Where possible, pipe diameters can be increased to reduce pumping energy requirements, but the energy savings due to increased pipe diameters must be balanced with increased costs for piping system components. Increasing pipe diameters will likely only be cost effective during greater pump system retrofit projects. Xenergy estimate typical industrial energy savings in the 5% to 20% range for this measure. Adjustable-speed drives . Pumps that experience highly variable demand conditions are often good candidates for ASDs. As pump system demand changes, ASDs adjust the pump speed to meet this demand, thereby saving energy that would otherwise be lost to throttling or bypassing. The resulting energy and maintenance cost savings can often justify the investment costs for the ASD. However, ASDs are not practical for all pump system applications—for example, pump systems that operate at high static head and those that operate for extended periods under low-flow conditions .Refrigeration systems are a significant consumer of electrical energy in the U.S. fruit and vegetable processing industry, particularly in the frozen fruit, juice, and vegetable manufacturing sub-sector . The most significant applications of refrigeration systems in the industry are in the generation of chilled water for various process cooling applications and the in generation of cold air for cold storage and fruit, vegetable, and juice concentrate freezing.

There are four primary components to the typical refrigeration system: the compressor, plastic round plant pots the condenser, the expansion valve, and the evaporator. In the first stage of the refrigeration cycle, refrigerant enters the compressor as a low pressure gas and is pressurized by the compressor into a hot, high pressure gas. The high pressure gas leaves the compressor and is circulated to the condenser. In the condenser, the high pressure gas is cooled via a heat exchanger with a cooling medium , which causes it to condense into a hot liquid. The hot liquid refrigerant then proceeds through an expansion valve, which decreases the pressure of the refrigerant, causing it to cool. The cool refrigerant is then circulated to an evaporator. In the evaporator, the refrigerant accepts heat from its surroundings, causing it to vaporize into a low pressure gaseous state. In direct expansion evaporators, the evaporator coils are in direct contact with the object or fluid that is being refrigerated. In indirect expansion evaporators, the evaporator coils are in contact with a carrier medium, such as water or brine, which is then pumped to the object that is being refrigerated. From the evaporator, the low pressure gas is fed back to the compressor, completing the cycle. Most refrigeration systems in the U.S. fruit and vegetables processing industry use ammonia as a refrigerant. Some favorable properties that make ammonia the refrigerant of choice include its high latent heat of vaporization, its classification as a non ozone-depleting substance, the fact that it is non-corrosive to iron and steel, and because ammonia leaks can often be easily detected by smell .

Because many fruit and vegetable processing operations are concentrated in the warmest months of the year, refrigeration systems must often be operated under heavy loads during daytime hours when electrical costs and outdoor temperatures are at their highest. Energy efficiency improvements to refrigeration systems can therefore lead to significant cost and energy savings in many fruit and vegetable processing facilities. This chapter discusses some of the most significant energy efficiency measures available for industrial refrigeration systems. Measure descriptions are grouped under the following four major categories, based on their applicability: refrigeration system management, cooling load reduction, compressors, and condensers and evaporators.Monitoring system performance. Monitoring systems can help detect refrigeration system performance issues before they become major problems, helping to avoid major repair costs and keeping the system running at optimal efficiency. Monitoring involves the installation of sensors at key points in the refrigeration system, which can be as simple as visual gauges or as advanced as computer-based sensor and control networks. A basic monitoring system should include ongoing measurement and logging of compressor suction and discharge pressures; a drop in suction pressure typically indicates a refrigerant leak, while a rise in discharge pressure can indicate a blocked condenser . Ideally, monitoring systems should also have the ability to provide system and component level information to operating and maintenance staff as well as high-level performance summaries for management.

In a review of energy efficiency opportunities for refrigeration systems in wineries, the energy savings associated with the installation of monitoring systems were estimated at 3% . Ensuring proper refrigerant charge. Low refrigerant charge affects many small direct expansion systems, and, if left unchecked, can lead to significant deteriorations in system performance and energy efficiency over time. Additionally, too much refrigerant charge can also reduce energy efficiency. Galitsky et al. report that a low refrigerant charge or over-charging can increase the energy use of direct expansion systems by as much as 20%. Regular monitoring and maintaining of refrigerant charge is therefore critical for ensuring optimal system performance. The refrigerant sight glass should be checked periodically for bubbles , which can indicate that refrigerant is leaking somewhere in the system . Refrigeration system controls. Control systems can help improve the energy efficiency of refrigeration systems by ensuring optimal matching of cooling demand and component loads. Optimal matching is usually done by monitoring the temperature of the space, object, or media that is being cooled and adjusting the operation of key system components to maintain the desired temperature in the most efficient manner. For example, Doble Quality Foods, a frozen food manufacturer in Cornwall, England, installed electronic controls on the expansion valves of its refrigeration system, which allowed for more precise evaporator temperature control. The control system saved the company £2,150 in annual refrigeration system energy costs with a payback period of just 1.4 years . Fetzer Vineyards, a winery in Hopland, California, experienced even more impressive savings with the installation of an advanced refrigeration control system in 2001. Programmable logic controls and sensors were used to monitor return glycol temperature and pressure, allowing for efficient cycling of the system’s compressors to maintain the desired glycol conditions. The controls installation lowered the winery’s annual electricity use by over 168,000 kWh, saving the company $21,250 per year with a simple payback period of roughly three years . Another important application of control systems is to ramp down or turn off system components during periods of non-use. For example, automatic switches or ASDs can be used to turn down or off system fans and pumps where feasible, with typical payback periods of one year or less .Piping insulation. Pipes containing cold refrigerant should be properly insulated to minimize heat infiltration. Galitsky et al. estimate the typical energy savings attributable to improved piping insulation at 3% with a payback period of less than two years. Minimizing heat sources in cold storage areas. Sources of heat within cold storage areas such as lights, forklifts, motors, and even personnel, should be minimized because the refrigeration system must remove the additional heat that they produce. For example, it has been estimated that up to 15% of the refrigeration load in cold storage is due to heat from evaporator fans, and that lighting heat can add an additional 10% to the refrigeration load . Thus, heat generating equipment should be switched off when not needed. Also, where feasible, product entering the cold storage area should be as close to the desired cold storage temperature as possible .

Reducing heat infiltration in cold storage areas. The infiltration of warm outside air can be reduced through proper door management and the use of tight sealing doors. Door seals should be inspected regularly, hydroponic nft channel as faulty door seals can increase refrigeration system energy consumption by up to 11% . Where strip/walk-in curtains are used, they should be periodically checked to ensure that they are intact and positioned properly. Additionally, doors should always be closed immediately after personnel or forklifts enter and leave the cold storage area; where feasible, doors that close automatically should be considered. In total, the energy losses associated with improper door management in cold storage areas have been estimated at 10% to 20% of the total cooling load .Reducing building heat loads. Refrigeration system compressors in poorly ventilated areas surrounded by warm air will run hotter than necessary, which will reduce compressor reliability and energy efficiency. Compressor areas should be adequately ventilated so that cool air is allowed to circulate around the compressor. Similarly, for air-cooled condensers, an ample supply of cool ambient air is necessary to keep condenser temperatures low. Energy efficiency measures aimed at the building structure, such as the use of adequate insulation and reflective roofing materials, can help reduce the heat load on compressors and condensers, helping them to run efficiently. These building energy efficiency measures and others are discussed further in Chapter 11. Free cooling. Free cooling makes use of outside air for process and building cooling applications when outdoor air conditions are appropriate, which can reduce the load on refrigeration systems. According to Schepp and Nicol , free cooling is suited for locations where many hours are below 40 degree Fahrenheit, and has led to energy savings of up to 15% in some Canadian facilities. Although not expected to be widely applicable in the U.S. fruit and vegetable processing industry, given that most operations are concentrated in warm weather months, this measure might be applicable for plants operating year-round in cold weather climates. The payback can be immediate where outdoor air makeup ducts and ventilation control systems already exist, but can range from two to four years when building retrofits are required . Nighttime air cooling is a form of free cooling, in which cooler outside air is allowed into facility and office areas at night to reduce daytime building heat loads. Properly sized motors. Oversized motors on pumps and fans in refrigeration systems can result in unnecessary energy losses. It has been estimated that correcting for motor oversizing can save 1.2% of motor electricity consumption . Hydrocooling. In hydrocooling, fruits and vegetables are cooled using chilled water just prior to freezing to reduce the cooling demand on freezers. Chilled water is typically produced using a heat exchanger and put into direct contact with the fruits and vegetables, either in shower-type units or immersion-type units. Hackett et al. report that using hydrocooling to cool fruits and vegetables down to just above freezing is much more energy efficient than using the evaporators in freezers to perform the same service. Removal of surface water before freezing. Excess water on the surfaces of fruits and vegetables prior to freezing leads to unnecessary energy consumption in the freezing tunnel because water must be frozen along with the product. The removal of residual water on products prior to freezing can be accomplished by using a vibrating mesh or a perforated belt to convey products into freezing chambers .Geothermal cooling. Geothermal cooling takes advantage of underground temperatures that stay cool and constant throughout the year. Geothermal cooling systems circulate water below ground through a series of pipes where it is cooled by the surrounding earth and subsequently pumped back to the surface. Where feasible, such systems can replace or augment existing refrigeration systems, leading to significant energy savings. In 2005, Aohata Corporation, a jam manufacturer in Japan, began operating a new geothermal cooling system that provided its facility with 260 kW of additional cooling capacity. Water is circulated below ground through a series of pipes placed in 37 holes that are drilled to a depth of 100 meters. The company reported that the geothermal cooling system uses only about 25% of the electricity required by a traditional refrigeration system .Compressor control systems and scheduling. The compressor is the workhorse of the refrigeration system, and the use of control systems to effectively match compressor loads to cooling demands is often a sound strategy for energy efficiency. Control systems can help compressors operate at optimal efficiency by monitoring and adjusting to system flow conditions and by scheduling the operation of multiple compressors to minimize part-load operation . Compressor control systems are discussed in further detail in Chapter 10. Rainier Cold Storage, a cold storage warehouse and frozen seafood products company located in Seattle, Washington, used to run its seven refrigeration plant compressors manually before a computer control upgrade in the early 1990s.