Recirculating fluid pump control system

A recirculating hot water system includes a hot water supply pipe and a hot water return pipe connected in a loop between a hot water outlet of a hot water tank and a return inlet to that tank. An electrically controlled recirculating pump is placed in the return pipe between the inlet to the hot water tank and the supply pipe which has hot water taps located at various points along it. Manually operated push buttons are located adjacent at least some of these hot water taps to operate a time delay circuit, which turns on the recirculating pump for a pre-established time interval determined by the parameters of the time delay circuit. Thus, the recirculating pump is turned on only when there is a demand for hot water circulating through the system. To prevent unnecessary operation of the pump, a thermostatically controlled switch may be coupled to the return pipe to override any signals from the time delay circuit and prevent the pump from operating if the water in the return pipe is at or above some minimum temperature determined by the setting of the thermostat.

BACKGROUND OF THE INVENTION 
Recirculating hot water systems are frequently used in hotels, motels and 
other large buildings where many hot water faucets or outlet taps are used 
at various locations throughout the buildings. In such systems, the hot 
water is supplied from the hot water tank or reservoir through a supply 
pipe to the hot water faucets and then is returned by way of a return pipe 
through a pump back to the hot water reservoir. The pump is operated to 
circulate water from the top or hot water side of the storage reservoir 
back to the bottom, so that hot water is continuously available throughout 
the length of the supply pipe. The result is the availability of "instant" 
hot water at any one of the faucets or taps throughout the system. 
An alternative system for providing the availability of nearly 
instantaneous hot water at the hot water taps is to use a gravity system 
instead of a recirculating electrically controlled pump. In a gravity 
system, each hot water tap or faucet which is successively farther from 
the hot water reservoir is supplied from a supply line that is lower in 
height from the preceding faucet or tap in the system. The supply line 
from the last hot water tap in the system then is connected to a return 
line to supply the cooler water back to the hot water heater or reservoir. 
Natural gravity circulation takes place in such a system, because hot 
water rises and cold water sinks. An advantage of gravity systems is that 
the natural gravity circulation also is self-limiting after the entire 
line heats up. 
Each of the recirculating hot water systems which have been described above 
and which are available in the prior art saves water which otherwise would 
be wasted by the user running hot water from a hot water faucet until the 
water leaving the faucet becomes hot. As a consequence, such systems are 
especially attractive in areas where water supplies must be carefully 
conserved. A disadvantage of recirculating hot water systems, however, is 
that even if the water supply pipes are well insulated, there is a 
substantial waste of energy to maintain the water throughout the system 
hot at all times. Because of the significantly increasing costs of energy 
over the past few years, the advantages of water savings in recirculating 
hot water systems are substantially offset by the energy wasted in 
maintaining the water throughout the system hot at all times. Furthermore, 
this wasted energy results in considerably increased costs for 
recirculating hot water systems, as compared with nonrecirculating 
systems; so that such recirculating systems have generally been limited to 
commercial uses, such as hotels and motels and have found only limited use 
in homes and individual residences. 
In an effort to reduce the waste of energy and expense of operating 
recirculating hot water systems, heat sensing thermostats have been used 
to sense the water temperature in the return pipe and to control the 
turning on and off of the recirculating pump motor in accordance with the 
temperature sensed in the line. While this reduces the cost of the system 
somewhat, the inherent nature of such thermostatically controlled systems 
is that the temperature of the water in the pipes still is maintained at a 
fairly high level, so that the reduction in energy waste is not 
particularly significant. Such a system is disclosed in the prior art 
patent to Laube et al., U.S. Pat. No. 3,383,495, issued May 14, 1968. 
A system which limits the operation of the recirculating pump of a 
recirculating hot water system to those times when instant hot water 
demands are most likely to occur is disclosed in the patent to Durdin, 
U.S. Pat. No. 1,780,379, issued Nov. 4, 1930. The Durdin system employs a 
timer to override the thermostatically controlled operation of the pump 
and prevent its operation during certain times of the day, such as during 
the night when there is little likelihood of demand for hot water in the 
system. 
The Durdin system, however, has a gravity bypass in it; so that even though 
the electrically operated recirculating pump may be prevented from 
operation at certain times of the day, the recirculating system still 
operates under the gravity bypass principle. While some advantages may be 
present in the Durdin system, it clearly arbitrarily limits the operation 
of the pump in the system to the preset control of the timer. If this 
preset control does not coincide with the times of usage of the persons 
desiring to draw hot water from the system, the disadvantages of hot water 
systems which are not recirculating (that is relatively cold water in the 
line) may be present as if the recirculating system were not even used. In 
addition, if the gravity bypass part of the Durdin system is correctly 
installed, there would appear to be little need for the recirculating pump 
(except that it does speed up the distribution of hot water throughout the 
system); so that the wasted energy which occurs from constantly 
maintaining the line hot still is present in Durdin. 
Another disadvantage of clock-controlled or time-controlled systems for 
operating the pump is that if a power failure should occur, the settings 
of the timer have to be readjusted or the system supplies hot water in the 
line at times other than the times intended. 
Accordingly, it is desirable to provide a recirculating hot water system 
which has the advantages of providing nearly instantaneous hot water 
availability at the hot water taps or faucets when needed and yet which is 
more conservative of energy consumption than previous recirculating hot 
water systems. In addition, it is desirable to provide a recirculating hot 
water system which is simple to operate and simple to install. 
SUMMARY OF THE INVENTION 
It is an object of this invention to provide an improved recirculating 
fluid supply system. 
It is a more specific object of this invention to provide an improved 
recirculating hot water system. 
It is another object of this invention to provide an improved control 
system for a recirculating hot water system. 
It is an additional object of this invention to provide an improved 
semi-automatic control system for a recirculating hot water system. 
It is a further object of this invention to provide a recirculating hot 
water system with manually operated demand controls adjacent the various 
points of use of hot water in the system for operating the recirculating 
system upon demand of pre-established time intervals. 
In accordance with a preferred embodiment of this invention, a fluid 
circulating system, particularly suited as a recirculating hot water 
system, includes a source of fluid or hot water with an outlet and an 
inlet. A supply pipe and a return pipe are interconnected in a loop 
between the outlet and inlet of the fluid supply source; and outlet taps 
or faucets are connected to the supply pipe to draw fluid from the system 
as desired. An electrically controlled pump is placed in the return pipe 
of the system between the outlet taps and the inlet to the fluid supply 
source. The pump is turned on for pre-established time intervals by a time 
delay switch connected in series between the pump and a source of 
electrical power for operating it. Manually controlled switches are 
located adjacent the different outlet taps or faucets for initiating 
operation of the time delay switch to cause the pump to operate to 
recirculate fluid in the system. The remainder of the time the pump is 
inoperative, so that recirculation is effected on demand when hot water is 
needed at one or more of the outlet taps or faucets in the system.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
Reference now should be made to FIGS. 1 and 2 of the drawing in which the 
same or similar reference numbers are used in both figures to designate 
the same components. 
FIG. 1 is a diagrammatic representation of a recirculating hot water line 
in a home, hotel or other installation to which has been added a control 
system in accordance with the preferred embodiment of this invention. Cold 
water is supplied from a source (not shown) through a pipe 10 to a 
conventional hot water tank 11, from which hot water is drawn as needed 
through a hot water pipe 13 shown exiting from the top of the tank 11. The 
system shown in FIG. 1 is a recirculating system, so that the pipe 13 
makes a loop through the house or hotel to deliver hot water to various 
hot water outlet taps or faucets connected to the pipe 13. These taps have 
been pictorially represented as including a kitchen sink faucet 15, a 
bathroom faucet 16, a shower 17, and a washing machine outlet faucet 18. 
In a nonrecirculating type of hot water system, the last faucet or tap on 
the line simply terminates the hot water pipe 13 and no return is made to 
the hot water tank 11. In the system shown in FIG. 1, however, a provision 
is made for recirculating hot water through the pipe 13 back to the tank 
11; so that a return pipe 14 (which actually forms a noninterrupted 
continuation of the supply pipe) is shown extending beyond the washing 
machine 18, the last outlet tap or faucet in the system shown in FIG. 1, 
through a shut-off valve 15 and a check valve 16 to a recirculating pump 
17. 
The pump 17 may be any one of a number of different conventional small 
fractional horsepower electrically operated pump commonly used in 
recirculating hot water systems. The water passing through the pump 17 is 
supplied through a second shut-off valve 19 to a return fluid inlet 21 
located at the bottom of the water heater 11. As illustrated in FIG. 1, a 
drain valve 22 is located at the inlet 21 to permit drainage of the water 
from the system for performing maintenance or when it is necessary to 
replace the hot water heater 11. 
Also illustrated in FIG. 1 is a thermostatically controlled switch 25 which 
may be of various types to sense the temperature of the water passing 
through the return pipe 14 as it leaves the pump 17. The switch 25 is 
connected to a pump control circuit 27 and cooperates with the circuit 27 
to control the turning on and turning off of the pump 17. The operation of 
the switch 25 and control circuit 27 is explained in detail subsequently 
in conjunction with FIG. 2. 
Illustrated in each of the pictorial representations of the kitchen sink 
15, bathroom sink 16, shower 17 and washing machine 18 are wall mounted 
push-button switches 35, 36, 37 and 38, respectively. These push-button 
switches are operated manually to supply signals to the control circuit 27 
for turning on the pump 17 for preset time intervals on demand, whenever 
one of the switches 35 through 38 is depressed or operated. At all other 
times, the recirculating hot water system shown in FIG. 1 resembles a 
conventional nonrecirculating system since the pump 17 normally does not 
operate; and the check valve 16 prevents the withdrawal of water through 
the return pipe 14 from the bottom of the tank 11. 
For example, assume that the pump 17 has been inoperative throughout the 
night. A user upon first arising in the morning then depresses the switch 
36 or 37 located adjacent the sink or the shower in the bathroom to start 
the pump 17. The control circuit 27 operates to maintain operation of the 
pump 17 for a sufficient time interval (of the order of 4 or 5 minutes) to 
pull hot water into the entire supply pipe 13 throughout the house. 
"Instant" hot water then is available at any one of the outlet taps 15 
through 18. 
The time interval during which the pump 17 runs is pre-established and the 
user does not have to remember to turn the pump 17 off. It is turned off 
automatically at the end of the time interval. The thermostatically 
controlled switch 25 is provided to override any controls supplied to the 
control circuit 27 from the switches 35 through 38 in the event that the 
water in the line already is above some pre-established minimum 
temperature. This means that subsequent depressions of any one of the 
push-button switches 35 through 38 will not turn on the pump unless the 
water temperature in the return line 14 is below the minimum temperature 
to which the thermostat switch 25 has been set. 
Reference now should be made to FIG. 2 which shows the details of the 
control circuit 27 used to control the turning on and turning off of the 
pump 17. 
Operating power for the pump and the control circuit is shown in FIG. 2 as 
being supplied from a conventional 110 volt AC household supply applied 
across a pair of input terminals 40 and 41. One side of this supply is 
connected to the pump 17, and the other side is connected to the 
thermostat switch 25. In addition, the 110 volt AC supply applied to the 
terminals 40 and 41 is supplied to the primary winding of a step-down 
transformer 45, the secondary winding of which produces a 24 volt 
alternating current supply for the control circuit 27. 
The heart of the control circuit 27 is a time delay relay which provides a 
preset time delay on drop-out following its initial actuation. The relay 
which is illustrated in FIG. 2 is shown as a conventional ARTISAN brand 
No. 429-3-D-1 relay which is commercially available from the Artisan 
Electronics Corporation. This relay may be factory set to a delay of up to 
300 seconds after drop-out. It operates in response to the closure of a 
switch to move three sets of single-pole double-throw switches 50, 51 and 
52 from the position shown in FIG. 2 (the upper position of each of these 
switches) to the lower contact set for each of the switches 50, 51 and 52. 
All of these switches are operated simultaneously by a relay coil 55. 
Energization of the relay coil 55 is effected by closure of any one of the 
push buttons 35, 36, 37 or 38 which are shown connected in parallel with 
one another across one leg of the AC supply, which is connected through 
the upper terminal of the switch contact 50 to pin 1 of the relay, and 
internally from pin 1 through pin 2 to the coil 55. The other side of the 
coil 55 of the relay is connected through a normally closed switch contact 
58 to pin 10 of the relay, which in turn is connected with the opposite 
side of the secondary winding of the transformer 45 to complete the 
operating circuit for the relay coil 55. It should be noted that in the 
normal unoperated state of the relay, as illustrated in FIG. 2, a set of 
lamp filaments 35A through 38A (each of which is connected across the 
respective ones of the push-button switches 35 through 38) are connected 
in series circuit (and in parallel with one another) with the relay coil 
55. In addition, a resistor 57 is connected across pins 1 and 10 of the 
relay through the normally closed switch 52, so that this resistor also is 
in parallel with the relay coil 55 during the unoperated state of the 
relay. Because of the resistances of the lamp filaments 35A through 38A 
and of the resistor 57, insufficient current flows through the relay coil 
55 to operate it and the circuit is in its standby or unoperated state. 
Whenever any one of the push-button switches 35 through 38 is momentarily 
depressed, it effectively shunts or short circuits all of the lamp 
filaments 35A through 38A. Increased current then flows through the relay 
coil 55, causing the relay to operate. When this occurs, all of the 
switches 50, 51 and 52 are operated to close against the lower contacts of 
the switches. When the swinger of the switch 50 engages its lower contact, 
a holding path for the relay coil 55 is established by way of the shunt 
lead 59 connected to the lower contact of the switch 50. At the same time, 
operation of the switch 52 takes the resistor 57 out of the relay circuit; 
so that maximum current flows through the coil 55. 
The shunt lead 59 maintains the shunt or short circuit of all of the 
push-button switches 35 through 38 and the lamp filaments 35A through 38A 
associated with each of these switches. As a consequence, the lamp 
filaments are turned off or dimmed, providing an indication at each 
location throughout the system that the pump 17 is activated to 
recirculate hot water through the system. Thus, additional depression of 
any one of the other push buttons 35 through 38 has no effect on the 
circuit since the shunt 59 provides the holding path for operating the 
relay. 
In addition to providing operating current for the relay 55, the 
connections between pins 1 and 2 and pin 10 of the relay energize a timing 
circuit or timer device 60 which is set at the factory to the desired 
delay for the relay. As mentioned above, the particular relay which is 
depicted in FIG. 2 can be factory preset to provide a delay on drop-out of 
up to 300 seconds, which is generally sufficient for the operation of a 
recirculating hot water system used in a typical home installation. When 
the relay is operated, the time delay of the timer portion of the circuit 
60 is initiated; and at the end of that time delay the switch 58 is 
momentarily opened. Opening of the switch 58 breaks the holding current 
through the relay coil 55, and it releases to return the circuit to the 
state shown in solid lines in FIG. 2, readying it for the next operation 
of any one of the push buttons 35 through 38. The value of the resistor 57 
is selected to be small enough to prevent operation of the clock drive 
circuit 60 during the standby state of the system, but large enough to 
allow relay switching when any one of the push buttons 35 through 38 is 
depressed. 
When the relay 55 operates to close the switch 51 to its lower contact, a 
series circuit is completed from the terminal 41 through the pump 17, the 
switch 51 and the thermostatically controlled switch 25 back to the 
terminal 40 of the AC power supply. Thus, if the switch 25 is closed at 
this time, the pump 17 is operated. The duration of time the pump 17 is 
operated depends upon the drop-out or time-out period of the operation of 
the relay 55. Upon termination of that operation, resulting in the opening 
of the switch 51 to the position shown in FIG. 2, the pump energizing 
circuit is broken and the pump 17 is turned off. 
If the water temperature in the return line 15 reaches the desired minimum 
level set by the thermostatically controlled switch 25, the switch 25 is 
opened and the pump operation terminates irrespective of the operation of 
the relay 55. In this manner, maximum efficiency of operation of the 
system is realized with minimum energy waste. 
Once the relay coil 55 is de-energized, and the contact 50 returns to its 
original position, as shown in FIG. 2, current once again flows through 
the filaments of the lamps 35A through 38A illuminating the lamps to 
indicate the users of the system that the pump 17 is turned off. This 
provides an extra indication to system users of the status of operation of 
both the control circuit 27 and the pump 17. 
The push-button switches 35 and the lamp filaments 35A can be incorporated 
into a single unit, and ideally are the same type of switches which are 
commonly used for the illuminated push-button switches in widespread use 
as door bell buttons. Time delay relays other than the one specifically 
described in conjunction with FIG. 2 may also be used. Another approach is 
to use a thermal delay relay which, upon operation of the relay coil, also 
passes a heating current through or near a bimetallic strip. The strip 
then bends to open contacts after the pre-established time delay interval 
to break the holding path for the relay coil and terminate operation of 
the relay. In many applications, thermal delay relays are not considered 
appropriate since their time delay interval is somewhat dependent upon 
ambient temperature and therefore is not precise. For the type of system 
under consideration here, however, thermal delay relays are appropriate. 
This is especially true where, in most situations, if the ambient 
temperature rises the time required to heat up a hot water line should 
decrease. Thus, the use of a thermal delay having a negative temperature 
co-efficient of delay is appropriate for the system. 
The system which has been described above constitutes a simple demand 
control (with thermostatic override) for the operation of a recirculating 
pump in a recirculating hot water system. The check valve 16 prevents 
reverse flow through the system, and the utilization of the low voltage 
wiring results in economies in installation. In addition, conventional 
door bell buttons and the low voltage relays, currently available on the 
market, can be employed for the operating components of the control 
circuit 27 in the system; and no custom designed components need to be 
used. 
Variations of the system will occur to those skilled in the art after 
review of the preferred embodiment described above and shown in the 
drawings. The embodiment of FIGS. 1 and 2 of the drawing is merely shown 
for purposes of illustration and is not to be considered limiting of the 
true scope of the invention. Modifications which can be made to the system 
described could include a parallel clock-controlled pump power supply to 
activate the pump 17 at known times of hot water consumption in the 
particular installation in which the system is used. The addition of a 
ratcheting relay which, on successive pressings of a pump control button, 
would add up increments of the basic proposed 300 second interval may be 
advantagous to maintain the hottest water temperatures during some cycles 
of operation or times of day of use of the system. 
Another alternative is to control the pump from settable time delay 
switches at one or more locations in the system. The predetermined time 
interval then can be adjusted at each such switch to fit the particular 
needs of the system and this time interval may be varied, if desired.