Ground loop bypass for ground source heating or cooling

A ground source heat transfer system circulates transfer fluid between heat exchange units and a ground loop. The system includes a bypass which allows the transfer fluid to continue to circulate past the exchange units while bypassing the ground loop. Monitoring the conditions of the system with temperature sensors allows the system to selectively activate the bypass whenever diverting fluid away from the ground loop can save heat or energy.

FIELD OF THE INVENTION

The invention is generally related to ground source heating or cooling, and more particularly to the use of ground loops to aid in thermal transfer.

BACKGROUND OF THE INVENTION

Energy conservation is an increasingly important consideration for businesses and individuals alike as energy becomes more expensive. Both heating and cooling represent a major source of energy expense, and so alternative methods of heating and cooling are becoming more popular and viable.

Geothermal ground loop heating is used to defray costs associated with heating (or cooling) air and water within a building by taking advantage of the natural temperature differential between the surface air and underground. Such systems typically include a ground loop of underground pipes largely situated below a permafrost layer such as in the earth or in a lake bed or the like, a building loop of pipes largely situated within a structure such as a building, and a fluid pump to pump a heat transfer fluid through the ground and building loops. Within the building loop, the transfer fluid is pumped through a heat exchanger where heat is extracted and used in the building. The fluid is also pumped through underground pipes of the ground loop where it absorbs more heat and carries it back into the building. A similar process can be used for cooling, the transfer fluid being used to move heat out of the building and into the cooler ground.

The fluid pump maintains a generally even and constant flow of the transfer fluid through the entire system, even during times that heat is not being exchanged, such as when the system is otherwise idle or the building is not occupied, for example. Variable-speed drives can be installed to reduce the pump speed and save energy during such idle and unoccupied periods, but the pump still needs to run at some minimum speed on a continuous basis just in case one or more of the heat exchangers is activated, so that the exchangers can use the heat capacity of the fluid.

SUMMARY OF THE INVENTION

I have discovered that operating the fluid pump to move fluid evenly through the entire system is not always necessary. Indeed, operating the pump in order for the fluid to circulate through the entire system itself consumes a significant amount of energy, and can also run the risk of moving heat in the wrong direction, such as when the ground loop is not closer to the desirable temperature than is the building temperature, for example. To that end, and in accordance with the principles of the present invention, I provide a bypass such that when the system is called upon for normal heat exchange, fluid is pumped through the system as conventional, but during other times, some or all of the fluid is pumped through the bypass so as to divert fluid flowing out of the building loop away from the ground loop and back into the building loop. As a consequence, the energy necessary to circulate fluid through the system is substantially reduced or eliminated. Furthermore, the risk of improper heat loss or gain between the building loop and the ground loop during idle or unoccupied periods, for example, is also substantially reduced or eliminated.

The system operates by switching between a normal mode and a bypass mode. In the normal mode, transfer fluid runs from the building loop out and through the ground loop, then back into the building loop as in conventional ground source heating systems. In the bypass mode, at least some (but advantageously all) of the transfer fluid is diverted to run through the bypass instead, re-entering the building loop without first passing through the ground loop. The state of the system, including temperature data for one or more parts of the system, may be used to determine when to operate in normal mode or bypass mode.

In some embodiments, the flow rate of fluid diverted to bypass the ground loop may be greater than the flow rate of fluid circulating through the ground loop when fluid is diverted. The flow rate of fluid circulating through the ground loop when fluid is diverted advantageously drops to approximately zero, such that substantially all fluid passing through the building loop is diverted to bypass the ground loop, but may also remain above zero, such that a portion of fluid continues to circulate through the ground loop when fluid is diverted. Some amount of fluid may also be permitted to circulate through the ground loop or might be unavoidable. And while such circulation may somewhat reduce the energy savings or slightly increase the risk of unwanted heat gain or loss, the benefits of the bypass are still considered sufficient to present a substantial overall reduction in energy consumption including a reduced risk of unwanted heat gain or loss.

By virtue of the foregoing, there is thus provided a more efficient ground source heating system and method which selectively diverts fluid away from the ground loop to recirculate within the building loop at select times, reducing the energy necessary to operate the system and reducing counterproductive thermal transfer within the system.

DETAILED DESCRIPTION

The present invention overcomes the limitations and problems of prior art ground loop heating systems by including a bypass that diverts fluid away from the ground loop under certain conditions.

In many buildings, the geothermal heating system may not represent the only source of heat. Heat expelled from other refrigeration systems, heat from fuel-burning heaters, incidental heat from the sun as well as planned solar heating systems, and even exhaust heat from people and appliances may increase the temperature of the building air over and above the performance of the geothermal heat exchange system. In some cases, particularly at night, these additional sources of heat may result in a building that is warmer than the ground source from which the ground loop exchanges heat. In this case, continuing to run the transfer fluid through the ground loop can actually cool the building, in contravention of the system's purpose. Running heat exchange units during the day to heat a building for its occupant and then losing that heat during the night only to have to repeat the cycle the next day may waste considerable energy. Diverting fluid away from the ground loop to recirculate through the building loop helps to alleviate this problem. Because the system has to spend less energy reversing unwanted thermal transfer, reducing counterproductive heating and cooling during off-peak times may also potentially reduce energy demand during peak times.

In addition to reducing energy costs by reducing the amount of counterproductive heat transfer as described above, the addition of a bypass may also reduce the pump energy required to move the transfer fluid. The ground loop, which may represent hundreds or thousands of feet of pipe, may add significant resistance to the pump, and so bypassing this portion of the circuit at times would allow the pump to operate at a lower speed. In one embodiment, where the energy needed to run a pump is approximately proportional to the third power of the pump's speed, a pump speed reduction of just 10% translates into a pump energy savings of 29%. Therefore, any meaningful reduction in pump speed during off-peak times can greatly increase efficiency.

With reference toFIGS. 1 and 2, there is shown an exemplary ground source heating system10including a ground loop12of underground pipes14placed within the ground16; a building loop18of building pipes20extending within the building22in thermal communication with a plurality of heat exchange units24; and a fluid pump26to circulate thermal transfer fluid28through the pipes14,20. In accordance with the present invention, the system10also includes a bypass30with valves32,34as further described below.

During normal operating mode of the heating system10, geothermal transfer fluid28, for example a water/glycol solution, is pumped through the loops12,18by a fluid pump26. The pump26may represent a single fluid pump or may represent a set of pumps operable to circulate the fluid; where the pump26functions by virtue of multiple pumps, those pumps may be positioned in different locations along the flow path of the heating system10in order to more adequately circulate the fluid28. In some embodiments, the pump26may run twenty-four hours a day year-round.

Within the building loop18is connected a number of heat exchange units24, which extract heat from the transfer fluid28. The heat exchange units24may represent liquid-to-air or liquid-to-water heat pumps as known in the art. The heat exchange units24may support space heating and cooling, water preheating and demand heating, or any other need for heat within the building22where the units are deployed24. The heat exchange units24may be positioned at different locations within the building22and be designed to serve different areas, or may collectively process the transfer fluid28from a common location. Although multiple heat exchange units24are shown, a geothermal heating system10as described may function with only one heat exchange unit24and still incorporate the features of the present invention.

The heat exchange unit24may operate by means of a vapor-compression refrigeration cycle as known in the art, with the heat transfer fluid28acting as the refrigerant, and the ground source16acting as a medium for heat exchange that is preferred over ambient air36. Any other method by which a unit24may transfer heat between the fluid28and the environment to be heated or cooled may be consistent with the teachings of the present invention.

The ground loop12may be located within any ground-based heat source16known in the art. It is understood that “ground” in this context refers to any outdoor area with a significantly different temperature profile from the ambient air. The ground loop12moves the transfer fluid28through this area16in order to bring the transfer fluid28closer to the ground temperature. Ground loops12include horizontal loops (as exemplified inFIG. 1), vertical loops (as exemplified inFIG. 2), or a combination of both vertical and horizontal loops buried below the surface of the ground16, or placed in a variety of natural or manmade geological features. Ground loops12may be buried in generally dry ground or in an area exposed to ground water, or may be immersed in a natural or artificial body of water such as a lake or river. In some embodiments, the ground loop12delivers water into the ground and picks up different water from a ground-based water source, such that the transfer fluid28is this water and the loop is termed an “open” loop. Other ground loops12are brought into thermal contact with the ground16but remain “closed”; in this case the transfer fluid28may be a high heat capacity mixture such as a mixture of water and an anti-freeze fluid. AlthoughFIGS. 1 and 2illustrate the ground loop12as having pipes14forming a single flow path, it is contemplated that the ground loop12could be a branching pipe system representing pipes14having a plurality of flow paths in parallel.

The heat exchange units24may be disposed and may operate separately. For example, each area of the building22may have its own heat exchange units24that operate according to the control of a thermostat (not shown) associated with that area of the building22. The thermostats may have different settings in accordance with the preferences of the users. Even if heat exchange units24covering different areas have similar settings, they may still carry different temperature profiles or heating loads and may still be on or off at different times of day. Because the control of the heat exchange units24may potentially run at any time according to their independent control, the heat transfer fluid28is often made to circulate past the exchange units24at all times.

However, there are conditions under which the building loop18may be under conditions closer to the target temperature than the ground loop12—for example, the ground loop12is colder than the building loop18when heating is desired, or the ground loop12is warmer than the building loop18when cooling is desired. Under these conditions, the continued circulation of heat transfer fluid between the building loop18and the ground loop12is undesirable. The heat transfer fluid28may move further from the target temperature by passing through the ground loop12.

Under these conditions, heat transfer fluid28may be diverted from the ground loop12by means of a bypass30as shown. As the fluid28passes the junction point38, it normally flows past an open bypass valve32and into the pipes14of the ground loop12. However, when the system10is in bypass mode, the bypass valve32closes and the valve34opens. Fluid28flows past the now-open valve34into and through the pipes40of the bypass30, eventually passing a second junction42to re-enter the pipes20of the building loop18. Fluid28so diverted flows out of the building loop18and through the bypass30to recirculate into the building loop18, bypassing the ground loop12. Valves32,34determine whether the bypass30is active at any given time, with an open valve32and closed valve34corresponding to an inactive bypass30where transfer fluid28flows into the ground loop23as normal, while a closed valve32and open valve34corresponds to an active bypass30where fluid28is diverted back into the building loop18. One of ordinary skill will recognize that the function of valves32,34could instead be performed by a single valve such as a two-way valve disposed at the junction38.

The valves32,34of the bypass30may be opened and closed in accordance with the activities of a controller44, which may represent any manual or automated device as known in the art. As shown inFIG. 2, the controller44may be in communication with temperature sensors46,48,50as well as the bypass valves32,34. In one embodiment, the controller44may report temperature settings to an operator and may manipulate the bypass valves32,34in accordance with operator instructions. Alternatively or in addition, the controller44may act according to an automated process as illustrated by the action blocks ofFIG. 3.

One automated process300for determining whether the bypass should be active begins with a decision to run a bypass check (block302). In one embodiment, the bypass check302may be run periodically such as once per hour, or may be run whenever an automated system such as the controller44reaches a predetermined step in a diagnostic or other operating cycle. The bypass check may be initiated manually by a user, or may run only at predetermined times of the day. The steps of the process300may be carried out manually or by the controller44(as shown inFIG. 2) or other device known in the art.

As illustrated by decision block304, in some embodiments the bypass30may only be active during times of low demand, also known as off-peak times. The decision as to whether the system is on peak or off-peak may be based solely on the time of day or may be determined empirically by the current or recent usage patterns of the system10. For example, exceeding a certain level of heat exchange unit24usage over a window of time prior to the bypass check could result in a determination of peak time and a decision not to use the bypass30(block306). In some systems, this step is absent and whether to use the bypass30is based on other factors as further discussed below.

Assuming that the time of day and/or usage limitations are met, the next evaluation depends on whether the system10is currently understood to be within a heating mode or a cooling mode (decision block308). This determination may be made based upon the time of year, may be made based upon one or more measured temperatures (as further described below), or may be made based upon the settings of the exchange units24. However the system mode is determined, the relative temperature of the ground16is then evaluated to determine whether or not it meets this goal.

As shown in decision block310, if the system is in a heating mode, then the ground16needs to be warm enough to accommodate that mode. The evaluation as to the need for the ground temperature may be measured directly by means of a temperature sensor (not shown) located in the ground. It can then be compared against a known reference temperature, or alternatively against an ambient or indoor air temperature or water temperature. However, as the primary concern of the geothermal system10is the temperature of the heat transfer fluid28, a more direct method is to measure the temperature of the fluid28before it enters and after it leaves the ground loop12, as shown inFIG. 2. Here a temperature sensor46is located downstream of the heat exchangers24but upstream of the junction38to evaluate the temperature of the transfer fluid28before it enters the ground loop12, and a second temperature sensor48is located near the building loop inlet52to evaluate the temperature of the transfer fluid28as it leaves the ground loop12. Where it is desired that the ground16is warm in order to facilitate heating, comparing the readings of the sensors46,48may determine whether the ground is warm enough to leave the bypass off. Where the second temperature sensor48reads a higher temperature than the first temperature sensor46, the bypass30shuts off (block314); where the first temperature sensor46reads higher, the bypass30turns on (block316). A third temperature sensor50, located downstream of the junction42, may also communicated temperature measurements T3to the controller44which are used as further described below.

One of ordinary skill will recognize that, in order to avoid a rapidly fluctuating valve32,34in response to minor changes near the critical point in temperature, a threshold difference might be required to either turn the bypass30on when it is inactive or shut the bypass30off when it is active, and that these values may differ from those required to leave the bypass30in its current state (whether active or inactive). In one embodiment, the bypass30may only turn on when the reading of the first temperature sensor46exceeds the reading of the second sensor48by at least 3 degrees, but may then remain on until the reading of the second sensor48exceeds the reading of the first sensor46, and not shut off immediately when the temperature difference drops below the 3 degree mark.FIG. 4Aillustrates this logic process through the use of supplemental flowchart400, which can be seen as one embodiment of decision block310fromFIG. 3. Here, if the bypass30is active (block402), then the difference between the reading of the second sensor48(represented by T2) and the first sensor46(represented by T1) is compared to a first reference value C1(decision block404). The bypass30stays active (block402) until the heat difference (T2−T1) exceeds the reference value C1, at which point the bypass shuts off (block406). If the bypass30is inactive, it remains inactive (block408) until the temperature difference (T2−T1) drops below a second reference value C2(decision block410), at which point the bypass30turns on (block412). The supplemental flowchart400is represented as a continuous loop, although if used as part of the bypass check process illustrated by flowchart300, the process may only run through once, from initiation at a status block402or408until it returns to one of those two status blocks402or408.

Returning to the previous decision block308of flowchart300inFIG. 3, if the system10is understood to be in cooling mode, then the critical values are reversed. A lower reading for the second temperature sensor48than the first sensor46reflects ground16at a desired temperature and the bypass30can be inactive, while a higher reading for the second sensor48than the first46represents ground16that is warmer than desired and conditions where the bypass30may be active. If reference values are used in comparing temperature differences, these may be the same as the reference values associated with the heating cycle or may be different values.FIG. 4Billustrates by means of a supplemental flowchart400′ how the same process may be used as described above, only with reversed signs for the equations and possibly different reference values C3, C4, so that the equations associated with decision blocks404′ and410′ are different than the equations in blocks404and410described above.

As the temperature T2may be measured based on transfer fluid48exiting the pipes14of the ground loop12, it may be recognized that these temperature measurements may not be available when the bypass30is active, and that other methods may be necessary to determine when the bypass30should be shut off. For example, temperature measurements of the ground source16, ambient air36, or building22may be used in addition to the temperature measurements used above. Alternatively, a periodic evaluation may include briefly increasing the fluid flow through the ground loop12in order to evaluate the temperature of the transfer fluid28as discussed above. Even in the advantageous case of a complete lack of fluid flow past the temperature sensor48, the temperature T2of the fluid28left in the pipes20near the sensor48may continue to be used. Alternatively, further comparisons involving the temperature T2may be based on the last temperature T2taken before the bypass30was active, or on another reference value. The third temperature sensor50and temperature measurements T3may also be used to determine whether the system10should be in its normal or bypass mode.

In some embodiments, a portion of the fluid28will continue to flow through the ground loop12even while much of the fluid is diverted into the bypass30. It will be recognized that some minimal fluid flow through the ground loop12may prevent damage to the pipes14and allow continued temperature measurements T2as described above while still allowing the system10to benefit from use of the bypass30. Similarly, it will be understood that in some embodiments, a portion of the fluid28may continue to flow through the bypass pipes40even when the bypass30is inactive.

It will be recognized that a given embodiment of this system may be more limiting than the above—for instance, a ground-source system may be configured to work only in a heating mode or a cooling mode, in which case the logic to determine which mode the system is in would be unnecessary. Similarly, the decision to switch between a heating mode and cooling mode may be made manually, and in one embodiment may occur only during a perceived transition in seasonal weather patterns.

Although illustrated inFIGS. 1 and 2as a region of pipe40, one of ordinary skill will recognize that the bypass30may represent other methods of fluid conveyance known in the art. For example, the bypass30may itself represent a branching valve capable of diverting fluid flow from the ground loop12directly back into the building loop18while using little or no independent pipe40not found in the ground loop12. One of ordinary skill in the art will also recognize that the fluid conveyance circuit diagram ofFIG. 2is an illustration which is not designed to be limiting as to the relative positions, numbers, or sizes of various elements, and that one of ordinary skill will take a variety of structural and fluid dynamic considerations into account when designing each system without departing from the teachings of the present invention.

Many features have been listed with particular configurations, options, and embodiments. Any one or more of the features described may be added to or combined with any of the other embodiments or other standard devices to create alternate combinations and embodiments.

While the present invention has been illustrated by the description of an embodiment thereof and specific examples, and while the embodiment has been described in considerable detail, it is not intended to restrict or in any way limit the scope of the appended claims to such detail. Additional advantages and modifications will readily appear to those skilled in the art. For example, it is contemplated that the bypass30which is discussed above as present within the building22could instead be within the ground loop12in order to bypass a portion of the ground loop12. A bypass30within the ground loop12could act to significantly shorten the flow path of the transfer fluid28during a bypass mode of operation without completely removing the ground loop12from the flow path. It is also contemplated that multiple bypasses30could be included at different locations in the heating system10, and that such bypasses30might be activated in tandem or separately to respond to different conditions in parts of the heating system10. The invention in its broader aspects is therefore not limited to the specific details, representative apparatus and methods and illustrative examples shown and described. Accordingly, departures may be made from such details without departing from the scope or spirit of applicant's general inventive concept.