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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.

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Presentation on theme: "The House as a System 1. Systems in a Home Electrical Plumbing Comfort Control (HVAC) Structural Moisture Control Air Infiltration Thermal Insulation."— Presentation transcript:

1 The House as a System 1

2 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

3 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

4 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

5 House as a System Issues Air leaks Air pressures Liquid water Water vapor Vapor pressures Cold surfaces Attic Indoors Crawlspace/Basement Outdoors

6 A Balanced HVAC System 6 1,200 cfm

7 - 500 cfm 700 cfm 1,100 cfm 100 cfm More Supply Leaks 7

8 - 100 cfm 700 cfm 1,100 cfm 500 cfm More Return Leaks 8

9 - 9 Closing Doors Changes Pressures

10 HVAC R DHWDryer Louvered Door House as a System Gone Wrong 10

11 Negative Pressures R ++ ++ - - CO HVAC blower comes on; with doors closed and exhausts on, pressure imbalances occur 11

12 “House As A System” Approach R Fresh 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)

13 Why is Air Leakage Control Important? A Myth – Never build a house “too tight!” 13

14 Let It Breathe? From Where? Crawlspace/Basement Outdoors Attic Indoors -

15 Which Air Do You Want? 15 Basic Ingredients Oxygen Nitrogen Water vapor Carbon dioxide Carbon monoxide Nitrogen oxides Particulates 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

16 What About Heat Transfer?

17 Heat Transfer Basics 3 Modes: _________________________

18 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 = 1.0 Fiberglass = 3.1 to 4.3 Expanded polystyrene=4 Extruded polystyrene=5 Cellulose = 3.7 Icynene = 3.6-3.7 Polyurethane/ Polyisocyanurate = 6.8

19 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

20 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?

21 Answer to Example Area: Perimeter x height = Perimeter - 2*(30 + 40) = 140 feet Area = Perim. x height = 140 feet * 10 feet = 1,400 sq ft Solid 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

22 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 =

23 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

24 Hot Roof Deck Radiant Heat Flow Absorbed by Insulation/ Drywall Conducted Into House Heat Transfer Basics and Attics

25 Attic + Summer Comfort Complaints Hot Roof Deck Radiation Convection Conduction Radiation Conduction

26 Summer Attic Experiment 93 Heat Lamps for Mock-Up Attic Radiant Heat Barrier – reinforced foil under rafters

27 Summer Attic Experiment Attic air – 20 degrees cooler No RHB With RHB

28 Summer Comfort Complaint Customers complain about hot indoor temps Option 1 Seal air and duct leaks Tune up HVAC Tune up insulation Install radiant heat barrier Cost -- $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?

29 New Employment Opportunities

30 Insulation Must Be Continuous

31 Voids Galore Continuous Insulation?

32 Air Temperature and Water Vapor

33 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

34 Crawl Space Moisture Problems 34 92/ 70%RH 72/ 100%RH 92/ 70%RH

35 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

36 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

37 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. (

38 Indoor Air Quality and RH Total Water Vapor Air Can Hold

39 Common IAQ pollutants Radon Radon Volatile Organic Compounds or VOC’s Volatile Organic Compounds or VOC’s Dust and dust mites Dust and dust mites Allergens Allergens Carbon Monoxide Carbon Monoxide Mold and Mildew Mold and Mildew Household Chemicals Household Chemicals

40 Which Subcontactors Are Key? Simple answer – all – Excavation – Foundation – Waterproofing – Framers and roofers – Insulators/ air sealers – Mechanical, electrical, plumbing


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