Air Cooled Liquid Chillers - Page 14

Selection Procedure

The chiller capacity tables presented in the "Performance Data" section cover the most frequently encountered leaving water temperatures. The tables reflect a 10°F temperature drop through the evaporator. For temperature drops other than 10°F, fouling factors other than 0.00025 (per ARI Standard 590-92) and for units operating at altitudes that are significantly greater than sea level, refer to the "Performance Adjustment Factors" section and apply the appropriate adjustment factors. For chilled brine selections, refer to the "Performance Adjustment Factors" section for ethylene glycol adjustment factors.

To select a Trane air-cooled chiller, the following information is required:

1. Design system load (in tons of refrigeration).
2. Design leaving chilled water temperature.
3. Design chilled water temperature drop.
4. Design ambient temperature.
5. Evaporator fouling factor.

Evaporator chilled water flow rate can be determined by using the following formula:

NOTE: Flow rate must fall within the limits specified in the "General Data" section of this catalog.

SELECTION EXAMPLE

Given:

Required System Load = 53 tons

Leaving Chilled Water Temperature (LCWT) = 45°F

Chilled Water Temperature Drop = 10°F

Design Ambient Temperature = 95°F

Evaporator Fouling Factor = 0.00025 T Ñ

1 To calculate the required chilled waterflow rate we use the formula:

From the 60 ton unit table in the "Performance Data" section of this catalog, a CGAF-C60 at the given conditions will produce 56.8 tons with a system power input of 70.0 kw and a unit EER of 9.7

2 To determine the evaporator water pressure drop we use the flow rate (gpm) and the evaporator water pressure drop curves found in the "Performance Adjustment Factors" section of this catalog. Entering the curve at 136.3 gpm, the pressure drop for a nominal 60 ton evaporator is 16.5 feet.

3 For selection of chilled brine units or applications where the altitude is significantly greater than sea level or the temperature drop is different than 10°F, the performance adjustment factors should be applied at this point. For example: Corrected Capacity = Capacity (unadjusted) x Appropriate Adjustment Factor Corrected Flow Rate = Flow Rate (unadjusted) x Appropriate Adjustment Factor Corrected KW Input = KW Input (unadjusted) x Appropriate Adjustment Factor

4 Verify that the selection is within design guidelines. The final unit selection is:

• Quantity (1) CGAF-C60
• Cooling Capacity = 56.8 Tons
• Entering/Leaving Chilled Water Temperatures = 55/45°F
• Chilled Waterflow Rate (GPM) = 136.3
• Evaporator Water Pressure Drop = 16.5 ft.
• System Power Input = 70.0 KW
• Unit EER = 9.7 Ñ Ñ

MINIMUM LEAVING CHILLED WATER TEMPERATURE SETPOINTS

The minimum leaving chilled water temperature setpoint for water is listed in the following table:

Table 15-1 — Minimum Leaving Chilled Water Temperature Setpoints for Water

¹ These are for units without HGBP, for units with HGBP, add 2°F to each minimum temperature in the table.

For those applications requiring lower setpoints, a glycol solution must be used. The minimum leaving chilled water setpoint for a glycol solution can be calculated using the following equation:

LCWS = Leaving Chilled Water Setpoint (F)

GFT = Glycol Freezing Temperature (F)

T = Delta T (the difference between the temperature of the water entering and leaving the evaporator)

Solution freezing point temperatures can be found in Tables 16-1 thorough 16-2 and the number of stages of capacity can be found in the general data section.  For selection assistance, refer to the CGA Chiller Selection program.