Resource Stewardship and Sustainability: AC Systems

The Facility Service group is taking the following actions to reduce the environmental impact of Baylor College of Medicine's operations through the following AC Systems initiatives:

V belt drive systems work on the principle of tangential friction allowing the energy produced by a motor to be transferred to a fan by using belts and pulleys. In this system there is always some amount of energy lost as the belts slip as a result of the loss of tension as the belt stretches with age. The timing belts have teeth on the inside of the belt which are used to create a positive lock between the motor pulley and the fan pulley. The design of the timing belt system eliminates the possibility of belt slippage. These belts are used in many applications including replacing chain drives on motorcycles. Changing the belt results in an energy savings of 4 percent to 6percent with a payback of 8 to 14 months. The additional benefit of using the timing belts is that they save maintenance labor as they last over three times as long as V belts and never need to be adjusted.

As part of the infrastructure renewal process at Baylor College of Medicine, the Facility Services department manages the replacement of four to seven air handling units a year. The new air handling units we are installing are constructed to provide the highest energy efficiency combined with the longest life of any of the equipment we have ever installed. We are using all the technologies mentioned above to minimize the energy consumption and carbon footprint of our facility. The air handling units are designed with direct drive fans which eliminates any inefficiency associated with belt slippage, variable speed drive units which match the fan speed exactly to meet the air demand at any time, and UV lights in front of the cooling coils to minimize the pressure drop across the chilled water coil, kill all organic or bacterial life forms thus improving the indoor air quality. We also utilize double wall construction to keep the air stream free of any insulation contaminates.

We adjust the heating hot water temperature based on the outside air temperature. When the outside air temperature is below 38 deg. F we set the heating hot water temperature at 180 deg. F. When the outside air temperature is above 85 deg. F we set the heating hot water temperature at 105 deg. F. We use a linear formula to adjust the heating hot water temperature when the outside air temperature is between these two values. By doing this we minimize our natural gas consumption and meet the needs of the building occupants. This energy management program saves Baylor over 5,000 MMBTU of natural gas consumption annually ($35,000 annually).

We adjust the chilled water temperature based on the outside air temperature. When the outside air temperature is below 50 deg. F, we set the chilled water temperature at 49 deg. F. When the outside air temperature is above 75 deg. F, we set the heating hot water temperature at 44 deg. F.

Using variable speed drives on the cooling tower fans allows us to control the condenser water temperature to within a half of a degree F. This accuracy allows us to reduce the condenser water supply temperature to 70 deg. F when the outside air temperature is below 60 deg. F. The air conditioning system is designed for the condenser water supply temperature to be 85 degrees. The savings associated with reducing the condenser water temperature is 1.5 percent per degree reduction. So a 15 degree reduction equates to a 22.5 percent reduction in air conditioning system energy consumption. Using this process we have reduced our energy consumption by over 2.8 million KWH per year ($270,000 annually).

In 1994, we implemented a program to measure and adjust the air flow through our laboratory fume hoods to meet the National Institute of Health standards for the work taking place in the specific laboratory. Prior to this time, the philosophy had been to set up each hood to support the most aggressive chemicals that would potentially ever be used or simply put, to run the exhaust at the designated CFM for the highest category of activity (most dangerous work). Through this effort and working with the Baylor College of Medicine Office of Environmental Health and the individual investigators, we reduced the amount of air we were exhausting by 25 percent over all. The beginning effort was the start of the annual lab hood exhaust testing program we now have at Baylor College of Medicine. We manage this testing (and flow adjustment) program through our Energy Management group.