CH-2432 (RP-152) -- Pulldown Load Calculations and Thermal Storage During Temperature Drift PDF

Most design day cooling load calculation methods, including that developed in RP-138(l) and the Total Equivalent Temperature Difference (TETD) method, are based on a system operation that maintains the indoor design temperature at a constant value over the day. The peak load thus obtained is generally used to make an equipment selection, also with the usual assumption that there is a steady state set of operating conditions. It is often desirable to evaluate the cooling load when the system is operated intermittently with the temperature floating during the off-time. The cooling load imposed on the system at start-up, that is, during the pulldown period of the temperature, is greater than when the temperature is held constant. Since many systems are operated with shutdown periods at nights or weekends, the ratio of the cooling load with intermittent operation to that with constant temperature can be useful for designing systems to handle these loads. Another design consideration is the temperature drift of the room temperature when the cooling capacity is limited.

The plan for this work was to develop a model room which would isolate the load source or parameter to be studied. The room model was run with a range of variables for each load source through the NBSLD computer program. The resulting loads were analyzed to extract a simplified set of values.