Department of Mechanical and Materials Engineering Florida International University, Miami, FL. EML 4905 Senior Design Project

Transcription

1 Department of Mechanical and Materials Engineering Florida International University, Miami, FL EML 4905 Senior Design Project HVAC Design for Green Building Miami Green Final Report Submitted By: James Klein Alejandro Franyie November 28, 2007 FACULTY ADVISOR x Dr. Yong X. Tao This report is written in partial fulfillment of the requirements in EML The contents represent the opinion of the authors and not the Department of Mechanical and Materials Engineering.

2 The Green Machine The Green Machine is comprised of students from Florida International University s Department of Mechanical and Materials Engineering. The Green Machine is a committed multi-disciplinary team working together to achieve a final goal. Each team member shall work together in a balanced and dedicated effort to attain the best design possible. Name / Signature PID # Title Alejandro Franyie Team Leader / Designer / Draftsman x James Klein LEED Specialist/ Designer/ Draftsman x 1

3 Ethical Design Statement The Green Machine has thoroughly studied the NSPE Code of Ethics for Engineers and fully understands the conduct that is expected from an engineer. Furthermore, every member of the Green Machine vows to be ethical in every aspect of his work and will strive for the highest ethical behavior. Every member of the Green Machine understands that his ethical behavior is not only a reflection of himself and the team, but also a reflection of the engineering profession as a whole. Environmental Impact Statement The Green Machine holds human safety and the environment at the paramount of consideration during design and construction. Each member vows to not deliberately make any decisions which may negatively influence the life of a human being. Human safety and comfort will be held in the highest regard. The main goal of the Miami Green project is to reduce the environmental impact caused by high-rise buildings. The Green Machine vows to eliminate the use or production of toxic materials and harmful emissions. The Green Machine will strive to make its design as energy efficient as possible thereby reducing the emission of harmful greenhouse gases. 2

4 Chapter 1 Miami Green Overview 1.1 Goal Statement 1.2 Scope 1.3 Miami Green 1.4 Intended Clients 1.5 Design Organization 1.6 Challenges and Constraints Table of Contents Chapter 2 Load Calculations 2.1. Concept Overview 2.2. Heating Load 2.3. Cooling Load 2.4. Miami Green Break-Down and Parameters 2.5. Results and Sizes Chapter 3 Energy Analysis 3.1. Concept Overview 3.2. Energy Baseline and Optimization 3.3. EQuest and Results Chapter 4 Life Cycle Cost Analysis 4.1. Concept Overview 4.2. Input Parameters 4.3. Life Cycle Cost Analysis 4.4. Ownership and Initial Cost 4.5. System Specification and Details Chapter 5 LEED Certification 5.1. Overview 5.2. Energy and Atmosphere (EA) 5.3. Indoor Environmental Quality (EQ) 5.4. Conclusion References 3

5 Appendix Appendix A Cooling and Heating Loads Appendix B Energy Modeling Appendix C Economic Analysis Appendix D Equipment Specification Appendix E Mechanical Drawings Appendix F Design Organization 4

6 Chapter 1 Miami Green Overview 1.1 Goal Statement The goal of this project is to select and design a preliminary HVAC system for a highrise Green Building that is both economical and energy efficiency. Green building is the practice of making sustainable buildings that minimize negative impact on the environment and the inhabitants of the building. For a mechanical engineer this means maximizing energy efficiency, minimizing refrigerant impact on the environment and improving indoor air quality. This project will primarily focus on maximizing the energy efficiency of the building but will also deal with other green concepts such as refrigerant management, increased ventilation, and indoor pollutant control. 5

7 1.2 Scope Miami Green is in the preliminary design and development stage where the owner is still gathering cost and feasibility estimates before pursuing construction. Drawings have been provided to the mechanical engineers, Green Machine, by the architect to begin schematic drawings of the HVAC systems design. The Green Machine has been contracted to calculate heating/cooling loads and perform a study of different HVAC systems that can be used in Miami Green. The study will include: energy performance analysis, life cycle cost analysis and schematic drawings of the recommended system. Also, the mechanical engineer will provide recommended constructions to be used in the buildings envelope. Since architectural drawings are still in the design stage and interior space layouts have not been designed, the scope of the mechanical engineer is to treat Miami Green as a shell building. Shell building means that the exterior and dividing walls of the building will be treated as permanent but the space contained is to be designed later. This means that ductwork and space design will be done as soon as the architect completes interior layouts. Therefore, Green Machine will only provide a schematic design of the system and not detailed interior layouts. Also, Green Machine has been contracted to make Miami Green a green building. Green Machine shall design Miami Green using principles provided by the USGBC (United States Green Building Council.) This will ensure that Miami Green becomes a certified green building and will comply with the USGBC s LEED rating method. The LEED rating method is the topic of chapter 5. 6

8 1.3 Miami Green Miami Green (Fig. 1.1) is a 13 story, high-rise office/retail building located in Miami, FL. The first floor contains a double height lobby, retail/office space and equipment rooms. The second floor contains two offices and a veranda overlooking the lobby. Floors 3-13 are typical floors that will only be used as office/retail space. The interior layouts of these floors have not yet been designed by the architect but future plans are to provide different office layout for future tenants. Potential future layouts will be discussed in the next chapter. Figure 1.2 shows the shell layout of the typical floors. Figure 1.1 Artists rendering of Miami Green 7

9 Figure 1.2 Typical Floor Layout There is a central elevator bank located on every floor the opens to public corridors. The corridors serve at the main entrance to all of the offices. On each extreme of the corridor there is a stairwell that serves as a secondary link between floors and the primary means of emergency egress. On the other side of the corridor is a garage that runs from the ground floor to the roof. 8

10 1.4 Intended Clients The client for Miami Green is the developer that is constructing the building. The developer has hired Green Machine to provide an economic analysis and schematic plans of the recommended HVAC. The developer has also hired a structural, electrical, plumbing and civil engineer, as well as an architect and construction contractor. The developer is building Miami Green to sell the individual retail spaces upon completion. This developer is seeking a profit. Therefore, it is upon Green Machine to provide an economic design to maximize the owner/developers profits. Also, we must consider the future occupants of the building as clients. We do not work directly for these people, but we do have a responsibility to them. Our design must keep them safe and comfortable even if it makes the design more expensive and less desirable for the developer. 9

11 1.5 Design Organization Three different HVAC systems will be analyzed to compare energy efficiency, cost, and green-ability. Some primary assumptions that will be made are: 100% outside air in the corridors Increased outside air supply to other spaces Changes shall be made to improve envelope High efficiency equipment shall used Pursuing LEED certification Comply with energy codes (ASHRAE 90.1 and Florida Mechanical Code Ch. 13) Interior spaces will be designed later Allow flexibility for future interior design Software shall be used to compute heating/cooling loads, energy performance, and life cycle cost. The programs used will be discussed in the respective sections of the calculations mentioned above. Also, AutoCAD shall be used to provide the schematic drawings of the building with the recommended system. Appendix F contains a function analysis diagram, a drawing tree, a failure modes and effects analysis (FMEA) and a project timeline. 10

12 1.6 Challenges and Constraints In a project such as this, the greatest challenges are unforeseeable. Conflicts with the architectural layout are inevitable. The main challenge that will arise is where to put all the equipment necessary to achieve the desired objectives. Often times extra mechanical rooms must be added to the architectural design to house equipment. Our goal will be to find solutions to these problems to minimize the change to architectural design and maintain an aesthetic working and shopping environment for the buildings inhabitants. The other main challenge of this design is the maximization of energy efficiency. There are many different techniques and strategies to achieve an energy efficient design, the challenge will be to find the route that yields the highest efficiency at the most reasonable cost. Another main challenge of this building is to provide an economical and environmentally safe design. Economical and environmental are opposites of each other. The more economical the design the less environmentally safe it is and vice versa. We must find a balance between the two satisfy both the client and the environment. Also, the design must comply with Florida Building Code before it can be approved for construction. The design will be constrained by the following: Must comply with Florida Building Code and good engineering practice Must achieve a certain indoor design temperature (74ºF winter and 78ºF summer) o This will correspond to approximately 1 ton cooling capacity per 300 square feet Must have high indoor air quality (approximately 30% fresh air) Must be economical and environmentally safe o Pass LEED standard for green building Must minimize change to the architectural design o Reduce need for extra mechanical rooms and chases Maximum energy efficiency o Overall cooling efficiency of over 14 EER 11

13 Chapter 2 Load Analysis 2.1 Concept Overview The heating/cooling load is the first major step in designing an HVAC system. All of the buildings parameters are taken into account to create a minimum measure of the amount of heating/cooling capacity needed in the building. Building parameters include things such as floor area, wall/window area, wall construction, orientation and many other key factors. Since this building is located in Miami, the heating load will be small in comparison to the buildings cooling load. This chapter describes the methods used to calculate the heating and cooling loads of a typical zone. For the Miami Green project, each floor was split up into different zones and cooling/heating loads were performed using specialized software. Each zone was analyzed and the cooling/heating loads were calculated using Hourly Analysis Program (HAP). This software is a well known and widely used tool created by Carrier, an HVAC equipment manufacturer. The following sections provide the theoretical basis for how this program functions. 2.2 Heating Load In cold weather there are small variations in the outdoor temperature. This allows the heat loss to be analyzed as steady state. The heating load consists of two kinds of heat losses that a zone could experience, the heat transmitted through the walls, ceiling, floor, glass, and other surfaces, and the heat required to warm outdoor air entering the space. To compute the heating load the indoor and outdoor design conditions must be defined. The outdoor design condition is defined by the location of the structure being analyzed. The indoor design condition is defined by the temperature and humidity that define the comfort level of the occupants. 12

14 The heat losses transferred through the walls, ceilings, roof, window glass, floors and doors is all sensible heat transfer, referred to as transmission heat loss, and computed using the equation below. In order to calculate this heat loss, the heat transfer coefficient of the material that make up the envelope of the structure must also be defined. Where: q ( ) = UA t i t o U = overall heat transfer coefficient (Btu/hr-ft 2 -F) A = the net area for the given component for which U was calculated ( t t ) i o = the temperature difference on the two sides of the surface being analyzed. Infiltrating air entering a building must be conditioned to satisfy the indoor design conditions. The mass flow rate and the specific heat of the air must be determined to calculate the amount of sensible heat required to condition the infiltrating air. The sensible heat required to heat the outside air can be calculated with the following equation. q s = m o c p ( t t ) i o Where: m o = the mass flow rate of the infiltrating air, lbm/hr c p = the specific heat of the air, btu/(lbm-f) ( t t ) i o = the temperature difference between the infiltrating air and the indoor air. The enthalpy and the humidity ratio of the infiltrating air affect the humidity of the indoor conditioned air. The latent heat required to humidify the air is given by the equation below. q l = m o i fg ( W W ) i o i fg =the latent heat of vaporization at the indoor conditions, Btu/lbmv ( Wi Wo ) = the difference in design humidity ratio, lbmv/lbma 13

15 2.3 Cooling Load Solar radiation has important effects of both heat gain and the heat loss of a building. A strong transient effect is created because solar radiation varies significantly with time. Thermal radiation energy falls on the envelope of the structure and is subjected to absorption, reflection and transmission through transparent bodies. Heat that is absorbed by the surfaces is stored, causing an appreciable difference between the heat gain of a structure and the heat removed by the cooling equipment. In order to size the cooling equipment the heat gain must be computed for the following. Solar radiation through fenestrations Heat conduction through boundaries with convection and radiation from the inner surfaces into the space. Sensible heat convection and radiation from internal objects. Ventilation and infiltration air Latent heat gains generated within the space. The Solar Heat Gain Coefficient method can be used to calculate the heat gain from solar radiation through fenestrations. A coefficient defined by the glazing of windows is multiplied by the total irradiation of the sun. Where: G i = incident irradiance q i = (SHGC) = solar heat gain coefficient G i ( SHGC) To calculate the remaining heat gains, heat balance on each surface that makes up the envelope of the zone must be analyzed. Every surface of a zone should be analyzed considering energy balance. Heat is absorbed by the wall from radiation of the sun, radiation of objects near the 14

16 structure, and convection caused by the outside air. The heat balance on an exterior surface can be calculated considering the equation below. q '' conduction, ext = q' ' solarheat, ext + q'' convection, ext + q' ' radiation, ext Where: q ' conduction, ext ' = conduction hear flux through the wall, Btu/(hr-ft 2 ) q ' solarheat, ext ' = absorbed solar heat flux, Btu/(hr-ft 2 ) q ' convection, ext ' = convection heat flux from the outside air, Btu/(hr-ft 2 ) q ' radiation, ext ' = thermal radiation heat flux form other external objects, Btu/(hr-ft 2 ) The heat absorbed by the envelope of the structure is conducted through the material to the interior surface. Heat is transferred through convection to the inside conditioned air. Heat is also radiated to and from inside object to the interior surface. The heat balance on the interior surface can be calculated considering the equation below. q '' = q + q + q conduction, int '' solarheat,int '' convection,int '' radiation,int Where: q ' conduction, ext ' = conduction hear flux through the wall, Btu/(hr-ft 2 ) q ' solarheat, ext ' = absorbed radiation from other objects, Btu/(hr-ft 2 ) q ' convection, ext ' = convection heat flux to the air, Btu/(hr-ft 2 ) q ' radiation, ext ' = thermal radiation heat flux to other objects, Btu/(hr-ft 2 ) Considering that the air inside the building has no thermal storage, the sum of all the heat transfers is equal to zero. The heat gained/lost by the heating and cooling system must be equal to the amount of heat gained/lost by convection from the wall, infiltrating air and the heat 15

17 transferred to the conditioned air from the people lights and equipment inside. Finally the heat balance of the zone air may be represented by the equations below. Where: A= area of internal surface Aq '' convection int qinf iltration + qsystem + qradiation,int + qint ernal, q inf iltration = heat gain due to infiltration, BTU/hr, + conv = q '' system = heat gain to do heating/cooling system, BTU/hr 0 q '' int ernal, conv = convective portion of internal heat gains The mathematical analysis of the heat balance on the envelope of the structure of a large building is too tedious to calculate without the aid of computer software. The specifications of the Miami Green building were determined by using the Carrier software to calculate the heating and cooling loads. Using the results of the calculations the equipment can be selected. 2.4 Miami Green Break-Down and Design Parameters As mentioned in the previous section, software shall be used to perform the cooling loads for Miami Green. The software to be used is called Hourly Analysis Program (HAP) by Carrier. This software is widely used and respected as the industry standard for accurately calculating a spaces heating and cooling load. Even though software will be used to perform the load calculations, the designer must prepare accurate data to input into the program. This data includes internal loads, material constructs used and building geometry, which will be organized in a space breakdown table. 16

18 Figure 2.1 and figure 2.2 show floor plan layouts of two typical floors in Miami Green. The units are called Penthouse, unit C1 and Unit C2. Figure 2.2 Layout Penthouse Figure 2.2 Layout C General Some key elements in performing a cooling/heating load are general parameters that have to do with the basic geometry of building. Things such as floor area, ceiling height, and building weight are all crucial to a buildings required cooling and heating. Table 2.1 shows a breakdown of the different zones and areas to be calculated. Table 2.2 shows the wall/window area breakdown of the typical floor. The material and the thermal characteristics of the walls and windows will be specified later. 17

19 Table 2.1 Area Breakdown Zone Description Area (Sq. Ft.) Ceiling Height (Ft.) Typical Floor Entire Conditioned Area 8,355 9 Penthouse Large Layout 7,715 9 C1 Half Layout 2,827 9 C2 Half Layout 4,888 9 Corridor Hallway Table Wall and Window (Area and Exposure) Construct Direction Length (ft) Area U value N Glass E S E Wall S W Corridor Wall Partition The building weight is assumed to be medium density (70 lb/ft 2 ). This is a standard assumption for a building made of lightweight concrete and steel. The building weight affects the thermal retention characteristics of the building and describe how easily cooled/heated a building is. Internals Internal loads deal with heat generated within the buildings envelope. Internal loads are things such as lighting, electrical equipment, and people. The heat produced by these elements do not cross the buildings walls and is generated within the cooled space. The following are some assumptions that have been made for this project: 18

20 Internal Lighting 1.2 W/sf Electrical Equipment 0.75 W/sf Occupancy 60 persons per level Persons Activity Level Office Work o Sensible Load 245 BTU/ hr o Latent Load 205 BTU/ hr Walls/Partitions For most spaces, the wall construction is one of the highest transmitters of heat. Since the exterior of Miami Green is mostly glass, the walls are primary partitions used between the conditioned corridor and the non-conditioned garage. To calculate the cooling load a typical wall construction will be used. A typical exterior/partition used in this application is 8 lightweight concrete, stucco finish and ½ interior gypsum board with ½ air gap. A wall with this BTU construction has a U-value of This U-value has been inserted into table 2.2. h ft 2 F In chapter 3 the overall U-value of the wall will be improved by adding insulation. The reason the overall U-value is not being considered in the cooling load is because it does not affect the overall system to be used. It does change the sensible heat load and that is something that will have to be recalculated before the tenant spaces are built. Windows/Doors Windows and doors are also called fenestrations. Since Miami Green is a high rise building, the only exterior doors to be considered are on the ground floor (lobby entrance). These doors are made of frameless glass and are considered more as glass than as doors. Therefore, all the fenestrations in this project will be considered as glass. 19

21 The most important window factors to consider when performing a cooling load are window area, overall U-value, and solar heat gain coefficient (SHGC). These factors determine how much heat enters a space by means of radiation due to U and solar radiation due to SHGC. For this application the SHGC is not used directly. It is used by means of a shading coefficient (SC). The SHGC and SC is a measure of how much radiation is transmitted, absorbed and reflected by the glass. BTU For the purposes of the cooling load we will use an overall U-value of 0.52 h ft 2 F and a shading coefficient of This corresponds to ½ high impact glass with a tint. In the next chapter the specification of the glass to be used in Miami Green will be done in much more detail. Roof For most applications, the heat gain through the roof is a significant factor. In Miami Green this is not as important because only the top floor roof is exposed to the outside. All other typical levels will not be affected by heat gain through the roof because they are located directly below a conditioned space. There is zero heat transfer across a surface when the temperature on both sides is equal. According to energy codes, the minimum insulation value for a roof in this application is R-15. Therefore, the cooling load will be performed so that the roof construction has an overall BTU U-value of The conversion between resistance value (R) and heat transfer h ft 2 F coefficient (U) is the following: U = 1 R 20

22 Infiltration Infiltration is the introduction of unconditioned air into a conditioned space or conditioning system. It is important to take infiltration into account because it is heat added or removed from the system in the form of convection. Miami Green will be a pressurized building meaning that all infiltration will be controlled in the form of fresh air supply to the spaces. So measuring the infiltration into the spaces is a matter of calculating the amount of fresh air that the design will supply to the spaces. Fresh air is also called outside air (O/A). Outside air requirements are set forth by ASHRAE Standard 62. For a building of this type, the O/A is calculated by measuring the expected occupancy for this type of space and multiplying that quantity by 20 CFM/person of air supply. The expected occupancy for office space is 7 persons per 1,000 ft 2. Table 2.3 shows the outside air calculations for Miami Green. Space Area (S.F.) Table O/A Calculations Occupancy (Persons) Requirement (CFM/person) Min. Air (CFM) Provided (CFM) Penthouse 7, ,080 1,404 C1 2, C2 4, The above table shows minimum O/A required by code and also shows the air that is going to be provided in Miami Green. The reason the project is going to be provided with more fresh air is to improve the indoor air quality (IAQ) and achieve LEED credit points. LEED credit points will be discussed in chapter 5. Also, it should be noticed that O/A was not calculated for the corridors. This is because the corridors will be provided with air conditioning units that will supply 100% outside air. Doing this will greatly improve the IAQ, pressurize the building, and serve as smoke control in the event of a fire. 21

23 2.5 Results and Sizes The above parameters were inputted into the Hourly Analysis Program (HAP). HAP then simulates the building/space parameters according to the weather data from Miami, Florida. The results of this simulation are detailed summaries of the heat gain and loss to the spaces during different times of the year. The summaries provide total, sensible and latent cooling as well as recommended air flow rates and other crucial sizing data. Below, Table 2.3 contains key sizing information and each space has a suggested equipment layout. As expected, the heating load for these spaces is relatively low. It is common practice in Miami to provided heating by using electric strip heaters inside of the air handling units. Therefore, all units in Miami Green will use electric strip heating. Space Total Load (Tons) Table 2.3- Cooling Load and Equipment Data Sensible Total Load Load (BTU/h) (BTU/h) Equipment Size & Quantity To Be Used Penthouse ,500 (1) 12.5 Ton & (1) 7.5 Ton Unit C (1) 7.5 Ton Unit C (1) 12.5 Ton Unit Corridor , ,800 (2) 15 Ton 100% O/A RTU A types (5) 5 Ton Units Appendix A, Cooling Loads, contains all the detailed calculations and summaries calculated by HAP. As can be seen, the cooling load of the penthouse is equal to the sum of the C units. Also, the last row of the table shows the proposed (5) A units shown in figure 2.3, which also equal a total of 20 tons. 22

24 Figure 2.3 Layout A As a result of the cooling load calculations and equipment sizing, the following is the cooling equipment breakdown for all of Miami Green. 1 st Floor / Lobby o 22.5 Total Tons of Cooling (3) 7.5 Ton Units 2 nd Floor o 22.5 Total Tons of Cooling (3) 7.5 Ton Units 23

25 11 Typical Floors o (3) Layout Penthouse 20 Total Tons of Cooling (1) 12.5 Ton Unit (1) 7.5 Ton Unit o (4) Layout C 20 Total Tons of Cooling (1) 12.5 Ton Unit (1) 7.5 Ton Unit o (4) Layout A 20 Total Tons of Cooling (5) 4 Ton Units Corridor o (2) 15 Ton 100% O/A Roof-Top Units The system type for these units mentioned above has yet to be determined. The choice of which system to use will be a result of the next two chapters. From Chapter 2, the size and quantity of the units that will be used have been determined. 24

26 Chapter 3 Energy Modeling 3.1 Concept Overview The energy modeling portion of this project is the most crucial and design intensive. One of the most important aspects of building green is energy conservation and sustainability. Our goal is to save as much energy as possible. Some of the factors that contribute to a buildings energy usage are HVAC, lighting, water heating, electrical equipment, and miscellaneous loads. In South Florida, one of the primary contributors to energy usage is the HVAC system. Therefore it is critical that the HVAC system is as energy efficient as possible. Computer energy modeling is the most useful tool for determining HVAC systems energy efficiency. There are many computer programs designed to this, but for this project equest shall be used. There are three basic cooling systems that will be modeled in this project to determine which is the most energy efficient and cost effective. The three systems are DX (Air Cooled) split units, DX Water Cooled system, and chilled water system. For a building this size, it is not known which system will be the most energy efficient until an energy model is created. Besides potential energy efficiency, each system has pros and cons in their applications to this building. Another primary factor in choosing the system to be used is the economical factors of initial cost and life cycle cost. For all systems, heating will be done by electrical resistance heaters located within air handler units, because in South Florida, heating loads are relatively small and do not justify a centralized boiler system. A direct expansion (DX) split air conditioning system uses a pressurized refrigerant and expansion valve to create cooling effect at in a cooling coil. It is called a split system because the four main components of a cooling cycle are divided between the air handler unit (AHU) and the condensing unit (CU). The AHU contains the expansion valve and the evaporator (cooling) coil, while the CU contains the compressor and the condenser coil. A DX split system is air- 25

27 cooled, meaning the refrigerant is cooled being blown by the condenser coil. A DX split, air-cooled system is schematically represented in figure 3.1. Figure 3.1 DX Split System There are many advantages to a DX system. They are available in extremely high EER (Energy Efficiency Ratio) ratings, meaning much lower energy costs for an individual tenant. DX systems are easily installed, maintained, and there is less potential for major malfunctions. The primary disadvantages to high SEER DX systems are extremely high initial cost and quantity of refrigerant used. Another goal of building green is to minimize refrigerant impact on the ozone layer. Even though current refrigerants, such as R-410a, are much more earth-friendly, they have an impact on ozone depletion. A DX Package system (also commonly called condenser water system) has several packaged water-cooled equipments that use a centralized cooling tower to provide condenser water. A condenser system is similar to a DX split system in that they both use refrigerant to cool air. The two systems differ in that the condenser water system uses packaged units where all four major components are located together. It uses piped water to cool the refrigerant at the 26

28 condenser section. The water is then taken to a cooling tower which transfers heat to the environment. A DX package, water-cooled system is schematically represented in figure 3.2. Figure 3.2 DX Package System A chilled water system is very different from the previous two systems discussed. The primary difference is that the cooling coil uses chilled water to directly cool the air as it passes through to the space. A chilled water system uses a central chiller to chill the water using the same principles as DX but on a larger scale. Chillers come in a variety of options including aircooled (fan and condenser coil) and water-cooled (cooling tower). In this project a water-cooled chiller will be under consideration because it has the potential of yielding a higher energy savings. A chilled water, water-cooled is schematically represented in figure

29 Figure 3.3 Chilled Water Water-Cooled 3.2 Energy Baseline and Optimization Measuring the energy efficiency of a building is done by comparing the proposed building to a baseline model. The method for creating a baseline model is set forth by ASHRAE Standard 90.1 Energy Standard for Buildings Except Low-Rise Residential Buildings. The baseline building must use the same building geometry and fundamental zoning definitions. The baseline building must be modeled using the minimum performance requirement set forth by Table 3.1 is a summary of the energy efficiency requirements. Table 3.1 Minimum Requirements from ASHRAE 90.1 Type Requirement Climate Zone 1 Walls Mass Wall Above Grade No insulation required Roof Insulation entirely above deck R-15 Windows Maximum U-1.22 Lighting Maximum of 1.2 W/SF for office space Air Conditioners 10.3 EER 28

30 The baseline building shall be modeled using these minimum requirements to determine the maximum allowable energy usage for the building. The proposed building will differ from the baseline by improving mechanical equipment performance, envelope specifications (insulation, glazing, glass thickness, etc.), and lighting efficiency. By improving these parameters, the overall building performance improves thereby creating an overall reduction in energy usage. Since different HVAC systems will be modeled, the first step shall be to improve the buildings envelope and lighting characteristics. Improving the buildings envelope and lighting is a basic step in improving the buildings overall energy performance. These changes to the building will be constant regardless of the HVAC system chosen. Envelope Improving a buildings envelope is a broad statement. For Miami Green the most important factor is improving the envelope is to improve window performance since the façade of the building is over 80% glass. This is where the major reduction in energy usage shall occur. By decreasing the overall U value (heat transfer coefficient) and increasing the shading coefficient, the heat that enters the condition space by conduction and radiation is reduced. The reduction in the heat that enters the space is reflected by lowering the amount of electricity needed to cool the space. For a high rise building the use of impact resistant glass is mandated by the state of Florida. Therefore 0.5 impact resistant glass shall be used. This glass not only serves for safety, but it also drastically reduces heat gain and noise pollution. It has also been specified that the glass shall be covered in a blue-green tint to further reduce the heat that enters due to radiation. Also, a second low-e glazing with a 0.5 inch air gap shall be added to reduce the amount of heat 29

31 that enters due to thermal conduction. Figure 3.4 shows a dimensioned cross-section of the glass to be used. Figure 3.4 Window Section This specified glass drastically reduces the amount of heat that enters the space. This will give the proposed Miami Green design a large advantage over the baseline model. The U-Value BTU of the glass construction specified is 0.42 h ft 2 F and the shading coefficient is equal to The second most important step in improving the building envelope is to decrease the overall U value of the exterior walls and partitions. The difference between an exterior wall and a partition wall is that an exterior wall is exposed to solar radiation while a partition is not. An exterior wall experiences the combined effects of solar radiation and conduction. A partition wall only experiences heat conduction. Regardless of the type of wall, the overall U value is extremely important. 30

32 Figure 3.5 illustrates the wall section specified for Miami Green. As can be seen, R-20 insulation has been added greatly reduces the baseline U value. The total U-value of the wall BTU shown in the figure is h ft 2 F Figure 3.5 Window Section Lighting Improving lighting efficiency is the easiest way to go green. Everyone can change regular incandescent light bulbs to more energy efficient Compact Fluorescent Light (CFL) lights. In the scope of Miami Green, all interior and some exterior lights will be fluorescent lights. Fluorescent lights are more efficient because they produce more Lumens per Watt. Simply stated, they output more light with less power. ASHRAE Standard 90.1 allows a maximum of 1.2 W/S.F. for office lighting. Due to multiple reasons, Miami Green will use approximately 0.9 W/S.F. One of these reasons is the widespread use of fluorescent lighting instead of incandescent lights. But since ASHRAE has already assumed the primary use of fluorescents, the energy use reduction is not substantial. 31

33 The primary reason for the reduction in lighting wattage is as follows. Since Miami Green is for office/retail usage, its primary use shall be during the day. And since Miami Green is over 80% glass, the need for interior lighting during the day is greatly reduced. Therefore, the amount of glass on the building decreases the efficiency of the HVAC system but also reduces the amount of interior lighting required. Another way Miami Green is reducing energy is by using smart lighting systems. For example, bathrooms and closets will be equipped with motion sensors to activate only when occupied. Basically, reducing the amount of time non-essential lighting is on. Interior smart lighting will also shut down lighting when the building occupancy is sensed to be low. These times shall correspond to night time and holidays. HVAC The three HVAC systems being used considered in Miami Green were explained in the previous overview section. The energy efficiency of these three systems differs with different application. There is no system which is generally more efficient. Within each system there are varying efficiencies available with a certain cost associated with them. For instance, the minimum efficiency required for a DX air-cooled system over 65,000 BTU/h cooling capacity is 9.5 EER (Energy Efficiency Ratio). Systems of this type are available with EER values up to 15 but are also much more expensive. The EER of equipment is calculated by the following formula: Cooling Capacity (BTU/h) EER = Input Power(KW) Packaged DX water-cooled systems are also rated by the value of the EER. Package watercooled systems are more efficient by also require a cooling tower and water pumps. Generally, 32

34 for larger scale projects, the water-cooled systems are preferable because they save space and can sometimes be more efficient. Therefore, the choice is between the two is not clear. A chilled water system is sometimes more desirable because all refrigeration is localized to the chiller. In this system the chiller is primarily responsible for energy usage. In Miami Green the chiller necessary will need to have approximately 300 tons cooling capacity. Chiller efficiency is measured in COP (Coefficient of Performance). For a 300 ton centrifugal watercooled chiller the minimum efficiency required is 5 COP. The conversion from tons of refrigeration to BTU/H and the formula for COP are shown below. Chiller efficiencies are available up to 6.5 COP but with significant cost associated with them. Also, chilled water systems are only feasible in larger scale applications. 1 Ton Refrigeration = 12,000 BTU/H Cooling Capacity(BTU/H) COP = Input Power(BTU/H) Since the choice between systems is vague, it is up to the energy modeling and life cycle cost analysis to determine the system to be used. The life cycle cost analysis is a study of the economics involved in an HVAC system. Parameters such as initial cost, service life, maintenance costs and energy costs by a role in the life cycle cost analysis. Often times, ownership and future plans play a significant role in the choice of the HVAC system to be used. The importance of the life cycle cost analysis and ownership will be discussed in the next chapter. 3.3 EQuest and Results As mentioned at the start of this chapter, equest shall be used to measure and analyze the building s overall energy usage. EQuest is software based on another energy analysis program 33

35 called DOE-2. This software began development in the 1970 s with collaborative efforts by ASHRAE, NASA, the US Postal Service, and energy industry leaders. It was created to answer a growing concern in the industry, that society as a whole was not leading a sustainable lifestyle. DOE-2/eQuest is the most widely used and respected software in field of energy modeling. The results of an energy model cannot be assumed to be 100% accurate but do serve as a basis of comparison to determine that one alternative is more energy efficient than another. This will be the usefulness of equest in Miami Green. This software will serve as a benchmark to gauge how energy efficient the proposed building has become in comparison to a baseline building. The measure of improvement will be shown as a percent reduction in the baseline energy usage. Below is the formula used to find the percent reduction, Baseline Usage - Proposed Usage % Reduction = 100% Baseline Usage where the energy usage is measured in kwh. As previously mentioned, the baseline building is modeled using all the minimum requirements of Table 3.1. The results of this model shall be the basis of comparison for all other proposed building designs. Below, Figure 3.6 is a summary of the gross energy usage broken down into different classifications and months of the year 34

36 Figure 3.6 Baseline Electric Consumption of Miami Green As seen in Figure 3.4, the total annual electric consumption of the baseline model is 2,820 MWh. This means that Miami Green will use 2,820 Megawatt-hours of electricity annually if it is build to minimum standards. Our primary goal is reduce this gross energy usage as much as possible while maintaining a safe, comfortable environment at a reasonable cost. Now we will make improvements to the shell/envelope, lighting, and HVAC system. In order to present the results of our comparisons in an organized fashion, Table 3.2 will show designations and nomenclature used for different test runs with different specifications. 35

37 Table 3.2-Nomenclature and Designations Used Designation DXS DXWC CHW Shell Only EER * COP * Detailed Description DX Split System Air-Cooled DX Packaged System Water-Cooled Chilled Water System Water Cooled Improvements made to Shell and Lighting only (Min. HVAC efficiency Improvements made to Shell, Lighting, and HVAC efficiency Improvements made to Shell, Lighting, and Chiller efficiency Baseline Building Baseline Model Created according to ASHRAE 90.1 Table 3.3 shows the energy model results for different scenarios. The first model shown in table is the baseline model shown in detail in figure 3.6. The energy usage of the baseline model is the basis for measuring the % reduction as previously discussed. The last column shows the percent reduction of all the different models. Appendix B Energy Analysis contains the complete summary of all the models created and their respective breakdowns and electric consumptions. Table Energy Model Results Model Name Energy Usage (kwh x 000) Description % Improvement Baseline 2,820 Model According to ASHRAE 90.1 n/a DXS Shell 2,328 Shell/LTG Improvement Only 17.45% DXS EER 12 2,164 Shell and HVAC (12 eer) 23.26% DXWC Shell 2,289 Shell/LTG Improvement Only 18.83% DXWC 14 EER 2,107 Shell and HVAC (14 eer) 25.28% CHW Shell 2,277 Sh ell/ltg Improvement Only 19.26% CHW 6 COP 2,088 Shell and Chiller (6 COP) 25.96% 36

38 For each different system (DXS, DXWC, and CHW) two models were made. First, the shell only run, which only improves the building envelope and lighting efficiency while maintaining the minimum HVAC equipment efficiency allowable by code. The second run makes improvements upon the HVAC system efficiency. The data shown in table 3.3 shows that with specifications made the chilled water system (CHW) is the most energy efficient followed by the DX packaged system and then the DX split system. Using minimum and maximum efficiency equipment the DX split system is the least efficient when compared respectably to the other system types. The two other systems are very close in energy efficiency and the difference is almost negligible. Also, it should be noted that the greatest improvement in energy efficiency was done by improving the envelope/shell (walls and windows) and lighting efficiency. This upgrade accounted for approximated 18% reduction. Improving the HVAC efficiency alone accounted for only an additional ±6% reduction. Therefore, the primary energy savings is made by improving the structures thermal properties. Improving equipment efficiencies is a good step but not as drastic a change. The choice of which system to use is still not complete. The energy efficiency of the systems has been measured and a distinction has been made between them. We cannot simply choose the most efficient system. Other factors such as ownership type, useful life and initial cost must be accounted for. All of these factors will be weighted and balanced and the system type will be chosen in the next chapter. 37

39 Chapter 4 Cost Analysis and System Selection 4.1 Overview A cost analysis is one of the most important factors to consider when selecting the cooling system to be used in a building. For Miami Green, the type of ownership combined with the initial cost of the building will most likely be the settling factor of which system shall be chosen. This will be the topic of a later section in this chapter. Factors to be considered when performing a life cycle cost analysis are things such as initial cost, life of equipment, operating costs and present worth. Initial cost includes things such as equipment costs and installation costs. Operating costs include things such as annual maintenance costs and energy usage. For the purposes of this project a program called Engineering Economic Analysis by Carrier will used to perform the life cycle cost analysis. The three different systems under consideration will be compared by initial cost, annual operation cost and present worth over a period of time. 4.2 Input Parameters The life cycle cost of Miami Green will be analyzed over a period 31 years to ensure that all of the three alternatives must be replaced at least once. A standard assumption of 6% minimum attractive rate of return will be assumed. Also, the three systems will be analyzed completely independent of each other. The following is a break-down of the three systems and the costs associated with them. Table 4.1 contains the initial cost of the DX Split system for Miami Green. Note that the unit cost includes air-handler unit (AHU), condenser unit (CU) and installation of all associated ductwork and equipment. The estimated life of a system of this type is approximately 10 years. 38

40 At the end of the expected life there are replacement costs. This system must be replaced two times in a span of 31 years. Equipment (AHU and CU) Table DXS Cost Installed Cost/Unit ($) Quantity Cost ($) Life (years) 12.5 T. Unit 29, , T. Unit 17, , T Unit 11, , Total Initial Cost = 661,200 The annual costs for DXS include maintenance and energy costs. The annual maintenance cost for this system can be estimated at $200/AHU for filter, fan and coil maintenance and $200/CU for refrigerant and compressor maintenance. Since there are 40 AHU and CU in this proposed design, the average annual maintenance cost for this system is $16,000/year. The annual energy usage of this system is the topic of the previous chapter. Using the results from the last chapter, the local energy costs are applied to find that this system will have an energy cost of approximately $152,000/year. Table 4.2 contains the initial cost of the DX package system for Miami Green. Note that the unit cost includes equipment costs, ductwork, piping and installation. The estimated life of packaged units (PU) and pumps is approximately 15 years. The estimated life of a cooling tower is 20 years. Therefore, this system must be replaced once in a span of 31 years. This replacement cost along with inflation must be taken into account. 39

41 Table DXWC Cost Equipment (PU) Installed Life Cost/Unit Quantity Cost ($) (years) ($) 12.5 T. Unit 30, , T. Unit 18, , T. Unit 12, , Cooling Tower 38, , Pumps 4, , Total Initial Cost = 751,700 The annual maintenance costs of this system are similar to that of the DXS system. An average of $400/PU equals to a total of $16,000 per year. Cooling tower maintenance and water treatment must also be considered for this system. These costs can be estimated at $5,000 per year. Therefore, the total maintenance cost of the DXWC system is $21,000 per year. Using the energy usage results from the last chapter, the annual energy cost of this system can be estimated at $142,000 per year. Table 4.3 contains the initial cost and life of the chilled water system for Miami Green. Note that the unit cost includes equipment costs, ductwork, piping and installation. The estimated life of fan coil units (FCU) and pumps is approximately 15 years. The estimated life of a cooling tower and chiller is 20 years. Therefore, this system must be replaced once in a span of 31 years. This replacement cost along with inflation must be taken into account. Table CHW Cost Installed Equipment Life Cost/Unit Quantity Cost ($) (FCU) (years) ($) 12.5 T. Unit 26, , T. Unit 18, , T. Unit 11, , Cooling Tower 38, , Chiller 205, , Pumps 4, , Total Initial Cost = 900,300 40

42 The annual maintenance costs of this system much lower than the previous two since there is one centralized compressor. An average of $200/FCU equals to a total of $8,000 per year. Cooling tower, Chiller maintenance and water treatment must also be considered for this system. These costs can be estimated at $6,000 per year. Therefore, the total maintenance cost of the DXWC system is $14,000 per year. Using the energy usage results from the last chapter, the annual energy cost of this system can be estimated at $141,000 per year. 4.3 Life Cycle Cost Analysis All of the above parameters were input to the Engineering Economic Analysis software. The results are summarized below. For the complete results and report see Appendix C Economic Analysis. Initial Cost o DXS - $661,200 (winner) o DXWC - $751,700 o CHW - $900,300 Total Present Worth o DXS - $3,619,000 o DXWC - $3,347,000 o CHW - $3,205,000 (winner) Annual Operating Costs o DXS - $168,000 o DXWC - $163,000 o CHW - $155,000 (winner) The above data shows that the DX split system (DXS) has the lowest initial cost and the chilled water system (CHW) has the lowest total present worth and annual operating costs. It should be noted that the DX packaged water-cooled system is in second place in all three categories. Also, DXS is the worst in total present worth and annual operating costs. Using this data, the next section will determine which system shall be used. 41