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

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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

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Negative Pressures

R

+ +

+ +

-- -

CO CO

COCO

CO

HVAC blower comes on;with doors closed andexhausts on, pressure imbalances occur

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“House As A System” Approach

RFresh Air Ducts

Transfer Grilles Minimize Pressure Imbalances

Sealed Ductwork

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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