Energy from the Earth. Geothermal Two very different methods Tides, waves, currents. Unit 12 Energy from the earth - Slide 1

Size: px
Start display at page:

Download "Energy from the Earth. Geothermal Two very different methods Tides, waves, currents. Unit 12 Energy from the earth - Slide 1"

Transcription

1 Energy from the Earth Geothermal Two very different methods Tides, waves, currents Unit 12 Energy from the earth - Slide 1

2 Remember efficiency e = What you want out What you had to put in Electrical energy out Thermal electrical energy in = Q H - Q c Q H < T H - T c T H Unit 12 Energy from the earth - Slide 2

3 Geothermal Energy Open Loop Wet System Unit 12 Energy from the earth - Slide 3

4 Example 12.1: Geothermal efficiency Let s assume a small geothermal plant receives steam from underground at 350 o F and returns it below at 120 o F. What is the maximum possible efficiency of the plant? How does this compare to a coal plant which gets steam at around 1000 o F and exhaust it at around 80 o F? Unit 12 Energy from the earth - Slide 4

5 Problems with geothermal Small temperature difference makes plants inefficient (but it s free energy?) Open Loop system can release gas that were mixed in water CO2, sulfur dioxide Open Loop system returned is not a great as removed. Ground can subside Open Loop or dry system injected water can cause small earth quake Closed Loop system complex and expensive Unit 12 Energy from the earth - Slide 5

6 Thermodynamic Engine Gas burns in your engine High Temperature Reservoir Engine Work Exhausted out your tailpipe Low Temperature Reservoir Unit 12 Energy from the earth - Slide 6

7 Air Conditioner Outside your House High Temperature Reservoir Air Conditioner Work Inside your House Low Temperature Reservoir Unit 12 Energy from the earth - Slide 7

8 Heat Pump Inside your House High Temperature Reservoir Heat Pump Work Outside your House Low Temperature Reservoir Unit 12 Energy from the earth - Slide 8

9 Coefficient of Performance (COP) e = COP = What you want out What you had to put in Heat into your home Work from electrical energy COP = Q H Q H - Q c < T H T H - T c Unit 12 Energy from the earth - Slide 9

10 Summer (90 o F) Cool Warm Energy (Heat) Window AC unit Unit 12 Energy from the earth - Slide 10

11 But what about Winter (25 o F)? Warm Cool Energy (Heat) Flip unit around Unit 12 Energy from the earth - Slide 11

12 Example 12.2: Heat Pump Limit Let s you have a heat pump in your home in Atlanta. The average cold temperature is 34 o F and you keep your house at 75 o F. Assume your heatpump works at 20% of its maximum theoretical efficiency and get s it energy from 35% efficient generating plant. Which uses more energy, your heat pump or an 85% efficient gas furnace? Unit 12 Energy from the earth - Slide 12

13 Example 12.3: Heat Pump Limit Let s you have a heat pump in your home in Chicago. The cold temperature is 0 o F and you keep your house at 75 o F. Assume your heatpump works at 20% of its maximum theoretical efficiency and get s it energy from 35% efficient generating plant. Which uses more energy, your heat pump or an 85% efficient gas furnace? Unit 12 Energy from the earth - Slide 13

14 But a Chicago Winter (0 o F!!!)?!! Warm Cold Energy (Heat) 47 o F Ground Water Unit 12 Energy from the earth - Slide 14

15 Details HEAT PUMP GROUND LOOPS 4 ton (TR) 1 Water Furnace Heat Pump Two stage compressor and fan Auxiliary Backup Heating Coils Ground loop is closed (no water extracted) ~100 feet of moist contact per to of capacity Loops may be vertical or horizontal 1 1 ton refrigeration (TR)= 12000BTU/hr = 3517W ~ energy to cool 1 ton of water 1 o F in 10 minutes Unit 12 Energy from the earth - Slide 15

16 Use the waste heat HEAT PUMP 4 ton (TR) 1 Water Furnace Heat Pump Two stage compressor and fan Auxiliary Backup Heating Coils Waste heat can Heat hot water tank Ground loop is closed (no water extracted) ~100 feet of moist contact per to of capacity Loops may be vertical or horizontal 1 1 ton refrigeration (TR)= 12000BTU/hr = 3517W ~ energy to cool 1 ton of water 1 o F in 10 minutes Unit 12 Energy from the earth - Slide 16

17 Example 12.5: Ground source Heat Pump Let s you have a heat pump in your home in Chicago. You keep your house at 75 o F and you get your heat from 60 o F ground water. Assume your heatpump works at 20% of its maximum theoretical efficiency and get s it energy from 35% efficient generating plant. Which uses more energy, your heat pump or an 85% efficient gas furnace? Unit 12 Energy from the earth - Slide 17

18 Key points A geo-thermal heat pump does not heat your home by drawing energy from the earth s core (e.g. maga) Better term is a ground source heat pump A geo-thermal heat pump does not cool your home by blowing air across cool water from the ground. Electrical Energy Heating COOP ~5 for GSHP (~0.9 for furnace) Cooling COOP ~9 for GSHP (~4.5 for normal AC) Unit 12 Energy from the earth - Slide 18

19 Drawbacks Problem #1: Complex system Problem #2: Space for loop field Okay if new construction Problem #3: Cold heat Air is 83 o F from vents Unit 12 Energy from the earth - Slide 19

20 Electricity Use (kilowatt-hr) Changes Peak Period Monthly Electricity Use (kwh) Annual Totals : 6850 kwh kwh oct n dec jan f march april may jun e july aug sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Unit 12 Energy from the earth - Slide 20

21 Total Energy Use (GJoule) But saves energy Annual Totals : 162Gj Gj oct n dec jan f march april may jun e july aug sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep 1 108MJ/CCF Nat Gas; 3.6MJ/kWh Elec Unit 12 Energy from the earth - Slide 21

22 CO2 Produced (lbs) Cuts back CO 2 output 3500 Annual Totals : lb lb oct n dec jan f march april may jun e july aug sep Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep 1 12lb CO2/CCF Nat Gas, 1.2lb CO2/kWh Elec Unit 12 Energy from the earth - Slide 22

23 But energy is just too cheap. Monthly Energy Cost ($) Annual Totals : $ $1390 Oct Nov Dec Jan Feb Mar Apr May Jun Jul Aug Sep Unit 12 Energy from the earth - Slide 23

24 Energy from tides Similar to hydro-electric dam Turns potential energy from difference in heights into electrical energy Needs large height difference to be effective Bay of Fondy 50feet! Environmental effects of blocking off bay? Largest is Sihwa Lake Tidal Power Station in Korea (254MW) Unit 12 Energy from the earth - Slide 24

25 Energy from waves and currents Still in the testing stages Largest wave farm is Agucadoura Wave Farm off Portugal. 2.25MW No existing power from ocean current although some are planned (Gulf Stream?) Very rough environment for equipment How to get power to the shore? Effect on environment? Unit 12 Energy from the earth - Slide 25

26 My Summary thoughts Geothermal from earth good for heating home in certain places Small power generation in certain places Possible environmental impacts Ground source heat pumps Proven to save power Electricity and gas are too cheap to have most people bother Shift in power consumption patterns Unit 12 Energy from the earth - Slide 26

27 My Summary thoughts Power from Tides Moderate amounts of power at certain positions. Possible environmental impacts Power from Current and waves Still in testing stages. Largest system ~ size of one wind turbine. Tough environment for equipment Possible environmental impacts Unit 12 Energy from the earth - Slide 27