Residential Mechanical Ventilation Systems
|Publication Date:||1 January 1991|
This Standard applies to detached, Semidetached, duplex, and row housing. With semidetached or row housing units, the assumption is made that there is no significant air leakage between adjacent units at the pressure differencesxreated by the operation of the ventilation systems, and that the interior area of the building envelope, for the purposes of Clause 6.1 , does not therefore include common separations.
This Standard is not intended for multiple dwelling units of the apartment type, although the ventilation air provisions of Table 1 may be applicable.
This Standard is intended to apply to houses incorporating any type of heating system, whether forced air, electric baseboard, hydronic, or radiant. The implementation of the requirements in this Standard will require different approaches for the particular heating system being used.
This Clause allows for the possibility that ventilation systems conforming to this Standard may not be mandated, and that certain packaged ventilators might therefore be installed in a dwelling without a ventilation system. It also applies to the installation of ventilation equipment beyond that required to meet the minimum ventilation air requirements of this Standard.
All of the relevant clauses of Clause 7 on Equipment Requirements, and Clause 8 on Installation Requirements, apply to such ventilation equipment components. General requirements for all packaged ventilators are given in Clauses 7.7 and 8.1 3. Specific requirements are given in Clauses 7.7.4 and 8.1 3.3(d) for heat-recovery ventilators, in Clause 8.1 3.3 for exhaust air heat recovery devices, in Clause 8.1 3.4 for kitchen exhaust devices, in Clause 8.1 3.5 for range hoods and range-top fans, and in Clause 8.1 3.6 for bathroom fans.
Clause 8.1 3.2 specifies house depressurization requirements for all packaged ventilators installed in addition to, or in lieu of, ventilation systems conforming to the ventilation air requirements of this Standard.
Where, for example, a recirculating forced air heating system is to be used to distribute ventilation air in accordance with this Standard, the requirements of this Standard apply to the air moving and distribution components of the system.
Clause 5.1 1 requires provision for the adjustment of air flow rates and for shutting down the system by the occupants. More complex controls are not precluded, if the system is capable of operating continuously to provide the required minimum flow rates. For example, if the system were being controlled by a humidistat, provision would be required to override the humidity control to allow continuous operation. Occupants may wish to adjust the air flow rates to account for opening of windows or other conditions of use. They may wish to shut off the system during periods when the house is unoccupied.
Clause 5.1 1 also prevents the use of systems which have a "lower" speed that is not significantly lower than the minimum Ventilation capacity. Such systems are sometimes defeated by the occupants due to perceived over-ventilation. Other speed settings below 40% of the minimum ventilation capacity are not precluded, nor are other speeds which may be more than 60% of the minimurn ventilation capacity. System controls are allowed which have operating rates which are both higher and lower than the minimum ventilation capacity as long as one of those rates or settings is between 40 and 60% of the minimum ventilation capacity.
Control humidity senting, carbon-dioxide sensing or occupancy sensing may also be used for rate variation in addition to direct occupant input.
It should be noted that in certain household configurations where the number of bedrooms is high with respect to other rooms, a continuous ventilation rate of 40 to 60% of the minimum ventitation rate may be lower than 7.5 L/s, but it will not usually be lower than 6 L/s per person.
For sedentary persons, current knowledge calls for a rate of ventilation air supply of 7.5 L/s to control contaminants arising from human bioeffluents. For reclining persons at rest, this corresponds to about 5 L/s per person, assuming that the rate of emission of bioeffluents is proportional to the rate of emission of C02. This is the basis for the minimum ventilation air requirements for bedrooms in this Standard. The rates of ventilation air supply called for in this Standard will normally provide a rate of 7.5 t/s per person, on average, for typical families.
Where the number of occupants to be accommodated is known, the total base flow rate of ventilation air established from Clause 5.1 should be compared with a value obtained by multiplying the number of occupants by 7.5. The base flow rate should be adjusted upwards, if necessary, to achieve this flow rate. The base flow rate called for in master bedrooms is based on two occupants and that for other bedrooms on one occupant. If it is known that more than one person will occupy a bedroom, the base flow rate should be adjusted to correspond to a minimum of 5 L/s per person.
Air contaminants also arise from sources such as construction materials, furnishings, cleaning chemicals, combustion products including cigarette smoke, moulds and soil gas. Exposure guidelines for some of these products have been established for residential occupancies (Exposure Guidelines for Residential Indoor Air Quality, Department of National Health and Welfare, April 'I 987). Acceptable concentration limits for other air contaminants are less well defined. The adequacy of the ventilation rates specified in this Standard for maintaining acceptable indoor air quality will depend on these limits and on the contaminant generation. Where abnormal contaminants or unusually high rates of emissions occur, or where unusually low concentration limits are specified, measures going beyond the provisions of this Standard may be required. Even with normal rates of contaminant generation, measures for air quality control beyond those provided may be required for persons who are hypersensitive to certain air contaminants.
Regarding tobacco smoke, the above reference recommends that any exposure in indoor environments be avoided. Therefore, with respect to tobacco smoke, and other contaminants, this Standard cannot ensure the avoidance of all possible health effects. From the standpoint of controlling odour levels, about six times as much ventilation air is required for each smoker as for each non-smoker.
The humidity in dwelling units during the heating season is mainly dependent on the rate of moisture generation, the extent of removal of moist air at its source before it can spread throughout the dwelling unit, and the dehumidifying effect of ventilation air. This Standard requires the capability to exhaust air from kitchens and bathrooms, which are usually significant sources of moisture. The rates of ventilation air supply specified in this Standard will usually be sufficient to maintain the humidity of the dwelling unit below values at which condensation on the inside surfaces of windows becomes excessive. Where house humidities are too high, attention should be given to reducing the rate of moisture generation and to making effective use of the air exhaust capabilites in kitchens and bathrooms. This may call for the installation of timing switches on bathroom exhaust fans so that they continue to operate for some time following bathing or showering.
The pressure difference across the house envelope is dependent on its air-tightness and on the imbalance of outdoor air supply to, and exhaust from, the house. The maximum allowable house depressurization depends, among other things, on the venting characteristics of any installed vented corn bustion appliances.
When wind velocities and temperature differences across the building envelope are low, ventilation by uncontrolled means will be low. The airtightness of Canadian houses has been increasing and this trend is expected to continue. Many newer dwelling units are already quite airtight and the rate of ventilation air supplied by uncontrolled air leakage is very small when intentional openings are closed. Thus, naturally induced ventilation is not considered in this Standard as contributing to the minimum ventilation requirements.
Openings of windows can resutt in substantial flow rates of ventilation air, depending upon design, use and weather factors. Any outdoor air flow through open windows, along with air leakage, will augment that provided by the mechanical ventilation system.
See Clause 1.8 above. In meeting the dwelling unit pressure design requirements of Clause 6, the allowable imbalance of outdoor air supply to, and exhaust from, the house depends on the air leakage characteristics of the house envelope.
The Standards referred to in Clause 4.2 specify the minimum sizes of outdoor air supply openings needed to provide combustion and dilution air for appliances drawing air from the dwelling unit. These openings are intended to provide the required air within acceptable depressurization limits for the venting system. (See Clause 6.3.2.)
Control of combustion air supply for some vented combustion appliances (eg, some solid fuel-burning appliances) may be adversely affected by excessive house pressurization. This is accounted for in Clause 6.1 (b).
CSA Standard CAN/CSA-A405, Design and Construction of Masonry Chimneys and Fireplaces, requires that all fireplaces have provision for an adequate supply of combustion air from outside the dwelling. However, the Standard does not require that all fireplaces be fitted with tight-fitting glass doors. These doors act to aerodynamically isolate the house from the fireplace. Without them, a fireplace operating alone, or in combination with other exhaust devices, could cause depressurization exceeding the pressure design requirements of Clause 6.3.2, possibly resulting in venting problems with other vented combustion appliances. Flue gas spillage may also be a problem with open fireplaces, when the fire is at the final smouldering stage, if the depressurization limits of Clause 6.3.2 are exceeded. These potential problems have been recognized and a Standard for glass doors for fireplaces is being developed by ULC. It is the intention of the CSA Committee on Masonry Chimneys and Fireplaces to refer to this new Standard when it is available.
To reiterate, in order to prevent venting problems, fireplaces should be aerodynamically isolated from the dwelling unit. This might be accomplished, for example, by supplying direct outdoor air to a fireplace fitted with tight-fitting glass doors.
Where summer cooling is not provided by mechanical means, the rate of outdoor air supply required to provide relief from heat gains during hot summer weather will usually be several times the minimum values called for in this Standard. This is usually provided by openable windows, sometimes augmented by high-volume exhaust fans.