Method and apparatus for recovering heat from waste water

The apparatus comprises a first container for receiving waste water. Inlet means in the upper portion of the first container are adapted to be connected to a drain pipe. Outlet means in the bottommost portion of the container are provided for draining the waste water from the container. Valve means are provided which are operable to control the outlet means in response to a waste water level and relative heat indicator in said first container, and a second container for receiving a liquid is adjacent but sealed from said first container. Heat pump means include heat exchanger means in said first container and communicate with heat exchanger means in the second container whereby heat is extracted from relatively warm waste water in the first container and can be transferred to the heat exchanger in said second container for warming a relatively cooler liquid in said second container.

BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to the conservation of energy, and 
particularly to a method and apparatus for recovering heat from waste 
water. 
2. Description of the Prior Art 
In the light of rapid increases in energy costs coupled with the 
realization that our energy resources are limited, ways must be found to 
utilize to the maximum such energy sources as heat. One area where heat is 
wasted is in the household. For instance, energy resources are utilized in 
order to heat cold water entering a building from the water main. However, 
the use of the hot water in a house is often only momentary, i.e., a 
shower, bath, dishwashing, clothes washing, etc. The water that goes down 
the drain, from such usage, still retains a high percentage of its heat. 
However, the energy from the draining hot water is not utilized. 
U.S. Pat. No. 3,946,802, issued Mar. 30, 1976, Christenson, describes the 
utilization of heat from waste water in a dwelling. The system describes 
collecting drain water in a vertically aligned heat exchanger through 
which is passed the cold in-coming water in coils in the heat exchanger. 
SUMMARY OF THE INVENTION 
It is an aim of the present invention to provide an improved, more 
efficient method and apparatus for removing heat from waste water. 
It is a further aim of the present invention to provide an improved method 
and apparatus for utilizing the heat recovered from the waste water to 
preheat the cold water entering the house from the water main. 
A construction in accordance with the present invention comprises a first 
container for receiving waste water, inlet means in the upper portion of 
said first container adapted to be connected to a drain pipe, outlet means 
in the bottommost portion of the container for draining the waste water 
from the container, valve means operable to control the outlet means in 
response to a waste water level and relative heat indicator in said first 
container, a second container for receiving a liquid adjacent but sealed 
from said first container, heat pump means including heat exchanger means 
in said first container and communicating with heat exchanger means in the 
second container whereby heat is extracted from relatively warm waste 
water in the first container and can be transferred to the heat exchanger 
in said second container for warming a relatively cooler liquid in said 
second container. 
A method in accordance with the present invention includes the steps of 
accumulating waste water in a first accumulation container, accumulating a 
relatively cooler liquid in a second container, passing a refrigerant 
fluid through an expansion heat exchanger in the first container, 
compressing the fluid and condensing it in a condenser heat exchanger in 
the second container allowing the liquid in the second container to be 
warmed, allowing the refrigerant gas to expand in the heat exchanger in 
the first container thereby absorbing heat from the warmer liquid in the 
first container, and draining said first container when the temperature of 
the waste water has been sufficiently reduced. 
In a more specific embodiment, the second container includes an inlet 
connected to a cold fresh water source and an outlet connected to the 
intake of a hot water tank.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
Referring now to FIG. 1, there is illustrated the prewarmer unit 10 having 
the overall shape and size of a typical 60-gallon hot water insulated tank 
which would normally be installed adjacent a conventional hot water tank 
in a household. The unit 10 includes a lower portion containing the waste 
water container 12. Disposed vertically above the waste water container is 
the fresh water container 14 and separating the two containers 12 and 14 
is the heat pump apparatus 16 and a control panel 18. 
The lower section includes a floor support 20 and an insulated cylindrical 
lower wall 22. The wall 22 might be double walled as shown by the inner 
sheet 24 and outer sheet 26 and be filled with insulation material. The 
container 12 includes a wall section 28 of cylindrical shape termination 
in a lower conical segment 30 which in turn defines a drain opening 32. 
The inside of the container 12 is covered with a smooth surface of 
polytetrafluoroethylene and all the corners are rounded. A top cover 34 is 
bolted to a flange 36 on the periphery of the cylindrical wall 28. An 
intake pipe 38 is located in the top portion of the container 12 and is 
adapted to be connected to the waste water drain of a household. It is to 
be noted, however, that the plumbing must be modified such that the drain 
from the toilets is kept separate from the waste water drain. 
A shower apparatus 40 is associated in the top of the container 12 and is 
connected to the cover 34 and directed downwardly within the container. In 
this embodiment, two shower heads 40 are shown. The shower heads are 
connected by pipes 41 to a water main 68. A valve 66 controls the water to 
the shower system 40. 
The drain 32 connects to a drain pipe 33 in which is provided a valve 42 
operated by a gear 46 which in turn is rotated by means of a motor 44. 
Within the waste water container 12, there is provided a continuous heat 
exchanger tube, either in coil or in the pattern shown schematically in 
FIGS. 1 and 2, and is supported or hung from the cover 34 by means of the 
supports 52. Insulation material 54 is provided on the cover 34. 
A compressor 58 is illustrated above the cover 34 and forms part of the 
heat pump 16. A tube 60 extends from the heat exchanger 50 to communicate 
with the compressor 58. A sensor device 64 is located centrally of the 
waste water container 12 and is supported by the cover 34 by means of a 
bushing 56. 
The top section includes an insulated upper wall 70 having thick insulation 
material and the inner wall 71 terminates in the bottom wall section 72. 
An inlet 74 is provided in the bottom wall 72 and communicates with the 
cold water main 68. A baffle 78 is provided to cover the inlet 74 to 
prevent splashing of the cold fresh water onto the heat exchanger 76 which 
is supported and located centrally within the container 14. The tank 14 is 
also provided with an outlet 80 in the upper section thereof which 
communicates with the conventional hot water tank of the household. A tube 
62 leads from the compressor 58 to the heat exchanger 76 in the fresh 
water container 14. Finally, in order to complete the circuit of the heat 
pump, a tube 82 extends from the heat exchanger 76 to the heat exchanger 
50. An expansion valve 86 is provided in the tube 82 and is connected to a 
thermostat 84 located in the tube 60. A thermostat 88 is provided in the 
tube 82 and leads to the control box at terminal Tc. 
An overflow pipe 90, as shown in FIG. 2, is connected to the waste water 
line prior to the inlet 38. A thermostat 92 is located in the overflow 
drain pipe 90 and is connected to the terminal To in the control box 18. 
The overflow 90 leads to the drain eventually. 
Referring to FIG. 2 as well as to the circuit diagram of FIG. 3, the 
remaining terminals of the control box are connected to the sensor device 
64 and include a thermostat, connected to the terminal Tw, a freeze 
protection thermostat Tp, and a minimum level switch connected to terminal 
L. These devices are more clearly shown in the circuit diagram of FIG. 3. 
T.sub.1 is a time delay device for maintaining the valve 42 open for 
draining the container 12 and the valve 66 for operating the showers 40, 
thus washing the container 12 while the drain is opened. The valves may be 
kept open for a short period of time, sufficient to flush out the 
container 12. The time delay device T.sub.2 is used to maintain the valve 
42 opened a short period of time after the valve has been opened in 
response to the thermostat 92 connected to terminal To when there is an 
overflow in pipe 90 so as to allow the colder water in the bottom of 
container 12 to be drained in order to make room for newer warmer drain 
water. 
In operation, the waste water coming from a shower drain or other hot water 
appliance in the household enters through the inlet 38 into the waste 
water container 12. The waste water in the tank will merely accumulate 
until it reaches a predetermined level approximately half the height of 
the tank, whereby the minimum level switch in the sensor device 64 
connected at L in the control box 18 will start the compressor 58, 
assuming the thermostat in the sensor 64 identified by the terminal Tw 
indicates that the water temperature of the waste water is above a 
predetermined temperature such as +8.degree. C. The compressor 58 
compresses the refrigerant gas in the heat pump system and forces the gas 
into the condenser heat exchanger 76 whereby the refrigerant gas will be 
condensed giving off heat to the water in the tank 14. The water in the 
container 14 will thereby be warmed, and fresh water coming from the main 
which is cold enters through the inlet 74 displacing the warm water 
through the outlet 80 to a hot water tank (not shown). 
As the cool condensed refrigerant fluid exits from the condenser 76 through 
the tube 82, the temperature thereof is sensed by means of thermostat 88 
connected to the terminal Tc in the control box. The fluid then passes 
through the expansion valve 86 which is controlled by a thermostat 
connected in the tube 60 leading to the compressor from the expansion heat 
exchanger 50. The cool refrigerant then enters the expansion heat 
exchanger 50, and the heat of the waste water in the container 12 will 
further expand the refrigerant gas which will again start the cycle. Of 
course, if the refrigerant gas exiting from the heat exchanger 76 through 
pipe 82 is above a certain predetermined temperature, as will be sensed 
comparatively by the thermostat 88, the compressor 58 will be deactivated. 
Only if it is sensed that the fluid is below a certain temperature will 
this system be kept activated. 
Once the temperature of the waste water held in the container 12 is lowered 
below a certain predetermined temperature sensed by the sensor 64 and the 
temperature of the fresh water in the container 14 has increased, the 
drain valve 42 will be opened, allowing the waste water to empty from the 
container 12. At that time, the valve 66 will be opened to operate the 
shower system thereby washing out the container 12. After a certain time 
delay, the valve 42 will again be closed, and waste water will again be 
allowed to enter into the tank 12 without being drained. 
When the waste water fills the tank 12, any further waste water will be 
bypassed to the overflow pipe 90. The thermostat 92 connected to terminal 
To in the control box will record the temperature of the waste water being 
bypassed, and if it is found that, on comparison with the waste water in 
the container 12, the temperature of the water being bypassed is above a 
certain temperature, then the valve 42 will be operated to drain the 
colder waste water from the bottom of container 12 and allow newly used 
warmer waste water to collect in the container 12.