Principles of Active Desiccant Operation Presented by Tom Peterson, CEO and Founder Climate by Design International www.cdihvac.com Owatonna, MN 507-451-2198 4 02/2014 1 Dehumidification CDI is the Premier Provider of Desiccant and Air Handling Systems 1
Heating Air is NOT Dehumidification Sensible Heating or Cooling TM Sensible Heating or Cooling 2
Dehumidification Removing Moisture 1.Cooling the air, condensing moisture out of the air Mechanical DH 2.Removing the moisture with Desiccants Latent Cooling Latent Cooling 3
Mechanical DH Limits Energy and Ice Condensing moisture = 1060 BTUH per LB Extra energy to do that 50% more at 45 degrees Up to 100% more at 30 degrees. And then there s ICE! Assume 10 F Approach approach on Coil Danger! Coil Ice 7 7 Dehumidification Removing Moisture 1.Cooling - Mechanical DH *1500 to 2000 BTUH per pound 2.Desiccants start at around *2000 BTUH per pound *applied energy 4
Mechanical Dehumidification Cooling equipment can have a modest dehumidification effect at control levels approaching 50Fdp. They excel as the control level climbs above this point Assume 10 F approach on Coil Danger! Coil Ice 9 9 14 04/2016 Active Desiccant DH Reactivation Outlet 130-140 F Reactivation Air (Outside Air) 285 F Inlet Air 45 F at 35 Grains/LB 15 RPH Warm Dry Supply Air 75 F at 6 Grains/LB 5
Which One? Above the 45 F Dew Point Line Refrigeration Can Handle The Load Below the 45 F Dew Point Line Desiccant Can Handle The Load 45F dew point 11 11 Desiccant Dehumidification Desiccant Dehumidification 6
Desiccant Media Construction Ceramic fiber before silica-gel synthesized Rotor Surface Silica-gel synthesized in fiber Vapor Pressure Desiccants utilize the significant force of vapor pressure differential to function. Remember- vapor always moves from higher pressure to lower pressure. CDI is the Premier Provider of Desiccant and Air Handling Systems 7
Vapor Pressure Moves from High to Low 8
Vapor Pressure Desiccants Operate on VP Differential Desiccants Adsorb and Desorb through Vapor Pressure Differential In Hg inches of Mercury TM Moisture Adsorption The desiccant pore is empty and thereby has a lower vapor pressure than the air. Water vapor is propelled to porous openings in the crystal structure of desiccant by the pressure differential. Incoming Air (Process Entering) flows through the process sector of the rotor. Vapor Adsorption into the Desiccant The dry air then leaves the rotor at an approximate 30 to 40 grain/lb depression. 18 9
Reactivation -Normally 100 % Outside Air -Reactivation entering air is heated to 250-284 F (Some applications can be up to 320 F) -Heating air reduces its relative humidity. Heated air also increases the temperature of the desiccant particles. CDI is the Premier Provider of Desiccant and Air Handling Systems Desorption -Desorption happens when you supply enough energy to the water molecule that it shakes/vibrates loose from the bond holding it to the desiccant surface. -Water vapor is transferred from the desiccant to the low RH reactivation air. -Warm humid air is rejected to ambient away from controlled environment. CDI is the Premier Provider of Desiccant and Air Handling Systems 10
Moisture Transfer -Rotor spins between Process and Reactivation. (16 RPH) CDI is the Premier Provider of Desiccant and Air Handling Systems Desiccant Dehumidifier 22 11
Technology of Desiccants Phases 1. Sorption 2. Desorption 3. Cooling 1 2 3 23 Infrared Photo Cooling Sector Depiction 12
Effect of Process Velocity on Cooling Sector 400 FPM 800 FPM Green Purge 13
Process Temperature Rises Air leaves the Unit @ 14 gr/lb 1. Follow wet bulb line between entering humidity ratio and leaving 2. Follow Dry bulb 3. Add 15% for regeneration heat carryover Air Entering @ 50.0 F and 53 gr/lb Solution = 86.3 F Actual Process Psychrometric Process Temperature Rise Estimate 85.9 F 14
Reactivation Out Reactivation Inlet Process Inlet Reactivation Heated Process Outlet Equilibrium -Dehumidifiers operate in equilibrium. -The total energy on the process side is balanced by the energy in reactivation. (Mass Balance) -If the system is not in equilibrium-which can occur if airflows and temperatures are not controlled- a dehumidifier will not perform in an easily predictable manner. 15
Reactivation Energy Modulation -As load on process drops less energy is required to maintain outlet temperature. -Reactivation Energy Input is modulated to maintain constant reactivation outlet temperature. (130-140F) -Reactivation Input temperature is monitored to protect rotor from overheat damage. CDI is the Premier Provider of Desiccant and Air Handling Systems CDI - Dual Sensors Protected on both sides 04/2016 32 16
Factors Effecting Performance Process inlet moisture Process inlet temperature Process velocity Reactivation input energy Amount of desiccant presented to air stream CDI is the Premier Provider of Desiccant and Air Handling Systems Amount of Desiccant Presented to Air Stream Wheel Depth 100MM, 200MM, 400MM 4 8 16 P to R Ratio 3-1 (75% to 25%), 1-1 (50% to 50%) Rotor Speed CDI is the Premier Provider of Desiccant and Air Handling Systems 17
Moisture Removal Humidity Modulation 1. On/Off Unit Operation 2. Face and Bypass Rotor Modulation 3. Reactivation Heat Modulation 4. Process Flow Modulation (Supply Fan VFD) CDI is the Premier Provider of Desiccant and Air Handling Systems 18
Moisture Removal Desiccant Dehumidifier 38 19
Capacity Control When to Precool? 20
When to Post Cool? Some spaces like the warm temperature like Ice Arenas & WWTP. Post-cool to remove excess heat Include in the CDI unit or not Sensible only device (Chilled Beam) CDI is the Premier Provider of Desiccant and Air Handling Systems Copyrights CDI presentations use materials from the following Sources: -Internal CDI equipment pictures, installations, performance data, etc 1985-2018 Climate by Design International, Inc. -ASHRAE, AORN, ASHE and other public Standards and Engineering documents in the Public Domain -Pictures and graphics from the Public Domain 20 02/2014 21
A special thanks to the following organizations to help make this presentation possible: Scott Limberg at Limberg Productions for his video work. www.limbergproductions.com 22