What are the considerations for the illustrated system regarding safety of the mechanical components? There are no low limits or high limits, the compressed supply air pressure must be below the actuators' maximum allowable pressure rating, The mixed air temperature must be known and not allowed below 55°F. Added 30# relief valves after each PRV. What are the considerations for the illustrated system regarding energy use? The actuators’ spring ranges must be known. The temperatures of the OSA, return air, mixed air and supply air must be known. The mixed air must be held at the minimum ventilation rate until the heating is completely shut down and cooling is required. Mechanical cooling is gradually used only after free cooling cannot achieve the desired supply air temperature goal. Mixed air to go back to minimum when it is easier to cool return air than OSA. What is a typical application of the type of system illustrated? Office, classroom, gym, auditorium store. Where and what safeties should be installed? High limits (HL) and low limit (LL) and smoke detectors (SD). Where is the mixed air plenum and what are the mixed air’s three purposes? Ventilation, pressurization and cooling. How would you manually operate this fan system to address ventilation, comfort and energy use requirements under these different conditions? (1) At unoccupied times when the outside air (OSA) temperature is below 35°F? (If the fan is the only source of heating? If adequate perimeter heating also exists?) Duty cycle with dampers in full recirculation if possible via a night stat setting if only source of heat. Shut down if not required controlling heat from mixed air at 55°F, with OSA and exhaust dampers closed. (2)At occupied times when the OSA temperature is below 35°F? The mixed air must be held at the minimum ventilation rate until the heating is completely shut down and cooling is required. (3)At unoccupied times when the OSA temperature is above 35°F? Duty cycle with dampers in full recirculation if possible via a night stat setting if only source of heat. Shut down if not required controlling heat from mixed air at 55°F, with OSA and exhaust dampers closed. (4)At occupied times when the OSA temperature is above 35°F? The mixed air must be held at the minimum ventilation rate until the heating is completely shut down and cooling is required. Revert back to minimum ventilation when the return air is easier to cool than the OSA. 10-186 RETURN FAN SUPPLY FAN SUPPLY AIR COOLING COIL HEATING COIL ------- ---------- PRV2 PRV3 PRV1 DM1 DM2 DM3 CWR CWS HWR HWS C NC NO NC C NO V2 V3 MAIN AIR SUPPLY OUTDOOR AIR EXHAUST AIR
RkJQdWJsaXNoZXIy ODY1ODQy