In Double Duct system, two separate ducts are run from the central unit to each of the air terminals, as shown in figure below. In winter two warm air streams, of different temperatures, are carried to the air terminals, for individual mixing. The temperatures of both air streams are automatically controlled. In summer the air temperature leaving the cooler is controlled by a multi-step thermostat in the re-circulating air stream, which governs the automatic capacity control of refrigerating plant, as with the zone control. Steam is supplied to one of the heaters, so that two air streams are available at the air terminals for individual mixing.

1. Filter
2. Cooler
3. Low duty heater
4. High duty heater
5. Pre-insulated pipes delivering air
6. Sound attenuating air terminal, with volume and temperature control
7. Automatic steam valve for tempered air stream
8. Automatic steam valve for warm air stream
9. Steam traps
10. Multi-step cooling thermostat
11. Compressor
12. Automatic Capacity Control valves
13. Condenser
14. Thermostatic expansion valve
15. Sea water pump
16. Fan starter
17. Compressor starter
18. Sea water pump starter

 

References

“Marine Auxiliary Machinery” by H.D. McGeorge