Chapter 6: Energy Efficiency for Buildings

• Energy for buildings is the most important sector of energy demand in the United States

  • Energy for building operations accounts for 40% of U.S. primary energy demand

  • Transportation accounts for 28% and the industrial sector accounts for 32%

• The total energy demand for the building sector grows to almost half of all U.S. primary energy when embodied energy is included

• Buildings are responsible for almost 40% of all U.S. carbon emissions

• Better windows, insulation, building envelopes, and ducts can reduce the energy demand for heating and cooling in buildings

• Solar energy can be used to heat buildings in the winter, provide natural daylight, and supply energy for water heating

6.1 Residential and Commercial Buildings

• Almost two-thirds of the total energy demand in buildings is for space heating and cooling, lighting, and water heating

• Controlling plug loads is an emerging challenge in terms of total energy demand and peak power demand

• Residential buildings have higher energy demands than commercial buildings

• Commercial buildings have different energy characteristics, such as higher illumination levels and higher internal thermal gains

6.2 Site Energy versus Primary Energy

• Site energy refers to the energy consumed at the building site, while primary energy includes the energy losses in power generation and transmission

• Primary energy accounts for all the energy inputs needed to deliver a unit of energy to the site

• Site energy ignores losses in power generation and transmission

• Electricity delivered to the site can be expressed in kWhe (kilowatt-hours electrical) to differentiate it from other energy streams

Page 4: Energy for Sustainability

• Subscript "e" indicates electricity, and subscript "t" indicates on-site fuel for heating the building.

• Two units of site energy and four units of primary energy in the example.

• Primary energy is a better measure for characterizing the overall energy efficiency of a building.

• The primary energy metric allows for normalized efficiency ratings for individual buildings.

• The Passive House Institute uses an overall efficiency measure of 120 kWh/m2 of primary energy per year for household space heating, water heating, and domestic electricity for certification.

Page 5: Introduction to Heat Loss Calculations

• Space heating is the largest energy demand category in U.S. buildings, accounting for almost one-quarter of all building energy.

• Improving the energy efficiency of the building envelope can significantly reduce heating demands.

• Passive solar ideas and efficient heating and cooling systems can help minimize energy demand.

• Heat loss occurs through walls, windows, doors, ceiling, floors, and infiltration.

• Infiltration refers to air leakage through cracks and holes, while ventilation is intentional fresh air intake.

• Heat loss rate through each component of the building envelope is calculated using the equation qtot = qwalls + qwindows + qceiling + qfloor + qdoors + qinfiltration.

• The U-value represents the thermal conductance and is used to calculate the heat loss rate.

Solution Box 6.1: Site versus Primary Energy

• Site energy and primary energy are two different ways to characterize building energy demand.

• Site energy considers the energy used on-site, while primary energy accounts for the energy used at the power plant and grid losses.

• A comparison is made between two identical houses with different heating systems.

• The gas furnace house uses 100 units of fuel at 90% efficiency to deliver 90 units of heat.

• The electric resistance heating house requires 90 units of site electricity to deliver 90 units of heat.

• Using the 3:2:1 ratio, 270 units of heat are needed at the power plant to deliver 90 units of electricity to the electric house.

• When using site energy, the electric house appears more efficient, but when considering primary energy, the gas furnace is more efficient, using only 100 units compared to 270 units for the electric heater.

Page 6:

• Introduction of the concept of the R-value of a building component

  • The R-value is the inverse of the U-value

• Equation 6.3: q = UA∆T = 1/A∆T R

  • This equation relates heat transfer rate (q) to the R-value, surface area (A), and temperature difference (∆T)

• Comparison of Eq. 6.3 to an electrical equivalent

• Example calculation of heat loss rate through a wall using Eq. 6.3

• The R-value summarizes heat transfer mechanisms including radiation, convection, and conduction

• Introduction of the three basic heat transfer processes: radiation, convection, and conduction

• Four temperatures to track: inside air temperature (Ti), outside air temperature (Ta), surface temperatures of the wall or window on the room side (T1), and surface temperatures on the ambient side (T2)

• Thermal resistances represented by nodes in a series combination

Page 7:

• Figure 6.7 shows thermal and electrical analogies

• Figure 6.8 illustrates heat transfer through a window

• Total resistance to heat flow can be modeled as a series combination of conduction, convection, and radiation thermal resistances

Page 8:

• Equation 6.5: Conductive resistance (RC) = t/k

  • RC is a measure of thermal resistance

• R-value per inch thickness of a material is 1/k

• Table 6.2 provides R-values per inch for common building materials

• Example of using R-value for conductive resistance calculation

• Concrete conducts heat well but has a low R-value

• Comparison of concrete wall thickness to a fiberglass-insulated wall framed with two-by-fours

• Introduction of heat transfer by convection

• Warm molecules in a fluid transfer heat to cooler objects

• Example of convection in the window example from Figure 6.8

• Table 6.1 provides thermal conductivity values for selected materials

Page 9:

• Convective heat transfer in buildings

  • Air in contact with cold window surface transfers heat to the window

  • Cools the air and increases its density

  • Cold, dense air falls toward the floor

  • Warmer room air moves toward the window and dumps heat onto the window surface

  • Creates convective air currents in the room

  • Can cause discomfort and drafts

• Factors influencing convective heat transfer

  • Speed of air movement along the surface

  • Faster-moving air transfers heat more easily

  • Heating and cooling calculations based on assumed windspeeds

  • Direction of heat flow (easier through the ceiling than at the cold floor)

  • Surface roughness (bumpy surfaces encourage heat transfer)

• Radiation heat transfer

  • Occurs even in a vacuum

  • Every object radiates energy to its surroundings

  • Rate of radiation is proportional to emissivity, surface area, and temperature raised to the fourth power

  • Objects in a room radiate energy that can be absorbed by surrounding surfaces

  • Absorptivity for thermal radiation is usually above 90% for typical surfaces

  • Shiny, metallic surfaces reflect outgoing radiation back into the room

  • Insulating materials and low-e windows use reflective surfaces to reduce heat loss

Page 10:

• Combined convective-radiative R-value

  • Convective and radiative components of heat transfer lumped into a single R-value

  • Rcvi for indoor surfaces and Rcvo for outside surfaces

  • Standard values for Rcvo: 0.17 hr-ft2-°F/Btu for winter, 0.25 hr-ft2-°F/Btu for summer

• Rcvi values depend on direction of heat flow and surface properties

  • Ordinary surfaces (emissivity e ≈ 0.9)

  • Reflective surfaces (e ≈ 0.20)

  • Shiny surfaces (e ≈ 0.05)

• Total R-value for a building surface is the sum of R-values due to conduction, convection, and radiation

• Table 6.3 summarizes convective-radiative R-values for various building surfaces

• Figure 6.9 illustrates the application of convective-radiative heat transfer coefficients in a building

Page 11: Energy Efficiency for Buildings

• Heat loss through windows is a major concern in buildings

  • Single-pane windows are the biggest source of heat loss

  • New construction uses double-glazed windows

• Cold windows can cause discomfort and condensation problems

  • The indoor surface temperature of the glass can be very cold

  • The heat loss rate from the room to the inside surface of the glass can be calculated using the formula: q = A(Ti - T1) = A(Ti - Ta)/Rtot

• Condensation problems are more associated with the window frame than the glass itself

Page 12:

• The dew point is the temperature below which air can no longer hold moisture

• Improving the R-value of windows

  • Double-pane windows with low-e coatings improve the R-value from about R-2 to R-3

  • Filling the air gap with argon or krypton gas further improves the R-value

  • High-performance glazing systems with suspended polyester films and low-emissivity coatings achieve exceptionally high R-values

• Window heat losses are complicated by edge effects associated with the window frame

Page 13:

• The choice of window framing materials can negate the advantages of high-efficiency glazing systems

• Center-of-glass R-values and edge effects need to be considered in the heat loss analysis of windows

• Comparing the room-side surface temperature of single-pane and low-e, double-pane windows

  • The single-pane window has a room-side surface temperature of 35°F

  • The low-e, double-pane window has a room-side surface temperature of 60°F

Page 14:

• Fiberglass frame for a window increases overall R-value compared to an aluminum frame

• Example of high-performance windows with low-e coatings and krypton gas fillings

Page 15:

• Heat transfer pathways in windows: frame, glass area near the frame, and center-of-glass (COG) area

• Analysis of R-value impacts for a double-glazed window with different frames

• Importance of the frame in maintaining R-value

• Energy advantage of bigger windows compared to smaller windows

Page 16:

• Heat loss calculations for walls, ceilings, and floors are more complicated than windows

• Walls have parallel conduction paths through framing members and wall cavities

• Introduction of U-values for analyzing heat loss rate in walls

• Formulas for calculating average U-value and R-value for walls

• Changes in wall framing can reduce wood materials and increase cavity area for insulation

Page 17:

• Example of wall R-value calculations for a typical wall and an improved wall

• Use of two-by-sixes on 24-inch centers and exterior insulating sheathing to increase R-value

• Solution box with calculations for finding the overall R-value of a wall with two-by-fours on 16-inch centers and R-11 fiberglass insulation

Page 18:

Ceilings and Roofs

• Heat loss through a vaulted or cathedral ceiling is an extension of wall calculations.

• For homes with ventilated attic spaces, heat loss calculation is complicated by heat loss from the room into the attic and from there to the outdoors.

• The attic can be assumed to be at the same temperature as ambient for simple calculations.

Floors

• Heat loss calculations for floors are complicated due to different ways of building them.

• Heat loss through floors is only a modest fraction of the total heat loss.

Page 19:

Floors (continued)

• For a floor built over a crawl space, the heat loss rate is determined by the R-value of the flooring, insulation, and the crawl space itself.

• Adding R-6 to the insulation R-value accounts for the impact of the crawl space.

• For unheated basements, adding R-6 provides a reasonable first approximation.

• For small slab-on-grade floors, heat transfer is dominated by losses through the perimeter of the slab to ambient.

Page 20:

Slab-on-Grade Floors

• Slabs are often insulated along the perimeter to reduce heat losses.

• The equation used to estimate slab losses is based on the linear feet of perimeter rather than floor area.

• The heat loss factor F2 depends on the R-value of the insulation and the vertical dimension of that insulation.

Heat Loss due to Infiltration

• Infiltration losses occur when cold air leaks into the house while warm indoor air leaks out.

• Infiltration losses are driven by the temperature difference and pressure differences caused by wind.

• Stack-driven infiltration is caused by warm indoor air rising and creating higher pressure indoors, drawing in cold air near the floor.

• Wind-driven infiltration is caused by pressure differences and is most important to plug in the walls.

Stack-Driven and Wind-Driven Infiltration

• The most important leaks to plug for stack-driven infiltration are near the ceiling and floor.

• For wind-driven infiltration, the leaks in the walls are most important.

Table 6.4 Values of Slab Heat Loss Factors, F2 (Btu/hr-ft-°F)

• Provides examples of the F2 factor for different slab surfaces and insulation levels.

Page 21: Energy Efficiency for Buildings

• Estimating Infiltration Rate (Blower-Door Approach)

  • qinf = rcnV(Ti −Ta)

    • qinf: heat loss due to infiltration (Btu/hr)

    • r: density of air (0.075 lb/ft3)

    • c: specific heat of air (0.24 Btu/lb-°F)

    • n: number of air changes per hour (ach)

    • V: volume of air per air change (ft3/ac)

  • qinf = 0.018 nV(Ti −Ta)

• Estimating n (number of air changes per hour)

  • Infiltration rates:

    • Years ago: 1.5 ach

    • Good, tight new home: 0.5 ach

    • Below 0.35 ach, indoor air quality becomes an issue

  • Measurement of infiltration rates:

    • Artificially pressurizing or depressurizing a house using a large fan and nylon door insert

    • Air change rate at 50 Pa (ACH50) = Airflow rate at 50 Pa / House volume

  • Rule of thumb for estimating annual average infiltration: n (ach) ≈ ACH50

Page 22: Energy Efficiency for Buildings

• How Tight Is "Too Tight" for Healthful Indoor Air Quality?

  • Guideline for healthful indoor air: 15 cfm of fresh air per person

  • Calculation for air changes per hour needed: n = 15 ft3/min-person × 60 min/hr × 4 people / (2000 ft2 × 8 ft)/ac

  • Minimum fresh air requirements can be reduced using construction techniques

  • Passive House Institute requires less than 0.6 air changes per hour at the full 50-Pa blower door test pressure

• Example of estimating heat loss caused by infiltration using ACH50

  • Blower door test on a 2000-square-foot house showed 4000 cfm of airflow was needed to pressurize the house to 50 Pa

  • ACH50 = 15 ach

  • Heat loss rate due to infiltration at specified temperatures: qinf = 0.018 Btu × 0.75 air change × 2000 ft2 × 8 ft × (70−30)°F = 8640 Btu/hr

Page 23: Energy Efficiency for Buildings

• Impact of Tightness on Indoor Air Quality and Energy Efficiency

  • Tightness without mechanical ventilation creates unhealthful indoor conditions

  • Heat recovery ventilator (HRV) helps address the problem by transferring heat from warm exhaust air to cool incoming air

  • Energy recovery ventilators or enthalpy wheels can capture both sensible and latent heat

• Test based on indoor CO2 concentration to determine if enough fresh air is present

  • Indoor air with less than about 1000 ppm of CO2 meets the 15 cfm per person fresh air guideline

  • HVAC systems in large buildings can control ventilation using the CO2 test

  • Relationship between measured indoor CO2 and fresh air per person in the room

Page 24: Indoor Air Quality

• Testing the ventilation guideline that suggests an indoor CO2 concentration exceeding 1000 ppm means the room is getting less than 15 cfm of fresh air per person.

• Using stoichiometry to calculate the amount of CO2 emitted per kcal.

  • C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + 2551 kJ/mole of glucose

  • 264 g CO2 × 4.187 kJ × 24.46 × 103 cm3/mol = 241 cm3 CO2/kcal

• Calculating the CO2 emission rate for an "average" 140-lb person at rest.

  • CO2 emission rate = 140 lb × 0.48 kcal/hr/lb × 241 cm3/kcal = 16,195 cm3 CO2/hr

• Determining the CO2 added to the 15 cfm/person of incoming air.

  • CO2 @ 15 cfm/person = 16,195 cm3 CO2/hr × 35.3 ft3/m2 = 635 ppm

• Total indoor concentration of CO2 when 15 cfm of fresh air per person is provided.

  • Total indoor concentration = 635 ppm + 395 ppm = 1030 ppm

Page 25: Overall Heat Loss Factor

• Summing up the contributions of each component (windows, walls, floors, ceilings, doors, infiltration) to calculate the overall heat loss rate of a house.

• Using Table 6.5 to obtain typical R-values for each component.

• Setting up a spreadsheet approach to evaluate the heat loss rate for the entire building.

• Each row in the spreadsheet summarizes a major building element, providing its area, R-value, U-value, UA product (Btu/hr-°F), and its percentage of the total (UA)-value.

• Infiltration is treated as the product of a U-value and an area to have the same Btu/hr-°F units as other components.

Page 26:

• Infiltration loss can be accounted for in the table by converting it into an equivalent (UA) product using the relationship Eq. 6.19.

  • (UA)inf = 0.018 nV (Btu/hr-°F)

• A heat recovery ventilator (HRV) may be included in tight houses to increase ventilation without losing exhaust heat.

  • The UA equivalent for the HRV is given by Eq. 6.20.

    • (UA)HRV = 0.018 nHRV V · (1−ηHRV)

• Table 6.6 shows an example of a spreadsheet created for a small, well-insulated house.

  • The house features two-by-six walls with R-21 insulation, double-pane aluminum frame windows, R-30 insulation in the ceiling, and R-21 floor insulation with one-inch of XPS.

  • The infiltration rate is 0.6 ach, and there is no HRV.

  • The dominant sources of heat loss are the windows (37%) and infiltration (27%).

  • The table also includes a normalized measure of the efficiency of the house called the thermal index.

    • The thermal index is defined as Eq. 6.21.

      • Thermal index (Btu) = 24 hr/day × (UA)tot Btu/hr-°F ft2-°F-day / Floor space area (ft2)

    • The thermal index for this example house is 7.7 Btu/ft2 per degree-day.

Page 27:

• Furnaces are sized to deliver enough heat to keep a house at a desired thermostat set point while the ambient temperature drops to the coldest temperature likely for that location.

• Furnaces are usually somewhat oversized to ensure an adequate heat supply and to allow for a little extra boost called the pick-up factor.

• Furnaces are most efficient if they run continuously rather than turning on and off frequently.

• The furnace output needed for a house can be calculated using Eq. 6.22.

  • qfurnace = (UA)tot (Tset − Tdesign) · pick-up factor ηdistribution

• Table 6.7 provides a brief sample of design temperatures for a few U.S. cities along with their heating degree days (HDD).

• The table also mentions that furnaces are most efficient if they run continuously and oversizing is often restricted to about 40% above the design load.

• The furnace converts fuel to heat that is delivered to the house through a heat distribution system.

Page 28:

• Furnace sizing depends on output, not efficiency

  • Furnaces are rated by their output (Btu/hr)

• Internal heat gains are not included in furnace sizing

  • Furnace has to provide enough heat even when no one is home

• Goal is to estimate economic value gained by improving house efficiency

  • Need to consider local climate and cost of fuel

• People and appliances in homes provide internal heat gains

  • Example: 3 people contribute 350 Btu/hr each, appliances contribute 500 kWh/mo

  • Internal gains help heat the house depending on the (UA) value of the house

• Example of sizing a furnace for a house in Blacksburg, Virginia

  • (UA)tot = 482 Btu/hr-°F heat loss factor

  • 75%-efficient forced-air heat distribution system

  • 70°F thermostat set point and a 1.4 pick-up factor

  • qfurnace = 67,620 Btu/hr

Page 29:

• Internal gains of 3000 Btu/hr raise indoor temperature above ambient by 6°F

• Balance point temperature (Tb or Tbal) is the temperature the furnace has to raise the house to, with internal gains providing the rest

  • Tb = Tset - qint / (UA)tot

• Heating degree-days (HDD) and cooling degree-days (CDD) are indicators of climate

• HDD are accumulated on days when average temperature is less than 65°F

• CDD are accrued on days when average temperature is above 65°F

• Equation 6.25 relates HDD and CDD to average annual ambient temperature for a site

Page 30:

• Adjusting the base temperature for HDD

  • Degree-day tables for other base temperatures are available on the web

  • Empirically derived adjustment formula: HDD (Tb) = HDD65 − (0.021 · HDD65 + 114) · (65 − Tb)

• Example calculation for Denver using base temperature of 60°F

  • HDD60 = 6016 − (0.021 · 6016 + 114) · (65−60) = 4814°F-day/yr

• Calculation of annual heating load

  • Formula: Qdel = 24 (UA) × HDD(Tb)

  • Qdel represents the total amount of heat needed (Btu/yr)

  • "24" refers to hours per day

  • HDD is at the base temperature Tb

• Calculation of fuel needed

  • Formula: Qfuel = Qdel / (ηfurnace · ηdistribution)

  • Qfuel represents the fuel needed

  • ηfurnace represents the furnace efficiency

  • ηdistribution represents the distribution efficiency

• Spreadsheet analysis for evaluating home heating costs

  • Spreadsheet allows for easy modification of assumptions and immediate determination of implications

  • Example spreadsheet provided in Table 6.10

Page 31:

• Exploration of energy savings through construction modifications

  • Efficiency improvements in windows, furnace, distribution system, house tightness, and heat recovery ventilator

  • Spreadsheet analysis allows for easy determination of energy savings

• Heating and cooling degree-days

  • Table 6.8 illustrates heating and cooling degree-days at a base temperature of 65°F

• Rough costs of home heating fuels

  • Table 6.9 provides unit costs for commonly used home heating fuels

• Annual fuel consumption and furnace sizing spreadsheet

  • Table 6.10 shows the annual fuel consumption and furnace sizing spreadsheet for a specific home in Blacksburg, Virginia

  • Includes values for total (UA) value, fuel price, furnace efficiency, distribution efficiency, internal gains, indoor set point, HDD65, Tdesign, and furnace pick-up factor

  • Calculations are performed to determine balance point temperature, HDD at the balance point, Qdel, Qfuel, annual fuel bill, and furnace output

Page 32:

• Energy for Sustainability value for Blacksburg house reduced from 482 Btu/hr-°F to 236 Btu/hr-°F

• Table 6.12 shows additional heating system improvements for the new house, resulting in an 80% reduction in the original annual fuel bill

• Step-by-step approach starting with fixing leaky ducts and replacing the furnace saves 30% of the original energy demand

• Calculations include balance point temperature, HDDTb, Qdel, Qfuel, annual fuel bill, and furnace output

• Efficiency improvements in the Blacksburg house are listed in Table 6.11

Page 33:

• Marginal benefit of each additional efficiency measure is diminished when done in a step-by-step basis

• Treating the whole set of measures together may make more sense, especially for new construction

• Forced-air central heating systems are popular in the United States, with advantages such as rapid heat delivery and versatility

• Ducts in forced-air systems can be a weak link, often poorly insulated and plagued by leaks

• Hydronic systems use boilers and pumps to distribute hot water, with small, efficient pumps and negligible distribution losses

• Compressive air conditioning systems are based on the principle of compressed gas expanding and getting cold

Page 34:

• Duct losses in forced-air systems can account for 20%–30% of heating bills

• Hydronic systems are described as the most comfortable heating systems available

• Hydronic systems can use baseboard radiator/convectors or tubing embedded in subflooring or concrete floor slabs

• Radiant floor slab systems provide stable indoor temperatures due to their thermal flywheel effect

• Boilers used in radiant systems have slightly lower efficiencies but make up for it with higher distribution efficiencies and lower thermostat settings

• Compressive air conditioning systems work by allowing compressed gas to expand and get cold

Page 35:

• Components of an air conditioner:

  • Compressor

  • Condenser coil

  • Expansion valve

  • Cold evaporator coil

• Types of air conditioning systems:

  • Packaged systems

  • Split systems

• Cooling capacity of air conditioners is measured in "tons of cooling"

• Description of a split system air conditioner

Page 36:

• Efficiency ratings for air conditioners:

  • Energy efficiency ratio (EER)

  • Seasonal energy efficiency ratio (SEER)

• Different approaches to cooling:

  • Evaporative coolers

  • Absorption cycle air conditioners

• Introduction to heat pumps and their operation

• Efficiency measures for heat pumps:

  • SEER (as an air conditioner)

  • Heating season performance factor (HSPF) (as a heater)

• Energy efficiency standards for split-system heat pumps

Page 37:

• Coefficient of performance (COP) as a measure of efficiency

• Comparison of air conditioner costs using SEER ratings and running costs

• Calculation of simple payback period for a more efficient air conditioner

Page 38:

• Equations 6.33 and 6.34 provide conversions for energy and thermodynamic evaluations.

  • Eq. 6.33: COP = HSPF (Btu heat per Wh electricity) = HSPF * 3.412 Btu/Wh

  • Eq. 6.34: COP = SEER (Btu/hr cooling per W of electricity) = SEER * 3.412 Btu/Wh

• Sadi Carnot developed efficiency limits for heat pumps in the 19th century.

  • Eq. 6.35: COP (heating) ≤ TH = 1 / (TH - TC) * (1 - TC/TH)

  • Eq. 6.36: COP (cooling) ≤ TC = 1 / (TH - TC) * (TH/TC - 1)

• Higher efficiencies are possible for heating systems with modest delivery temperatures.

• Heat pumps run at constant power, so as the ambient temperature drops, the COP and heating output decrease.

Page 39:

• Heat pumps may require electric resistance heating strips in cold climates, reducing overall efficiency.

• Geothermal heat pumps (GHPs) have better efficiencies by utilizing more constant underground temperatures.

  • GHPs can be 40%–60% more efficient than conventional air-source heat pumps.

• Ductless mini-split heat pumps have no ducts and can reduce energy losses.

• Mini-splits have individual indoor units with their own heat exchangers and fans.

• A new generation of mini-splits with adjustable-speed drives addresses cold weather limitations.

Page 40:

• Mini-splits have a single outdoor unit and one or more indoor units.

• Refrigerant lines connect the indoor and outdoor units.

• Inverter-driven mini-splits deliver rated heating capacity at temperatures well below freezing.

• Geothermal heat pumps have one of their heat exchangers located in the earth, either in deep boreholes or shallow horizontal arrays.

Page 41:

• Mini-splits are energy-efficient heating and cooling systems for buildings.

  • They have inverter-driven compressors that convert AC power to DC power and then back to variable-frequency AC power.

  • Each indoor unit has its own controls, allowing occupants to heat or cool specific spaces.

  • They can be easily retrofitted without replacing existing inefficient furnaces, ducts, and controls.

  • Mini-splits can be used in conjunction with rooftop photovoltaics to create a carbon-free home heating and cooling system.

Page 42:

• Buildings account for nearly half of all energy consumed in the United States.

  • The residential sector accounts for slightly more energy consumption than the commercial sector.

• Buildings also account for approximately three-fourths of electricity demand and contribute to carbon emissions and other power-related environmental problems.

• By implementing best-building practices, heating bills in a simple house can be reduced by over two-thirds.

  • The key areas for improvement are better windows, lower infiltration rates, and reduced distribution system losses.

• Tightening up a building can potentially lead to poor indoor air quality.

  • Monitoring indoor CO2 levels can help determine if fresh air is needed.

  • Demand-controlled ventilation, such as heat recovery ventilators, can effectively improve indoor air quality in large commercial buildings.

• Conventional fossil fuel-fired forced-air systems in the residential sector can be significantly improved, but the goal is to replace them with electricity-driven heat pumps.

• The combination of photovoltaics on the roof and heat pumps or mini-splits can create eco-friendly