By Mike Lawler, Data Aire

Whether your emphasis is on pioneering technology, developing life-saving drugs or managing the integrity of sensitive documents or artifacts, maintaining the perfect environmental envelope is vital to your success.

• Require tight control over temperature and humidity
• Have large swings in cooling requirement daily & annually
• Must dehumidify when little or no cooling is required

What Type of HVAC Provides Precision Air Control for Low Load Applications?

Applications that require both temperature and humidity control must use equipment that is capable of cooling, heating, humidifying and dehumidifying modes. The most effective way to address this need is to provide one piece of equipment that provides all those modes of operation. If the load in the space is large, over 40 or 50 tons, a custom package unit can provide this function.

It can be challenging, however to find equipment in smaller tonnages that can do the job. In response to this, engineers often attempt to use Computer Room Air Conditioners (CRAC) equipment in laboratories, libraries, archives, and medical imaging rooms that have lower cooling requirements. CRAC units provide all the modes of operation needed and they are available in sizes as small at 2 tons. A deeper look into these applications, however, will show that standard CRAC units are not suited to these applications.

Standard Computer Room Air Conditioning         

• Cooling runs more than half the time to cool the room
  Minimal moisture removal (80-90% SHR adequate) needed
  Dehumidifies <10% of running time.

Highly Variable Cooling Load Rooms

• Zero cooling load at times
• 60-70% SHR needed
• May have to dehumidify half of the run hours

Design Day Reasonable Tolerances

Standard CRAC units do a good job of controlling temperature and humidity when they are required to produce cooling that is at or near their maximum capacity. Maximum cooling capacity is called for on days when the outdoor ambient temperature nears its annual maximum and, at the same time, internal heat generation from lights people, and equipment are at their maximum. This condition is known as a design day with a concurrent design load in the space. Unfortunately, these conditions only occur a few hours a year. The farther the conditions fall below the above described maximums, the more difficult it becomes to control humidity in the space to within a reasonable tolerance. When the cooling requirements fall much below 50% of maximum, the space is often subject to wide swings in temperature & humidity that are totally unacceptable to the occupants of the space.

The reason is that the standard CRAC units are not designed to remove a significant amount of humidity per hour. The dehumidification in a CRAC unit is done by the cooling coil. As long as there is a call from the thermostat to deliver cooling to the space, dehumidification happens as a byproduct of cooling down the room. When the thermostat requires that cooling be delivered for 70% or 80% of the time, the CRAC unit can keep up with the dehumidification requirements in the space. But think about how few hours per year this requirement exists in rooms that are not data rooms. Essentially, those conditions only exist in the daytime, during the hottest part of the summer.

Understanding Dehumdification and Cost Controls

Dehumidification mode, by definition, means removing humidity from the air without sending any cool air into the space. Since the cooling coil removes the moisture this means that the CRAC unit must run the cooling and the heating in the unit at the same time.

There are two problems with this. First there is only ½ as much heat capacity in a standard CRAC unit as there is cooling capacity. That means the already minimal amount of dehumidification available at full load is cut in ½. You cannot increase the cooling capacity to get more dehumidification. If you do, there is not enough heat in the unit to offset the increased cooling capacity. Cold air would be delivered to the space and the space temperature will begin to drop too low. Unless it is hot outside and there is a significant requirement for cooling from the space a standard CRAC units simply cannot reach the desired humidity setpoint.

The second problem is that heat in CRAC units is provided by electric resistance heating elements. From a power cost standpoint, this is absolutely the most expensive source of heat anyone can use. In a data room the electric heat runs only a handful of hours a year so this is not an issue. In other applications though, the electric heat runs hundreds or even thousands of hours per year while in the dehumidification mode.

These problems are particularly acute in laboratories, archives, libraries, clean rooms, dry storage and other applications that require that humidity be controlled in the absence of a need for cooling.

Small clean rooms are usually rooms surrounded by a space that already has temperature, but not humidity control. Like an archive, there is very little need to cool the space and the primary mode of operation is dehumidification. Laboratories, libraries, museums, MRI suites, CT scan rooms, art vaults and many other applications face the same challenge, dehumidification is needed more than cooling is needed.

Interpret the Temperature and Humidity Needs of Your Space with an All-In-One HVAC

Data Aire has solved these challenges by introducing InterpretAireTM, a packaged cooling, heating, humidifying, and dehumidifying unit that has all of the advantages of a standard CRAC unit and none of the drawbacks. The thing that sets InterpretAireTM apart from the competition is its ability to dehumidify when there is no need for cooling. Humidifying is relatively straightforward and easy for a standard CRAC to accomplish. Precise temperature control is not that difficult in most applications either. There are multiple strategies that standard CRAC units can use to deliver good temperature control. None of those strategies allow the CRAC unit to deliver better dehumidification control.

The Data Aire InterpretAire climate management system can be programmed to maintain constant temperature and humidity within a laboratory, clean room, museum, library or archive to ensure a desired outcome. Consistency and precision were key drivers in the development of the InterpretAire solution. InterpretAire quite literally interprets the needs of the space, and maintains the unique temperature and humidity perimeters mandated for high-accuracy standards.

Your application needs are specific; your environmental control equipment should be, too.