Building Energy Efficiency Measures

Buildings consume a substantial fraction of all energy; consequently, they are responsible for much of the anthropogenic carbon dioxide emissions that contribute to climate change. In the U.S., about 40% of carbon dioxide emissions are attributable to energy use in buildings [1]. To reduce future climate change it will be necessary to substantially reduce building energy consumption; thus, broad application of energy efficiency measures in buildings is expected as climate change advances. Some entities, such as the state of California, aim to make buildings energy neutral, producing as much energy as they consume over the long term.

Many energy efficiency measures for buildings will influence comfort conditions or indoor air quality, either positively or negatively [2-6]. Some measures are expected to have both positive and negative effects. For energy efficiency, new homes are built with airtight, well-insulated building envelopes. On one hand, this can improve thermal comfort and decrease outdoor ozone and particles from entering, but on the other hand, it may increase indoor concentrations of air pollutants emitted from within the home.

In some areas, new homes are required to have mechanical ventilation. A California new home study [7] found that the combination of mechanical ventilation and implementation of a standard that reduced the allowable formaldehyde emissions from manufactured wood products resulted in about 40% lower in formaldehyde concentrations compared to homes built prior to the standards. This study shows that new homes can be built to stringent energy efficiency standards while maintaining indoor air quality. However, ventilation fans were operating in only 1 in 4 of the homes when first visited. The formaldehyde concentrations mentioned above were measured while the ventilation fans were operating. Other studies have also reported problems with operations, maintenance, and installation, which affect the reliability and performance of these systems [8-11].

A recent literature review on the associations of home energy efficiency retrofits with indoor environmental quality, comfort, and health shows mixed results depending upon the outcome being assessed. The review considered the following outcomes that were reported in studies comparing before and after energy retrofits: formaldehyde, volatile organic compounds (VOCs), nitrogen dioxide (NO2), carbon dioxide (CO2), radon, dampness and mold, asthma, non-respiratory outcomes, along with thermal comfort, mental health and general health. Many of the health outcomes were self-reported, and the data were obtained mostly in low-income housing.

Table 5 below summarizes the main findings. Overall, measured concentrations of radon and formaldehyde concentrations tended to increase after retrofits that did not add mechanical ventilation. Indoor concentrations of NO2 and VOCs other than formaldehyde increased and decreased with approximately equal frequency. Dampness and mold, usually based on occupant’s reports, almost always decreased after retrofits. Thermal comfort, non-asthma respiratory symptoms, general health, and mental health nearly always improved after retrofits. For asthma symptoms, the evidence of improvement slightly outweighed the evidence of worsening.

The net effect of building energy efficiency, motivated by climate change, on indoor environmental quality, comfort, and health can be complex. There are some measures for which further input is warranted, where concentrations of potentially harmful pollutants are found to increase [12]. There is also a potential to improve comfort and health conditions for many. Table 4 below lists examples of building energy efficiency measures expected to influence either thermal comfort conditions or indoor air quality and health and summarizes their expected or hypothesized effects. Better outcomes can be achieved through strategic implementation of energy efficiency measures by also considering the effects on health, as related guidance becoming available [13-15].

Table 4. Examples of demonstrated or hypothesized effects of energy efficiency on indoor environments.

Thermal insulation of building envelopes
Positive Effects	Negative Effects
Improved thermal comfort Reduction in adverse health effects of heat stress during heat waves from attic or roof insulation Health benefits of avoiding low winter indoor temperatures	Increase in adverse health effects of heat stress during heat waves with addition of insulation to the internal surfaces of external solid masonry walls Some insulation can emit pollutants, e.g., spray foam insulation if not properly installed Lower sensible cooling loads may lead to reduced moisture removal by the air conditioner, increasing indoor humidity and associated risks of indoor microbial growth Risks of dampness and mold in building envelope
Energy efficient windows, window shading
Positive Effects	Negative Effects
Improved thermal comfort Improved control of indoor lighting levels	Lower sensible cooling loads may lead to reduced moisture removal by the air conditioner, increasing indoor humidity and associated risks of indoor microbial growth
Air seal building envelopes
Positive Effects	Negative Effects
Improve comfort Decreased indoor concentrations of ozone and particles from outdoors	Increased concentrations of pollutants from indoor sources Sealants can be sources of indoor pollutants Risks of dampness and mold in building envelope
Sealed crawl spaces and attics
Positive Effects	Negative Effects
Reduced moisture and mold problems (if well implemented)	May increase indoor radon when crawl spaces are sealed Larger fraction of pollutants from construction materials enters occupied space
Add outdoor air economizer to cooling system
Positive Effects	Negative Effects
Often large time-average decrease in concentrations of pollutants from indoor sources	Increases in indoor concentration of ozone from outdoor air In some buildings, will increase indoor concentration of particles from outdoor air
Increase ventilation and add ventilation energy recovery
Positive Effects	Negative Effects
If outdoor air ventilation rate is increased when heat recovery is added, decreased indoor concentrations of pollutants from indoor sources	If outdoor air ventilation rate is increased when heat recovery is added, indoor concentrations of ozone will usually increase, indoor concentrations of particles from outdoor air may also increase although some level of particle filtration is often provided in energy recovery ventilation systems.
Natural ventilation
Positive Effects	Negative Effects
Reduced sick building syndrome symptoms	Increased indoor levels of ozone and particles from outdoors
Evaporative cooling
Positive Effects	Negative Effects
Some systems increase outdoor air ventilation; thus, decrease indoor concentrations of pollutants from indoor sources	Increase indoor humidity, dust mite allergen levels, risks of mold growth, particularly for direct evaporative cooling which supplies humidified air to the building's interior
High efficiency power-vented and sealed-combustion furnaces and water heaters
Positive Effects	Negative Effects
Many high efficiency furnaces and water heaters use a fan and sealed piping to push combustion gases to outdoors, reducing the risk that these gases spill into indoor air, which can occur with natural draft appliances	N/A
Eliminating Wood-based heating
Positive Effects	Negative Effects
Reduced leakage of combustion pollutants to indoors Reduced combustion pollutants to outdoors which, in turn, decreases indoor air concentrations	N/A
Increased temperature set points in summer
Positive Effects	Negative Effects
N/A	Reduced thermal comfort Higher emission rates of pollutants from building materials and furnishings, increasing indoor air concentrations
Decreased temperature set points in winter
Positive Effects	Negative Effects
Reduced emission rates of pollutants from building materials and furnishings, reducing indoor air concentrations	Possible increase in mold growth and mold exposures due to cooling of building envelope and increased condensation or locally high humidity Decreased thermal comfort

Table 5: Health and comfort outcomes after energy efficiency building retrofits from 2020 literature review [12]

Radon

Negative Effects: There is an Increase in exposure to radon after retrofits. The expected health impact of increasing radon in homes is an increase in the risk of lung cancer.

Formaldehyde

Negative Effects (limited data): There is a tendency for formaldehyde concentrations to increase after basic retrofits for strong findings, except in the case of green retrofits, where formaldehyde levels decrease. However, the data is insufficient to determine whether the changes in indoor VOC concentrations vary depending on type of retrofit. Overall, there is a tendency for indoor concentrations to increase after basic retrofits, but the data are limited.

Volatile Organic Compounds (VOCs) and Nitrogen Dioxide (NO2)

Insufficient Data: VOCs - No strong evidence of an overall tendency for either increases or decreases after ventilation-added and green retrofits.

Insufficient Data: NO2 - Insufficient study strength and data to determine effects of retrofits on indoor NO2.

Carbon Dioxide (CO2)

Negative Effects (very limited data): Very limited data suggests increases in concentrations after basic retrofits and decreases after ventilation-added and green retrofits, but the data are not sufficient for conclusions.

Temperature

Positive Effects: Mean indoor temperatures during winter increased after retrofits or were higher in homes that had been retrofit. Most studies reported mean increases across the retrofit homes of less than 1.5 C. Even with warmth retrofits, which had increased indoor temperatures as the primary objective, most sample-average temperature increases were less than 2 C. Only about half of the temperature increases were statistically significant. Many of the findings received a weak strength rating, often because of short periods of temperature measurement.

Dampness and Mold

Positive Effects: Reported dampness and mold diminished after retrofits. Often diminished by 40% or more.

Thermal Comfort

Positive Effects: Large percentage increases in thermal comfort, most from warmth retrofits. Reduction in thermal discomfort, with reductions greater than 40%. The improvements in thermal comfort are always greater than 80% and improvements in thermal discomfort range from 28% to 94%.

Asthma

Positive Effects (limited): Finding of reduced symptoms moderately outnumber findings of increased symptoms, although more of the reductions in symptoms are far from statistically significant, and there is weak evidence for the improvements in asthma symptoms. Most of the assessed asthma symptoms decreased following retrofits that added ventilation or focused on warmth. Except for two weak findings, all changes in asthma symptoms were modest reduction or increases of 31% or less. No clear trend of improvement or worsening after retrofits is evident and most study findings that were rated as moderate or strong were changes of less than 30%.

Respiratory Non-Asthma Outcomes

Positive Effects: Outcomes improved after retrofits. Data suggest overall improvement in non-asthma respiratory outcomes after retrofits. Non-asthma respiratory outcomes and general health typically improved after retrofits, regardless of type of retrofit.

Mental Health

Positive Effects: Improvement or no statistically significant change in mental health. Mental health changes were always shown as improvements.

1. Department of Energy. The 2010 Building Energy Data Book. 2010; Available from: http://buildingsdatabook.eren.doe.gov/ChapterIntro1.aspx?1#4.

2. Crump, C., A. Macmillan, and M. Swainson, Indoor air quality in energy efficient homes - a review. 2009, IHS BRE Press: United Kingdom.

3. Shrubsole, C., et al., 100 Unintended consequences of policies to improve the energy efficiency of the UK housing stock. Indoor and Built Environment, 2014. 23(3): p. 340-352. https://dx.doi.org/10.1177/1420326X14524586.

4. Davies, M. and T. Oreszczyn, The unintended consequences of decarbonising the built environment: A UK case study. Energy and Buildings, 2012. 46: p. 80-85. https://dx.doi.org/10.1016/j.enbuild.2011.10.043.

5. Fisk, W.J., Climate change and IEQ. ASHRAE Journal, 2009. 51(6): p. 22-23.

6. IOM, Climate change, the indoor environment, and health. 2011, Washington, D.C.: The National Academies Press.

7. Brett Singer, W.R.C., Yang-Seon Kim, Francis J. Offerman, Ian S. Walker, Indoor air quality in California homes with code-required mechanical ventilation. Indoor Air, 2020. 30: p. 885-899. https://dx.doi.org/10.1111/ina.12676.

8. Rik Bogers, R.J., Irene van Kamp, Atze Boerstra, Froukje van Dijken, Mechanical ventilation in recently built Dutch homes: technical shortcomings, possibilities for improvement, perceived indoor environment and health effects. Agricultural Science Review, 2012. 55(1): p. 4-14. https://dx.doi.org/10.1080/00038628.2011.641736.

9. Jelle Laverge, M.D., Arnold Janssens, Carbon Dioxide Concentrations and Humidity Levels Measured in Belgian Standard and Low Energy Dwellings with Common Ventilation Strategies. International Journal of Ventilation, 2015. 14(2): p. 165-180. https://dx.doi.org/10.1080/14733315.2015.11684078.

10. K Eklund, R.K., A Banks, D Hales, Pacific Northwest Residential Effectiveness Study - FINAL REPORT, W.U.E. Program, Editor. 2015.