GEOTHERMAL HEAT PUMP FREEZE PROTECTION WITH ELECTRIC HEATER STAGING

A method of auxiliary heat staging in a heat pump system having a geothermal water source or open loop. The method includes receiving a demand for heating in the heat pump system, receiving a temperature signal indicative of a temperature associated with a liquid in the geothermal loop, determining if the temperature associated with the liquid in the geothermal loop is lower than a first selected threshold. If the temperature is lower than the first selected threshold, then operating the heat pump system and the auxiliary heat at an increased capacity.

BACKGROUND

The present disclosure relates to control of a geothermal system. More particularly, to a geothermal heat pump device having circulation control of the ground circulating loop in a geothermal system and an auxiliary heating source staging.

Heat pumps are used in a variety of settings, for example, in HVAC systems that provide a desired air temperature in a facility. Such heat pumps commonly include a compressor, evaporator, expansion valve, and condenser. The heat pumps input work to the refrigerant, e.g., by driving the compressor, thereby enabling the refrigerant to extract heat from a source and reject it into a conditioned space, and conversely extract heat from a conditioned space and reject it into a heat sink.

In geothermal applications the “outside” heat exchanger includes a buried loop or well for closed loop and open loop systems respectively. After refrigerant expanded by the heating expansion valve, heat is exchanged with water of the well, heating the refrigerant and cooling the water in the loop or well. In the in the geothermal well circulation circuit, a circulating liquid such as water flows through a circulation path, and exchanges heat with the ground ambient. In the heat pump device at the contact point between the circulating water from the geothermal well, the heat of the circulating liquid transfers the thermal energy to the circulating liquid of the refrigerant by heat exchange. Since circulating fluid or air from the building extracts heat from the refrigerant then circulates in the building to be heated, the interior of the building is heated using this thermal energy.

However, in an environment where the temperature drops below the freezing point, extended periods of low geothermal loop temperatures for example, resulting from high heating loads, or undersized geothermal loops, the circulating liquid circulating in the source side circulation circuit may freeze and the geothermal system may not function properly. As a countermeasure against potential freezing, it is sometimes necessary to take measures to replace the water content of the circulating liquid with a liquid having a lower freezing point such as an antifreeze solution. Other countermeasures include sensors and freeze protections that monitor the temperature of the refrigerant circuit and/or loop fluid circuit and disable the geothermal loop to avoid excessively cooling the water. Other techniques are to automatically heat the water in the geothermal loop using stored heat or heating elements, or even temporarily reversing the operation of the heat pump. Yet another technique is to employ an “off” time, automatic/timed staging of auxiliary heat, or scheduled rest time for the geothermal loop to permit the geothermal loop to recover. Another approach is to never stage down auxiliary heat; utilizing supplemental heating to increase heating capacity, thus allowing longer time between heat pump start-ups. Operating on supplemental heating, or turning it on prematurely is generally much more expensive than operation of the ground source heat pump alone.

Accordingly, it is desirable to provide an uncomplicated method for ensuring geothermal loop freeze protections while upstaging utilization of supplemental heating in advance to improve efficiency under selected conditions and/or to keep equipment in operation trouble free.

SUMMARY

According to one embodiment described herein is an A method of auxiliary electric heat staging in a heat pump system having a geothermal loop. The method includes receiving a demand for heating in the heat pump system or building thermostat, receiving a temperature signal indicative of a temperature associated with a liquid in the geothermal loop, determining if the temperature associated with the liquid in the geothermal loop is lower than a first selected threshold. If the temperature is lower than the first selected threshold, then operating the heat pump system and the auxiliary heat at a reduced loading or just heat pump only with no auxiliary heating based on the heat demand. The method also includes determining if the temperature associated with the liquid in the geothermal loop is lower than a second selected threshold. If the temperature is lower than the second selected threshold, then operating the heat pump system and the auxiliary electric heater at full capacity and then shut down the whole system when the demand is satisfied.

In addition to one or more of the features described above, or as an alternative, further embodiments of the system may include that the at least one valve is a reversing valve and is included in said refrigerant circuit for effecting operation respectively in the heating mode and in a cooling mode.

In addition to one or more of the features described above, or as an alternative, further embodiments of the system may include a thermostat, the thermostat providing a signal to the controller indicative of at least the demand for heating in the heating mode.

In addition to one or more of the features described above, or as an alternative, further embodiments of the system may include a circulation fan or pump for the ambient air or fluid associated with the first heat exchanger for circulating ambient air past the first heat exchanger to facilitate refrigerant to ambient air or hydronic fluid heat exchange.

In addition to one or more of the features described above, or as an alternative, further embodiments of the system may include that the controller determines if the temperature associated with the liquid in the geothermal loop is lower than a first selected threshold, if the temperature is lower than the first selected threshold, then the controller operates the heat pump system and the auxiliary heat at an increased capacity.

In addition to one or more of the features described above, or as an alternative, further embodiments of the system may include that the controller determines if the temperature associated with the liquid in the geothermal loop is lower than a second selected threshold, then the controller operates the heat pump system and the auxiliary electric heater at a further increased capacity.

In addition to one or more of the features described above, or as an alternative, further embodiments of the system may include that the determining if the temperature associated with the liquid in the geothermal loop increases above a third selected threshold, if the temperature associated with the liquid in the geothermal loop is greater than the third selected threshold, then operating the heat pump system with the auxiliary heat at, at least the increased capacity.

In addition to one or more of the features described above, or as an alternative, further embodiments of the system may include that the first selected threshold is selected for the temperature of the liquid in the geothermal loop at a temperature far enough away from a freezing temperature of the liquid to permit the heat pump system to partially extract the geothermal heat from the geothermal loop.

In addition to one or more of the features described above, or as an alternative, further embodiments of the system may include that the first selected threshold is established at a user selected temperature based at least in part on the fluid used. In one example 45° F. is used.

In addition to one or more of the features described above, or as an alternative, further embodiments of the system may include that the second selected threshold is selected for the temperature of the liquid in the geothermal loop at temperature to avoid a freezing temperature of the liquid to permit the heat pump system to rest the geothermal loop. This can be done by increasing the capacity using auxiliary heating to reach the desired building temperature faster, allowing the loop to rest.

In addition to one or more of the features described above, or as an alternative, further embodiments of the system may include that the second selected threshold is established at a user selected temperature based at least in part on the fluid used. In one example a temperature of 34° F. is used.

In addition to one or more of the features described above, or as an alternative, further embodiments of the system may include that determining if the temperature associated with the liquid in the geothermal loop increases above a third selected threshold, if the temperature associated with the liquid in the geothermal loop is greater than the third selected threshold, then operating the heat pump system with the auxiliary heat at a reduced capacity.

In addition to one or more of the features described above, or as an alternative, further embodiments of the system may include that the third selected threshold is selected for the temperature of the liquid in the geothermal loop at temperature far enough away from a freezing temperature of the liquid to permit the heat pump system to partially extract the geothermal heat from the geothermal loop.

Also disclosed herein in another embodiment is a method of auxiliary electric heat staging in a heat pump system having a geothermal loop. The method includes receiving a demand for heating associated with a facility in the heat pump system, receiving a temperature signal indicative of a temperature associated with a liquid in the geothermal loop, determining if the temperature associated with the liquid in the geothermal loop is lower than a first selected threshold. If the temperature is lower than the first selected threshold, then operating the heat pump system and auxiliary electric heater at an increased capacity.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method of auxiliary electric heat staging may include determining if the temperature associated with the liquid in the geothermal loop is lower than a second selected threshold and if the temperature is lower than the second selected threshold, then operating the heat pump system and the auxiliary electric heater at a further increased capacity including full capacity.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method of auxiliary electric heat staging may include that the demand is generated by a thermostat in the facility that measures the temperature of the facility and determines that the temperature measured is at or below a selected threshold.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method of auxiliary electric heat staging may include that the first selected threshold is selected for the temperature of the liquid in the geothermal loop at a temperature far enough away from a freezing temperature of the liquid to permit the heat pump system to partially extract heat from the geothermal loop.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method of auxiliary electric heat staging may include that the first selected threshold is established at a user selected temperature based at least in part on the fluid used. In one example 45° F. is used.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method of auxiliary electric heat staging may include that the second selected threshold is selected for a temperature of the liquid in the geothermal loop at temperature to avoid a freezing temperature of the liquid to permit the heat pump system to rest the geothermal loop.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method of auxiliary electric heat staging may include that the second selected threshold is established at a user selected temperature based at least in part on the fluid used. In one example 34° F. is used.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method of auxiliary electric heat staging may include determining if the temperature associated with the liquid in the geothermal loop increases above a third selected threshold, if the temperature associated with the liquid in the geothermal loop is greater than the third selected threshold, then operating the heat pump system with the auxiliary heat at the increased capacity.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method of auxiliary electric heat staging may include that the third selected threshold is selected for the temperature of the liquid in the geothermal loop at a temperature far enough away from a freezing temperature of the liquid to permit the heat pump system to partially extract heat from the geothermal loop.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method of auxiliary electric heat staging may include that the circulation of a heat exchange fluid through a heat exchanger is stopped when too much heat is removed from the geothermal loop connected in a heat exchange relationship with the heat exchange fluid, as determined by a sensed temperature of the liquid in the geothermal loop.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method of auxiliary electric heat staging may include that the geothermal loop may be at least one of a closed circuit loop or an open circuit well or pond.

In addition to one or more of the features described above, or as an alternative, further embodiments of the method of auxiliary electric heat staging may include that the thresholds are based on whether the geothermal loop is a closed circuit loop or an open circuit well or pond.

Additional features and advantages are realized through the techniques of the present disclosure. Other embodiments and aspects of the disclosure are described in detail herein and are considered a part of the claimed disclosure. For a better understanding of the disclosure with the advantages and the features, refer to the description.

DETAILED DESCRIPTION

For the purposes of promoting an understanding of the principles of the present disclosure, reference will now be made to the embodiments illustrated in the drawings, and specific language will be used to describe the same. It should nevertheless be understood that no limitation of the scope of this disclosure is thereby intended. The following description is merely illustrative in nature and is not intended to limit the present disclosure, its application or uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. As used herein, the term controller refers to processing circuitry that may include an application specific integrated circuit (ASIC), an electronic circuit, an electronic processor (shared, dedicated, or group) and memory that executes one or more software or firmware programs, a combinational logic circuit, and/or other suitable interfaces and components that provide the described functionality.

In general, embodiments herein relate to an application of a method and/or system for staging auxiliary heat (commonly electric coil) in a heat pump system having a geothermal loop or water source heat pump. Demand for upstaging and activating supplemental auxiliary heating is configured to be independent of building load demand to ensure continual operation of the system. Activating auxiliary electric heat earlier than demand requests facilitates additional rest time for the geothermal loop or well by increasing the time between cycles. Upstaging shall be done with an algorithm based on entering water temperature of medium in the closed loop and/or facility demand.

FIG. 1illustrates an exemplary heat pump system100, according to an embodiment. The heat pump system100having an indoor portion102positioned inside a facility103and an outdoor portion104positioned outside the facility103; however, in various embodiments, the heat pump100may instead be housed in a single casing and/or disposed partially inside and partially outside, or either completely inside or outside the facility103.FIG. 1may illustrate default or “normal” operation of the heat pump100, with the heat pump100being configured to heat the facility103; however, it will be readily appreciated that the heat pump system100can be reversed to cool the facility103. It should be appreciated that while the heat pump system100is depicted as a split system with separated indoor portions102and outdoor portions104, such description is merely illustrative. The heat pump system100could also be a split system of different packaging or integration, stand-alone packaged product, or even a fully contained roof-top type of configuration. In these other configurations the indoor portion and the outdoor portion or at least parts thereof may be integrated.

The heat pump system100includes a compressor106, which may be located, for example, in the outdoor portion104. The compressor106includes an inlet107aconfigured to receive a lower-pressure refrigerant and an outlet107bconfigured to discharge a higher-pressure refrigerant. The refrigerant can be or include, without limitation, Freon, R134a, propane, butane, methane, R410A, carbon dioxide, nitrogen, argon, other organic or HCFC refrigerants, combinations thereof, or the like.

The compressor106can be any suitable single or multistage compressor, for example, a screw compressor, reciprocating compressor, centrifugal compressor, scroll compressor axial-flow compressor, or the like. The compressor106may also be representative of multiple discrete or cooperative compressors, or be inverter driven/variable speed with modulating output. Further, the compressor106may include a motor (not shown), which may be electrically powered to drive the compressor106. In some embodiments, however, other energy sources may be employed to drive the compressor106, such as, for example, natural gas. The compressor106may be “energized” and “de-energized,” for example, by controlling the power to the motor. In a single-stage embodiment of the compressor106, power can be provided to the motor, which in turn, supplies mechanical energy to the compressor106, thereby “energizing” the compressor106. Further, power can be turned off to the motor, or the motor can be mechanically decoupled from the compressive portions of the compressor106, such that the compressor106is “de-energized” and therefore ceases to compress refrigerant. In multi-stage or multi-unit embodiments of the compressor106, the compressor106can be “de-energized” by stopping the supply of mechanical energy to one, some, or all of the compression stages (or units) of the compressor106.

The heat pump100also includes a first heat exchanger108, which may be disposed in the indoor portion102, and may be fluidly coupled to the compressor106. The first heat exchanger108may be any suitable type of heat exchanger configured to transfer heat between a refrigerant and air or another medium (e.g., water). For example, the first heat exchanger108may include one or more coils of thermally conductive material, such as copper, aluminum, alloys thereof, combinations thereof, or the like. In other embodiments, the first heat exchanger108may be or additionally include a shell-and-tube heat exchanger, a printed circuit heat exchanger, a plate-fin heat exchanger, combinations thereof, or the like. The air (or other medium) may be motivated past the first heat exchanger108via a blower110, which may be any suitable air moving device, including one or more axial, radial, or centrifugal fans, blowers, pumps, compressors, combinations thereof, or the like.

The heat pump system100may further include at least one expansion device, for example, an indoor expansion device112positioned in the indoor portion102, and an outdoor expansion device114positioned in the outdoor portion104. At least one of the indoor and outdoor expansion devices112,114may be fluidly coupled to the first heat exchanger108. The expansion devices112,114may each be or include one or more types of thermal expansion valves (TEVs), Joule-Thomson valves, electronic expansion valves (EXVs) or the like. In other embodiments, one or both of the expansion devices112,114may be a turbine or other type of expander. Although not shown, the heat pump system100may include one or more valves and/or bypass lines to enable bypass of the indoor and/or outdoor expansion devices112,114, for example, according to whether the heat pump100is set to cool a facility or heat a facility, as will be described in greater detail below.

The heat pump system100may also include a second heat exchanger116fluidly coupled at least one of the indoor and outdoor expansion devices112,114. In an embodiment, the second heat exchanger116may be disposed about the outer extent of the outdoor portion104of the heat pump system100, as schematically depicted inFIG. 1. However, in other embodiments, the second heat exchanger116may be disposed in any location within, around, and/or proximal to the outdoor portion104. The second heat exchanger116may be any suitable type of heat exchanger configured to transfer heat between a refrigerant and air or another medium (e.g., water for the geothermal loop). For example, the second heat exchanger116may include one or more coils of thermally conductive material, such as copper, aluminum, alloys thereof, combinations thereof, or the like. In some embodiments, the second heat exchanger116may be or additionally include a shell-and-tube heat exchanger, a printed circuit heat exchanger, a plate-fin heat exchanger, twisted tube coaxial, combinations thereof, or the like.

The heat pump100may include a pump to urge or otherwise motivate the liquid past (or through) the second heat exchanger116. The pump150may include a motor120and one or more blades or impeller (not shown), and may be, in at least one embodiment, positioned in line with the geothermal loop152. The pump may be configured to the fluid into and through the second heat exchanger116, returning it to the loop152as shown.

The heat pump system100may also include an accumulator128disposed upstream from the compressor106. The accumulator128may be a pressurized vessel configured to store extra refrigerant, which may provide refrigerant inventory control in the heat pump system100and/or may store excess refrigerant. The accumulator128may be in line with the compressor106, or may be selectively branched off upstream of the compressor inlet107a, for example, by a three-way valve (not shown). The heat pump100may further include a muffler130to attenuate the propagation of noise from the compressor106. The muffler130may be any suitable noise-attenuating device. Further, one or more service valves132may be disposed, from a fluid-flow standpoint, between the compressor106and the first heat exchanger108. The service valve132may be or include one or more gate valves, ball valves, check valves, or any other valves which are operable to facilitate decoupling the indoor and outdoor portions102,104for maintenance, repair, replacement, installation.

The heat pump100may also include a reversing valve134, according to an embodiment. The reversing valve134may be positioned in the outdoor portion104and, from a fluid flow standpoint, between the compressor106and the first heat exchanger108and between the second heat exchanger116and the compressor106. The reversing valve134may include two flowpaths therethrough: a first flowpath136and a second flowpath138. In one or more embodiments, the first and second flowpaths136,138may be discrete, preventing fluid flowing through the first flowpath136from mixing with fluid flowing through the second flowpath138and vice versa. In other embodiments, some intermixing between the first and second flowpaths136,138may be allowed. The flowpaths136,138selectable to implement a cooling mode, a heating mode, or a dehumidification mode for the heat pump system100.

Further, the reversing valve134may have a default state and an energized state. For example,FIG. 1may illustrate the default state of the reversing valve134. In the illustrated embodiment, when in the default state, the reversing valve134may be configured such that the first flowpath136fluidly connects the compressor outlet107b(e.g., via the muffler130) to the first heat exchanger108and the second flowpath138fluidly connects the second heat exchanger116to the compressor inlet107a(e.g., via the accumulator128).

The heat pump system100may also include an auxiliary heater139positioned in the indoor portion102, proximal to the blower110. The auxiliary heater139may be an electrical resistance or inductive heater, hydronic coil, a gas heater or furnace, a combination thereof, or the like. The auxiliary heater139may be configured to provide supplemental heat for the air moved into the facility103by the blower110during heating mode or when the geothermal loop152is either not operational (e.g., freeze condition).

The heat pump100may also include a controller140and one or more sensors such as a temperature sensor142, which may be coupled together such that the controller140is configured to receive a signal from the temperature sensor142. The temperature sensor142may be a thermistor, thermocouple, thermostat, infrared sensor, combinations thereof, or the like, and may be in contact with or disposed closely proximal to the second heat exchanger116so as to gauge a temperature of the second heat exchanger116. The controller140and the temperature sensor142may be disposed within the outdoor portion104, or outside thereof.

The controller140may be or include one or more programmable logic controllers and may be additionally coupled with the compressor106, reversing valve134, fan118, auxiliary heater139, and any other components of the heat pump100so as to communicate therewith. The controller140may be configured to receive an input from the temperature sensor142and provide output signals to one or more of the compressor106, reversing valve134, fan118, and auxiliary heater139. Such output signals may control whether each component is energized or de-energized.

In operation, the controller140is configured to control the heat pump system100in a manner to address and provide for a calls for heating or cooling of the facility, e.g., the building space to be conditioned. A thermostat160measures the temperature, humidity and the like in the conditioned space of the facility and calls for heating or cooling accordingly.

When the heat pump system100is providing cooling under some conditions (extreme cold, high heating load, undersized geothermal loop, and the like) the geothermal loop152can experience temperatures that may cause the liquid circulating in the loop152to freeze and the geothermal system may not function properly. As a countermeasure against potential freezing, sensors and freeze protection algorithms are employed that monitor the temperature of the geothermal loop and disable the geothermal loop to avoid excessively cooling the water. One technique employed is an “off” time or rest time for the geothermal loop152to permit the geothermal loop to recover to a higher temperature. However, during such a rest time or after a period of no heating, the supplemental auxiliary heater139is typically activated and required to operate at its highest stage levels to satisfy the demand for heating in the facility103. Commonly, this heating is achieved by not down-staging the auxiliary electric heat139and to finish/satisfy the heating call employing the highest electric heat stage from the auxiliary electric heater139. Alternatively, the thermostat160may determine that the heating demand is not being satisfied within a selected time period and determine that the geothermal loop is insufficient to/incapable of satisfying the heating demand. As a result, a rest/off time is employed to permit the geothermal loop to recover.

In an embodiment, the controller140or the thermostat160employs and executes a methodology to enable down-staging of the electric auxiliary heater139to reduce energy consumption and/or help satisfy the temperature demand of103. The algorithm is based upon demand (heating) and temperature of the liquid in the geothermal loop152. In the described embodiments the temperature of the liquid (typically water and antifreeze mixture) in the geothermal loop152is monitor Temperature sensor142monitors the entering water temperature. The temperature of the liquid in the geothermal loop is compared with a first selected temperature threshold. If the temperature of the liquid in the geothermal loop decreases below the first selected threshold, the auxiliary electric heater is activated (if not operating) and/or operated at an increased capacity, but not necessarily a maximum capacity output for a selected duration. If the temperature of the liquid in the geothermal loop decreases to below a second selected threshold temperature (e.g., near the freeze temp), the methodology causes the auxiliary electric heater to operates at a further increased capacity up to and including at full stage or power to provided heating for the facility103and satisfy the heating demand Thereby permitting the geothermal loop an opportunity to rest and recover to an operable temperature and state. Advantageously the electric heat up/down-staging algorithm of the described embodiments reduces energy consumption may be readily automatically controlled and requires minimal user interaction and configuration. The described embodiments also aid in continual operation of the system to help ensure temperature demand is met in the facility.

Turning now toFIG. 2depicting the method200of staging auxiliary heating in a geothermal heat pump system100having a geothermal loop152. The method200initiates with process step205including receiving a demand for heating in the heat pump system100. The demand is usually generated by a thermostat160in the facility103that measures the temperature and160, or in combination with160and140, determines that the measured temperature is at or below a selected threshold. At process step210, the method200continues with receiving a temperature signal indicative with a temperature associated with a liquid in the geothermal loop152. It is then determined if the temperature associated with the liquid in the geothermal loop152is lower than a first selected threshold as depicted at process step215. In an embodiment, the first selected threshold is selected for a temperature of the liquid in the geothermal loop152at temperature far enough away from the freezing temperature to permit the heat pump system to partially extract heat from the geothermal loop152. In one embodiment the first selected threshold is established at a temperature of 45° F. Though other temperatures are possible for the first selected threshold. In an embodiment, the thresholds are configurable as a function of the geothermal loop152or well design as well as the fluid employed. An installer can configure the freeze limits as part of system commissioning as needed and the thresholds may be adjusted automatically based on the selected freeze limits. If the temperature exceeds (is lower than) the first selected threshold, then the heat pump system100operates the heat pump system100and the auxiliary heat139at an increased capacity or increased or full capacity based on demand of103inFIG. 1as depicted at process step220. Optionally the method200continues at process step225with determining if the temperature associated with the liquid in the geothermal loop152is lower than a second selected threshold. If the temperature is lower than the second selected threshold, then the heat pump system operates the heat pump system100and the auxiliary heat139at further increased/higher capacity including full capacity independent of the demand of103inFIG. 1as depicted at process step230. In one embodiment the second selected threshold is established at a temperature of 34° F. Though other temperatures are possible for the second selected threshold as described herein. In an embodiment the auxiliary heat is operated at full capacity independent of the demand. For example, a higher threshold may be employed for water alone in the geothermal loop, while lower thresholds could be employed if the geothermal loop employs various additive antifreeze solutions. For example, with, a 15% propylene glycol solution the first threshold may be lowered to approximately 38° F., while the second threshold might be reduced to 26° F. Likewise, for other antifreeze additives various thresholds may be employed as described.

Continuing with the method200, as depicted at process step235, optionally it is determined if the measured temperature associated with the liquid in the geothermal loop increases sufficiently to be above a third selected threshold. If it is determined if the temperature associated with the liquid in the geothermal loop152is greater than the third selected threshold, then the heat pump system100operates with the auxiliary heat139in a reduced capacity as depicted at optional process step240. Once again, in an embodiment, the first selected threshold is selected for a temperature of the liquid in the geothermal loop152at temperature far enough away from the freezing temperature to permit the heat pump system to extract heat from the geothermal loop152. Steps235and240optional, and such are shown inFIG. 2as a dashed.