ASHRAE Journal - August 2012 - 54

2012 Technology Award Case Studies
Cold Fog Humidifier DOA Unit Existing AHUs Typical of 4
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Cold fog.

$500,000/year amounting to a 58% reduction from the original utility and operating budgets. Per the terms of the guarantee, if the savings are not realized in an annual measurement and verification process, the guarantor pays the museum by the amount of the shortfall. If savings exceed the guarantee, the museum retains the excess savings. After five years of operation, the museum has achieved more than 60% savings per year.

52°F Dew Point 50 45 40 C 35 30

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Figure 2: Dew-point cooling.
Cold Fog Humidifier DOA Unit Existing AHUs Typical of 4
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180 With no opportunities to save energy from tem170 perature setbacks, all savings had to come from 160 150 improved HVAC system processes and equip) 75 140 (°F ment efficiency. There were six main enhancee 130 ur at 120 ment areas. 70 er p 110 m 1. Dedicated Outside Air Unit Te 100 65 lb u 90 • 30,000 cfm (14 158 L/s) outside air unit; -B 60 et 80 W • Preheat and cooling coils with high-pressure Mixing Line 55 70 52°F Dew Point 50 60 E F cold fog humidification; Reheat A 50 45 • Constant dew-point control; and D 40 40 35 30 Zone Heat 30 • Airflow measuring stations used to control 20 B outside airflows. 10 C 2. Boiler Plant 0 30 35 40 45 50 55 60 65 70 75 80 85 90 95 100 105 110 • Since steam was no longer required, the Dry-Bulb Temperature (°F) steam boilers were replaced with a skid-mounted Figure 3: Dew-point heating. hot water boiler system; • Five modular, copper-tube hot water boilers; and culate without mechanical compression (strainer cycle). The • Primary/secondary pumping. free cooling mode satisfies 100% of the museum’s cooling 3. Variable Speed High DT Chiller Plant load requirements when the outside air wet-bulb temperature • Two VFD controlled centrifugal chillers; drops below 37°F (3°C). • Reduced evaporator and condenser flows: 2.0 gpm/ton 5. Chiller and Tower Optimization Control (0.037 L/s·kW) for the evaporator and 2.4 gpm/ton (0.043 This control routine minimizes the chiller and tower sysL/s·kW) for the condenser; and tem’s total energy use. This approach uses outdoor wet-bulb • Variable primary chilled water pumping with more than conditions in real time, as well as chiller loading to calculate 70% evaporator flow turndown capability. the optimal cooling tower setpoint. 4. Refrigerant-Free Cooling 6. DDC System When outside air temperature is at or below 37°F (3°C), A new DDC system was installed replacing the old pneuthe chiller compressor is turned off and bypass valves in the matic control system. Also, wireless thermostats were used to chiller refrigerant circuit are opened to allow refrigerant to cir- simplify installation.

Control Box 80

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ASHRAE Journal

ashrae.org

August 2012

Humidity Ratio

Humidity Ratio

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180 170 160 150 140 130 120 B 110 100 90 80 Mixing Line 70 60 Reheat 50 40 30 Zone Heat 20 10 0 95 100 105 110
ASHRAE Journal - August 2012

Table of Contents for the Digital Edition of ASHRAE Journal - August 2012
