More on Chapter 7 Energy Conservation

More on Chapter 7 Energy Conservation Lecture #16 HNRS 228 Energy and the Environment

Overview of Chapter 7 • Energy Conservation • Space Heating • Thermal Insulation • Air Infiltration • Lighting • Appliances • Some considerations of agriculture and industry

iClicker Question • How many fewer power plants might be needed if every household changed to compact fluorescent lighting? • A About one • B More than one • C More than 100 • D Depends on power plant output

iClicker Question • Which type of washing machine conserves the most energy and water? • A Top loader • B Front loader

iClicker Question Turning off your computer will harm it. A True B False

iClicker Question Leaving your heat on is more efficient than turning it down because you need so much energy to heat the house back up. A True B False

iClicker Question • Which unit is used to measure insulation of walls? • A Q-value • B R-value • C S-value • D T-value • E U-value

iClicker Question • Which unit is used to measure insulation of windows? • A Q-value • B R-value • C S-value • D T-value • E U-value

iClicker Question • Which of the following will conserve more energy. • A A wall with R-value 12 • B A wall with R-value 14 • C A wall with R-value 16 • D A wall with R-value 18 • E A wall with R-value 20

iClicker Question • Which of the following will conserve more energy. • A A window with U-value 0.12 • B A window with U-value 0.14 • C A window with U-value 0.16 • D A window with U-value 0.18 • E A window with U-value 0.20

National Average Home Energy Costs

70 'F 30 F Furnace Why do we need Heating?

Typical Heat losses- Conventional House

iClicker Question • Energy transfer by electromagnetic waves is • A Radiation • B Convection • C Conduction

iClicker Question • Energy transfer by the bulk motion, or large scale motion of molecules in gas or liquid form from one location to another is • A Radiation • B Convection • C Conduction

iClicker Question • Energy transfer by contact of molecule with another molecule is one way to define • A Radiation • B Convection • C Conduction

Conduction Energy is conducted down the rod as the vibrations of one molecule are passed to the next, but there is no movement of bulk material

Convection Energy is carried by the bulk motion of the fluid

Radiation Energy is carried by electromagnetic waves. No medium is required

Degree Days • Index of fuel consumption indicating how many degrees the mean temperature fell below 65 degrees for the day • Heating degree days (HDD) are used to estimate the amount of energy required for residential space heating during the cool season. • Cooling degree days (CDD) are used to estimate the amount of air conditioning usage during the warm season

How do we calculate HDD? • HDD = Tbase - Ta • if Ta is less than Tbase • HDD = 0 • if Ta is greater or equal to Tbase • Where: Tbase = temperature base, usually 65 F Ta = average temperature, Ta = (Tmax + Tmin) / 2

Heating Degree Days • Calculate the number of degree days accumulated in one day in which the average outside temperature is 17ºF. Degree days = 1 day ( 65 – Tout) = 1 (65-17) = 48 degree days

Heating Degree Days in a Heating Season • Calculate the degree days accumulated during a 150-day heating season if the average outside temperature is 17ºF Solution: Heating Season Degree days = 150 days ( 65 – Tout) = 150 (65-17) = 7,200 degree days

Degree Days for the Heating Season For Virginia data see http://cdo.ncdc.noaa.gov/climatenormals/clim81/VAnorm.pdf Sterling, VA 5237

Significance of HDD • Mrs. Young is moving from Anchorage, Alaska (HDD =10,780) to State college, PA (HDD = 6,000). Assuming the cost of energy per million Btu is the same at both places, by what percentage her heating costs will change? Solution HDD in Anchorage, Alaska = 10,780 HDD in State College PA = 6,000 Difference = 10,780 - 6,000 = 4,780 Saving in heating fuel costs are

Home Energy Saver Online • http://homeenergysaver.lbl.gov/

Home Heating Costs in State College, PA Average House Energy Efficient House Total $1,891 Total $1,019

Home Heating Costs • Related to amount of insulation, material that resists the flow of heat • Insulation is rated in terms of thermal resistance, called R-value, which indicates the resistance to heat flow. The higher the R-value, the greater the insulating effectiveness. The R-value of thermal insulation depends on the type of material, its thickness, and density. • R-30 better than R-11

Places to Insulate • Attic is usually the easiest ad most cost effective place to add insulation • Floors above unheated basements should be insulated • Heated basements should be insulated around the foundaton

R-values for Building Materials

Thickness of various materials for R-22

R-Value for a Composite Wall

Home Heating Energy • Heat loss depends on • Surface Area (size) • Temperature Difference • Property of the wall ( R value) Outside 30¨F Inside 65¨F Q (Btus) 1 A (area) x Temperature Diff (Ti – To) = t (time, h) R

Q Q t t Heat Loss Tcold Thot Heat Loss = Id Q/t is in Btu/h Area in ft2 Tin-Tout in °F Then the thermal resistance is R-value. The units of R-value are

Wall loss rate in BTUs per hour • For a 10 ft by 10 ft room with an 8 ft ceiling, with all surfaces insulated to R19 as recommended by the U.S. Department of Energy, with inside temperature 68°F and outside temperature 28°F:

Calculation per Day • Heat loss per day = (674 BTU/hr)(24 hr) = 16,168 BTU • Note that this is just through the wall • The loss through the floor and ceiling is a separate calculation, and usually involves different R-values

Calculate loss per "degree day" • If the conditions of case II prevailed all day, you would require 40 degree-days of heating, and therefore require 40 degree-days x 404 BTU/degree day = 16168 BTU to keep the inside temperature constant. • This is the loss per day with a one degree • difference between inside and • outside temperature.

Heat Loss for Entire Heating Season. • The typical heating requirement for a Pittsburgh heating season, September to May, is 5960 degree-days (a long-term average). Heat loss = Q/t = 404 Btu/degree day x 5960 degree days = 2.4 Million Btus

Economics of Adding Insulation • Years to Payback = C(i) x R(1) x R(2) x E------------------------------------- C(e) x [R(2) - R(1)] x HDD x 24 • C(i) = Cost of insulation in $/square feet • C(e) = Cost of energy, expressed in $/Btu • E = Efficiency of the heating system • R(1) = Initial R-value of section • R(2) = Final R-value of section • R(2) - R(1) = R-value of additional insulation being considered • HDD = Heating degree days/year • 24 = Multiplier used to convert heating degree days to heating hours (24 hours/day).

More on Chapter 7 Energy Conservation