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 [118]. 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 [60, 119-122]. Some measures are expected to have both positive and negative effects. Table 4 [1, 60, 122] 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.

Two of the very common energy efficiency retrofit measures for homes with a potential to affect indoor environmental quality are envelope tightening to reduce outdoor air ventilation and addition of thermal insulation to the building envelope. In addition, new homes may be constructed with nearly airtight building envelopes and low rates of mechanical ventilation supplied with mechanical systems employing fans. The associated empirical data on how these measures affect comfort and health are sparse.

Four studies have found statistically significant increases in some, but not all, allergy or asthma symptoms in homes with less ventilation [123-126] while two additional studies found no statistically significant direct effects of ventilation rates on health [127, 128]. Milner et al. [129] estimated with models that increases in home air tightness in England, without compensating measures, would increase indoor radon concentrations by 57% (radon is a naturally-occurring radioactive gas) with an associated peak increase of 278 deaths per year.

With respect to addition of thermal insulation, data from a study of 79 U.S. homes [130] suggest about a 0.5 °C increase in temperature after retrofits, implying a modest increase in winter-time comfort. A larger study of low income dwellings in the United Kingdom [131] reported an increase in average indoor temperature from 17.1 to 19.0 °C and a rise in percentage of households reporting comfortable or warmer conditions from 36% to 79%, after adding thermal insulation and also replacing the heating systems with an energy efficient heating system. A study of adding thermal insulation to homes serving a low income population in New Zealand [32, 33] also provides evidence of improvements in temperatures, comfort and several health or health-related outcomes (self-reported colds and flu, wheeze, sleep disturbed by wheeze, visits to a general practitioner, and days of missed work and school) However, there was a large reported decrease in mold in the homes after addition of insulation; thus, it is not certain that the improvements in health in this study are a consequence of the increases in indoor air temperature, which were modest, averaging 0.5 °C (1 °F). Also, relative to temperatures in homes in North America and Europe, indoor temperatures in the New Zealand study population were low, averaging less than 14 °C (57 °F) in the bedroom. Based on a rigorous review of published literature including the aforementioned studies from New Zealand, Thomson et al. [132] concluded that "housing investment which improves thermal comfort in the home can lead to health improvements, especially where the improvements are targeted at those with inadequate warmth and those with chronic respiratory disease. However, the interventions considered in the review by Thomson et al. extend beyond the addition or upgrading of thermal insulation. Thus, the available data suggest, but do not confirm, widespread health benefits of adding thermal insulation.

Often, multiple building energy efficiency measures are implemented at the same time, making it difficult to assess how individual measures affect comfort or health. A study performed of 706 dwellings for low income residents in the United Kingdom found a statistically significant increase in current asthma in dwellings with a higher energy efficiency rating [133], after controlling for other asthma risk factors. The risk of current asthma increased monotonically as the energy efficiency rating increased and the findings were not a consequence of an association of energy efficiency with indoor visible mold. The prevalence of current asthma was approximately twice as high among occupants of homes with the highest quartile in energy efficiency rating compared to occupants of homes with the lowest quartile of energy efficiency rating.

The net effect of building energy efficiency, motivated by climate change, on indoor environmental quality, comfort, and health cannot be predicted with confidence. Data suggest a potential to improve comfort and health conditions through strategic implementation of energy efficiency measures. While most building energy efficiency measures are currently implemented without serious consideration of the effects on health, practices could change and related guidance is becoming available [134-136].

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

Energy Efficiency Measure

Effects

+ = positive/desirable effects; - = negative/undesirable effects

Thermal insulation of building envelopes

+ improved thermal comfort

+ reduction in adverse health effects of heat stress during heat waves from attic or roof insulation [19-21]

- increase in adverse health effects of heat stress during heat waves with addition of insulation to the internal surfaces of external solid masonry walls [19-21]

+ health benefits of avoiding low winter indoor temperatures [33, 137]

- 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

+ 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

+ 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

Reduce mechanical ventilation rate

+ decreased indoor concentrations of ozone and particles from outdoors

- increased concentrations of pollutants from indoor sources

- increased risks of adverse health effects and reduced work performance

Add outdoor air economizer to cooling system

+ 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

+ 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.

Sealed crawl spaces and attics

+ 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

Natural ventilation

+ reduced sick building syndrome symptoms

- Increased indoor levels of ozone and particles from outdoors [111]

HVAC systems with less air recirculation

- less particle removal by filtration of recirculated airstream, higher indoor particle concentrations

Evaporative cooling

+ 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

+ 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

Wood-based heating

- leakage of combustion pollutants to indoors

- increases outdoor air combustion pollutants which, in-turn, increases indoor air combustion pollutants

Increased temperature set points in summer

- reduced thermal comfort

- higher emission rates of pollutants from building materials and furnishings, increasing indoor air concentrations

Decreased temperature set points in winter

+ 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

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