Deck 8: Direct Use of Solar Energy

Question 1

Compare the R-values of:
(a) Two pieces of 3-mm thick glass in thermal contact.
(b) Two pieces of 3-mm thick glass with a 1-cm air space between them.

Answer 1

Question 2

A homeowner in Allentown, PA installs a 60° south-facing solar collector

Answer 2

Question 3

Consider a house that is approximated as a cube that is 8 m on a side and has

Answer 3

The total surface area is

Question 4

A house is heated with electricity at a cost of $0.10 per kWh. The building

Question 5

Calculate the power radiated by a woodstove of dimensions 65 cm high by 55
cm deep by 85 cm wide with a surface temperature of 120°C. Assume that heat is radiated
from all surfaces of the stove and that the stove has an emissivity of 1. Note that
woodstoves are painted black because black surfaces have high absorptance, and objects
with high absorptance also have high emissivity.

Question 6

(a) Calculate the power transferred through a 10 cm diameter iron rod that is

Question 7

The average monthly temperatures in Anchorage, AK are given in the table

Question 8

A two storey house in Portland, ME with dimensions 8.5 m by 12.0 m with

Question 9

Question 10

A cylindrical water tank 1.5 m in diameter and 2.5 m high is surrounded on

Question 11

A home uses a concrete floor to store passive solar energy. If the floor heats

Question 12

Consider a vertical south facing window in a house at 40ºN latitude. For an

Question 13

A wood stove has a total surface area of kW. Make a plot of its surface temperature in °C as a function of emissivity.

Question 14

Compare the masses and volumes of water, concrete, sand and wood needed

Question 15

A 300 liter electric hot water heater uses 9000 W of power to heat water. If will it take for

Question 16

A window with an R-value of 0.18 receives 300 W/m2 of insolation. If the
interior of the building is at 20°C, what is the minimum outside temperature for which
there is a benefit from passive solar heating?

Question 17

Approximate a house as a cube with an edge length of 7 m. The house loses

Question 18

A homeowner sells an electrically heated ceilings in Minneapolis and purchases an identical home in San Francisco. Estimate the
expected savings in annual heating costs.

Question 19

Locate information about the current cost of home heating oil or natural gas
in your area (whichever is in common use) and the cost of residential electricity. Assuming
an efficiency of 85% for an oil furnace and 100% for electric heat, calculate the relative
cost of electric heat compared with oil heat or natural gas if both heating systems require
the same net energy to heat a house.

Question 20

Compare the total solar energy received at the surface of the earth in one year
to the total annual global energy requirements.