4.0 Mechanical Redesign

Transcription

1 4.0 Mechanical Redesign As my depth area of research, I have performed a detailed analysis of the existing air handling units and the existing conditions of the FIT Science Lab. After one semester of breaking down the building piece by piece (Fall 2004 AE 481W), I chose to conduct my thesis research on the addition of desiccant technology. A desiccant wheel is used to remove moisture from the air. As shown in the desiccant diagram (Figure 4.1), supply air (process inlet) passes through the desiccant wheel. On the desiccant wheel is a Figure 4.1: Desiccant Wheel Diagram special desiccant coating with a rating for the size of the openings in the wheel. The wheel is to act as a sieve for the moisture. Typical opening sizes range from 3 4 angstroms. After leaving the wheel, the supply air continues to provide air to the space (process outlet). In the return or exhaust duct, the air returning to the unit or leaving the building passed through a heat source (reaction inlet to reaction heat source). This warmed air then passes back through the desiccant wheel, evaporating the moisture off of the wheel and then continuing to the ambient air if it is exhaust or to the air handling unit if it is return air (reaction outlet). At first glance, the state of the FIT Lab and its air system is perfect. Designed by TLC Engineering for Architecture in Cocoa, Florida, the standards and rules of thumb were Olin Science Laboratory Pastor 18

2 followed to a tee. However, with the climate of a coastal city in Florida, humidity can pose as a huge problem to those who inhabit the area. Along with the stickiness you feel due to humidity comes water vapor which has the ability to produce mold and mildew on items throughout the building system. Ductwork insulation can grow mold on it and when the air is passing through to classrooms and laboratories, the air particles carry those spores with them, causing sick building syndrome. I have always been interested in Desiccant Technology although it is not typically seen in normal building applications. It is known that most people do not choose desiccant wheels for their mechanical system because it is more costly for the equipment and perhaps in the long run for maintenance. As will be shown through my research of this depth area, the cost of the air handler and wheel will be lower and the energy savings is enormous. Another issue that seems to arise about desiccant wheels in laboratory applications is the fact that cross contamination could occur and harmful gases can leak through the exhaust stream back into the supply air stream. This also will be proven false for my application to the Olin Lab, therefore proving the addition of the wheels to be beneficial to the. 4.1 Introduction of Desiccant Wheels to All the Air Handling Units My first task was to find a desiccant wheel that would be capable to fit into my existing air handling units. Since I have eight M Series Trane Air Handling Units, my first option was to look at their manufacturing catalogs to see if a wheel was available for purchase or if it was even an option for the Modular Climate Changers (MCC). Olin Science Laboratory Pastor 19

3 After a brief chat with a Trane representative, it was determined that they do not offer that type of product for their MCC units. He did, however, lead me to SEMCO, manufacturer of desiccant wheels and the Pinnacle Unit with a wheel built into it. Due to the fact that the existing units in the FIT Olin Lab are brand new, I decided that I would not replace the whole unit, but just look for a desiccant wheel with casing to add into the 8 MCC units. SEMCO offers a packaged energy recovery system that has a desiccant wheel in casing with optional heating and cooling coils. The technical guide on SEMCO s website, provided a detailed, step-by-step way to calculate the size of the Packaged Energy Recovery System (Figure 4.2) that I would need for each of the individual MCC units. Figure 4.2: SEMCO Packaged Energy Recovery System Along with a calculation to size the desiccant wheel, SEMCO offered a way to calculate the size of the heating and cooling coil that you would need to produce the air temperature to remove the moisture from the air. This was important to me because I theorized that adding a Figure 4.3: SEMCO EP Series, No Coils desiccant wheel would lower the load on the heating and cooling coils and therefore, downsize them. This would produce a huge savings on first cost and on energy. Olin Science Laboratory Pastor 20

4 Since the Trane Units were already equipped with cooling and reheat coils, I chose to use the described selection process from SEMCO and apply it to the Trane coils. I then would double check my answers based on Trane s selection standards for cooling and heating coils. Also, since the Trane Units were equipped with coils, I was able to select the EP Series of the Energy Recovery System because it offered the most flexibility and lowest cost. Figure 4.3 shows the diagram for the SEMCO EP Series without coils. After selecting the size of the Energy Recovery System that I would need for each air handler, the problem arose as to how I was going to insert these into the existing Trane Units. Compatibility was not a problem; a Trane representative sent me to the SEMCO site for the desiccant wheels. Since the Modular Climate Changer Units are built up air handlers, each section is attached to each other with nuts and bolts. The build up of my specific units is as follows: Fan Mixing Box (FMB) Cartridge Filter (CF) Cooling Coil (CC) Small Access (SAC) Reheat Coil (RHC) Fan (FAN) Since the desiccant wheel requires both cooling and heating coils for proper moisture removal, I decided to split the system between the cartridge filter and the cooling coil. This would allow me to insert the EP Series Energy Recovery System and allow for the heating and cooling coils to be used. Figure 4.4a and 4.4b are typical air handling unit as they currently existing in the FIT Olin Lab. The room shown in 4.4a is the First Floor Mechanical Room on the left side of the building, Room 134. Figure 4.4b is the second mechanical room on the First Floor, Room 116. Olin Science Laboratory Pastor 21

5 Figure 4.4a: First Floor Mechanical Room 134 Figure 4.4b: First Floor Mechanical Room 116 As you can clearly see, the spaces allotted for the mechanical rooms are big enough to house the existing equipment only. Therefore, upon insertion of the Desiccant System into the existing Air Handling Units, I came across a space problem. The Energy Recovery System package did not fit in the room. Even with the downsizing of the cooling and heating coils, the space cleared up by the removal of a few rows of coils did not equate to the space I would need for the ER Package. This problem could be resolved by moving the exterior wall out by several feet. The extension of the wall would allow for the exterior door to be moved and the Desiccant Wheel and necessary equipment to be placed in without problem. Appendix D contains all of my detailed excel spreadsheets for my process of selecting the desiccant wheels for each of the Trane MCCs. As can be seen in Appendix E, a total of tons of cooling can be saved by adding a desiccant wheel in the form of the SEMCO EP Series Energy Recovery System Unit. As for cost, a total of $166, (based on $400/ton of cooling) can be saved on coil load alone. This reduction will be found in the first cost. Olin Science Laboratory Pastor 22

6 4.2 Construction and Structural Issues Since the FIT Olin Lab is currently in construction and almost 100% complete, a renovation would need to be done for the mechanical rooms. The sizes of the desiccant wheel packages that are to be inserted into the mechanical rooms range from to This posed as a problem because there was no room in the existing space to put in these units. Along with the lost space from the insertion of the units comes the addition of several thousand pounds. For this reason, I would need to look at the structural system of the building and the first cost associated with a renovation. I had not chosen to do structural or construction management as breadth options; however, since these issues needed to be addressed, I have touched upon them briefly in this section. The first floor mechanical rooms are on the back corners of the building, Room 134 on the back left of the building and Room 116 on the back right of the building. The extension of the second mechanical room wall, Room 116 (Figure 4.4b), would pose no issue because there is enough space on the exterior of the building for the exterior wall to be moved. This concurrently would then allow the mechanical room above it on the second and third floors (Rooms 214 and 319) to be extended too. The length of the desiccant wheel packages that need to be inserted can be found in Figure 4.5 below. As you can see, the longest unit of the three stacked mechanical rooms would be Therefore, for safety purposes and for margins of error, I would ask that the exterior wall for Mechanical Rooms 116, 214 and 319 be extended Olin Science Laboratory Pastor 23

7 Figure 4.5: Length of Desiccant Packaged Units For Mechanical Room 249, which lies in the middle of the very back of the FIT Olin Lab, an extension of the exterior wall would need to be completed by approximately My real problem lies in the mechanical rooms that are on the bottom left corner of the FIT Lab. As you can see from the site plan in Figure 4.6, the Chiller Building that supplies the chilled water to the air handling units in the Lab Building lies only 16 away from that exterior wall. Mechanical Room 134 holds AHU 1 1 and AHU 1 2. The minimum amount of space that the exterior wall would need to move out would be This could not Figure 4.6: Site Plan Showing Mechanical Room in relation to Chiller Building happen because of the Chiller Building. Since the first floor mechanical room could not be moved, the two other mechanical rooms stacked above it, Rooms 230 and 344, would not be able to provide the necessary room. Another alternative setup would need to be devised so that the desiccant systems can fit on that half of the building. Olin Science Laboratory Pastor 24

8 The only costs associated with the extension of a wall would be the first cost of materials, demolition, removal of materials from the site and labor. Since these are only first costs, the payback associated with these compared to the amount of energy cost savings predicted as above ($166,787.00) would be minimal. 4.3 Ductwork Layout and Changes Due to the fact that I have not changed the sizes of any of the laboratory or classroom spaces, the amount of supply air that is provided by the air handling units would not change. My fan size and the amount of air supplied by it would not be affected by the addition of a desiccant wheel. Because I would be breaking apart the existing unit and adding the ER System into it, some transition ductwork would be necessary for connection of the two pieces of equipment. The amount of ductwork needed was very minimal and would not have an adverse affect on the cost of the building s mechanical system. 4.4 VOC Sensors and Cross Contamination As with any laboratory, issues will arise with the amount of chemical fumes that are being released by the building and the equipment inside of it. 25 of the 35 laboratory spaces are equipped with fume hoods. These fume hoods, used for chemical and physical science lab tests, are controlled by Phoenix Valves that modulate the amount of exhaust needed based on position of the fume hood s sash. When a sash is in use, a scientist typically has the sash in the fully opened or 80% open position. The control valve will read this positioning. The valve then varies the amount of exhaust needed. As a room becomes unoccupied, it is hoped that the scientists would fully close the sash Olin Science Laboratory Pastor 25

9 or close it to a 20% open position. The process of closing or partially closing the fume hoods makes for a huge energy savings on the FIT Olin Lab and helps to keep the exhaust gases from leaking back into the space. With the addition of a desiccant system, the exhaust or return air line must be used so that a reheating process can occur and the moisture collected on the wheel by the supply air can be evaporated. If the exhaust line is contaminated with chemical fumes, this can cause a potential cross contamination problem. Cross contamination is the leaking of harmful chemical gases into the supply air stream that is used to condition occupied spaces. There are many pieces of literature regarding the issues of cross contamination and desiccant systems with the use of exhaust from a laboratory space. However, all the literature does not choose one side or the other. It is all dependent on the application and the specific building type. A cross contamination issue will only occur if the equipment installed is put in improperly. For this reason, I have paid close attention to how my desiccant system was set up. Using many resources, including the expertise of one particular engineer at Hammel, Green and Abrahamson (HGA), I learned that there are three or four ways for cross contamination to occur, each of which must be individually addressed. The first way for cross contamination to occur is for exhaust air to leak into the supply air by way of the seals in the wheel. The leakage problem, which occurs at the perimeter of the wheel as it rotates, can be solved by controlling the relative air pressures such that the air leaks in the opposite way you are concerned. For example, Olin Science Laboratory Pastor 26

10 in this application, I would cause the supply air to leak into the exhaust air by making the pressure greater on the exhaust side. Another way for cross contamination to occur is for chemicals to stick to the wheel on the exhaust side and get thrown off into the supply air side as it rotates around. This will not happen because of the purge section where the air blows backwards across the wheel as it transitions between the dirty and clean side. Most of the harmful particles will get purged off. SEMCO guarantees that no more than % will be stuck on the wheel. One other way for cross contamination to occur is for the bad chemicals to get absorbed into the desiccant and then release on the other side. Most of the chemicals used in laboratories have a large chemical structure and are not an issue; they will stay in the exhaust stream and not get stuck in the desiccant. I have solved this problem by choosing a wheel that has a desiccant coating with only 3 angstrom sized openings. The chemicals physically do not fit in these size openings. There are times when other chemicals with smaller structures will be used and these structures will fit into the 3 angstrom sized openings. Although the list of chemicals is much smaller, radon and ammonia are included on it. These will pass through very easily. However, if you look at the system as a whole, with all the exhaust streams coming together, with the chemical needing to pass through a fume hood and with all the ductwork that the chemical will actually be going through, the exhaust air stream is very safe. SEMCO can guarantee only 0.005% crossover. The system can be tested every five years to make sure it is still within that range. Olin Science Laboratory Pastor 27

11 Finally, regarding corrosion, it was found that the dilution level of laboratory exhaust is so great that the exhaust air stream is relatively harmless. 4.5 Conclusions of Mechanical Depth My final conclusions for my mechanical depth work is that the addition of a desiccant wheel into the 8 existing Modular Climate Changers is a cost saving and energy saving decision tons of cooling, or $166,787.00, will be saved on this addition. With space being an issue, renovations would need to be conducted as well as structural studies for the additional weight added to the building. Secondly, there will not need to be any ductwork sizing or layout changes because all of the work was done in the mechanical room. The size or usage of the rooms throughout the FIT Lab has not changed, therefore, not changing their air flow requirements. The slight alteration that I have made to the units requires a minimal amount of ductwork and would not be a huge factor in the overall cost. Lastly, the addition of a desiccant wheel to a laboratory application and the continuing debate on cross contamination is resolved by taking a few simple steps. The selection of my wheel was based on size of the desiccant coating, i.e. the size of the opening on the wheel. A change in relative air pressure to cause the supply air to leak into the exhaust stream and not vice versa will prevent leakage into the supply air stream. The purge section of the wheel prevents the dirty side of the desiccant wheel to become clean before rotating to the supply air side. Olin Science Laboratory Pastor 28