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The House as a System
1
Systems in a Home
• Electrical • Plumbing• Comfort Control (HVAC)• Structural• Moisture Control• Air Infiltration• Thermal Insulation
• Cable/Internet• Land Line• Fire Alarm• Security• Radon Mitigation• Pest Control
2
A House Should Work as a System• Control relative humidity• Control liquid water to prevent
high relative humidity, mold formation, and potential decay of building ingredients
• Comfortable indoor temperatures and low energy bills; lack of drafts
• Provide low indoor pollutant levels
House as a System – Keys for Low Energy
Building Envelope Continuous Air Barrier Complete Insulation
Coverage with Insulation in Contact with Air Barrier
Quality Heating and Cooling Systems
Controlled Ventilation
4
House as a System Issues
• Air leaks• Air pressures• Liquid water• Water vapor• Vapor pressures• Cold surfaces
Attic
Indoors
Crawlspace/Basement
Outdoors
A Balanced HVAC System
6
1,200 cfm
1,200 cfm
-
500 cfm
700 cfm
1,100 cfm
100 cfm
More Supply Leaks
7
- 100 cfm
700 cfm
1,100 cfm
500 cfm
More Return Leaks
8
-
9
Closing Doors Changes Pressures
HVAC
R
DHWDryer
Louvered Door
House as a System Gone Wrong
10
Negative Pressures
R
+ +
+ +
-- -
CO CO
COCO
CO
HVAC blower comes on;with doors closed andexhausts on, pressure imbalances occur
11
“House As A System” Approach
RFresh Air Ducts
Transfer Grilles Minimize Pressure Imbalances
Sealed Ductwork
12
Solid, Weatherstripped Door,
Insulated, Air Sealed Walls
Best approach is to use all sealed combustion appliances (or non-combustion appliances)
Why is Air Leakage Control Important?
A Myth – Never build a house “too tight!”
13
Let It Breathe? From Where?
Crawlspace/Basement
Outdoors
Attic
Indoors
-
Which Air Do You Want?
15
Basic IngredientsOxygenNitrogenWater vaporCarbon dioxideCarbon monoxideNitrogen oxidesParticulates
Water vapor, dust, dust mites, allergens, mold spores, bacteria, radon
Water vapor, dust, dust mites, allergens, mold spores, bacteria, uncomfortable temperatures
Mold, Volatile Organic Compounds, Carbon Monoxide, Allergens, Bacteria, Duct Mites
Water vapor, dust, allergens, uncom- fortable temperatures
What About Heat Transfer?
Heat Transfer Basics
3 Modes:• _________________________
• _________________________
• _________________________
Conduction
• What 2 factors does conduction depend on?
• ___________ and ______________
• R-values = Resistance to heat flow:• Examples: (R-value per inch)Wood =0.9 - 1.1 Concrete=0.20 Drywall = 1.0Fiberglass = 3.1 to 4.3 Expanded polystyrene=4Extruded polystyrene=5 Cellulose = 3.7 Icynene = 3.6-3.7 Polyurethane/ Polyisocyanurate = 6.8
Conduction Example
• Example: How much heat transfers via conduction through a wall that measures 500 square feet and has R-20?
• Answer: Heat transfer coefficient =Area / R-value =
• A/R = 500/20 = 25 Btu/degree-hour• To find Btu’s lost over time, multiply the Heat
Loss Coefficient by the difference in temperature T and the number of hours
In Class Example
• A house measures 30 feet by 40 feet and has 10-foot ceilings. 80% of the wall is solid and insulated (the other part is made up of windows and doors). If the wall has R-15, how many Btu’s does the wall lose over 24 hours if the average inside temperature is 70 degrees and the average outside temperature is 20 degrees?
Answer to Example
• Area: Perimeter x height =Perimeter - 2*(30 + 40) = 140 feetArea = Perim. x height = 140 feet * 10 feet = 1,400 sq ftSolid area = 1,400 * 0.80 = 1,120 sq ft
• Heat loss coef. = A/R = 1,120/15 = 74.67• Heat loss (Btu’s) = Heat loss coef x T x hours =
74.67 * (70-20) * 24 = 89,600 Btu
Heat Transfer Mode 2: Radiation
• Requires two surfaces of different temperatures separated by an air space (or other space with gas between the surfaces)
• Important factors– Temperature– Emissivity of the
“releasing” (emitting surface)– Reflectivity/ absorptance of the receiving surface
• Heat transfer =
Mode 3: Convection
• Convection is heat carried by moving air• Examples include:
– Air leakage into and out of a home– Blower pushing conditioned air via ductwork into
a home– Strong winds carrying cooler air– Hot air rising off of hot pavement– We will cover much more on convection later in
the section on air leakage
Hot Roof Deck
Radiant Heat Flow
Absorbed by Insulation/ Drywall
Conducted Into House
Heat Transfer Basics and Attics
Attic + Summer Comfort Complaints
Hot Roof Deck
Radiation
Convection
Conduction
RadiationConduction
Summer Attic Experiment• 93 Heat Lamps for Mock-Up Attic• Radiant Heat Barrier – reinforced foil under rafters
Summer Attic Experiment
• Attic air – 20 degrees cooler
No RHB
With RHB
Summer Comfort Complaint
Customers complain about hot indoor tempsOption 1• Seal air and duct leaks• Tune up HVAC• Tune up insulation• Install radiant heat barrierCost -- $1,600 to $2,500
Option 2• Install larger HVAC system• Cost -- $6,000 to $7,000
Larger HVAC!Builder felt that owner would perceive it as a higher value
Which option was followed?
New Employment Opportunities
Insulation Must Be Continuous
Voids Galor
e
Continuous Insulation?
Air Temperature and Water Vapor
How Does Condensation Occur?• As air cools, its relative humidity
increases• If the relative humidity climbs to 100%, it
has reached its dew point• The resulting liquid water formation can
deteriorate building components and possibly result in mold formation
• Single paned windows have cooler temperatures on their indoor surfaces in winter and are more likely to experience condensation
Crawl Space Moisture Problems
34
92/ 70%RH
72/ 100%RH
92/ 70%RH
Poor Insulation • Missing insulation or
insulation not touching air barrier
• Summer– Drywall cooler in
summer due to air conditioning inside
– Attic air may reach dewpoint when contacting drywall and cause condensation
Poor Insulation • Winter
– Interior side of OSB cooler due to exposure to cold exterior air
– Interior air may reach dewpoint when contacting OSB and cause condensation
Indoor Air Quality Is Important
• Indoor air pollution can have significant health effects.
• Environmental Protection Agency studies of human exposure to air pollutants indicate that indoor levels of pollutants may be 2-5 times higher than outdoor levels, and occasionally more than 100 times higher.
• These levels of indoor air pollutants may be of particular concern because most people spend about 90% of their time indoors. (www.epa.gov/iaq)
Indoor Air Quality and RH
Total Water Vapor Air Can Hold
Common IAQ pollutants
• RadonRadon• Volatile Organic Compounds or VOC’sVolatile Organic Compounds or VOC’s• Dust and dust mitesDust and dust mites• AllergensAllergens• Carbon MonoxideCarbon Monoxide• Mold and MildewMold and Mildew• Household ChemicalsHousehold Chemicals
Which Subcontactors Are Key?
• Simple answer – all– Excavation– Foundation– Waterproofing– Framers and roofers– Insulators/ air sealers– Mechanical, electrical,
plumbing
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