HYBRID VERTICAL DRAINPIPE HEAT EXCHANGER
A low-cost hybrid heat exchanger uses sheet copper and rigid plastic tubing. Copper is used only where actual heat transfer takes place, adjacent the drainpipe wall. All other components are plastic to lower cost. It pre-heats fresh cold water using waste heat from the drain such as from a shower drain. The heat exchanger comprises an inner copper conduit or drainpipe, a rolled sheet copper cylinder, an outer plastic tube and manifolds, and O-ring. On assembly, inserting the drainpipe results in the O-ring being compressed between the copper cylinder and the plastic tube. The result is a sealed water chamber wherein heat transfer takes place. The ends of the plastic tube have radially spaced water distribution holes into the chamber and inlet and outlet manifolds, each with water connections to the building's cold water supply. A method of recovering heat from non-shower hot water uses using a separate reservoir is also disclosed.
The present invention is in the field of heat exchangers and more particularly drainpipe heat exchangers for drainwater heat recovery from vertical drainpipes.
BACKGROUND OF THE INVENTIONDrainwater is a low-level heat source. As such it requires a low cost heat exchanger in order that home and building owners can recover its cost in a reasonable time.
SUMMARY OF THE INVENTIONWhile it may be used in a variety of heat transfer applications, instant heat exchanger's use in heat recovery from a building's wastewater drainpipe will be described in detail herein. The instant heat exchanger is suitable for both vertical and horizontal installations. When installed vertically it operates as a falling film heat exchanger where the drainwater flows circumferentially on the inner wall which maximizes the wetter surface area needed for heat transfer. Typically, vertical installations are limited in length by ceiling-to-floor dimensions in buildings which, in turn, limits the wetted surface area.
By moving the relative locations of its plumbing fittings, it can be used horizontally, where it is preferably made as long as possible to maximize wetted surface area for heat transfer which directly affects performance and cost-effectiveness.
The heat exchanger comprises a set of concentric cylindrical components. At the center is a conduit such as a standard drainpipe made of copper or other thermally conductive material.
Around it is a shorter cylinder of sheet copper (or other thermally conductive material). This cylinder is open along its length to define a small gap. Concentric with the cylinder and spaced from it (i.e., of larger diameter) is a outer tube of plastic or other rigid, low-cost material, which has a ring of spaced holes that are covered by a manifold at each end.
Next is a unique gasket-spacer, such as a common O-ring, that follows the perimeter of the copper cylinder and thereby defines the boundary of a sealed chamber one wall of which is the cylinder and the other the plastic tube. The inner openings of the ring of holes are also enclosed by the gasket.
The short cylindrical plastic manifolds are sealed to the outside of the plastic tube and have has an internal circumferential groove and a water fitting. The fitting opens into the groove within which the outer openings of the ring of hole are located.
Thus water (or other fluid) for heat transfer with the central drainpipe, enters the sealed chamber at one end and exits at the opposite end of the outer tube.
Heat transfer takes place in the chamber, either heating or cooling, depending on the relative temperatures of the drainwater and the fresh water. For most uses heating of the freshwater will be the goal. However, for example, a drinking fountain can use the instant invention to cool the delivered water using draining cold water to cool fresh incoming warmer water.
The diametric dimensions of the components ensures that upon final assembly of the components, the first described drainpipe, which is inserted last, is a press fit into the cylinder which causes the O-ring to compress sealing the chamber.
Inside the chamber, the building's normal water pressure exerts enormous force on the cylinder close the gap slightly to create an extremely tight clamping action around the drainpipe for maximum thermal conductivity. For example with water pressure of 50 psi and a cylinder area of 200 square inches, the circumferential clamping force onto the drainpipe is 10,000 pounds.
Referring to the drawings,
Inlet manifold 4 (lower) and outlet manifold 4a (upper) have inlet 5 and outlet 6 fittings (inlet flow 15a, outlet flow 15b) and an internal circumferential flow channels 10 that communicate with their respective distribution holes 9 in outer tube 1. As shown in
The manifolds 4 and 4a are orientated such that the inlet 5 and outlet 6 are positioned opposite to where the gasket O-ring gap 3c will be located on assembly. For horizontal operation, a third centralized manifold 4b may be added for the inlet 5 and the two end manifolds 4, 4a used collectively as outlet 6.
The manifolds can be fabricated from four parts: a short section of plastic tube with two spaced plastic rings 11 inside, and a plastic pipe fitting, all bonded together and defining a circumferential flow channel 10. Alternatively flow channel 10 may be formed internally by machining an internal groove in a piece of thick wall tube or pipe. The manifolds are bonded to secure and seal them to outer tube 1. The manifolds may also be fitted with O-rings (not shown) that seal against the outer wall of outer tube 1. Of course the flow channel 10 may be formed in the outer circumference of outer tube 1 instead of, or, in addition to, its indicated location inside the manifolds 4, 4a (not shown). A plurality of flow channels may be formed using a plurality of elements extending between the O-rings.
A third manifold 4b (dashed outline) of the same design may also be added around the middle of the outer tube inclosing a ring of distribution holes (not shown) and with a water fitting. Using manifold 4b as the water inlet the water flow therefrom is both up and down (or left and right if horizontal, with gasket gap 3d downwards). In this way a remote water tank or reservoir can be plumbed inline with the instant heat exchanger to enable thermosiphonic flow therebetween for heat exchange with batch water flow.
Inlet manifold 4 may have a fluid pressure regulator fitted (not shown) to limit the internal pressure in chamber 15.
Cylinder 2 may be least expensively formed from sheet copper which remains open (un-seamed) along its length. Preferably it has at least one longitudinal flange 2a shown in
Once assembled the O-ring elements maintain a sealed spacing between cylinder 2 and outer tube 1 which defines a chamber 15 (
Cylinder 2 may be fabricated with an angled gap 7a as shown in
In
Note that with this arrangement lower branch 104 can see two way flow at different times (double-ended arrows): if there is cold water flowing through branch 102, flow through branch 104 (and branch 103) is to the left into reservoir 110; if only used hot water is draining, then the flow in branch 104 will be to the right into heat exchanger 100 because of the above described thermosiphonic phenomena.
Although the invention has been shown and described with respect to detailed embodiments thereof, it should be understood by those skilled in the art that various changes in form and detail thereof may be made without departing from the spirit and the scope of the claimed invention.
Claims
1. A vertical drainpipe heat exchanger for transferring heat from a drainpipe, said drainpipe heat exchanger comprising:
- a conductive layer surrounding said drainpipe;
- a gasket spacer, said gasket spacer having channels to permit flow of fluid therethrough adjacent said conductive layer; and
- an outer cylinder surrounding said gasket spacer, an inlet and an outlet within said outer cylinder to permit fluid access to said channels.
2. The vertical drainpipe heat exchanger of claim 1 wherein said conductive layer has a vertically extending opening therein.
3. The vertical drainpipe heat exchanger of claim 1 wherein said gasket spacer comprises an upper ring, a lower ring, and a plurality of legs extending therebetween.
4. The vertical drainpipe heat exchanger of claim 2 wherein said outer cylinder has a plurality of inlets and a plurality of outlets to permit fluid access to said channels.
5. The vertical drainpipe heat exchanger of claim 3 wherein said conductive layer has a vertically extending opening therein, said conductive layer having a flange adjacent said opening, said legs of said gasket spacer being located adjacent said flange and said opening.
Type: Application
Filed: May 16, 2013
Publication Date: Nov 21, 2013
Inventor: Winston MacKelvie (Knowlton)
Application Number: 13/986,583
International Classification: F28F 1/00 (20060101);