Redesign of Bennett Hall HVAC System _____________________________________________________________________________________________________________________________ Greg Andreasen, Michael Chicoine, Florent Hoxha, Jason Jacobe Advisor: Michael “Mick” Peterson, Ph.D. and Justin Poland, Ph.D. Background Heat Ventilation and Air Conditioning (HVAC) systems are systems that treat and circulate the air of a building to make it comfortable for people to work in. The HVAC system consists of a series of fans, pumps, and coils that heat or cool the air as needed and transport the air to desired destinations throughout the building. An HVAC system also regulates the humidity of the air in the building by cooling the air to very low temperatures and heating it back up. The figure below is a schematic of the HVAC system in Bennett hall. The Central Air Handler takes the air in from outside and it either cools it by running it through cooling coils, or it heats it passing through heating coils (depending on the season). The air is then brought to the individual room unit coolers which mix re-circulated room air with the ventilation air and provide additional cooling, in summer, as needed. This way each room in the building becomes a comfortable working area.   Figure 1. Problem When the Bennett Hall HVAC system was installed, the system was designed to control only the temperature of the building. The humidity level was not factored into the system’s design. The humidity however is high enough sometimes, to cause concern for the scientists. Experiments conducted in the basement cause very low equipment temperature. This, in turn, causes the air closely surrounding the equipment to drop below its dew point. Condensation and sometimes frost will form on equipment. This is not acceptable for the professors working in the area. In one case this condensation forms on a piece of equipment that creates a very high voltage and makes testing unsafe. Frost has also been forming on a hydrogen Dewer, another apparatus used in the basement. This freezing makes performing slight adjustments to the equipment difficult, and the professor claims, it “effectively creates a hydrogen bomb in the Bennett Basement.” In addition to experimental equipment being sacrificed by the unacceptable relative humidity, the shop equipment has been suffering as well. The poor humidity level has been allowing rust to form on shop equipment, sacrificing its quality, and shortening its useful life. Figure 2. High Voltage Equipment Hydrogen Dewer Rusty Shop Equipment Figure 2 Objective Our objectives are as follows: Redesign system for 50% relative humidity Use as many existing system components as possible Maintain comfortable temperature conditions Design The first approach in finding the solution to the problem was to find the overall heat load that the building is under. The heat load was found by applying heat transfer analysis to the wall, windows and ceiling of the building using summer temperatures. Once the heat loads on the building and the rooms were calculated, these were used in generating two possible solutions. Solution 1 The first solution was to put a new cooling coil in the main air handling unit which would cool the air to the temperatures of 63F db and 62F wb. This air would then be sent to the individual room air units, where it would be mixed with the room air and cooled again for comfort. This would then be blown into the room resulting in room temperatures of 75F(+/-)3F db and 62F wb. Figure 3 shows the schematic of this solution Figure 3 Solution 2 The second solution considered, was to put a larger cooling coil in the main air handling unit, which would cool the air to 57F db and 56F wb. Then there would be a reheat coil which would heat the air up to 70F db while maintaining the wb at 56F. The air would be sent to the individual room air units and would mix with the room air and come out of the units mixing with room air providing 75F(+/-)3F db and 56Fwb. Figure 4 shows the schematic of this solution Figure 4 Solution 2 was picked as the better solution because the first solution relies more on a constant strong heat load being placed on the building. Thus, when there are small heat loads and room is settled at lower temperature such as 72F, this will result in a cooler mix air temperature and possible cold working environment. This would work, but wouldn’t give a consistent room temperature. For the second solution the air is at 70F when it comes to the room air unit so the mixed air will always be at comfort zone between 70F and 75F and will satisfy the acceptable humidity levels. Economics Since the only changes to the system will be made for its operation during the summer months, the cost analysis was run only for May through September. The graph below shows how much money each unit uses for operating. The system will run with only minor variations to flow rates. The price for a new coils is the only additional charge. At present the cost to run this system is about $3000 and this will not change with the new coil. The price of the new coil is yet to be determined. Figure 5 Future Work Our design results and the feasibility of our choices will be documented and saved. The redesign has already been done and our solution will be compared to facilities solution. Acknowledgement We would like to acknowledge those who helped us throughout the design process. These include Professors Justin Poland and Michael Peterson. We would also like to acknowledge Facilities Management Stewart Harvey and Trane salesman Nick Veccchione. The Team Main Air Handling Unit Room Unit Cooler Cooling Coil Room Air Mixed Air at 75 db, and 62 wb 87F db 71F wb 63F db 62F wb Main Air Handling Unit Room Unit Cooler Cooling Coli Room Air Mixed Air at 75 db, and 56 wb Heating Coil 87F db 71F wb 70F db 56F wb