Mechanical Redesign Existing System: The mechanical system explained in the existing conditions was simulated on an energy modeling system call equest. This program was used because of its strong detailed calculation system, and the information knowledge of California weather data and utility rates held in the program. All building and design parameters (See Appendix) were entered into a simulation. Then, the building dimensions were input and separated into 15 foot perimeter zones. Fig 6.1 This figure shows the zones created in the energy simulation model. The respective designations are on the left of the figure. The following schematic was devised below. Figure 6.1 Fig 6.2 -This figure shows the 3 dimensional Toyota building constructed in equest. The blue on the sides of the building represents the glazing area of each side of the building. The zones are shown on the left. Senior Thesis 2003 6. 1
The water side of the HVAC System was then developed in the detail mode of the equest system and is shown below. The red shows the hot water loop system; the blue shows the chiller system, and the green shows the condensed water loop system. While there are seven chillers on the Toyota site, the simulation was limited to two absorption chiller applications, thus the total tons (2700) of all the chillers was divided by two, giving each chiller a simulated capacity of 1350tons. Figure 6.3 The domestic hot water is not shown in this system due to the fact that it has its own hot water loop. Senior Thesis 2003 6. 2
The detailed air side system for each zone is then created and shown below. Within this detailed mode, one can click on each part of the air system, such as the supply fan and detail the system specifics for a certain zone. Due to the limited mechanical knowledge needed for each exact space, a default setting could be used in order to simulate the building without having undefined answers. Figure 6.4 Senior Thesis 2003 6. 3
Energy Output: The energy for the chiller system is based on electric and gas rates. The electric rates are based on a kwh (kilowatt per hour) usage and a demand (KW) charge. The electrical rates are more exspensive during the peak hours of noon to 6pm. The gas rates are charged by peak and non-peak conditions as well. The results are summarized in the following charts. The annual utility charge totaled $761, 667. Figure 6.5 Figure 6.6 Senior Thesis 2003 6. 4
Figure 6.7 Figure 6.8 Figure 6.9 Senior Thesis 2003 6. 5
Mechanical Redesign Geothermal Heat Pump: The idea of redesigning the mechanical system is attributed to its wide use in California as can be scene in the figure below. There are many advantages to possibly consider from the system. The required mechanical equipment is reduced, thus saving building space. This could virtually eliminate the Central Plant space. The piping can also be reduced due to localized systems, and thus can reduce the floor to floor slab height. The pipes in the Toyota building currently run through the ground floor and are 3 feet deep (See Existing Conditions). Another possibility is to collaborate the geothermal system with an under air floor distribution allowing for the systems to run through the core only and break into 4 zones (north, east, south, and west) for each floor. A geothermal heat pump system runs extremely quiet and therefore can be on the other side of a wall to a private office and not disrupt the occupant. The maintenance cost is about that of a typical electrical resistance or gas cooling system. The COP (Coefficient of Performance) is exceptionally high at about 4 (producing 4 units for every 1 unit put in). The EER (Energy Efficiency Ratio is high as well). The energy consumption is typically lower than that of a gas system and this system is commonly used in the south. Fig 6.11 Soure: Next Wave Energy Figure 6.10 Design Parameters: There were many hours of design parameters put into the design of this system. A Vertical Well system was chosen due to the fact that more length of pipe needed to be run in southern areas since the ground Senior Thesis 2003 6. 6
temperature was higher. The space requirement is generally huge, but should be no problem on the allotted 50 acres that Toyota owns. The design entails 25 separate systems, each consisting of a 2 by 10 well configuration. It was essentially to minimize the run distance from the building to the wells, so long and narrow well configurations were used. The reason for having many systems is due to the fact that as the system tonnage increases, studies have shown that the efficiency of the system drastically reduces. The temperature parameters consist of a running high of 105 degrees and a running low of 55 degrees. The pipe can be made of polyurethane or copper tubing. The copper was chosen due to the suggestion of a California Installer that recommends the copper due to its flexible properties and provides less maintenance or breakage due to damage from earthquakes. Installation: The vertical type of loop configuration is ideal for buildings large heating and cooling loads, when the earth is rocky or of dense sand, both of which the Toyota soil consists of. Clay is also present with a percentage of ground water held. This will help to maintain the temperature of soil and also helps in the Fig 6.12 conductivity of the pipe. Contractors will bore vertical holes in the ground of 200-250 feet deep. Each hole contains a single loop of pipe with a U-bend at the bottom. After the pipe is inserted, the hole is backfilled or grouted. Each vertical pipe is then connected to a horizontal pipe, which is also concealed underground. The horizontal pipe then carries fluid to and from the heat pump, or heat pumps. Vertical loops are generally more expensive to install, but require less piping than horizontal loops because the earth deeper down is alternating cooler in summer and warmer in winter. EQuest Simulation: The chosen design and correlating parameters were entered into Equest to formulate annual energy consumption. Figure 6.13 Fig 6.14 Senior Thesis 2003 6. 7
Figure 6.15 Figure 6.16 Figure 6.16 Senior Thesis 2003 6. 8
Figure 6.17 Fig 6.18 Figure 6.18 Fig 6.19 Fig 6.20 Figure 6.21 Figure 6.22 Senior Thesis 2003 6. 9
Recommendation: Surprisingly, the geothermal heat pump system proved to be about $136,000 more expensive in annual utility costs. This can be attributed to the fact that California has extremely high electrical rates. The heat pump system only runs on electrical energy while the absorption chiller runs on natural gas and electrical energy. The ratio of gas cost in mcf to electrical cost in kwh can be calculated with the following conversions: 1mcf = 1,020,000Btu 1kwh = 3413 Btu At average costs of the 2002 March rates (15.52 cents/kwh & $5.57/mcf), the ratio of electrical cost to gas cost in California is 1: 8.7 or $46.38/mcf (electrical) to $5.57/mcf (gas). In addition to the high costs, the temperature of the ground is much higher in the south and would be much more condusive to satisfying heating loads. The building geometry produces a situation where cooling is essentially needed for the interior spaces year-round. Heating is rarely needed as the heat from the interior of the space can be transferred to the outside of the space. The final reason why the absorption chiller has a lower energy rate is due to the fact that the California wet bulb is near the national low of 64 degrees. In the direct evaporative cooling process, the air into which the water is evaporated supplies the heat for an overall adiabatic system. The amount of heat removed from the air equals the amount of heat absorbed by the water evaporated as heat of vaporization. Additionally, the economizer cycle needs little energy to run the system and bring in 100% outdoor air. My final recommendation is to keep the current absorption chiller system. The current system is cheaper in annual costs and based on national averages, cheaper to install. In addition to this, natural gas is a natural resource. Less electrical energy is being used which means that less harmful chemicals are being released into the environment. Senior Thesis 2003 6. 10