LEGEND RETURN AIR TEMPERATURE RETURN AIR RELATIVE HUMIDITY OUTSIDE AIR TEMPERATURE OUTSIDE AIR RELATIVE HUMIDITY RETURN AIR ENTHALPY OUTSIDE AIR ENTHALPY ENTHALPY SWITCH SIGNAL ENTHALPY COMPARATOR PERFORMANCE GRAPH B M 1 3 2 B M 1 3 2 PT1 PT2 PT3 PT4 PT5 PT6 PT7 DATA LOGGER RC2 RC4 RC5 ENTHALPY RETURN AIR ENTHALPY OUTSIDE AIR ENTHALPY SWITCH RA, 2 POS. PB 4% SET 9.0 PSIG RETURN ENTHALPY OUTSIDE AIR 2 21 BTU TO 39 BTU 21 BTU TO 39 BTU 1 PER LB DRY AIR PER LB DRY AIR 3 M SUBR1 SET P3- P2 = 9.0 PSIG M RC4 AND RC5 RESET RH% TEMP. VALUE 60% 80°F 33.80 BTU 40% 70°F 23.70 BTU MANUAL ADJUSTMENTS MANUAL ADJUSTMENTS RET. AIR RET. AIR OSA TEMP. OSA %RH TEMP. %RH RES. RES. RES. RES. RC4 RC5 The graph illustrated above presents the values regarding temperature, relative humidity and enthalpy with the presented test values colour matched to the graph colours. The control circuit illustrated below allowed simulation of various relative humidity and temperature values, causing variations in the enthalpy values regarding both the return air and the outside air. The values were recorded via pressure transducers and collected through a data logger. The conclusion of the enthalpy comparison, allowing selection of the air stream with the lesser enthalpy value, is represented by the black line. ENTHALPY TEST CIRCUIT 72F 40%RH 70F 40%RH 24.60 BTU 23.60 BTU FREE COOL ON 72F 40%RH 72.5F 40%RH 24.60 BTU 24.75 BTU FREE COOL OFF 72F 45%RH 72.5F 40%RH 25.50 BTU 23.6 0 BTU FREE COOL ON 72F 45%RH 72.5F 46%RH 25.50 BTU 26.25 BTU FREE COOL OFF 75F 45%RH 72.5F 46%RH 27.30 BTU 26.20 BTU FREE COOL ON 75F 45%RH 72.5F 53%RH 27.10 BTU 27.90 BTU FREE COOL OFF 75F 50%RH 72.5F 53%RH 28.50 BTU 28.20 BTU FREE COOL ON OSA ENTH. < OSA ENTH. < OSA ENTH. < OSA ENTH. < RET. ENTH. RET. ENTH. RET. ENTH. RET. ENTH. OSA ENTH. > OSA ENTH. > OSA ENTH. > RET. ENTH. RET. ENTH. RET. ENTH. B M 1 8-111
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