Twin-Cel Energy Recovery Systems Engineering Reference Guide

Transcription

1 Twin-Cel Energy Recovery Systems Engineering Reference Guide Reliable, high efficiency desiccant dehumidification systems 1

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3 Table of Contents General Description...2 Operating Principle... 4 Enthalpy Recovery Advantages..6 Performance Estimating Summer... 7 Winter...8 Economic Analysis 10 Unit Drawings 11 Installation Notes...13 Sample Specifications

4 Kathabar Dehumidification Systems Kathabar Dehumidification Systems, Inc., the world leader in industrial humidity control, has manufactured dehumidification equipment for more than 75 years. The name "Kathabar," which is derived from Greek words meaning clean or pure air, describes what Kathabar equipment does best. The primary use of Kathabar is to provide precise and energy efficient air temperature and humidity control. Kathabar maintains the process or space at the required condition regardless of weather or process variations. The "bacteria-free" benefit of Air-to-Air Energy Recovery in Building HVAC The purpose of all air-to-air energy recovery systems is to reduce the energy costs required to air condition a building and to reduce the size of the heating and cooling plants required. Energy recovery systems reduce energy usage by preconditioning the ventilation air entering a building using the available energy in the exhaust air leaving the building. During the summer, hot/humid ventilation air is pre-conditioned using the relatively cool/ dry building exhaust air. During the winter, ventilation air is preheated/ Kathabar is an added feature to temperature and humidity control. Over the last 75 years, the design of Kathabar equipment has been continually evolving. Advances in heat/ mass transfer technology and construction materials have been incorporated. New product lines have been developed to serve the changing needs of industrial, institutional, and commercial users as well as to reflect changes in the cost and availability of energy. These energy cost and availability issues have resulted in the development of the Twin-Cel air-to-air enthalpy recovery system. humidified using the relatively warmer/ wetter exhaust air from the building. Use of air-to-air energy recovery equipment substantially reduces air conditioning energy costs. In addition, installation of air-to-air energy recovery equipment substantially reduces the installed size of heating and cooling equipment required to air condition a new building and, with Twin-Cel, eliminates humidifiers as well as their associated appurtenances, and controls. Types of Air-to-Air Energy Recovery Equipment There are two basic types of air-to-air energy recovery equipment: sensible heat devices and total heat or enthalpy devices. Sensible heat devices transfer only temperature between ventilation and exhaust airstreams. Examples are heat wheels, flat plate exchangers, and coil loops. Total heat devices transfer both temperature and moisture between airstreams. Examples are enthalpy wheels 2 and Twin-Cel. Figure 1 shows that enthalpy recovery allows much greater energy savings than recovery of sensible heat only. Generally in comfort conditioning applications, enthalpy recovery equipment will save about three times as much energy in summer and about 20% more energy in winter than sensible only equipment of the same effectiveness.

5 FIGURE 1 Energy Savings Comparison Sensible Only vs. Enthalpy Recovery SAVINGS WITH SENSIBLE RECOVERY ONLY ADDITIONAL SAVINGS WITH ENTHALPY RECOVERY VENTILATION AIR (SUMMER) SAVINGS WITH ENTHALPY RECOVERY Building Exhaust Air (Summer) AIR HUMIDITY, GRAINS/LB. SAVINGS WITH SENSIBLE RECOVERY ONLY Building Exhaust Air (Winter) VENTILATION AIR (WINTER) 20 The Twin-Cel system consists of one or more supply units pretreating building ventilation air and one or more exhaust units recovering energy from building exhaust air. In operation, supply and exhaust airstreams are scrubbed with a sorbent brine solution that can transfer both temperature and humidity between the airstreams. Enthalpy transfer between supply and exhaust airstreams is accomplished by continuously recirculating the solution between supply and exhaust air units. Building ventilation air is pre-cooled and dehumidified during warm weather, and pre-heated and humidified during cold weather. During mild spring and fall weather, air temperature leaving the supply unit can be limited to any desired value. During extremely cold weather, temperature of the ventilation air delivered by the supply Twin-Cel can be maintained 55 AIR TEMPERATURE F Operating Principle during the winter months at any desired value by adding heat with a solution heater. The relative humidity of the delivered air can be maintained at any value up to 80% by adding makeup water to the supply Twin-Cel. Combining the above control features, the Twin-Cel system can deliver air at a fixed temperature and humidity all winter, regardless of weather conditions (see Figure 2). The system in Figure 3 shows a simple arrangement utilizing one supply unit and one exhaust unit at different elevations. Typical variations include multiple supply or exhaust units and multiple unit systems with units at different elevations. A solution pump can often be eliminated in systems where the elevation difference between supply and exhaust units is great enough to overcome piping friction.

6 100 FIGURE 2 Twin-Cel Energy Recovery Delivered Air Temperature F Solution Heating Winter Operation Pumps Off (Null Cycle) Summer Operation Outside Air Temperature F 125 FIGURE 3 Twin-Cel System Schematic 4

7 Effect of Ventilation Air on Building HVAC Load The ventilation air load represents a substantial portion of the total air conditioning load. Figure 4 shows the percentage of total load represented by ventilation air for cooling and heating in a typical comfort conditioning system without energy recovery. In systems using 100% ventilation air, about 65% of the cooling load and 80% of the heating load is caused by the ventilation air at typical outside design conditions. In 10% ventilation air systems, about 15% of the cooling load and about 30% of the heating load is caused by the ventilation air. % of Total Load Caused by Ventilation Air FIGURE 4 Effect of Ventilation Air on Heating/Cooling Load HEATING COOLING % Ventilation Air Reduction in HVAC Load by Air-to-Air Energy Recovery % Reduction in Air Conditioning Load By Air-to-Air Energy Recovery FIGURE 5 Energy Savings of Air-to-Air Energy Recovery (Based on 65% Recovery Effectiveness) Summer Design % Ventilation Air Winter Design 100 Figure 5 shows the savings in heating and cooling energy requirements when air-to-air energy recovery equipment is applied to building ventilation air. Enthalpy recovery is shown with solid lines, and sensible only recovery is shown with dashed lines. Enthalpy recovery equipment effects about three times as much cooling load reduction as sensible only heat recovery equipment and about 20% more heating load reduction. * Dashed lines indicate savings with sensible recovery * Solid lines indicate savings with enthalpy recovery 100

8 Enthalpy Recovery Advantages Efficient Microbiological Decontamination Both Kathene and Kalsorb solutions are bactericidal and virucidal to most airborne microorganisms. This enables Twin-Cel systems to efficiently decontaminate both ventilation and exhaust airstreams. No Cross-Leakage Since ventilation and exhaust air are handled by separate Twin-Cel units, no cross-leakage of exhaust air to ventilation air can occur. Sensible and Latent Recovery from Remote Airstreams Coil loop systems can recover energy from remote airstreams, but are limited to sensible recovery only. Wheel-type units can recover both sensible and latent energy, but require that the exhaust air be ducted to the same location as the ventilation air, limiting design flexibility. Twin-Cel systems recover both sensible and latent energy from remote air streams. They handle ventilation air and exhaust air in separate units connected only with piping. The Twin- Cel units can be located wherever it is convenient in the air system design. Constant Delivered Air Temperature and Humidity All Winter When other air-to-air recovery equipment is used, an additional heating coil and humidifier are required during winter operation to deliver air at a constant temperature and humidity. Twin-Cel systems can automatically heat and humidify air to a constant delivered air temperature and humidity all winter. This is possible without additional pre-heat or reheat coils or humidifiers and their associated controls. Frost-Free Operation To prevent frosting on the exhaust air side, sensible-only recovery equipment usually must be operated at reduced recovery effectiveness during very cold weather. Wheel-type enthalpy recovery equipment usually requires pre-heating of ventilation air during very cold weather to prevent frost buildup in the wheel, which can block airflow. Twin-Cel systems are designed to operate continuously at outside air temperatures as low as -40 F without frosting, freezing, or icing. Twin-Cel systems do not require ventilation air pre-heating coils, regardless of the humidity of the building exhaust air. Insensitive to Static Pressure Wheel-type equipment requires that the proper static pressure balance be maintained between ventilation and exhaust air to minimize cross-leakage. This usually requires that ventilation and exhaust air fans be located where the density change of the air from summer to winter is greatest. This can affect the building air balance. Twin-Cel units are not affected by the static pressure of ventilation and exhaust airstreams. Ventilation and exhaust fans can be located wherever convenient in the air system for the simplest design. Large Airflow Capacities Several wheel-type units are required to handle airflows in the 80,000 CFM range. Multiple-wheel installations require complex field-built plenums which are costly, can limit maintenance access, and add design complexity. Up to 84,000 CFM can be handled by a single, factory-assembled Twin-Cel unit. This can significantly reduce installation costs, maintenance costs, and control complexity. 6

9 Summer Performance Estimation The enthalpy recovery performance of a Twin-Cel system during summer operation can be estimated using the graphs and procedure given below. The exact performance can be obtained through your Kathabar representative. The recovery effectiveness of a Twin-Cel system is primarily a function of the sensible heat ratio between the outside air and the building exhaust air. The sensible heat ratio can be calculated from the outside air and building air temperatures and humidities and using Figure 6. Example: Outside air 95ºF, 120 Gr/Lb, 50,000 CFM Building air 75ºF, 65 Gr/Lb, 45,000 CFM Air temperature difference (95ºF - 75ºF)= 20ºF Air humidity difference (120ºF - 65ºF) = 55 Gr/Lb From Figure 6, SHR = FIGURE 6 Sensible Heat Ratio (SHR) FIGURE 7 Enthalpy Recovery Effectiveness Air Humidity Difference (Gr/Lb) Air Temperature Difference ºF Effectiveness Sensible Heat Ratio (SHR) Once the sensible heat ratio has been determined, the enthalpy recovery effectiveness can be found using Figure 7. Example: For SHR = 0.36, effectiveness = 63% Effectiveness is always based on the smaller airflow. If the supply airflow is larger than the exhaust airflow, the supply effectiveness must be corrected: E SUPPLY = Exhaust Airflow x E FIG.7 = 45,000 x.63 = 56% Supply Airflow 50,000 Calculate Temperature and Humidity Delivered from the Supply Twin-Cel Unit T DEL = 95ºF -.56ºF(95ºF - 75ºF) = 83.8ºF W DEL = 120ºF -.56ºF(120ºF - 65ºF) = 89.2 Gr/Lb 7

10 Winter Performance Twin-Cel systems are usually installed with a winter solution heater and automatic water makeup in cold climates. This arrangement enables the Twin-Cel supply units to deliver air at a constant temperature and humidity all winter long, regardless of outside air conditions. Furthermore, dry steam humidifiers and preheat coils are not required, even under arctic weather conditions. The recovery effectiveness of a Twin-Cel system and the amount of solution heating required at winter design conditions can be estimated using a psychrometric chart and Figure 8 and the procedure given below. The exact performance should be obtained through your Kathabar representative. Example: Outside air 55,000 CFM at 0ºF, 4 Gr/Lb Exhaust air 50,000 CFM at 72ºF, 42 Gr/Lb (35% R.H.) Desired supply air at 52ºF, 42 Gr/Lb (73% R.H.) Airflow Ratio: Outside Air 55,000 Exhaust Air = 50,000 = 1.1 Enthalpy: h at 0ºF, 4 Gr/Lb = 0.6 BTU/Lb h at 72ºF, 42 Gr/Lb = 23.8 BTU/Lb h at 52ºF, 42 Gr/Lb = 18.5 BTU/Lb Enthalpy Ratio = h Supply ( ) = h Total ( ) = 0.77 From Figure 8, enthalpy recovery efficiency = 0.48 Heat into supply air = 55,000 x 4.5 x ( ) = 4,430,250 BTU/Hr Heat recovered = 0.48 x 50,000 x 4.5 x ( ) = 2,505,600 BTU/Hr Additional heat required = 1,924,650 BTU/Hr FIGURE 8 Winter Enthalpy Recovery Efficiency Enthalpy Ratio, h Supply h Total % 45% 50% 55% 60% Airflow Ratio, SCFM Supply SCFM Exhaust 8

11 Turndown Cycle The purpose of the turndown cycle is to prevent the system from delivering air to the building warmer than desired. This may occur during spring, fall, and warm winter weather. With the turndown cycle, no additional cooling is necessary to maintain desired delivered air temperature. Turndown is accomplished by reducing the recirculation rate of the solution in the system. An automatic turndown is controlled by the supply unit leaving air temperature controller and is staged with the solution heater steam valve. Staging the turndown with the solution heater ensures that the solution is never heated and in turndown at the same time. The turndown set point, which is the supply unit maximum winter leaving air temperature set point, is normally in the range of 50ºF - 60ºF. The turndown temperature is set 5ºF higher than the low temperature setting of the null cycle. This is done to prevent the system from operating when the energy recovery of the system is less than the energy required to run the solution pumps. Null Cycle The null period or null cycle occurs when the outside air temperature is nearly the same as the temperature of the air being exhausted from the building. This temperature range is normally between 50ºF - 70ºF. During this period, energy recovery could cause the leaving air to exceed the desired delivered temperature and humidity. Therefore, the solution pumps are automatically shut down during null cycle operation. Automatic shutdown and restart is controlled by an outside air temperature sensing controller. Outside Air Operating Cycle 55ºF and below Winter 55ºF - 75ºF Null 75ºF and above Summer Summer Operation During the summer operating cycle, the Twin-Cel system is used to cool and dehumidify the outside air entering the building. At this time, it is desirable to recover as much cooling energy as possible. To accomplish this, the supply unit leaving air temperature controller is bypassed and the solution turndown valve is opened fully. This maximizes solution flow between units and energy recovery between airstreams. If the outside air is very hot and dry, water makeup may be required. Fixed Level Units All Twin-Cel systems are designed with at least one Twin-Cel unit operating at a fixed solution level. Multiple fixed level Twin-Cel units are used when the system consists of more than two units. In operation, a modulating level controller (MLC) senses the solution level in the unit pump tank and controls a modulating valve in the Twin-CeI unit pump discharge line. This valve throttles the flow of solution, leaving the unit to keep it in balance with the solution entering the unit. Solution level is also monitored by a limit level controller (LLC) which controls safety functions such as high and low level. 9

12 Economic Analysis Kathabar can provide an estimate of annual utility cost savings and estimated payback for your Twin-Cel installation. This analysis is based on your specific capital and operating costs for utilities and ownership cost for the Twin-Cel equipment. The analysis uses ASHRAE TMY2 weather data, which is available for about 240 locations in the U.S., as well as the design airflows and temperature and humidity conditions specific to your application. A copy of this page may be used to transmit the data required to perform the analysis. This can be ed to sales@kathabar.com. Job name: Location: Engineer: Date: Summer outside design: Summer exhaust design: Winter outside design: Winter exhaust design: Desired winter supply: Supply airflow: Exhaust airflow: ºF, Gr/Lb ºF, Gr/Lb, %R.H. ºF, Gr/Lb ºF, Gr/Lb, %R.H. ºF, Gr/Lb CFM, Unit location CFM, Unit location Operating hours (check one): All day Days only Nights only Cost of owning refrigeration: Cost of operating refrigeration: Cost of owning heating plant: Cost of operating heating plant: Cost of electric power: $ /Ton $ /Ton/Hr $ /HP or MMBTUH $ /Therm $ /KW/Hr 10

13 Module Dimensions FIGURE 9 Unit Size, Airflow Rating, and Dimensions Horizontal Twin-Cel Vertical Twin-Cel UNIT SIZE AIRFLOW (CFM) DIMENSIONS (INCHES) MINIMUM MAXIMUM L H W B C D E F G 800 5,000 10, ,500 15, ,000 20, S 12,500 25, ,000 24, ,000 30, ,000 36, ,000 48, ,000 60, ,000 72, ,000 84, (Dimensions are approximate, for roughing-in) 11

14 UNIT SIZE * AIRFLOW (CFM) MIN. MAX. FIGURE 10 Engineering Data HORIZONTAL T.C. SHIP- PING WEIGHT (LBS) MAX. OPERAT- ING VERTICAL T.C. SHIP- PING MAX. OPERAT- ING PUMP ** 800 5,000 10,000 2,500 7,600 2,000 7, ,500 15,000 3,000 9,800 2,500 9, ,000 20,000 3,500 12,000 3,000 11, S 12,500 25,000 N/A N/A 4,000 14, ,000 24,000 5,400 14,500 4,800 13, ,000 30,000 6,200 17,000 5,600 16, ,000 36,000 7,200 19,800 6,400 18, ,000 48,000 9,000 25,100 7,900 23, ,000 60,000 10,700 30,300 9,400 28, ,000 72,000 12,400 35,500 10,800 33, ,000 84,000 14,300 40,900 12,400 38, * Smaller unit sizes and non-standard sizes are also available. ** Based on 200 ft. equivalent run of pipe, two units at the same elevation. *** Use air face area and actual airflow to determine unit pressure drop. H.P. PIPE SIZE 12

15 Installation Notes The following equipment is normally supplied by Kathabar: Supply and exhaust Twin-Cel units Turndown controls and hardware Winter solution heater and control valve (if required) Control panel Sensors Desiccant solution charge The following equipment may be required for a complete system installation but are not normally supplied by Kathabar: Ductwork Interconnecting solution piping Interconnecting electrical and control wiring Any insulation required Any sound attenuation and vibration isolation required Pre-installation Storage Equipment should be stored indoors or protected outdoors prior to installation. Site Preparation Supply and exhaust units should be set on a level concrete floor, housekeeping pad, or piers. Curbing is recommended with a floor drain located inside the curbing. At least three feet of maintenance clearance should be provided around the equipment. The floor should be sealed with an epoxy sealant before the equipment is set in place. Rigging and Handling Twin-Cel equipment should be lifted only from the bottom, using lifting lugs (if provided) or slings. Spreader bars should be used. Contact Kathabar Engineering for any additional advice you may require. Plenums and Ductwork Twin-Cel units are provided with a two and one-half inches flange at the air supply and discharge openings for connecting ductwork. Supply and discharge plenums should be bolted to the flange with minimum one-quarter of an inch thick closed-cell foam gasketing, supplied by Kathabar. Access doors must be provided in supply and discharge plenums for servicing diffusers and eliminators. Ductwork at the supply plenum should have a design air velocity of 1500 ft/ min or less. Ductwork at the exhaust plenum should have a design air velocity of 1000 ft/min or less. Solution Piping All pipe and fittings in contact with the solution must be CPVC or FRP. Black iron, galvanized and stainless steel pipe must not be used. CPVC piping should be schedule 80, Type IV, Grade I, 4120, in accordance with ASTM Standard Recommended FRP piping is Smith Green Thread or Fibercast Centricast III EP. Valves in the solution piping should be made of CPVC, FRP, or thermoplasticlined cast iron with a non-metallic disc. Contact Kathabar for more detailed materials and construction information, if required. Thermowells in the solution piping must be titanium (available from Kathabar). Stainless, galvanized carbon steel, and copper Thermowells must not be used. All pipe fittings should be socket fittings, and all connections with valves and other components must be flanged. Red rubber or neoprene full-face gaskets are recommended for flanged connections. 13

16 The piping must be supported so no stress is placed on connections to the equipment. Pipe supports and anchors must be installed in accordance with the pipe manufacturer s recommendations. It is important to constrain the piping to prevent lateral and longitudinal motion. If the piping cannot drain completely by gravity, low-point drains with lined metal or non-metallic hand valves must be provided. Insulation Twin-Cel exhaust units need not be insulated. Twin-Cel supply units and interconnecting solution piping need not be insulated unless the equipment is located in areas that will be maintained at 30% R.H. or higher during cold winter weather. If insulation is used, closedcell flexible rubber insulation at least one inch thick is recommended. Insulation exposed to direct sunlight should be covered or treated for ultraviolet resistance. Twin-Cel Sample Specifications The air-to-air enthalpy recovery equipment shall be a Twin-Cel liquid desiccant system as supplied by Kathabar Dehumidification Systems, Inc. The system shall be capable of transferring both sensible and latent energy between supply and exhaust airstreams. The supply and exhaust airstreams shall be handled by separate units. The manufacturer shall guarantee that there will be no cross-leakage of air between supply and exhaust airstreams, and no cross-contamination of dust or microorganisms between supply and exhaust airstreams. The system shall be capable of continuous operation at an outside air temperature as low as -40ºF without frosting, freezing, or icing, and without the need for air preheating or air bypass dampers of any kind. The system shall be capable of automatically conditioning the outside air to a fixed temperature and humidity throughout the winter, regardless of outside air conditions. Supply and exhaust units shall consist of a watertight housing containing the solution-to-air contact surface, solution distribution system and mist eliminator system, a freestanding pump assembly with tank, vertical sealless solution pump and motor, full-flow solution filter screen, and bypass polishing filter. The unit and pump tank housing shall be of vinylester FRP construction with fire retardant additive and UV stabilizer. Internal parts shall be of engineered plastics. The winter solution heater (if required) shall be of the plate-and-frame type, with a steel frame and tie bolts and titanium plates with EPDM gaskets. The heater shall be supplied complete with control valve. 14

17 Notes 15

18 673 Ontario Street Buffalo, NY KATHABAR / 16