Stopping Heat From Going Down the Drain

August 31, 2000
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It was an invention by accident. Carmine Vasile was in his basement when he inadvertently touched the copper drainpipe, which was hot from someone taking a shower upstairs. He thought that there must be a way to recover the heat from the hot water going down the drain.

Vasile has an engineering background, so he made some quick heat transfer calculations and realized that there were some significant heat recovery possibilities by wrapping a coil of copper tubing around a copper drain pipe.

The first prototype of his gravity falling film heat exchanger, or GFX, was tested in April 1980, shortly after conception of the idea. The actual heat recovery was very close to the predicted calculations.

Although this invention is now 20 years old, it still can be considered a new, and different, type of heat exchanger.



SHELL-AND-TUBE comparison

When compared with a shell-and-tube heat exchanger, having a single wall and same tube id, the GFX requires one-fourth the wetted surface to exchange the same amount of heat. That means GFX heat exchangers are cheaper than shell-and-tube heat exchangers because they have less copper in them.

In one installation, the owners of a textile plant wanted to put in a heat recovery system to recover heat from wash water and dye water. The company had a $200,000 budget for the project.

A design for shell-and-tube heat exchangers, which included installation, could recover about 30% of the net energy going down the drain. The GFX system could recover 83% of the available energy, making it 2.77 times more efficient for the same capital expenditure.

The GFX has also been installed in hotels in New Zealand and Australia. Manitoba Hydro has several dozen systems in houses in Canada, and it is in the Toronto Healthy House. The system has been installed in a HUD rehab project in Madison, WI.

The heat exchanger was also featured on the Bob Vila Home Again show in September 1999. A number of systems were installed as a consequence of it being featured on the show.

Doucette Industries, York, PA, has been licensed by Vasile, who holds a patent, to manufacture GFX heat exchangers. Doucette is presently negotiating with a major stocking distributor of hvac and plumbing products to have a chain of supply houses stock the heat exchangers, so they will be readily available to contractors.



SOLVING PROBLEMS

An important feature of the unit is that it increases the capacity of the domestic hot water heater, since many residences have undersized systems. Another problem is that many hot water heaters lime up and lose capacity.

Liming up will not occur in the GFX heat exchanger, since it only preheats the cold water going to the hot water heater. Further-more, it operates at a lower temperature (below the point where liming occurs).

A common problem in areas such as Long Island, NY, is that tankless coils cannot supply enough hot water while the boiler is also attempting to heat the house. The GFX solves that problem by cutting the domestic hot water load, such as a shower, in half.

With a shower head using 4.5 gal of hot water per minute, you need 136,000 Btuh (electrical equivalent is 40 kW) to heat the domestic hot water in winter, when the incoming cold water from the street is between 40°F and 45°F. The GFX is a simple solution to the problem of not getting enough hot water.

Vasile told of a person in Vermont who heats his entire house µ a well-insulated 2,000-sq-ft home µ using a 40-gal, propane-fired hot water heater. A circulating pump is used to distribute hot water from the hot water heater to the radiators and to the radiant heating system. Because the GFX cuts the shower load in half, his family of four never runs out of hot water.

The GFX could also bring a tax credit or rebate. Installing the unit will bring a 25% tax credit starting this year in the state of Oregon. This is the first state to offer this tax credit. Minnesota Power will be giving a $100 rebate for each installation.



Sidebar: Meltdown With Cool Results

A visitor at a recent trade show told inventor Carmine Vasile of a totally unexpected application of the GFX heat exchanger. It can be used to precool cold water from ice melt dumped down the drain.

The individual who applied this learned of the GFX on the Bob Vila show and told his wife that he could use it in his ice factory in New Jersey. He said his machine dumps 4.5 gpm of ice melt at 32°F down the drain. His incoming cold water temperature rises above 70° in summer months. So, he has 9,365,200 gal of cold water he can use to precool city water being fed to the ice machines.

In the summer, the differential between the city water and the ice melt is 40°. The GFX can recover 70% of the differential, or 28°, which also leads to increased production of ice from the ice machines.

The amount of “cold” energy that is being saved is 62,748 Btuh. Assuming a COP of 1, 18.4 kW of power would be saved. At a cost of $0.12/kWh, the cost savings would be $2.20/hr. The cost of the GFX heat exchanger is $1,200 without installation, so the payback period for this installation was 3.2 weeks.



Sidebar: Wringing Out Heat for Reuse

A commercial laundry in New Hampshire is making efficient use of the GFX heat exchanger. Four units are ganged together using a PVC manifold to evenly distribute the facility’s hot gray water to each of the heat exchangers (see Figure 1). The total cost of the heat exchangers was $1,600.

As propane was also being used to operate the laundry dryers, it was impossible to determine water heater energy savings. However, total usage of propane went up only 3% while the business expanded 17%. Thus, for this application, the GFX system is increasing energy efficiency by about 14%.

Cost savings during summer months were about $75/month. The savings are expected to be greater in winter months, when the temperature of incoming cold water drops to about 40°F. Conservative cost savings are about $900/year, but more importantly, the firm did not have to purchase another hot water heater with the expansion of business.

The system was installed to just preheat the cold water going to the water heaters. However, by preheating the water going to the washing machines as well, one can use warm water for the rinse cycle. This warm water is essentially “free,” so the clothes coming out of the washing machines are somewhat warmer.

The net result is that the amount of propane necessary to dry the clothes in the dryers is reduced, cutting costs even more.

Karpen, P.E., is a consultant and certified energy manager. He can be reached at 3 Harbor Hill Drive, Huntington, NY 11743; 631-427-0723. Inventor Carmine Vasile can be reached at P.O. Box 48, Oakdale, NY 11769; 631-758-6271. Doucette Industries can be reached at 701 Grantley Rd., York, PA 17405; 800-445-7511; www.doucetteindustries.com (website).

Publication date: 09/04/2000

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