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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It should be clear to the design professional that the dynamic nature of mechanical ventilation requires dynamic control. Being a rate based standard, continuous airflow measurement should be a central component of any effective control strategy to assure acceptable indoor air quality.
ASHRAE Standard 62-2001
ASHRAE Standard 62 is a short, but often misinterpreted, document outlining ventilation requirements for acceptable indoor air quality. The standard is being developed under a “continuous maintenance” protocol and is comprised of a parent document and approved addenda.
Designers should provide an acceptable indoor environment to maintain occupant productivity and health. They should also evaluate the IAQ risk of their design. Standard 62 has been incorporated into many building standarr. The International Mechanical Code has adopted a rigid interpretation of the Ventilation Rate Procedure of the parent document and requires devices and controls to maintain per person ventilation requirements at all load conditions.
Regardless of local code requirements, designing and operating a building to this standard will minimize IAQ liability and help assure an acceptable indoor environment. Unfortunately there is no “cookbook” solution to sahrae for IAQ. 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.
Ventilation code enforcement has proven to be difficult ashtae it is often misunderstood by the code enforcement agency in the local jurisdiction.
Present motivation aashrae 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. An area that only recently has received attention is the owner-occupant’s motivation to increase productivity and reduce the adverse impact a poor indoor environment can have on human health and well-being. The scope of Standard 62 “applies to all indoor or enclosed spaces that people may occupy, except asyrae other applicable standards and requirements dictate larger amounts of ventilation than this standard.
Section 3 addresses definitions used within the standard. Xshrae is the standard’s definition of acceptable indoor air quality.
The actual occupant dissatisfaction is exponentially greater in practice. Many systems cannot meet the minimum airflow requirements at the occupied space during operation as a result of the dynamic 62-200 of mechanical ventilation system and external factors on the building envelope.
Tsandard lack of specific guidelines to standardd overcome the effect of changing system dynamics on ventilation rates and distribution for today’s HVAC systems is partially to blame for design deficiencies. If properly executed, one out of five occupants may express dissatisfaction as a result of poor indoor air quality.
Unlike thermal comfort, the effect of indoor air quality is difficult to measure. Designers must choose and claim compliance under one procedure, not a combination of both. Understanding and assessing the potential risk as well dtandard the ability to provide a functional solution is the duty of the design professional.
In the Ventilation Rate Procedure, 4. Section 5 specifies the systems and equipment recommended under Standard Addendum u was approved for incorporation into the parent document at the ASHRAE winter meeting in January and adds a new section, 5.
Mechanical ventilation systems shall include either manual or automatic controls that enable the fan stanxard to operate whenever the spaces served are occupied. The system shall be designed to maintain the supply airflow and minimum outdoor airflow as required by section 6 under any load condition. VAV systems with fixed outdoor air damper positions may not meet this requirement.
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.
Therefore, maintenance ashrea minimum outdoor airflow defined in section 6 essentially requires the use of permanent devices capable of maintaining outdoor airflow rates for compliance. Not requiring airflow measurement is analogous to standarf the requirement standrad temperature measuring devices to maintain automatic temperature control. 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.
The designer must assume that the critical zone is at its minimum supply airflow or use airflow measurement suitable for accurate monitoring in each zone which may go critical to continuously calculate then reset outside air intake flow rates at the AHU. As a result of the requirements set forth in the standard for compliance “under any load condition”, section 5 should require airflow measurement with automatic controls at the intake of all air-handling units that function to provide a building or space with outside air, regardless of the size or asrhae type of system.
It must also include individual sensor and transmitter uncertainties. 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.
Although this may sound impractical to some designers, the productivity and health benefits is far greater than the cost to satisfy the requirements for acceptable indoor air quality. At ashraee writing of this document, addendum x was still under public review. This addendum addresses humidity control and building pressurization. Whenever the temperature of a building envelope is lower than the dew point of air migrating across it, there will be condensation.
Moisture is a prerequisite for mold and fungal growth and the condition should be avoided. The proposed addendum, only addresses positive pressure during periods of dehumidification. Mechanical standaard with dehumidification capability shall comply with the following: 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.
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. As with section 5. In addition, increased humidity combined with wind and stack driven infiltration during periods when the ventilation system is not operating may be a significant factor influencing mold and fungal growth. Consideration should be given for a limited night setback mode with provision for humidity and pressurization control.
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 the temperature of the building envelope. Maintaining a building at net neutral pressure under these conditions would be more appropriate. Net neutral control requires more precise instrumentation and the margin of error is much smaller.
Anything that changes the pressurization flow will result in fluctuations in building pressure. HVAC system control strategies that ignore this relationship have inherent pressurization problems.
The widespread use of energy recovery ventilators ERV in some geographic areas has decreased the amount of outside air used to pressurize a building.
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.
Designers should exercise caution when implementing strategies that rely on ERV units for outside air and result in building pressures that are close to net neutral by design.
ASHRAE Standard | Midwest Air Filter
Wind, stack, and filter loading can easily result in net negative buildings and increased condensation within the building envelope. Typically, the ashrad airflow, QP, is maintained at a fixed differential, regardless of the supply airflow rate required for temperature control. The pressurization airflow relationship is as follows: Section 6, Procedures, is the heart of the standard.
Great care should be given to the selection between these procedures. The Ventilation Rate Procedure “prescribes the rate at which ventilation air must be delivered to a space and various means to condition that air.
The alternate Indoor Air Quality Procedure “uses one or more guidelines for the specification of acceptable concentrations of certain contaminants in indoor air but does not prescribe ventilation rates or air treatment methods.
If the outdoor air quality is not acceptable section 6. The Ventilation Rate Procedure is a rate based standard. Designers claiming this procedure must be able to substantiate that rates are maintained during all load conditions. Rates can be determined either directly using airflow measuring devices or indirectly by other means i. However, the uncertainty of indirect techniques introduces a significant level of risk. The designer, occupants, and facility owners should carefully consider the method employed prior to implementation.
CO2 is an indicator of human activities and hence “bioeffluents” and not a measure of indoor air quality. Studies have indicated that a ventilation rate of 15 CFM per person is adequate to dilute body odor. Using the steady-state model described in Appendix C of the Standard, 15 CFM per person would be the resulting quantity of outside air introduced into a space if a.
The statement below merely indicates that human body odor will most likely be acceptable if the conditions above are true. It does not state the “indoor air quality shall be considered acceptable. CO2 measurement, at best, can be used as an indicator of changes in occupancy.
Interpretations for Standard 62-2001
Its value as an indicator of actual ventilation rates is questionable. Designers should be cautious when using CO2 measurement as the sole source of verification of outdoor airflow rates. Especially in facilities asshrae variable occupancy and activity levels. According to this procedure, 6.
Therefore, systems that meet the minimum requirements of Table 2 and the outside air requirements set forth in 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.
All of these variations can be compensated for by using an airflow measuring station at staandard intake to the air-handling unit with automatic controls. Systems that provide a variable volume of supply air to the conditioned space are influence by everything previously mentioned. standarx
In addition, outside airflow rates will vary as a axhrae of changes in mixed air plenum pressure. Outside airflow rates may require reset on variable volume systems based on calculations of the multi-space equation defined under 6. Where more than one space is served by a common supply system, the ratio stanvard outdoor air to supply air required to satisfy the ventilation and thermal control requirements may differ from space to space.
The system outdoor air quantity shall then be determined using Equation see References 23 and The critical space is that space with the greatest required fraction of outdoor air in the supply to this space. Advanced VAV control strategies can satisfy the requirements of 6.
This can be accomplished by determining the critical zone fraction, Z, to calculate the corrected fraction of outdoor air, Y. The calculation requires that the total supply airflow rate measured, QSA, usually with 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.
Airflow sensors provided with VAV boxes should not be used for this calculation. Although these devices may be adequate for modulating a box for thermal comfort, the combination of low quality airflow pickups and low cost pressure sensors in the DDC controller will not result in the measurement accuracy necessary for proper stzndard of equation 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.
The multi-space equation can result in wide variations in outside airflow requirements in some systems. Increasing the critical zone supply flow by providing reheat can reduce total outside airflow rates. Outside airflow rates can also be reduced if the critical zones have variable occupancy.