Figure A-6.2.3.8.(10)(b)
Operation diversity factor
A-6.2.1.1. Building Pressurization. New buildings tend to be considerably more airtight than older ones. Consequently, these buildings may have a reduced pressurization requirement compared to the normal requirement in order to limit drafts and provide a reasonable level of comfort.
The humidification and relative pressurization of buildings and individual spaces in buildings can be significant factors in compromising the on-going performance of the building envelope and other environmental separators.
In new construction, HVAC designers should take this issue into consideration and confer with those responsible for the design of the environmental separators so as to limit stress where these building elements are not intended to resist or accommodate such loads. In existing buildings, the ability of the environmental separators to resist or accommodate increases in pressure differential or moisture loading should be considered before changes are made to the HVAC system.
A-6.2.1.3. Structural Movement. This article is intended to remind designers and installers of mechanical systems of one aspect of the “good engineering practice” referred to in Article 6.2.1.1.
In determining how to accomodate structural movement, there are two important principles to bear in mind:
For example, a gas line supported on columns that also support a crane must be installed in such a way that the movement of the columns, which occurs many times daily, does not cause the lines to break, thus creating a hazard. Even if the gas line installation could somehow be designed to break in a non-hazardous manner, it would hardly be recognized as good engineering practice if movement that occurs so frequently could disrupt the operation of the mechanical system.
On the other hand, earthquakes occur far less frequently and it would not be surprising to have a non-critical mechanical system fail as a result of an earthquake. However, even in this situation, the failure must occur in a manner that does not create a hazard to building occupants. For example, heavy mechanical equipment should be properly anchored so that it does not topple on building occupants during an earthquake. The design of the anchors should take into account accelerations consistent with the seismic data given in Appendix C for the location of the building. Part 4 provides guidance on the calculation of the loads such equipment would exert on the building structure during an earthquake; these same loads can be used in designing the anchors.
Some mechanical equipment can be an important component of post-disaster life safety systems. In these cases, the measures needed to accommodate the movements caused by an earthquake become even more critical since failure of the equipment would not be acceptable.
Clearly, complying with this requirement will, in most cases, necessitate close coordination between the mechanical designer and the structural designer.
A-6.2.1.8.(1) Installation General. Ducts or pipes without dampers or valves are generally not considered to constitute “equipment” and are therefore not subject to this requirement.
A-6.2.2.2.(1) Ventilation and Multi-Unit Residential Buildings. This provision requires that the individual apartments within multi-unit residential buildings be ventilated by mechanical means. To meet this requirement, it has been typical for corridor ventilation systems to be installed to deliver outdoor air to corridors and to rely on air infiltration under apartment-corridor doors to deliver ventilation air to adjacent apartments. Research has shown that such approaches are neither efficient nor effective in the provision of ventilation air to apartments. Such systems are susceptible to stack and wind effects, door gaskets installed by occupants, the leakage of supplied air to vertical shafts and stairwells, and air contamination within the corridor due to occupant activities, cooking and smoking odours. It is difficult, if not impossible, to ensure that each apartment will receive adequate amounts of uncontaminated outdoor air for ventilation purposes.
Air transfer ducts between corridors and adjacent apartments have been proposed to ensure that the leakage area between apartments and an adjacent corridor supplied with outdoor air is adequate to ensure ventilation. Apart from noise, corridor odours and the potential for smoke contamination during fire emergencies, in order for transfer ducts to function properly, knowledge of the corridor/apartment pressure regimes and available corridor leakage areas to other zones is required, but such knowledge is not readily available or predictable.
Ducts to deliver air from the central corridor's ventilation system directly to each apartment can be effective. Alternatively, outdoor air can be mechanically introduced directly into each apartment by an ensuite ventilation system.
Within each apartment, all rooms and spaces must be mechanically ventilated. Effective ventilation may be achieved by making use of fan-coil systems to deliver ventilation air via the forced-air space conditioning system. Alternatively, ventilation air may be ducted independently to each room via a dedicated ventilation system. In bathrooms and kitchens, it has not been considered necessary to both supply and exhaust ventilation air; typically, air is exhausted from these rooms.
For more guidance on the design of mechanical ventilation systems for residential spaces, refer to CAN/CSA-F326-M, “Residential Mechanical Ventilation Systems.”
Mechanical ventilation systems designed and installed in accordance with Section 9.32. comply with the requirements of Article 6.2.2.2., provided that they serve only one dwelling unit (apartment or suite).
A-6.2.2.2.(1)(a) Natural Ventilation. This clause precludes the designer from using natural ventilation in buildings of other than residential occupancy when the occupant load is greater than one person per 40 m2. However, consideration would be given to projects using natural ventilation or natural ventilation in conjunction with mechanical ventilation, provided a comprehensive engineering design was undertaken demonstrating that the proposed design was equivalent to the prescribed mechanical design. This equivalent approach would require compliance to Article 2.3.1.1. of Division C.
A-6.2.2.3.(2) Ventilation of Storage Garages. Storage garages are ventilated to protect occupants from exposure to carbon monoxide and other vehicular exhaust fumes. In certain cases, such as small two- or three-bay storage garages that are used for occasional vehicle storage, and where occupants are not present, carbon monoxide or nitrogen dioxide monitoring devices may be omitted if the ventilation system is interlocked with a local light switch or other controls to ensure continuous system operation whenever the area is occupied. In any event, the ventilation system capacity must be designed to limit the concentrations of carbon monoxide or nitrogen dioxide at or below the prescribed values.
A-6.2.2.4.(3) Minimizing Growth of Micro-organisms. Sources for microbial growth causing hypersensitivity, pneumonitis and humidifier fever include drain pans, spray-water air-washers, contaminated filters, poorly maintained cooling coils, water incursion into ductwork, cafeteria dishwasher drainage leaks, high humidity and stagnant water. Some of the control measures are as follows:
(a) Drain pans should be pitched toward the drain outlet and the outlet bottom should be flush with the drain pan bottom, otherwise there will be standing water in the pan, exposed to the supply air passing through the cooling section of the air-handling unit.
(b) Access into air-handling equipment should be provided for maintenance of filters, cooling coils and condensate drain pans located below the cooling coils. Access doors should be large and easy to open to facilitate thorough and regular maintenance. Hinged access doors are preferable to bolted access panels.
(c) If moisture is added to commercial building ventilation air (such as in hospital operating rooms and dedicated computer rooms) to maintain humidity levels in a designated range (for example, 40% to 50% relative humidity), humidifiers that inject steam or water vapour into central air-handling units or main supply ducts are normally used. Injection nozzles should not be located in air-handling unit plenums or ductwork that is insulated with internal fibrous lining. If the lining becomes wet, conditions conducive to microbial growth will result.
The above only addresses built-in features of an HVAC system that can help to minimize growth of micro-organisms. Even more important than the built-in features is a program of regular maintenance and cleaning of those portions of the system where such growth is likely to occur.
A-6.2.2.5.(1) NFPA Publications Pertaining to the Heating, Ventilating and Air-Conditioning of Spaces Containing Hazardous Gases, Dusts or Liquids.
NFPA 30 “Flammable and Combustible Liquids Code”
NFPA 30A “Motor Fuel Dispensing Facilities and Repair Garages”
NFPA 32 “Drycleaning Plants”
NFPA 33 “Spray Application Using Flammable or Combustible Materials”
NFPA 34 “Dipping and Coating Processes Using Flammable or Combustible Liquids”
NFPA 35 “Manufacture of Organic Coatings”
NFPA 36 “Solvent Extraction Plants”
NFPA 40 “Storage and Handling of Cellulose Nitrate Film”
NFPA 50A “Gaseous Hydrogen Systems at Consumer Sites”
NFPA 50B “Liquefied Hydrogen Systems at Consumer Sites”
NFPA 51 “Design and Installation of Oxygen-Fuel Gas Systems for Welding, Cutting, and Allied Processes”
NFPA 51A “Acetylene Cylinder Charging Plants”
NFPA 61 “Prevention of Fires and Dust Explosions in Agricultural and Food Products Facilities”
NFPA 68 “Venting of Deflagrations”
NFPA 69 “Explosion Prevention Systems”
NFPA 81 “Fur Storage, Fumigation and Cleaning”
NFPA 85 “Boiler and Combustion Systems Hazards Code”
NFPA 86 “Ovens and Furnaces”
NFPA 88A “Parking Structures”
NFPA 91 “Exhaust Systems for Air Conveying of Vapors, Gases, Mists, and Noncombustible Particulate Solids”
NFPA 96 “Ventilation Control and Fire Protection of Commercial Cooking Operations”
NFPA 204 “Smoke and Heat Venting”
NFPA 303 “Marinas and Boatyards”
NFPA 307 “Construction and Fire Protection of Marine Terminals, Piers, and Wharfs”
NFPA 409 “Aircraft Hangars”
NFPA 415 “Airport Terminal Buildings, Fueling, Ramp Drainage, Loading Walkways”
NFPA 484 “Combustible Metals, Metal Powders, and Metal Dusts”
NFPA 654 “Prevention of Fire and Dust Explosions from the Manufacturing, Processing, and Handling of Combustible Particulate Solids”
NFPA 655 “Prevention of Sulfur Fires and Explosions”
NFPA 664 “Prevention of Fires and Explosions in Wood Processing and Woodworking Facilities”
NFPA 2001 “Fire Protection Guide to Hazardous Materials”
A-6.2.2.6.(3) Refer to the City of Vancouver’s Kitchen Ventilation Guidelines for further information. Included is information on Design Considerations for Development Permit, Vancouver Coastal Health policy, checklists for inspections, and requirements for maintenance. This guideline is available on the City of Vancouver website at http://vancouver.ca/commsvcs/CBOFFICIAL/.
A-6.2.2.6.(4) The termination is also to be designed to the satisfaction of the Director of Planning. Where there is a canopy or awning, the discharge should be located above the canopy or awning. The exhaust and make-up air locations should be determined respectful of existing discharge, make-up air, operable window, and door locations of neighbouring properties. In some cases, the Director of Planning may not approve exhaust or make-up air wall terminations on street frontages. Wall terminations should be located where they have the least impact on nearby properties, suites, amenity areas, the public realm, windows, and building design. Generally, roof terminations are preferred and wall terminations should be located in the lane.
A-6.2.2.7.(1) Ventilation and Venting of Crawl Spaces and Attic or Roof Spaces. The cross-reference to Part 5 pertains to unconditioned and unoccupied crawl spaces, and attic or roof spaces, which are effectively within the building envelope. That is, unconditioned and unoccupied attic or roof spaces are located between the roof deck and roofing above, and the insulation, air barrier system and vapour barrier below. Unconditioned and unoccupied crawl spaces are located between the ground cover below and the insulation, air barrier system and vapour barrier above. Venting of these spaces has implications for the performance of the building envelope rather than having direct effects on indoor conditions. The ventilation of conditioned or occupied crawl spaces and attic or roof spaces must comply with Part 6.
The requirements in Part 5 are stated in terms of loads that must be resisted rather than in terms of building elements. Thus, the Code user will not find explicit references in Part 5 to crawl spaces, or attic or roof spaces. Part 5 makes reference to the need for venting environmental separators, i.e., the dissipation of heat or moisture.
Sentence 6.2.2.7.(1) requires that crawl spaces be ventilated either by natural (above-grade only) or mechanical means. High moisture levels within the crawl space can lead to problems such as the formation of mould, lifting of flooring or long-term damage to structural components.
Crawl space ventilation cannot be expected to correct moisture-related problems caused by other factors like inadequate surface drainage from the foundation walls or improper protection against moisture from the ground. These conditions must be properly addressed so that crawl space ventilation can meet its intended objectives.
Several factors favour the use of mechanical ventilation rather than reliance on natural drafts. Local conditions, such as areas with high water tables, may dictate the need for mechanical ventilation to remove excessive moisture.
Crawl spaces should be maintained at a negative pressure relative to the conditioned area above to prevent the migration of moisture into occupied areas. This can be achieved through the use of an exhaust fan and relying on air transfer through floor penetrations, such as pipes.
A-6.2.3.8.(5) and (6) Exhausting to Garages. A frequent practice in the design of ventilation systems serving buildings which have associated parking garages is to discharge exhaust air from the building to the garage in order to reduce the cost of heating the garage or reduce the length of the exhaust ducts. However, this practice entails a certain amount of risk since, when the exhaust system is not running, stack effect may turn the exhaust outlets into intakes and exhaust fumes (including carbon monoxide) can be drawn from the garage into the building. Incorporating a backdraft damper at the exhaust outlet provides some additional protection but backdraft dampers are generally not regarded as being very reliable. Therefore this practice is only permitted in very limited circumstances.
A-6.2.3.8.(6)(b) Air Contaminants. For the purpose of Clause 6.2.3.8.(6)(b), washroom exhaust air is not considered to contain contaminants that would adversely affect the air quality in the storage garage.
A-6.2.3.8.(10)(b) Operation Diversity Factor. The operation diversity factor has to be assessed for each specific application. Good engineering practice (see Article 6.2.1.1.) design guidelines can provide information on the subject. Figure A-6.2.3.8.(10)(b), which originates from ASHRAE handbooks, provides an example of factors that can be used for general applications.
Figure A-6.2.3.8.(10)(b)
Operation diversity factor
A-6.2.4.1.(2)(c) Carbon Monoxide Alarms. Battery-powered carbon monoxide alarms are acceptable provided that they are mechanically fastened in place.
A-6.2.9.2.(2) Temperature of Exposed Piping. Normally piping carrying steam or high-temperature hot water at pressures above atmospheric (corresponding temperature 100°C or above) will be insulated to reduce heat losses as an economy measure. Above a temperature of approximately 70°C, however, a bare pipe can cause a burn to human flesh coming in contact with the pipe. If pipes above this temperature are normally out of reach of all persons other than maintenance personnel or are properly guarded, it would be expected that no insulation would be needed for public safety.