Patent Application
20200355399
The invention relates to an improved interface between existing hot water circulating systems and existing residential (and light commercial) tank-style hot water heaters.
A typical hot water heater system intended for residential or light commercial purposes, such as shown in
In each implementation of tank-style heaters, heated water will rise to the top of the tank while cooler water sinks to the bottom. A typically configured tank will include two nipples at the top of the tank from which hot water may be withdrawn from the top of the tank and cold water fed in as the hot water is drawn out. While both nipples are often at the top of the tank, the cold water feed nipple when so placed will be attached to a pipe that feeds to the bottom of the tank. (Alternatively, cold water may be fed into the bottom of the tank from a nipple placed on the side at or near the bottom of the tank.) In addition to the two nipples dedicated to withdrawing hot water from and feeding cold water into the tank, typical residential hot water heaters will also have a spigot at the bottom of the tank in order that the tank may be drained on a periodic basis or when repair or replacement is necessary.
In a steady state, the temperature in the water tank will be close to uniform from top to bottom. However, when hot water is drawn from the tank (for instance, to fill a bathtub or large pot) cold water will be drawn into the bottom of the tank. Because the cold water is denser than the hot water, it will tend to stay at the bottom of the tank separated from the warmer water by a distinct thermocline.
The standard electric tank water heater contains upper and lower heating elements (also incorporated into hybrid heat pump/electric resistance heaters) designed to maximize first-hour hot water delivery and recovery. As hot water is drawn from the top of the tank, the lower element begins heating incoming replacement water. Following an extended draw, and as the colder water in the bottom of the tank rises, eventually the upper element is triggered, so as to most quickly heat water at the top of the tank, which is subsequently drawn before the colder water at the bottom.
Whether in a combustion, electric, or hybrid heater, the reasonably defined separation of hot and cold water is useful in maximizing the utility of a given size tank as can be demonstrated by the following example: a 50 gallon tank is maintained at 140° F. A residential occupant is the first to shower on a given morning and drains 20 gallons of hot water replaced by 20 gallons of incoming cold water at, for example, 55° F. Following the first shower, a second occupant takes a second shower drawing another 20 gallons of hot water replaced by another 20 gallons of cold water. The tank continues to heat from the bottom, and another half-gallon can be withdrawn from the top at or close to 140° F. in order to make the morning coffee.
Many higher-quality and newly constructed homes will add a “hot water recirculated system” to this standard set up that assures the near immediate availability of hot water at taps that may be distant from the heater. Absent such a system, and using the foregoing example, the first person to shower would not immediately have hot water but instead would have to run the hot water faucet until water that had been heated overnight in the tank replaced the cold water that had already lost its heat sitting overnight in the hot water pipe. The second person would not face the same delay if immediately using the same shower but may face the same delay if utilizing a shower in a different location in the home as cold water sitting in the hot water pipe running to the second location is displaced by newly heated water. A hot water recirculated system avoids the wait by constantly circulating hot water in a loop through the home thus reducing the delay in the supply of hot water which need only displace the limited distance between the loop and the tap.
Notwithstanding that hot water recirculated systems have become relatively common in new construction and higher end improvements (and are required in certain circumstances under various building codes), current tank-style residential and light commercial hot water heaters are not designed to integrate with hot water recirculating systems. In particular, such heaters are not equipped with a dedicated return nipple for the recirculating system. In the absence of a dedicated return nipple, installers of hot water recirculated systems have improvised a return inlet by removing the faucet and valve assembly from the drain, adding a “T” fitting, replacing the valve assembly at the end of the T, and fitting the hot water return to the remaining portion of the T.
Reliance on the tank drain for hot water return has at least two drawbacks. First, because a drain remains necessary, additional plumbing hardware must be installed on the tank to provide a drain for the tank to allow the existing drain apparatus to accept return water front the circulating system.
More significantly, the tank drain is poorly placed for this function. To take our example, immediately after the first resident showers, water at the top of the tank will be close to 140° and water at the bottom close to 55°. If the second resident waits a period of time before taking a shower, however, the hot water recirculating system will disrupt the thermocline and mix the water in the tank such that the entire tank will reduced to a lukewarm state—in the above example, perhaps 100°—thus precluding a second hot shower.
This issue is particularly apparent in hybrid water heater installations, in which a heat pump is used to heat the tank with electric resistance supplemental heaters. If run in pure heart pump mode (which provides the greatest efficiency), it may take several hours to reheat the full tank following a substantial withdrawal. Yet, the entire hot water tank will typically recirculate within an hour of the first draw, thus thoroughly mixing the tank and either triggering the (markedly less efficient) resistance elements or greatly extending the recovery time and significantly reducing the amount of available hot water.
In order to resolve the foregoing problem with tank-style water heaters as currently designed, the user or designer of the hot water delivery system must either oversize the hot water tank or maintain the hot water temperature at a much higher level than otherwise would be necessary so as to increase the overall temperature of the tank after use and agitation. While both solutions create significant energy inefficiencies, neither approach fully resolves the problem with tank mixing, which inevitably reduces the total amount of hot water available as well as the recovery rate for a subsequent draw of adequately heated water.
The dynamics of the foregoing problems are not obvious—and in fact are hidden from the user and the industry—by virtue of the fact that typical hot water tanks do not report internal temperatures, thus hiding the problems associated with the hot water return system as applied to existing tank heaters.
While this invention is susceptible of an embodiment in many different forms, specific embodiments thereof will be described herein in detail with the understanding that the present disclosure is to be considered as an exemplification of the principles of the invention. It is not intended to limit the invention to the specific illustrated embodiments.
Embodiments of the claimed invention can include a hot water system that includes dedicated hot water return to interface between the traditional tank-style heater and an existing hot water re-circulating system. Such a dedicated return can include a third nipple or fitting, a return line, and a valve designed to confine return water to the upper portion of the water tank when installed with a recirculating system, or to close the third nipple or fitting for installations lacking a need for a hot water return. In some embodiments, the third nipple or fitting and return line can be placed at the top of the tank along with the cold and hot water nipples or fittings with a vertical pipe added to direct water into the upper portion of the tank (but below the point from which the hot water is drawn and sufficiently distanced so as to not cause the circulation of too limited a quantity of water). In other embodiments, the third nipple or fitting and the return line can be placed on a side of the tank while feeding into the upper portion of the tank (but again, at a distance below that of the hot water intake so as to avoid the direct exchange of water).
In some embodiments (including for electric and hybrid tanks), the return can be placed immediately above an upper heating element in the upper portion of the hot water tank. In other embodiments of the same style tank, the return can be placed at the top of the hot water tank with a discharge pipe extending down a distance not extending beyond the upper heating element. In embodiments where the hot water tank includes a combustion-heated tank, placement of the return can be similar. In particular, the return can be routed to a location within the upper portion of the combustion-heated tank, whether from the side or the top.
In operation, the upper heating element 4 and the lower heating element 5 heat water or liquid fed into the tank 1 through the cold water inlet or fitting 2 and the cold water feed pipe 8. During periods in which hot water is not being draw from the tank 1 for external use (such as overnight), the circulating pump 10 can constantly draw heated water or liquid out of the tank 1 through the hot water outlet 3 and into the hot water pipe 9, and return the water or liquid, at modestly reduced temperature, to an area between a middle and top of the tank 1. As applied in a two-element electric heater, the return nipple or fitting 12 can be situated such that the water or liquid returned to the tank 1 can be fed into the tank 1 immediately above the upper heating element 4. When a temperature drop to the water or liquid being circulated through the hot water pipe 9 exceeds a predetermined threshold, the returned water or liquid can trigger activation of the upper heating element 4 or, after falling to a bottom of the tank 1 through convention, trigger activation of the lower heating element 5. In the case of a combustion tank, a single heating mechanism can be activated by the temperature drop from the recirculated water or liquid. In either case, the natural separation of hot and cold water will be maintained.
Following a draw of hot water, a thermocline can rise in the tank 1 and leave the water or liquid at the top of the tank 1 at maximum temperature. Then, additional cold water or liquid can be fed into the tank 1 via the cold water inlet 2 and the cold water feed pipe 8 to a point at which the return water or liquid is fed into the tank 1 by the dedicated hot water recirculating system return 11. At this point, the mixing effect seen in existing tank heaters can occur after the bulk of the tank 1's designed capacity is withdrawn, but after a much greater volume of water has been held and discharged at higher temperature.
The foregoing design improvements will thus lead to significant improvements in comfort and efficiency in all manner of tank heaters but with particular improvements in the context of hybrid electric resistance/heat pump applications.
From the foregoing, it will be observed that numerous variations and modifications may be effected without departing from the spirit and scope of tire invention, it is to be understood that no limitation with respect to the specific system or method described herein is intended or should be inferred. It is, of course, intended to cover all such modifications as fall within the spirit and scope of the invention.
This application claims priority to U.S. Provisional Patent Application No. 62/844,519 filed May 7, 2019 and titled “DEDICATED RETURN FOR HOT WATER CIRCULATING APPARATUS AS APPLIED TO TANK-STYLE HOT WATER HEATERS.” U.S. Provisional Patent Application No. 62/844,519 is hereby fully incorporated by reference as if set forth fully herein.
| Number | Date | Country | |
|---|---|---|---|
| 62844519 | May 2019 | US |
