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Technical Papers33rd Annual Meeting International Institute of Ammonia RefrigerationMarch 27–30, 20112011 Industrial Refrigeration Conference & Heavy Equipment ShowCaribe RoyaleOrlando, FloridaACKNOWLEDGEMENTThe success of the 33rd Annual Meeting of the International Institute of Ammonia Refrigeration is due to the quality of the technical papers in this volume and the labor of its authors. IIAR expresses its deep appreciation to the authors, reviewers and editors for their contributions to the ammonia refrigeration industry.Board of Directors, International Institute of Ammonia RefrigerationABOUT THIS VOLUMEIIAR T echnical Papers are subjected to rigorous technical peer review.The views expressed in the papers in this volume are those of the authors, not the International Institute of Ammonia Refrigeration. They are not official positions of the Institute and are not officially endorsed.International Institute of Ammonia Refrigeration1001 North Fairfax StreetSuite 503Alexandria, V A 22314+ 1-703-312-4200 (voice)+ 1-703-312-0065 (fax)2011 Industrial Refrigeration Conference & Heavy Equipment ShowCaribe RoyaleOrlando, Florida© IIAR 20111AbstractOne method of reducing system charge is through the use of secondary coolants. There are a number of advantages that can be realized including close humidification control, minimization of airborne contaminants, and elimination of the defrost cycle. This paper demonstrates the system and offers details of operation.Technical Paper #1Minimize Refrigerant Charge Using LiquidDesiccant DehumidificationMike HarveyNiagara Blower CompanyBuffalo, New Y orkMinimize Refrigerant Charge Using Liquid Desiccant DehumidificationReduced charge refrigeration systems which use desiccant technology can offer additional benefits such as:• Increased safety• Energy recovery• Sanitized air• Opportunity for LEED credit• Humidity controlIntroductionEnvironmental, regulatory, and economic concerns are driving industrial facilities to design refrigeration systems which utilize the smallest refrigerant charge possible.Light commercial and comfort conditioning systems already have relatively small refrigerant charges by using packaged rooftop equipment or using chilled water as a secondary coolant. However, process air conditioning system applications for food-related plants (including meat and poultry processing, processed foods production,and brewing) and cold storage facilities have to date, primarily used distributed refrigeration systems. One method to reduce the system charge is by eliminating refrigerant distribution piping and replacing it with the distribution of secondary coolants, which are cooled by a low charge central chilling refrigeration system.While this type of system obviously has the advantage of lowering refrigerant charges, there are several other benefits which can be derived.Distributed Refrigerant SystemsDistributed refrigerant systems (shown in figure 1) utilize three basic connected components to provide cooling; an evaporator, a condenser and a compressor.In order to carry the necessary refrigerant between the components, industrialsystems have extensive piping loops throughout each conditioned space which are Technical Paper #1 © IIAR 2011 32011 IIAR Industrial Refrigeration Conference & Heavy Equipment Show, Orlando, Floridaoften occupied. The piping system and each of the components carry refrigerant,sometimes in very large volumes. In addition, distributed refrigeration systems canhave relatively high maintenance costs associated with refrigeration replenishmentand leak control. But distributed refrigerant systems have many advantages such as low cost for refrigerant distribution (pumping power), close approach temperatureswhich result in good overall system efficiency, and the availability of hot refrigerant gas for defrost cycles. Large distributed systems with 10,000 lbs of ammoniarefrigerant require regulatory programs to address health and safety. Concernsurrounding these regulatory issues has created a demand for designs which allowfacilities to carry less refrigerant, but do the same work.Countless food-related facilities require air to be delivered at or below freezingtemperatures. The additional costs associated with coil defrost cycles, such asadditional refrigerant piping, controls repair and the frequent cleanings necessaryto minimize microbiological/bacteria growth on the evaporator coils can becomesignificant. Although defrost efficiencies of 20% are possible with hot gas, almost one third of the ice melted will sublimate and be reintroduced to the space.Secondary RefrigerantsOne common alternative to reduce refrigerant charge is the use of a primary/secondary refrigeration loop (Figure 2). With this approach, the primary refrigerantcharge remains in the equipment room and the secondary coolant is piped to andfrom the processing room air handling equipment. There are several inexpensiveand proven secondary coolants available, including various glycols and halide saltsolutions. Salt solutions have very good heat transfer and viscosity characteristicscompared to glycol however; non-metallic components are required to reduce thepotential for corrosion. Calcium Chloride mixed with water is a common secondary coolant due to its low cost, excellent heat transfer characteristics and a low working temperature down to –50F. Even though glycols typically require more pumping4 © IIAR 2011 Technical Paper #1Minimize Refrigerant Charge Using Liquid Desiccant Dehumidificationhorsepower and are not as good at transferring heat at cold temperatures as salts, Ethylene and Propylene glycols are commonly used because they are not corrosive. Propylene glycol can be considered food grade by the USDA depending on the other additives in solution and can even be found in many cosmetic products such aslipstick and makeup. Due to its non aggressive nature it can be used with steel piping and metallic components.Using heat exchangers for the evaporator and possibly the condenser, the primary refrigerant volume can be greatly reduced, in most cases decreasing the volumebelow the threshold for onerous reporting and regulatory requirements. Distributed ammonia systems can require approximately 20 lbs of refrigerant per ton of cooling, where designs utilizing secondary brine loops are currently available utilizingless than one pound of per ton. In addition, by containing the primary refrigerantto mechanical rooms, the health and safety concerns related to the presenceof refrigerant in the processing areas is eliminated, potentially creating a safer environment for workers.This common alternative is not commonly applied to applications requiring air witha temperature or dew point requirement below freezing. Frost management becomes difficult with a secondary refrigerant system because hot gas is not available for defrost. Although warm coolant systems exist, due to the thermal mass of the coolantit is not practical to warm a secondary coolant for defrost. Where installed, specialcoils are utilized which have hot coolant and cold coolant loops. Electric and water defrost are other common defrost methods.Secondary Refrigerant Systems Using Liquid DesiccantsFor applications requiring sub-freezing refrigerants, liquid desiccant equipment (figure 3) coupled with a secondary refrigerant has the advantage of providingcooling of the process air down to temperatures of -60F without frost build-up. Liquid Technical Paper #1 © IIAR 2011 52011 IIAR Industrial Refrigeration Conference & Heavy Equipment Show, Orlando, Floridadesiccant systems work by passing air over a finned cooling coil while at the sametime spraying a liquid desiccant solution over the same surface (see figures 3 and4). Liquid desiccant cooling equipment is referred to as conditioning equipment (orconditioner) due to its ability to affect temperature, humidity and purity of the airpassing through it. As the air comes in contact with the desiccant solution it is cooled and/or dehumidified to reach the desired leaving air condition. Frost and moisturethat would otherwise condense on the coil surface is absorbed into the desiccantsolution. This completely eliminates potential frost or bacteria buildup as well asthe hardware, controls, and complexity required for a defrost cycle. By removingthe defrost cycle and the energy swings associated with the phase change whilemelting the frost, the process area will remain constant and the refrigeration system will operate more consistently. Nor will accumulated frost sublimate back into theconditioned spaces or the cooling equipment. The compressor and evaporator loads will vary proportionally with the airside load. This can be extremely beneficial inspaces that have a critical need for a dry environment such as food preparation areas or automated storage facilities with sensitive electronics.Air sanitation is one of the foremost concerns in the food & beverage industries.Liquid desiccant equipment eliminates the potential breeding ground associated with conventional wet coils while acting as a continuous air scrubber to provide sanitized process air. Supplying clean, dust-free air from which microbiological contaminants have been removed decreases housekeeping requirements and significantly reduces the potential for bacteria, virus, and mold growth in processing areas. As illustrated for a packed tower conditioner you can see in figure 6 the particulate removal affect of a single pass of air. Figure 5 represents the distribution of particle sizes in a typical industrial environment.Moisture absorbed by the airside conditioner(s) in the desiccant solution istransferred to a concentrator (regenerator) via a small slipstream. The concentrator(figures 2 and 3) can be located anywhere, but is commonly placed outside ofthe process area in a place that can be easily maintained. There are a variety of6 © IIAR 2011 Technical Paper #1Minimize Refrigerant Charge Using Liquid Desiccant Dehumidificationcommercially available methods to remove water from desiccant solutions, however;the principals are the same. By heating the desiccant in a process opposite of the conditioner, the moisture is liberated either via the scavenger air stream or in theform of distilled water to a drain. T emperatures required to regenerate a liquid desiccant can be as low as 130F. Recovered heat from the condenser side of the refrigeration process or other waste heat sources such as compressor lubrication oilcan be used to provide part or all of the heat required for desiccant regeneration.The use of low grade, low cost heat energy for the regeneration process (such as condenser heat, cogeneration waste heat, compressor lubrication oil heat, etc.)allows for a shift in cost. Instead of paying for defrost twice, once by a blockedcoil and again by defrosting with expensive prime compressor energy; it becomes shifted to the lower cost heat sources mentioned with no adverse affect on process temperatures.Unconventional Design OptionsLiquid desiccant equipment also offers many facilities the ability to utilize the same solution for both the secondary coolant and the desiccant solution. See Figure7. In this arrangement, the piping serves the dual purpose of secondary coolant distribution and desiccant distribution thus minimizing installation costs. This approach can eliminate one of the plate and frame heat exchangers and its associated approach temperature. This allows the compressor suction temperature increase as much as 10 degrees Fahrenheit, further increasing the overall efficiency.Energy RecoveryCertain applications lend themselves to a specific glycol based liquid desiccant distillation column type concentrator (figure 8) which has the ability to recover upto 70% of the energy used for desiccant regeneration in the form of hot water. Please Technical Paper #1 © IIAR 2011 72011 IIAR Industrial Refrigeration Conference & Heavy Equipment Show, Orlando, Floridanote as illustrated in figure 7 the difference in energy between the coolant water inlet and hot water outlet is the recovered energy. This is advantageous to customers with high heat loads for clean-in-place type systems, making the desiccant system evenmore energy efficient. With a payback period typically in the range of three to fiveyears, this technology has been associated with lower cost per ton of refrigerationwhich can lead to increased building values for a greater return on investment. Also, tax benefits for green buildings are offered in many states.Increased EfficiencyThe nature of a sprayed coil or sprayed packing results in very consistent leaving air temperature and humidity. The coolant can modulate from 0% to 100% of its design capacity based completely on the needs of the process. There is never a need to raise or lower refrigerant temperatures due to a defrost cycle, or a partially blocked coil.This allows the compressor and condenser to operate in a very smooth, consistentand efficient manner.Sanitized AirAssociated with improved air quality, liquid desiccant technology provides criticalbacterial control by capturing and neutralizing airborne bacteria, viruses, and mold.Many different liquid desiccant formulations (such as salt-, glycol-, or calcium-based) are available. Independent testing has been performed for these formulations demonstrating that they:• are biocidal to air-transmitted bacteria, mold, viruses, and pathogens• will not support life or growth of any microorganism tested• have a 100% neutralization rate in solution8 © IIAR 2011 Technical Paper #1With the ability to manage mold and bacteria, liquid desiccant technology can prevent outbreaks of bacteria such as Listeria, Salmonella and Y ersinia, which can result in plant inspections, a compromised company/brand reputation, product recalls, and plant shut downs. The air sanitizing contamination control benefit is highly valuable to food and beverage plants. All desiccant solutions mentionedare industrially available today and are approved for use in food plants. Saltand glycol based liquid desiccant systems have been operating in thousands of facilities worldwide, many dating back to the 1930’s. Although the technology isnot mainstream, it is very common and maintainable. An additional benefit of the scrubbed air is a dramatic reduction of dust. When the technology is applied to refrigerated warehouses, this can reduce housekeeping efforts and provide a better looking product for delivery.Opportunity for LEEDIt is possible that the use of desiccant equipment can help obtain the following LEED credits. These include:Energy & Atmosphere• EA CR1 Optimizes energy performance• EA CR4 Enhanced refrigerant managementIndoor Environmental Quality• EQ CR1 Outdoor air delivery monitoring• EQ CR7.1 Thermal comfort–designConclusionIt is sometimes in the best interest of large food and beverage processing facilities and refrigerated storage or distribution facilities to utilize a technology with a reduced refrigerant charge. The smallest possible refrigerant charge will help insure the safety of your employees, while reducing potential environmental, regulatory, and economic issues. Considering a liquid desiccant solution can offer the benefits of heat recovery, sanitized air, controlled humidity and an opportunity for LEED credits. Food and beverage and other critical environment facilities should explore technology options to determine what best meets their needs.F i g u r e 1. D i s t r i b u t e d R e f r i g e r a t i o n S y s t e mF i g u r e 2. S e c o n d a r y R e f r i g e r a t i o n S y s t e mF i g u r e 3. N o -F r o s t S y s t e m S c h e m a t i cF i g u r e 4. K a t h a p a c S y s t e m S c h e m a t i cFigure 5. Particulate Size ChartFigure 6. Liquid Desiccant Particulate Removal EfficiencyF i g u r e 7. K a t h a p a c S y s t e m S c h e m a t i c – R e m o t e C o o l e rF i g u r e 8. D i s t i l l a t i o n C o l u m n C o n c e n t r a t o r。