in this method is the CLTD, or the Cooling Load Temperature Difference. This factor is used to represent the temperature difference between indoor and outdoor air with the inclusion of the heating effects of solar radiation. The second factor is the CLF, or the cooling load factor. This coefficient accounts for the time lag between the outdoor and indoor temperature peaks. Depending on the properties of the building envelope, a delay is present when observing the amount of heat being transferred inside from the outdoors. The CLF is the cooling load at a given time compared to the heat gain from earlier in the day. The SC, or shading coefficient, is used widely in the evaluation of heat gain through glass and windows. Finally, the SCL, or solar cooling load factor, accounts for the variables associated with solar heat load. These include the global coordinates of the site and the size of the structure. Equations The equations for the use of the data retrieved from these tables are very simple. Q= heat gain, usually heat gain per unit time A= surface area U= Overall heat transfer coefficient CLTD= cooling load temperature difference SCL= solar cooling load factor CLF= cooling load factor SC= shading coefficient For heat gain through walls, doors, roofs, and windows (only window conduction) Q = U*A*CLTD Q = U*A*(T2-T1) Where Q = Overall heat transfer in Btu per hour U = Overall heat transfer coefficient in Btu/(ft2-hr-deg F) A = Area in square feet T1 = outdoor temperature in degrees F T2 = indoor temperature in degrees F For heat gains due to people, equipment (hooded and unhooded), and lighting Q = Q*CLF For solar heat gains through windows and glazed surfaces Q = A*SC*SCL Data tables In addition to tables published by ASHRAE for select latitudes, a computer program called CLTDTAB, available since 1993, can be used to generate custom CLTD/CLF/SCL tables for a specific zone type for any latitude and month. This allows the use of this method, without interpolation, for any area in the world. If the program CLTDTAB is used, the results obtained using this method will tend to be very close to the more rigorous TFM Method mentioned earlier. References Heating, ventilation, and air conditioning