Analysis > Implementation

Laundry Dryer Exhaust

Based on our consultations with Tim Tilley of Envirosep (Georgetown, South Carolina) we could expect an efficiency rating of about 70% for a counter-flow heat exchanger placed around the exhaust tube. At this efficiency, potential savings would be less than $5,400 a year, based on current natural gas prices. With the significant complications that could arise from condensation in the exhaust stack, the economic benefit of recovering waste heat from the dryers was not clearly evident.

Greywater Heat Recovery

Because the drain pipes from the men's and women's locker room showers, the largest source of heated greywater, run through the concrete slab, the installation of a vertical drop heat exchanger would require significant renovations. Additionally, because these locker rooms are in the basement, the wastewater would have to be pumped up to enter the exchanger, reducing the savings from the systems and increasing the complexity of the system. The electricity to power this pump would reduce the energy costs avoided.

The best way to recover the waste heat from the sources in the basement would be to install a heat recovery system in the sump tank adjacent to the lap pool. The majority of shower water used in the basement passes through this sump tank, and the tank is in the same room as the lap pool heater. A simple system could be fabricated to pass cold water going to the pool through the sump tank before it goes to the pool heater. Because all of this equipment is in the same room, few physical changes to the building itself would be required (a small hole in an interior wall). A minimum amount of copper piping would be needed, reducing the initial cost of the system and heat lost in transportation of the liquids. The pressure of the water entering the building would drive the water through the heat exchanger and into the pool. The hot water in the sump is circulated by the draw of the sump pumps.

If we estimate that 50% of the heat reaching the sump tank could be recovered, energy savings would amount to $15,000 per year (using February 2001 value of $1.28/therm). The payoff time for this system would certainly be less than one year, more likely in the range of two to three months.

The heat from the showers in the residence and women's fitness center could be recovered used in a vertical-drop heat exchanger or at the sump tank. This water has a long vertical drop from the fourth floor to the basement. This has a number of advantages over a home-built system installed in sump system:

• Third-party tested commercial systems are available. These systems have been rated for efficiency, which makes estimates of cost savings more accurate. The GFX system (model GS-60) is rated at 60% efficiency.
• The exchanger would be closer to the source of greywater, less heat lost in pipes
• More options for where the heat is recovered and where it is used. Water heated could be routed to showers on second floor and above, to water heater in basement, or to both.

If 60% of the heat reaching the heat exchanger was recovered, the YMCA could save $6,500 annually. The GFX system, costs around $1,000 uninstalled. A home built system could be substituted, but this would probably be less efficient.

(all estimates and calculations are explained and available in an Excel spreadsheet downloadable from the appendix)