ASHRAE Chapter on Tall Buildings - Stack Effect

The stack effect occurs in buildings when the outdoor temperature is lower than the indoor temperature. The building acts as a chimney with air entering the lower floors and exiting from the upper floors. The pressure differential is directly proportional to the building height and temperature difference. In summer, it's possible to have a reverse stack effect with air entering the higher floors and exiting the lower but it is less significant because of the lower magnitude of the temperature differences. Chapter 16 of the 2009 ASHRAE handbook covers how to calculate the stack effect.

The stack effect often causes major problems including:

• Elevator Doors - may fail to close because the pressure difference causes the door to bind in its guideway
• Manual Doors - difficulty in opening and closing because of the strong pressure
• Smoke and Odor Propagation - through the air path of the stack effect
• Heating Problems - the lower areas of the buildings may be difficult to heat because of the influx of unheated outdoor air

It is not possible to completely seal a building but the following steps can minimize the problems of the stack effect:

• Revolving Doors - entrance doors should be revolving doors that balance the pressure between in and out
• Two-door Vestibules - these types are acceptable in loading dock areas but are not acceptable as personnel entry because of the large numbers of people entering the building at times
• Create Elevator Vestibules - use doors at the entrance of elevator banks.  Also, seal the vertical faces of the elevator shaft
• Interrupt Vertical Stairways - use well-sealing doors in fire stairs that run the height of the building
• Tight Exterior - ensure that specifications for the exterior wall include proper testing and selection of quality contractors  
• HVAC - ensure that the design include positive pressurization.  Consider using a separate system for lobby pressurization

2011 ASHRAE HANDBOOK HAS NEW CHAPTER ON TALL BUILDINGS

The newly published 2011 ASHRAE Handbook-HVAC Applications has a new chapter that focuses on the unique design issues that tall buildings present.

The chapter covers various topics including:

• Stack Effect
• Building Systems Selection Criteria
• Central Plants
• Water Distribution Systems
• Life Safety Systems

We'll cover each topic in future blogs.

  

Climate Change, Ventilation, And Indoor Air Quality

The Institute of Medicine of The National Academies has released the study "Climate Change, the Indoor Environment, and Health".  One of the findings is that climate change may make ventilation problems in buildings more common or more severe in the future by "stimulating the implementation of energy-efficiency (weatherization) measures that limit the exchange of indoor air with outdoor air."

Other findings:

·        Research indicates that poor ventilation in homes, offices, and schools is associated with occupant health problems and lower productivity.

·        Proper design, operation, hygiene, and maintenance of HVAC systems contribute to lower microbial contamination, decreased disease incidence, and increased occupant productivity.

·        Problems will persist until the weatherization workforce is properly trained to recognize and avoid problems of indoor environmental quality, the efficacy of guidelines and codes is validated, and they are widely implemented.

·        Introduction of new materials and weatherization techniques may lead to unexpected exposures and health risks. Energy-efficiency programs must therefore take emissions of building materials and products into account and incorporate tracking mechanisms to identify problems of indoor environmental quality as they arise and solutions as they are developed and implemented.