PERFORMANCE ANALYSIS OF TWO ALTERNATIVE HVAC SYSTEMS FOR THE UNT ZERO ENERGY LAB. Naimee Hasib. Thesis Prepared for the Degree of MASTER OF SCIENCE

Transcription

1 PERFORMANCE ANALYSIS OF TWO ALTERNATIVE HVAC SYSTEMS FOR THE UNT ZERO ENERGY LAB Naimee Hasib Thesis Prepared for the Degree of MASTER OF SCIENCE UNIVERSITY OF NORTH TEXAS August 2013 APPROVED: Yong Tao, Committee Chair and Chair of the Department of Mechanical and Energy Engineering Mihai Burzo, Committee Member Rambod Rayegan, Committee Member Costas Tsatsoulis, Dean of the College of Engineering Mark Wardell, Dean of the Toulouse Graduate School

2 Hasib, Naimee. Performance Analysis of Two Alternative HVAC Systems for the UNT Zero Energy Lab. Master of Science (Mechanical and Energy Engineering), August 2013, 74 pp., 17 tables, 42 figures, 33 numbered references. This paper covers the simulation and comparison among three different HVAC (heating, ventilation & air conditioning)systems to achieve the goal of finding the most effective HVAC among these three in terms of human comfort, efficiency and cost considering North Texas climate. In the Zero Energy Lab at the University of North Texas, Denton, TX, the HVAC system of the building assembles with geothermal heat source. Here, water to water heat pump with radiant floor and water to air heat pump with air ducts provide heating & cooling of the building. In this paper electricity consumption, comfort, cost & efficiency analysis is done for the existing system using Energy Plus simulation software. Calibration of the simulated data of the existing system is done comparing with the actual data. Actual data is measured using 150 sensors that installed in Zero Energy Lab. After the baseline model calibration, simulation for ground source water to water heat pump, evaporative cooler with baseboard electric heater and water cooled electric chiller with baseboard electric heater (as a conventional system) is shown. Simulation results evaluate the life cycle cost (LCC) for these HVAC systems. The results of the comparison analysis among all the three HVAC systems show the most effective HVAC system among these three systems in North Texas weather. The results will make UNT Zero Energy lab a standard model towards a sustainable green future.

3 Copyright 2013 by Naimee Hasib ii

4 ACKNOWLEDGEMENTS First and foremost, I want to thank God for providing me with the strength and determination in utilizing my skills and knowledge required throughout this study. I want to extend my sincerest gratitude to my advisor, Dr. Yong Tao, for his invaluable support and guidance throughout this research and my other studies. I want to express my heartfelt appreciation to him for having given me the opportunity to work as a research assistant which has led to both my personal and professional development. Thanks to Dr. Junghyon Mun & Dr. Rambod Rayegan for having the utmost confidence in me and encouraging me to excel throughout my studies. I will also take this opportunity to thank my committee member Dr. Mihai Burzo for always being available to provide much needed help and advice. Most importantly, I want to thank all my friends and family for their prayers and continuous words of support. To my parents, I say thank you for being there for me in every way possible. iii

5 TABLE OF CONTENTS Page ACKNOWLEDGEMENT... iii LIST OF TABLES... vi LIST OF FIGURES... vii NOMENCLATURE... ix CHAPTER 1 INTRODUCTION...1 CHAPTER 2 BACKGROUND Motivation behind This Research Zero Energy Research Laboratory (ZØE) Simulation Software Selection of Three HVAC Systems and Description of the Systems Literature Review...12 CHAPTER 3 METHODOLOGY ZØE Modeling ZØE Base Model Calibration Basis of Comparison System Modeling Compared Parameters...30 CHAPTER 4 RESULT AND DISCUSSION Indoor Air Temperature Relative Humidity Total Cooling Energy Supplied Electricity Consumption Daily Energy Efficiency Ratio (EER) Energy Savings COP of WWHP Required Water Volume Life Cycle Cost Analysis...52 iv

6 CHAPTER 5 CONCLUSION...59 CHAPTER 6 RECOMMENDATION...62 APPENDICES...63 REFERENCES...72 v

7 LIST OF TABLES Page 1. Some Characteristics of ZØE Input Parameters for ZØE Modeling Input Parameters for WAHP Modeling of ZØE Basis of Three HVAC System Comparison Plan & Condenser Loop Equipment for Different HVAC System Modeling Input Parameters for Water-to Water Heat Pump with Radiant Floor Modeling Input Parameters for Ground Loop Heat Exchanger Model Input Parameters for Evaporative Cooler Model Fan & Cooling Coil Input Parameters for Modeling Cooling Water & Condenser Water Circulating Pump Input Parameters Water Cooled Electric Chiller & Cooling Tower Input Parameters Net Present value of Installation Cost for Ground Source WWHP Net Present Value of Installation Cost of Evaporative Cooler Net Present Value of Installation Cost for Water Cooled Electric Chiller System Net Present Value of Operational Cost of All Systems Maintenance Cost of All Systems Energy Savings Percentage from Water-to-Water Heat Pump...48 vi

8 LIST OF FIGURES 1. Percentage of Building Primary Energy Consumption in U.S (2006) Percentage of HVAC Energy Consumption in Building (2006) Zero Energy Research Laboratory (ZØE) at Discovery Park, UNT Ground Heat Exchanger with Six Boreholes in ZØE Grouted GLHE [ref-26] & Radiant Floor of ZØE Difference between Outdoor Dry Bulb & Wet Bulb Temperature Heat Pump Working Principle Evaporative Cooler Working Principle & Picture of Cellulose PAD Cooling Coil Working Principle Geometry of ZØE Drawn by Google SketchUP Flow Chart for Water to Water Heat Pump Equation Fit [16] Overall HVAC System Diagram for ZØE Comparison between Real Total HVAC Electricity Consumption with Simulated Value (in KWh) Simulated & Real Indoor Air Temperature Comparison (in C) Water-to-Water Heat Pump with Ground Loop Heat Exchanger & Radiant Floor Model diagram Evaporative Cooler System Model Diagram Water Cooled Electric Chiller with Cooling Tower System Model Diagram Denton Outdoor Dry Bulb Temperature for Total Cooling Season Comparison of Indoor Air Temperature among All Systems Comparison of Indoor Air Temperature of WWHP & Evaporative Cooler with Baseboard Electric Heater for Whole Year Comparison of Indoor Relative Humidity among All Systems...38 Page vii

9 22. Comparison of Percentage of Relative Humidity in an Hourly Basis for a Day Total Cooling Energy Supplied by All the Systems in Cooling Season Water-to-Water Heat Pump Electricity Consumption per Day Evaporative Cooler System Electricity Consumption per Day Electric Chiller System Electricity Consumption per Day Comparison of Total Electricity Consumption of Different parts among Three Systems Total Electricity Consumption by three Systems in Cooling Season Comparison of Energy Efficiency Ratio in BTU/Watt-hr among All Systems EER Changing with Outdoor Dry Bulb Temperature EER Changing with Outdoor Relative Humidity Comparison of Seasonal Energy Efficiency Ratio among All Systems COP Value of WWHP in January 1st Required Daily Make Up Water for Cooling Towe Relation Between Cooling Tower Inlet Temperature & Make up Water Volume Required Daily Water Volume for Evaporative Cooler Ground Source Heat Pump Installation Cost Comparison of Operation & Maintenance Cost among All Systems per Year Comparison of Life Cycle Cost without Incentives Comparison of Life Cycle Cost with Incentives Comparison of Life Cycle cost Analysis among All Systems Considering both Heating & Cooling for Whole Year Comparison of Life Cycle cost Analysis among All Systems Considering both Heating & Cooling for Whole Year with Incentives...58 viii

10 NOMENCLATURE Heating, ventilation & air conditioning HVAC EnergyPlus E+ Zero Energy Research Laboratory Life cycle cost Heat pump Water-to-water heat pump Water-to-air heat pump Evaporative cooler for cooling season Water cooled electric chiller Ground source heat pump Ground loop heat exchanger Air Handler unit ZØE LCC HP WWHP WAHP EC CS GSHP GLHE AHU ix

11 CHAPTER 1 INTRODUCTION Building sector consumes a major portion of energy of the total energy consumption among all other sectors. In between building sector; Heating, ventilation & air conditioning (HVAC) system is the main energy consuming part of a building. So, it is also the major source of emissions from a building through the life cycle. To serve better human comfort, most of the buildings facilitate with HVAC system now a day. In this consequence, increasing of HVAC system energy consumption turns into a very important issue. Growing sustainability on HVAC system has become vitally important for conservation of energy. So, before construction of a building, investigation on the HVAC system efficiency is essential to choose the best energy efficient heating & cooling system. Conservation & efficient use of energy in HVAC sector can save a lot of energy consumption. Performance analysis of a HVAC system includes comfort analysis, energy consumption, energy efficiency, economic analysis, environmental impact etc. In this paper performance analysis of three different heating & cooling systems is done in terms of human comfort, primary energy consumption, system efficiency, and annual operating cost, life cycle cost (LCC) analysis. In this research project, LCC has been compared among all the three systems over a 30 years period. All of the systems are modeled & simulated using EnergyPlus (E+) simulation software. Each system performance is evaluated based on north Texas climate. All systems are compared against same building. Zero Energy Research Laboratory (ZØE) which is located at Discovery Park in University of North Texas, Denton, TX is the base model for all the systems analysis. ZØE is assembled with geothermal heat source. Two heat pumps (HP), combined with 1

12 ground source, supplies heating & cooling energy into ZØE. Two HPs are; (1) Water-to-water heat pump (WWHP) & (2) Water-to-air heat pump (WAHP). At first base modeling is done with E+ software, and then the model is simulated & calibrated with real data developed from TAC Vista installed in ZØE. Base model calibration is done based on two different operating parameters like power consumption by WWHP & WAHP & indoor air temperature. After the calibration of the base model is done, analysis of the three other HVAC systems has been done. One conventional system is chosen for the comparison. Three systems those are chosen for comparison analysis are; (1) Ground source water-to-water heat pump with radiant floor for both heating & cooling season, (2) Evaporative cooler for the cooling season (EC), (3) Water cooled electric chiller as a conventional system (CS) for the cooling season. From the careful evaluation & comparison among all the three systems, it is shown that which system is the best in terms of efficiency & cost. The system that has the greatest impact on the environment is also determined. At first all the comparison results are shown only for cooling season with only a cooling system. Cooling systems are WWHP, evaporative cooler & electric chiller. Heating equipment is added with this cooling system to provide heating energy to the zone. The whole year simulation is done with a dual setpoint thermostat control for providing both heating & cooling. Ground source WWHP can provide both heating & cooling energy. So no additional heating equipment is needed to provide heating energy to the building. For evaporative cooler & electric chiller additional heating equipment is needed to provide heating energy. So, Baseboard electric heater is added with evaporative cooler & electric chiller to supply heating energy. When heating will be needed then baseboard electric heater will work & when cooling will be needed then evaporative cooler & chiller will work. Comparison analysis is done on yearly basis for both heating & cooling. 2

13 CHAPTER 2 BACKGROUND 2.1 Motivation behind This Research According to primary energy consumption building sector consumes around 39% of energy among all other sectors (Figure 1). Within residential, commercial or industrial building HVAC system consumes around 39% of energy (Figure 2) [24]. Several researches are going on to improve the performance of HVAC system in terms of human comfort, energy consumption, efficiency, economic analysis, environmental impact, life cycle assessment analysis. It is essential to do the optimization between comfort, energy efficiency, and cost analysis. In this respect, a research project on comparison analysis among three different HVAC systems has been chosen to identify the best HVAC system in terms of the most energy efficient, economically effective with a lowest environmental impact. Figure 1: Percentage of Building Primary Energy Consumption in U.S (2006) 3

14 Figure 2: Percentage of HVAC Energy Consumption in Building (2006) 2.2 Zero Energy Research Laboratory (ZØE) Figure 3: Zero Energy Research Laboratory (ZØE) at Discovery Park, UNT ZØE (Figure 3) is a unique research laboratory in TX where researches on renewable energy generation, HVAC technologies are being carried out. With the renewable feature of solar & wind energy generation its heating, ventilation & air conditioning system is also based on renewable resource. Ground is acting as the heat source & heat sink for the HVAC system. WWHP with radiant floor and WAHP with air ducts are constructed in ZØE to provide heating 4

15 & cooling energy of the building. Some general characteristic of ZØE is shown in Table 1. All systems of ZØE laboratory are managed by TAC Vista building management system. Sensor network with around150 sensors is connected with this TAC vista data acquisition system. Energy consumption by the HVAC systems, performance of heat pump, input or output water temperature from the ground heat exchanger etc. can be monitored & controlled from TAC vista. Characteristic Total building area Net Conditioned Building area Table 1: Some Characteristics of ZØE Value m m 2 Window Opening Area m 2 (for Conditioned Zone) Window-wall ratio [%] Floor area Cooling load/year Wall/Roof Window HVAC System Power Production 1200 sq. ft GJ Structural Insulated Panel Low e insulated glazing Geothermal heat pump with WWHP with radiant floor WAHP with air duct & Photovoltaic panel Wind turbine Ground works as the heat sink in the cooling season & heat source in the heating season. Ground heat is transferred to the WWHP & WAHP through vertical ground heat exchanger Figure 4. There are six boreholes each of 225 feet deep. 5

16 Figure 4: Ground Heat Exchanger with Six Boreholes in ZØE U-bend polyethylene pipe is inserted into the boreholes. Then vertical tubes are grouted Figure 5 so that heat can be transferred from ground to the tube wall. [26] Figure 5: Grouted GLHE [ref-26] & Radiant Floor of ZØE WWHP is connected with radiant floor Figure 5 to supply radiant cooling energy or to supply radiant heating energy into the zone. WAHP that is connected with air duct, supply heating or supply cooling energy into the zone. 6

17 2. 3 Simulation Software EnergyPlus software is used here for the all the systems modeling & simulation purpose. This software is suitable for HVAC performance analysis. Version 8.0 is used in this paper for the modeling & simulation purpose. At first the building geometry is drawn with Google SketchUp. That geometry works as the input files for E+ software. 2.4 Selection of Three HVAC Systems and Description of the Systems Different types of HVAC systems may be assembled in building for heating or cooling purpose. Some systems are for only air conditioning (Cooling) while some are for only heating and some are for both options. In this paper at first comparison among three cooling systems is analyzed. Among all the three systems, WWHP can be used for both heating & cooling season. So, no additional heating equipment is needed for this system. Heat pump can be run by a geothermal system. Ground source heat pump (GSHP) uses ground as a heat source or sink. From thermodynamic viewpoint ground is effective as a heat source or heat sink, because ground temperature is usually near to the indoor temperature than outdoor air temperature. Among the renewable energy source HVAC system, water source heat pump is the fastest growing system. Uses of ground source heat pump for building heating or cooling is increasing day by day for its consistent heating & cooling supply, high efficiency, low operating cost, low environmental impact. According to the DOE Report [18] GSHP system consumes less energy in comparison to conventional Air source heat pump (ASHP) system on an annual basis regardless of the ground loop type, size of the system and the building application. So ground source WWHP is chosen as one of the three systems. Also WWHP is one of the heating & cooling supply equipment in ZØE. So, it is compared with two other systems to see the performance of ground source heat pump among all the three systems. 7

18 Temperature in Degree C Denton Outdoor Dry Bulb & Wet Bulb Temperature in Cooling Season 07/22 07/22 07/22 07/22 07/23 07/23 07/23 07/24 07/24 07/24 07/24 07/25 07/25 07/25 07/26 07/26 07/26 07/26 07/27 07/27 07/27 07/28 07/28 07/28 07/29 07/29 07/29 07/29 07/30 07/30 07/30 07/31 07/31 07/31 07/31 08/01 08/01 08/01 Environment:Site Outdoor Air Drybulb Temperature [C](Hourly) Environment:Site Outdoor Air Wetbulb Temperature [C](Hourly) Figure 6: Difference between Outdoor Dry Bulb & Wet Bulb Temperature Evaporative cooler (EC) performance significantly depends upon the temperature & humidity of that location. EC system performs well in dry weather. This system cools the air by reducing the dry bulb temperature. Where wet bulb temperatures are lower than dry bulb temperature, there EC system can work well. In North Texas region, outdoor wet bulb temperature is lower than dry bulb temperature. So the performance of EC system can be analyzed here. In Figure 6, it is shown that, outdoor wet bulb temperature is always lower than dry bulb temperature in Denton. So the weather is nearly dry because of low humidity in the air, so performance analysis of EC is necessary here. Thus, EC system is chosen as one of the three systems. Evaporative cooler can only supply cooling energy to the zone, so additional heating equipment is necessary. Baseboard Electric heater is added with evaporative cooler system to see the overall performance of both heating & cooling throughout the year. Comparison with a conventional system is required as a base situation. So a conventional system like water cooled electric chiller (CS) is chosen. Water cooled electric chiller & WWHP cooling mechanism is near similar. Both of the systems maintain vapor-compression cycle. In case of 8

19 WWHP system, cooling energy from radiant floor is distributed into the building by radiation. CS system works by exchanging heat of room s hot air with circulated cold water. Water cooled chiller system is efficient for high distribution of cold air throughout the room. So it is compared with WWHP system. As a heating equipment Baseboard electric heater is also considered. From the analysis of evaporative cooler with baseboard electric heater required electricity to supply heating of the zone is calculated. That amount of required electricity, to supply the needed heating energy to the zone, is added with this electric chiller requirement. Finally, in this research-comparison analysis between renewable HVAC systems like WWHP with the conventional system like EC & CS system is done. System 1: Ground source water-to-water heat pump with radiant floor System 2: Direct evaporative cooler System 3: Conventional system-water cooled electric chiller with cooling tower Heating Equipment-As the ground source water-to-water heat pump can supply both heating & cooling energy, so no additional heating equipment is needed for the zone to supply heating energy. But the evaporative cooler & electric chiller can supply only cooling energy to the zone, so additional heating supply equipment is needed here. Assuming electric baseboard heater is supplying heating energy to the zone if necessary. Baseboard electric heater is controlled by the heating setpoint which is 20 C Ground Source Water to Water Heat Pump with Radiant Floor Heat pump performs according to vapor compression thermodynamic cycle. Main component of vapor compression cycle is evaporator, compressor, condenser & expansion valve (Figure 7). [27] 9

20 Figure 7: Heat Pump Working Principle Evaporative Cooler Evaporative cooler can be designed in three ways. (1) Direct evaporative cooling or open circuit; (2) Indirect evaporative cooling or closed circuit; (3) Direct-indirect evaporative cooling. EC system supply cooling energy into the building by the evaporation of the moisture. Fan draws outside air through the pad. Water circulates over the pad & pad becomes sodden Figure 8 [28]. There is a spray header to spray the water over the pad [29]. When outside air passes through the soaked pad it takes the water moisture. Thus by the evaporation of water air becomes cold. This cold air passes through the duct into the building. Water source may be the city water connection. It flows by a pump. [1] Figure 8: Evaporative Cooler Working Principle & Picture of Cellulose PAD 10

21 Baseboard electric heater works as a convective heat transfer. Hot air is less dense than cold air. When air near to the heater becomes hot, it goes up due to the buoyancy force. Cold air comes near to the heater and becomes hot. Thus electric heater supplies heat energy to the zone Water Cooled Electric Chiller with Cooling Tower There are two types of Chillers: (1) Air-cooled chiller. (2) Water cooled chiller. In this paper, water cooled chiller is taken as one of the systems. Cold water for the condenser demand is coming from a cooling tower. Water cooled chiller works as a vapor-compression cycle to reject heat from the building to the environment. Chilled water circulates from the evaporator section of the chiller to the Air Handler unit (AHU). [19] HVAC with air handler unit (AHU) - AHU is a part of HVAC system that is used to condition & circulate air. AHU device can be constructed with a blower, fan, heating or cooling coil, and filter & damper. Damper is a valve; it is used to control the air flow inside a duct or AHU. Duct is used to deliver the air. Air handler unit with constant air volume (CAV) system here flow rate of air remains unchanged, but the air temperature varies to meet the required set point air temperature. Air handler unit with variable air volume (VAV) system - here flow rate of air varies to meet the required set point temperature. AHU draws hot air from the zone by a fan & by exchanging heat with the cooled water in cooling coil (Figure 9) inside the AHU [30], air becomes cold. This cold air then distributes in the zone through an air duct. By exchanging heat in cooling coil, cooled water is converted into hot water & return into the evaporator. The liquid refrigerant inside the evaporator evaporates through latent heat of vaporization by getting heat from the hot water: evaporated cold refrigerant passes through compressor & transform into high pressured hot refrigerant vapor by 11

22 the addition of heat of compression. This high pressure hot vapor while passes through the condenser, it exchanges heat by the latent heat of condensation with the cold water that comes from cooling tower. Hot refrigerant vapor turns into liquid refrigerant again to continue the process. On the other hand, by the cooling tower circuit, cold water that becomes hot in condenser, again convert in cold water by removing heat through the air from cooling tower. [20] Figure 9: Cooling Coil Working Principle 2.5 Literature Review From the literature review, it is noticeable that many works have been done so far regarding performance analysis of different HVAC systems. Energy consumption analysis, life cycle cost analysis, life cycle impact analysis are done for different systems. In ref. [8] performance analysis was done in an office building among three different systems, such as (1) a system with a natural gas boiler and convective baseboard heaters for water space heating and window air conditioners for air space cooling; (2) a system with a natural gas boiler and individual air reheaters for air space heating and a chiller plant for air space cooling; (3) an air-to-air heat pump for air space heating and cooling. Modeling & simulation of the 3 systems was done by E+ 12

23 software. From the simulation result, it was found that; in terms of efficiency, cost & environmental impact first system was the best as water was used as a heating medium & natural gas as a fuel. It was suggested that, for conservation of primary fuel & environment the third system will be the best. In ref. [5] cost analysis of gas engine heat pumps (GEHP) for residential and commercial buildings in different weather of Iran was investigated. Compressor of a heat pump can be driven by an electrical motor or internal combustion engine. In this paper, it was concluded that, operating cost for electricity driven heat pump is higher than GEHP. In terms of economic analysis, it was concluded that; in residential building for different weather GEHP is more economical but for commercial building electricity driven HP is more economical. GEHP system capacity increases results with a decrease of payback period. In ref. [7], in a residential building, five HVAC systems energy savings options are analyzed using E+ software. The performance analysis were examined in three different weather conditions of Italy; Milan, Rome & Palermo. The systems are (1) Ground coupled heat pump (GCHP), (2) Ground water heat pump (GWHP), (3) Air-to-water heat pump (AWHP), (4) Air-to-air heat pump (AAHP), (5) Boiler & split system (B&S). It was concluded that, GWHP & GCHP perform better with greater energy savings than AAHP, AWHP & B&S system in all places. In ref. [9], in south European region energy performance comparison was shown between ground coupled heat pump (GCHP) & air-to-air heat pump. It was found that, in heating mode GSHP saves 41% primary energy consumption than AWHP & in cooling mode GSHP saves 38% than AWHP. In ref. [10] life cycle assessment of (1) warm-air furnace and air-conditioner; (2) hot water boiler and air- conditioner and (3) air to air heat pump is compared and analyzed in four locations within USA 13

24 CHAPTER 3 METHODOLOGY 3.1 ZØE Modeling In the first step of ZØE modeling with EnergyPlus software, geometry/building envelope of the ZØE lab is created with Google SketchUp 8. A side view of the drawing is shown in Figure 10. OpenStudio application suite helps to perform the simulation in EnergyPlus using SketchUp. The building has been divided into three zones. One Conditioned Zone; One Mechanical Zone & One Electrical Zone. Figure 10: Geometry of ZØE Drawn by Google SketchUP As the WWHP & WAHP work in cooling & heating mode simultaneously as needed, all year round heating & cooling go on together as needed. So in the modeling set point is also set as dual set point. That is both of the heat pumps will work in heating mode when the indoor temperature goes below lower set point, will work in cooling mode when the indoor 14

25 temperature goes above the higher set point. For the modeling & calibration the set point is set as the actual set point taken from the TAC vista. Calibration of the model is done comparing the simulated result with the real data taken from TAC vista. Lower setpoint acts as heating set point, that is 18.3 C & higher setpoint acts as cooling set point that is 21.1 C. Minimal shadowing is assumed for solar distribution. That means all beam solar radiation from the outside of the window falls in the floor, not in the wall. Specification of the entire equipment like-geothermal pipe, radiant floor, all material used in ZØE have been collected & given as input for the model. Table 2: Input Parameters for ZØE Modeling Parameters Thermostat Control Heating set Point Cooling set point Value Dual Set Point 18.3 Degree C 21.1 Degree C Ground Source WWHP with Radiant Floor System Description In ZØE WWHP is connected with a vertical closed-loop ground heat exchanger for both heating & cooling. WWHP capacity is tons to 2.32 tons, depending on the entering or leaving fluid temperature. Ground heat exchanger consists of 6 boreholes of m radiuses. Length of the borehole is 68.6 m. U-bend pipes manufactured by Polyethylene material are inserted into the boreholes. The boreholes are then grouted with thermal conductivity of W/m-K. Flow rate within the heat exchanger is m 3 /s. The WWHP is then connected with radiant floor. Radiant tubes are made of Polyethylene of thermal conductivity W/mk. 573m long tube s inside diameter is m. Maximum flow rate of water is m 3 /s. Radiant floor with the WWHP acts as a plant loop in the model. Source of heat & cold is the 15

26 ground water. In heating mode, ground heat exchanger acts as a heat source & in cooling mode, ground heat exchanger acts as a heat sink. WWHP Model: WWHP as a plant heating or cooling equipment can be modeled in two ways using EnergyPlus. One is Parameter estimation & another is Curve fit or Equation fit model. In this paper curve fit model is used for modeling of WWHP. Ten Co-efficient for capacity (five for heating capacity & five for cooling capacity) and ten Co-efficient for compressor power (five for heating & five for cooling) are needed for this curve fit model, these co- efficient have been calculated from Co-efficient generator Excel spreadsheets using the catalog data of the HP manufacturer. After this co-efficient is calculated, a long with some other input parameters, heat pump model is generated in the E+. Compressor of this heat pump & water-circulating pump is driven by electricity. [16] Figure 11: Flow Chart for Water to Water Heat Pump Equation Fit [16] 16

27 Ground-loop heat exchanger model: In this model GLHE with the HP acts as a condenser loop. g- function, which is a set of non-dimensional temperature response factors, is used for temperature response of the borehole field. G-function allows the calculation of the temperature change at the borehole wall in response to a step heat input [17]. g-function values have been calculated from GLHEPRO software WAHP Model Like WWHP, WAHP is also connected with vertical ground heat exchanger. GLHE acts as the heat source or heat sink for WAHP system. WAHP condenser is also water cooled condenser. Such as in the cooling season, underground cold water comes into the WAHP through the ground heat exchanger. Exchanging heat with the refrigerant of the heat pump & getting hot. This hot water returns to the ground loop. In WAHP, the refrigerant becomes condensed by rejecting heat into the ground cold water. This condensed liquid refrigerant passes through the expansion valve to the evaporator section. Getting heat from the indoor air the refrigerant evaporates & thus the indoor air becomes cold. Air terminal single duct is used for the model. Table 3 shows some of the input parameters for WAHP model. Table 3: Input Parameters for WAHP Modeling of ZØE Parameters Fan pressure rise Maximum flow rate Rated air flow rate in WAHP Rated water flow rate in WAHP Rated total cooling capacity in WAHP Rated heating capacity in WAHP Value 600Pa 1 m 3 /sec 0.34 m 3 /sec m 3 /sec 7444W 88264W 17

28 Denton Weather: Weather data has been taken from a weather station that is placed near the Z Ø. Denton, TX weather data is used for this simulation purpose. Weather data includes outside air temperature, relative humidity, wind speed etc. The sequence of operation of two heat pumps is that after WWHP runs at full load, if the set point still doesn t meet then WAHP works. Figure 12 shows the simplified overall HVAC system diagram for ZØE. Figure 12: Overall HVAC System Diagram for ZØE 3.2 ZØE Base Model Calibration ZØE building is consisted with WWHP with radiant floor & WAHP with air duct system. Hundreds of sensors are networked within the ZØE building. These sensors are connected with a TAC Vista building management system. Total electricity consumption by the HVAC systems of ZØE building that includes-wwhp compressor electric power consumption, WAHP compressor electric power consumption, cooling or heating water circulating pump & fan electric power consumption. Actual data of total 18

29 80 Comparison Between Real HVAC Electricity Consumption (KWh) with Simulated Result HVAC Electricity Consumption in KWh Time in Day Basis Real Total HVAC Electricity Consumption from TAC Vista Simulation Result of Total HVAC Electricty Consumption Figure 13: Comparison between Real Total HVAC Electricity Consumption with Simulated Value (in KWh) electricity consumption is matched with simulated total electricity consumption (Figure 13). Data is taken from April 09 to May 03. Because, on that time, both of the heat pump was on in ZØE. Some of the day s error percentage is higher. Because for real case some days the window may be opened, there may be some visitors in ZØE. But for simulation all days are same. So, in some days simulated results varies from the real results. Percentage of error is shown in Appendix-A. Also, indoor air temperature from the TAC vista value is equated with the simulated zone mean air temperature value (Figure 14). Set point or schedule in simulation was selected as the real set point. Cooling set point was 21.1 C & heating set point was 18.3 C. Zone control thermostat dual set point. That is simultaneously heating & cooling will work together. To maintain the correct temperature, thermostat switches heating or cooling devices on or off, or regulates the flow of a heat transfer fluid as needed. 19

30 Temperature in Degree Celcius Real & Simulated Indoor Air Temperature Comparison (April 19-May 3) 04/19 10:00:00 04/19 16:45:00 04/19 23:30:00 04/20 06:15:00 04/20 13:00:00 04/20 19:45:00 04/21 02:30:00 04/21 09:15:00 04/21 16:00:00 04/21 22:45:00 04/22 05:30:00 04/22 12:15:00 04/22 19:00:00 04/23 01:45:00 04/23 08:30:00 04/23 15:15:00 04/23 22:00:00 04/24 04:45:00 04/24 11:30:00 04/24 18:15:00 04/25 01:00:00 04/25 07:45:00 04/25 14:30:00 04/25 21:15:00 04/26 04:00:00 04/26 10:45:00 04/26 17:30:00 04/27 00:15:00 04/27 07:00:00 04/27 13:45:00 04/27 20:30:00 04/28 03:15:00 04/28 10:00:00 04/28 16:45:00 04/28 23:30:00 04/29 06:15:00 04/29 13:00:00 04/29 19:45:00 04/30 02:30:00 04/30 09:15:00 04/30 16:00:00 04/30 22:45:00 05/01 05:30:00 05/01 12:15:00 05/01 19:00:00 05/02 01:45:00 05/02 08:30:00 05/02 15:15:00 05/02 22:00:00 05/03 04:45:00 05/03 11:30:00 05/03 18:15:00 Environment:Site Outdoor Air Drybulb Temperature [C](TimeStep) Real Indoor Temperature from TAC Vista Heating SetPoint Simulated:Zone Mean Air Temperature [C](TimeStep) Cooling SetPoint Figure 14: Simulated & Real Indoor Air Temperature Comparison (in C) 3.3 Basis of Comparison The following parameters are taken similar for the comparison of all systems: Same ZONE & same environment: To take all the system in the same platform, ZØE laboratory is considered as the building for all the three systems. That is building envelope, material, people, electric equipment, lighting schedule are equal for all systems. All the systems comparison is based on the conditioned zone of the base model. Same weather data is considered. Heating & cooling set point and heating & cooling season: For base modeling, the set point was taken as dual setpoint, in comparison among all the cooling systems for cooling control & thermostat setpoint is considered as single cooling. For the cooling season, there will 20

31 be no heating & vice versa. Heating season is assumed from October 1 to April 30, cooling season is assumed from May1 to September 30. Heating set point is set as 20ºC & cooling set point as 24 ºC. Daily, hourly or 15 minutes time step basis simulation has been done here. Holidays or weekends are not taken into consideration for all systems. At first comparison among all the cooling systems is shown considering only cooling season Table 4: Basis of Three HVAC System Comparison Season & Setpoint Time & Value Heating Season From October 1 to April 30 Cooling Season May 1 to September 30 Heating setpoint 20 Cooling setpoint 24 Cooling capacity: Cooling or heating capacity of a system is the heat removal rate from the conditioned zone & heat addition rate into the conditioned zone. It can be expressed in British Thermal Units (BTUs) per hour or in tons. Required cooling or heating capacity of a system depends on the volume of the space being cooled or heated and the air temperatures both inside and outside of the zone. In this paper for the comparison among three systems, similar cooling capacity of WWHP, EC & CS systems are taken Heat pump & water cooled electric chiller of 3 ton cooling capacity is taken here. For EC system capacity is recognized by air-changes per hour, not in terms of a ton, because EC system substitutes continually the air of the indoor room with fresh cool air. Where the CS system supplies cooling energy to the indoor air, by exchanging heat of the hot air with the cooled water flow through the coil. In case WWHP with the radiant floor cooling energy is supplied to the zone by radiation. WWHP & baseboard electric heater is providing same amount of heating energy to achieve the setpoint. Set point for all year simulation: For the whole year modeling & simulation for both heating & cooling purpose, setpoint is changed to dual set point. Heating will be supplied by the 21

32 ground source WWHP & baseboard electric heater when the temperature goes below the lower setpoint (20 C). Ground source WWHP, evaporative cooler & electric chiller will supply cooling energy to the zone when the temperature goes higher than the setpoint temperature 24 C. 3.4 System Modeling As E+ does the modeling of any system through two loop systems: Plant loop & Condenser loop. Here, it is discussed the main equipment for all the systems plant & condenser equipment. Table 5: Plan & Condenser Loop Equipment for Different HVAC System Modeling Plant & Condenser Loop GSHP Evaporative Cooler Conventional System Plant Heating Equipment Water to water heat pump Baseboard Electric Heater Baseboard Electric Heater Plant Cooling Equipment Water to water heat pump Evaporative cooler Water cooled electric chiller Condenser Equipment & Heat Exchanger Vertical ground heat exchanger Cooling Tower Cooling supply unit to the zone Radiant floor Single duct air terminal Single duct constant volume air distribution unit Ground Source Heat Pump GSHP with Radiant Floor-Water to water heat pump is working as a plant heating or cooling energy supply. According to the base model, here also equation fit or curve-fit model is used for heat pump modeling. Calculation of the co-efficient [Appendix-A] for heat pump modeling is done with a XCEL calculator. In the base model WWHP is supplying cooling or heating energy along with WAHP. So, this WWHP capacity is higher than the WWHP used for the base model. Ground source heat pump is supplying cooling/heating energy inside of the zone by radiation through a radiant floor. This radiant floor along with the WWHP is the plant loop in 22

33 the model. All other parameters are same as used in base model. A pump is used for Cooling or heating water circulation. WWHP, radiant floor & water circulating pump input parameters for cooling are given below Table 6: Input Parameters for Water-to Water Heat Pump with Radiant Floor Modeling Parameters Values Rated load side flow rate of WWHP m 3 /sec Rated source side flow rate of WWHP m 3 /sec Rated cooling capacity of WWHP W Rated cooling power consumption WWHP 4790 W Hydronic tubing inside diameter (Radiant floor) m Hydronic tubing length(radiant floor) 573m Maximum hot/cold water flow(radiant floor) m 3 /sec Flow rate of the pump m 3 /sec Rated pump head Pa Rated power consumption 246 W Motor efficiency 0.87 Cooling water set point from the outlet of heat pump is set different for daytime & night time. Because generally nighttime outdoor temperature is lower than daytime. Figure 15: Water-to-Water Heat Pump with Ground Loop Heat Exchanger & Radiant Floor Model diagram 23

34 Condenser Equipment or Heat Exchanger loop model-vertical ground loop heat exchanger is working as condenser equipment in the model. GLHE supply cold water from the ground through a condenser circulating pump in to the WWHP. All Input parameters for the Vertical GLHE & condenser pump are shown below Table 7: Input Parameters for Ground Loop Heat Exchanger Model Parameters Value Maximum flow rate for GLHE m 3 /sec Number of bore holes 6 Bore hole length 68.6m Bore hole radius 0.063m Ground thermal conductivity W/m-K Ground thermal heat capacity 2160 J/m 3 -K Ground temperature 19.4C Grout thermal conductivity 1.69W/m-K Pipe thermal conductivity 0.4W/m-K Pipe out diameter m U-tube distance m Pipe thickness m Flow rate of the condenser circulating pump m 3 /sec Rated pump head Pa Rated power consumption 568 W Motor efficiency Evaporative Cooler Modeling Constant volume fan & single duct air terminal is used. Maximum air flow rate 1.5m 3 /sec. Direct evaporative cooler with CelDek Pad is another system to compare. CelDek pad is made of cellulose. Flow rate of water depends on the depth of the pad. Pad area & depth is taken in such a way that it provides similar cooling energy like other two systems. Input parameters for Evaporative cooler & fan are given below. Direct or open circuit evaporative cooler is taken into 24

35 consideration. In case of direct evaporative cooler 100% air comes from outside. Indoor air continuously gets moisture from the water. Thus indoor humidity of the air rises very high. There should be a purging system for the indoor air after some time interval to reduce the indoor humidity. In this paper it is assumed that100% air is coming from the outside. Return air is used to close the circuit. Not any percentage of air is returning through the mixing box. All the air is coming from outside. Any schedule like window open can be added to reduce the indoor humidity. Figure 16: Evaporative Cooler System Model Diagram Table 8: Input Parameters for Evaporative Cooler Model Parameters Value Fan efficiency 0.7 Fan pressure rise 600 Pa Maximum flow rate 2.25 m 3 /sec Fan motor efficiency 0.9 Direct pad area of evaporative cooler 1.5 m 2 Direct pad depth 0.6m Recirculation water pump power consumption of EC 300 w 25

36 Direct evaporative cooler pump, constant volume fan are controlled by high temperature turn on, low temperature turn off availability schedule. System will be turned on when temperature goes higher than 24 C, system will be turned off when temperature goes below 20 C. Electricity consumption of Evaporative cooler is coming from recirculating water pump power consumption. Here, direct evaporative cooler is considered. Depending upon Pad material the efficiency of EC may also vary. Different types of pad material such as, Cellulose material (CL), Aspen (AS) media gives different efficiency. EC pad made of AS material gives higher efficiency than CL pad, because the wetted surface area of AS material is higher than CL material. [25] In this simulation CL material is used as the EC pad material Electric Chiller with Cooling Tower As a conventional model Water-cooled electric chiller with a cooling tower is compared with others two systems. Normally around 85 F condenser water temperature is used to design a water-cooled chiller. In this paper 29.4 C or 84.9 F temperature is used as designed condenser inlet temperature [20]. Here, 3 ton or btu/hr cooling tower is used. Single duct constant volume air terminal system is considered for supplying cooling energy to the zone. Electricity is consumed by fan, electric chiller, cooling tower, water circulating pump, condenser circulating pump. Cooling set point is same as other two systems. Fan consumes constant electric power because the fan speed, air flow rate, and pressure raise everything assumed as constant. Zone control thermostat is taken as a single heating or single cooling setpoint. That is only cooling will take place in the cooling season towards set point, there will be no heating. Also, single heating set point means heating towards setpoint but there will be no cooling. Amount of Baseboard electricity consumption from evaporative cooler 26

37 system is calculated. That amount of electricity consumption is also added with electric chiller system for heating purpose. Cooling tower loop acts as the Condenser loop. Cooling tower flow rate is for 1 ton it is 3GPM. So for 3 ton 9gallon/minute Or m 3 /sec. Assuming 1 ton of cooling tower is required for 1 ton of electric chiller for supplying cooling water [31]. For 3 ton of cooling tower 1/6 horse power fan motor is needed. That means 124 W fan motor is considered here. For 3 ton electric chiller 3 horse power of Compressor is needed. So 2237 watt is taken as electric chiller power consumption. Cooling water circulating pump power.75 KW (1 HP). Maximum flow rate of chilled water at 10 c (L/min) = 125, gal/min=3303 or.002 m 3 /sec. Constant volume fan with maximum flow rate of 0.47 m 3 /sec, 600 Pa pressure rise is added here for supplying cold air to the coil. [32] Detail Cooling Coil- Cooling Coil (heat exchange happens between cold water and air 6 rows with 16 tubes per row for cold water in & hot water out with a maximum water flow rate m 3 /sec. Tube outside diameter & inside diameter is m & m in order. Fin diameter m with a thickness of m. Fin & Tube thermal conductivity if assumed to be W/m-K & W/m-K. A sensor attached to the air loop outlet node, senses the temperature, and according that temperature, actuator attached in cooling coil water inlet node, changes the water inlet temperature. Single duct constant volume air terminal is used for the modeling of water cooled electric chiller. Constant volume fan and cooling coil are used as air handling unit. Input parameters for fan & cooling coil are given below in table 9. 27

38 Figure 17: Water Cooled Electric Chiller with Cooling Tower System Model Diagram Table 9: Fan & Cooling Coil Input Parameters for Modeling Parameters Value Maximum air flow rate for the air terminal 0.47 m 3 /sec Fan efficiency 0.7 Pressure rise in fan 600Pa Maximum flow rate in fan 1.3 m 3 /sec Fan motor efficiency 0.8 Maximum water flow rate for the cooling coil m 3 /sec Tube outside surface area 6.2m 2 Fin surface area 101 m 2 Coil depth 0.165m Fin diameter 0.43m Fin thickness 0.001m Tube inside diameter m Tube outside diameter m Tube thermal conductivity 385 W/m-K Fin thermal conductivity 203 W/m-K Fin spacing m Tube depth spacing m Number of tube Rows 6 Number of tubes per row 16 28

39 Cooling water circulating pump is modeled to supply cold water from the electric chiller to the cooling coil. Table 10: Cooling Water & Condenser Water Circulating Pump Input Parameters Parameters Value Cooling water circulating pump rated flow rate m 3 /sec Cooling water circulating pump rated pump head Pa Cooling water circulating pump rated power consumption 246 W Cooling water circulating pump motor efficiency 0.87 Condenser water circulating pump rated flow rate m 3 /sec Condenser water circulating pump rated pump head Pa Condenser water circulating pump rated power consumption 568 W Condenser water circulating pump motor efficiency 0.87 A condenser circulating pump is used to circulate water from cooling tower to the chiller. Input parameters for pumps are given below Water cooled electric chiller is used for the plant cooling supply equipment [33]. Table 11: Water Cooled Electric Chiller & Cooling Tower Input Parameters Parameters Value Nominal capacity of the electric chiller W Design condenser/cooling tower inlet temperature 29.44C Design chilled water outlet temperature from chiller 18C Design chilled water flow rate from chiller m3/sec Design condenser/cooling tower water flow rate m3/sec Design air flow rate for cooling tower 16 m3/sec Fan power at design air flow rate for cooling tower 124 W In this model cooling tower acts as condenser equipment & heat exchanger. Cooling tower supplies cold water to the chiller. Input parameters for the cooling tower are as follows. 29

40 3.5 Compared Parameters Indoor air temperature, electricity consumption, energy efficiency ratio, seasonal energy efficiency ratio, operational cost, percentage of energy savings these all parameters are compared here among the three systems. As the heating or cooling load for all the three systems is same, from the SEER value of all three systems energy savings percentage of WWHP in compare to CS & EC system has been calculated. Using this (1- SEER CS /SEER WWHP )*100 theoretical formula percentage of energy savings is calculated. [9] Economic analysis- all cost data considered here are taken from the literature review. Labor cost is not taken into consideration. Cost analysis is done considering the following factors. Initial cost that includes purchase & construction Costs Energy (electricity) Costs or Operating Costs Maintenance Costs Parameters for Present-Value analysis include cost period & Discount rate. Ground source WWHP system cost mainly segmented in three different parts: [15] (1) Ground loop with condenser pump. Ground source loop cost mainly includes cost related to vertical ground heat exchanger that is consisted of Polyethylene pipe. Grouting material cost [15]; (2) WW Heat Pump with cooling/heating water circulating pump cost & (3) Radiant Floor cost. Conventional system water cooled electric chiller system cost [2] mainly divided into 3 ton electric chiller, 3 ton cooling tower & air handler fan & coil parts. Evaporative cooler cost is taken from these references. [2] Life-cycle Cost analysis Initial or construction cost [15] of ground source WWHP is calculated as follows (Table 12): 30

41 Table 12: Net Present Value of Installation Cost for Ground Source WWHP WWHP with Radiant Floor Component Cost ($) 6 Borehole Drilling with 68 m depth 3000 Vertical ground heat exchanger made of Polyethylene pipe with construction 1505 Grouting material with insertion 1126 Radiant floor construction with of hydronic tube 3648 Pipes, fittings & valves 1000 Circulating Pump for water flow 100 WW Heat Pump purchase with installation 4573 Total Cost Net Present Value of Ground Source WWHP Installation Cost 3459 Table 13: Net Present Value of Installation Cost of Evaporative Cooler Evaporative Cooler with Air loop Component Cost ($) Air Handler Unit Single Duct CAV air terminal, Air distribution unit, Fan 1177 Pipes, fittings & valves 1000 Evaporative cooler (in built Circulating Pump for water flow) 3000 Total Cost 5177 Net Present Value of EC Installation Cost 1197 Table 14: Net Present Value of Installation Cost for Water Cooled Electric Chiller System Water Cooled Electric Chiller with Cooling Tower Component Cost ($) Air Handler Unit: Single Duct CAV air terminal, Air distribution unit, Fan 1177 (Constant volume), Cooling Coil Pipes, fittings & valves 1000 Circulating Pump for water flow (Condenser + Water Circulating Pump) 100 Electric Chiller (3 ton)

42 Cooling Tower (3 Ton) with water 1040 Total Cost 9707 Net Present Value of CS Installation Cost 2245 Table 15: Net Present Value of Operational Cost of All Systems System Water to Water Heat Pump with Radiant Floor Evaporative Cooler with Air Loop Water Cooled Electric Chiller Operational Cost of All Cooling Systems Total Electricity Total Water Total Cost ($/Year) Cost ($/Year) Operational Cost ($/year) Electricity Used (KWh)/ year 2378 Electricity Rate ($/kwh) Total Water Consumption (Gallon/ year) 0 Water Rate ($/Gallon) Electricity Water Net Present Value of Operational Cost in $ for 30 Years Life Cycle Assuming 740 Gallon water rate $2. Daily around $4 of water is needed for cooling tower make up water. Around 26400Gallon of water initially needed for the cooling tower. That cost goes to installation cost. Maintenance cost for CS system is 2.4 times higher than geothermal heat pump [18]. Maintenance cost includes leakage, valve fitting etc. Salvage value, Inflation rate, Replacement cost is not taken into Consideration 32

43 Table 16: Maintenance Cost of All Systems System Total Maintenance Cost ($)/year Water to water Heat Pump with radiant floor 43 Evaporative cooler with air loop (Includes maintenance of PAD) 112 Water Cooled Electric chiller (Conventional System) 112 Incentives-two kinds of incentives are available for renewable energy systems. A Tax credit up to 30 % of initial cost from a Tax credit program is assumed from DOE report [18]. Some energy companies offer 300$/ton rebate for renewable energy use. Life Cycle Cost analysis of each system is done on a present value basis with an assumed life of 30 years. If proper maintenance is maintained then, GSHP system can attain 30 years of lifespan. Replacement cost is not taken into consideration. Net Present value Calculation is done using this formula R t /(1+i) t where t= time of cash flow, i= discount rate & R t = net cash flow LCC = I + R + E + M LCC= Total LCC in present-value (PV) I = Initial or Construction cost in PV E= Energy cost or operating cost in PV M= Maintenance cost in PV R= Replacement cost in PV Life cycle cost analysis LCC= Initial cost + Operating Cost + Maintenance Cost + Replacement Cost. Seasonal Energy Efficiency Ratio (SEER): It is the ratio of cooling in British thermal unit (BTU) to the energy consumed in watt-hours. SEER near BTU/Watt-hr is an efficient system. Primary Energy consumption: Total yearly electricity/natural gas consumption of all systems is calculated from the summation of pump electricity consumption & compressor (in case of WWHP)/fan & pump (in case of evaporative cooler) electricity consumption 33

44 CHAPTER 4 RESULT AND DISCUSSION As identical building envelope, weather & operating condition has been used here for comparison of all of the three system, so the cooling load for all the three systems modeling is taken similar. The simulation results of all the three systems have been analyzed on the basis of Energy analysis Cost analysis In this paper ground source water to water heat pump, evaporative cooler with baseboard electric heater & water cooled electric chiller with cooling tower are compared with respect of various parameters: such as relative humidity, supplied cooling energy, energy efficiency ratio, seasonal energy efficiency ratio, electric consumption, annual electricity cost, life cycle cost analysis in north Texas weather for ZØE building and for the cooling season & all the year. Simulated results for the cooling season of three systems those are supplying cooling energy to the zone are shown here. Then life cycle cost analysis for both cooling & heating equipment is evaluated. These results are analyzed in terms of energy, cost & comfort. From all the discussions, a conclusion is made here about which system performs better in north Texas region. Figure 18 shows the outdoor air temperature for the assumed cooling season (May 1 to September 30) in Denton, TX. Cooling setpoint is set to 24 C & heating setpoint is 20 C. From the figure it can be seen that sometimes within this cooling season, outdoor temperature goes below heating setpoint. So heating is needed for that time. As the thermostat controlling parameter is set as a single cooling mode for the cooling season, within this cooling season period, only cooling energy will be supplied to the zone. From the figure it can be seen that, near July 22 to August 08, solely cooling is required for the zone. So, some output value is analyzed 34

45 within this time period. Later on simulation result for whole year is shown for both considering both heating & cooling. Outdoor Temperature in Cooling Season (May 1st-September 30) Environment:Site Outdoor Air Drybulb Temperature [C](TimeStep) Cooling Set Point Temperature in Degree Celcius /01 00:15:00 05/04 22:30:00 05/08 20:45:00 05/12 19:00:00 05/16 17:15:00 05/20 15:30:00 05/24 13:45:00 05/28 12:00:00 06/01 10:15:00 06/05 08:30:00 06/09 06:45:00 06/13 05:00:00 06/17 03:15:00 06/21 01:30:00 06/24 23:45:00 06/28 22:00:00 07/02 20:15:00 07/06 18:30:00 07/10 16:45:00 07/14 15:00:00 07/18 13:15:00 07/22 11:30:00 07/26 09:45:00 07/30 08:00:00 08/03 06:15:00 08/07 04:30:00 08/11 02:45:00 08/15 01:00:00 08/18 23:15:00 08/22 21:30:00 08/26 19:45:00 08/30 18:00:00 09/03 16:15:00 09/07 14:30:00 09/11 12:45:00 09/15 11:00:00 09/19 09:15:00 09/23 07:30:00 09/27 05:45:00 Figure 18: Denton Outdoor Dry Bulb Temperature for Total Cooling Season In terms of following parameters, performances of three HVAC systems are being discussed here. 4.1 Indoor Air Temperature Figure 19 shows the comparison of the indoor air temperature for all the three systems (from July 22 to August 08). Red line shows the cooling setpoint. As the outdoor air temperature always higher than the cooling setpoint, cooling energy is supplied continuously from all the systems. Thus, indoor air temperatures for all the systems decrease near cooling set point. The indoor air 35

46 temperatures operated by WWHP & EC systems are closer to each other. So each of the system maintain moderately comfort in the zone in terms of indoor air temperature. Indoor Temperature in Degree C Zone Indoor Temperature from July 22 to August 08 (15 minutes timestep) 07/22 00:15:00 07/22 07:15:00 07/22 14:15:00 07/22 21:15:00 07/23 04:15:00 07/23 11:15:00 07/23 18:15:00 07/24 01:15:00 07/24 08:15:00 07/24 15:15:00 07/24 22:15:00 07/25 05:15:00 07/25 12:15:00 07/25 19:15:00 07/26 02:15:00 07/26 09:15:00 07/26 16:15:00 07/26 23:15:00 07/27 06:15:00 07/27 13:15:00 07/27 20:15:00 07/28 03:15:00 07/28 10:15:00 07/28 17:15:00 07/29 00:15:00 07/29 07:15:00 07/29 14:15:00 07/29 21:15:00 07/30 04:15:00 07/30 11:15:00 07/30 18:15:00 07/31 01:15:00 07/31 08:15:00 07/31 15:15:00 07/31 22:15:00 08/01 05:15:00 08/01 12:15:00 08/01 19:15:00 08/02 02:15:00 08/02 09:15:00 08/02 16:15:00 08/02 23:15:00 08/03 06:15:00 08/03 13:15:00 08/03 20:15:00 08/04 03:15:00 08/04 10:15:00 08/04 17:15:00 08/05 00:15:00 08/05 07:15:00 08/05 14:15:00 08/05 21:15:00 08/06 04:15:00 08/06 11:15:00 08/06 18:15:00 08/07 01:15:00 08/07 08:15:00 08/07 15:15:00 08/07 22:15:00 08/08 05:15:00 08/08 12:15:00 08/08 19:15:00 Environment:Site Outdoor Air Drybulb Temperature [C](TimeStep) CS:Zone Mean Air Temperature [C](TimeStep) Cooling Set Point WWHP:Zone Mean Air Temperature [C](TimeStep) EC:Zone Mean Air Temperature [C](TimeStep) Figure 19: Comparison of Indoor Air Temperature among All Systems Both heating & cooling equipment is considered throughout the year to simulate the indoor air temperature. Figure 20 shows the indoor air temperature for the systems for whole year. Orange line shows the indoor air temperature by Evaporative cooler with Baseboard electric heater. When indoor temperature goes below lower setpoint then both the system work in heating mode & when indoor temperature goes higher than cooling set point, then both systems work in cooling mode. 36

47 Temperature in Degree C Yearly Indoor Temperature 01/01 01/15 01/29 02/12 02/26 03/12 03/26 04/09 04/23 05/07 05/21 06/04 06/18 07/02 07/16 07/30 08/13 08/27 09/10 09/24 10/08 10/22 11/05 11/19 12/03 12/17 12/31 Date from January 1st to December 31 Environment:Site Outdoor Air Drybulb Temperature [C](Daily) Cooling Setpoint Heating Setpoint Evaporative Cooler with Baseboard electric heater:zone Mean Air Temperature [C](Daily) WWHP :Zone Mean Air Temperature [C](Daily) Figure 20: Comparison of Indoor Air Temperature of WWHP & Evaporative Cooler with Baseboard Electric Heater for Whole Year 4.2 Relative Humidity Figure 211 shows the human comfort in terms relative humidity. The results are analyzed within July 22 to August 08 time period. The blue line represents the environment outdoor air relative humidity percentage. In comparison of RH%, it is shown that evaporative cooler gives the highest indoor RH% because in EC system air takes the moisture from the water to make the air cool & thus increase the humidity percentage in indoor air. For WWHP system RH builds near 80% & electric chiller produces near 75% of relative humidity. If indoor humidity falls below 25% then human does not feel comfortable because of dryness & if indoor humidity goes beyond 65% it also feels uncomfortable for occupants. Human feels most comfortable within the range of (25-65) % RH. From the comparative analysis of WWHP, EC & CS systems, it can be seen that human comfort in terms of humidity best attainable for CS system. For EC system it is the least comfortable because of high indoor humidity. To maintain a good humidity for EC 37

48 system continuous purging of indoor air is necessary so that moisture cannot accumulate in the indoor air. Considering hourly RH% in for a day such as August 03, it shows that during day Comparison of Relative Humidity among All Systems 100 Environment:Site Outdoor Air Relative Humidity [%](Daily) EC:Zone Air Relative Humidity [%](Daily) WWHP:Zone Air Relative Humidity [%](Daily) CS:Zone Air Relative Humidity [%](Daily) Relative humidity in % /22 07/23 07/24 07/25 07/26 07/27 07/28 07/29 07/30 07/31 08/01 08/02 08/03 08/04 08/05 08/06 08/07 08/08 Date from July 22 to August 08 Figure 21: Comparison of Indoor Relative Humidity among All Systems time RH% become lower than night time. So in day time all the systems RH% is lower than night time. For night a dehumidifier can be used for EC system to make the indoor air comfortable for occupants. As direct EC system is considered here so RH% become higher, indirect or two stage EC systems can reduce the RH% to a comfortable region. From the analysis of dependency of indoor air temperature with outdoor temperature & relative humidity, it shows that, CS system does not have much effect on outdoor RH%. Indoor air temperature by CS system gradually changes as the outdoor air changes. But in case of EC system outdoor RH% affect a lot. When the outdoor RH% becomes near 50% (from 08/03 12:00), EC system works better than other systems. The more the difference between dry & wet bulb temperature is raised, the more EC system works better. At that time it makes the indoor air temperature near set point temperature. 38

49 120 Hourly Relative Humidity of All Systems Relative Humudity in % Environment:Site Outdoor Air Relative Humidity [%](Hourly) WWHP:Zone Air Relative Humidity [%](Hourly) EC:Zone Air Relative Humidity [%](Hourly) CS:Zone Air Relative Humidity [%](Hourly) Time in Hour August 03 Figure 22: Comparison of Percentage of Relative Humidity in an Hourly Basis for a Day 4.3 Total Cooling Energy Supplied As the cooling capacity of all the systems were taken similar so cooling energy supplied by all the systems are also pretty close. Figure 23 shows the cooling energy supplied by all the systems in cooling season. Cooling season is assumed to be from May 1 st to September 30th. Within this period cooling energy supplied by CS & WWHP systems are near same, 24.6 & 24.9 GJ. For CS total cooling energy is supplied by the air system cooling coil. From the graph it is shown that cooling energy supplied by WWHP is 14.06% higher than EC system & 7.08% higher than Electric Chiller system. As evaporative cooler cooling supply greatly depends on outdoor humidity, so it s cooling energy supply is little lower than other two systems. 39

50 Total Cooling Energy Supplied in the Cooling Season Cooling Energy Supplied in GJ EC:Zone Air Total Supplied Cooling Energy [GJ] CS:Air System Cooling Coil Total Cooling Energy [GJ] May 1st to September 30th WWHP:RADIANT FLOOR:Zone Radiant HVAC Cooling Energy [GJ] Figure 23: Total Cooling Energy Supplied by All the Systems in Cooling Season Cooling & heating energy supplied for the whole year is also analyzed in this paper. Considering only cooling season & single cooling thermostat control, there was no heating energy supplied by the heat pump. But heating is needed in this cooling season period as the temperature goes below the cooling set point. So, electricity consumption by the WWHP in cooling season is far less than whole year electricity consumption. For whole year simulation both heating & cooling energy is supplied by the system so electricity consumption is higher than cooling season electricity consumption. WWHP yearly electricity consumption 11183KWh & Evaporative cooler with baseboard electric heater yearly electricity consumption is KWh. 4.4 Electricity Consumption Ground source water to water heat pump use ground as a heat source or heat sink. So its main heating or cooling source is coming from renewable sources. But to run the WWHP some electricity is needed. Compressor of the HP consumes the major portion of electric energy of 40

51 WWHP system. Also some portion of electric energy is needed for the water condenser circulating pump to flow the water within the condenser loop & a little electric energy consumes WWHP System Electricity Consumption Per Day Water to Water Heat Pump Electric Energy [KWh] Cooling Water Circulating Pump Electric Energy [KWh] Condenser Circulating Pump Electric Energy [KWh] Figure 24: Water-to-Water Heat Pump Electricity Consumption per Day by the water circulating pump to flow cold or hot water from the WWHP to the radiant floor. Figure 24 shows daily electric energy consumption by ground source WWHP system with radiant floor. It shows compressor of the WWHP is consuming 11.23KWh, water circulating pump 1.08KWh & condenser circulating pump is consuming 2.43KWh of electric energy daily. Evaporative Cooler System Electricity Consumption Per Day Supply Fan Electric Energy [30.85 KWh] Pump Electric Energy [7.2 KWh] 81% 19% Figure 25: Evaporative Cooler System Electricity Consumption per Day Figure 25 shows the electric energy consumption by the evaporative cooler. In EC system also consume less electric energy. Only electric energy consuming parts are the supply fan & pump of the evaporative cooler to circulate the water in the cooler. EC system supply cooling energy 41

52 through the air movement from outside to inside. So, relatively higher amount of fan power is needed than the pump section of the cooler. Figure shows that supply fan consumes 30.85KWh of electric energy daily which 81% of the total electricity consumption by the EC system & pump consume 7.2KWh daily which is 19% of total electric energy consumption. Electric Chiller System Electricity Consumption Per Day Supply fan Electric Energy [9.7 KWh](Daily) 38% 6% Chiller Electric Energy [19.89 KWh](Daily) 11% Cooling Tower Fan Electric Energy [2.97 KWh](Daily) 19% 26% Water Circulating Pump Electric Energy[5. 9 KWh](Daily) Condenser Circulating Pump Electric Energy [13.6 KWh](Daily) Figure 26: Electric Chiller System Electricity Consumption per Day Figure 26 shows daily electric energy consumption by a water cooled electric chiller system with a cooling tower. Number of equipment that consumes electricity consumption is higher in case of this CS system than WWHP & EC systems. For cooling season, total HVAC electricity consumption is the sum of supply fan electricity consumption, chiller electricity consumption, cooling tower, cooling water circulating pump, condenser circulating pump electricity consumption. Highest electricity consuming part is the electric chiller. It is consuming around 38% of electricity among all other sections. Other than main equipment-electric chiller auxiliary equipment such as supply fan consume19%, cooling tower fan consumes 6%, water circulating pump consumes 11% & condenser circulating pump consumes 26% of electricity. Fan efficiency is assumed to be 0.7. If efficiency of the fan can be increased, daily 9.7KWh fan electric energy 42

53 consumption will be reduced. Condenser water circulating pump power consumption is also high. Yet a pump with a little lower rated power consumption might be used without affecting the cooling energy supply to the zone. Total Electricity Consumption from July 22 to August 08 Electric Chiller System(937.4KWh) Water to Water Heat Pump Electric Energy [KWh] WWHP:Cooling Water Circulating Pump Electric Energy [KWh] WWHP:Condenser Circulating Pump Electric Energy [KWh] EC:Supply Fan Electric Energy [ KWh] EC:Pump Electric Energy [ KWh] Evaporative Cooler System( KWh) CS:Supply fan Electric Energy [KWh] CS:Chiller Electric Energy [KWh] Water to Water Heat Pump System(265.2KWh) CS:Cooling Tower Fan Electric Energy [KWh] CS:Water Circulating Pump Electric Energy[ KWh] CS:Condenser Circulating Pump Electric Energy [ KW] Figure 27: Comparison of Total Electricity Consumption of Different parts among Three Systems Figure 27 shows the comparison of total electricity consumption by different parts of all the three systems. This result is analyzed from July 22 to August 08. Within this time period CS system consuming total 937.4KWh, evaporative cooler system consuming KWh & ground source heat pump system consuming only 265.2KWh of electrical energy. From the graph it is found that water cooled electric chiller with cooling tower system consumes highest electric energy among all the systems. In terms of electricity consumption GSHP system is the best among all other three systems. So required electricity consumption is a great demerit for water cooled electric chiller. WWHP is also better than EC system in this regard. 43

54 Total Electricity Consumption in Cooling Season (KWh) WWHP:Total HVAC Electricity Consumption [KWh] EC:Total HVAC Electricity Consumption [KWh] CS:Total HVAC Electricity Consumption [KWh] Figure 28: Total Electricity Consumption by three Systems in Cooling Season Figure 28 present total electricity consumption in KWh for all the systems in whole cooling season. For total cooling season electric energy consumption by the WWHP system is 2378KWh, by EC system 4778KWh. Evaporative cooler system electricity consumption is almost doubles than WWHP consumption. Electric chiller consumes 9228 KWh, which is the highest electricity consumption among all the three systems 4.5 Daily Energy Efficiency Ratio (EER) Energy Efficiency Ratio is a parameter for evaluating cooling efficiency of a HVAC system. Energy efficiency ratio (EER) for all systems is calculated from the E+ modeling & simulation result. In the Figure 29 EER of three systems are shown from July 22 to August 08 on a daily basis. It can be seen that EER of EC & CS system are near similar. On an average EER for CS system is 3.36 BTU/Watt-hr, for EC system it is near 3.44 BTU/Watt-hr & for WWHP system it 44

55 Comparison of Daily Energy Efficiency Ratio (EER) EER in BTU/Watt-hr Electric Chiller EER Evaporative Cooler EER WWHP EER Figure 29: Comparison of Energy Efficiency Ratio in BTU/Watt-hr among All Systems is BTU/Watt-hr. So, in terms of EER, ground source heat pump system is the most efficient. From the figure it can be seen that EER varies for different days. EER for WWHP is the highest for WWHP in July 31 and in contrary EER for EC & CS systems is the lowest on that particular day. It can be explained from the Figure 31 & Figure 31. EER for 2 Systems EER (BTU/Watt-hr) Changing With Outdoor Dry Bulb Temperature 07/22 07/23 07/24 07/25 07/26 07/27 07/28 07/29 07/30 07/31 08/01 08/02 08/03 08/04 08/05 08/06 08/07 08/08 Evaporative Cooler EER WWHP EER Outdoor Dry Bulb Temperature in Degree C Figure 30: EER Changing with Outdoor Dry Bulb Temperature Figure 30 shows effect of outdoor dry bulb temperature on EER of WWHP & EC system. The green & red bar represents the EER for WWHP & WC system respectively. The 45

56 purple line presents the outdoor dry bulb temperature in degree Celsius. It shows that when outdoor drybulb temperature is the lowest then WWHP EER is the highest but EER is the lowest on that day. Because low dry bulb temperature represents minor difference between dry bulb & wet bulb temperature. That is percentage of outdoor relative humidity is higher in that time. Figure 31 shows the relation between EER of WWHP & EC system with outdoor RH%. Figure shows the lowest dry bulb temperature in July 31 & from Figure 31 it can be seen that outdoor RH% is the highest on July 31. As the humidity is higher on that day, so EC system performs worse on that day. EER is the lowest comparison to other days. But WWHP EER is the highest because of WWHP does not need to consume so much power to supply the same cooling energy. EER (BTU/Watt-hr) Changing With Outdoor Relative Humidity EER for 2 Syatems /22 Outdoor RH % 07/23 07/24 07/25 07/26 07/27 07/28 07/29 07/30 07/31 08/01 08/02 08/03 08/04 08/05 08/06 08/07 08/08 Evaporative Cooler EER WWHP EER Outdoor Air Relative Humidity [%] Figure 31: EER Changing with Outdoor Relative Humidity Seasonal Energy efficiency Ratio (SEER). From the total cooling season energy analysis SEER is calculated for all the systems. Figure 32 shows the SEER in BTU/Watt-hr for all the three systems for cooling season. Dividing by the total cooling energy supply to the total electricity consumption through the cooling season, SEER value has been calculated. Evaluated value of SEER shows that it is highest for WWHP than EC & CS systems. That means to supply 46

57 same amount of cooling energy WWHP is consuming the minimum primary energy. The higher the SEER value the higher the system efficiency. For ground source WWHP system SEER value is 9.94 BTU/Watt-hr, for EC system SEER is 4.25 BTU/Watt-hr & for CS system SEER is 2.52 BTU/Watt-hr. Seasonal Energy Efficiency Ratio in BTU/Watt-hr Electric Chiller SEER (2.52) Evaporative Cooler SEER (4.25) WWHP SEER (9.9) Figure 32: Comparison of Seasonal Energy Efficiency Ratio among All Systems 4.6 Energy Savings Extent of energy savings can be estimated from the seasonal energy efficiency ratio of different systems. Percentage of energy saving from WWHP system with respect to electric chiller system is 74%. & with respect to EC system energy saving is 57%. Thus WWHP system is consuming 74% & 57% less energy than CS & EC system respectively. So, in cooling season ground can be used as a heat sink or source of cooling, which will provide a great energy saving prospect. 47

58 Table 17: Energy Savings Percentage from Water-to-Water Heat Pump Percentage of energy saving from WWHP system In compare to Evaporative Cooler System In compare to Electric Chiller System 57% 74% 4.7 COP of WWHP Though evaporative cooler & electrical chiller with cooling tower work for only cooling season, heat pump can works in both cooling & heating season. HP performance for cooling season is evaluated by Seasonal energy efficiency ratio (SEER). It was found better than other two systems. For heating season the energy efficiency of heat pump can be measured as the coefficient of performance (COP). COP is the ratio of heating energy supplied by the heat pump to the electricity consumption. It is the measure of energy output by energy input. For WWHP the COP is calculated for heating season. COP = Q/W. Here, Q is the provided heating energy (W) Instantaneous COP for WWHP in January 1st Time in Hour 01/01 24:00:00 01/01 23:00:00 01/01 22:00:00 01/01 21:00:00 01/01 20:00:00 01/01 19:00:00 01/01 18:00:00 01/01 17:00:00 COP Value Figure 33: COP Value of WWHP in January 1st 48

59 as radiant heating & W is the electric energy (W) consumption by the ground source heat pump. Figure 33 shows the COP for WWHP. Dividing radiant heating power supply (in Watt) by electric power consumption (in Watt) the COP is calculated. Data is analyzed for January 1 st from 5pm to 12pm. From the graph it can be seen that COP ranges from 9 to 19. So, ground source WWHP also performs better in heating mode. In case of baseboard electric heater this higher COP value is not attainable. The data is taken instantaneously so, it may be called instantaneous COP. 4.8 Required Water Volume To supply cooling energy from the water cooled electric chiller constant cold water supply is necessary for the condenser section of the chiller. Refrigerant of the electric chiller become condensed by rejecting heat to this cold water. Cooling tower supplies this cold water. Simulation result shows that initial required water volume for the cooling tower is 106 m 3 and it needs around 6 m 3 make up water per day. In the day time, required water volume is larger due to the higher outdoor temperature. The Figure 34 shows the relation between required water volumes for the cooling tower with the outdoor air temperature. Data are analyzed from July 22 to August 08. Figure shows that required water volume changes as the outdoor air temperature changes. As normally C is considered as a condenser water temperature to design a watercooled chiller. In this model cooling tower is the condenser, so condenser inlet temperature is assumed as 29.4 C. Using this temperature as a design condenser inlet water temperature, CS system is supplying required cooling energy to the zone. But as the inlet temperature of the 49

60 cooling tower is high, to supply enough cooling water to the chiller required makeup water volume Required Make Up Water for Cooling Tower Required Make Up Water Cooling Tower Make Up Water Volume [m3](daily) Outdoor Air Temperature [C](Daily) 07/22 07/23 07/24 07/25 07/26 07/27 07/28 07/29 07/30 07/31 08/01 08/02 08/03 08/04 08/05 08/06 08/07 08/ Outdoor Air Temperature Figure 34: Required Daily Make Up Water for Cooling Towe for the cooling tower becomes high. If condenser water inlet temperature is reduced from 29.4 C to C, then from the Figure 35 it can be seen that required daily makeup water volume will be reduced but, then indoor air temperature will not be maintained within the set point. So by optimization, this amount of makeup water is required daily to get proper cooling energy. Figure 35 shows CS systems Indoor air temperature dependency on required daily makeup water volume. In Figure 35 right side vertical axis signify the required makeup water volume in m 3 and left vertical axis represent indoor air temperature in degree C, analysis shows that, reduction of makeup water volume also reduce the indoor air temperature comfort. For EC system water is circulated through the cooler & warm air takes moisture from water & become cold air. So continuously supply of water is required for evaporative cooling operation. From the simulated results required water volume for this EC system is evaluated. Water consumption for EC system is m 3 /hr. Consumed water is divided into two segments; 50

61 Relation between Cooling Tower Inlet Temperature & Make up Water Volume Indoor Air Temperature in Degree C /22 07/23 07/24 07/25 07/26 07/27 07/28 07/29 07/30 07/31 08/01 08/02 08/03 08/04 08/05 08/06 08/07 08/08 Axis Title MakeUp Water Volume in M Condenser Inlet tempearture CS:Zone Mean Air Temperature [C](Daily) 29.4 Condenser Inlet temperature CS:Zone Mean Air Temperature [C](Daily) Condenser Inlet Water Temperature:Cooling Tower Make Up Water Volume [m3](daily) 29.4 Condenser Inlet Water Temperature:Cooling Tower Make Up Water Volume [m3](daily) Figure 35: Relation Between Cooling Tower Inlet Temperature & Make up Water Volume evaporation & drain of water. As simply the uncontaminated water evaporates so other solid minerals portion of the water remains in the water. If these minerals portion accumulated Required Water Volume for Evaporative Cooler Required Water Volume Outdoor Air Temperature /22 07/23 07/24 07/25 07/26 07/27 07/28 07/29 07/30 07/31 08/01 08/02 08/03 08/04 08/05 08/06 08/07 08/08 Evaporative Cooler Water Volume [m3](daily) Outdoor Air Temperature [C](Daily) 24 Figure 36: Required Daily Water Volume for Evaporative Cooler 51

62 day by day, it will damage the pad & also decrease the efficiency of the EC performance. So water should be drained to keep it clean enough for evaporation. Also sometime if the water is hard enough that damages the pad, so it desires to be softened. Evaporative Cooler Water Volume (m 3 /Day) Electric Chiller: Cooling Tower Make Up Water Volume (m 3 /Day) Life Cycle Cost Analysis Economic analysis is a crucial factor for the comparison of different HVAC system. In this paper comparison of different systems are evaluated in terms of life cycle cost analysis. In the methodology chapter LCC analysis process for all the systems is shown. Installation cost analysis shows that ground source water to water heat cost the maximum to install. Figure 37 shows percentage analysis of different segments installation cost for the ground source water to water heat pump. It indicates that, rather than heat pump purchasing cost borehole drilling & construction of radiant floor also consume much amount of installation cost. Installation cost for other two systems is lower than GSHP. For the LCC analysis installation, operation & maintenance cost has been taken into consideration. 52

63 Ground Source Heat Pump Installation Cost WW Heat Pump purchase with installation 31% 6 borehole drilling with 68 m depth 20% Vertical ground heat exchanger made of Polyethylene pipe with construction 10% Circulating Pump for water flow 1% Pipes, fittings & valves 7% Radiant floor construction with hydronic tube 24% Grouting material 7% Figure 37: Ground Source Heat Pump Installation Cost Operational cost Operational cost for all the systems are calculated from the output value of the simulation result. Annual electricity consumption is analyzed & multiplying by the electricity rate operational cost has been calculated. For WWHP system, electricity cost is the only operational cost but for EC & Operation & Maintenance Cost Per Year 1000 Cost in $/Yr Maintenance Cost Water Cost 0 WWHP System Evaporative Cooler System Electric chiller System Electricity Cost Figure 38: Comparison of Operation & Maintenance Cost among All Systems per Year 53

64 CS system water consumption cost is added with the electricity cost as an operational cost. assuming electricity rate as $/KWh the annual electricity cost is calculated for all systems. FromFigure 38 shows the comparison of annual operational & maintenance cost among the three systems. As the electricity consumption is the highest for CS system so annual electricity cost is also highest for CS system. Operational cost for electricity is the lowest for WWHP system. For calculating water consumption cost by the EC & CS system assuming $2 cost for 740 gallons of water. Simulation result shows water consumption by EC system annually is gallons, which will cost like $47 annually & for CS system annual water consumption cost will be $641. As the WWHP has a higher EER value so, with a little operating cost higher amount of cooling or heating energy can be obtained from this system. Maintenance cost-- In case of EC system the PAD can last up to 3 to 5 years. Without proper maintenance this can be damaged early. So, maintenance cost is higher for EC system than WWHP system. Electric chiller also needs proper maintenance. So, maintenance cost of three systems is calculated assuming it lower for WWHP than other two systems. Because of the ground as a heat source or sink it remains stable so maintenance cost is lower for WWHP system. Life Cycle Cost Analysis for only cooling equipment considering only cooling season- 30 years is assumed as a life cycle for each of the system. Installation cost of each of the system is converted into net present value (NPV) assuming 5% discount rate for the 30 years life span Then operation & maintenance cost for thirty years is calculated & converted into NPV. By adding the NPV of installation cost and O & M cost LCC has been calculated. Figure 39 shows the LCC for all systems for 30 years period (neglecting maintenance cost). Here incentives for renewable sources are not considered. Figure 39 shows that LCC is the highest for conventional 54

65 electric chiller system in all systems. Without considering incentives EC system LCC is little higher than WWHP systems LCC. Life Cycle Cost Analysis (30 Years) Without Incentives LCC of Electric chiller LCC of Evaporative Cooler LCC of WWHP Operation & Maintenance Cost LCC of WWHP LCC of Evaporative Cooler LCC of Electric chiller Initial Cost Figure 39: Comparison of Life Cycle Cost without Incentives Cooling capacity of direct EC is increased with the increase of air mass flow rate. But then fan power will also increase & EC electricity consumption will increase as well. As a result EC O & M cost will increase, thus LCC will also increase. On the other hand if WWHP cooling capacity is increase, that O & M cost will not be increased that much. Considering incentives for using renewable energy Figure 40 shows that LCC for WWHP is largely reduced than EC Life cycle cost. 55

66 Life Cycle Cost Analysis (30 Years) With Incentives LCC of Electric chiller LCC of Evaporative Cooler LCC of WWHP Operation & Maintenance Cost with Rebate LCC of WWHP LCC of Evaporative Cooler LCC of Electric chiller Initial Cost with Tax Credit Figure 40: Comparison of Life Cycle Cost with Incentives LCC analysis for whole year considering both heating & cooling also evaluated in this paper. Life cycle cost analysis for the whole year is analyzed here Figure 41. For ground source WWHP there is no other additional heating equipment is needed. WWHP itself supplies heating & cooling energy to the zone throughout the year. The systems are working in dual thermostat controlling mode. In case of evaporative cooler to supply heating a baseboard electric heater is added with the evaporative cooler system. EC system is providing cooling energy & baseboard heater is providing heating energy to the zone as needed. Thermostat controlling mode is dual set point. Heating & cooling is happening as needed. From the EC system with baseboard system electric energy needed for heating supply is calculated by subtracting required electric power from total electric power needed. That amount of electric power required for heating supply is added with the electric chiller system & assumed that this much amount will be needed for heating supply. 56

67 Life Cycle Cost Analysis (30 Years) Without Incentives LCC of Electric chiller LCC of Evaporative Cooler LCC of WWHP LCC of WWHP LCC of Evaporative Cooler LCC of Electric chiller Operation& Maintenance Cost Initial Cost Figure 41: Comparison of Life Cycle cost Analysis among All Systems Considering both Heating & Cooling for Whole Year Figure 41 shows the life cycle cost analysis of ground source heat pump, Evaporative cooler with baseboard electric heater & electric chiller with baseboard electric heater. Whole year operational cost is considered here. Without considering incentives LCC by WWHP is near equal to evaporative cooler with baseboard electric heater LCC cost. Figure 42 shows the LCC analysis of three systems considering the incentives. Considering incentives WWHP cost is lower than two other systems. 57

68 Life Cycle Cost Analysis (30 Years) With Incentives LCC of Electric chiller LCC of Evaporative Cooler LCC of WWHP Operation & Maintenance Cost with Rebate LCC of WWHP LCC of Evaporative Cooler LCC of Electric chiller Initial Cost with Tax Credit Figure 42: Comparison of Life Cycle cost Analysis among All Systems Considering both Heating & Cooling for Whole Year with Incentives Environmental Impact As the GSHP consuming less electricity so it produces less greenhouse gas other than two systems. 58