analysis HVAC VOLUME ONE NUMBER ONE I S S U E S A N D A N S W E R S F O R T H E C O N S U L T I N G / S P E C I F Y I N G C O M M U N I T Y In this issue... What standards should be adhered to when designing and upgrading mechanical equipment rooms? Many of the primary answers are found in ASHRAE Standard 15-1994: Safety Code for Mechanical Refrigeration. While there is no substitute for reading the document itself, ASHRAE 15-1994 is written in code language, which is sometimes complex and difficult to understand. Your best strategy is to obtain a copy of the standard and read it thoroughly, then use this newsletter as a point of reference. ASHRAE 15-1994 is a guideline, but it is being used to formulate codes for the safe installation and operation of mechanical refrigeration systems in the United States and beyond. To find out how the standard is being adopted in your area, invite your local Carrier representative to discuss ASHRAE 15-1994... before you design or implement any mechanical room changes. Educate Your Customers: The highlights of ASHRAE 15-1994 are summarized in Carrier s SYNOPSIS newsletter, which is written specifically for building owners and managers. To receive copies at no charge, call 1-800-CARRIER and request SYNOPSIS, Vol. 1, No. 1. ASHRAE 15 1994: Implications for Mechanical Room Design Introduction First issued as a safety code (Standard B9) in 1930, the same year that CFC (chlorofluorocarbon) refrigerants were introduced in the United States, ASHRAE Standard 15 has undergone unusually rapid change over the last half-decade. During this same period, the air conditioning industry and its customers have been faced with The Clean Air Act Amendments of 1990, which legislated the phaseout of CFC production at the end of 1995. Although the regulations permit the responsible use of these refrigerants, intentional venting is strictly prohibited. At the time of this legislation, neither ASHRAE nor ARI safety standards had been updated to address the new alternative refrigerants that were already appearing in the marketplace. Thus, ASHRAE 15 was revised in 1992 and again in 1994. The current standard is now being used to formulate 1
Purge vents to outside? codes for the safe installation and operation of mechanical refrigeration systems throughout the United States and beyond. Code Compliance and Safety ASHRAE Standard 15-1994 was intentionally written in code language so it could be adopted nearly verbatim, if desired, by model code associations. The primary goal of this standard is to mitigate safety risks to the environment, to mechanical room operators and, ultimately, to the general public. With the introduction of alternative refrigerants such as HCFCs (hydro-chlorofluorocarbons), HFCs (hydrofluorocarbons), and mixtures of refrigerant compounds known as blends, new refrigerant safety classifications have been added under the ASHRAE 34-1992 Standard, Number Designation and Safety Classification of Refrigerants. Allowable exposure limits for the various refrigerants range from a low of 10 ppm (parts per million) to a cap of 1,000 ppm. Some blends are comprised of one or more flammable compounds, introducing yet another safety concern. Using ASHRAE 34-1992 as a starting point, ASHRAE 15- Mechanical Room Safety Check Location of inlet vents in relation to exhaust outlets? Rupture disc outlet locations? Are drain valves connected to evacuation devices? Are there any pit areas in the room? Where do the floor drains empty to? Location of roof drains? Is there a tight seal on doors? Are safety rupture *#@&(*) lines the right size? Is access to mechanical room restricted? Is there self contained breathing apparatus outside of the room? 1994 and its subsequent addenda have been written to help professionals minimize risk and promote safety stewardship. The purpose of this article is to provide a basic overview of mechanical room safety issues in relation to the ASHRAE Standard. It is not intended to be a comprehensive review of all requirements. While this is by no means a substitute for reading the document itself, it will help you to know what to look for when reading the standard. Mechanical Room Safety Check FIGURE 1 For many building owners, mechanical rooms are virtually unknown portions of the property. Out of sight, out of mind rings true in far too many cases. Most owners understand only that the equipment in the mechanical room supplies chilled water for air conditioning. Equipment may be ten, 20, 30 or even 50 years old each unit installed to comply with the codes of the day. Given the new ASHRAE Standard and the approaching CFC and HCFC production phaseout, now is the right time for owners, operators and engineers to conduct a complete mechanical High Flammability Low Flammability No Flame Propagation room safety check and review potential liability problems. The following checklist highlights the many important items to look for (Fig. 1): Are exhaust outlets located near inlet vents? Safety relief devices on chillers are typically vented to the outside, most often through the roof. It is important to know how close this vent is to the air intakes on the roof and to insure that there is at least 20 feet between them. Are roof drains vulnerable to collecting refrigerant? If you lose refrigerant from an exhaust outlet and it vents a few feet above a flat, curbed roof, the refrigerant could very well lay across the roof and find the first exit probably down the roof drains. Most roof drains lead directly to a sewer system. Where does the purge vent? A conventional purge (not a new, high-efficiency model) loses three to 20 pounds of refrigerant for every pound of noncondensible air it removes from the system. Most vent directly into the mechanical room, which may invite unnecessary problems. All purges should vent outside. Where are safety rupture disk outlets located? On a CFC-11 or HCFC-123 chiller, the safety device is a thin carbon rupture disk that s meant to shatter at 15 psig, allowing the charge to safely exit the system. These disks are often vented through the roof or side of the building. Yet in climates with warm days and cool nights, moisture often condenses in the pipes before it can evaporate off. Then, along with the rust and other accumulations in the pipe, it ends up sitting on the rupture disk. Over time, it may corrode the joint and result in failure of the seal. Are rupture lines the right size and length? For convenience, safety devices sometimes run into a common header. However, an improperly sized header can exacerbate problems in an emergency, when the discharge capacity of safety lines is put to the test. Are chiller drain valves secured? More often than not, chiller drain valves are an easy way for an inexperienced technician to get into trouble. Make sure the valves are locked off. Is access to the mechanical room restricted? Most mechanical rooms have neither a door nor anything to restrict people from entering unsupervised. (There may be a fire door, but it is typically left open.) Not only are Safety Group Examples A3 Propane A2 R-142b, 152a A1 R-11, 12, 22, 114, 500, 134a Lower Toxicity B3 B2 Ammonia B1 R-123, SO 2 Higher Toxicity FIGURE 2 2
Discharge Capacity of Pressure Relief Devices mechanical rooms potentially hazardous places, they contain systems critical to a building s operation. Restricting access is only common sense. The mechanical room door should have a tight seal to isolate the room in case of an emergency. Is a self-contained breathing apparatus (SCBA) located outside of the room? In an emergency, a properlyused SCBA can mean the difference between life and death but not if it s stored inside the room where the contamination is likely to occur. Are there any pits (low areas) in the room? Check the condition of any pits or other areas below floor level. They may house a host of unwanted chemical residues such as acids, spilled refrigerant, cleaning solvents, etc. Where do the floor drains empty? Most floor drains were constructed to handle wash-water and empty into the sewer system. But if your chiller and occupied space share the same floor, they may also share drainage systems. Check to see if drains in the occupied space (i.e., in restrooms) are connected to those in the mechanical room. Imagine losing a full charge and finding it in a restroom! C = f D L C = minimum required discharge capacity of relief device in pounds of air per minute (kg/s) D = outside diameter of vessel in feet (m) L = length of vessel in feet (m) f = factor dependent upon type of refrigerant These are some of the many factors to consider when evaluating the safety of your mechanical room. For potential building owners, the condition of the mechanical room and its equipment are significant considerations in the decision to purchase a particular property. Applying ASHRAE 15-1994 FIGURE 3 What is your compliance obligation to ASHRAE 15-1994? If you re a professional engineer, a manufacturer or an owner, you are liable for ASHRAE 15-1994 simply by being aware of the standard. Compliance to the standard is also mandated in the following situations: Contracts. The specification that equipment and service must be in compliance with the latest ASHRAE 15 has become standard contract language for installation submittals and service agreements. Equipment Design. Manufacturers labels reference compliance with the standard. Safety Stewardship. Professionals who can prove that they have gone to the furthest extent possible to promote safety will minimize their legal liability. Mechanical Room Changes. The CFC production phaseout has raised the critical issue of what to do with an existing CFC chiller. Each solution containment, conversion or replacement brings with it new concerns. Yet it is important to understand that if the type of refrigerant in a chiller is changed or if the chiller itself is replaced, ASHRAE 15-1994 applies. Section 5.3 of the standard reads: A change in the type of refrigerant in a system shall not be made without the notification of the authority having jurisdiction, the user and due observance of safety requirements. The refrigerant being considered shall be evaluated for suitability. The cost of mechanical room upgrades typically 11-13% of the total chiller conversion/replacement project cost, depending on the room s age and location should be factored into the refrigerant planning cost analysis. On the other hand, the addition of containment devices to your existing CFC equipment does not trigger application of the standard. Building Code Compliance. The major U.S. building code jurisdictions are currently in various stages of incorporating ASHRAE 15-1994 into their model codes. As this progresses, the updated codes will ultimately be passed down to state and municipal levels. For this reason, it is always a good idea to meet with your building inspector up-front, before mechanical room changes have been made. Find out what s happening to codes in your area, then decide how to proceed. ASHRAE 15-1994 Overview A walk through ASHRAE 15-1994 begins with a general look at the property in question and its mechanical refrigeration systems. The type of occupancy institutional, public assembly, residential, commercial, large retail, industrial or mixed occupancy determines which system application rules apply. The next step is to identify the type of refrigerant system involved: Direct or Indirect. Direct Systems are those in which the chiller sends refrigerant out into the cooling coils near the occupied spaces. In Indirect Systems, the refrigerant runs only through the chiller and chilled water in a separate circuit produces the cooling in the airside system. Discharge Capacity of Rupture Member 2 C = 0.64 p d 1 0.5 d = 1.25 (c/p ) 1 C = rated discharge capacity in pounds of air per minute (kg/s) and d = smallest of the internal diameter of the inlet pipe, retaining flanges, fusible plug, and rupture member in inches (mm) p = (rated pressure psig [kpa gage] x 1.10) + 14.7 (101.33) FIGURE 4 3
Maximum Length of Discharge Piping 2 5 2 L = 9 P d / 16Cr C r = rated discharge capacity as stamped on the device by the manufacturer in pounds of air per minute (kg/s) d = internal diameter of pipe in inches (mm) L = length of discharge pipe in feet (m) Indirect systems include Double Indirect Open Spray Systems, Indirect Closed Systems and Indirect Vented Systems (all described in ASHRAE 15-1994). The probability of refrigerant reaching the occupied spaces depends in large part upon the type of system involved. To characterize the degree of risk, ASHRAE 15-1994 introduces the broad categories of Low- Probability and High- Probability Systems. Low- Probability Systems are those in which the leakage of refrigerant from a failed component cannot enter the occupied spaces. Examples of Low-Probability Systems include Indirect Closed Systems, Double Indirect Systems and Indirect Open Spray Systems where the secondary coolant pressure exceeds refrigerant pressure. Conversely, High- Probability Systems are described in the standard as those in which leakage of refrigerant from a failed component will enter the occupied space. High- Probability Systems include all Direct Systems as well as Indirect Open Spray Systems where the refrigerant pressure always exceeds the secondary coolant pressure. Refrigerant Classifications FIGURE 5 In its 1992 update, ASHRAE 15 introduced a refinement in the way refrigerants are classified for toxicity. Refrigerant compounds were divided into two groups, low-toxicity and high-toxicity, designated by the letters A and B. Refrigerants with allowable exposure limits (AELs) of more than 400 ppm are classed as type A (lower toxicity) refrigerants, and those with AELs of less than 400 ppm are type B (higher toxicity). ASHRAE 15-1994 further classifies refrigerants according to their degree of flammability: (1) no flame propagation, (2) low-flammability, and (3) high-flammability (Fig. 2). Ammonia, for example, is considered a low-flammability refrigerant, while refrigerants like HCFC-22 and HFC-134a have no flame propagating properties. It should be noted that the ingredients R-600a and R-1270a, found in some blends, are flammable and would fall into Class 2 or 3 if they were used as single compounds. Although their flammability is mitigated when they are mixed into a blend, flammability may still be an issue in leak situations. When blends leak, the highest-pressure compound exits first, mixed with the next highest-pressure compound. The lowest-pressure compound, then, is likely to be left in the vessel, and in this state the mixture may be flammable. A recent addendum to ASHRAE 34-1992 reflects the fact that the flammability classification of a blend may change as it leaks. The addendum states that a blend will be classified to reflect the highest potential flammability of its components. Complying with ASHRAE 15-1994 When examining a mechanical equipment room for compliance with ASHRAE 15-1994, here are some of the primary issues to consider: Maximum Refrigerant Without a Mechanical Room. In Table 1 of the ASHRAE Standard, allowances for all refrigerants are listed in pounds of refrigerant per thousand cubic feet of occupied space. Often misinterpreted, the figures in Table 1 (of ASHRAE 15) represent the maximum refrigerant levels allowable without a separate mechanical equipment room. If you have more than the allowable amount of refrigerant, the system must be housed in a separate mechanical room. Purge System and Relief Devices. The standard specifies that all purge systems, including high-efficiency systems, and other relief devices must vent outside. Note: It may be economical to tap into existing rupture disk lines, but do consider putting a drain valve in the line or wrapping the line in heater tape. As discussed above, even the highest-efficiency purges lose some refrigerant. When warm gas hits a cold pipe it will condense down into the pipe, depositing refrigerant against the safety rupture disk. These disks are usually a 0.03 thick layer of carbon and are not tolerant of corrosive conditions. Sizing of Relief and Rupture Devices. ASHRAE 15-1994 specifies the appropriate sizing of pressure relief devices based on a minimum required discharge capacity in pounds of air per minute. The equation, shown in Fig. 3, includes an f factor, which is identified in the standard for most refrigerants (if not, consult your equipment or refrigerant manufacturer). When converting a chiller to a new refrigerant, it is critical to check the size of existing safety devices to be sure they are suitable. The new standard also includes rating formulas for Discharge Capacity of Rupture Members and Maximum Length of Discharge Piping (Fig. s 4, 5). Refrigerant Sensors. According to ASHRAE 15-1994, all mechanical rooms must have a sensor capable of detecting refrigerant loss. The sensor should be positioned in areas where vapor from a refrigerant leak would most likely concentrate, thus providing personnel with a means to avoid catastrophic refrigerant loss (Fig. 6). Sensors should be calibrated so that the allowable exposure limit for the refrigerant will not be exceeded. Rather than a refrigerant detector, the preceding standard, ASHRAE 15-1992 required an oxygen deprivation sensor for Class A1 refrigerants. The standard stated that the sensor should 4
Examples of Sensor Locations Open Drive Seals Just Above floor Next to Chillers Pits (examples not in standard) Entrance / Exits Refrigerant Storage Drains Ventilation FIGURE 6 FIGURE 6 be capable of detecting a.5% decrease in room oxygen levels (air is typically 20% oxygen, so the sensor would detect a drop to 19.5%). In this old scenario, 67,000 ppm refrigerant concentrations could accumulate before the sensor issued a warning! Safety stewardship and refrigerant containment are better served by using a quality refrigerant sensor with all refrigerants. Mechanical Ventilation to the Outdoors. Mechanical rooms must be vented to the outdoors using mechanical ventilation. The formula ASHRAE provides for calculating ventilation capacity requirements is shown in Fig. 7. Access Restrictions. The revised standard specifies that access to mechanical rooms should be restricted to authorized personnel. In addition, the room must have tight-fitting doors that open and close freely (i.e., no fire doors), and any other opening that would permit the passage of refrigerant must be sealed. Refrigerant Storage. Section 11.5 of ASHRAE 15-1994 reads: The total amount of refrigerant stored in a machinery room in all containers not provided with relief valves and piped in accordance with the standard should not exceed 330 lbs. This is designed to allow owners to take separate, approved storage tanks and store adequate quantities of refrigerant for chiller servicing. This is completely allowable under EPA, and many owners are opting to contain their CFC chillers and safely store service refrigerant on-site. It should be noted, however, that the ASHRAE recommendation is for a maximum of 330 lbs. per system. Local building and fire codes should be referenced for possible exceptions. Self-Contained Breathing Apparatus. The updated standard requires that a selfcontained breathing apparatus (SCBA) be located outside of the mechanical room, along with a second SCBA for back-up. It s a good idea to check OSHA regulations regarding SCBA use (i.e., SCBAs cannot be worn by personnel with beards, and potential users must pass a pulmonary test). Another issue is the optimum location of the SCBA gear in applications where the mechanical room opens to the outdoors: Should the gear be housed in an enclosure? Should the enclosure be locked? How does that affect access? Be sure to purchase a SCBA with an adequate air supply. Large mechanical rooms may require an extended air supply in an emergency situation. Relief Discharge Location. The discharge location of relief devices must be positioned at least 20 feet away from any ventilation openings, and not less than 15 feet above ground level (to avoid spraying someone with refrigerant). Combustion Device (i.e., Boiler) Limitation. ASHRAE 15-1994 prohibits the location in a mechanical room of any open-flame device using combustion air from inside the room. On the other hand, an open-flame device such as a boiler may be located in a mechanical room if combustion air is drawn from outside. Two acceptable alternatives are to duct outside, sealed ventilated air in or to install a sensor that shuts the flame off in the presence of refrigerant gas. Most refrigerant sensors are multi-port, so they can run to several spots in the mechanical room and be programmed to shut the boiler down if a chiller leak is detected. Yet another option (though not specified in ASHRAE 15) is to isolate the boiler or open-flame device with a wall or separate enclosure. Room Dimensions. The new standard defines an appropriately sized mechanical room as one that allows access to all equipment, including adequate space for service and maintenance as well as operation. Periodic Testing. Ventilation systems and sensors must be periodically tested in accordance with the manufacturer s recommendation and/or local jurisdiction. This is particularly important for refrigerant sensors that are detecting compounds with low allowable exposure limits. Many of these sensors require frequent recalibration. Read ASHRAE 15-1994 Mechanical Ventilation Q = 100 x G 0.5 Clearly, there are many issues for professionals to consider in order to achieve compliance with ASHRAE 15-1994. Your best strategy is to obtain a copy of the standard and read it thoroughly, perhaps using this article as a point of reference. ASHRAE 15-1994 offers many good, safe solutions. Not only is it a good idea to follow the new standard, it may very soon be the law in your jurisdiction. To find out how the standard is being adopted in your area, invite your local code inspector to discuss ASHRAE-15 1994... before you make any changes to your mechanical room. Q = the air flow in ft. per min. (liters per second) G = the mass of refrigerant in lbs. (kgs) in the largest system, any part of which is located in the machinery room 3 FIGURE 7 5
Highlights: ASHRAE Standard 15 was revised in 1992 and 1994 to address the phaseout of CFC production and the increased use of alternative refrigerants. The Standard is being adopted nearly verbatim by many model code associations. Professional engineers, manufacturers and owners are liable for the Standard simply by being aware of it. Owners and engineers can use the Standard to conduct a complete mechanical room safety check. If the type of refrigerant in a system changes, ASHRAE 15-1994 applies. Mechanical room upgrades typically add 11-13% to the total cost of a chiller conversion/replacement project. Which system application rules apply depends on the type of building occupancy, refrigerant system and refrigerant classification. The Standard specifies the maximum amount of refrigerant that can be stored on site with and without a mechanical room. All mechanical rooms must have a sensor capable of detecting refrigerant loss. Mechanical rooms must ventilate to the outdoors using mechanical ventilation. There is no substitute for reading the standard itself. Obtain a copy and use this newsletter as a reference. ASHRAE 15: Implications for Mechanical Room Design in Different Types of Facilities The type of occupancy of a building determines which system application rules of ASHRAE 15 apply. For buildings that fall under more than one classification, the Standard asks if the areas are isolated from the rest of the building by tight walls, floors, ceilings and self-closing doors. If so, each space may be treated as a separate area. However, if the occupancies are not isolated, the classification with the most stringent rules applies for the entire building. ASHRAE 15 classifies buildings by the ability of people to respond to potential refrigerant exposure as follows: Education - An educational facility, such as a college or school, may contain residential and/or public assembly spaces. Public assembly is defined as a premise where large numbers of people congregate and cannot quickly vacate. A residential structure is one that provides residents with complete living facilities, including permanent provisions for living, sleeping, eating, cooking and sanitation. Health Care - Whether it is a hospital or an extended care facility, a health care building is likely to fall under the institutional classification in ASHRAE 15. This is defined by ASHRAE 15 as a building that occupants cannot readily leave without the assistance of others. Hospitality - Similar to an educational facility, a hotel or motel may contain both residential and public assembly areas. Manufacturing - A manufacturing facility may have both commercial and industrial areas. A commercial space is one where people transact business, receive a service or purchase products. This includes office space and work or storage areas that do not qualify as industrial. Industrial areas are defined as not open to the public and used to manufacture, process or store goods such as chemicals, food, ice, meat or petroleum. Office - Many office buildings will fall under the commercial space definition. However, they could also include areas of industrial or large mercantile space. Retail - Most big retail stores and shopping malls are considered to be large mercantile by the Standard. This is defined as a space where more than 100 people congregate to purchase merchandise. A small retail establishment, such as a restaurant, may be considered to be a public assembly space. Apartments - Multi-family, multi-story dwellings are considered to be residential premises. Warehouse - Depending on the use of the facility and the types of goods stored there, a warehouse may fall under the commercial or industrial classifications. In addition, equipment (other than piping) located within 20 feet of any building opening is governed by the classification of the building. How are these classifications used in the Standard? The classification of a building determines the refrigerant quantities and types of systems allowed. Please refer to the Standard for more information. 6