CHAPTER 2 Energy Fundamentals for Energy Auditors

Transcription

1 CHAPTER 2 Energy Fundamentals for Energy Auditors

2 What is Energy? 2

3 Energy Lets Us Do Work Energy is the ability to do work. As such, energy is important to all living things in order to maintain life functions from the smallest part of a cell to the organism as a whole. Humans also use energy to modify their environment and perform work. Energy is measured by the amount of work it is able to do. The units for measuring energy are Joules (J). One Joule is a very small amount of energy, but 1000 Joules is roughly the heat energy produced by burning a blue tip kitchen match. 3

4 Sources of Our Energy The energy sources that we use every day are divided into two groups: Renewable an energy source that we can use over and over again, and can be replaced naturally in a short period of time. Non-renewable an energy source that we are using up and cannot recreate in a short period of time. 4

5 Sources of Our Energy The renewable energy sources include solar energy, which comes from the sun and can be turned into electricity and heat. Wind, geothermal energy from inside the earth, biomass from plants, and hydropower from water are also renewable energy sources. 5

6 What Is Power? Work can be done at different rates, sometimes slow, sometimes fast. Since work involves the transformation of energy, the faster the work is done, the quicker energy must be transformed. Power is the term used for the measure of how fast work can be done. Or in other terms, power is defined as the rate at which work is done. 6

7 What Is Power? In mathematical terms power equals work done divided by time required, so the units of power would be Joules per unit time, most commonly Joules per second, or watts: Work Done Power = Time Required Power is an important concept because it ties the dimension of time into the energy picture. 7

8 Almost all mechanical and electrical equipment have nameplate ratings in terms of the maximum power that they can supply, not the energy they can supply. As we will see later, almost all mechanical devices like motors are rated in terms of their maximum power output, while almost all purely electrical devices are rated in terms of their maximum power input. 8

9 Energy and power are often confused with each other. A useful analogy can be found in our car where we have both the speedometer that tells us how fast we are going in kmph, and we also have an odometer which tells us how far we ve gone in km. KMPH 9

10 The odometer is like an energy meter that tells us the total amount of energy in Joules that we ve used. The speedometer is like a power meter that tells us the rate at which we have used that amount of energy in Joules per second, or watts. KMPH With our car, the quantities of interest are km and kmph. With our electrical and mechanical equipment, the quantities of interest are Joules and Joules per second, or watts. 10

11 Electrical Power When dealing with electricity, power is defined in the same way. Electrical devices provide resistance which describes the amount of work that needs to be done for a specific task. A certain amount of work must be done to move electrons through the resistance. More resistance means more work must be done to move electrons through the resistance and allow the device to operate. 11

12 Electrical Power The rate which that work is accomplished is related to the power applied. More electrical power means energy is being converted at a faster rate. This electrical energy is supplied by the source of the electrical current like a battery or electrical generator. 1 watt = 1 Joule/second Electrical power is measured in units called watts, which are related to the number of Joules of energy expended per second. 12

13 This means the energy can be expended at different rates depending on how fast the work needs to be done. Some devices use more power to accomplish a task that others do with much less power. For example light bulbs come in different sizes meaning different wattages. Some light bulbs are rated 60 watts while others are rated 100 watts. The 100 watt bulb will give off more light than the 60 watt bulb but if you only need the amount of light from the 60 watt light bulb, you are using more power than necessary. 13

14 Units of Electrical Energy The watt (W) is a physical unit which is named for James Watt, the inventor of the steam engine. Since the unit refers to a person s name, we abbreviate it with a capital W. The basic unit of electrical energy is the watt-hour, or Wh. 1 Wh = 3600 Joules 1 kwh = 1000 Wh = Joules = 3.6 MJ 1 MWh = 1000 kwh 1 GWh = 1000 MWh 1 kw = 1000 W 1 MW = 1000 kw 14

15 One barrel of oil produces about 550 kwh in a thermal power plant 15

16 One kg of coal produces about 2 kwh 16

17 degrees Celsius Energy Units And Energy Conversions minutes 17

18 Energy Units And Energy Conversions The basic unit of energy is the Joule (J) One thousand Joules is about equal to the heat produced by burning an ordinary blue-tip, kitchen match. One Joule is not a very large amount of energy, so you will often see one of two common multipliers of Joules; the kj, or one thousand Joules; or the MJ, which is 1000 kj, or one million Joules. For even larger amounts of energy, the GJ = 1000 MJ. 18

19 Word and Numerical Equivalents One J = 1 J. One thousand J = 1000 J = 10 3 J = 1 kj One million J= 1,000,000 J = 10 6 J = 1 MJ One billion J = 1,000,000,000 = 10 9 J = 1 GJ 19

20 Energy Conversion Unit Table 1 kwh MJ 1 m 3 LPG GJ 1 kg #2 fuel oil MJ 1 m 3 natural gas.. 37 MJ 1 m 3 #2 fuel oil GJ 1 litre LPG gas kwh 1 kg LPG gas kwh 1 litre #2 fuel oil kwh 1 kg #2 fuel oil kwh 20

21 Energy Unit Conversions and the Railroad Track Method Since we have several different basic energy units and many different energy unit multipliers, energy managers must often convert from one set of energy units to another. There is a very systematic approach that can be applied to basic conversions, and also to more complex conversions and calculations. The principle of this unit conversion method is simply to carry out algebraically correct multiplications and divisions using correct units at each step, starting with the given piece of information and transforming it into the desired units using one or more conversion factors. 21

22 For example, if we want to find the number (X) of Joules in 1000 cubic metres of natural gas, we can use this method as follows: X GJ of gas 1000 = 1000 = m m 3 3 m 3 37,000 kj m 3 37,000 kj From Table C-20 = ,000 kj = 37,000,000 kj = J = 37 GJ 22

23 In the above calculation, cubic metres in the numerator and cubic metres in the denominator cancel out, and the remaining unit on the right side of the equation is J. Our goal was to end up with J as our desired unit on the right, and we made our unit conversions on the right side until we had the same unit as on the left side. 23

24 If we ever perform one of these basic unit conversion calculations, and find that we have different units on the left and the right we do not have the correct answer in terms of the desired units. This method is given the colloquial name Railroad Track Method, because the vertical separation lines remind us of railroad tracks. 24

25 Example Problem Find the number (X) of kwh in 1000 cubic metres of natural gas. X kwh of 1000 gas = 1000 = m 3 m m ,000 kj 3 m 37,000 kj kj 1 kwh 3600 kj 1 kwh 3600 From Table C-20 = ,000 kwh/3600 = 10,278 kwh 25

26 Example Problem How many J are in 10 kwh? Solution X J = 10 kwh 3.6 MJ kwh = 36 MJ In this example, the two kwh units cancel out, leaving the remaining unit on the right side as J. 26

27 Example Problem How many kwh are in 2500 mj? Solution: X kwh = 2500 = MJ kwh 3.6 kwh MJ In this example, the two MJ units cancel out, leaving the remaining unit on the right side as kwh. 27

28 Example Problem A tank is filled with 100 litres of Number 2 fuel oil. How many GJ of energy is contained in the tank of oil? Solution From Table C-20, there are 39 MJ per litre of oil. 100 L 39 MJ 1 GJ X GJ = 1 L 1000 MJ = 3.9 GJ In this example, the two litre units cancel out, and the two MJ units cancel out, leaving the remaining unit on the right side as GJ, our desired unit. 28

29 Example Problem A tank is filled with 100 litres of Number 2 fuel oil. How many kwh of energy is contained in the tank of oil? Solution From Table C-20, there are 39 MJ per litre of oil. X 100 kwh = L 39 1 MJ L 1 kwh 3.6 MJ = kwh In this example, the two litre units cancel out, and the two MJ units cancel out, leaving the remaining unit on the right side as kwh, our desired unit. 29

30 Benchmarking A benchmark is a value you compare something against. 30

31 Energy Benchmarking for Buildings Building energy benchmarking is the comparison of whole-building energy use relative to a set of similar buildings. It provides a useful starting point for individual energy audits and for targeting buildings for energy-saving measures in multiple-site audits. Benchmarking is of interest and practical use to a number of groups. Energy service companies and performance contractors communicate energy savings potential with typical and best-practice benchmarks. 31

32 Control companies and utilities can provide direct tracking of energy use and combine data from multiple buildings for benchmarking. Benchmarking is also useful in the design stage of a new building or retrofit to determine if a design is relatively efficient. Energy managers and building owners have an ongoing interest in comparing energy performance to others. Large corporations, schools, and government agencies with numerous facilities also use benchmarking methods to compare their buildings to each other. 32

33 Benchmarking Audit Benchmarking Audits are associated with the idea that after the energy bill data is collected and processed, some facility information will be collected on a walkthrough, and the data will be run through some benchmark to determine if there is a potential for significant improvement in energy efficiency and reduction in energy operating cost. 33

34 Benchmarking Criteria Energy Use Index -MJ/m 2 /year, kwh/m 2 /year Total, Electric, Gas, Oil Energy Cost Index -$/m 2 /year Total, Electric, Gas, Oil Productivity Index kj/kg, kj/person, kj/student, kj/tonne, kj/item kwh/kg, kwh/person/ kwh/tonne, kwh/item L H 2 O/kg, or /student, or /item (also sewer) System performances kwe/kw cooling, LPS/kW air, kwh/l pumping 34

35 Basic Energy Accounting Basic energy accounting deals with the following ideas: Recognizing different energy and fuel types Electricity, gas, light oil, steam, chilled water Understanding energy related units kwh, kj, MJ, kw, kj/h, L or kg of oil, m 3 of gas Performing conversions to different energy related units For example, 1 kwh = 3600 kj = 3.6 MJ 35

36 The Facility Energy Use Index The facility Energy Use Index (EUI) is a statement of the number of MJs (or kwh) of energy used annually per square metre of conditioned space (heated or cooled, or both). It is a basic measure of the facility s energy performance the lower, the better. To compute a facility s EUI Identify all the energy used in the facility Add up all the MJs (or kwh) of energy Find the total square metres of conditioned space Divide the total MJ (or kwh) used per year by the square metres of space. 36

37 Example A facility with 1,000 square metres of conditioned space uses 100 GJ of gas and 150,000 kwh of electrical energy in one year. What is the facility s EUI? 37

38 Solution (in MJ/m 2 yr) MJ gas = 100 GJ yr 1000 MJ GJ = 100,000 MJ / yr MJ elect = 150,000 yr kwh 3.6 MJ kwh = 540,000 MJ / yr EUI = (100, ,000) 1,000 m 2 yr MJ = 640 MJ / m 2 yr 38

39 Solution (in kwh/m 2 yr) EUI = 640 MJ m 2 = yr 1 kwh 3.6 MJ kwh / m 2 yr 39

40 1999 CBECS EUI Data - USA kwh/m 2 /yr All Bldgs 236 Education 208 Vacant 44.5 Food Sales 561 Food Service 669 Health Care 490 Lodging 278 Retail Stores 200 Office 251 Assembly 228 Safety 242 Churches 88.9 Service 346 Warehouse 122 Other

41 Energy Use Index for Commercial Buildings kwh/sq metre/yr All Bldgs Education Food Sales Food Serv Health Lodging Retail Office Assembly Safety Churches Service Warehouse Other Vacant