V. Active Solar System Introduction After the energy crises of the 1970s and the subsequent increases in the cost of petroleumbased fuels, interest in active solar energy systems surged. Thousands of active solar systems were installed from the late 1970s through the mid 1980s. In 1982 the existing BCDC structure employed an active solar system design. The building uses flat plate solar collectors on a closed loop system. The picture below shows the collectors located on the roof of the existing structure. Figure 5-1: Solar Panel on Existing BCDC The addition to the detention center was designed with an integrated space-water heating system rather than an active solar system. This analysis proposes that the expansion of the BCDC should also implement alternative energy sources for the building s systems. In this analysis the new building will be redesigned using a similar active solar system to that of the existing structure and compared to the cost of the original expansion design. Original Existing System The existing system is composed of 525 flat plate collectors mounted south 50 off the roof of the BCDC. These collectors have a gross area of 18 ft 2 and are on a closed loop system. The closed loop system uses propylene glycol as the heat transfer fluid. Once the propylene glycol is pumped through the collectors and heated the glycol goes to a heat exchanger. The glycol releases the heat to the domestic water by conduction via the heat exchanger coils. The heated water is then stored in two 20,000-gallon tanks located underground in front of the existing BCDC. The current active solar system fulfills 60% of the BCDC space heating needs and 35% of the BCDC hot water needs. When the active solar system is not available auxiliary heating fueled by gas is used. The diagram below in Figure 5-2 shows a schematic layout of the closed loop system the existing BCDC uses. Erin Sharkey CM Emphasis Spring 2004 35
1. Collector 6. Collector Return 11. Circulating Pump 16. Solar Hot Water Tank 2. Collector Sensor 7. Check Valve 12. Pressure Relief Valve 17. Immersion Heater 3. Manual Air Valve 8. Hose Bibs (Fill/Flush) 13. Pressure Gauge 18. USDT 2004 Controller 4. Hot Water to Taps 9. Expansion Tank 14. Collector Supply 5. Tempering Valve 10. Air Scoop & Vent 15. Heat Exchange Coil Figure 5-2: Schematic Layout of Closed Loop Active Solar System The cost associated with the existing BCDC active solar systems are as follows: Description Cost Initial Cost of System $400,000 Annual Heat Bill (natural gas): 7/1/2002-6/30/2003 $78,750 Average Annual Utility Savings $15,000 20,000 Figure 5-3: Cost Associated w/ Existing BCDC Active Solar System Upon a telephone conversation with the head of maintenance, Captain Steven Tignor at the BCDC this system was confirmed as a reliable and cost effective system. There has been occasional maintenance required with the pumps located throughout the system as well as the replacement of the glycol when its ph levels require adjustments. Due to the confirmed success of this system a similar system was designed for the BCDC Expansion. Original Expansion System The original design of the BCDC Expansion consisted of an integrated space-water heating system. The expanded BCDC hot water needs were to be met using two horizontal fire-tube boilers and domestic hot water generators. The submitted specifications for these machines can be found in Appendix E. According to the schedule of values from the mechanical /plumbing contractor on the BCDC the initial cost for this equipment is listed below in Figure 5-4. Erin Sharkey CM Emphasis Spring 2004 36
Description Cost Furnish & Set Boilers $105,000 Furnish & Set Domestic Hot Water Generators $169,487 Total Initial Cost $274,487 Fuel Cost Annually (Annual Heat Bill Existing BCDC/65%) $121,154 Maintenance (Assume 15% of initial cost) $27,449 Life Cycle Cost w/ Maintenance (30 years) $3,936,556 Figure 5-4: Cost of Original Expansion System The initial total cost for the intended design for the BCDC Expansion is $274,487. The life cycle cost was also calculated in Figure 5-4. The annual cost of fuel was estimated using the annual cost of fuel shown in Figure 5-3. The existing BCDC solar system has annual fuel cost of $78,750. Since the BCDC solar system only heats 35% of the required load this annual cost is for 65% of the required load. Based on the existing system utility cost to accommodate 100% of the load the annual fuel cost would be $78,750/0.65 = $121,154. Therefore, the original expansion design has a life cycle cost (30 years) of $3,936,556. These values will be compared later to the proposed active solar system. Proposed Expansion System The proposed redesign for the BCDC Expansion is the same as the existing system of the BCDC; flat plate solar collectors on a closed loop system. However, the active solar system for the expansion will only accommodate the detention center s hot water needs unlike the existing BCDC system, which provides for the space heating and hot water demands. The active solar system design was based on the following: Existing BCDC & BCDC Expansion Water Needs Existing Expansion 40,000 gallons stored 50 gallons per person per day 864 inmates currently in BCDC 784 inmates in the new facility 46.3 gallons per person per day 39,200 gallons daily 50 gallons per person daily 40,000 gallons daily Flat Plate Collectors (specifications located in Appendix E) - 750 Collector Panels - Collector Area 40 ft 2 - SRCC Rating: Test Slope (FR*UL) = 0.727 Test Intercept (FR*α*τ) = 0.714-50 Collector Slope - Collector azimuth = 0 (directly south) - Glazing 2 - Black Chrome Absorber Coating Erin Sharkey CM Emphasis Spring 2004 37
Active Domestic Hot Water System (specifications located in Appendix E) - Located in Baltimore, MD - Water Set Temperature - 135 F - Storage Tank: 40,450-Gallon Capacity 24-8 Diameter & 11-3 Height U value = 0.07 - Heat Transfer Fluid Propylene glycol Specific Heat: 0.85 - Heat Exchanger - Auxiliary Heat - Natural Gas The above design criteria were plugged into the solar system analysis software called f-chart. The entered parameters were modified to optimize the design. Ideally, an f value of 1.0 would be attained in the summer with a yearly f-value of 0.6-0.7. The f-value represents efficiency of the solar design to accommodate the required load. A system achieving an f- value of 1.0 the summer will maximize the use of the solar panels in peak environment conditions without producing waste. The below table in Figure 5-5 shows the amount of energy required (dhw), the amount received by the solar panels (solar) and the amount required by auxiliary heating (aux). SOLAR [10 6 Btu] DHW [10 6 Btu] AUX [10 6 Btu] F Value Month January 986 841.1 501.9 0.403 February 1052 758.8 383.1 0.495 March 1323 834.9 349.8 0.581 April 1391 804.0 281.4 0.65 May 1459 825.7 267.7 0.676 June 1483 794.0 220.6 0.722 July 1530 818.4 217.2 0.735 August 1480 819.5 230.1 0.719 September 1371 796.0 256.5 0.678 October 1294 828.7 329.1 0.603 November 978 807.0 446.8 0.446 December 861 839.1 548.7 0.346 Yearly 15208 9767.3 4033.0 0.587 Figure 5-5: Energy Requirements Calculated by F Chart The outputted results from f-chart show that the designed active solar system will accommodate for 58.7% of the BCDC Expansion s annual hot water needs. The monthly percentages of the hot water needs that will be provided by the active solar system based on the f-values are shown graphically below in Figure 5-6. Erin Sharkey CM Emphasis Spring 2004 38
Figure 5-6: Monthly F-value The outputted results from f-chart also showed the monthly requirements for the total hot water needs, auxiliary heat and the amount of solar energy collected. These results are shown visually below in Figure 5-7. Figure 5-7: Monthly Solar, Auxiliary & DHW Requirements According to the parameters inputted into f-chart the designed active solar system has the following cost over a period of 30 years. Description Cost Initial Cost of System $700,000 Cost of Fuel $1,936,456 Maintenance (Assume 15% of initial cost) $2,636,456 Life Cycle Cost w/ Maintenance (30 yrs) $2,741,456 Figure 5-8: Cost of Expansion Redesign Erin Sharkey CM Emphasis Spring 2004 39
These costs were based on a 30-year economic analysis since the equipment has a life expectancy of 45 years and a 20-year warranty. Also, the cost of fuel was calculated assuming a 50% increase in the price natural gas within the next 20 years. According to the calculations provide within this analysis an active solar system as designed above has a 6 year payback period and can save the owner $1,195,100 over 30 years or approximately $40,000 annually in utility cost. Original BCDC Expansion Design $3,936,556 Redesign Active Solar System $2,741,456 Savings Over 30 Years $1,195,100 Annual Savings $39,837 Below in Figure 5-9 is a table summarizing a cost comparison between the original BCDC Expansion design of the integrated system and the proposed BCDC Expansion design of the active solar system. Original Expansion Design Boilers/Generators Proposed Expansion Design Active Solar System Initial Cost of System $274,487 $700,000 Life Cycle Cost $3,936,556 $2,741,456 Payback Period 1.75 years 6 years Figure 5-9: Cost Comparison between the Original & Proposed BCDC Expansion Systems Conclusions As natural gas and electricity prices continually increase alternative energy sources will become a more implemented preference. Initially the cost of the active solar system is $425,513 more than integrated design with a 6-year payback period. However, the life cycle cost savings of the active solar system is substantially outweighs the additional initial cost of the system. Proposing the use of an active solar system in place of the boilers and hot water generators can save Baltimore County $1,195,100 over 30 years or $39,837 annually. Since the existing BCDC already uses flat plate solar collectors implementing this same design on the expansion to save the owner and taxpayers money is an excellent alternative. Erin Sharkey CM Emphasis Spring 2004 40