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					Energy Units, Fuel Conversions and Understanding Energy Bills

Recap from last class
• R-value – a measure of thermal resistance measured in ft2 F° hr/BTU • U-value – is the reciprocal of R value. It is a measure how well a building element conducts heat (1/R-val) • Shell area – Includes all envelope elements; windows, floor, walls, etc. • Degree days – difference between out and inside temp. averaged over the day.

• Leakage ratio – leakage area / shell area determined by blower door test

The R-Value of Insulation
• An R-value indicates an insulation's resistance to heat flow. The higher the R-value, the greater the insulating effectiveness. • Typical R-value is R-19 (minimum code) • What does this mean?
– All building components (in a wall) added together, have a thermal resistance of 19.

Calculating R value and U value

R value = 1/U value U value = 1/R value Answer: If R value = 10, What is the U value? R value = 1/U U value = 1/R U = 1/10  0.1

Calculate U value if R = 50
• R=1/U • U=1/R Answer: 50 = 1 / U 50*U = 1  U = 1/50 = 0.02

Heating degree days:
Definition: Difference between outside and inside temp. averaged over the day.
• If the average temperature is 55 degrees (a 24 hour span, from 12:00AM – 11:59PM)… • And the temperature inside of a house is 65 degrees…

What is the difference between outside and inside temp?

Calculations:
Assume a 65 degree indoor temp. year round • If the avg. temp. in January (31 days) was 30 degrees, what is number of the heating degree days?
• Hint: Multiply the difference in indoor and outdoor by the number of days.
Answer: (65 – 30) * 31 days  35 degrees * 31 days  1085 HDD

Calculations:
• Assume a 65 degree indoor temp. year round • If the avg. temp. in June (30 days) was 85 degrees, what is number of the heating degree days?
• Hint: Multiply the difference in indoor and outdoor by the number of days.
Answer: (65 – 85) * 30 days  -20 degrees * 30 days  - 600 HDD

We are in a 6500 heating degree day zone

6500 HDD zone: What does this mean?
• The average temperature each day is subtracted from the indoor air temperature (65 degrees). • A heating degree day is calculated for each day over an entire year. • The total heating degree days over an entire year is roughly 6500 in Mass.

Why is HDD important?
• Engineers, architects, designers want to know the HDD of a particular climate…
– The greater the HDD, the larger a heating system must be. – South has less HDD, therefore only a small heating system is necessary

• Most systems are oversized. • Home builders and owners should know about HDD for replacing an older system (which may have been larger than needed)

Types of energy transfer
• Conduction – Heat flow between molecules (roof, walls, slab edges, floor slab, windows, doors… through solid materials) • Convection – heat flow in a fluid (gas or liquid) moving from one place to another (around windows and doors, heat / steam rising from a cup of coffee) • Radiation – Transport of energy in the form of electromagnetic waves (body heat, sun light) • Air leakage – Also known as infiltration, occurs when outside air enters a house uncontrollably through cracks and openings.

Calculating conduction
U-value x Surface Area x (Temp. inside – Temp. outside) • • • • Walls Floors Doors and Windows Ceilings

Recap from last class
• Walls:
– – – – R-value of 15 Surface Area of 1,000 square feet 6500 HDD 24 hours / day

U * A * HDD * 24 1/15 * 1,000 * 6500 * 24 .067 * 1,000 * 6500 * 24 = 10,399,989 Btu/Yr
What does this mean?

Heat Loss Through Conductance
Floor Heat loss (per year in BTU’s) − 1/19 x 1344 x 6500 x 24 = 11,034,930 Btu/yr Ceiling Heat loss (per year in BTU’s) − 1/38 x 1344 x 6500 x 24 = 5,517,454.8 Btu/yr Windows & Doors Heat loss (per year in BTU’s) − 1/3 x 368 x 6500 x 24 = 19,135,997 Btu/yr

TOTAL HEAT LOSS PER YEAR:

46,088,371 Btu/yr

Don’t Forget Air Leakage…
0.018 Btu x Volume of air x ACH x HDD/yr x 24 hrs/day
• 0.018 (This value never changes) • Volume of air = Length (of building) x Width x Height (in this case, 48' x 28' x 8', as given above, which equals 10,752 cubic feet) • ACH = Air Changes per Hour (Given as 0.60) • HDD = Heating degree days. The difference between outside temperature and inside temperature over an entire year. In Western Massachusetts where we live, HDD is equal to 6500. • Multiply by 24 hours per day

0.018 Btu x 10,752 ft3 x 0.60 AC x 6500 x 24 = 18,114,969 Btu/year of AIR LEAKAGE heat loss

Grand Total Heat Loss
Conductance heat loss: 46,088,371 Btu/yr Air leakage heat loss: + 18,114,969 Btu/yr
64,203,340 Btu/yr
Let’s take a closer look: • Where is the most heat loss happening?

Where is the heat being lost?
1. Windows and doors are responsible for 30% of the H.L. (in this particular house)
Keep heat in, and radiation out!

How do we calculate % of H.L. through doors and windows?
1. Note the total amount of heat loss 2. Note the amount of heat loss through doors and windows Windows & Doors Heat Loss  Total Heat Loss 

19,135,997 Btu/yr
= 29.8% 64,203,340 Btu/yr

3. Divide windows & doors H.L. by total

Calculate the percentages of heat being lost in:
• Ceiling • Walls • Floor
Ceiling/Walls/Floor Heat Loss 
Total Heat Loss  ???????? Btu/yr = ??? % 64,203,340 Btu/yr

Answers
1. Ceiling only 8.5% (due to R-38 insulation… if there was not this much insulation there would be MUCH more heat loss through the ceiling) 2. 16% of the heat loss in this house is conducted through the walls (need more insulation… only R-15) 3. 17% is conducted through the floor

You pay to heat or cool the air in your home.
• An average home leaks 60% of its air every hour. • This leakage rate changes depending on weather:

• A large percentage of that conditioned air escapes to the outside. • An equal amount of outside, unconditioned (usually cooler air) enters your home. • Your bill is significantly more to heat or cool the air in a leaky home.

– Higher (more leakage) during extreme weather – Lower when it’s mild.

Where the leaks are (typically)
Ceiling: 40%

Ceiling: 40%
Doors and Windows: 10%

Walls: 14%

Floor: 36%

Air Leakage
• Air leakage accounts for 28% of the heat lost in this home.
– How do we fix this? – Let’s see another blower door test...

BREAK
The fun will resume in 10

Understanding Air Flow
• Air is constantly moving in a house:
– through walls, – floors, – ceilings, – doors and windows.

Someone describe the “Stack Effect”

Air infiltration
When air goes out, an equal amount comes in • Air infiltration can account for 30 percent or more of a home’s heating and cooling costs • Creates problems with:
– – – – Moisture, Noise, Dust, The entry of pollutants, insects, and rodents.

Reducing infiltration…
• Cuts annual heating and cooling costs • Improves building durability • Creates healthier indoor environments But how do you reduce infiltration?
Remember, if air goes out then air also comes in…

Simple Caulk and Seal System
1. Think methodically before construction 2. Order gaskets & caulk in advance 3. Mark extremes of envelope on plan 4. Seal joints & seams in air barriers 5. Seal HVAC 6. Keep HVAC ducts within envelope 7. Assign tasks to responsible people 8. Clearly articulate goals 9. Provide marked details & plans to team members

Avoid Heat Loss & Air Transported Moisture
• Eliminate uncontrolled air exchange • Seal air leakage points during construction • Provide controlled air exchange • Design to avoid wind washing • Design to avoid convective loops
- Air rises along a warm surface and falls along a cold surface, creating 

What is wind washing?

Wind washing:
What is happening in this picture?

What is wind washing?

AVOID HEAT LOSS

AT ALL COSTS!

Otherwise you will pay the price…

Cost Comparison of Fuels
• Fuels are measured in:
– Physical units – Heat content

Energy Conversions
1. British Thermal Units (Btu) = Oil & as conversion base for all fuels (heat content) 2. Kilowatt Hours (kWh) = Electricity 3. Therms = Natural Gas 4. Gallons = Oil and Propane 5. Cord = Wood

Selection of Heating System
Things to consider: • Cost of fuel • Availability of fuel • Type of conversion appliance • Cost of conversion system • System efficiency • Environmental impacts of system • Comfort, Convenience & Utility

Next Class
• Guest Lecture:
Dr. Simi Hoque Green Building Professor University of Massachusetts Amherst

• Subject: Heating Systems


				
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