined as 30 to 80% speed. Once all condensers are online, fan speed can be allowed to rise to 100% LOW- AND NO-COST TIPS FOR SAVING ENERGY: REFRIGERATION SYSTEM

12 SYSTEM OPPORTUNITIES Purger Performance Ensure that the purger is operating properly. The purger counter should show a reasonable level of purging, but note that no system is perfect. There are control fuses, check valves or solenoids that can fail and prevent proper operation. Water in the System Regularly test the system refrigerant for excessive water content. Excessive water will change the properties of the refrigerant and substantially reduce system performance and efficiency. Pump Drum Tuning A gas pressure system (also called a Phillips or Pumper Drum System) has a number of critical pressure control regulators. Flash gas from a controlled-pressure receiver (CPR) or low pressure vessels should be properly routed to an appropriate suction (or economizer ports). Any hot gas supply regulators should be carefully adjusted to prevent false loading of the system. Liquid transfer units (LTUs) that utilize hot gas for dumping and liquid transfer should be carefully set up to avoid false loading of the system. Set CPR pressure to the lowest allowable value to maximize subcooling and prevent the CPR from acting as a barrier to minimum allowable condensing pressure. Repair Faulty or Leaking Float Drainers Liquid float drainers may be installed on main hot gas defrost headers, individual evaporator defrost relief, under-floor glycol heat exchangers, or other applications. If the float drainer is leaking hot gas, it will false load the system. Ensure that all liquid drainers are functioning properly. Water in a refrigeration system dilutes and impacts the boiling point of the system s ammonia. A water removal system or hybrid air/water purger should be installed to maximize efficiency LOW- AND NO-COST TIPS FOR SAVING ENERGY: REFRIGERATION SYSTEM

13 SYSTEMS INFLUENCING REFRIGERATION LOAD Door Performance Dock, cooler, or freezer door performance directly impacts refrigeration load and defrost requirements. Door seals, door defrost heaters, sensors, closing delays, and other characteristics are extremely important to minimizing refrigeration load. If re-circulatory air doors are used, proper control of air heaters (electric or hot gas), adjustment of air flow directional vanes, and clean return air screens or grates are key to efficiency. Lighting Performance Warehouse lighting controls, including motion sensors, bi-level control on high-intensity discharge lighting, manual or time clock controls all directly impact refrigeration load. Every watt of light fixture power ends up as refrigeration load in the space. Ensure that freezer under-floor heating systems are set to the minimum required ground temperature to prevent heaving. This should be carefully considered and implemented. Install motion controls and set sensor time delays to the minimum allowable delay for facility use patterns, safety, and manufacturer specifications LOW- AND NO-COST TIPS FOR SAVING ENERGY: REFRIGERATION SYSTEM

14 POINTS TO CONSIDER THINK ABOUT THE FOLLOWING AS YOU PURSUE LOW- AND NO-COST EFFICIENCY GAINS: Be willing to experiment while maintaining system stability and reliability. Every refrigeration system is unique and displays its own quirks and character. For this reason, each system must be poked, prodded, and otherwise forced to show its limitations and capabilities. It is important to remember that functional does not imply efficient. In most cases, a well-tuned and properly maintained system is more efficient. A small group of people dictates the energy use for the refrigeration system. These people are critical to reducing energy use. You must understand more than how a refrigeration system operates. It is important to understand what drives the energy use for each component or system in a way that allows you to make wise decisions regarding configuration, set points, and strategies. Consider a taking class that focuses on efficiency to improve your understanding and skill set. It is possible that there are misconceptions that have been passed on by other system operators, contractors, or vendors that are limiting efficiency of the system. Ask questions, do research, and talk to experts. Trust but verify. Design conditions are just that information used to select components and configure the system. Often, design conditions are not intended for day-to-day operation, particularly when pursuing efficiency gains. Avoid clinging to these values unless there is a strong, reasonable, or justified case. Some system inefficiencies or barriers can only be seen during certain seasons. For example, high condensing pressure may only manifest during the summer whereas limits to system minimum allowable condensing pressure may only be addressed during winter. If you utilize a third-party contractor to operate or maintain your system, the contractor must be involved in pursuit of energy efficiency. Implement processes, goals, or requirements to ensure alignment and accountability LOW- AND NO-COST TIPS FOR SAVING ENERGY: REFRIGERATION SYSTEM

15 Cascade Energy provides corporations and utilities with the industrial strength expertise needed to realize their energy efficiency potential. With a full complement of services and engineering know-how based on 20 years of hands-on experience, Cascade has a proven track record of reducing industrial energy consumption and costs. 20 YEARS Deep, hands-on technical expertise over a 20-year span. 2,000 PROJECTS Analyzed and implemented more than 2,000 energy efficiency projects. 350 SITES Monitor energy performance at over 350 industrial sites. 250 FACILITIES On-site tune-up and retrocommissioning at over 250 industrial facilities. INDUSTRY EXPERTISE Refrigerated storage Food processing and distribution Pulp and paper Oil and gas Steel and heavy industry High technology Water and wastewater Chemicals Manufacturing Agriculture SYSTEM EXPERTISE Refrigeration Compressed air Fans, pumps, blowers Manufacturing processes Controls and VFDs Chillers Cooling towers HVAC systems Thermal systems Lighting TALK TO CASCADE ENERGY TODAY! cascadeenergy.com energysensei.com info@cascadeenergy.com EBOOK REV 24-MAR-2013