Designing energy plants the smart way A critical review of the
expected spectrum of operating loads, including the maximum
design, average, low, and minimum loads, is necessary to develop
a generating plant design. By Grahame E. Maisey, PE, Building
Services Consultants, Wyncote, Pa. Low-load control is essential
for efficient operation of heating and cooling plants and
providing comfort during low-load and changeover conditions
between heating and cooling. Complaints from occupants to
maintenance personnel often peak during times of low load.
Generally, low-load and changeover conditions occur for many
hours during a year, many more times than high and low design
loads. Low-load and changeover occurs when the outside
temperature is between 45 and 75 F. Philadelphia, for example,
has approximately 1800 hours annually of low-load and changeover
operation during office hours compared with 150 hours of high-
load operation. This is equivalent annually to 160 working days
of low loads compared with 13 days of high