- Burden on Industry --> make more efficient devices
- Burden on the Consumer --> Accountability behind closed
doors
- Force consumer to pay the real cost of Energy --> high
energy costs promote conservation

- Insulation is the Key:

Q_{e} = (kA/L)*T_{d}

- Q
_{e}= energy lost in units of BTUs per hour - A = area of the wall
- l = wall thickness
- k = conductivity of the wall which depends on the material in the wall
- T
_{d}= difference in temperature between inside and outside

T_{d} is defined in units of degree days.

A degree day = T_{in} - T_{out} where
in and out refer to the *inside* and
*outside* temperatures.

By convention:
T_{in} = 65^{o} F

So, if T_{out} averaged over one 24 hour period is,
say, 30^{o} F, then that day is equivalent to

When you go to the store and buy insulation the label tells you its R-value

R-values of materials just add. In other words, the total insulation in a wall would be

Where the individual R values are associated with different kinds of materials in your wall.

General Rules:

- Insulation usually pays for itself in reduced heating bills relatively soon (2-3 years).
- Many houses and buildings were constructed when energy was cheap and therefore are not adequately insulated most insulation is therefore retrofitted (meaning its more expensive).

Note, a heating season is just the cumulative number of degree days. Consider the following 5 day heating season:

## Day |
## Average Outside Temperature |
## Degree Days |
## Total Degree Days in Season |
---|---|---|---|

## 1 |
## 40 |
## 25 |
## 25 |

## 2 |
## 30 |
## 35 |
## 60 |

## 3 |
## 35 |
## 30 |
## 90 |

## 4 |
## 0 |
## 65 |
## 155 |

## 5 |
## 50 |
## 15 |
## 170 |

so the total heating season in this case is 170 degree days and the one coldest day (0 degrees) makes up about 40% of the total heating season.

Example Insulation Calculation:

Inputs:

- assuming a heating season of 6000 degree days
- assume an 8x20 foot wall
The wall has the following components:

- 3/4 inch slab of insulating sheathing on the outside with R=2.06
- 1/2 inch gypsum board with R = 0.45
- Outside and Inside air layers give R = 0.85

- Total R for these components is 2.06 + 0.45 + 0.85 = 3.36

What is the Heat Loss through our Wall

Since Q_{e} is in units of heat loss per hour or BTUs per
hour we need to multiply T_{d} which is in degree days,
by 24 hours per day to get the total heat loss in BTUs.

Other variables are:

- A = 8x20 = 160
- R
_{t}= 3.36 - T
_{d}= 6000

So our heat loss averaged over the heating season is:

So in our uninsulated 8x20 foot wall we lost 6.85 million BTUs in the heating season.

Approximate cost of natural gas is $4 per million BTUs which would be about $28 for this wall.

Now lets add some fiberglass insulation with R=12.95.

Now R_{t} = 3.36 + 12.95 = 16.31 so the total heat loss is
reduced to:

Total cost savings to you for this one wall is then

If it costs you $60 in insulation for this one wall then you recover that cost in 3 years and you really win big should you have a particularly severe heating season.

Hence it pays to have insulation and insulation technology is getting better (spray on expanding foam, etc).