The 2012 edition of the Uniform Mechanical Code (UMC©) represents the most current approaches in the mechanical field. It is the fourth edition developed under the ANSI Consensus process is designated as an American National Standards by the American National Standards Institute (ANSI). Contributions to the content of this code were made by every segment of the built industry, including such diverse interests as consumers, enforcing authorities, installers/maintainers, labor, manufacturers, research/standards/ testing laboratories, special experts and users.
The UMC provides complete requirements for the installation and maintenance of heating, ventilating, cooling and refrigeration systems, while at the same time allowing latitude for innovations and new technologies.
Key changes to the 2012 UMC include new provisions for piping, tubing, balancing, louvers, ductwork, safety requirements for refrigeration machinery rooms and an alternative to calculate ventilation efficiency.
Significant improvements in Chapter 3 include provisions for a heating or cooling air system that provides specific requirements with return air, outside air or both, which are designed to replace required ventilation arranged to discharge into a conditioned space not less than the outside air specified in Chapter 4. Standards are referenced for louvers and their locations where installed in hurricane prone regions by providing minimum performance ratings for water rejection abilities and high-velocity wind conditions.
Provisions added in Chapter 4 offer an alternative for calculating ventilation efficiency through ASHRAE Standard 62.1 and updating minimum ventilation rates in breathing zones based on occupancy.
Safety requirements are updated and revised for refrigeration machinery rooms on vapor alarms, emergency control over the ventilation systems, control of ventilation systems and emergency controls. In addition, machinery room ventilation is addressed through the central control over the ventilation system and adding safety provisions for the emergency control through an identified switch. Detector location is critical to early leakage warning in refrigeration machinery rooms. Because machinery rooms are unattended most of the time, once the refrigerant gas is detected at the levels noted in Chapter 11, a local alarm must be initiated. The alarm is intended to alert occupants inside the area of detection and in the immediate vicinity to prevent any refrigerant gases that might escape from causing harm to those outside the area of release. In addition, the required detectors have the added important role of activating the emergency ventilation/exhaust systems in the machinery rooms. The intent of this section is to provide a safe environment for emergency response personnel when responding to an incident in a refrigeration room. The emergency control switch is a tamper-resistant type that requires more than one action to actuate it. To prevent an accidental start-up, the switch must be capable of only stopping the controlled machinery, not restarting it. The switch must not affect the operation of such life-safety systems as detectors and exhaust equipment. In addition to the manual switch, the required refrigerant room detector must also shut down the same equipment when the vapor concentration exceeds the lesser of the detectors’ upper detection limit or 25 percent of the refrigerants’ lower explosive limit.
Refrigeration port protection in the form of a locking-type, tamper-resistant cap is added to address illegal venting of refrigerant service ports by unauthorized individuals. This inhalant sometimes poses a serious threat to human life and safety. The typical condensing unit is located outdoors and is equipped with access ports on the vapor and liquid refrigerant lines. These access ports allow for the connection of diagnostic gauges so the refrigerant may be added to or taken from the unit during servicing. The purpose for this section is to prevent exposure to the refrigerant by illegal venting of refrigerant or the intentional inhalation of refrigerant and refrigerant leaks that contribute to the greenhouse gases in our atmosphere.
A new appendix provides a comprehensive set of technically sound provisions for sustainable practices and works toward enhancing the design and construction of mechanical systems that result in a positive long-term environmental impact. Practices include water efficiency in systems through the use of a submeter to monitor large water usage; including make-up water to cooling towers, evaporative condensers and boilers; establishing efficiency measures for cooling towers evaporative coolers; increased air quality provisions to reduce air contaminants; and establishing minimum equipment efficiencies, system balancing, duct leakage, system sizing and systems controls add to the overall design and construction practices. A key feature is system commissioning that ensures such systems are designed, installed and maintained to function as intended over their life cycle that provides the most cost-effective strategy for reducing energy usage.