1 February 1999
indoor design relative humidity will be 50 percent. The indoor design temperature provided by
evaporative cooling or comfort mechanical ventilation will be 26.7 degrees C (80 degrees F).
(2) The indoor design temperature for comfort heating will be 20 degrees C (68 degrees
F) in areas with low levels of physical activity and 12.8 degrees C (55 degrees F) in areas with
moderate to high levels of physical activity. The indoor design temperature for freeze protection
will be 4.4 degrees C (40 degrees F). Where the indoor relative humidity is expected to fall
below 20 percent for extended periods, humidification may be added to increase the indoor
relative humidity to 30 percent.
2-3. INFILTRATION. Design air distribution systems for central HVAC systems to maintain a
slightly positive pressure within the area served in order to reduce or eliminate infiltration unless
there is a valid need to maintain a negative pressure in that area.
2-4. VENTILATION. Ventilation will be in accordance with ASHRAE Standard 62.
a. Provide a complete ventilation analysis in each HVAC design analysis. The ventilation
analysis will consist of a room-by-room breakdown of the anticipated number of occupants, the
amount of ventilation air required, and any applicable adjustments such as multiple spaces
factor, intermittent or variable occupancy factor, flow reduction factor, and ventilation
effectiveness factor. Where these adjustments are significant, explore design alternatives to
reduce life cycle costs. Ventilation for variable air volume systems will ensure proper ventilation
rates at low and high system airflow.
b. Provide a ventilation schedule on the drawings, perhaps combined with the
diffuser/register schedule. This schedule should assist the building occupants when performing
future renovations. List the total supply air and the number of anticipated occupants for each
room in the schedule. Add a footnote to each schedule indicating that the number of occupants
listed is for information purposes only.
c. Locate outdoor air intakes in areas where the potential for air contamination is lowest.
Basic guidelines include the following:
(1) Maximize distance between intakes and cooling towers, plumbing vents, loading
docks, traffic, etc.
(2) Maintain a minimum distance of 10 meters (30 feet) between intakes and exhausts,
more if possible.
(3) Locate intakes and exhausts on different building faces.
d. Where desirable, the designer may incorporate a purge mode into system design. This
mode could be used, for example, to purge the building with outside air during off-hours or to
purge an area of the building undergoing maintenance, such as painting.
e. Where practical, locate photocopiers and laser printers in a separate room or group
them together and provide local exhaust. Maintain the separate room at a negative pressure
relative to adjacent areas by transferring air from these adjacent areas to the separate room.