SINT OOLING :SINT VNTILTION OMS OF G MRGING OPPORTUNITIS N SINT OOLING SYSTMS JGP SINGH rctic India ngineering Pvt. Ltd. STRT Researchers, designers and manufacturers of refrigeration and air-conditioning systems and equipment today are focusing on new and alternative technologies in view of the phasing out of Fs. This has brought about a revolution in HV industry with the advent of new replacement technologies that operate independent of refrigerants. esiccant-based and desiccant assisted air-conditioning systems are currently emerging from a - year industrial heritage and expanding into commercial applications. Today, both the user and the consultant opt to adopt non-conventional approach case by case rather than sticking to conventional method of designing systems. ffort at all levels is being made to identify new slots / areas where desiccant cooling system provides immediate applicability i.e. stand alone as well as provides economical and efficient alternative, by way of lowering TR (Reduce impact of Fs). This paper deals with options and opportunities of viable applications of desiccant augmented cooling systems e.g. Stand lone HV systems, industrial ventilation, Integration of esiccant ooling in commercial HV system, pplication of a esiccant ooling System to super markets, Integrated esiccant old ir istribution Systems (I), esiccant ehumidifiers in ice arenas, lean Room pplication, etc. nergy shortage is something which we live with day in and day out. This energy shortage is expected to increase as more and more population shifts to air conditioned buildings. This presents the air conditioning industry with several challenges. mong these are demands for increased energy efficiency and improved indoor air quality, growing concern for improved comfort and environmental control, increased ventilation requirements, phase-out of chlorofluorocarbons (Fs), and rising peak demand charges. TOUGH ISSUS FING TH HV&R INUSTRY The air-conditioning industry, worldwide, has been battling to meet new economic, environmental, and regulatory challenges: improved ventilation-rate standards, upgraded indoor air quality demands, reduced levels of gaseous emissions, phase-out of F refrigerant, and peak electric demand. To meet these challenges, the industry and the government in the West, specially in the United States are focusing on alternative and new technologies like desiccant cooling and dehumidification technology. New approaches and options to air conditioning such as esiccant cooling and dehumidification is providing important advantages in solving many of these problems. However, these options have to be evaluated to resolve economic, environmental, and regulatory issues.
esiccant technology has become an important alternative amongst the options available to the industry for space-conditioning. In many cooling applications, desiccant cooling units provide advantages over the more common vapour-compression and absorption units. For example, desiccant systems do not need ozone-depleting refrigerants and are very effective at treating the large humidity loads resulting from ventilation air. lso, they use natural gas, solar thermal energy, or waste heat, thus lowering peak electric demand. s a result, the use of desiccant cooling and dehumidification systems for building comfort conditioning has increased steadily during the past several years in the West. Recent advances in adsorptive materials, in conjunction with dehumidifier design innovations, are making the technology increasingly attractive. SVING NRGY N THUS, TH NVIRONMNT esiccant cooling systems are energy efficient and environmentally benign. In humid regions, desiccant dehumidification can reduce electricity demand considerably by providing a drier, more comfortable, and cleaner indoor environment with a lower energy bill. esiccant systems allow more fresh air into buildings, thus improving indoor air quality without using more energy. esiccant systems also displace chlorofluorocarbon-based cooling equipment, the emissions from which contribute to the depletion of the arth's ozone layer. esiccant dehumidification technology provides a method of drying air before it enters a conditioned space. When combined with conventional vapour compression systems, desiccant dehumidification systems are a cost-effective means of supplying cool, dry, filtered air. In the last decade, desiccant dehumidification technology has emerged as an alternative or as a supplement to conventional vapour compression systems for cooling and conditioning air in commercial and institutional buildings. typical hybrid system combines a desiccant system with a conventional vapour compression cooling system. esiccant-based systems are cost-effective because they use low-grade thermal sources to remove moisture from the air. In general, the benefits of desiccant-based systems are greater where the thermal energy required for regenerating the desiccant is readily available, the electricity price is high, and the latent load fraction is high (>5%). If there is no difference in energy costs, the factors that influence the economy include climate conditions (humidity levels) and high outdoor-air requirements. In other situations, the important variables that drive the economics should be carefully evaluated. There are, however, a few applications where the technology's benefits have been so extensively demonstrated that no detailed analysis is required: storage spaces, ice arenas, most supermarket applications, military commissaries, hospital operating rooms, and as an add-on to existing air conditioning systems with inadequate dehumidification capacity. SINT THNOLOGY There are three basic types of gas cooling technologies: absorption system, gas engine chiller systems and desiccant cooling cycle and the regenerative cycle. In the dehumidification/cooling cycle the moist (humid) return air from the storage area and some makeup air from outside is filtered and then passed through the very slowly rotating fluted desiccant media [rotor/wheel] which adsorbs moisture.
5 5 5 5 5 asic ir esiccation Process with xchange air that is returned back outside. 7 5 This air comes out of the wheel/rotor as warm dry air which is then passed through the air handling unit to be cooled and distributed back to the storage area. The regenerative cycle is basically regenerating the moisture laden section of the desiccant wheel so that as it rotates back into the supply air stream it is ready to extract moisture from the process air. ir is taken from outside and heated by gas to be hot enough to remove the moisture from the wheel, resulting in warm moist Using psychrometrics the properties of the air can be followed through the system. In the conventional system it is seen that the air is cooled to the pparatus ew Point (P) temperature so that the moisture can be removed, then the air is reheated to the desired temperature resulting in wasted energy where as the esiccant based systems removes the latent load from the HV system thus saving energy. One must understand that both the latent load an important role in designing of an airconditioning system. The advantage of the desiccant system is that it removes the latent load by the use of a lower cost 195 energy alternative, i.e. gas. xchanger 5 7 5 7 1 1 TMPRTUR 5 7 Room ir esiccant Matrix esiccant Process Vapor ompression Process Regeneration ir Freezing Limit of vaporator 5 7 5 7 1 1 17 1 TMPRTUR omparison of esiccant and Vapor ompression ehumidification Processes 1 1 1 1 1 1 1 15 1 5 5 HUMIITY RTIO 195 15 1 5 5 HUMIITY RTIO s the process air is already been dry only sensible cooling is required, so the evaporator coils can be operated at higher temperatures. Thus, hybrid systems with a combination of the desiccant wheel and the existing air conditioning system operates on less energy input than the conventional system. SINT SIS desiccant material
naturally attracts moisture from gases and liquids. The material becomes saturated as moisture is adsorbed or collects on the surface; but when heated, the desiccant dries out or regenerates and can be used again. onventional solid desiccants include silica gel, activated alumina, lithium chloride salt, and molecular sieves. New solid desiccant materials like zeolites are designed to be more effective for cooling applications. Liquid desiccants include lithium chloride, lithium bromide, calcium chloride, and triethylene glycol solutions. In a dehumidifier, the desiccant removes moisture from the air, which releases heat and raises the air temperature. The air is then cooled by heat-recovery units and cooling devices such as indirect evaporative coolers or the cooling coils of a conventional air conditioner. In a stand-alone desiccant cooling system, air is first dried, and then cooled by a heat exchanger clubbed with evaporative coolers. This system is free of ozone-depleting F and HF refrigerants. In most systems, a wheel containing desiccants continuously dehumidifies outside air entering the cooling unit. The desiccant is then regenerated by thermal energy supplied by natural gas, waste heat, or the sun. desiccant system can also supplement a conventional air-conditioning system; the desiccant removes the humidity load while the evaporator of the air conditioner lowers the air temperature. SINT OOLING SYSTM OPRTION The dehumidifier is the heart of a Indoor ir F G H 5 7 vaporative esiccant xhaust ooler xchanger Wheel ir F G H I vaporative ooler I 5 7 5 7 1 1 17 1 TMPRTUR Input Ventilation Mode esiccant ooling 1 Outdoor ir 1 1 1 desiccant cooling system. It efficiently removes the moisture (latent load) from the process air; the temperature (sensible load) of the dried air is then reduced to the desired comfort conditions by sensible coolers (i.e., rotary heat exchangers, direct and indirect evaporative coolers, cooling coils). The latent and sensible loads are handled more efficiently than in vapor compression cooling equipment because the components are optimized to independently remove these separate loads. The desiccant in the dehumidifier is regenerated (reactivated) when heat is applied to release the moisture, which is exhausted outdoors. The heat for regeneration can be provided from a number of energy sources such as natural gas, waste heat, solar, and off-peak electricity. The process air to be dried is passed through a fluted desiccant media. Water vapour is adsorbed into the fluted desiccant media driven by the vapour pressure differential between the process air and the desiccant surface. When the desiccant is nearly saturated, hot air is 195 15 1 5 5 HUMIITY RTIO
passed through the bed to release the moisture. The desiccant media typically takes the form of a rotor (wheel) so that it may be conveniently rotated between the process and regeneration airstreams. esiccant cooling systems are energy efficient, cost effective, and environmentally safe. They can be used as stand-alone systems or with conventional air-conditioning to improve the indoor air quality of all types of conditioned spaces. In such systems, the desiccant removes moisture from the air, which releases heat and increases the air temperature. The dry air is cooled using either evaporative cooling or the cooling coils of a conventional air conditioner. The adsorbed moisture in the desiccant is then removed (the desiccant is regenerated to its original dry state) using thermal energy supplied by natural gas, electricity, waste heat, or the sun. ommercially available desiccants include silica gel, activated alumina, natural and synthetic zeolites, titanium silicate, lithium chloride, and synthetic polymers. OPTING SINT OOLING OPTIONS onventional vapour-compression cooling systems are not designed to handle temperature and humidity loads separately. s Outdoor ir vaporative esiccant a result, oversized compressors ooler xchanger Wheel xhaust ir F G H I are often installed to dehumidify Indoor ir the incoming air. lso, vapor- Input compression systems are often operated for long cycles and at vaporative Outdoor ir ooler low temperatures to meet humidity requirements, which I 195 reduces their efficiency and requires reheating the dry, cold air to achieve some degree of 7 G H 15 comfort. oth methods are F 1 expensive. 5 5 7 5 7 1 1 17 1 TMPRTUR Total Ventilation Mode esiccant ooling 1 1 1 1 esiccant systems, however, can supplement conventional air conditioners. Working in conjunction, the systems can handle temperature and humidity loads separately and more efficiently. HV designers and consultants can thus design systems which will reduce compressor size and eliminate excess chiller capacity. nother emerging application of the desiccant cooling systems is the increasing use of combined cooling, heating, and power (HP) systems for buildings. Facilities with HP systems recover waste heat from generators, turbines, or engines and use it for heating and cooling to maximize overall facility efficiency. esiccant systems use these large quantities of low-temperature heat to provide dry, cool, comfortable fresh air to building occupants. 5 5 HUMIITY RTIO
FROSTLSS FRZRS N HLTHY IR esiccant technologies can be used to great advantage in many applications like super markets, ice arenas, etc. Though, esiccant vaporative Wheel xchanger ooler desiccant systems are not yet the allin-all solution for all cooling and I H G F Outdoor ir Input humidity problems but certain areas Indoor ir are particularly well suited for vaporative ooler desiccant applications, based on both technical merits and cost. Many supermarkets in the US use I 195 them to reduce frost buildup on refrigerated cases and frozen products, extending product shelf G 7 15 life, as well as the intervals between F H 1 1 expensive, energy-consuming defrost 5 1 5 cycles. esiccants contribute to a 1 drier, cleaner, more comfortable environment in stores of all kinds. 1 5 For example, supermarkets must control moisture levels in freezer display cases, but antisweat heaters 5 7 consume considerable energy. 5 7 1 1 17 1 TMPRTUR Recirculation Mode esiccant ooling commercial desiccant dehumidification system has helped many supermarkets save on energy costs by controlling humidity independent of temperature. The desiccant system reduces frost build-up on frozen products and refrigerated cases. dditionally, the system extends product shelf life and contributes to a drier, more comfortable store environment for shoppers and employees. The merican Hotel and Motel ssociation has reported that repair of mold and mildew damage to wallpaper, paint, carpet, and other materials caused by high humidity levels could cost hotels and motels $ million annually. esiccant systems can lower the humidity levels in these spaces, saving millions of dollars in unnecessary repairs. esiccant systems also improve indoor air quality, improve ventilation rates, and remove air pollutants and odors benefits demonstrated in two hotels in Florida. Similarly restaurants, schools, and hospitals can use desiccants to remove moisture, odors, and pollutants for a healthier, more comfortable and productive environment. New building standards (e.g., SHR R) that require more outside air for ventilation are also increasing demand for dehumidification products. Highlights * Independent humidity control. * Improved presentation of frozen foods and refrigerated products. * Lower temperature in refrigeration cabinets. urrently in the United States, desiccant cooling and dehumidification systems are being used successfully in industrial and many commercial applications with technology
advancements which has helped to improve the performance, reliability, and costeffectiveness of desiccant equipment. ecause desiccant systems perform differently from vapour-compression systems, performance-rating procedures, test methods, and standards are being developed to permit HV-system designers to compare various desiccant systems with competing technologies. Separate procedures are being developed by the SHR(merican Society of ing, Refrigerating, and ir-onditioning ngineers, Inc.), and the RI(ir-onditioning and Refrigeration Institute) to revise conventional comfort standards based primarily on temperature to include humidity and indoor air quality. GNRTING WRNSS IN TH OUNTRY The need of the day is to generate awareness, identify barriers to wider acceptance and finding solutions through commercialization of the technology in the country. ollaboration between government and industry is necessary to develop cost-effective, marketable systems that are energy efficient and environmentally safe. To make desiccant systems more marketable, the industry along with the government must work as partners to * dopt advanced desiccant materials, components available in the country to design systems with lower costs and improved performance * emonstrate desiccant systems in real-world environments * evelop markets for desiccant systems that will improve indoor air quality and reduce environmental pollution. The information and data generated through this collaboration should be disseminated to the HV industry, the desiccant community, architects, engineers, builders, utilities, and other end users through industry and professional society meetings, publications, conferences, and workshops. In conclusion, the main goals of a esiccant ooling Program in India should typically focus on * Reduction of energy consumption * Reduction of carbon dioxide emissions * Initiate training programs to educate design, engineering, and architectural firms and natural gas end users about the desiccant technology and its benefits. * onvert designers and consultants of conventional air-conditioning systems to opt for esiccant based Systems