Saint Francis Hospital Realizes Over
$100,000 in Energy Cost Avoidance with New Chiller Energy Efficiency Program
Founded in 1960, Saint Francis Hospital has become a medical leader in northeastern Oklahoma. What began as a 275-bed facility has grown into a facility licensed for 918 beds. From the beginning, physicians and staff at Saint Francis have distinguished themselves as leaders in healthcare. Saint Francis� traditions of excellent patient care, continuing education and clinical research have made it stand apart. These traditions of excellence and leadership hold true for the Saint Francis facility maintenance department.
The chiller plant consists of three older 1,920-ton Carrier and three newer 2,000-ton York centrifugal chillers, totaling 11,760 tons of cooling capacity, along with a five-cell, 10,000-ton Marley cooling tower system with variable speed fans. The facility utilizes a total of 1,300 tons of free cooling capacity through plate exchangers during winter months. The plant runs four 6,000 Gallon Per Minute (GPM) (24,000 total GPM), variable speed chill water pumps to create a secondary loop to the hospital, which increases overall efficiency by maximizing flow without bringing additional chillers online. COMMITMENT TO EXCELLENCE Operators endure a three-year apprentice program, going from limited experience to licensed operators of a chiller/boiler plant (a requirement of the City of Tulsa), to a first class unlimited licensed operator. This process provides additional training coordinated by hundreds of years combined experience within the maintenance department. To ensure the facility maintains high performance, it utilizes automation where economically feasible. This includes Direct Digital Controls (DDC) in the chiller plant along with state-of-the-art automated equipment to help manage the water treatment program. The chillers are sequenced to ensure the cooling load is met with the least amount of equipment in operation. Equipment operates near full capacity when possible, but averages 60 to 80 percent load, rarely falling below 50 percent. To help further reduce the Kw/Ton for each chiller, the Entering Condenser Water Temperature (ECWT) is dropped to its lowest possible temperature based on wet bulb and design conditions. In short, this is a world-class maintenance program, with top of the line equipment and a maintenance team that prides themselves on their expertise.
Committing to best practices and the need to save time analyzing log sheet data, the maintenance department was interested in an easy to use, cost-effective tool that evaluates log data, trends and verifies chiller performance levels and provides cost analysis. In the late fall of 2003, Saint Francis contracted to beta-test a new Internet-based chiller energy efficiency tool developed by Efficiency Technologies, Inc. (EffTec) called EffHVAC™. The operators input their daily chiller logs into EffHVAC, which calculated the chiller�s performance and compared Kw/Ton to full load design conditions to determine efficiencies, tonnage and costs. It was immediately apparent that it was difficult to determine actual chiller performance by comparing to full load design. The results were an exaggerated efficiency and inaccurate cost analysis. Realizing the impact that ECWT and part load values have on chiller efficiency, EffTec promptly developed a proprietary Calculated Part Load Value (CPLV) that greatly increased the predictability of the Kw/Ton for a chiller under all conditions. CPLV Kw/Ton is compared to the Actual Kw/Ton produced by the chiller, resulting in extremely accurate efficiency measurements and cost analysis. Along with this improvement, advances in charting and data collection make it possible to view and verify even the slightest changes in operations that effect efficiency. Other improvements to EffHVAC include chiller alarms, comprehensive troubleshooting guidelines and water usage calculations. The troubleshooting guidelines have helped identify problems such as a defective temperature sensor and pressure gauge. The water usage calculations determine the facilities projected evaporation credits and cycles of concentration in the tower system, further improving overall plant cost analysis. BASELINE DATA Baseline (or historical) data is taking the past chiller logs and entering the data into EffHVAC, which establishes a starting point for current analysis. Any improvements or operational changes, past or present, are immediately reflected for review. Log sheet data was input for 2003 and the reports were compared to the reports for 2004. This increased awareness and improved general operations such as ECWT adjustments, gauge and sensor calibrations, scheduled maintenance, monitoring weather conditions and adding/shedding chillers. Two other significant operational changes that improved efficiency were flow adjustments and changing the chiller configuration. MAINTENANCE Electrical/Mechanical Problem The reports have helped identify an electrical problem in Chiller #5 that may have gone undetected for an indefinite period of time. The chiller was sporadically unloading and having difficulty loading. By examining the reports (Figure 1) it was obvious that the condition was having an effect on the Kw/Ton and daily operation of the chiller. This chiller had been taken off-line several times after this condition was diagnosed. The cause was an automatic refrigerant level controller, that when replaced corrected the problem. Figure 1. Kw/Ton Spikes on Chiller #5 Associated with an Electrical/Mechanical Problem.
Tower/Condenser Biocide Sterilization and Cleaning Microbiological organisms can have a tremendous effect on heat transfer. It is not uncommon for their impact to be a 10 to 15 percent reduction in efficiency, and even more in extreme cases. On July 20th, the plant operators performed a routine scheduled tower/condenser sterilization, which included hyperchlorination and biodispersants to strip away all biofilms that may have existed throughout the tower/condenser system. The overall efficiency improvement is noticeable on the Monthly Calendar Report and is a 2 to 3 percent improvement in efficiency system-wide (Figure 2). Figure 2. Biocide Sterilization and Tower Cleaning Impact for Chiller #1.
MONITORING WEATHER CONDITIONS The effects of dramatic weather change can immediately be seen in the reports (circled in gold Figures 6 and 10). On July 9th, an unusual cold front blew in between 12:00 and 14:00, dropping the temperature 17�F from 87.7�F to 70.2�F. This dropped the Kw/Ton in Chiller #1 6.8 percent, from .673 to .627 Kw/Ton and dropped the ECWT 7�F from 81.4�F to 74.4�F. The Kw/Ton in Chiller #6 dropped 6.3 percent, from .634 to .594 Kw/Ton and the ECWT dropped 6.9�F from 81.9�F to 75.0�F. This further validates the effect ECWT has on efficiency. ADDING AND SHEDDING CHILLERS Consider determining when a chiller should be added or shed. If the efficiency is improved when you add a chiller, you should add the chiller sooner. If the efficiency falls, you have added the chiller to soon.1 This is authenticated by analysis of the reports. In Figure 3, the gold circle represents the impact on Chiller #1 by the addition of Chiller #5 at 09:30 and shed at 15:00. The introduction of Chiller #5 dropped the efficiency of Chiller #1 from 76 percent to 52 percent at 10:00 and returned to 79 percent efficiency at 12:00. The impact is temporary and the system should adjust after a short period of time provided the system load increases. The shedding of Chiller #5 was done very well, indicated by the minimal impact on the Kw/Ton of Chiller #1. Figure 3. Impact on Chiller #1 When Adding Chiller #5.
FLOW ADJUSTMENTS It became apparent from analyzing the reports that the chiller system flow had become out of balance due to seasonal adjustments (additional chillers being brought on-line in April). Figures 4 and 8 show the efficiency of Chillers #1 and #6 prior to any adjustments in the flow rates. On July 8th between 08:00 and 10:00 (military time), flow valves for Chiller #1 were adjusted and measured by a delta P gauge to achieve design flow rates. Flow valves for Chiller #6 were adjusted between 12:00 and 14:00 hours. The results were immediately apparent in increased efficiency (Figures 5, 6, 9 and 10) and lower costs (Figures 7 and 11). The increase in efficiency for Chiller #1 was ~17 percent, cost avoiding ~$144 per day in energy. The increase in efficiency for Chiller #6 was ~12.5 percent, cost avoiding ~$130 per day. The awareness gained from this experience makes it possible to anticipate and adjust to the effect seasonal changes have on flow rates. Note: The Kw/Ton values scale for each chart change, essentially �zooming in� for more detailed analysis when the CPLV Kw/Ton and Actual Kw/Ton values get closer. For example, the Kw/Ton scale in Figure 4 is from 0.55 to 0.80 and the Kw/Ton scale in Figure 6 is from 0.50 to 0.675. Figure 4. Chiller #1 Before Flow Adjustments.
Figure 5. Chiller #1 During Flow Adjustments.
Figure 6. Chiller #1 After Flow Adjustments.
* A third chiller was brought online at 6:30 a.m. and
a fourth at 9:30 a.m. anticipating a typical hot summer day. Instead, an unusual cold front moved in, impacting the plant cooling load and chiller configuration.
Figure 7. Calendar Summary of Flow Adjustment Results for Chiller #1.
Figure 8. Chiller #6 Before Flow Adjustments.
Figure 9. Chiller #6 During Flow Adjustments.
Figure 10. Chiller #6 After Flow Adjustments.
* A third chiller was brought online at 6:30 a.m. and
a fourth at 9:30 a.m. anticipating a typical hot summer day. Instead, an unusual cold front moved in, impacting the plant cooling load and chiller configuration.
Figure 11. Calendar Summary of Flow Adjustment Results for Chiller #1
CHILLER CONFIGURATION (LOAD PROFILES)In 2003, the #5 cooling tower was down for repairs, limiting the use of the new Chiller #6. In 2004 the repairs were completed, allowing the full use of Chiller #6 (Figure 12). This increased the flexibility of the plant and reduced the demand on the older, less efficient chillers (#2, #3 and #4). The plant load also increased approximately 23.7 percent to 23,074,439 tons through October, which included the addition of a new complex. By utilizing the more efficient chillers (#1, #5 and #6) and decreasing the use of the less efficient chillers, this helped lower the overall plant electrical costs while meeting the increased cooling demand. Figure 12. 2003 vs. 2004 Chiller Configuration
CONCLUSIONChiller Specific Improvements Table 1 shows a comparison of the improvements made on the individual chillers from January through October 2003 versus January through October 2004. Subtract the Kw/Ton of 2004 from the Kw/Ton of 2003 to get the Kw/Ton variance. Multiply the Kw/Ton variance by the total tonnage produced in 2004 to get the Total Kw Used. Multiply the Total Kw Used by the Cost of Kw (which is $0.05) to get the dollars saved year-to-date. The total of the chiller specific cost avoidance through October 2004 equates to $67,110. Table 1. Chiller Specific Improvements
Total Plant Improvement
These overall plant improvements have resulted in substantially lower energy costs. From January to October 2003, the plant produced 18,650,119 tons of cooling at a cost of $667,880 ($0.0358 per ton). From January to October 2004, the plant produced 23,074,439 tons of cooling at a cost of $726,066 ($0.0314 per ton). This equates to a $100,373 total cost avoidance in energy usage (Table 2). Subtract from this the cost avoidance from chiller specific improvements of $67,110 and it equals $33,263 from modifying the chiller configurations.
For a not-for-profit hospital that operates on a 2 percent profit margin, $100,373 in cost avoidance is equivalent to bringing in $5,018,650 in new business (101,373 X 50). The total energy cost avoidance through 2004 is conservatively expected to be over $120,000. The continual improvement through 2005 is expected to yield even greater results. The investment in the EffHVAC tool was $3,000 for 2004, which was recouped in approximately 9 days of energy cost avoidance. Finally, this tool has allowed management to accurately evaluate chiller performance and enabled the plant operators to use their skills to refine the best practices for their plant. Table 1. Chiller Specific Improvements Based on the successful operational achievements, plans to even further increase efficiency and reduce energy costs are being developed. Knowing the relationship between flow and efficiency will allow the operators to monitor chiller performance and make immediate adjustments to ensure optimal efficiency. Chillers will be added and shed with greater predictably, minimizing unnecessary energy consumption. Load profiles associated with real-time energy pricing are being studied to determine potential cost avoidance and impact on plant operations. References 1. Hartman, T. P.E. (2001, January 3). Steps to a More Efficient Chiller Plant. Automated Buildings.com Article. Referenced June 16, 2004. |
 |
