Install Ducts in Conditioned Space
Ducts: Conditioned Space vs. Unconditioned Space
Designing buildings with ducts in conditioned space to eliminate the heat loss associated with duct leakage.
Synopsis:
In most cases, heating and cooling ducts are located outside the thermal and pressure boundary of the conditioned space. A wide body of literature has found that distribution system conduction and air leakage can cause 30-40% energy losses before cooling and heating air reaches the conditioned space.
This strategy is typically impractical as a retrofit application because ductwork can be difficult to access and expensive to retrofit. Since even well-sealed and insulated ducts will leak conditioned air, many new energy-efficient homes now place the duct system within the conditioned space of the home. Not only does this ensure that leaked air is entering the conditioned space, but it also reduces the temperature gradient between the conditioned air travelling through the duct and its environment. This reduction in temperature gradient reduces the loss of energy via conduction through the duct’s insulated sleeve.
Duct air leakage has also been implicated in indoor air quality problems, including backdrafting of combustion appliances, causing vehicle exhaust to enter the living space, and transporting pollutants (including moisture) from unconditioned to conditioned spaces.
This strategy may be accomplished in part by air sealing and insulating the attic space and adding additional fresh-air supply, and by placing ducts in chases. Although this strategy will result in greater surface area to the outside for heat transfer and a bigger volume of air to condition, these relatively small increases in energy use are offset by the benefits of capturing duct losses.
Energy Savings: 10%
Energy Savings Rating: Extensive Assessment
What's this?
| Level | Status | Description |
| 1 | Concept not validated | Claims of energy savings may not be credible due to lack of documentation or validation by unbiased experts. |
| 2 | Concept validated: | An unbiased expert has validated efficiency concepts through technical review and calculations based on engineering principles. |
| 3 | Limited assessment | An unbiased expert has measured technology characteristics and factors of energy use through one or more tests in typical applications with a clear baseline. |
| 4 | Extensive assessment | Additional testing in relevant applications and environments has increased knowledge of performance across a broad range of products, applications, and system conditions. |
| 5 | Comprehensive analysis | Results of lab and field tests have been used to develop methods for reliable prediction of performance across the range of intended applications. |
| 6 | Approved measure | Protocols for technology application are established and approved. |
Simple Payback is one tool used to estimate the cost-effectiveness of a proposed investment, such as the investment in an energy efficient technology. Simple payback indicates how many years it will take for the initial investment to "pay itself back." The basic formula for calculating a simple payback is:
Simple Payback = Incremental First Cost / Annual Savings
The Incremental Cost is determined by subtracting the Baseline First Cost from the Measure First Cost.
For New Construction, the Baseline First Cost is the cost to purchase the standard practice technology. The Measure First Cost is the cost of the alternative, more energy efficienct technology. Installation costs are not included, as it is assumed that installation costs are approximately the same for the Baseline and the Emerging Technology.
For Retrofit scenarios, the Baseline First Cost is $0, since the baseline scenario is to leave the existing equipment in place. The Emerging Technology First Cost is the Measure First Cost plus Installation Cost (the cost of the replacement technology, plus the labor cost to install it). Retrofit scenarios generally have a higher First Cost and longer Simple Paybacks than New Construction scenarios.
Simple Paybacks are called "simple" because they do not include details such as the time value of money or inflation, and often do not include operations and maintenance (O&M) costs or end-of-life disposal costs. However, they can still provide a powerful tool for a quick assessment of a proposed measure. These paybacks are rough estimates based upon best available data, and should be treated with caution. For major financial decisions, it is suggested that a full Lifecycle Cost Analysis be performed which includes the unique details of your situation.
The energy savings estimates are based upon an electric rate of $.09/kWh, and are calculated by comparing the range of estimated energy savings to the baseline energy use. For most technologies, this results in "Typical," "Fast" and "Slow" payback estimates, corresponding with the "Typical," "High" and "Low" estimates of energy savings, respectively.