Drain-Water Heat Recovery
Drain Water: Heat Recovery Coil vs. No Heat Recovery
Copper-coiled heat exchanger to recover heat from waste hot water. For showers or other domestic hot water.
Synopsis:
A typical drain water heat recovery system may comprise a 3-inch-diameter copper drainpipe wrapped by a coil of 1/2-inch-diameter copper water supply pipe. This coil may extend for 4 feet to 7-feet in length. The longer the coil, the better the heat transfer capability. This type of system naturally heats the incoming cold water using the principle of gravity film heat exchange. As wastewater flows down a drainpipe, it naturally clings to the inside of the pipe in a thin film. Heat from this thin film of water conducts to the cold water traveling up through the supply copper pipe coiled around the drainpipe. This preheated supply water then travels to the shower or the hot water heater (Moore, 2013).
Approximately 90% of the heat contained within shower water is lost as waste heat and showering accounts for 50% to 70% of residential hot water energy use. A good drainwater heat recovery system can recapture up to 60 percent of this waste heat. The double-walled configuration of a GFX system prevents potable water from mixing with graywater, so the system complies with plumbing codes. Little, if any, upkeep or maintenance is necessary. Depending on the application, GFX systems can reduce water heating costs by 20 to 35 percent. Costs are between $500 and $1,000 per system, which includes installation costs (Moore, 2013). Costs increase if a storage tank is necessary.
Drain water heat recovery systems can be installed with any type of drainage pipe and fresh water piping (ABS, PVC, cast iron, copper, PEX) and can work well with demand water heaters or storage water heaters.
Energy Savings: 30%
Energy Savings Rating: Not rated.
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.