Maintenance is the work of keeping building components and equipment in good condition. Although major building components can be maintained to last indefinitely, usually they are replaced—not because they wear out, but because they become obsolete or can no longer be maintained economically. Maintenance is necessary to assure continuous performance and also to minimize operating costs.
The primary enemies of operating equipment are:
Heat is a form of energy that is generated as machines operate. For example, most of the energy developed by a fan motor in an HVAC system is imparted to the wheel of the fan then dissipated into the air passing through the fan. The increase in temperature of air passing through a fan ranges from less than 1 degree to as much as 6 degrees. The remaining energy is dissipated as the heat from the motor. The motor can be cooled by passing air through or around it. When air is restricted or heat transfer is impeded by the accumulation of dirt, motors can overheat and fail.
All HVAC equipment is designed to operate over certain temperature schedules. Chiller and condenser equipment in air-conditioning systems operate with a temperature differential as great as 30°F. Heating systems are designed for a temperature differential of over 100°F.
The capacity of HVAC systems depends on rates of heat transfer, which in turn depend on temperature differentials. Insufficient maintenance can reduce capacity by changing the operating temperature of its components. For example, interfering with the heat transfer of a chilling coil in an air-handling unit can reduce cooling capacity to the zone it supplies. Interfering with the heat transfer of a primary system component, such as the condenser, can reduce the efficiency and capacity of the entire system. Scale, dust, and dirt accumulation the thickness of just a sheet of paper can cause a substantial reduction in heat transfer as well as higher operating costs.
Properly contained and controlled, water is useful. It contributes significantly to our comfort and convenience in buildings, most notably in its use for sanitary purposes and as a heat transfer medium in HVAC systems.
Uncontrolled moisture, however, reacts with metals to cause corrosion; it enhances microbiological growth; and it reacts with airborne contaminants to form harmful acids and deposits. Water is commonly referred to as the “universal solvent” because it dissolves a little of almost everything it contacts. When deposits caused by dirt, debris, scale, and bacteria—along with various gases, solids, and other matter—are dissolved in water, serve to compound its corrosive effect.
Controlling moisture is important in effective management of indoor air quality. Totally dry surfaces will not normally support microbiological life.
For the building occupants’ and components’ health, maintenance programs must limit uncontrolled sources and accumulations of moisture.
Dirt, usually in the form of dust, soot, smoke, or lint, collects and accumulates on air filters, air passages of motors, the contacts of electric switches, and open bearings.
Corrosive gases resulting from combustion or manufacturing processes cause some of the dirt found in an urban environment. These gases include carbon monoxide, carbon dioxide, sulfur dioxide, and nitrogen oxides. When combined with moisture, they form corrosive acids.
Dirt or foreign matter that affects the interior of mechanical systems may be airborne, may enter with a system fluid such as water, or may have been left during construction. Airborne dirt can enter the condenser water at the cooling tower. Water contains dissolved solids such as calcium and magnesium that, without proper water treatment procedures, can be deposited on interior piping surfaces. Foreign matter left by construction includes sand, stone, welding chips, mill scale, soldering paste, and oils used for pipe threading or gasket seals.
Accumulations of dirt, foreign material, and corrosion can cause several problems, such as:
- decreased capacity of individual components or the entire system, through interference with heat transfer functions
- increased energy consumption to compensate for higher temperature differentials than originally intended
- unnecessary repairs and replacements and reduced useful life of components
Wear is the gradual erosion or using up of a component material, usually a moving part. Wear is accelerated by the presence of dirt, moisture, or heat.
Most equipment that uses air or water in motion requires maintenance. Air is never completely free of dust and other contaminants, and water contains dissolved minerals, which can lead to such problems as corrosion and scale. Excessive wear results from this abrasive dust and corrosion.
Using the appropriate lubricants, as recommended by the manufacturer, protects precisely machined and aligned moving parts from wear throughout their useful lives. However, if overheating occurs or the lubricants become contaminated, they lose their protective quality. Bearings must be kept clean and lubricated, with adequate clearances.
Building Maintenance Decisions
In the absence of proper maintenance, the effects of heat, moisture, dirt, and wear eventually accumulate to cause malfunctions or failures. Proper maintenance of a building and its operating equipment can produce several benefits:
- Prolonged equipment life
- Prolonged efficient operation
- Improved equipment and operation reliability
- Reduced frequency of complaints
- Minimized operating costs
- Smoother maintenance work flow
- Reduced overall maintenance and repair costs
When planning maintenance tasks, it is important to consider the consequences of a failure on normal operation. For example, you could greatly improve the reliability of your building’s air-conditioning equipment by installing two 1,000-ton chillers to meet its building load of 1,000 tons. However, this redundancy is expensive and few operations require this level of reliability. With reasonable maintenance, chillers should not experience significant downtime. By contrast, critical laboratory or computer operations often require an emergency generator to pick up the entire load in the event of power failure. Some installations even have a second emergency generator, in case the first one fails. In very large or critical businesses, a separate electric utility power source is installed and switched over to during power failures.
Maintenance program planning must consider operation failure, equipment value, replacement availability, and the conditions under which the equipment is operated. Consider the maintenance requirements and the potential consequences of failure for an automobile and airplane. Although maintenance tasks are similar for each, there is a considerable difference in the potential for injury or loss of life in an accident caused by machine failure. Therefore, the maintenance program for an airplane is significantly more comprehensive and rigid than an automobile’s.
This article is adapted from the BOMI International course Building Design and Maintenance, part of the Systems Maintenance Administrator designation program. More information regarding this course and the SMA is available by calling 1-800-235-2664. Visit BOMI International’s website, www.bomi.org.