Humidification Methods for Environmental Chambers

Environmental chambers for insect and plant research
are common applications requiring humidity control.\
Image courtesy Percival Scientific

Many environmental chambers utilized in research or production applications have a requirement to maintain a specified moisture level in the controlled space. Most often, the moisture level is specified as relative humidity. Some moisture levels may require the removal of moisture from the space, but the focus of this article is those instances where moisture must be added to the air in order to maintain the setpoint.

In designing a humidified environmental chamber, or specifying one for your own application, the challenge is to add moisture to the air in a fashion that does not result in detrimental effects on the contained materials or work. Additionally, the humidification system operation must work in concert with, not adversely to, other elements of the system that are tasked with maintaining other environmental conditions, such as temperature. With some awareness of the various methods available for humidification and their potential impact on your work and your budget, you will be better positioned to make an informed selection and achieve your desired outcome.

Several humidification methods are widely available for commercial use, all of which result in the same thing; adding water vapor to the air in the controlled space.

• Steam introduction directly into the space: This direct addition of water vapor using low pressure steam should only be used when the sourced steam is positively known to be suitable for introduction into an occupied space. Any treatment chemicals used for efficient boiler and steam system operation could possibly travel with the steam into the controlled space. If the steam is clean, the main concerns are potential heating of the air by the sensible heat of the steam and the reliability of the steam source. An advantage of this method is that it is very rapid in response to a control signal. The hardware to regulate and control the steam injection can be costly, and present a challenge to some service techs.
• Passive evaporating of water using the chamber air: Water will evaporate into air at differing rates under differing conditions. Directing a flow of air from the space over a water surface or falling stream of water will result in some degree of evaporation, with a corresponding increase in relative humidity. These systems come in many configurations designed to fulfill a range of requirements and available installation space, some with heating of the water to increase the evaporation rate. They are inexpensive and slow to respond. A major issue for some applications is the tendency for the water sitting in the evaporating pan to harbor biological contaminants. Frequent cleaning is a characteristic maintenance item for these systems. Cleaning reduces contamination levels and also removes the accumulated mineral deposits and other debris left behind by the evaporating water. This method of moisture addition will result in a small amount chamber air cooling.
• Evaporating water using electric heat - This humidifier is similar to the passive evaporating method just described, but with the addition of a controlled heating system that can increase the evaporation rate. Consisting essentially of electric heaters immersed in water contained in a comparatively compact unit, these humidifiers can be selected to deliver very large amounts of vapor from a small package. The electric heat is the primary driver of evaporation. Heat applied to the water can be regulated in very fine increments to provide accurate humidity control, with little excursion from the setpoint. It is not uncommon for these units to boil the water contained in the unit, so one concern is the amount of sensible heat that is delivered with the water vapor and its potential impact on room temperature. Cost is moderate. Maintenance levels are low, but a treated water supply is recommended to minimize scale formation. Biological contamination is of little concern with these units due to the temperature at which they operate. Several configurations of this type of humidifier allow for a broad choice of installation options.
• Evaporating water using steam - With essentially the same operation as described above for the electrically heated unit, a steam heated humidifier utilizes steam as the heat source. Precise control of a steam supply is generally more difficult and expensive than a comparable capacity electric heating system. These systems are generally available as larger capacity units.
• Water dispersion devices - Several technologies are utilized to increase the surface area of a water supply and disperse it into the controlled space where it is evaporated by the air. Simple and inexpensive centrifugal atomizers create fog of tiny water droplets that evaporate as they contact the chamber air. Other devices employ compressed air and specialized spray nozzles to create very small water droplets that produce a similar result. Ultrasonic transducers aer also employed to atomize water into a fine mist. Centrifugal atomizers are probably the least expensive option, but may not provide the level of control accuracy needed, since they are not well suited to rapid on/off cycling. Ultrasonic transducers and spray nozzles can be sized or configured to provide better levels of output modulation, but come with a higher cost. Maintenance requirements for water dispersion devices should be considered. Another consideration for this type of humidification is water supply quality. Liquid water is dispersed in the air, then evaporated. Anything contained within the water droplet that is not water will be liberated in the controlled space. Over time, particulates and once dissolved minerals can accumulate on environmental chamber surfaces and require cleaning and removal.

There are many facets of humidification to consider for an environmental chamber or room. The less expensive first cost option may not be the best overall selection. Share your requirements with an environmental chamber specialist and leverage your own knowledge and experience with their application expertise to develop an effective solution.

Full Featured Environmental Chamber Control System

The IntellusUltraConnect C9 adds a range of remote
connectivity functions to the operational functions of the
IntellusUltra C8.
Image courtesy Percival Scientific

Percival Scientific has a long history of designing and manufacturing environmental chambers and plant growth chambers for life science industries and institutions. Those years of experience are part of the IntellusUltra series of control units that serve as the user interface and operating unit of the company's line of environmental rooms and chambers.

Ease of use is the hallmark of the controllers. Some applications, especially those for plant studies, can require multi-step profiles that change temperature, humidity, lighting, and other functions. Entering or editing a profile with IntellusUltra is intuitive and simple.

In addition to a plethora of operational features, the "Connect C9" version offers a range of remote connectivity functions that can keep users in touch with their equipment and research anytime and anywhere. From the Percival Scientific website...

• Remote connectivity and monitoring with e-mail notifications.
• On-board USB connection allowing for real time data logging with up to four gigabytes of data storage. Simply use a portable USB stick to download your data to analyze on any other capable device.
• An on-board Ethernet connection allows direct monitoring and analysis of chamber conditions.
• Available remote monitoring software has been optimized to interface with the major web browsers.
• Ability to upgrade to our cloud-based service securely and confidently monitor and backup your research data

Solid control of environmental parameters, plus connectivity that enables access to the system from anywhere. More detail is provided in the document included below. Share your environmental room and chamber plans and challenges with experienced lab equipment professionals, leveraging your own knowledge and experience with their product application expertise to develop effective solutions.

Plant Growth Chamber Environmental Controller from Atlantic Technology Group, Inc.

Controlled Environment Room Air Flow Matters

Matching controlled environment air flow pattern, velocity,
and volume to the application is part of delivering a well
performing system
photo courtesy Percival Scientific

Environmental chambers, whether of the reach-in or walk-in variety, all rely on the movement of air within their controlled space to attain performance specifications. Various manufacturers will employ differing strategies for chamber air movement, and the manner in which their designs disperse air flow throughout a chamber of any size can have an impact on the work or process held within the chamber.

This article is about controlled environment rooms, but much of what is included here is also applicable to smaller sized chambers.

The design of air flow in a controlled environment room can be impacted by a number of factors, some of which may be based on specific application requirements, and others that may be influenced by cost, production simplicity, or other factors unrelated to the performance goal of the equipment.

What aspects of controlled environment room air flow bear on performance?

• Velocity - In the common usage of the term when referring to air flow, the speed of the moving air. Depending upon the air moving equipment arrangement and any dispersion devices, such as perforated suspended ceilings or wall plenums, air velocity can vary throughout a chamber. Users should consider how their work may be impacted by air flow velocity. The storage of material in closed and sealed containers may be impervious to air velocity effects because the "product" within the container is not in contact with the moving air. Plants and insects, on the other hand, are an example of items that may be significantly or severely impacted by air velocity. Higher air velocity at a chamber location exposes that location to more air per unit of time. Desiccation is one possible concern that is exacerbated by increased air velocity. Higher velocity can also be beneficial, even necessary, for some applications. Rapid cooling or heating of materials placed within a chamber is enhanced by increased air movement across the material surface.
• Volume - The volumetric flow of air through a controlled space or chamber is needed to transfer heat to or from the space in order to maintain temperature control. Much of the air in a controlled environment room is recirculated, with cooling, heating, and in some cases moisture applied to condition the air in the room to the setpoint. The volume of air movement is loosely related to velocity, so increasing volume will result in an increase in velocity unless other design changes are made with respect to how the air is dispersed throughout the room. Higher volume, or turnover rate, contributes to better temperature uniformity in the room. As with velocity, there may be application specific requirements for low air movement. Keep in mind that low air movement creates challenges to the attainment of close temperature control and uniformity. 
• Pattern - The way in which air is distributed throughout the controlled environment room can impact system performance once materials are placed in the room or process work is commenced. Empty chambers generally perform well, regardless of the air flow pattern, because there is little in the way of a load on the system and no solid materials in place to block or redirect air flow. Consideration should be given to the way in which air is dispersed throughout the work area. Loading patterns for stored product or the placement of work in process should be accommodated by the air flow pattern.

Matching the right air flow characteristics to the work to be achieved in a controlled environment room will result in better overall performance, not just when empty chamber tests are conducted, but when real work is being accomplished. 

Share your environmental chamber and controlled environment room requirements and challenges with application experts. The combination of your own experience and knowledge with their specialized technical expertise will yield an effective solution.

Environmental Chambers - Difference Between an Alarm and a Limit Control

Walk-in Controlled Environment Room
Courtesy Percival Scientific

Users of controlled environment equipment are generally not process control experts. The user's interest in the equipment is, and should be, focused on how it furthers their own work and effort.

Lab equipment that provides a temperature control function will often have an integrated heating or cooling means that is regulated by the unit controller. Controlled environment chambers, including benchtop, floor standing, and walk-in types often are provided with sufficient heating of cooling capacity to do damage to the equipment, the contained product or work materials, even surrounding spaces if allowed to run out of control. Why so much power? Designing a chamber of any size to provide fast recovery after a disturbance, like a door opening, will boost the capacity requirements for the heating and cooling portions of the system. Similarly, equipment with extended temperature range is likely to have expanded cooling or heating, and there are many other performance requirements that have the same impact on the unit capacity. The key element for placing this type of equipment in an occupied space is how malfunction resulting in uncontrolled operation of the environmental conditioning system is handled to prevent catastrophe.

An alarm is an annunciation of an adverse condition. Alarm function may be, and often is, provided as part of the temperature controller, utilizing the same device, same sensor. Alarms tell the operator something has gone wrong, is about to go wrong, or is currently going wrong. The nature of most alarms allows the user to set the conditions at which notification occurs. Additionally, some equipment provides options for how alarms are handled. Audio and visual indication are common features, and some equipment is provided with alarm relay contacts that can be connected to building management systems or other remote monitoring equipment. Whether an alarm will automatically reset if proper conditions are restored, or manual intervention is required to stop any alarm related activity once the alarm has occurred can also be different ways in which alarm functions are implemented by manufacturers. The overall range of alarm functionality combinations is extensive, with some equipment providing richer feature sets than others.

Alarms, in some controlled environment systems, are configured to take some sort of action to remediate the adverse condition. This activity is separate from the announcement of the alarm condition. While having corrective action taken by the control system may seem advantageous, and in some cases it may help prevent loss or damage to product contained within the environmental chamber, this is not true limit control action and is not the best practice for assuring safe operation of machinery with the capacity to do real damage to itself or surrounding spaces.

A limit control may appear at the user interface level to mimic the function of an alarm. There is a difference, though. Properly done, a limit control operates with total independence from any part of the regular temperature controller. The limit controller will be a separate device and not share any operating hardware with the temperature controller device chain. What does this mean for the user?

Relying on the temperature controller to respond to an adverse condition has some potential flaws. The temperature controller, or any of the components in the temperature control device chain, could be the root cause of the adverse condition through malfunction or outright failure. Reliance on a control circuit, likely with a malfunction of one or more of its components, to prevent further temperature excursion is not good practice. A properly designed limit control circuit does not rely on any of the components in the potentially failed circuit to stop heating or cooling.

Not all failures are a single event. Chains of failure can trigger, or one failure can expose the existence of another system weakness or failure that was previously undetected. Having a positive and independent means to reliably stop system operation is not costly to implement and can head off catastrophes resulting in substantial loss of time and money. Catastrophe, for an environmental chamber, can look like this...

• Freezing of product that should not be frozen
• Freezing and bursting of pipes in a walk-in chamber
• Destruction of work or product contained within a chamber due to excessively hot or cold temperatures
• Excessively hot temperature that activates a fire protection sprinkler head in walk-in unit

In essence, the purpose of an environmental chamber is to create and maintain a single condition at any point in time. There is only one way that things can go right, and countless ways they can go wrong. Having an independent watchdog controller that prevents the worst from happening is good practice. Share your controlled environment chamber requirements and concerns with an application specialist. The combination of your process knowledge and experience with their product application expertise will yield an effective solution.