Abstract:
An antifreeze heating system which prevents the freezing of water present in an instant water heater of the type having a primary heater which remains inactive under static flow conditions. A secondary heater is placed within an enclosed housing volume of the instant water heater, and electrically connected to a temperature-sensitive switch which activates the secondary heater when a monitored temperature, such as the ambient temperature, falls below a threshold value.

Description:
BACKGROUND OF THE INVENTION 
     The field of the invention generally pertains to heaters and heating systems. The invention relates more particularly to a secondary heating system which prevents the freezing of static water present in an instant water heater, wherein a temperature-sensitive switch monitors the temperature of a designated area or space and activates a secondary heating element when the monitored temperature falls below a threshold level. 
     Various types of water heating systems have been developed to provide hot running water in homes, commercial buildings, and the like. One notable innovation in water heating has been the advent of instant water heaters which heat water on demand independent of a centralized water heating system. Such instant water heaters are typically small, electrically operated, and self-contained units which are interposed in water lines near the spout ends, e.g. a faucet. Because of the close proximity between the instant water heater and the spout end, conductive heat loss through the piping is substantially reduced. Moreover, because the primary heating unit of an instant water heater is typically activated only during flow conditions, i.e. when a valve is opened at a spout end, energy is conserved when not in use. One example of an instant water heater of this type is marketed under the trademark, “Hotman” by Acorn Engineering in Chino, Calif. 
     However, it has been observed that when used in cold climates, the water remaining in a conduit portion (see  22  in FIG. 1) of such instant water heaters can freeze when the temperature falls to freezing levels. Although the conduit portion is sheltered within the housing, it is typically not additionally insulated, as is commonly provided for traditional hot water lines. Moreover, because the housing body is typically constructed from a metallic material, such as aluminum, the inner housing temperature can quickly reach levels of the outside ambient air. It is also appreciated that while continuous operation of the primary heating unit alone would prevent freezing, the high efficiency and energy cost savings provided by an “on-demand” heating system would be lost. 
     Thus, it would be advantageous to provide a low-power secondary heating system which prevents water remaining in the instant water heater from freezing under static, no-flow conditions. Moreover, it would be beneficial to automate activation of the secondary heating system by monitoring the temperature of a designated area or space, and activating the secondary heating unit when the monitored temperature falls below a threshold level. In this manner, the instant water heater would be available for service at all times, and under all temperatures and climates, while minimizing energy consumption. 
     BRIEF SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a simple secondary heating system which is utilized in conjunction with an instant water heater of the type having a primary heater which is activated only during flow conditions, with the secondary heating system preventing water within the instant water heater from freezing during static flow conditions. 
     It is a further object of the present invention to provide an automated secondary heating system which monitors the temperature of a designated area or space, such as the ambient temperature outside of the instant water heater, and activates a secondary heating unit when the monitored temperature falls below a threshold value. 
     A still further object of the present invention is to provide an efficient, low-power secondary heating system which requires substantially less energy than the primary heater of the instant water heater. 
     It is a still further object of the present invention to provide a secondary heating system which comprises a simple electrical circuit utilizing common electrical components, for facilitating manufacture and assembly. 
     The present invention is for an antifreeze system for use with an instant water heater of the type having a housing body which encloses a housing volume, a water conduit mounted within the housing volume with an inlet and an outlet, and primary heater means for heating water in the water conduit when water flows therethrough from the inlet to the outlet. In a first preferred embodiment, the antifreeze system comprises secondary heater means for heating the housing volume to prevent water from freezing in the water conduit, and a temperature-sensitive switch operatively connected to the secondary heater means, for switching on the secondary heater means when a monitored temperature falls below a threshold value. And in a second preferred embodiment, the antifreeze system comprises secondary heater means positioned within the housing volume for heating the water conduit to prevent water from freezing therein, and a temperature-sensitive switch discussed above. 
     Furthermore, the present invention is for an improved instant water heater having a housing body which encloses a housing volume, a water conduit mounted within the housing volume with an inlet and an outlet, primary heater means for heating water in the water conduit when water flows therethrough from the inlet to the outlet, secondary heater means for preventing water from freezing within the water conduit, and a temperature-sensitive switch operatively connected to the secondary heater means, for switching on the secondary heater means when a monitored temperature falls below a threshold value. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a rear perspective view of the instant water heater incorporating a first preferred embodiment of the antifreeze system of the present invention. 
     FIG. 2 is a cross-sectional side view taken along line  2 — 2  of FIG.  1 . 
     FIG. 3 is an enlarged rear elevational view of a first preferred mounting arrangement of the temperature-sensitive switch. 
     FIG. 4 is an enlarged rear elevational view of a second preferred mounting arrangement of the temperature-sensitive switch. 
     FIG. 5 is an enlarged rear elevational view of a third preferred mounting arrangement of the temperature-sensitive switch. 
     FIG. 6 is a rear perspective view of the instant water heater incorporating a second preferred embodiment of the antifreeze system of the present invention. 
     FIG. 7 is a cross-sectional side view taken along line  7 — 7  of FIG.  1 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring now to the drawings, FIGS. 1-5 show an instant water heater, generally indicated at reference character  9 , and incorporating a first preferred embodiment of an ancillary antifreeze or secondary heater system, generally indicated at reference character  10 . And FIGS. 6-7 show the same instant water heater  9  incorporating a second preferred embodiment of the ancillary antifreeze or secondary heater system, generally indicated at reference character  10 ′. 
     The instant water heater  9  is of the type having a rigid housing body  11  with a metallic construction, such as aluminum. And the housing body  11  is shown having an open-sided configuration with a front wall  18 , a pair of side walls  12 , a top wall  17  and a bottom wall  14 , which together define and enclose a housing volume  20 . As shown in FIGS. 2 and 7, the open side of the housing body  11  is positioned adjacent a mounting wall  21  to fully enclose the housing volume  20 . Though not shown in the figures, the housing body  11  and the instant water heater  9  may be suitably mounted to the mounting wall  21 , e.g. by screw or bolt type fasteners. While a back wall is not shown, it is appreciated that one may also be provided and positioned opposite the front wall  18  to form a housing body which fully encloses the housing volume without the mounting wall. 
     Furthermore, the instant water heater  9  includes a water conduit  22  which is suitably mounted within the housing volume  20  of the housing body  11 . The water conduit  22  functions to lead water into and out of the housing body  11  where heating takes place, as will be discussed below. As can be seen in FIGS. 1 and 2, the water conduit  22  has an inlet  23  and an outlet  24  which extend through the bottom wall  14 . The inlet  23  is suitably adapted to connect to a water line (not shown) which delivers water from a water source. And the outlet  24  is also suitably adapted to connect to a hose, pipe, or other water conduit leading to a spout end (not shown). It is understood that the term “spout end” as used herein and in the claims indicates any point from which the transported hot water may be received and used. Examples of spout ends include, but are not limited to, a faucet, shower head, washing machine, etc. 
     Connected to the water conduit  22  is a primary heater, which typically includes a heater control unit  25  electrically connected to an energy source, e.g. a standard wall outlet (not shown), via an electric cord  28 . In FIGS. 1 and 6, the heater control unit  25  is shown having connector wires  26  leading into the water conduit  22 , where they connect to a thermogenerator, i.e. a heat generating element or device. Though not shown in the drawings, the thermogenerator is typically a series of heater coils which surround a flow path through the water conduit  22 . It is appreciated that the heater coils may be formed as an integrated component of the water conduit construction  11 , or separately attached as an independent component, as dictated by the particular design of the instant water heater. Moreover, it is also appreciated that the heater control unit  25  has suitable means for detecting flow conditions in the flow path through the water conduit  22 , and activating and deactivating the primary heater accordingly. In this manner, the primary heater is turned on when water flows through the water conduit  22 , and shuts off when flow conditions cease, e.g. when a faucet valve is closed at the faucet end. 
     As can be best seen in FIG. 1, the first preferred embodiment of the antifreeze system  10  is positioned within the housing volume  20  of the housing body  11 . Generally, the antifreeze system  10  includes a secondary heat generating element or device  30 , i.e. the secondary heater, and a temperature-sensitive switch  31  which operates to activate or deactivate the secondary heater  30 . As shown in FIG. 1, the secondary heater  30  and the temperature-sensitive switch  31  are electrically connected to an energy source by circuit wires  33  to form an electric circuit. Preferably, the secondary heater  30  shares the same energy source as the primary heater via the electric cord  28 . Thus, as illustrated in FIG. 1, electrical contacts  29  may be provided on the heater control unit  25  of the primary heater to which the circuit wires  33  are connected. 
     As can be seen in FIG. 3, the switch  31  is mounted on an inner surface  15  of the bottom wall  14 , with the sensor element  32  positioned away from the inner surface  15 . This arrangement provides monitoring of a housing volume temperature. And as can be seen in FIG. 4, the switch  31  is mounted on an outer surface  16  of the bottom wall  14 , with the sensor element  32  positioned away from the outer surface  16 . This arrangement provides monitoring of the ambient temperature outside of the housing body  11  of the instant water heater  9 . And finally, in FIG. 5, the switch is mounted on bottom wall  14  such that the sensor element  32  contacts the inner surface  15  of the bottom wall  14 , and the monitored temperature is that of the housing body  11 . Based on fundamental principles of heat transfer, it is appreciated that the arrangement shown in FIG. 4 would provide the earliest detection of freeze temperatures, while the arrangement of FIG. 3 would provide the latest detection. This is due to the intermediate location of each of the mediums between the water conduit and external conditions. It follows therefore based on the same heat transfer principles, that monitoring the temperature of any one of these three mediums, which are external to the water conduit, provides an earlier detection of an environmental temperature change than monitoring the temperature of the water directly. 
     Additionally, FIGS. 1 and 2 illustrate a first preferred mounting position of the secondary heater  30 , i.e. heating pad, to heat the housing volume  20 . It is appreciated that heating of the housing volume  20  effectively functions to prevent freezing of water remaining within the water conduit  22  based on fundamental heat transfer principles. As shown, the heating pad  30  is contactedly attached, e.g. adhered, to an inner surface  19  of the front wall  18  which is adjacent the water conduit  22 . This arrangement heats the housing volume  20  by way of transferring heat to the housing body  11 , as well as by direct heating of the housing volume  20  via boundary layer heat conduction. It is appreciated, however, that the heating pad  30  or other heat generating element may be generally positioned anywhere within the housing volume  20 , as well as beyond the housing body  11 , in order to keep the water conduit  22  from freezing. 
     FIGS. 3-5 show three different embodiments of the system  10  where the temperature-sensitive switch, generally indicated at reference character  31 , is positioned to monitor a designated area, space, or object. It is appreciated that the switch  31  is of a type commonly known in the electrical and electronic arts. Switch  31  may be adjustable to turn on the heating pat at a preset combustion, such as 40° F. Alternatively, a manual on/of switch may be used in place of the temperature sensitive switch. As shown in the figures, the temperature-sensitive switch  31  has a sensor element  32  where the temperature is preferably actually monitored, and is connected to the circuit wires  33  of the antifreeze system circuit. Furthermore, the switch  31  is adapted to close the circuit and activate the heat generating element  30 , upon the sensor element  32  of the temperature-sensitive switch  31  detecting that a monitored temperature has fallen below a predetermined threshold value. It is appreciated that the threshold value may be assigned based on the application of fundamental heat transfer principles to the design parameters of an instant water heater. 
     As can be seen in FIG. 3, the switch  31  is mounted on an inner surface  15  of the bottom wall  14 , with the sensor element  32  positioned away from the inner surface  15 . This arrangement provides monitoring of a housing volume temperature. And as can be seen in FIG. 4, the switch  31  is mounted on an outer surface  16  of the bottom wall  14 , with the sensor element  32  positioned away from the outer surface  16 . This arrangement provides monitoring of the ambient temperature outside of the housing body  11  of the instant water heater  9 . And finally, in FIG. 5, the switch is mounted on bottom wall  14  such that the sensor element  32  contacts the inner surface  15  of the bottom wall  14 , and the monitored temperature is that of the housing body  11 . Based on fundamental principles of heat transfer, it is appreciated that the arrangement shown in FIG. 4 would provide the earliest detection of freeze temperatures, while the arrangement of FIG. 3 would provide the latest detection. 
     It is notable that while the switch  31  is shown mounted on the bottom wall  14 , it is not limited only to such. Any of the front, top, bottom, or side walls would serve to provide a suitable mounting location for the switch  31 , and particularly the sensor element  32 . It is further notable that the switch  31  may be suitably mounted to the housing body  11  or other structure of the instant water heater  9  by conventional fasteners, such as mounting screws (not shown). 
     As can be seen in FIGS. 6 an  7  the second preferred embodiment of the antifreeze system  10 ′ is shown positioned within the housing volume  20  of the housing body  11  for heating the water conduit  22  to prevent water from freezing therein. Generally, the second preferred embodiment comprises the same components as the first preferred embodiment, including: a secondary heater  30 , and a temperature-sensitive switch  31 , which are electrically connected by circuit wires  33  to form an electric circuit. However, the second preferred embodiment has the secondary heater  30 , e.g. the heating pad, which is preferably mounted directly to the water conduit  22  for heating the water conduit  22  directly. As illustrated, the heating pad  30  is contactedly attached, e.g. adhered, to the water conduit  22  to heat the water conduit  22  directly. It is appreciated that direct heat conduction may provide faster heating of the water conduit  22  than boundary layer heat conduction to the housing volume  20  as discussed above. 
     The present embodiments of this invention are thus to be considered in all respects as illustrative and not restrictive; the scope of the invention being indicated by the appended claims rather than by the foregoing description. All changes which come within the meaning and range of equivalency of the claims are intended to be embraced therein.