HVAC systems with evaporator bypass and supply air recirculation and methods of using same

An HVAC system includes an evaporator coil disposed between a return air duct and a supply air duct. The system includes a compressor fluidically connected to the evaporator coil, and a blower for providing a flow of air through the HVAC system. The HVAC system includes a supply air recirculation line with a recirculation damper and an evaporator bypass line with a bypass damper. A controller of the HVAC determines a recirculation portion of a flow of air and causes the recirculation damper to move to divert the recirculation portion to the recirculation line, so the air recirculates through the HVAC system. The controller determines a bypass portion of a flow of air and causes the bypass damper to move to divert the bypass portion to the bypass line, so the bypass portion does not contact the evaporator coil.

TECHNICAL FIELD

This disclosure relates generally to heating, ventilation, and air conditioning (HVAC) systems and methods of their use. In particular, this disclosure relates to HVAC systems for improved dehumidification of air supplied to an enclosed space.

BACKGROUND

Heating, ventilation, and air conditioning (HVAC) systems are used to regulate environmental conditions within an enclosed space. Typically, HVAC systems have a blower, or recirculation fan, that pulls air from an enclosed space through a return duct and pushes the air back into the enclosed space through one or more supply air ducts after conditioning the air (e.g., heating, cooling, humidifying, or dehumidifying the air). HVAC systems generally include a controller to direct operation of the blower and other components of the system. In addition to directing operation of the HVAC system, the controller may be used to monitor various components of the HVAC system to determine if the components are functioning properly.

SUMMARY OF THE DISCLOSURE

HVAC systems are typically configured to supply an enclosed space with conditioned air that is comfortable for occupants of the space by adjusting the temperature and relative humidity of the conditioned air. The air supplied by the HVAC system has an associated temperature and an associated relative humidity. In some HVAC systems, the temperature and/or humidity of the supply air may be adjusted in order to meet the occupant's desired comfort. However, dehumidification using conventional HVAC systems is far from optimal and can result in over-cooling of the conditioned air, waste of energy, and damage to components of the HVAC system, as described in greater detail herein.

This disclosure contemplates an unconventional HVAC system that solves problems of conventional systems. The HVAC system, in certain embodiments, includes an evaporator bypass line and a supply air recirculation line which allow the HVAC system to operate under more optimal conditions for the removal of water from air. A portion of the air that would typically pass through the evaporator coil is diverted through the bypass line (i.e., and not pass through the evaporator coil), allowing the evaporator to more effectively dehumidify the air and improving the overall operation of the HVAC system. Recirculating conditioned air through the HVAC system via the supply air recirculation line also allows the system to more effectively and efficiently provide supply air to a conditioned space at a desired temperature and humidity without wasting energy and without adversely affecting the HVAC system.

According to an embodiment, an HVAC system includes an evaporator coil disposed between a return air duct and a supply air duct. The HVAC system also includes a compressor fluidically connected to the evaporator coil, and a blower disposed between the evaporator and the supply air duct for providing a flow of air through the HVAC system. The HVAC system includes a supply air recirculation line fluidically connecting the supply air duct to the return air duct and bypassing the conditioned space. The supply air recirculation line comprises a recirculation damper for adjusting a first flow of air to a conditioned space via the supply air duct and a second flow of air from the supply air duct to the return air duct via the supply air recirculation line. The HVAC system also includes an evaporator bypass line fluidically connecting the return air duct to the output airstream of the evaporator coil. The evaporator bypass line comprises a bypass damper for adjusting a third flow of air to an input of the evaporator coil and a fourth flow of air to the output of the evaporator coil via the evaporator bypass line. The HVAC system also includes a controller operatively coupled to the compressor, the blower, the recirculation damper, and the bypass damper. The controller is operable to determine a recirculation portion of the first flow of air to divert from the supply air duct to the return air duct based at least in part on a minimum operating flow rate of the blower. The controller is also operable to cause the recirculation damper to move to divert the recirculation portion of the first flow of air from the supply air duct to the return air duct via the supply air recirculation line. The controller is operable to determine an operating mode of the HVAC system. The controller is also operable to determine a bypass portion of the third flow of air to divert from the return air duct to the output of the evaporator coil based at least in part on the operating mode of the HVAC system. The controller is also operable to cause the bypass damper to move to divert the bypass portion of the third flow of air from the return air duct to the output of the evaporator coil via the evaporator bypass line.

According to another embodiment, an HVAC system includes an evaporator coil disposed between a return air duct and a supply air duct, a compressor fluidically connected to the evaporator coil, and a blower disposed between the evaporator and the supply air duct for providing a flow of air through the HVAC system. The HVAC system also comprises an evaporator bypass line fluidically connecting the return air duct to an output of the evaporator coil. The evaporator bypass line comprises a bypass damper for adjusting a first flow of air to an input of the evaporator coil and a second flow of air to the output of the evaporator coil via the evaporator bypass line. The HVAC system also comprises a controller operatively coupled to the compressor, the blower, and the bypass damper. The controller is operable to determine an operating mode of the HVAC system. The controller is operable to determine a bypass portion of the first flow of air to divert from the return air duct to the output of the evaporator coil based at least in part on the operating mode of the HVAC system. The controller is operable to cause the bypass damper to move to divert the bypass portion of the first flow of air from the return air duct to the output airstream of the evaporator coil via the evaporator bypass line.

Certain embodiments provide one or more technical advantages including or in addition to those described above. For example, an embodiment reduces energy waste by reducing unnecessary cooling of the flow of air to achieve a desired relative humidity. As another example, an embodiment allows a portion of the flow of air from the return air duct to bypass the evaporator coil so that evaporator coil may more effectively remove moisture from the flow of air while at the same time maintaining adequate ventilation airflow needs in the conditioned space. Certain embodiments may include none, some, or all of the above technical advantages. One or more other technical advantages may be readily apparent to one skilled in the art from the figures, descriptions, and claims included herein.

DETAILED DESCRIPTION

Embodiments of the present disclosure and its advantages are best understood by referring toFIGS. 1 through 5of the drawings, like numerals being used for like and corresponding parts of the various drawings.

As described above, HVAC systems are typically configured to supply an enclosed space with conditioned air that is comfortable for occupants of the space. The air supplied by the HVAC system has an associated temperature and an associated relative humidity. In some HVAC systems, the temperature and/or humidity of the supply air may be adjusted (e.g., using a thermostat) in order to meet the occupant's desired comfort.

However, dehumidification using conventional HVAC systems is far from optimal. This is because an HVAC system's ability to dehumidify air in an enclosed space is tied to the extent to which the HVAC system cools the air in the enclosed space. Indeed, HVAC systems remove moisture from the air by circulating moisturized air over and/or through evaporator coils that are colder in temperature than the moisturized air (e.g., because of the temperature of refrigerant circulating through the evaporator coils). As a result of heat-exchange principles, the circulating air is cooled and the moisture from the moisturized air condenses on the evaporator coils, thereby producing dehumidified cold air which may then be directed to an enclosed space via a return air duct. Generally, an HVAC system ceases to operate once a predetermined temperature has been reached. For example, most HVAC systems will discontinue operation once an enclosed space has reached a programmed temperature setpoint (e.g., 73° F.). Although the temperature of the enclosed space may be at a desired temperature setpoint (e.g., 73° F.) when the HVAC system ceases operation, the relative humidity of the enclosed space may not be at a desired humidity value (e.g., 80% relative humidity). In such cases, the temperature setpoint may be adjusted to an undesirably low temperature (e.g., 65° F.) in order to decrease the relative humidity of the enclosed space to a more desirable value (e.g., 44% relative humidity).

The extent of cooling and dehumidification an HVAC system can achieve is generally determined by its sensible capacity (Sc) and latent capacity (Lc). Each HVAC system has a total capacity (Tc), which is calculated as the sum of the sensible capacity and a latent capacity (i.e., Tc=Sc+Lc). Generally, sensible capacity refers to an ability of the HVAC system to remove sensible heat from conditioned air (e.g., to cool the air). As used herein, sensible heat refers to heat that, when added to or removed from the air, results in a temperature change of the conditioned air. Comparatively, latent heat refers to the ability of an HVAC system to remove latent heat from conditioned air (e.g., to dehumidify the air). As used herein, latent heat refers to heat that, when added to or removed from the conditioned air, results in a phase change of, for example, water within the conditioned air. Sensible capacity and latent capacity may vary with environmental conditions.

A sensible-to-total ratio (“S/T Ratio”), calculated using sensible and latent capacity values where S/T Ratio=Sc/Tc, may represent the comfort of an occupant within a conditioned space. Generally, a lower S/T ratio is indicative of a greater capacity for dehumidification, while a higher S/T ratio is indicative of a lesser capacity for dehumidification. Thus, if the sensible capacity value is very high, the HVAC system will have a high S/T ratio (e.g., 0.9). In the example of a 0.9 S/T ratio, the HVAC system is devoting 90% of its total capacity to removing sensible heat and 10% of its total capacity to remove latent heat. Such a scenario may lead to humidity problems.

As described above, an existing approach to achieving a substantially low S/T ratio for air dehumidification involves lowering the temperature setpoint of the HVAC system until the desired dehumidification is achieved. This approach reduces both the temperature and humidity of the conditioned air. However, this approach causes the HVAC system to operate for longer periods of time than if the temperature setpoint of the HVAC system were set to a higher temperature. As such, this approach results not only in over-cooling of the conditioned air (and the consequent occupant discomfort) but also wasted energy for the extended HVAC system run times. Another approach to air dehumidification involves re-heating air leaving the evaporator coil of the system. While this approach can provide conditioned air at a more comfortable temperature for occupants, additional energy is wasted, as energy is expended to first over-cool the air to achieve a comfortable relative humidity value before the air is re-heated to achieve a more comfortable temperature for occupants.

The present disclosure provides solutions to the above-described problems and encompasses the recognition that the S/T ratio of an HVAC system can be optimized, by operating the HVAC system at a predetermined optimal rate of air flow per ton of cooling provided by the compressor. For example, in HVAC systems with a variable-speed compressor, the compressor speed, may be modulated. Similarly, a rate of air flow provided by the blower (e.g., a blower “speed”) may be adjusted to achieve a desired predetermined rate of airflow per actual ton of cooling for a given operating mode.

In practice, however, appropriately adjusting the rate of airflow per actual ton of cooling for an HVAC system can be difficult or impossible because of mechanical limitations of the blower. A blower generally has a minimum flow rate at which it is designed to operate (e.g., a minimum rated speed that is established by the manufacturer of the blower). Additionally, flow rate cannot generally be decreased below a minimum target flow rate that is required to properly service (e.g., cool and/or dehumidify) a given space. For instance, low flow rates can result in poor air distribution within a large conditioned space, such as a large non-residential space that comprises multiple sub-spaces, each of which requires an adequate flow of conditioned air. An office building, for example, may require a certain minimum air flow rate to ensure substantial airflow is received in offices that are distant from the blower.

It is also generally difficult or impossible, in some instances, to adjust the rate of airflow per actual ton of cooling by increasing the speed of the compressor of the HVAC system, because operating a compressor at an excessively high speed can adversely impact the HVAC system by decreasing its performance and possibly damaging itself and/or other components of the HVAC system. Increasing the speed of the compressor can result in over-cooling of the air. To prevent the conditioned space from being cooled to an uncomfortably low temperature, the compressor will also need to cycle on and off at a greater frequency. This cycling can cause re-evaporation of the moisture on the evaporator coil in the system, which will counterproductively increase the humidity of the air supplied to the conditioned space. This increased frequency of power cycling can stress the compressor and other components of the HVAC system, resulting in increased maintenance costs and an increased probability of premature system failure. Additionally, when the compressor is operated at a high speed, the turndown ratio, or the ratio of the maximum and minimum discharge pressures of the compressor, is generally decreased resulting in a narrower operational range of cooling and dehumidification for the HVAC system.

This disclosure contemplates an unconventional HVAC system that includes an evaporator bypass line and a supply recirculation line which allow the S/T ratio of the HVAC system to be optimized while mitigating the problems described above. Recirculating conditioned air through the HVAC system effectively decreases the temperature and humidity of the return air directed to the evaporator coil of the HVAC system, allowing the system to more effectively dehumidify this air. In the systems described herein, a damper in the recirculation line can be moved (e.g., to an appropriate angle) to divert a portion of the flow of conditioned air to recirculate back through the HVAC system. For example, the portion of the flow of conditioned air that is not needed to the conditioned space (e.g., the flow that is in excess of a target air flow required by the HVAC system) can be recirculated through the HVAC system to improve the S/T ratio of the system.

A bypass damper in the bypass line can similarly be used to improve the S/T ratio of the HVAC system. The bypass damper can be moved (e.g., to an appropriate angle) to divert a portion of the air that would normally pass through the evaporator coil (i.e., return air+any recirculated supply air from the supply recirculation line) to bypass the evaporator coil. Causing air to bypass the evaporator coil results in a decreased flow of air through the evaporator coil. When the flow of air through the evaporator coil is decreased, the airside convective heat transfer coefficient is reduced, which lowers the coil temperature leading to higher dehumidification or latent capacity at the expense of decreased sensible and total cooling capacities. This results in an improved S/T ratio.

FIG. 1illustrates an HVAC system, according to an illustrative embodiment of the present disclosure. In a typical embodiment, HVAC system100is configured to condition a flow of air (e.g., by cooling and dehumidifying the flow of air) that is received via a return air duct140and supplying the conditioned air to a conditioned space via a supply air duct160. The conditioned space may be, for example, a house, an office building, a warehouse, or the like. Thus, HVAC system100can be a residential system or a commercial system such as, for example, a roof-top system. For exemplary illustration, the HVAC system100as illustrated inFIG. 1includes various components. However, in other embodiments, the HVAC system100may include additional components that are not illustrated but typically included within HVAC systems.

HVAC system100includes an evaporator coil105, a blower110, a compressor115, and a controller180. HVAC system100also includes a supply air recirculation line120with a recirculation damper125disposed therein and an evaporator bypass line130with a bypass damper135disposed therein. The recirculation damper125of supply air recirculation line120can be moved to divert a portion of the supply air from the supply air duct160to the return air duct140to improve the removal of water from air passing through the HVAC system. Evaporator bypass line130allows a portion of air from the return line140to be bypassed around evaporator coil105so that the portion of air does not pass through the evaporator coil105. This allows the flow of air to the conditioned space and the flow of air through the evaporator coil105to be decreased while the flow of air through the blower110is maintained at or above its minimum flow rate. This also facilitates improved dehumidification of air passing through the HVAC system100. In general, the various air lines, including the supply air recirculation line120and the evaporator bypass line130, and ducts, including the return air duct140and the supply air duct160, may be any appropriate duct or passage for facilitating a directed flow of air.

The blower110is any mechanism for providing a flow of air through the HVAC system100. For example, the blower110may be a constant-speed or variable-speed circulation fan. In certain embodiments, it may be beneficial for the blower110to be operable at different capacities (i.e., variable motor speeds) to circulate air through the HVAC system100at different flow rates.

The evaporator coil105is generally a heat exchanger for providing heat transfer between air flowing through the evaporator coil (i.e., contacting the outer surface of the evaporator coil105) and refrigerant175passing through the interior of the evaporator coil105. The evaporator coil105is fluidically connected to the compressor115, such that refrigerant175flows from the evaporator coil105to the compressor115.

During operation, low-pressure, low-temperature refrigerant175is circulated through the evaporator coil105. Refrigerant175is initially in a liquid/vapor state upon entering the evaporator coil105. In a typical embodiment, the refrigerant175is, for example, R-410A, R-134a, R-22, R-744, or any other suitable type of refrigerant as appropriate for particular design requirements. Air entering the evaporator coil105via air line145is typically warmer than the refrigerant175entering the evaporator coil105and is circulated through or around the evaporator coil105by the blower110. In a typical embodiment, the refrigerant175in the evaporator begins to boil after absorbing heat from the air and changes state to a low-pressure (compared to the condenser), super-heated vapor refrigerant175. Saturated vapor, saturated liquid, and saturated fluid refers to a thermodynamic state where a liquid and its vapor exist in approximate equilibrium with each other. Super-heated fluid and super-heated vapor refer to a thermodynamic state where a vapor is heated above a saturation temperature of the vapor at a given pressure. Sub-cooled fluid and sub-cooled liquid refers to a thermodynamic state where a liquid is cooled below the saturation temperature of the liquid at a given pressure.

The low-pressure, low-temperature, super-heated vapor refrigerant175from the evaporator coil105is directed to the compressor115. The compressor115may be a constant-speed or variable-speed compressor and may have a single stage or multiple stages. In a typical embodiment, the compressor115increases the pressure and temperature of the low-pressure, low-temperature, super-heated vapor refrigerant175to form a high-pressure, high-temperature, superheated vapor refrigerant175, which exits the compressor115and is directed to the condenser coil165.

Outside air is circulated around the condenser coil165, for example, by a condenser fan. The outside air is typically cooler than the high-pressure, high-temperature, superheated vapor refrigerant175that enters the condenser coil165. Thus, heat is transferred from the high-pressure, high-temperature, superheated vapor refrigerant175to the outside air. Removal of heat from the high-pressure, high-temperature, superheated vapor refrigerant causes the high-pressure, high-temperature, superheated vapor refrigerant175to condense and change from a vapor state to a high-pressure, high-temperature, sub-cooled liquid state. In certain embodiments, the HVAC system100may include a three-way valve (not shown) to divert at least a portion of the high-pressure, high-temperature, superheated vapor refrigerant from compressor115to a re-heat coil (not shown) positioned in the supply air duct160. The re-heat coil facilitates transfer of a portion of the heat stored in the high-pressure, high-temperature, superheated vapor refrigerant175to the flow of air in the supply air duct160thereby heating the flow of air output to the conditioned space.

The high-pressure, high-temperature, sub-cooled liquid refrigerant175exits the condenser coil165and is directed to a metering device170, which abruptly reduces the pressure of refrigerant175. The metering device170may be a thermostatic expansion valve. Abrupt reduction of the pressure of the high-pressure, high-temperature, sub-cooled liquid refrigerant175also causes sudden, rapid, evaporation of a portion of the high-pressure, high-temperature, sub-cooled liquid refrigerant175, commonly known as “flash evaporation.” Flash evaporation lowers the temperature of the resulting liquid/vapor refrigerant mixture to a temperature lower than a temperature of the air in the conditioned space. The liquid/vapor refrigerant mixture leaves the metering device170and returns to the evaporator coil105. While the illustrative example ofFIG. 1includes the components described above, fewer, more, or other components may be used to achieve an appropriate flow of low-pressure, low-temperature refrigerant to the evaporator coil105.

The controller180is operatively coupled to the compressor115, the blower110, the recirculation damper125, and the bypass damper135and is operable to cause dampers125and135to move based on determinations related to monitored properties of the HVAC system100and/or the conditioned space, as described in greater detail herein. The controller180may be an integrated controller or a distributed controller that directs operation of the HVAC system100. In a typical embodiment, the controller180includes an interface to receive, for example, thermostat calls, temperature setpoints, blower control signals, environmental conditions, and operating mode status for the HVAC system100. For example, in a typical embodiment, the environmental conditions may include indoor temperature and relative humidity of the conditioned space. In a typical embodiment, the controller180also includes a processor and a memory to direct operation of the HVAC system100including, for example, an angle to which the bypass damper135should be moved to direct a desired portion of the flow of air from the return air duct passed the evaporator coil (without passing through the evaporator coil).

The processor of the controller180is any electronic circuitry, including, but not limited to microprocessors, application specific integrated circuits (ASIC), application specific instruction set processor (ASIP), and/or state machines, that communicatively couples to memory and controls the operation of HVAC system100. The processor of controller180may be 8-bit, 16-bit, 32-bit, 64-bit or of any other suitable architecture. The processor may include an arithmetic logic unit (ALU) for performing arithmetic and logic operations, processor registers that supply operands to the ALU and store the results of ALU operations, and a control unit that fetches instructions from memory and executes them by directing the coordinated operations of the ALU, registers and other components. The processor may include other hardware and software that operates to control and process information. The processor executes software stored on memory of the controller180to perform any of the functions described herein. The processor may be a programmable logic device, a microcontroller, a microprocessor, any suitable processing device, or any suitable combination of the preceding. The processor is not limited to a single processing device and may encompass multiple processing devices. Similarly, the controller180is not limited to a single controller but may encompass multiple controllers.

Memory of controller180may store, either permanently or temporarily, data, operational software, or other information for a processor of the controller180. The memory may include any one or a combination of volatile or non-volatile local or remote devices suitable for storing information. For example, the memory may include random access memory (RAM), read only memory (ROM), magnetic storage devices, optical storage devices, or any other suitable information storage device or a combination of these devices. The software represents any suitable set of instructions, logic, or code embodied in a computer-readable storage medium. For example, the software may be embodied in memory, a disk, a CD, or a flash drive. In particular embodiments, the software may include an application executable by a processor of controller180to perform one or more of the functions described herein.

The HVAC system100may also include environment sensors to provide environmental information about the conditioned space (e.g., temperature and humidity of the conditioned space) to the controller180. The sensors may also send environmental information to a display of a user interface of HVAC system100. In some embodiments, the user interface provides additional functions such as, for example, displaying operational, diagnostic, and status messages and providing a visual interface that allows at least one of an installer, a user, a support entity, and a service provider to perform actions with respect to the HVAC system100. For example, the user interface may be a thermostat of the HVAC system100.

In certain embodiments, connections between various components of the HVAC system100are wired. For example, conventional cable and contacts may be used to couple the controller180to the various components of the HVAC system100, including the blower110, the compressor115, the recirculation damper125, and the bypass damper135. In some embodiments, a wireless connection is employed to provide at least some of the connections between components of the HVAC system such as, for example, a connection between controller180and the variable-speed circulation fan110or any environment sensors of system100. In some embodiments, a data bus couples various components of the HVAC system100together such that data is communicated there between. In a typical embodiment, the data bus may include, for example, any combination of hardware, software embedded in a computer readable medium, or encoded logic incorporated in hardware or otherwise stored (e.g., firmware) to couple components of HVAC system100to each other. As an example and not by way of limitation, the data bus may include an Accelerated Graphics Port (AGP) or other graphics bus, a Controller Area Network (CAN) bus, a front-side bus (FSB), a HYPERTRANSPORT (HT) interconnect, an INFINIBAND interconnect, a low-pin-count (LPC) bus, a memory bus, a Micro Channel Architecture (MCA) bus, a Peripheral Component Interconnect (PCI) bus, a PCI-Express (PCI-X) bus, a serial advanced technology attachment (SATA) bus, a Video Electronics Standards Association local (VLB) bus, or any other suitable bus or a combination of two or more of these. In various embodiments, the data bus may include any number, type, or configuration of data buses, where appropriate. In certain embodiments, one or more data buses (which may each include an address bus and a data bus) may couple the controller180to other components of the HVAC system100.

The evaporator bypass line130is fluidically connected to the air line150that fluidically connects the outlet of the evaporator coil105to the inlet of the blower110. The bypass damper135of the evaporator bypass line130may be a motorized damper which is electronically adjustable based on a signal received from the controller180. The bypass damper135is operable to direct a first portion of the flow of air from the return airduct140to the evaporator coil105via air line145and a second portion of the flow of air from the return airduct140to the inlet of the blower110or to air line150, via the evaporator bypass line130. The controller180is operable to cause the bypass damper135to move in order to decrease the first portion of the flow of air from the return airduct140that is directed to the inlet of the evaporator via airline145and to increase the second portion of the flow of air from the return airduct140that is diverted passed the evaporator coil105via the evaporator bypass line130. This allows the total flow of air through the HVAC system100to reach the blower110, while a decreased flow of air passes through the evaporator coil105. In some instances, the evaporator coil105more effectively dehumidifies the flow of air when a decreased flow of air passes through the evaporator coil105, as described in greater detail herein.

The supply air recirculation line120fluidically connects the supply air duct160to the return air duct140. The recirculation damper125of the supply air recirculation line120may be a motorized damper which is electronically adjustable based on a signal received from the controller180. The recirculation damper125is operable to direct a first portion of a flow of air from the blower110to a conditioned space via the supply air duct160. The recirculation damper125is also operable to direct a second portion of air from the supply air duct160to the return air duct140via the supply air recirculation line120. The controller180is operable to cause the recirculation damper125to move (e.g., to an adjusted angle) to decrease the first portion of the flow of air supplied to the conditioned space and to increase the second portion of the flow of air directed to the return airduct140. This allows a portion of the conditioned air to be recirculated through the HVAC system100(i.e., recirculated towards the evaporator coil105for further cooling and/dehumidification), while the blower110still provides the total flow of air required for proper operation. As described in greater detail herein with respect toFIGS. 4 and 5, recirculating conditioned air through the HVAC system improve dehumidification performance of the HVAC system100.

While the illustrative embodiment ofFIG. 1includes the supply air recirculation line120and the recirculation damper125, other embodiments of the HVAC system100(not shown) do not include the recirculation line120or the recirculation damper125disposed therein, as described in greater detail below, for example, with respect toFIG. 3.

In an example operation of the HVAC system100, a flow of air is provided through HVAC system100by the blower110. In the illustrative example ofFIG. 1, the flow of air is provided to air line155which fluidically connects the output of blower110to the supply air duct160and the supply air recirculation line120. The controller180determines a portion of this flow of air to recirculate through the HVAC system100(via the supply air recirculation line120), rather than to supply to the conditioned space (via the supply air duct160). This determination can be made, for example, by determining whether a minimum flow rate of the blower is greater than a predetermined supply air flow rate of the HVAC system100. The predetermined supply air flow rate of the HVAC system100may be based on design specifications of the space being cooled and/or dehumidified by HVAC system100, as described herein. For example, a minimum rate of air flow may be required to provide an adequate flow of air throughout the conditioned space, and any excess flow of air beyond this minimum rate of air flow may be recirculated through the HVAC system100to improve dehumidification.

The controller180then determines the portion of the flow of air to recirculate through the HVAC system via the supply air recirculation line120. The controller180then causes the recirculation damper125to move (e.g., to an appropriate angle) such that the determined portion of the flow of conditioned air is diverted through the supply air recirculation line120. For example, if the required supply flow rate of the condition space is 800 CFM and the minimum flow rate of the blower is 900 CFM, controller180may determine that 100 CFM (i.e., 900 CFM-800 CFM) of air is to be recirculated through the HVAC system via the supply air recirculation line120. Controller180then causes recirculation damper125to move to an appropriate angle to direct 100 CFM of air through supply air recirculation line120. Although 800 CFM is provided to the conditioned space, blower110still provides the required minimum flow of 900 CFM, thereby allowing the blower110to function properly while system performance is improved via recirculation of conditioned air through the HVAC system100.

The controller180then determines how much air to divert through bypass line130to prevent this portion of the flow of air from passing through the evaporator coil105. Thus, the flow of air through the evaporator coil105is decreased, while the blower110still operates at its full minimum flow of air, corresponding to the flow of air through air line150and bypass line130. As described herein, decreasing the flow of air through the evaporator coil105(i.e., the air provided from air line145ofFIG. 1) facilitates improved removal of water from the air passing through the evaporator coil105.

To determine a portion of the flow of air from the return air duct to divert through bypass line130, the controller180first determines an operating mode of the HVAC system100. Typically, the controller180determines whether the system is operating in a cooling mode or dehumidification mode. Each mode is associated with a corresponding threshold value for the ratio of (i) the speed of the blower in terms of the rate of air flow provided by the blower (e.g., in CFM) to (ii) the compressor speed (e.g., in terms of a tonnage). For example, this threshold value may be 400 CFM/Ton for a cooling mode and 200 CFM/Ton for a dehumidification mode. It should be understood that these are example threshold values, and different threshold values may be appropriate, for example, depending on environmental conditions, design specifications of the HVAC system100and/or characteristics of the conditioned space.

The controller180then determines whether the ratio of (i) the flow of air provided by the blower110to (ii) the speed of the compressor115is greater than the predetermined threshold value for the operating mode. For example, for a blower operating at 900 CFM and a compressor operating at 1.5 Ton, this ratio is 600 CFM/Ton (i.e., 900 CFM/1.5 Ton), which is greater than the threshold value of 400 CFM/Ton for the cooling mode and the threshold value of 200 CFM/Ton for the dehumidification mode.

Responsive to this determination that the ratio (600 CFM/Ton) is greater than the predetermined threshold value for the operating mode (e.g., 400 CFM/Ton for the cooling mode), the controller then determines a portion of the flow rate of air from the return air duct to divert to the bypass line130. The controller180determines the portion of air to pass through evaporator coil105based on the threshold value for the operating mode such that the ratio of (i) the flow of air passing through evaporator coil105(via air line145) to (ii) the speed of the compressor is approximately equal to the threshold value. For example, in the example cooling mode, 600 CFM of air (400 CFM/Ton×1.5 Ton) should be directed to the evaporator coil105via air line145. In the example dehumidification mode, 300 CFM (200 CFM/Ton×1.5 Ton) of air should be directed to the evaporator coil105via air line145. The controller180then causes the bypass damper135to move (e.g., to an appropriate angle) to direct the determined flow of air for the operating mode to the evaporator coil105. The remaining flow of air is diverted to the bypass line130in order to bypass the evaporator coil105.

FIG. 2is a flow chart illustrating a method200for operating an HVAC system, according to an illustrative embodiment of the present disclosure. In particular embodiments, the HVAC system100ofFIG. 1performs method200. By preforming method200, the HVAC system100more effectively dehumidifies air without over-cooling the conditioned space or requiring compressor115to operate at an excessively high speed, which can result in problems such as the production of moisture in HVAC system100and damage to the compressor115or other components of the HVAC system100.

In step205, the controller180of the HVAC system100may first determine whether a minimum flow of the blower110is greater than a predetermined or target flowrate of the HVAC system100. If this condition is met, the controller180proceeds to step210and determines a recirculation portion of the flow of air from the supply air duct160to divert to the return air duct140via the supply air recirculation line120. This determination is based at least in part on a minimum operating flow rate of the blower110. For example, the portion of the flow of air to divert through the supply air recirculation line120may be determined based on a difference between the minimum operating flow rate of the blower110and the predetermined supply air flow rate required for the HVAC system. For example, if the target flow rate to the conditioned space is 800 CFM and the blower110has a minimum air flow rate of 900 CFM, then 100 CFM (900 CFM-800 CFM) of air may be determined as the recirculation portion of the flow of air to divert to the supply air recirculation line120.

In step215, the controller180causes the recirculation damper125disposed in the supply air recirculation line120to move so the recirculation portion of the flow of air is diverted to the return air duct140through the supply air recirculation line120. For example, the controller180may transmit a signal to the recirculation damper125which causes the damper125to move to an appropriate angle to achieve the appropriate flow of recirculated air through the supply air recirculation line120.

In step220, the controller determines an operating mode of the HVAC system. For example, the operating mode may be a cooling mode or dehumidification mode. As described elsewhere herein, each mode may have a predetermined threshold ratio value for the desired rate of airflow per actual ton of cooling. This predetermined threshold ratio value may be 400 CFM/Ton for a cooling mode and 200 CFM/Ton for a dehumidification mode.

In step220, the controller may determine whether the rate of airflow provided by the blower110per actual ton of cooling by the compressor115is greater than the threshold ratio value for the operating mode. If this ratio is greater than the threshold value, the controller proceeds to step230.

In step230, the controller180determines a portion of the flow of air from the return air duct140(i.e., the flow of air which would normally pass through the evaporator coil105) to divert through the bypass line130to bypass the evaporator coil105. In other words, the controller180determines a bypass portion of the flow of air from the return air duct to divert to an output of the evaporator coil105through the evaporator bypass line130. This determination is based at least in part on the operating mode of the HVAC system. For example, the portion of air to bypass the evaporator coil105may be determined such that the ratio of the flow passing through the evaporator coil105via air line145to the speed of the compressor115is approximately equal to the threshold ratio value for the operating mode. For example, if the total flow of air in the return air duct140is 900 CFM and the HVAC system100has a 1.5 Ton compressor115and is operating in a cooling mode (threshold ratio value=400 CFM/Ton), then the desired flow of air to pass through the evaporator coil105may be 600 CFM (400 CFM/Ton×1.5 Ton). The flow of air to divert to the bypass line130is thus 300 CFM (900 CFM-600 CFM). This allows an optimal flow of air (600 CFM) to flow through the evaporator coil105, while the blower110functions at its required minimum air flow rate required for proper operation, 900 CFM (600 CFM received from the outlet of the evaporator coil105+300 CFM received from the bypass line130).

In step235, the controller180may determine whether airflow to the evaporator coil105is less than the predetermined target flow of the HVAC system100. If the flow of air to the evaporator coil105is greater than the target flow, then air is not required to bypass the evaporator coil105and the controller returns to the start of method300. Otherwise, if the flow of air directed to the evaporator coil105is less than the target flow of the HVAC system100, the controller180proceeds to step240.

In step240, the controller180causes the bypass damper135to move to divert the bypass portion (determined in step230) of the flow of air from the return air duct140to the output of the evaporator coil105via the evaporator bypass line130. For example, the controller180may transmit a signal to the bypass damper135which causes the damper135to move to an appropriate angle to achieve the appropriate flow of bypass air through the evaporator bypass line130.

Modifications, additions, or omissions may be made to method200depicted inFIG. 2. Method200may include more, fewer, or other steps. For example, steps may be performed in parallel or in any suitable order. While primarily discussed as HVAC system100(or components thereof) performing the steps, any suitable HVAC system or any suitable components of the HVAC system may perform one or more steps of the methods.

As described above, in certain embodiments, system100does not include a supply air recirculation line120. For example, dehumidification can be improved with the bypass line130alone. The example method300illustrated inFIG. 300can be used to operate such a system.

If in step305, the controller180may determine whether the rate of air flow provided by the blower110is equal to the minimum required air flow of the blower110. In other words, the controller180determines whether the speed of the blower110can be decreased. If the blower110is not at its minimum flow rate, the controller180may proceed to step330to determine whether the flowrate is greater than or equal to some threshold times the minimum flowrate. If this condition is met, the damper is moved to a fully closed position so that no airflow bypasses the evaporator coil105(step335). The controller180may also cause the blower110to operate at a decreased flow rate. Otherwise, referring again to step305, if the blower110is at the minimum flow rate, the controller180proceeds to step310.

In step310, the controller180determines an operating mode of the HVAC system. For example, the operating mode may be a cooling mode or dehumidification mode. As already described, each mode may have a predetermined threshold ratio value for the desired rate of airflow per actual ton of cooling. This predetermined threshold ratio value may be, for example, 400 CFM/Ton for a cooling mode and 200 CFM/Ton for a dehumidification mode.

In step315, the controller may determine whether the rate of airflow provided by the blower110per actual ton of cooling by the compressor115is greater than the threshold ratio value for the operating mode. If this ratio is greater than the threshold value, the controller180proceeds to step320. Otherwise, the controller returns to the start of method300to monitor operating parameters of the HVAC system.

In step320, the controller180determines a portion of the flow of air from the return air duct140(i.e., the flow of air which would normally pass through the evaporator coil105) to bypass the evaporator coil105. In other words, the controller180determines a bypass portion of the flow of air from the return air duct140to divert to an output of the evaporator coil105through the evaporator bypass line130. This determination is based at least in part on the operating mode of the HVAC system, as described above with respect to step230of method200.

In step325, the controller180causes the bypass damper135to move to divert the bypass portion of the flow of air from the return air duct140to the output of the evaporator coil105via the evaporator bypass line130. For example, the controller180may transmit a signal to the bypass damper135which causes the damper135to move to an appropriate angle to achieve the appropriate flow of bypass air through the evaporator bypass line130.

Modifications, additions, or omissions may be made to method300depicted inFIG. 3. Method300may include more, fewer, or other steps. For example, steps may be performed in parallel or in any suitable order. While at times discussed as HVAC system100(or components thereof) performing the steps, any suitable HVAC system or components of the HVAC system may perform one or more steps of the method.

As described above, the systems apparatus, and methods described herein provide various advantages and improvements for the dehumidification of air by the HVAC system100.FIGS. 4 and 5show plots400and500, respectively, of example performance metrics of the HVAC system that exemplify these advantages and improvements of dehumidification performance.FIG. 4shows calculated latent capacities of the HVAC system100with different flows of air through the evaporator bypass line130and the supply air recirculation line120.FIG. 5shows calculated S/T Ratios of the HVAC system100with different flows of air through the evaporator bypass line130and the supply air recirculation line120. As shown inFIGS. 4 AND 5, optimum latent capacity and improved (i.e., lower) S/T Ratio can be achieved by increasing the portion of air diverted through the evaporator bypass line130. These exemplary performance metrics can be further improved through the synergistic combination of flowing air through both the evaporator bypass line130and the supply air recirculation line120. It should be understood that the above-described advantages are for illustrative purposes. These particular advantages do not need to be achieved in order to realize a benefit from the systems and methods described herein.

Modifications, additions, or omissions may be made to the systems, apparatus, and methods described herein without departing from the scope of the disclosure. The components of the systems and apparatuses may be integrated or separated. Moreover, the operations of the systems and apparatuses may be performed by more, fewer, or other components. For example, refrigeration system100may include any suitable number of compressors, condensers, condenser fans, evaporators, valves, sensors, controllers, and so on, as performance demands dictate. One skilled in the art will also understand that refrigeration system100can include other components that are not illustrated but are typically included with refrigeration systems. Additionally, operations of the systems and apparatuses may be performed using any suitable logic comprising software, hardware, and/or other logic. As used in this document, “each” refers to each member of a set or each member of a subset of a set.