AIVC Technical Reports

Efficacy of Intermittent Ventilation for Providing Acceptable Indoor Air Quality Only available for Subscribers 356 kB

M.H. Sherman
AIVC Technical Note 60, 2006, 27 pp, Code TN 60

Ventilation standards and guidelines typically treat ventilation as a constant and specify its value. In many circumstances a designer wishes to use intermittent ventilation, rather than constant ventilation, but there are no easy equivalencies available. This report develops a model of efficacy that allows one to calculate how much intermittent ventilation one needs to get the same indoor air quality as a the continuous value specified.

We have found that there is a simple relationship between three dimensionless quantities: the temporal ventilation effectiveness (which we call the efficacy), the nominal turn-over and the under-ventilation time fraction. This relationship allows the calculation of intermittent ventilation for a wide variety of parameters and conditions. We can use the relationship to define a critical time that separates the regime in which ventilation variations can be averaged over from the regime in which variable ventilation is of low effectiveness.

We have found that ventilation load-shifting, temporary protection against poor outdoor air quality and dynamic ventilation strategies can be quite effective in low-density buildings such as single-family houses or office spaces. The results of this work enable ventilation standards and guidelines to allow this extra flexibility and still provide acceptable indoor air quality.

Keywords: Ventilation, Air Exchange Rate, Indoor Air Quality, Ventilation Standards

Contents

ABSTRACT 1
1. INTRODUCTION 3
   1.1. BACKGROUND 3
2. MATHEMATICAL DESCRIPTION 5
   2.1. CRITICAL TIME 6
3. APPLICATIONS 7
   3.1. NOTCH VENTILATION 7
   3.2. PULSE VENTILATION 8
4. DISCUSSION 10
   4.1. LOW-DENSITY RESIDENTIAL BUILDINGS 13
   4.2. HIGH-DENSITY RESIDENTIAL BUILDINGS 14
   4.3. LOW-DENSITY COMMERCIAL AND INSTITUTIONAL BUILDINGS 15
   4.4. HIGH-DENSITY COMMERCIAL AND INSTITUTIONAL BUILDINGS 15
   4.5. ASSUMPTIONS AND LIMITATIONS 15
5. SUMMARY AND CONCLUSIONS 16
6. REFERENCES 17
APPENDIX: DEFINING EQUATIONS AND SIMPLIFIED PHYSICAL MODELING 18
   ZERO "OFF-CYCLE" VENTILATION 19
   NON- ZERO "OFF-CYCLE" VENTILATION 20

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