CA2550281A1 - Method of increasing heat recovered by gfxtm system - Google Patents

Abstract

GFX-STAR.TM. is the trade name of a drain heat recovery (DHR) system that can increase the amount of heat recovered by the conventional GFX.TM. system of U.S. Patent No.
4,619,311 by boosting the DHR-efficiency of its Gravity Film heat eXchanger (GFX) while it's recycling waste-heat from showers and sinks; in addition to enabling the same GFX to recycle waste heat from dishwashers, clothes washers and baths, without having to add convective chambers, means to store wastewater or separate solids as illustrated in U.S. Patent Nos. 6,722,421; 5,791,401;
5,740,857; 4,821,793 or prior art cited therein.

Description

Descripiirin BACKGROUND OF TBE INVENTION

1. Field of the Invention The instant invention relates to a method for increasing heat energy recovered by the apparatus disclosed in U.S. Patent No. 4,619,311 hereinatter called the GFXTM Patent;
the heart of which is a Gravity Film heat eXchanger (GFX).

Many coil & tube GFX units like those illustrated in FIGS. 1& 2 have been sold by various Licensees of the GFXTM Patent who have manufactured them using trade-secret coiling techniques and tools.
Other types of heat exchangers can also be used with the instant invention, which also anticipates multi-drain installations, does not require wastewater storage or other complex accessories, and can be used to increase energy savings of eacisting GFX uistallations.

2. Description of the Prior Art The prior art is exemplified by many examples of heat reclaimation systenis, most of which are expensive, complicated, may require convective chambers, means to store wastewater or separate solids and require periodic cleaning and maintenance in order to avoid fouling andlor degradation of heat recovery efficiency; examples of which are shown in U.S. Patent Nos.
6,722,421, 5,791,401, 5,740,857, or 4,821,793, and Foreign Patent Nos. 3011111, 3244600, 2165932, 57142488, for example.

A notable exception is the apparatus of U.S. Patent No. 4,619,311, which, as illustrated in FIG. 3 below, saves little energy in households where shower and small sink usage is low. According to FIG.
4, such usage represents 43% + 15% = 58% of the domestic hot water consumption in typical American homes.

G.,FX-STARTm Performam*
AM l~~i~
c~6o cFx so-" cFx 50 .
G -STA TM 1) 1 . tYloillis . lw 4ft .
~ .
?30 ~
OkAh"
42%
10 G rr[ ~' . .

Ratio of hot.-shower/faucet use to total hot water ("/=) FIG. 3 Energy saviags of a GF'X-STAR'rm DHR-system FIG. 4 From Heat Reroveryfrom Wactewater Using Gravity-compared to conventional GFX spstem oovered by U.S. Filnr Hed Exclianger, U.S.
Departmetrt of Energy (DOE) by Patent #4,619,311. the Oak Ridge Nationai Laboraiory, DOF/EE-0247, May *AssaYnes approximately 80% of a water heater's 2001.
heat reaches a Model G3-60 or S4-60 GFX. (From: htt :i! xtecli o1o e qu SUMMARY OF THE IliVENTION

In the present invention, the disadvantages of prior art and limitations of the GFXrm Patent are overcome by making a simple, cost-effective modification to a conventional GFX'rm system that not only can enhance heat recovery efficiency for its substantial infringing-use -from near 50% to about 59%, it can significantly improve energy savings in homes that use little to no hot water for showers and sinks --- from nil to about 50%, according to FIG. 3, while preserving GFX's self-cleaning, non-fouling, maintenance-free operation.

This improved performance is accomplished by simply adding a pump and check-or solenoid-valve to the patented GFXTM system as illustrated in FIG. 1 so as to cause GFX's coil flow rate to substantially exceed its drain flow rate, something that is not possible in a conventional GFXTm system.

For example a Model G3-60 GFX is rated @ 60% DHR-efl"iciency for equal coil &
drain flow rates of 2.25 GPM, but if a pump is instalied to double its coil-flow rate, its DHR
efficiency increases from 60 /a to about 77% if 2.25 GPM continues to flow down its drain tube. The G3-60's coil pressure drop wiil increase from 8 to about 32 PSI, so a pump offering sufficient head must be chosen. Similarly, a GFX-STARTm system can double an S4-60's coil flow rate to boost its DHR-efficiency increases from 62% to about 73% with 2.25 GPM flowing down its drain tube. The S4-60's coil pressure drop will increase to about 5 PSI, so a much snialier pump could be used than that required to force 4.5 GPM
through a G3-60's coil. Clearly, coil pressure drop and pump power requirements will limit the maximum practical ratio of coil- to waste-water flow rate. In addition to pressure drop, avoiding erosion corrosion in a GFX's coil will set a maximum flow rate for a G3-60 of about 4-5 CrPM, according to the Copper Tube Handbook of the Copper Development Association.
The limit on an S4-60 will be about 8-10 GPM

The use of a GFX, or any other heat exchanger, as taught herein is inventive because it discloses a cost-effective means to significantly improve the heat recovery of said conventional GFXTm system, with or without equal flow in its GFX, as well as a means for recovering heat lost to the sewer whenever hot drain water is flowing down its drain tube and no cold water would normally be flowing in its coil.

DESCRIPTION OF THE DRAWING

FIG. I of the drawing shows a system whereby cold feed water is preheated in a heat exchanger and is then further heated and stored in a conventional hot water heater. The same heat exchanger is used via pipe 27 to reduce the quantity of hot water required in preparing a tepid water mixtur.e for direct use as in showering, for example.

FIG. 2 of the drawing shows obvious variations of the basic GFX STARTM system illustrated in FIG.
1.

DESCRIPTION OF TH'E PREFERRED EMBODIlVIENT SHOWN IN FIG. 1 The prior art includes many techniques for the recovery of heat energy contained in wastewater. As disclosed, for example, in U.S. Pat. Nos. 6,722,421; 5,791,441; 5,740,857;
4,821,793; 4,619,311;
4,304,292; 4,300,247; 4,321,798; 4,150,787; 4,352,391; 4,372,372, and Foreign Patent Nos. 3,011,111;
3,244,600; 2,165,932; 57,142,488; for example, water used for showering and discharged through drain Iines can be placed into a heat exchange relationship with colder feed water 17 in order to preheat either water heater feed water 18 and/or cold water 27 prior to mixing with hot water 34 to provide tepid water for direct use 36. (See also A.A. Field, Heating/Piping/Air Conditioning, Volume 48, No.
3, pp. 87-91, "Solar Energy: Part II, The Continent," March 1976.) Said heat exchange relationship conserves energy by lowering the temperature of said wastewater by transferring heat energy to said feed water, or said cold water, or both, thereby reducing primaty hot water heater input energy requirements and the quantity of hot water used in showering, for example.
Maximum wastewater cooling, hence maximum energy savings, will occur when the volume of the coolant is made to exceed the volume of wastewater by as much as practical.

The present invention is directed at instaliations whereby tepid water is produced by mixing hot and cold water in a nnixing valve 34, for example, wherein a conventional GFX
system cannot recycle much of the heat wasted in a typical American household; about 48% from dishwashers, clothes washers and baths according to FIG. 4, for example.

Referring to FIG. 1 of the drawing, cold feed water enters the system through cold water pipe 16 which is connected to heat exchanger 30 at inlet 17 and exits heat exchanger 30 as preheated feed water at outlet 19 which is communicated to hot water heater 20 by pipe 18 where said preheated feed water is fiurther heated and stored for domestic hot water requirements. Wastewater pipe 10 is provided to take the wastewater from bathtubs, sinks, showers, hot industrial equipments and etc., and communicate same to the sewer.

The inventive feature illustrated in FIGS. 1 and 2 is the addition of means to prevent back-flow 74, such as a check- or solenoid-valve, for example, in series with a pump 72 to circulate potable water through a substantially vertically oriented heat exchanger 30, that is inserted directly into a common drain conduit 10. Exchanger 30 pre-heats a volume of feed water 18 and cold water 27 as determined by pump 72 capacity and back pressure and incoming cold water 16 line pressure.

For best heat recovery, said volume of feed water 18 and cold water 27 should equal or exceed the wastewater volume from drain 29 of tub 60 prior to mixing 50 with hot water 44 in valve 34, having shower outlet 36 and bath outlet 52, for example.

Without a pump 72, the laws of thermodynamics make it impossible to cool the wastewater more than that attained by the apparatus of the GFX patern (4,619,311) which teaches the significance of preheating both feed water 18 and cold water 27 prior to mixing 27 so that equal volumes of cold 17 and wastewater are flowing through the exchanger at the same rate.

For the example of FIG 3, if 1.125 GPM of cold water 50 were mixed with 1.125 GPM of hot water 44, 2.25 GPM would flow as wastewater 32 at a temperature equal to the average of the premixed two water temperatures. If said heat exchanger 30 is a selected to be a Model G3-60 or S4-60 GFX, for example, the most one can extract is about 60% of the wastewater's heat energy. This is because, in accordance with the laws of thermodynamics, the volume of the wastewater 32 is equal to that of the cold water 17 to which it is transferring heat. If the volume of cold water 17 entering said GFX 30 is reduced its effectiveness will increase, but according to the laws of thermodynamics, less energy will be recovered because the volume of the wastewater 30 wiil exceed that of the cold water 17 to which it is transferring heat. In contrast, if the volume of cold water 17 entering said GFX 30 is increasecl, its effectiveness will also increase, and more energy will be recovered because the volume of the wastewater 32 will be less than that of the cold water 17 to which it is transferring heat.

The present invention, however, teaches a method for causing optimal volumes of wastewater 32 and entering cold water 17 to exchange heat energy as determined by the parameters of the pump 72 and heat exchanger 30. Thus, as illustrated in FIG. 3, if a tub 60 were to dump 40 gallons of hot water down the drain 29 at a rate of 2.25 GPM after losing about 20% of its input heat, for example, said conventional GFX system would recover negligible energy from the wastewater 32, whereas a G3-60 or S4-60 could recover close to half of said "input heat" if the pump 72 were selected to circulate 40 galtons of cold water @ 2.25 GPM from the water heater 20 or storage tank 22.

A larger pump would save more energy by making the cold waterl7 flow rate exceed the wastewater 32 flow rate because it generally costs far more to heat water than to pump it absent excessive back pressure.

The present invention also teaches how to increase the amount of heat recovered by a conventional GFX system by using the pump 72 to increase the cold water input 17 while a shower is running, for example, thereby causing the volume of cold water 17 entering a GFX 30 to exceed the volume of wastewater 32 simultaneously flowing down the drain 29.

This is the essence of the present invention; it teaches a simple cost effective method that allows the apparatus of said GFX patent (4,619,311) to recycle waste heat from dishwashers, clothes washers and baths, without having to add convective chambers or means to store wastewater or separate solids as illustrated in U.S. Patent Nos. 6 722 4 1; 5391,401; 5.740.857; 4,821,793 or prior art.

The present invention fiirther facilitates incxeased savings compared to prior art m installations wherein it is not practical to simuttaneously feed preheated water 18, 27 to a water heater 20 and shower 36, for example. This is often the case in a multistory building having a central boiler 23 located far from showers and multiple drain 10 stacks as illustrated in FIG.
2(e).

In fact, many existing GFX insta.llations in hotels, college doms and other multi-family buildings were installed to preheat only cold water fed to the showers because it was not practical to preheat water fed to the central boiler. They can now be retrofit with a GFX-STARTm system to enhance savings.

While the form of apparatus herein described constitutes a preferred embodiment of the invention, it is understood that the invention is not limited to this precise fonm of apparatus and that changes may be made therein without departang from the scope of this invention.

xxxxx

Claims (8)

1. The apparatus disclosed in U.S. Patent No. 4,619,311 modified by the addition of a pump and suitable means to prevent back flow through it such as a check- or solenoid-valve as illustrated in the preferred embodiment of FIG. 1.

2. The apparatus of claim 1 wherein an existing water heater or auxiliary storage tank is used to store energy transferred from wastewater, as illustrated in FIG. 2 (a)(b)(c)(d)(e), for example.

3. The apparatus of claim 2 as illustrated in FIG. 2(c) wherein the pump 72 replaced with a means to enable a heat pump like that used in a heat pump water heater or geothermal return loop also extract heat from wastewater 32 to enhance energy savings.

4. The apparatus of claims 2 as illustrated in FIG. 2(e) wherein the pump 72 is removed or replaced with a check-valve, solenoid-valve, or other means to prevent back flow, and low capacity pumps are inserted in series with each check- or solenoid-valve 74.

5. The apparatus of claim 4 wherein said pump or pumps are operated intermittently to conserve energy if no recoverable energy is flowing in said wastewater.

6. The apparatus of claim 5 wherein an automatic control system is used to operate said pump or pumps intermittently if the temperature of said wastewater 32 is approximately 5° F above the water to be circulated from said storage tank or water heater through said heat exchanger 30.

7. The apparatus of claim 6 wherein a thermostat, differential temperature controller, or other suitable means is used to turn off said pump or pumps if their output water temperature exceeds the cold water temperature and becomes within approximately 5° F of the temperature of drain water entering said heat exchanger.

8. The apparatus of claim 7 wherein said pump or pumps have sufficient pressure and flow capacity to increase the effectiveness of said heat exchanger to values greater than the effectiveness of balanced-flow and/or equal-flow operation described in U.S. Patent No. 4,619,311.