Primary Faculty Advisor: Prof. Bahnfleth December 5, 2003 Mechanical Systems Proposal:
Executive Summary: My senior thesis redesign will focus on the mechanical aspects of1919 M St. 1919 is an 8-story, 265,000 sq.ft. multi-use office space located in the heart of downtown Washington, DC. The mechanical redesign of 1919 M St.will incorporate a thermal storage system. The ice storage takes advantage of the lower electrical rates during the night hours to produce ice in large tanks. This ice will be used to cool the building during the day, therefore, lowering the total electrical costs. My goals for installing the ice storage system are mainly to decrease the total electrical load placed on the building by the existing cooling system. In addition to decreasing the operating costs, I will attempt to lower the first costs of the building by supplying lower temperature air to the spaces and decreasing the duct size. I anticipate these measures will be able to lower the costs even with the high costs of the tanks. In addition to the in-depth mechanical analysis, I will look into a redesign of the electrical and structural systems. By using a thermal storage system, the existing mechanical equipment, including the chillers and cooling towers, will need to be resized leading to a change in the electrical supply. When the ice tanks in a thermal storage system are full, they produce a very large load on whatever surface they are placed. If the tanks are then placed on the roof, I must look into redesigning the current system to ensure it can handle the load. 2 of 9
I. Background: 1919 M St is an 8-story, 265,000 sq.ft. multi-use office space located in downtown Washington, DC. Four 13,000 cfm units serve the south end of the building while four 15,000 cfm units serve the north end -- two on each floor. The AHUs will in turn serve a VAV system that distributes air throughout the spaces. The VAVs utilize electric resistance coils to heat the air entering the spaces. Two 320-ton chillers, located in the mechanical penthouse, serve the building s cooling needs. Also, located on the roof is a 2400 gpm cooling tower. When specific conditions are met, 1919 utilizes waterside free cooling in order to save energy costs. The exclusive power supply for 1919 is electricity provided by PEPCO. The indoor conditions are designed to maintain 74 o DBT and 50% RH. The outdoor design conditions, 95 o DBT and 76.5 o WBT during the summer and 34 o DBT during the winter, are taken from ASHRAE Handbook of Fundamentals 2002 (.4%). The construction of 1919 M St. provided a very unique feature to the design process. The original building on the site was completely demolished to the structural concrete system and was fully renovated. The small spaces and layouts inherent in the existing structure proved to be a challenge for the design engineers. A problem associated with the original system was the very small floor-to-floor heights. This floor-to-floor height is on average 10-1, making the design very difficult. In several locations, the ducts require the entire plenum depth, making the layout of other systems more complex. II. The Problem: After conducting several analyses on the performance of 1919 M St. during the previous 4 tech assignments, the analyses have demonstrated that 1919 M St. is a very efficient, well-designed building. Through previous tests, it has been shown that 1919 M St. is energy efficient and greener than average similar office buildings. Its superior energy efficiency has enabled 1919 to receive an Energy Star. In addition, both the building envelope and lighting density pass the ASHRAE Standard 90.1 requirements. Although 1919 is very energy efficient, it is located in Washington DC, a very high-priced area. As a result, any additional savings in energy would be a major advantage for the owner. Due to the site requirements imposed by the existing structural system, another problem the building faces is the very limited floor-to-floor space in which the engineers had to work. 3 of 9
III. Redesign Alternatives: When deciding on a mechanical alternative for 1919 M St., several options were studied. After some research, the possibilities were narrowed down to two different methods--underfloor Air Distribution and Thermal Storage. 1. Underfloor Air Distribution: In an average office building with high turnover rates, underfloor air distribution (UAD) is an excellent system. An underfloor system delivers approximately 65 o air into the space through the diffusers in the floor. As the air mixes with the room air, the temperature begins to increase and rise to the ceiling due to convection forces. Along with the warmer air, particulates and pollutants are also forced to the ceiling. They are then removed from the space via the return air ducts, leaving cleaner more comfortable air around the occupant s level. Research has shown that by using a UAD system, occupant comfort and indoor air quality are improved. (Courtesy of York Modular Integrated Terminals) One reason the life cycle costs are much lower compared to a typical overhead system is because the system can be maintained with minimal changes when tenants renovate their spaces. In addition to the lower life cycles costs, the first costs are also lower. Without the need for supply ducts in the ceiling, both material and labor costs are reduced. Now to the negatives. Due to the extremely small floor-to-floor heights of 1919, it might prove to be very difficult to incorporate a raised floor, a ducted return and a suspended lighting scheme without creating a claustrophobic effect. Research has shown that a minimum of 8 is required to properly run an underfloor system. Knowing this, a safe design would use a 12 plenum leaving only 9 from finished floor to ceiling. In this case, a suspended ceiling is out of the question; therefore a ducted return system would be used. In addition to the ducts, the space must also contain lighting fixtures. These fixtures would be suspended, indirect fluorescent lamps. After taking into account all of this information, it is unlikely that a UAD system with suspended fixtures and a ducted return would be feasible for 1919 M St. 4 of 9
IV. Mechanical Proposal: Ice Storage with Low Temperature Air I plan to redesign the 1919 M St. mechanical system to incorporate a thermal storage system. During the semester, I will perform calculations to determine whether 1919 is a candidate for partial or full storage and the costs associated with both types. Once a system type has been chosen, I will begin to perform load calculations for the existing system in addition to the proposed system using Carriers Hourly Analysis Program, HAP. After the loads have been established, I will proceed with the sizing of the tanks using Calmac equations and/or software. When the ice tanks are determined, the additional mechanical equipment can be resized accordingly. After selection of the new mechanical equipment, the electrical system must be reworked. At that time I will review the location of the tanks to conclude whether it would be more feasible to strengthen and reposition the tanks on the roof or place them in the basement to reduce structural costs. The two main problems associated with 1919 M St. are the lack of plenum space and energy consumption costs. A thermal storage system has the opportunity to correct both of these problems. In addition, a thermal storage system can lower operating costs, and more importantly, reduce energy consumption. Because 1919 M St. is an office building, the main periods of occupancy are between 7am and 7 pm, the peak rate hours of the day. Using a thermal storage system, ice can be produced at night at a lower energy cost, therefore, providing cooling during the occupied hours. (Courtesy of Calmac webpage) By using an ice system, the two 320 ton chillers and the 2400 GPM cooling tower can be reduced in size. By using a partial storage system, the existing chillers can be reduced up to 50%. Along with the chillers and cooling tower, the ducts can be resized to a smaller dimension due to the low temperature air that is being supplied. With these reductions in equipment costs plus the lower cost of duct work, a lower first cost is possible even with the cost of the tanks. 5 of 9
V. Additional Analyses: In addition to my in-depth analysis, I plan to review several additional improvements that can be incorporated with thermal storage to further enhance the building. With 1919 already meeting several of the LEED requirements, I plan to look at what it would take to receive a LEED accreditation. During Tech 2a, I reviewed the points system, and I feel with some additions, 1919 has the opportunity to receive an accreditation. Another possible improvement that I am considering is the use of photovoltaic panels. If the positioning of the building is conducive, solar panels could possibly provide additional electrical power to the building, resulting in a small decrease in the amount of power the building has to purchase. Much more research must go into this idea; however, I am interested in learning more about the topic. VI. Electrical Breadth: The mechanical system and the electrical rework are integrated aspects of this design. After the mechanical system is resized, I must review the electrical system to determine what feeders, breakers, conduit, etc., can be resized. I will perform hand calculations utilizing equations and methods described in the National Electrical Code. VII. Structural Breadth: The basis for the thermal storage system is the large tanks in which the ice is created and melted. The larger storage tanks, with a storage capacity of over 500 ton-hrs, are very large and heavy. Weighing a total of nearly 50,000 lb, the filled tanks will place a load of approximately 400 lb/ft 2 on the concrete deck. If it is determined that the most beneficial place for the tanks is on the roof, a new system will be required. The existing concrete has a capacity of only 30 psf, therefore, requiring extensive strengthening. I will either use a program such as RISA to calculate the size of the new members or use an analysis program such as STAAD to establish the loads and then use hand calculations to determine the member sizes. If it is not feasible to strengthen the concrete structure to support such a load, 1919 has a parking garage located in its basement and the tanks could be placed there. The location of the tanks will be coordinated with the mechanical systems to ensure efficient operation will continue if the tanks are placed in the garage. A study on the costs of the two locations will also be conducted to determine whether it is more appropriate to locate the tanks on the roof and deal with strengthening the roof or placing them in the garage resulting in the loss of several parking spaces. 6 of 9
VIII. Justification: During the previous technical assignments it was obvious that the energy costs, although lower than a similarly sized office building, are still a substantial amount of money. I felt that with a building in a high rent area like Washington DC, any attempt at saving energy costs would benefit the owner. Another justification I had for using thermal storage for 1919 was because it is an all electric building creating a potential for high energy bills. In addition to the energy issue, I have been interested in thermal storage systems for a while and have not had many opportunities to work with them. I felt that this project would give me such an opportunity. From presentations I have attended, articles I have read, and conversations I have had with engineers in the industry, I feel that LEED accreditation is a very important, and soon to be a very highly sought after, commodity for buildings. It is for this reason, in addition to my interest in sustainable design that led me to consider reviewing my building s LEED status and attempting to pursue an accreditation. 7 of 9
IX. Work Plan: The following is a preliminary schedule to complete my thesis in time for presentations in April. The semester will commence with extensive research, primarily in thermal storage. I will research a few alternatives and additional systems. After the research is complete, I will start the process of learning the Calmac design methods and beginning my design. Once the thermal storage portion of my project is finished, I will begin working on the LEED accreditation requirements and any additional projects I wish to tackle. After the design period is concluded, I will wrap up the work and prepare the presentation. Week Description of work to be completed Starting 1/12/2004 Begin detailed research on thermal storage systems 1/19/2004 Review HAP from Tech 2b and make necessary changes. Use CALMAC program to calculate hourly loads. 1/26/2004 Size storage tanks 2/2/2004 Determine new equipment sizes 2/9/2004 Check duct sizes and determine if they can be reduced 2/16/2004 Electrical Breadth- Resize electrical lines and determine new energy costs 2/23/2004 Structural Breadth- Determine new roof design to support tanks 3/1/2004 Conduct a cost analysis for both tank placement and overall system advantages 3/8/2004 Spring Break 3/15/2004 Conduct a LEED analysis and determine what additional factors need to be pursued 3/22/2004 Complete all design work and begin writing report 3/29/2004 Finalize Report 4/5/2004 Design Power Point presentation 4/12/2004 Presentations 4/19/2004 RELAX 8 of 9
X. Bibliography 1. Calmac Webpage www.calmac.com/office 2. Clamac: A Technical Introduction to Thermal Energy Stroage Commercial Applications http://calmac.com/benefits/technical.pdf 3. York International Website www.york.com 4. York Modular Integrated Terminals: Convection Enhanced Ventilation Technical Manual http://www.york.com/products/esg/yorkengdocs/847.pdf 5. MacCracken, Mark M. Thermal Energy Storage Myths ASHRAE Journal September 2003 6. ASHRAE Handbook of Fundamentals; The American Society of Heating Refridgeration and Air Conditioning Engineers, Inc 2001 7. Database for State Incentives for Renewable Energy Website http://www.dsireusa.org/ 8. Million Solar Roof Webpage http://www.millionsolarroofs.org/ 9. Solar Electric Power Association http://www.solarelectricpower.org/ 9 of 9