American Standard CH530 Constant Return, Values for start reset types, Equation, Degrees of Reset

Machine Protection

and Adaptive

Control

Table 3. Values for start reset types

The values for “RESET TYPE” are:

Reset		Outdoor	Return	Const Return
Type:	Disable	Air Reset	Reset	Reset
The values for “RESET RATIO” for each of the reset types are:
Reset	Reset	Increment	Increment	Factory
Type	Ratio	English	SI Units	Default
	Range	Units		Value
Return	10 to 120 percent	1 percent	1 percent	50 percent
Outdoor	-80 to 80 percent	1 percent	1 percent	10 percent
The values for “START RESET “ for each of the reset types are:
Reset	Start	Increment	Increment	Factory
Type	Reset	English	SI Units	Default
	Range	Units		Value
Return	4 to 30°F	0.1°F	0.1°C	10°F (5.6°C)
	(2.2 to 16.7°C)
Outdoor	50 to 130°F	0.1°F	0.1°C	90°F
	(10 to 54.44°C)			(32.22°C)
The values for “MAXIMUM RESET” for each of the reset types are:
Reset	Maximum	Increment	Increment	Factory
	Reset	English	SI Units	Default
	Range	Units		Value
Return	0 to 20°F	0.1°F	0.1°C	5°F
	(0.0 to 11.11°C)			(2.78°C)
Outdoor	0 to 20°F	0.1°F	0.1°C	5°F
	(0.2 to 11.11°C)			(2.78°C)

Constant Return

CWS’ = CWS + 100 percent (Design Delta Temperature) - (TWE- TWL) and CWS’ > or = CWS and CWS’ -CWS < or = Maximum Reset

Notice that Constant Return is nothing more than a specific case of Return Reset offered for operator convenience.

When any type of CWR is enabled, the UCP will step the CWS toward the desired CWS (based on the above equations and setup parameters) at a rate of 1°F every 5 minutes until the Active CWS equals the desired CWS’. This applies when the chiller is running only.

Using the Equation for calculating CWR for Outdoor Air Temperature

Equation:

Degrees of Reset = Reset Ratio*(Start Reset - TOD)

The chiller will start at the Differential to Start value above a fully reset CWS or CWS for both Return and Outdoor Reset.

The graph on the next page, shows the reset function for Outdoor Air Temperature: Note: This graph assumes that Maximum Reset is set to 20 degrees.

Degrees of Reset:

Degrees of Reset = Active CWS - Front Panel CWS

or

Degrees of Reset = CWS’ - CWS

To obtain Active CWS from Degrees of Reset: Active CWS = Degrees of Reset + Front Panel CWS

(* = multiply)

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