Installing precision air conditioning systems

Computers, workstations, industrial controllers and other sensitive electronic equipment require high-performance precision air conditioning systems to maintain stringent control of temperature and humidity. For example, what happens if there is too little or too much humidity in the air? Excessively low humidity can cause static electricity that can interfere with proper equipment operation.

By Dave Kelley, Liebert Corp., Columbus, OH June 15, 2002

Key concepts

Proper installation optimizes system performance.

There is a difference between precision and comfort systems.

Commercial systems cannot provide precision control.

Sections: Steps to follow Other considerations Putting it all together

Sidebars: Desirable precision A/C features Installation considerations for a precision A/C system

Computers, workstations, industrial controllers and other sensitive electronic equipment require high-performance precision air conditioning systems to maintain stringent control of temperature and humidity.

For example, what happens if there is too little or too much humidity in the air? Excessively low humidity can cause static electricity that can interfere with proper equipment operation. Standards often call for 45-50% relative humidity, with a maximum swing of

Too much moisture in the air can corrode switching circuitry, causing malfunctions and equipment failures. Corrosion of contacts and components on circuit boards accounts for about 30-40% of all equipment failures.

One of the most important considerations in providing precision air conditioning is proper installation. Overall performance parameters can be severely impacted.

Fig. 1. When selecting a precision A/C system, look for well-crafted construction and high-quality components.

Steps to follow

A successful installation is the result of following some basic procedures.

Prioritize operations To choose the right protection system, first define which functions and applications are critical within the area of operation and which are not.

Identify vital equipment Identify the computerized equipment required to run each critical operational function. Describe in general terms the anticipated reliability of these systems or networks, then match these estimates against newly prioritized operations to determine the real costs of downtime by specific operational areas.

Match needs with available products Describe, as specifically as possible, the critical space characteristics needed for each application including how much space is to be cooled; what are the temperature and humidity tolerances; and what happens to the current cooling system at night and over the weekend. Then match these needs against the available power protection and conditioning systems available today .

Understand the basics All too often, the importance of providing precision air conditioning for electronic equipment is not given the consideration it deserves. There are major differences in performance between precision air conditioning systems needed for computers, workstations, and industrial controllers and comfort-cooling systems designed to suit people.

Other considerations

In manufacturing or process control settings, when the air conditioning system must be located outside the critical space, standard systems often fail to survive in the dusty, dirty, and corrosive environment in which they are often placed.

The panels and gasketing on commercial systems are not designed to prevent untreated plant air from infiltrating the air conditioning unit and the critical space it is intended to protect.

A precision air conditioning system should be designed specifically for, and not adapted to, a particular application. Different types of air conditioning equipment are manufactured specifically for each application. This is a key reason why installing the system properly is as important as the type of system itself in determining the level of environmental protection required for a particular operation.

Fig. 2. Piping below a raised floor must not obstruct airflow.

Putting it all together

In selecting an installation site for a precision air conditioning system, the first step is to consider the proximity of the critical space to related operations such as security and internal/external zones, as well as proximity of the environmental control system to an outdoor air cooled condenser, cooling tower, or drycooler. In general, critical space should be located in an area which is unaffected by outside temperatures or humidity.

Next, the critical space area should be evaluated in terms of accessibility and dimensional requirements for the primary control system along with related electronic equipment. Sufficient area for planned growth of critical space and redundancy in environmental control units should also be taken into consideration during the initial planning stage.

The room should be well insulated and must have a sealed vapor barrier. The ceiling must be protected against vapor migration by using a rubber or plastic-based paint on concrete walls and floors. Doors must not be undercut or have grilles. Lighting fixtures requiring room air for cooling should not be used.

Outside fresh air should be kept at a minimum since it can add to the site’s heating/cooling/humidifying loads. Outside air should be kept below 5% of the total air circulated in the critical space area.

An accessible raised floor is required for installing a downflow environmental control system, while additional pedestal support may be necessary to ensure maximum structural support.

Using a floorstand permits the precision environmental control system to be installed, piped, wired, and inspected prior to the installation of the raised floor to allow easy access. A floorstand also provides vibration isolation while eliminating the need for cutting special floor panel openings under the unit.

For underfloor air distribution on downflow systems, the units should not be placed too close together or in a long, narrow space. Units located relatively close to each other tend to reduce the effectiveness of air distribution.

Air supply grilles and perforated panels should be selected to minimize circuit pressure loss. Air volume dampers on grilles are usually detrimental to airflow.

It’s extremely important to confirm specifications before ordering panels and grilles required to handle airflow. Proper specification for grilles and perforated panels should indicate the total free area required for air delivery.

All refrigeration piping should be isolated from the surrounding environment by using vibration-isolating supports.

In the case of downflow systems, all piping below the raised floor must be located in such a way that it offers the least resistance to airflow discharging from the system (Fig. 2). Planning of the piping layout is required to prevent airflow from being blocked. Whenever possible, all piping should be run parallel to the airflow while all condensate and unit drain lines should be trapped and pitched.

Thorough site analysis and proper installation will result in a custom-designed precision air conditioning system that provides optimum performance in cooling and protecting sensitive electronic equipment.

Edited by Joseph L. Foszcz, Senior Editor, 630-288-8776,

Performance differences in A/C systems

Design considerations
Precision systems
Comfort systems

72 to 75 F
78 to 80 F

Relative humidity
45 to 50%,

Cold weather operation
Availability to -30 F
Usually not available

Sensible heat ratio (sensible capacity / total capacity)
Typically 0.90 to 0.99
Typically 0.67 to 0.75

Load density (sq. ft / ton)
50 to 100
200 to 400

8760 hr per year
Around 1200 hr per year

Humidification and dehumidification control
Not available; add-on system needed

Control stages
Multiple stages of control
Single-stage control

Not necessary

Not necessary

Air movement
550 to 600+ cfm
Typically 350 to 400 cfm

High efficiency—up to 85%
Standard disposable furnace filter

Desirable precision A/C features

Include cooling, heating, humidifying, and dehumidifying functions in a single package

Air-cooled, water-cooled, glycol-cooled, or chilled water configurations

Year-round operation, allowing equipment to run when needed, not just when the building cooling equipment is available

Precise microprocessor-based temperature and humidity control, minimizing compressor cycling and reducing component wear

Factory packaged and tested system with proven operation before installation

Tamper-proof design, controls should be secure so cooling parameters can’t be accidentally changed

Multiple levels of control, with optional connectivity to remote monitoring and control systems

Microprocessor monitoring and controls

Energy saving options, including highefficiency compressors, four-step capacity control, and dual cooling sources

Installation considerations for a precision A/C system

Critical space location

Proper room preparation

Type of environmental control system (downflow/upflow)

Air distribution and piping

Electrical requirements