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Controls, Start-Up, Operation, Service and ... - Climayoreo

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NOTE: If the user wishes to disable the st<strong>and</strong>ard enthalpy<br />

control from running concurrently, a field-supplied jumper<br />

must be installed between TB201 terminals 5 <strong>and</strong> 6.<br />

Outdoor Dewpoint Limit Check — If an outdoor relative<br />

humidity sensor is installed, the control is able to calculate the<br />

outdoor air dewpoint temperature <strong>and</strong> will compare this<br />

temperature against the outside air dewpoint temperature<br />

limit configuration (ConfigurationECONO.DEW). If the<br />

outdoor air dewpoint temperature is greater than O.DEW, free<br />

cooling will not be allowed. Fig. 12 shows a horizontal limit<br />

line in the custom curve of the psychrometric chart. This is the<br />

outdoor air dewpoint limit boundary.<br />

Custom Psychrometric Curves — Refer to the psychrometric<br />

chart <strong>and</strong> the st<strong>and</strong>ard Honeywell A-D curves in Fig. 11. The<br />

curves start from the bottom <strong>and</strong> rise vertically, angle to the left<br />

<strong>and</strong> then fold over. This corresponds to the limits imposed by<br />

dry bulb changeover, outdoor enthalpy changeover <strong>and</strong><br />

outdoor dewpoint limiting respectively. Therefore, it is now<br />

possible to create any curve desired with the addition of one<br />

outdoor relative humidity sensor <strong>and</strong> the options for changeover<br />

now available. See Fig. 12 for an example of a custom<br />

curve constructed on a psychrometric chart.<br />

Fig. 12 — Custom Changeover Curve Example<br />

69<br />

CONTROL POINT<br />

CONTROL CURVE<br />

(approx Deg) AT 50% RH<br />

A 73<br />

B 68<br />

C 63<br />

D 58<br />

Fig. 11 — Psychrometric Chart for<br />

Enthalpy Control

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