C NC NO P B M M 1 2 3 5 6 7 2 5 4 10 11 8 1 13 M IN IN OUT IN IN OUT 4 9 3 11 12 M M 10 8 6 M M 7 P M B 12 M NO NC C P IN OUT IN 13 9 7 M SEQUENCE OF OPERATION When the fan is off the outside air damper is closed, the return air damper is open and the steam valves are controlled by the mixed air low limit controller. When the fan is running the steam valves (V1), (V2), (V3) and (D3) and the mixing dampers (D1), (D2) are modulated in sequence, such that on a drop in room temperature: first the free cooling modulates back to the minimum ventilation position, then the steam valve (V1) opens as required; then V2 and V3 are opened and next D3 exposes the coil to an air flow if required. This loop is limited in the supply air to a minimum of 13°C and limited to a minimum in the mixed air at 15°C . When the outside air, enthalpy is greater than the return air enthalpy, D1 and D2 return to the minimum ventilation position. Enthalpy controller (EN1) from PH27A sends its signal to low selector (LS3) allowing free cooling with the air stream containing the lesser BTU content. 8.123 HUMIDEX CONTROL LOGIC WITH ENTHALPY CONTROL LOGIC RESTRICTOR RESTRICTOR RESTRICTOR RESTRICTOR RESTRICTOR RESTRICTOR RESTRICTOR RESTRICTOR EP1 SUMMER DRY BULB WINTER MIXED AIR ROOM AIR ENTHALPY TARGET POINT ROOM TEMPERATURE LOW LIMIT HUMIDEX CONTROL CHANGE-OVER B M 1 2 3 B M 1 B M 1 B M 1 2 B M 2 1 RC2 27˚C DA PROP. RC3 20˚C DA PROP. RC4 15˚C DA PROP. RC5 RA PROP. EN1 M B RC1 13˚C 1 LS2 SUPPLY LOW LIMIT LS1 MPR1 LS3 AV1 BR1 7# IN = 1# OUT CV1 N C SUPPLY ROOM OSA MIXED OSA RETURN TEMP. TEMP. TEMP. TEMP. ENTH. ENTH. ROOM %RH HT1 10% RH TO 90% RH G1 G2 ROOM ROOM TEMP. %RH TO LS3 IN PH27B PH27C & PH27D TT5, HT1, AND G2 ARE MOUNTED AT COLUMN J28 ON GROUND FLOOR. CONDENSATE STEAM TT5 50˚F TO 100˚F RC5 RESET SCHEDULE ROOM ROOM HUMIDEX TEMP. HUMIDITY 22˚C 90%RH 30˚C 27˚C 45%RH 30˚C TT4 TT2 LOW TT1 LIMIT HP M V2 3#-7# PP V3 3#-7# PP CWS CWR C NC NO ____ 8# - 14# SPH V4 NO D3 8# - 13# SPH LOW LIMIT D4 1# - 4# SET MAXIMUN DRIVE ON D3 AT .60"WG PRESSURE DROP ACROSS COIL WHEN D3 IS FULLY DRIVEN. V1 NO 3# - 6# PE1 ENT1 ENT2 D1 NC 11# - 15# PP PP PP SPH D2 NO 12#-16#
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