(c) Water Flowmeters. These meters are used for the same purpose
described in 6.1(c) above for combined pumping systems.
(d) Minimum Flow Switch. A minimum flow switch is incorporated in each
boiler flowmeter to terminate firing when the waterflow drops below a safe
( e ) Combustion Control Interlocks. T h e starting switches of the boiler
to prevent boiler operation without pump operation.
6 . 4 Zoning. When economically justified, zoning arrangements of the
d i s t r i b u t i o n circuits are provided where various groups of buildings with
different requirements of temperature, pressure, and flow must be served.
T h i s is generally the case when hospitals, laundries, airports, and kitchens
have to be supplied from the same distribution system. In those cases,
separate circulation pumps are used for each zone, which permits independent
r e g u l a t i o n of the flow, pressure, and temperature for each group of related
The zone temperature is controlled by an individual temperature
control valve through the blending connection for the zone. This permits
maintaining a constant supply temperature to each zone of a distribution
system and at the same time holding a constant expansion tank pressure. The
n e t result is higher economy and flexibility.