CDQ Desiccant Dehumidification
October 2004 CLCH-SLM014-EN
Trane, in proposing these system design and application concepts, assumes no responsibility for the performance or desirability of any resulting system design. Design of the HVAC system is the prerogative and responsibility of the engineering professional.
Trane and the Trane logo are registered trademarks of Trane, which is a business of American Standard Companies.
2004 American Standard Inc. All rights reserved. Confidential CLCH-SLM014-EN
This marketing guide introduces the Trane CDQ (Cool, Dry, Quiet) patented desiccant dehumidification option, and includes an overview, benefits, market drivers, and selling strategies.
Trane offers several dehumidification options. To understand which option is best for your application, you need to be knowledgeable about basic dehumidification principals. Recommended reading to familiarize yourself with dehumidification is the ASHRAE 90421 Humidity Control Design Guide for Commercial and Institutional Buildings.
The Trane CDQ is a new, unique dehumidification option that places a desiccant wheel in series with the unit cooling coil. (See Figure 1). The wheel is not an enthalpy recovery wheel, nor is it a high-temperature active desiccant wheel. It is an active desiccant wheel option, regenerated by return air, to enhance the dehumidifying performance of a standard air conditioning cooling coil. CDQ uses only one air stream; no exhaust air or second regeneration air stream is required.
For technical information on CDQ desiccant dehumidification, read CDQ Engineering Bulletin CLCH-PRB020-EN. Additional information can be found in the Air Handler Custom Toolbox.
Figure 1. CDQ places a desiccant wheel in series with a cooling coil
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CDQ Overview and Benefits
CDQ Product PositioningTrane CDQ fits between the cold coil systems and the conventional new- energy desiccant systems. Cool-reheat systems provide cold air that needs to be reheated. High-temperature active desiccant systems provide hot air that needs to be cooled. CDQ provides cool but dry air. CDQ is an integrated desiccant cold coil unit that gives a standard air handler or rooftop unit significantly better part-load dehumidification capability.
Selling CDQ dehumidification greatly depends on the customers awareness of humidity control and its effect on mold, health, comfort and processes. If a customer wants temperature independent humidity control, tight space relative humidity (RH) or dewpoint control, or simply a better part load dehumidifier, CDQ may be the answer.
Controlling Space HumidityA key question to ask is Will the space humidity be controlled with an RH or dew-point sensor? Actually measuring the space humidity means it is important and could be a CDQ candidate. If the answer is that they will be controlling space dewpoint or grains/lb. of water vapor - you have an excellent application for CDQ. Reason: Relative humidity has traditionally been used when controlling comfort dehumidification. Relative humidity fluctuates with the space dry bulb temperature. During night setback, in a hot humid outside climate, the indoor temperature and water content in the building will go up. The RH will show the building is in control, but it is not. Water is being stored in the furniture, carpeting and ceiling tiles. When the temperature is brought back down, the RH increases and it can take many hours to bring it back into control. Using dewpoint humidity control minimizes, if not eliminates, excessive moisture buildup in carpeting, furniture, etc. Result: a more stable humidity controlled environment. CDQ can use RH or dewpoint control, but dewpoint is recommended.
CDQ Overview and Benefits
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CDQ - How it WorksThe Trane CDQ desiccant wheel is used to enhance the dehumidification performance of a traditional cooling coil. The wheel is configured in series with the coil such that the "regeneration" side of the wheel is located upstream of the coil, and the "process" side of the wheel is located downstream of the coil. The CDQ desiccant wheel adsorbs water vapor from the air downstream of the cooling coil, and then adds it back into the air upstream of the coil, where it is removed by the coil through condensation. This is accomplished without the need for a second regeneration air stream.
CDQ Benefits Increased cooling coil latent (dehumidification) capacity
Lower supply air dew points
Decreased need for reheat
Lower unit cooling sensible heat ratios (SHR)
Warmer required chilled-water temperatures
Decrease the required cooling capacity when dehumidifying
Exhaust air is not required
All electric system no expensive gas heat needed
Lowers supply-air dew point
The addition of the CDQ desiccant wheel to the system enhances the dehumidification performance of the traditional cooling coil. The CDQ wheel transfers water vapor, and the cooling coil does all the dehumidification work in the system. The latent (dehumidification) capacity of the cooling coil increases without increasing its total cooling capacity. CDQ can achieve a lower supply-air dew point than the coil temperature.
Saves cooling and reheat energy
Utilizing the CDQ wheel enhances the dehumidification capabilities of a cooling coil. In order to remove the same amount of moisture, a cool-reheat system will require more cooling capacity and need to reheat. CDQ will generally save cooling and reheat energy, and may even allow for downsizing of the cooling equipment.
The cooling coil sensible heat ratio (SHR-the ratio of sensible cooling to total cooling), is also lowered with CDQ without using reheat. This helps the unit provide significantly better part load dehumidification (up to 200 percent better) and reduces the need for reheat.
CDQ Overview and Benefits
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Extends achievable dew points of traditional DX or chilled water systems
A unique benefit of the CDQ system is that it can deliver a lower supply air dewpoint than other technology that uses a traditional cooling coil. A cooling coil can typically dehumidify air to a dew point that is 5F to 10F above the temperature of the fluid or refrigerant that flows through its tubes. For example, 45F chilled water (depending on the flow rate and coil characteristics, of course) can dehumidify air to a dew point of 50F to 55F. By adding a CDQ desiccant wheel to the process, the supply-air dew point can be 0F to 10F below the chilled-water temperature. This can extend the achievable dew points of traditional DX or chilled-water systems.
Improves energy efficiency
A CDQ system can also improve the energy efficiency of chilled-water systems. Because the chillers can produce warmer water temperatures to achieve lower supply-air dew points, the chiller can be more efficient. CDQ may also reduce the pumping power by allowing reduced chilled-water flow rates, and may eliminate or reduce the need for glycol in the system. This allows building areas requiring lower dewpoints to use the same chilled-water temperature as the rest of the facility.
Finally, in low dew point applications, CDQ may reduce overall energy use by eliminating the need for a coil defrost system or an active (high-temperature regenerated) desiccant system.
CDQ Overview and Benefits
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Reduces path noise control options
CDQ is a blow-thru design, which means it is significantly quieter then a standard draw-thru unit. An example below (see Table 1), using the CLCHLw acoustical program found in the Custom Air Handler Toolbox, shows the CDQ configuration is significantly quieter from 125 Hz thru 8000 Hz. Replace the FC fan with a double-width AF or a Trane plenum fan and the sound levels are close to the top of the line Q fan units! Bottom line: Using CDQ can help reduce, if not eliminate, expensive path noise control options.
Control of the CDQ wheel itself is on/off. Control can be as basic as a humidistat, but most applications will require a programmable DDC controller, such as the MP580 controller. A CDQ unit can have up to three stages of dehumidification beyond cooling. Each system may or may not require all three stages. Sample sequences are outlined for the various component configurations for CV and VAV mixed air systems and for dedicated outside air units. These can be found in the Air Handler Custom Toolbox.
Table 1. CDQ sound levelsHertz 63 125 250 500 1K 2K 4K 8K
M-Series size 10 8-row coilDischarge Lw (draw-thru FC fan 101 93 91 85 86 84 81 74Unducted inlet Lw (draw-thru FC fan) 78 78 70 66 58 52 50 46
CDQ Blow-thru FC
M-Series size 10 CDQ configuration 8-row coilCDQ discharge Lw (FC fan) 100 82 76 67 66 60 54 45Difference from base -1 -11 -15 -18 -20 -24 -27 -29Unducted inlet Lw (FC fan) 84 82 76 72 66 60 60 58Difference from base 6 4 6 6 8 8 10 12
CDQ Blow- thru AF
M-Series size 10 CDQ configuration 8-row coilDischarge Lw (housed AF fan) 89 82 71 65 63 54 43 36Difference from base -12 -11 -20 -20 -23 -30 -38 -38Unducted inlet Lw (housed AF fan) 90 86 74 79 70 62 56 50Difference from base 12 8 4 13 12 10 6 4
Figure 2. Discharge sound comparisons
Discharge Sound Comparisons - Std unit versus CDQ
63 125 250 500 1K 2K 4K 8K
Discharge Lw (Draw thruFC Fan)CDQ Discharge Lw (FCFan)Discharge Lw (HousedAF Fan)
CDQ Overview and Benefits
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A cooling coil without a CDQ will dehumidify and have a typical sensible heat ratio (SHR) of 0.8. Turning on the CDQ wheel activates Stage 1 of dehumidification, with the same total capacity of cooling the latent capacity increases lowering the typical SHR to 0.6. In Stage 2 of dehumidification, reheat can be activated to obtain an SHR down to 0. If the dew point of the supply air is not low enough, Stage 3 of dehumidification can be activated. This increases the required total capacity of cooling, but lowers the achievable dew point. The typical SHR in this stage is 0.3 and reheat could be added to get down to 0. (See Table 2).
Humidity sensors are a critical part of a CDQ system. If the sensors are not calibrated or drift, the system may not dehumidify or over dehumidify. Trane has researched and tested numerous sensors. For most applications, use the Trane 3 percent RH sensor. For critical applications, 1 percent and 2 percent sensors are available as a CDQ special.
Patent InformationTrane CDQ has a patented dehumidification cycle, originally called the Cromer Cycle. It is important to understand that the patent is a concept patent, not a mechanical patent.
Semco is the only other company that has limited patent rights for this concept with their Pinnacle unit. The Pinnacle is a two-wheel 100 percent outside air (OA) ventilation energy recovery unit. It is a dedicated outdoor air unit that provides room neutral air. By comparison, Tranes CDQ is an enhancement to a mixed air unit that cools and dehumidifies. Trane has additional patents pending on the CDQ controls.
Table 2. Stages of dehumidification
CDQ Stage Configuration
Typical leaving dew point off unit with 45F coil
Typical leaving dew point off unit with 40F
heat ratio (SHR)
0 Cooling coil 50-60F 45-55F 1.0-0.751 Cooling coil, CDQ 43-50F 38-45F 0.50-0.752 Cooling coil, CDQ, reheat 43-50F 38-45F 0.00-0.503a Cooling coil, CDQ, preheat 38-43F 30-38F 0.25-0.40*3b Cooling coil, CDQ, preheat, reheat 38-43F 30-38F 0.00-0.40**The ratio of cfm/ton required in Stage 3 is lower than Stages 0, 1, and 2. Stage 3 is not used to obtain a lower SHR; it is reserved to obtain a lower dew point not achievable in Stages 1 or 2.
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ASHRAE Standard 62 and Its Impact on Indoor Humidity
Ventilation and humidity play a large role in the quality of indoor air. Since 1992, indoor air quality (IAQ) has become a major concern for many building owners.
Ongoing industry and manufacturer education programs are convincing end users of the importance of ventilation and space humidity control. This IAQ concern is helping drive the growth of the dehumidification markets. Current trends in HVAC design and utilities deregulation favor growth in enhanced dehumidification system markets.
More Outside Air
In 1989, ASHRAE increased the ventilation rates that apply to all non-residential buildings. This standard has been slowly adopted into codes. Today, most HVAC system designers are bringing in adequate amounts of outdoor air. With this outside air came more heat and humidity. This led to a dramatic increase in the use of airside energy recovery products such as coil loops, plate exchangers and energy recovery or heat wheels. These products have lower total cooling capacity needs thus often saving operating costs but they do not control space humidity. Only a cold coil or active desiccant wheel can lower indoor humidity levels.
Wetter outside air
Prior to 1997, most designers looked at only the design dry bulb/mean-coincident wet bulb temperatures in designing HVAC systems. This information allowed them to select the proper chiller and coil to handle the design load. Part load outdoor air humidity information was not generally available or not used. In 1997, ASHRAE incorporated part load outdoor humidity information into the ASHRAE Handbook of Fundamentals. Depending on the climate, HVAC equipment needed more total cooling capacity and significantly better part load humidity control. It is easy to upsize equipment. It is not easy to get a 0.5 or 0.3 SHR ratio. This is where CDQ comes to the rescue.
Dehumidification Market Drivers
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Growing numbers of design engineers understand the benefits associated with managing the increased latent loads resulting from accommodating the ASHRAE 62 ventilation standard. Acceptance of this fundamental change in system design should proliferate, as the impact of part load latent control is better understood. This trend can help sell CDQ.
In recent years, ASHRAE, the building industry, and insurance companies have focused on indoor air quality and specifically on humidity control in comfort applications. The emerging requirement is to keep the space inside the building vapor barrier below 60 percent relative humidity 24 hours a day, seven days a week. The focus on controlling indoor space relative humidity has created a market for dehumidification equipment that can control the space humidity (latent control) independent of the space temperature (sensible control).
Humidity Control Slows Building Component Damage High internal humidity can have a negative impact on the structure of a building component. High relative humidity can cause mold and mildew growth in walls, floors, and ceilings, adversely affecting wallpaper, carpeting and destroying the interior decoration. Hotels and motels often experience this problem.
Moisture-laden air affects building components if not properly controlled. The need for dehumidification is important for end users who must guard not only their interior decorations but other building components as well.
Humidity Control Disadvantages
First cost of any enhanced dehumidification is more than a standard HVAC system.
Operating costs of a humidity controlled building will often be higher then a temperature only controlled building. The reason is simple. The building is a temperature and a humidity controlled envelope. You need part load humidity control and some of the part load improvement options are expensive to run.
Operating costs could also be higher because the humidity controlled zone lacks a good vapor barrier. No vapor barrier means humidity will leak in from other areas, causing the dehumidification equipment to work harder.
Finally, reliability. Most dehumidification equipment has lots of components and therefore lots of controls. More controls means more items to maintain. A recent Department of Energy- (DOE) funded study of a new-energy, high-temperature desiccant unit showed several component and control problems that led to poor conclusions about the product. CDQ has a different type of desiccant wheel and the controls for it are straight-forward without the complexity of multiple units.
Dehumidification Market Drivers
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Methods of DehumidificationThere are two primary dehumidification methods. Cold coil dehumidifiers are the most common and usually applied to dew-point requirements of 45F and above, while desiccant dehumidifiers are more popular in the below 35F dew-point applications. However, a wide grey area exists between 20 grains and 55 grains. Both system types are promoted as the best solution.
Cold Coil Dehumidification
Cold coil dehumidification uses chilled water coils or DX cooling coils to dehumidify. Traditionally used where space requirements have a 45F dewpoint and greater.
Cold coil HVAC equipment controlled solely by a thermostat can only do a good job of controlling space humidity if the needed sensible and latent reductions occur at the same time, which seldom occurs. Often, the latent dehumidification need is not coincident with the sensible cooling need. New energy reheat after a cold coil is a common way to control unbalanced latent and sensible cooling needs. This system is called a reheat or terminal reheat system and adds energy consumption. To avoid using new reheat energy, some manufacturers use condenser waste heat from the chiller or compressor and pipe it to an auxiliary condenser coil in the reheat position downstream the cold coil. This saves reheat energy but not compressor or pump energy.
Another issue is icing. Deicing adds energy consumption and complexity. Cold coil dehumidification below 32F (0C) can cause ice to form on the coil fins and tubes. Refrigeration chilled-water coils can use glycol to keep the fluid moving inside the coil. But outside the coil, air passing over the coil will be cooled below 32F, which causes ice to form on the coil. To control the icing, coil deicing systems are used. These systems are effective and widely used, but they use energy and require a high degree of equipment complexity and cost. For this reason, cold coil applications below freezing are generally limited to process applications.
Table 3. Cold coil dehumidifier companies Company (ranked by greatest market share)DectronDesert AireHeat Recovery Technology (Poolpak)DumontDryAire Systems Inc., Ebac, Inc., Nautica Dehumidifiers, Inc., Air Technology Systems, Inc., Dehumidifier Corp. of America, Therm-Stor Products, DesChamps, Enviro-Air Control Corp., American Energy Exchange
Dehumidification Market Drivers
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Active Desiccant Dehumidification
Desiccant equipment was developed for the process industry and has moved into comfort applications on the perception of being energy efficient for dehumidification. This is not always true. Liberties can be taken in the energy analysis to swing the analysis. For example, not including gas consumption, comparing gas heat to electric heat, etc. When doing a comparison, do it at the full unit level with all components for all given operating points. For a full year, the analysis needs to be done with a full simulation program like the Trane Trace 700 program.
Active desiccant dehumidification uses a heat source in a second air stream to dry a portion of a rotating desiccant wheel and thus drive off the water vapor. In the process side of the wheel air is dry but it becomes really hot, typically 150oF+. Its important when comparing active desiccant and CDQ active desiccant systems that all of the energy going into both units be compared on an annual basis for equal operating conditions. When the total, unbiased costs of getting to the same point are considered, CDQ will have a strong financial justification.
Table 4. High-temperature active desiccant dehumidification companies
Company (ranked by greatest market share)
Air Technology System
Kathabar, Drykor, Ebac, Semco Inc., NovelAire Technologies, Advanced Thermal Technologies, Bay-Air Devices, Inc., Low Humidity Systems, Inc.
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CDQ Selling Strategies
Trane has a new opportunity in the dehumidification market. Major key selling points:
CDQ dehumidification is available with many Trane products. Additional products are in the development stage. For availability, see Table 5.
Focus on specifying leaving air dewpoint and temperature at design and part load. (See Table 6)
Focus on the need for Trane integrated controls to eliminate sensor drift and provide lower operating cost.
Focus on superior part-load performance
Table 5. Trane products with CDQ desiccant dehumidification
M-Series Ready today, select and price from toolbox
T-Series Not available
Custom Comfort Ready today, select from toolbox, Ft. Smith ASD prices
Custom Process Ready today, select from toolbox, Rockingham prices
Precedent Rooftops Clarksville Product Support
Intellipack Not available
Table 6. Application humidity targets
Application Target Dewpoint or RH
Laboratories 40 DP
Dry air storage (military) 35% RH
Ice rinks 25 DP
Dorms 47 DP
Elder-care facilities 47 DP
Hospitals (operating rooms) 40 DP
Museums, archives 35 DP
Libraries 47 DP
Schools 47 DP
Supermarkets (freezer area) 42 DP
Office buildings 47 DP
Hotels 47 DP
Restaurants 47 DP
CDQ Selling Strategies
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Applications to look for include:
One or several zones requiring lower than building average humidity equip just the units serving those zones with CDQ.
Entire building requires independent humidity control use CDQ on all units.
Entire building needs better part-load humidity control use CDQ on the hot spots.
Current building dehumidification equipment uses too much gas, is too complex, or needs too much maintenance replace units with CDQ enhanced units.
Dehumidification Option Analysis
Possible LEED points for CDQ Energy and Atmosphere (EA) 1 credit for optimized energy performance.
CDQ is an innovative system that performs better than condenser reheat or high-temperature desiccants.
Indoor Environmental Quality (IEQ) 7 credits for thermal comfort. Areas for credits: 1 point because CDQ will comply with ASHRAE 55-92 Addenda 95 for thermal comfort standards including humidity control within established ranges per climate zones. 2nd point can be gained through installing a permanent temperature and humidity monitoring system configured to provide operators control over thermal comfort performance and effectiveness of humidification and/or dehumidification systems in the building.
Table 7. First cost, operating cost, and control complexity for dehumidification options
Type of DehumidificationFirst Cost*
Condenser reheat 1 8 1
CDQ 1-wheel system 5 4 2
Series coil loops 4 7 2
Reheat 2 10 1
Series ATA plate (DesChamps, Wringer) 4 6 5
Series heat pipes 6 7 4
Advanced indirect/direct evaporator 2- and 3-wheel systems
10 2 10
Liquid desiccant systems 7-9 6 8
Gas-fired active desiccant 1-wheel (Munters Dry Cool)
6-8 9 8
*Rank is base on a scale of 1-10, with 1 being low.
CDQ Selling Strategies
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Support for CDQTrane has the knowledge and expertise to help you sell CDQ desiccant dehumidification.
Demo CDQ Unit
A fully functional CDQ demo unit is located in the Lexington manufacturing facility Customer Showcase area. It is a self-contained CDQ mock-up with operational display sensors showing dewpoint, RH, and dry bulb temperature at multiple points throughout the unit. Contact your Lexington product support team to set up a customer visit to demonstrate the unit.
CDQ Selection Tools
The CDQ performance selection program is available in the Air Handler Custom Toolbox for performance selections, drawings, and pricing. It even has an interactive psychometric chart to explain the CDQ process. Marketing and engineering information, such as ordering instructions, typical unit configurations, and much more is available.
CDQ Guide Specs
A CDQ guide specification can be found in the Air Handler Custom Toolbox. It is critical that the engineer specifies part-load performance as well as design performance. The part-load condition performance will keep contractors from trying to substitute alternative, less effective technologies.
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TraneA business of American Standard Companieswww.trane.com
For more information, contact your local Trane office or e-mail us at [email protected]
Literature Order Number CLCH-SLM014-EN
Date October 2004
Stocking Location Inland
Trane has a policy of continuous product and product data improvement and reserves the right to change design and specifications without notice.