P B M C 3 2 1 M M 1 2 3 4 5 6 RH 60% 80°F 40% 70°F 33.90 BTU 23.65 BTU 3 9 15 6 12 5 4 7 8 10 11 13 14 21 39 30 23 24 26 27 28 31 33 34 36 37 22 25 29 32 35 38 SEQUENCE OF OPERATION When the fan is off, solenoid valve (EP1) is de-energized. The outside air and exhaust air dampers close and the return air damper opens. Receiver controller (RC5) senses the outside air humidity and temperature via transmitters (HT2) and (TT2) respectively. RC5 produces a signal representing the outside enthalpy as the humidity and temperature vary according to the reset schedule. RC4 senses the return air humidity and temperature via transmitters (HT1) and (TT1). RC4 produces a signal representing the return air enthalpy as the humidity and temperature varies according to the reset schedule. Both RC4 and RC5 send their signals to subtraction relay (SUBR1). SUBR1 subtracts the return air enthalpy signal from the outside air enthalpy signal. SUB1’s output signal is 9 PSIG when both input signals are equal. If the outside air enthalpy is greater than the return air enthalpy SUB1’s output signal will start to rise by the difference that RC5’s signal is greater than RC4’s signal indicating that the outside enthalpy is greater than the return air enthalpy. SUB1’s signal goes to receiver controller (RC2), which prevents free cooling when the outside air enthalpy is greater than the return air enthalpy. RC2 receives its main air from receiver controller (RC3) which senses the return air temperature via TT1. RC2’s signal provides the main air for receiver controller (RC1) which senses the mixed air temperature via transmitter (TT3). RC1 sends its signal to minimum positioning relay (MPR1), which sends its signal through EP1 to modulate the mixing dampers. The safeties will shut down the fan when the temperature exceeds their set points. NOTE: The proportional band and authority may have different values, depending on the controller manufacturer. The subtraction relay may be obtained from Kreuter Marketing (RCC-1508). Kreuter Marketing manufactures the receiver controllers used in the testing. (CCC-1002) TEMP. PRESS. VALUE PB=25.8% AUTH. = 41.4% OSA ENTHALPY 21 TO 39 BTU RETURN AIR ENTHALPY 21 TO 39 BTU SUBR1 SET (P3 = P2) = 9 PSIG RETURN AIR SET 72˚F (22˚C) RETURN AIR ENTHALPY OSA ENTHALPY ENTHALPY SWITCH (RA) 2 POS. PB=4% SET 9.5 PSIG MIXED AIR TEMP. MIXED AIR LOW LIMIT SET 55˚F (13˚C) 6# MPR1 EP1 NC B M 1 RC1 B M 1 RC2 B M 1 RC3 RETURN TEMP. 0-100˚F RETURN %RH OSA TEMP. OSA %RH 0-100% 0-100˚F 0-100% RES. RES. RES. RES. RES. PSIG ENTHALPY BTU/LB TT2 HT2 TT3 LL1 HL2 SUPPLY FAN RETURN FAN HL1 TT1 HT1 NC NO NC OSA EX. RETURN AIR 6# - 10# 7# - 12# 4# - 9# 1 5 6 M M M 3 4 RC4 AND RC5 RESET 2 B M 1 2 3 B M 1 2 3 RC4 RC5 15 PSIG 3 PSIG 8-113
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