ASHRAE Journal - May 2009 - 58

ASHRAE 19 50 59–2009 YE A R S JOURNAL ship are not generally understood. Filtration of air is also not given proper consideration in many cases. Fig. 1, taken from Chapter 20 of the 1966 ASHRAE Guide And Data Book, shows the requirements of outside air to limit CO concentration and provide necessary oxygen content. It also shows the range of odor-free air to maintain an acceptable odor level in the classroom. This odor-free air could be outside air if that source is not odor contaminated, or it could be odor-treated re-circulated air. The amount of outside air required to maintain oxygen content and CO, dilution is approximately 4 cfm per pupil. The cfm of odor-free air to maintain an acceptable odor level varies from 11 cfm per person to a maxi-mum of 31 cfm per person, depending on the volume of the air space provided by the classroom for each pupil, and the dietary and hygienic habits of the pupils. The most economical method of treating recirculated air for odor control is through the use of spray washers. Charcoal filters provide an excellent method. Filtration of air is extremely important to reduce buildup of odor-laden lint and dust particles on coil surfaces. This, in turn, could reduce the breeding ground for staphylococcus infection. Also, the maintenance costs of the building will be reduced. We should be striving for filtration of 85% efficiency, or better, based on National Bureau of Standards tests. TYPES OF BUILDINGS Compact Schools The compact building must have air conditioning. There is very little perimeter glass in this type of building; in some cases, there may be no glass at all in the classrooms. In other cases, the glass-to-wall ratio may be approximately 5 to 10%. Fig. 2 shows the sensible heat loads encountered in a typical classroom of the compact building design. Superimposed on this same set of curves are the characteristic heat loads of a typical classroom in a finger-type or conventional design building. Classrooms having exterior walls with a high ratio of glass-to-wall area are characteristic of fingertype school room design. These glass-to-wall ratios are generally between 50 and 80%. In both cases, the latent heat load has been left out. Its main effect upon these curves would be simply to shift them. It will be seen from this figure that the dashed lines, which represent the compact building design, indicate that the classroom would need cooling on a year around basis when it is fully loaded and the lights are turned on. Thus, it can be seen that a compact building design must have a system which provides full cooling by one means or F I G . 2 Sensible heat load in typical classroom: Compact building, interior classroom, dotted line (A); Finger-type building, exterior classroom, solid line. F I G . 1 Ventilation requirements for typical classroom, odor dilution requirements: A) Outside air required to provide necessary oxygen content; B) Outside air required to limit C02 concentration to 0.6%; C) Air required to dilute objectionable body odors to acceptable threshold. 58 ASHRAE Journal a s h r a e. o rg May 2009

ASHRAE Journal - May 2009

Table of Contents for the Digital Edition of ASHRAE Journal - May 2009