HEAT  LOSS

 

The previous experiment has so many variables that it might have been difficult to get accurate results.  This experiment will be done under a more controlled environment so it should be easier to collect accurate data.  We will be comparing the temperature drops of two different cups of boiling water. One cup will be ceramic and the other will be made of Styrofoam. 

Get out your digital thermometer .  You could also make good use of a data logger  with this experiment.

 

 Take heat loss readings for hot cups of water. Every minute record the temperature of the cup of water for 30 minuets. 

 

1. A ceramic cup of boiling water.
2. A polystyrene foam cup of boiling water
3. A double polystyrene foam cup of boiling water
4. A polystyrene foam cup of boiling water with lid.

 

 

Plot four time vs. temperature graphs for the four heat loss experiments. Which one looses heat fastest. Which one retains it's heat the longest. Why? 

 

1.  What are some factors that contribute to home heating loss?

Low outside temperature is something we dont have much control over. Degree days are used to measure the extent and duration of low outside temperature. They are the average daily temperature differences between the inside temperature and 650 F.

DEGREE DAYS are used to determine how much fuel will be needed to heat a building in a given area. Individual degree days are calculated by subtracting the average outside temperature from the 65o F.


2. Calculate the degree days for January 5, 2003 when the average outside temperature is 25 degrees F.

All degree days in which the outside temperature is colder than the inside temperature are added together to arrive at the annual degree days (DD/year). The temperature difference between the inside and outside of the building is the primary cause of heat loss in the winter months. Other factors include insulation, surface area and air infiltration.

 

HEAT LOSS CALCULATIONS

 

In order to calculate the annual heat loss of a building we must first know the number of degree days per year for the area. Next we will have to examine the insulation factors (U) and the surface areas (A) in question. The following abbreviations are used in heat loss calculations.

 

DEGREE DAYS:                           DD = (Ti - Ta)/day
HOURLY HEAT LOSS:                  Q = UA(DD)/hr
YEARLY HEAT LOSS:                   E = UA(DD)/yr . 24hr

E               Energy needed per year               BTU

Q              Hourly rate of heat loss               (Btu/hr)

U               Heat transfer coefficient            (Btu/hr-ft2-F) = 1/R

A               Heat transfer area                      (ft2)

Ti                         Inside design temperature  (F) (65o standard)

Ta                        Outside average temperature      (F)

DD            Degree Day                                 (Ti - Ta) F

 

 

 

 

3. Calculate the heating needs of a simple shed roof house 12 feet wide, 20 feet long and eight foot high with one 3 X 6 foot air tight door. The average yearly degree days for this house are 5,000. Do not consider the heat loss from the floor or air infiltration.

R for walls           = 5         U =?
R for ceiling        = 10       U =?
R for door            = 2         U =?

REMEMBER E = UA (DD)/yr. 24hr

                    E = UA 5,000. 24
                    E = UA 120,000

 

 

A

R

U

UA (DD)/yr. 24hr

WALLS

sq ft

 

 

BTU

CEILING

sq ft

 

 

BTU

DOOR

sq ft

 

 

BTU

TOTAL

 

 

 

BTU

GALLONS

 

 

 

 gallons of oil

Now lets calculate the heat loss for the same shed in the same place after adding insulation. Lets give the walls an R factor of 15, the ceiling an R factor of 30 and then lets add a storm door to give our entry way an R factor of 4.

 

 

A

R

U

UA (DD)/yr. 24hr

WALLS

sq ft

 

 

BTU

CEILING

sq ft

 

 

BTU

DOOR

sq ft

 

 

BTU

TOTAL

 

 

 

BTU

GALLONS

 

 

 

gallons of oil

 

     

 

 


                           

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