The purpose of the flow switch or sail switch used with hot water coils is to
a) stop the fan and close the outside air dampers if the low limit temperature controller malfunctions or the heat source fails
b) open the outside air dampers wide when the outside air temperature rises
c) increase the heat source temperature if the outside air temperature decreases
d) close the outside air dampers and stop the fan if the flow of water is interrupted due to pump failure or closing of the hand valves
e) increase the hot water flow through the coil if the outside air temperature is too low
Answer: D