HeatingCooling Systems, Wind

1
ECE 333 (398RES)Renewable Energy Systems

• Lecture 17
• Heating/Cooling Systems, Wind
• Professor Tom Overbye
• Department of Electrical andComputer Engineering

2
Announcements

• Read Chapter 6
• Homework 7 is due now.
• Homework 8 is 5.14, 5.15, 5.16, 6.1, 6.2
• Wind farm field trip April 7 or 9 (still working
  on finalizing the date) to Grand Ridge Wind
  Energy Center in Ransom, IL

3
Cooling, Heating, and Cogeneration

• P/H (power-to-heat) ratio of buildings varies
  greatly, and we want to smooth it out
• Heat Pumps - Use electricity instead of heat in
  the winter
• Absorption Cooling - Use heat instead of
  electricity in the summer
• Cooling is a large part of the load, so it is
  important to consider

4
Vapor-Compression Refrigeration

• Challenge - absorb heat from cool environment and
  reject it to a warm environment
• Take advantage of the fact that highly compressed
  fluids will get colder when they expand

Low pressure vapor
High pressure vapor
50F
50F
95F
120F
Evaporator Coil
Condenser Coil
Compressor
100F
38F
45F
Expansion Valve
85F
Low pressure vapor/liquid
High pressure liquid
Figure 5. 12
5
Vapor-Compression Refrigeration

• Compressor refrigerant enters as low pressure,
  exits high
• Condenser cools and condenses from gas to
  liquid
• Expansion Valve pressure decreases
• Evaporator

Low pressure vapor
High pressure vapor
50F
50F
95F
120F
Evaporator Coil
Condenser Coil
Compressor
100F
38F
45F
Expansion Valve
85F
Low pressure vapor/liquid
High pressure liquid
Figure 5. 12
6
Refrigeration Cycle Coefficient of Performance
(COPR)

• A measure of refrigeration cycle efficiency
• QL heat extracted from refrigerated space
• W work put into compressor
• Dimensionless - QL and W must have the same units
• Tells how many units of heat are removed for each
  unit of energy consumed by the A/C
• Want this to be high- if it is low, you need more
  electrical input to provide the desired heat
  output

7
Energy Efficiency Rating (EER)

• Another way to express refrigeration cycle
  efficiency
• Typical EER for A/Cs is 9 to 17 Btu/W-hr (at 95?
  F)
• Related to COPR by
• Seasonal Energy Efficiency (SEER) an average
  rating over the course of the heating season.
  Above 13 is one requirement

8
One ton of cooling

• The rate heat is absorbed when a 1 ton block of
  ice melts
• Another efficiency measure tons/kW of cooling
• A 3-ton home-sized A/C uses approximately 2-3kW
• Chillers can make ice at night to melt during the
  day

9
Heat Pumps

• Move heat from a source to sink
• Have the ability to be reversed provide heating
  and cooling

Figure 5. 15
10
Heat Pumps

• Heat pumps, when used as a heater, deliver QL
  (heat removed from cold environment)W
  (compressor energy) QH
• Relationship between COPHP and COPR
• The vapor-compression refrigeration device shown
  earlier is a heat pump

11
Ground Source Heat Pumps

• Key idea ground temperature below surface is
  relatively constant
• Good for use in climates with cold winters and
  hot summers
• Have very high COPs
• but are somewhat expensive

http//www.igshpa.okstate.edu/geothermal/geotherma
l.htm
12
Ground Source Heat Pumps

• On US Department of Energy Website
• Also called Geothermal Heat Pump Systems
• 4 basic types horizontal, vertical, pond/lake,
  and open loop
• Horizontal typical for residential, needs to be
  at least 4 ft deep

http//apps1.eere.energy.gov/consumer/your_home/sp
ace_heating_cooling/index.cfm/mytopic12650
13
Absorption Cooling

• Heat-driven alternatives (instead of
  electricity-driven) for cooling
• Helps smooth the demand for thermal energy
  throughout the year
• Refrigerant is re-pressurized with heat instead
  of a compressor
• Current COPs are about 1.0 to 1.1

14
Desiccant Dehumidification

• Another heat-driven cooling technology
• Desiccants materials - when contact is made with
  water vapor, it readily condenses onto their
  surfaces
• Air passing through becomes much drier (latent
  cooling) and slightly warmer
• Must provide sensible cooling (lower the air
  temperature)
• Must regenerate desiccants with a hot air
  stream
• Good in humid climates

15
Distributed Generation (DG) Benefits

• Provide small increments in generation which can
  track load growth closely to reduce costs of
  unused capacity
• Can ease bottlenecks in distribution networks
• Improve voltages
• Improve power factor
• Reduce losses
• Provide power during outages
• Reduce emissions
• But they lose economics of scale!

16
Distribution Cost Deferral

• Utilities can identify portions of the system
  where distributed generation and demand side
  management would be the most beneficial
• Customers at those locations could be provided
  with incentives to generate their own power
• Distributed generation can help alleviate
  bottlenecks

17
Demand - Side Management (from Prof. Gross)

• Generation sources are supply-side resources
  they provide both energy (kWh) and capacity (kW)
• Supply-side resources also provide a variety of
  services such as reactive power support and
  system stability enhancement
• Unfortunately, supply-side resources may have
  undesirable environmental attributes

18
Demand - Side Management (from Prof. Gross)

• Also called demand side resources - any program
  that attempts to modify customers energy use
• Conceptually, lowering the load is a source of
  energy you can either raise generation or lower
  load
• These programs have beenaround for decades

19
Demand Side Management (from Prof. Gross)

• Efficiency improvement
• Conservation programs
• Load management programs
• Fuel substitution programs

Load Shape Objectives in DSM
20
Demand - Side Management (DSM)

• Part of an Integrated Resource Planning (IRP) or
  a Least Cost Planning (LCP) process
• Integrated means that supply and demand side
  resources are given equal consideration
• Necessary conditions for successful DSM programs
• Decoupling of utility sales from utility profits
  (disincentive more energy sold -gt higher profit)
• Recover DSM program costs
• Incentives to encourage utilities to prefer DSM
• DSM cost-effectiveness is difficult to measure

21
A Simple Cost Effectiveness Test (from Prof.
Gross)
22
Wind Power Systems
Photos taken near Moraine View State Park, IL
23
Historical Development of Wind Power

• The first known wind turbine for producing
  electricity was by Charles F. Brush turbine, in
  Cleveland, Ohio in 1888

• 12 kW
• Used electricity to charge batteries in the
  cellar of the owners mansion

Note the person
http//www.windpower.org/en/pictures/brush.htm
24
Historical Development of Wind Power

• First wind turbine outside of the US to generate
  electricity was built by Poul la Cour in 1891 in
  Denmark

• Used electricity from his wind turbines to
  electrolyze water to make hydrogen for the gas
  lights at the schoolhouse

http//www.windpower.org/en/pictures/lacour.htm
25
Historical Development of Wind Power

• In the US - first wind-electric systems built in
  the late 1890s
• By 1930s and 1940s, hundreds of thousands were in
  use in rural areas not yet served by the grid
• Interest in wind power declined as the utility
  grid expanded and as reliable, inexpensive
  electricity could be purchased
• Oil crisis in 1970s created a renewed interest in
  wind until US government stopped giving tax
  credits
• Renewed interest again since the 1990s

26
Global Installed Wind Capacity
Global Wind Energy Council http//www.gwec.net/fil
eadmin/documents/PressReleases/PR_stats_annex_tabl
e_2nd_feb_final_final.pdf
27
Annual Installed Wind Capacity
Global Wind Energy Council http//www.gwec.net/fil
eadmin/documents/PressReleases/PR_stats_annex_tabl
e_2nd_feb_final_final.pdf
28
Top 10 Countries - Installed Wind Capacity (as of
the end of 2008)
Global Wind Energy Council http//www.gwec.net/fil
eadmin/documents/PressReleases/PR_stats_annex_tabl
e_2nd_feb_final_final.pdf
29
Historical Development of Wind Power

• Leading states in installed capacity (US) as
  of 12/31/2007
• 1 Texas
• 4.356 MW
• 2 California
• 2,439 MW
• 3 Minnesota
• 1,299 MW
• 4 Iowa
• 1,273 MW
• 5 Washington
• 1,163 MW

http//www.awea.org/newsroom/
http//www.windpower.org/en/pictures/lacour.htm
30
Types of Wind Turbines

• Windmill- used to grind grain into flour
• Many different names - wind-driven generator,
  wind generator, wind turbine, wind-turbine
  generator (WTG), wind energy conversion system
  (WECS)
• Can have be horizontal axis wind turbines (HAWT)
  or vertical axis wind turbines (VAWT)
• Groups of wind turbines are located in what is
  called either a wind farm or a wind park

31
Vertical Axis Wind Turbines

• Darrieus rotor - the only vertical axis machine
  with any commercial success
• Wind hitting the vertical blades, called
  aerofoils, generates lift to create rotation

• No yaw (rotation about vertical axis) control
  needed to keep them facing into the wind
• Heavy machinery in the nacelle is located on the
  ground
• Blades are closer to ground where windspeeds are
  lower

http//www.reuk.co.uk/Darrieus-Wind-Turbines.htm
http//www.absoluteastronomy.com/topics/Darrieus_w
ind_turbine
32
Horizontal Axis Wind Turbines

• Downwind HAWT a turbine with the blades
  behind (downwind from) the tower
• No yaw control needed- they naturally orient
  themselves in line with the wind
• Shadowing effect when a blade swings behind the
  tower, the wind it encounters is briefly reduced
  and the blade flexes

33
Horizontal Axis Wind Turbines

• Upwind HAWT blades are in front of (upwind
  of) the tower
• Most modern wind turbines are this type
• Blades are upwind of the tower
• Require somewhat complex yaw control to keep them
  facing into the wind
• Operate more smoothly and deliver more power

34
Number of Rotating Blades

• Windmills have multiple blades
• need to provide high starting torque to overcome
  weight of the pumping rod
• must be able to operate at low windspeeds to
  provide nearly continuous water pumping
• a larger area of the rotor faces the wind
• Turbines with many blades operate at much lower
  rotational speeds - as the speed increases, the
  turbulence caused by one blade impacts the other
  blades
• Most modern wind turbines have two or three
  blades

35
Power in the Wind

• Consider the kinetic energy of a packet of air
  with mass m moving at velocity v
• Divide by time and get power
• The mass flow rate is (r is air density)

36
Power in the Wind

• Combining (6.2) and (6.3),

Power in the wind
PW (Watts) power in the wind ? (kg/m3) air
density (1.225kg/m3 at 15C and 1 atm) A (m2)
the cross-sectional area that wind passes
through v (m/s) windspeed normal to A (1 m/s
2.237 mph)
37
Power in the Wind (for reference solar is about
600 w/m2 in summer)

• Power increases like the cube of wind speed
• Doubling the wind speed increases the power by
  eight
• Energy in 1 hour of 20 mph winds is the same as
  energy in 8 hours of 10 mph winds
• Nonlinear, so we cannot use average wind speed

Figure 6.5