ANSI/ASHRAE Standard (Including ANSI/ASHRAE Addenda listed in Appendix H). Ventilation for Acceptable. Indoor Air Quality. Ventilation standards and mechanical codes have evolved to address ASHRAE Standard (2). Ventilation for .. ASHRAE Standard The Ventilation Rate Procedure found in ASHRAE Standard Addendum N was applied to Monmouth University’s Multipurpose Athletic.
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If atandard outdoor air quality is not acceptable section 6. A key distinction over the existing procedure will be the requirement for ventilation rates to be determined based on both occupant and space ventilation requirements. The calculation requires that the total supply airflow rate measured, QSA, usually ashras an airflow measuring station in the total supply air circuit and the airflow rate of the critical zones is measured with an airflow measuring station capable of accurate measurement.
Such systems shall be designed to maintain the building at net positive pressure with respect to outdoors, in the absence of wind and stack effect, during all hours of dehumidification. In addition, the section should strongly encourage the use of airflow measuring devices in critical zones of VAV systems for the continuous calculation and reset of the multi-space equation defined in section 6. For systems that provide a constant volume of supply air to the conditioned space, outside airflow rates will vary as a result of a.
Typically, the pressurization airflow, QP, is maintained at a fixed differential, regardless of the supply airflow rate required for temperature control.
The start-up phase, covered in section 7. Other distinguishing factors include a provision for zone distribution effectiveness based on the air distribution configuration, the modification of the multi-space equation for multi-zone recirculating systems, the consideration for varying operating conditions, the provision for dynamic reset, and specific requirements for exhaust ventilation.
As a result, this condition rarely, if ever, exists. It is unlikely that all contaminants of concern will be evaluated or reduced standwrd acceptable levels. Therefore methods that lag occupancy such as CO2 DCV should be carefully considered prior to implementation. The widespread use of energy recovery ventilators ERV in some geographic areas has decreased the amount of outside air used to pressurize a building. Its value as an indicator of actual ventilation rates is questionable.
Noteworthy is the standard’s definition of acceptable indoor air quality. Designers must choose and claim compliance under one procedure, not a combination of both. The purpose of ASHRAE Standard 62, as defined in Section 1, is to “specify minimum ventilation rates and indoor air quality that will be acceptable to human occupants and are intended to minimize the potential for adverse health effects. Airflow sensors provided with VAV boxes should not be used for this calculation.
HVAC system control strategies that ignore this asurae have inherent pressurization problems. However, contaminants that are not appreciably reduced by the air-cleaning system may be the controlling factor in design and prohibit the reduction of air below that set by the Ventilation Rate Procedure.
Present motivation to design to the standard has been driven mostly by liability and risk management concerns and in some cases the desire of the design professionals to meet their obligation by designing to national, professional standards. It is also not practical to measure all potential contaminants and in some cases, such as with fungus or mold, measurement may not be possible. When applied in accordance to manufacturer’s recommendations, airflow measuring devices such as those manufactured by EBTRON, only require the verification of operation by test and balance professionals.
Not requiring airflow measurement is analogous to ignoring the requirement for temperature measuring devices to maintain automatic temperature control.
Interpretations for Standard
The actual occupant dissatisfaction is exponentially greater in practice. According to the Indoor Air Quality Procedure, providing dilution ventilation as prescribed by the Ventilation Rate Procedure will provide acceptable indoor air quality “ipso facto”. Clearly airflow rates are part of this procedure.
Although this may sound impractical 26-2001 some designers, the productivity and health benefits is far greater than the cost to satisfy the requirements for acceptable indoor air quality. Regardless of local code requirements, designing and operating a building to this standard will minimize IAQ liability and help assure an acceptable indoor environment.
Maintaining a building at net neutral pressure under these conditions would be more appropriate. The air cleaning system efficiency for the troublesome contaminants present, both gaseous and particulate, 662-2001 be adequate to satisfy the Indoor Air Quality criteria of 6. Ventilation code enforcement has proven to be difficult because it is often misunderstood by the code enforcement agency in the local jurisdiction.
Outside airflow rates may require reset on variable volume systems based on calculations of the multi-space equation defined under 6. Whenever the temperature of a building envelope is lower than the dew point of air migrating across it, there will be condensation. At the writing of this document, addendum x was still under public review. In the Ventilation Rate Procedure, 4. Although outside airflow rates into many buildings have increased with the use of the technology, there is potential for an increase in building pressurization problems, which could lead to increased mold and fungal growth.
After determining the corrected fraction of outdoor air required, Y, the new outside airflow setpoint is determined by multiplying Y by the supply airflow rate, QSA.
It incorporates both quantitative and subjective evaluation. If approved, it will replace the entire Ventilation Rate Procedure in the parent document. The statement, “in the absence of wind and stack effect” is of concern since external factors can significantly influence infiltration and exfiltration across the building envelope.
ASHRAE Standard 62-2001
However, it neglects the significant influence of external pressure variations on all systems that result from changes in wind and stack pressures, which often exceeds 0. The scope of Standard 62 “applies to all indoor or enclosed spaces that people may occupy, except where other applicable standards stanrard requirements dictate larger amounts of ventilation than this standard. Conversely, “When contaminants are generated in the space or conditioning system independent of occupants or their activities, supply of outdoor air should lead occupancy so that acceptable conditions will exist at the start of occupancy.
Because many systems, especially VAV, have thermal load requirements that differ from the ventilation requirements for acceptable IAQ, the requirements of this section can only be realized if the multi-space equation is calculated under design and minimum supply flows to individual zones using the minimum outdoor air requirements to each zone.
Being a rate based standard, continuous airflow measurement should be a central component of any effective control strategy to assure acceptable indoor air quality. There is the potential for condensation to occur under a positive pressure environment during periods of humidification in cold climates since the dew point of the air within the building could potentially be greater than ashrse temperature of the building envelope.
Since airflow rates are typically reduced in the Indoor Air Quality Procedure, its measurement and control is even more critical, especially on systems where the thermal load changes independent of the occupants and their activities.
Indoor Air Quality Procedure. 6-2001
Interpretations for Standard 62-2001
Buildings that are likely to change use or be altered should consider a robust HVAC system design that could take into account changes in airflow rate requirements imposed by this standard. It must also include individual sensor and transmitter uncertainties. Unfortunately, almost every facility has contaminants generated from within the space i. Designers should be cautious when using CO2 measurement as the sole source of verification of outdoor airflow rates.
Where more than one space is served by a common supply system, the ratio of outdoor air to supply air required to satisfy the ventilation and thermal control requirements may differ from space to space. Anything that changes the pressurization flow will result in fluctuations in building pressure.