COMPRESSOR STAGING CONTROL ARCHITECTURE FOR HOT GAS REHEAT SYSTEMS

Abstract

A method is provided for controlling a heating, ventilation, and air conditioning (HVAC) system. The method includes measuring a temperature and controlling a compressor of the HVAC system. The temperature is measured by a temperature sensor located between a metering device of the HVAC system and an evaporator coil of the HVAC system. The temperature is representative of a refrigerant temperature. The refrigerant temperature is a temperature of a refrigerant fluid flowing from the metering device to the evaporator coil. The compressor is controlled by control circuitry that is configured to perform the controlling in a dehumidify mode based, at least in part, on a value of a humidity parameter of air of an airflow through an evaporator coil and a reheat coil, where the value is determined using the temperature.

Description

TECHNOLOGICAL FIELD

The present disclosure relates generally to heating, ventilation, and air conditioning (HVAC) engineering and, in particular, to one or more of the design, construction, operation, or use of HVAC systems.

BACKGROUND

The field of heating, ventilation, and air conditioning (HVAC) engineering often involves the design, installation and service of HVAC systems with equipment such as air handling units, variable air volume (VAV) units, compressors, air movers, chillers, furnaces, and ventilators. An HVAC system is generally configured to control environmental conditions for a facility such as an industrial facility, institutional facility, commercial facility, residential facility and the like. The facility may also include a building automation system (BAS) or other control system to provide some level of computerized central control of an HVAC system and perhaps other environmental control systems of the facility.

It is desirable to operate an HVAC system such that the conditioned air, provided to one or more enclosed spaces, maintains the relative comfort of the occupants of those enclosed spaces. As will be appreciated, factors affecting the occupants' comfort include the temperature and humidity maintained in those enclosed spaces. In certain situations, a desirable temperature and humidity can be achieved by controlling the temperature and humidity of the conditioned air using what are referred to as hot gas reheat techniques. As will also be appreciated, then, it is desirable to properly control the control of HVAC systems that employ such hot gas reheat techniques, in order to maintain such desirable temperatures and humidity levels.

BRIEF SUMMARY

Example implementations of the present disclosure are directed to the design, construction, operation, or use of HVAC systems. In terms of the present disclosure, HVAC systems that employ hot-gas reheat techniques can benefit from techniques such as those described herein, which provide compressor staging control for HVAC systems employing such hot gas reheat techniques.

Some example implementations provide a method for controlling a heating, ventilation, and air conditioning (HVAC) system. The method includes measuring a temperature and controlling a compressor of the HVAC system. The temperature is measured by a temperature sensor located between a metering device of the HVAC system and an evaporator coil of the HVAC system. The temperature is representative of a refrigerant temperature. The refrigerant temperature is a temperature of a refrigerant fluid flowing from the metering device to the evaporator coil. The HVAC system further comprises a reheat coil and a condenser coil. The compressor, the metering device, the evaporator coil, the reheat coil, and the condenser coil are in fluid communication with one another, with respect to the refrigerant fluid. The compressor is controlled by control circuitry that is configured to perform the controlling in a dehumidify mode based, at least in part, on a value of a humidity parameter of air of an airflow through the evaporator coil and the reheat coil, where the value is determined using the temperature.

Some example implementations provide a computer-readable storage medium, comprising program instructions for controlling an HVAC system, which, when executed by one or more processors, perform a method that includes measuring a temperature and controlling a compressor of the HVAC system. The temperature is measured by a temperature sensor located between a metering device of the HVAC system and an evaporator coil of the HVAC system. The temperature is representative of a refrigerant temperature. The refrigerant temperature is a temperature of a refrigerant fluid flowing from the metering device to the evaporator coil. The HVAC system further comprises a reheat coil and a condenser coil. The compressor, the metering device, the evaporator coil, the reheat coil, and the condenser coil are in fluid communication with one another, with respect to the refrigerant fluid. The compressor is controlled by control circuitry that is configured to perform the controlling in a dehumidify mode based, at least in part, on a value of a humidity parameter of air of an airflow through the evaporator coil and the reheat coil, where the value is determined using the temperature.

Some example implementations provide an apparatus for controlling an HVAC system, which can include a hot-gas reheat dehumidification circuit, a sensor, and a system control unit. The hot-gas reheat dehumidification circuit can include an evaporator coil, a compressor, a reheat coil, and a metering device that are in fluid communication with one another, with respect to a refrigerant fluid. The metering device is in fluid communication with the evaporator coil via a refrigerant fluid line. The sensor is positioned between the metering device and the evaporator coil such that the sensor is positioned to measure a parameter representative of a refrigerant fluid parameter of a portion of the refrigerant fluid flowing through the refrigerant fluid line. The system control unit is configure to measure the parameter and control the compressor in a dehumidify mode based, at least in part, on a value of a humidity parameter of air of an airflow through the evaporator coil and the reheat coil. The parameter is measured by the sensor, and the value is determined using the parameter.

These and other features, aspects, and advantages of the present disclosure will be apparent from a reading of the following detailed description together with the accompanying figures, which are briefly described below. The present disclosure includes any combination of two, three, four or more features or elements set forth in this disclosure, regardless of whether such features or elements are expressly combined or otherwise recited in a specific example implementation described herein. This disclosure is intended to be read holistically such that any separable features or elements of the disclosure, in any of its aspects and example implementations, should be viewed as combinable unless the context of the disclosure clearly dictates otherwise.

It will therefore be appreciated that this Brief Summary is provided merely for purposes of summarizing some example implementations so as to provide a basic understanding of some aspects of the disclosure. Accordingly, it will be appreciated that the above described example implementations are merely examples and should not be construed to narrow the scope or spirit of the disclosure in any way. Other example implementations, aspects and advantages will become apparent from the following detailed description taken in conjunction with the accompanying figures which illustrate, by way of example, the principles of some described example implementations.

BRIEF DESCRIPTION OF THE FIGURE(S)

Having thus described example implementations of the disclosure in general terms, reference will now be made to the accompanying figures, which are not necessarily drawn to scale, and wherein:

FIG. 1 illustrates a system for establishing a heating, ventilation, and air conditioning (HVAC) system, according to some example implementations of the present disclosure.

FIG. 2 illustrates certain aspects of an HVAC system such as that depicted in FIG. 1, according to some example implementations of the present disclosure.

FIG. 3 is a flowchart illustrating various example operations of a method for controlling an HVAC system, according to some example implementations of the present disclosure.

FIG. 4 is a flowchart illustrating various example operations of a multi-stage control process, according to some example implementations of the present disclosure.

FIG. 5 is an operating result graph illustrating an example of the operation of one multi-stage control process embodiment, according to some example implementations of the present disclosure.

FIG. 6 illustrates computing system suitable for use in certain embodiments of methods and systems such as those disclosed herein, according to some example implementations of the present disclosure

DETAILED DESCRIPTION

Some implementations of the present disclosure will now be described more fully hereinafter with reference to the accompanying figures, in which some, but not all implementations of the disclosure are shown. Indeed, various implementations of the disclosure may be embodied in many different forms and should not be construed as limited to the implementations set forth herein; rather, these example implementations are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art. Like reference numerals refer to like elements throughout.

Unless specified otherwise or clear from context, references to first, second or the like should not be construed to imply a particular order. A feature described as being above another feature (unless specified otherwise or clear from context) may instead be below, and vice versa; and similarly, features described as being to the left of another feature else may instead be to the right, and vice versa. Also, while reference may be made herein to quantitative measures, values, geometric relationships or the like, unless otherwise stated, any one or more if not all of these may be absolute or approximate to account for acceptable variations that may occur, such as those due to engineering tolerances or the like.

As used herein, unless specified otherwise or clear from context, the “or” of a set of operands is the “inclusive or” and thereby true if and only if one or more of the operands is true, as opposed to the “exclusive or” which is false when all of the operands are true. Thus, for example, “[A] or [B]” is true if [A] is true, or if [B] is true, or if both [A] and [B] are true. Further, the articles “a” and “an” mean “one or more,” unless specified otherwise or clear from context to be directed to a singular form. Furthermore, it should be understood that unless otherwise specified, the terms “data,” “content,” “digital content,” “information,” and similar terms may be at times used interchangeably.

As indicated above, example implementations of the present disclosure relate generally to heating, ventilation, and air conditioning (HVAC) engineering and, in particular, to one or more of the design, construction, operation or use of HVAC systems. In this regard, FIG. 1 illustrates a system 100 for establishing a HVAC system project, according to some example implementations. As shown, the system includes a facility 102 such as an industrial facility, institutional facility, commercial facility, residential facility and the like. In some examples, the facility includes one or more buildings such as industrial buildings, institutional buildings, commercial buildings, residential buildings and the like. Even further, examples of suitable commercial buildings include office buildings, warehouses, retail buildings and the like.

The facility 102 is generally any facility with one or more environmental control systems configured to control environmental conditions for the facility. The environmental control systems may include, for example, an HVAC system 104 with HVAC equipment 106 such as air handling units, variable air volume (VAV) units, compressors, air movers, chillers, furnaces, and ventilators. Other examples of suitable environmental control systems include lighting control systems, shading control systems, security systems, and the like. The facility may also include an industrial control system (ICS) such as a supervisory control and data acquisition (SCADA) system, distributed control system (DCS) or the like. A more specific example of a suitable DCS is a building automation system (BAS) 108. The ICS is configured to provide some level of computerized central control of at least some of the environmental control systems (including the HVAC system).

In the context of some example implementations of the present disclosure, the HVAC system 104 and perhaps also the BAS 108 may be installed at the facility, and then thereafter be placed in service at the facility. While in service and operated by a customer 112 such as a proprietor of the facility, the HVAC system and/or the BAS may be operated by the customer, but the owner of the facility, or by another party providing services with regard to the operation and maintenance of such HVAC systems.

As will also be appreciated, computers are often used throughout the installation and service of the HVAC system 104; and in this regard, a “computer” is generally a machine that is programmable to programmed to perform functions or operations. The installation and service of the HVAC system 104 at the facility 102 as shown makes use of a number of example computers. These computers may include communication devices 116, 118 and 120 used by a technician 110, a customer 112 and a service organization 114 to communicate with one another, such as during the operation of HVAC system 104. The service organization may also use a computer 122 for monitoring the operation of HVAC system 104, although this computer may be the same as the computer 120 used for communication. And in some examples, the service organization includes a number of units (e.g., offices) responsible for managing such systems.

A number of the computers 116-122 that may be used may be co-located or directly coupled to one another, or in some examples, various ones of the computers may communicate with one another across one or more networks. Further, although shown as part of the system 100, it should be understood that any one or more of the computers may function or operate separately from the system, without regard to any of the other computers. It should also be understood that the system may include one or more additional or alternative computers than those shown in FIG. 1.

Example implementations of the present disclosure are thus directed to the improved control of humidity in HVAC systems that employ hot-gas reheat techniques.

According to some example implementations, compressor staging control (e.g., combinations of manifolded compressors, specifying variable compressor speed, and/or other such alternatives) can be employed to good effect. For example, in such HVAC systems, compressor staging control with hot-gas reheat can take, as one of its inputs, the leaving air dew point is desirable. It will be appreciated in light of the present disclosure that while the dew point of the leaving air is preferred as a result of the dew point directly representing the point at which humidity in the air condenses, a measure of relative humidity can also be used to good effect.

However, directly measuring leaving air humidity is typically infeasible in at least certain HVAC systems, and using a leaving evaporator dry bulb temperature (of air between evaporator and reheat coil) as a proxy for the dew point is difficult to implement in the design of such HVAC systems. To address this need, a control architecture and logic has been developed that utilizes a parameter value of a parameter of the entering evaporator refrigerant fluid (e.g., a temperature representative of the refrigerant fluid temperature, the refrigerant fluid temperature itself, or a proxy therefor) as an input, in order to achieve a proxy for the dew point measurement, where the term “refrigerant fluid,” as used herein, reflects the fact that the refrigerant in question is in a liquid state, a gaseous state, or a combination thereof, including transitioning therebetween. It is noted at this juncture that the parameter value (e.g., temperature value) just noted is referred to as being “representative,” in that a temperature measured at the outside surface of the refrigerant fluid line (or elsewhere sufficiently proximate thereto) can vary from the temperature of the refrigerant fluid itself, as a result of any number of factors, including, for example, wall thickness of the refrigerant fluid line, the material(s) from which the refrigerant fluid line is constructed, the proximity of the sensor to the refrigerant fluid line, and/or other such considerations. It is to be appreciated that the direct measurement of refrigerant fluid temperature is also possible, as is also true of other types of parameters (e.g., pressure of the refrigerant fluid, such as can be used to determine the saturated suction temperature of the refrigerant leaving the evaporator coil), and is intended to be comprehended by the present disclosure.

Additionally, such techniques can further consider the humidity dynamics of the conditioned space. That said, it is to be appreciated that measuring the leaving air humidity directly can present disadvantages when effecting such control. Such issues can include slow response speed of a humidity sensor in the indoor airstream (e.g., a space humidity sensor that senses humidity at the output of the evaporator coil; e.g., 30 minutes), potential difficulties with the installation of such a sensor, and the cost associated with such a sensor and its installation. Therefore, finding a measurable refrigeration system attribute (parameter) that can serve as a sufficiently accurately proxy for the dew point is desirable when controlling HVAC systems employing hot-gas reheat techniques. For example, sensing the adjusted temperature value is more accurate and more responsive than the information provided by humidity sensor, and is also more accurate than a reading of temperature across the evaporator coil.

Embodiments such as those described herein address such problems by sensing a parameter value of a parameter representative of a refrigerant fluid parameter of at least a portion of refrigerant fluid flowing through the HVAC system, using a parameter sensor configured to measure such a parameter. In one such embodiment, the parameter value is a temperature value, as measured by a temperature sensor. Further, certain of such embodiments can effect such measurement using a single temperature sensor to measure a temperature value representative of the refrigerant fluid's temperature. Such information can be combined with an appropriately-configured control system (e.g., analog control circuitry, control logic, computer program instructions (e.g., firmware or software), and/or the like), to generate a leaving air dew point approximation that can be used to control the HVAC system's compressor speed/staging. It will be further appreciated in light of the present disclosure that, with regard to compressor staging/speed control (and while various examples herein are discussed in terms of temperature), another possibility for monitoring/estimating leaving humidity or dew point is the use of evaporator pressure as a proxy for the desired dew point information (e.g., a determination of the saturated suction temperature of the refrigerant fluid). Other alternatives, while potentially less desirable due to factors such as cost, design difficulties, and/or the like, are the use of leaving evaporator dry bulb temperature (i.e., the dry bulb temperature of the air between after the evaporator and before the reheat coil) and the direct measurement of the humidity of the supply air.

FIG. 2 illustrates certain aspects of an HVAC system such as that depicted in FIG. 1, according to some example implementations of the present disclosure. FIG. 2 thus depicts an HVAC system 200, which illustrates various example components of an HVAC system such as HVAC system 104. HVAC system 200 includes a compressor 205, a condenser coil 210, an evaporator coil 215, and a reheat coil 220. As will be appreciated, condenser coil 210, evaporator coil 215 and reheat coil 220 are, in essence, heat exchangers, and are designated thusly as a result of their respective positions in the refrigerant fluid circuits of HVAC system 200.

As illustrated and noted in FIG. 2, the arrows depicted therein indicate the direction of flow of the refrigerant fluid in certain of those refrigerant fluid circuits, which include various of the components noted, including various refrigerant fluid lines, valves, and other hardware. To this end, HVAC system 200 includes a number of such refrigerant circuits. For example, a number of refrigerant circuits can be traced in HVAC system 200, starting with compressor 205. It will be noted here that, while compressor 205 is depicted as a single compressor unit, other embodiments are intended to come within the scope of the present disclosure, as noted earlier herein. For example, rather than a single compressor unit, compressor 205 can be implemented using some number of tandem compressors.

In one such refrigerant circuit, refrigerant fluid flows from compressor 205 through a distribution valve 230, a portion of which then flows to condenser coil 210. An example of a distribution valve such as distribution valve 230 is a modulating valve (e.g., a proportional modulating valve). Such proportional valve can for example, provide a given percentage of the refrigerant fluid flow received to condenser coil 210, and a remaining percentage of the refrigerant fluid flow received to reheat coil 220 (where those percentages can be any combination that sums to 100%). In certain embodiments, distribution valve 230 may support other refrigerant lines/circuits, and provide refrigerant fluid in a manner appropriate to such other embodiments. Further, compressor 205, in certain embodiments, can provide multiple refrigerant output lines to support such functionality.

From condenser coil 210, that portion of the refrigerant fluid flows to a metering device 240, and then on through evaporator coil 215 and back to compressor 205. An example of a metering device such as metering device 240 is a thermostatic expansion valve (TXV), which is a metering device designed to regulate the rate at which the refrigerant fluid ultimately flows into evaporator coil 215. Metering device 240 can meter the refrigerant fluid based on parameters (e.g., temperature and pressure) detected by way of, for example, a metering device temperature sensor 242 and a sense line 244.

In a fashion similar to that described with respect to the foregoing refrigerant circuit, another such refrigerant circuit can also be traced beginning with compressor 205, which compresses the refrigerant fluid received and provides that to distribution valve 230, as noted. From distribution valve 230, another portion of which then flows to reheat coil 220, which receives this portion, and after the heat transfer of its operation, provides the exiting refrigerant fluid to metering device 240 via a check valve 237. As before, this refrigerant fluid transits metering device 240 and evaporator coil 215, and then returns to compressor 205.

In both the foregoing examples, the metered refrigerant fluid (that portion of the refrigerant fluid having flowed through and been metered by metering device 240) flows from metering device 240, through another of the refrigerant fluid lines (depicted in FIG. 2 as a refrigerant fluid line 246), to a refrigerant fluid distribution block 248, and then onward to refrigerant fluid distribution lines 249, which distribute the metered refrigerant fluid through evaporator coil 215. In this manner, the metered refrigerant fluid transits evaporator coil 215, subsequently returning to compressor 205 via yet another of the refrigerant fluid lines.

In the architecture depicted in FIG. 2, evaporator coil 215 and reheat coil 220, along with the various refrigerant fluid lines, valves, and other hardware, form a hot-gas reheat dehumidification circuit 250. As can be seen in FIG. 2, in the operation of hot-gas reheat dehumidification circuit 250, the air of an airflow 255 flows first through evaporator coil 215, and then through reheat coil 220. In so doing, evaporator coil 215 can be operated such that the air of airflow 255 flowing therethrough is cooled in a manner sufficient to cause humidity in the air of airflow 255 to condense (e.g., as a result of evaporator coil 215 cooling the air of airflow 255 to a temperature below the air's dew point). This reduces the humidity in the air of airflow 255 to a level that results in the humidity in the air in the conditioned space to a desired level, providing a comfortable atmosphere for the occupants thereof. However, such cooling results in an air temperature of the air of airflow 255 being, potentially, lower than desired. Reheat coil 220 reheats the air of airflow 255 exiting evaporator coil 215 to a temperature that results in the desired air temperature within the conditioned space.

The operation of compressor 205 is controlled by a system control unit 260. System control unit 260 can receive one or more signals from various sensors, such as may be included within HVAC system 200, within the building or other structure/conditioned space to which condition air is provided, outside the structure in question, or elsewhere. An example of such a sensor is sensor 270. In certain embodiments, sensor 270 is a temperature sensor situated on or near the surface of refrigerant fluid line 246, and can be implemented using, for example, a thermistor. Sensor 270 provides a signal or other information (depending on the analog and/or digital nature of sensor 270) to system control unit 260, which, in turn, uses this input (among other such inputs) in determining the appropriate control of compressor 205.

Sensor 270 can be implemented using a single sensor, as depicted in FIG. 2. Such an implementation is advantageous both for its simplicity and economy, but other implementations are possible. In the architecture depicted in FIG. 2, sensor 270 is depicted as being centrally located along the length of refrigerant fluid line 246, such being the case for purposes of clarity of presentation. In practice, sensor 270 will preferably be located as close to distribution block 248 along refrigerant fluid line 246, in order to provide improved accuracy in the measurement of the parameter value (e.g., in the case of temperature measurement). That having been noted, it is to be appreciated that multiple sensors can be employed. In such embodiments, for example, a sensor can be placed on one or more (or each) of refrigerant fluid distribution lines 249. While such an implementation is greater in both complexity and cost, at least as result of an increased number of sensors, the positioning of such sensors can, in certain embodiments, provide improved accuracy in the determination of the relevant temperature values.

Further, and as noted, in certain embodiments, sensor 270 is a temperature sensor such as a thermistor, although other types of temperature sensors can be employed to equally good effect. In fact, other sensor types (e.g., pressure, suction, and other such sensor types) can also be employed, given that the parameters measured by such sensors can be used as proxies for temperature values representative of refrigerant fluid temperatures.

Further still, it is to be appreciated that position can also be a consideration with regard to refrigerant fluid distribution lines 249 (e.g., micro-channels), as such structures can cause a pressure drop that is large enough to affect the validity of the parameter (temperature) used as a proxy for/representative of a refrigerant fluid parameter (refrigerant fluid temperature) of a portion of the refrigerant fluid flowing through the given refrigerant fluid line. In certain implementations, if the refrigerant fluid distribution lines cause the pressure drop to become too significant, affecting the saturated suction temperature (as a surrogate for the leaving air dew point), which would then need to be considered by the calculation of the adjusted temperature value. That said, such a system could, in fact, use a variable parameter offset (e.g., temperature offset) to manage such situations, where the risk of oscillation, the pressure drop encountered, and other factors could be considered.

In the manner noted, embodiments such as those described herein are able to provide partial-load refrigeration system capacity during a hot-gas reheat mode of an HVAC system such as that described herein. A system control unit such as system control unit 260 determines the appropriate compressor stage for the HVAC system (which can, for example, comprehend compressor speed and/or fan speed) by calculating a leaving air dew point target value based on the conditioned-space humidity dynamics. In order to make such as determination, the system control unit needs an input signal that can be used to generate a sufficiently-accurate proxy for the actual leaving air dew point. This is particularly relevant in circumstances in which a direct measure of humidity cannot reasonably be obtained (e.g., without undue expense, complexity, and/or other such considerations). Using techniques such as those described herein, a single refrigerant temperature input can be used to determine a proxy for dew point. The system control unit can also be designed to provide for appropriate compressor stage commands for HVAC system conditions in which the dew point proxy diverges the true dew point value. For an example of this divergence, and the manner in which such situations are addressed, the description in connection with FIG. 5 can be referenced.

In a system in which the compressor (e.g., compressor 205) supports some number of stages of operation (e.g., a multi-stage compressor), embodiments of the control logic can provide features that include:

• • When moving from cooling mode to reheat mode, the compressor is initially staged up one step. For example, if cooling mode is in stage 1 when reheat is initiated, the compressor load will start in stage 2.
  • In certain embodiments, the compressor's lowest stage (e.g., stage 1) is not used during reheat mode. This can be due, for example, to compressor oil management concerns.
  • During reheat mode, in certain embodiments, the controller monitors the refrigerant fluid temperature by monitoring temperature value that represents refrigerant fluid temperature, using a normalized value of this input (e.g., a preliminary temperature offset of the refrigerant fluid's temperature (e.g., according to (T_refrigerant+T_offset)) can be used as a proxy for the actual leaving air dew point.
  • While a T_offset of 0° is ideal, practically speaking, a T_offset of 1.5° can be used as the preliminary temperature offset noted above, and depending on conditions, HVAC system design, and other such considerations, a range of T_offset values in the range of 2°-5° can be employed to good effect.
  • The system control unit can be configured to, for example, “stage up” the compressor (increase the compressor's speed/stage) based on logic such as that described in connection with FIG. 4, subsequently. Typically, for most operating conditions, the compressor can be staged up based on comparing the dew point proxy with a target dew point, utilizing proportional/integral (PI)-based control techniques.
  • In certain embodiments, the compressor does no not stage down during call for reheat, in certain embodiments.
  • The compressor staging control performed by the system control unit can be made independent of other features in the controller, such as modulating valve control of the unit's Discharge Air Temperature (DAT).

Functionality such as that described above is now discussed in connections with FIGS. 3 and 4.

FIG. 3 is a flowchart illustrating various example operations of a method for controlling an HVAC system, according to some example implementations of the present disclosure. FIG. 3 thus depicts an HVAC control process 300. As will be appreciated, the operations depicted in HVAC control process 300 are merely examples of the operations relevant to the discussion herein, and as noted, other sensor inputs will be received by a system control unit such as system control unit 260, which will then perform operations relevant to those sensor inputs, and control various components within HVAC system 200 as appropriate.

HVAC control process 300 begins with the measurement of a parameter value such as a temperature value (e.g., as by sensing such a temperature value at or near the surface of a refrigerant fluid line) representative of the temperature of the refrigerant fluid at a point such as that depicted by the position of sensor 270 (between metering device 240 and distribution block 248) in FIG. 2 (310). In such an embodiment, the temperature value is provided to a system control unit, which can be an operation as simple as a sensor sending a signal to the system control unit, or can involve the digitization of such information and its transmission to the system control unit (e.g., as by wireless network devices or the like). The temperature value, having been thus provided, the system control unit then performs a multi-stage control process (320). An example of such a multi-stage control process is depicted in greater detail in FIG. 4, subsequently. HVAC control process 300 then proceeds with making a determination as to whether the control process should continue (330). In the case in which HVAC control process 300 is to continue operation, the process loops to the measurement of the temperature value (310). In the alternative, HVAC control process 300 concludes.

FIG. 4 is a flowchart illustrating various example operations of a multi-stage control process, according to some example implementations of the present disclosure. A multi-stage control process 400 is thus depicted, and begins with the system control unit's receipt of the measurement made by the sensor (410). For example, such a measurement can be a signal or other information representing the aforementioned temperature value. Multi-stage control process 400 then proceeds to a determination as to whether the given parameter value meets a minimum parameter threshold (420). An example of such a minimum parameter threshold is an adjusted temperature value of 30°, and meeting such a threshold being greater than that adjusted temperature value.

If the parameter value in question does not meet the minimum parameter threshold, the system control unit sends a signal to the compressor to shut down (430). The compressor is shut down in such situations as a failsafe—the HVAC system cannot provide the level of humidity needed to maintained the desired humidity, and in order to protect the system (e.g., the compressor), multi-stage control process 400 proceeds with having the system control unit send the compressor a shutdown signal. As will be described in connection with FIG. 5, this situation is the result of the given parameter value (e.g., the adjusted temperature value discussed elsewhere herein) diverging too far from the minimum threshold (reflecting that the HVAC system is unable to provide the level of humidity reduction desired). Multi-stage control process 400 then concludes, returning to HVAC control process 300 of FIG. 3.

In the alternative, if the parameter value meets the minimum parameter threshold, multi-stage control process 400 proceeds to a determination as to whether the parameter value meets a maximum parameter threshold (440). An example of such a maximum parameter threshold is an adjusted temperature value of 42°, and meeting such a threshold being greater than that adjusted temperature value.

In the case in which the parameter value does not meet the maximum parameter threshold, the system control unit sends a message to the compressor to increase its speed by staging up (470). Typically, this will mean that the system control unit will signal the compressor to immediately (or quickly) go to full load. This is also true of a high superheat condition, where such a superheat measurement is made by another sensor (e.g., temperature sensor) that measures the superheat of the refrigerant fluid leaving the evaporation coil. Examples of measurements of such superheat are presented in connection with FIG. 5, subsequently. Such an increase in speed can be continuous in nature (e.g., as in the case of a variable speed compressor, providing for continuously modulated reheating, and so, from a system perspective, a continuously variable reaction to humidity changes), or incremental (e.g., as in the case of a multi-stage compressor). In certain embodiments, the staging up of the compressor by the system control unit will also result in an increase in fan speed, and so in the velocity of the airflow through the evaporator coil and the reheat coil. Such higher airflow can, in certain embodiments, result in a more accurate representation of actual parameter values (e.g., improved agreement between the adjusted temperature value and the actual temperature (and so agreement between the estimated and actual dew points)), in situations where divergence becomes problematic. Higher airflow also results, in situations where capacity is too low, in an increase in capacity that can correct for such low capacity (e.g., in terms of superheat of the refrigerant).

At this juncture, it should be noted that such divergence can be the result of a low target temperature (used to represent the dew point of the air of the airflow (e.g., airflow 250), in which case such staging up will bring the proxy parameter (e.g., the adjusted temperature value) back into sufficiently-close agreement with the actual temperature, and so, the actual dew point. Alternatively, such divergence may represent a situation in which the HVAC system is overloaded (at the current compressor staging level), which can also result in an artificially low target temperature (and so, dew point), a condition referred to as a “starved evaporator” condition (equating to a problematically-low saturated suction temperature). In in this case, the increase in fan speed (and so, airflow) will assist in the increase in capacity, in order to counter the conditions experienced within the HVAC system, and again bring the proxy parameter (e.g., the adjusted temperature value) back into sufficiently-close agreement, as noted. That being the case, embodiments such as those described herein address situations that result in divergence due to inaccuracy and divergence due to actual low capacity with equal success. Here again, once such actions are taken, multi-stage control process 400 then concludes, returning to HVAC control process 300 of FIG. 3.

In a further alternative, if the parameter value meets the maximum parameter threshold (e.g., using the prior example of a threshold of 42°, and adjusted temperature value less than or equal to 42°), control systems (e.g., as may employ proportional (PI), proportional/integral/derivative (PID), and/or comparable techniques) can be configured to set the dew point target for the HVAC system based on the change in humidity of the conditioned space that is determined using an adjusted parameter value (460). In this case, the HVAC system is operating normally and the parameter in question (e.g., the adjusted temperature value) is not diverging unacceptably, and so the HVAC system's compressor can be staged appropriately in order to address any changes in the conditioned space's humidity.

Such an adjusted parameter value can be, in the case of temperature measurements (or their proxies), an adjusted temperature value. Thus, in those embodiments in which the parameter value is a temperature value (or such a temperature value is determined from a proxy therefor), the adjusted temperature value is determined by adjusting the temperature value by a temperature offset. As noted, such a temperature offset is used to determine the adjusted temperature value. For example, in certain embodiments such as those noted, the controller monitors the refrigerant fluid temperature by monitoring temperature value that represents refrigerant fluid temperature during reheat mode. This can be accomplished, as noted, using a normalized value of this input (e.g., a preliminary temperature offset of the refrigerant fluid's temperature (e.g., according to (T_refrigerant+T_offset)), which, as also noted, can be used as a proxy for the actual leaving air dew point. While a T_offset of 0° is ideal, practically speaking, a T_offset of 1.5° can be used as the preliminary temperature offset noted above, and depending on conditions, HVAC system design, and other such considerations, a range of T_offset values in the range of 2°-5° can be employed to good effect. The need to use a T_offset value greater than 0° is related to the real-world physics of such systems, and the need to avoid oscillations in the control thereof, which can result in increased cycling of the HVAC system and other untoward effects. This is a result of the preference for the adjusted temperature value to result in an estimated dew point that reflects the actual leaving air dew point as accurately as possible, while still avoid the effects noted.

FIG. 5 is an operating result graph illustrating an example of the operation of one multi-stage control process embodiment, according to some example implementations of the present disclosure. FIG. 5 thus depicts an operating result graph 500, with its x-axis reflecting temperature (in degrees Fahrenheit (° F.), in the given example) and its y-axis reflecting the given operational cycle (e.g., simply the cooling/dehumidification cycles following one after another).

Operating result graph 500 depicts data for the conditioned air in an enclosed space with various indoor and outdoor conditions. The attributes shown in operating result graph 500 include the temperature value (representative of the refrigerant fluid temperature), the dew point of the air leaving the reheat coil (e.g., airflow 250), and the superheat value for the evaporator coil (the leading evaporator superheat). As can be seen in operating result graph 500, the adjusted temperature value (e.g., representative of the refrigerant fluid temperature at the point at which the refrigerant fluid leads the metering device, adjusted by the aforementioned temperature offset) is effective as a proxy for the dew point of the air in most conditions depicted. However, as noted by the bold arrows depicted in FIG. 5, the adjusted temperature value can diverge to a lower value than the indoor leaving dew point. In such situations, advantageously, while the system control unit may read such divergence as a low dew point condition (even though such a partial load condition is the result of insufficient capacity being supplied to meet the latent cooling requirements of such situations), the system control unit reacts by signaling the HVAC system's compressor to stage up to full load, which, in certain embodiments, can also include increasing fan speed (potentially to a maximum band speed). As noted, the divergence of the adjusted temperature value (trending lower) than the dew point of the indoor air with in the conditioned space may be interpreted by the system control unit as being a low dew point, when in fact such a situation represents a partial load condition, where the HVAC system is not supplying sufficient capacity to meet the latent cooling requirement.

As can be seen in operating result graph 500, the result of these actions is to bring the adjusted temperature value back into sufficient agreement, such that the estimate of the dew point of the leaving air is sufficiently accurate. It will also be noted that, as reflected by a second sensor configured to detect the superheat of the refrigerant fluid leaving the evaporator coil, such actions also reduce such superheat to a level below the critical superheat value (e.g., in certain embodiments, a value of 24° F.).

According to example implementations of the present disclosure, the system 100 and its subsystems including computers 118-122 may be implemented by various computing architectures. Computing architectures for implementing the system and its subsystems may include hardware, alone or under direction of one or more computer programs (e.g., project-related software application 124) from a computer-readable storage medium. In some examples, one or more apparatuses may be configured to function as or otherwise implement the system and its subsystems shown and described herein. In examples involving more than one apparatus, the respective apparatuses may be connected to or otherwise in communication with one another in a number of different manners, such as directly or indirectly via a wired or wireless network or the like.

FIG. 6 illustrates an apparatus 600 according to some example implementations of the present disclosure. Generally, an apparatus of exemplary implementations of the present disclosure may comprise, include or be embodied in one or more fixed or portable electronic devices. Examples of suitable electronic devices include a smartphone, tablet computer, laptop computer, desktop computer, workstation computer, server computer, PLC, circuit board or the like. The apparatus may include one or more of each of a number of components such as, for example, a processor 602 connected to a memory 604.

The processor 602 is generally any piece of computer hardware capable of processing information such as, for example, data, computer programs and/or other suitable electronic information. The processor includes one or more electronic circuits some of which may be packaged as an integrated circuit or multiple interconnected integrated circuits (an integrated circuit at times more commonly referred to as a “chip”). The processor may be a number of processors, a multi-core processor or some other type of processor, depending on the particular implementation.

The processor 602 may be configured to execute computer programs such as computer-readable program code 606, which may be stored onboard the processor or otherwise stored in the memory 604. In some examples, the processor may be embodied as or otherwise include one or more microprocessors, ASICs, FPGAs or the like. Thus, although the processor may be capable of executing a computer program to perform one or more functions, the processor of various examples may be capable of performing one or more functions without the aid of a computer program.

The memory 604 is generally any piece of computer hardware capable of storing information such as, for example, data, computer-readable program code 606 or other computer programs, and/or other suitable information either on a temporary basis and/or a permanent basis. The memory may include volatile memory such as random access memory (RAM), and/or non-volatile memory such as a hard drive, flash memory or the like. In various instances, the memory may be referred to as a computer-readable storage medium, which is a non-transitory device capable of storing information. In some examples, then, the computer-readable storage medium is non-transitory and has computer-readable program code stored therein that, in response to execution by the processor 602, causes the apparatus 600 to perform various operations as described herein.

In addition to the memory 604, the processor 602 may also be connected to one or more peripherals such as a network adapter 608, one or more input/output (I/O) devices or the like. The network adapter is a hardware component configured to connect the apparatus 600 to one or more networks to enable the apparatus to transmit and/or receive information via the one or more networks. This may include transmission and/or reception of information via one or more networks through a wired or wireless connection using suitable wired or wireless communication protocols.

The I/O devices may include one or more input devices 610 capable of receiving data or instructions for the apparatus 600, and/or one or more output devices 612 capable of providing an output from the apparatus. Examples of suitable input devices include a keyboard, keypad or the like, and examples of suitable output devices include a display device such as a one or more light-emitting diodes (LEDs), a LED display, a liquid crystal display (LCD), or the like.

As explained above and reiterated below, the present disclosure includes, without limitation, the following example implementations.

Clause 1. A method for controlling a heating, ventilation, and air conditioning (HVAC) system, the method comprising: measuring a temperature (where the temperature is measured by a temperature sensor located between a metering device of the HVAC system and an evaporator coil of the HVAC system, the temperature is representative of a refrigerant temperature, and the refrigerant temperature is a temperature of a refrigerant fluid flowing from the metering device to the evaporator coil) and controlling a compressor of the HVAC system (where the HVAC system further comprises a reheat coil and a condenser coil, the compressor, the metering device, the evaporator coil, the reheat coil, and the condenser coil are in fluid communication with one another, with respect to the refrigerant fluid, the compressor is controlled by control circuitry, the control circuitry is configured to perform the controlling in a dehumidify mode based, at least in part, on a value of a humidity parameter of air of an airflow through the evaporator coil and the reheat coil, and the value is determined using the temperature).

Clause 2. The method of clause 1, wherein the humidity parameter is a dew point of the air.

Clause 3. The method of clause 1 or clause 2, wherein the metering device is a thermostatic expansion valve.

Clause 4. The method of any of clauses 1 to 3, wherein the temperature sensor is a thermistor.

Clause 5. The method of any of clauses 1 to 4, wherein the controlling comprises: determining whether the temperature is sufficient to perform a staging operation by comparing the temperature to a first temperature threshold and in response to a determination that the temperature is not sufficient to perform the staging operation, causing the compressor to shut down.

Clause 6. The method of any of clauses 1 to 5, wherein the controlling further comprises: in response to a determination that the temperature is sufficient to perform a staging operation, comparing the temperature to a second temperature threshold and in response to a determination that the temperature exceeds the second temperature threshold, performing the staging operation.

Clause 7. The method of any of clauses 1 to 6, wherein the humidity parameter is a dew point of the air, the staging operation comprises setting the dew point of the air by increasing a compressor load of the compressor using a proportional integral control process, and an input to the proportional integral control process is the temperature.

Clause 8. The method of any of clauses 1 to 7, wherein another input to the proportional integral control is a temperature offset.

Clause 9. The method of any of clauses 1 to 8, wherein the controlling further comprises: in response to a determination that the temperature does not exceed the second temperature threshold, performing another staging operation, wherein the another staging operation causes the compressor to increase operation to full load.

Clause 10. The method of any of clauses 1 to 9, wherein the HVAC system further comprises a fan, the fan causes to air to flow through the evaporator coil and the reheat coil, and the another staging operation causes the fan to increase a velocity of the air through the evaporator coil and the reheat coil.

Clause 11. A computer-readable storage medium for establishing a heating, ventilation, and air conditioning (HVAC) system, the computer-readable storage medium being non-transitory and having computer-readable program code including a software application stored therein that, in response to execution by processor, causes an apparatus to at least: measuring a temperature (where the temperature is measured by a temperature sensor located between a metering device of the HVAC system and an evaporator coil of the HVAC system, the temperature is representative of a refrigerant temperature, and the refrigerant temperature is a temperature of a refrigerant fluid flowing from the metering device to the evaporator coil) and controlling a compressor of the HVAC system (where the HVAC system further comprises a reheat coil and a condenser coil, the compressor, the metering device, the evaporator coil, the reheat coil, and the condenser coil are in fluid communication with one another, with respect to the refrigerant fluid, the compressor is controlled by control circuitry, the control circuitry is configured to perform the controlling in a dehumidify mode based, at least in part, on a value of a humidity parameter of air of an airflow through the evaporator coil and the reheat coil, and the value is determined using the temperature).

Clause 12. The computer-readable storage medium of clause 11, wherein the humidity parameter is a dew point of the air, the metering device is a thermostatic expansion valve, and the temperature sensor is a thermistor.

Clause 13. The computer-readable storage medium of clause 11 or clause 12, wherein the method further comprises: determining whether the temperature is sufficient to perform a staging operation by comparing the temperature to a first temperature threshold, in response to a determination that the temperature is not sufficient to perform the staging operation causing the compressor to shut down, and in response to a determination that the temperature is sufficient to perform a staging operation comparing the temperature to a second temperature threshold and in response to a determination that the temperature exceeds the second temperature threshold performing the staging operation.

Clause 14. The computer-readable storage medium of any of clauses 11 to 13, wherein the humidity parameter is a dew point of the air, the staging operation comprises setting the dew point of the air by increasing a compressor load of the compressor using a proportional integral control process, an input to the proportional integral control process is the temperature, and another input to the proportional integral control is a temperature offset.

Clause 15. The computer-readable storage medium of any of clauses 11 to 14, wherein the method further comprises: in response to a determination that the temperature does not exceed the second temperature threshold, performing another staging operation, where the another staging operation causes the compressor to increase operation to full load, the HVAC system further comprises a fan, the fan causes to air to flow through the evaporator coil and the reheat coil, the another staging operation causes the fan to increase a velocity of the air through the evaporator coil and the reheat coil.

Clause 16. A heating, ventilation, and air conditioning (HVAC) system, comprising: a hot-gas reheat dehumidification circuit, a sensor, and a system control unit. The hot-gas reheat dehumidification circuit can include an evaporator coil, a compressor, a reheat coil, and a metering device that are in fluid communication with one another, with respect to a refrigerant fluid. The metering device is in fluid communication with the evaporator coil via a refrigerant fluid line. The sensor is positioned between the metering device and the evaporator coil such that the sensor is positioned to measure a parameter representative of a refrigerant fluid parameter of a portion of the refrigerant fluid flowing through the refrigerant fluid line. The system control unit is configure to measure the parameter and control the compressor in a dehumidify mode based, at least in part, on a value of a humidity parameter of air of an airflow through the evaporator coil and the reheat coil. The parameter is measured by the sensor, and the value is determined using the parameter.

Clause 17. The HVAC system of clause 16, wherein the humidity parameter is a dew point of the air, the metering device is a thermostatic expansion valve, and the sensor is a thermistor.

Clause 18. The HVAC system of clause 16 or clause 17, wherein the parameter is a temperature, measurement of the temperature provides a temperature value, the temperature value is representative of a refrigerant fluid temperature, and the refrigerant fluid temperature is a temperature of the portion of the refrigerant fluid flowing through the refrigerant fluid line.

Clause 19. The HVAC system of any of clauses 16 to 18, wherein the system control unit is further configure to: determine whether the temperature is sufficient to perform a staging operation by comparing the temperature to a first temperature threshold, in response to a determination that the temperature is not sufficient to perform the staging operation, cause the compressor to shut down, and, in response to a determination that the temperature is sufficient to perform a staging operation, compare the temperature to a second temperature threshold and, in response to a determination that the temperature exceeds the second temperature threshold, perform the staging operation.

Clause 20. The HVAC system of any of clauses 16 to 19, wherein the humidity parameter is a dew point of the air, the staging operation comprises setting the dew point of the air by increasing a compressor load of the compressor using a proportional integral control process, an input to the proportional integral control process is the temperature, and another input to the proportional integral control is a temperature offset.

Clause 21. The HVAC system of any of clauses 16 to 20, wherein the system control unit is further configure to: in response to a determination that the temperature does not exceed the second temperature threshold, perform another staging operation, where the another staging operation causes the compressor to increase operation to full load, the HVAC system further comprises a fan, the fan causes to air to flow through the evaporator coil and the reheat coil, and the another staging operation causes the fan to increase a velocity of the air through the evaporator coil and the reheat coil.

Many modifications and other implementations of the disclosure set forth herein will come to mind to one skilled in the art to which the disclosure pertains having the benefit of the teachings presented in the foregoing description and the associated figures. Therefore, it is to be understood that the disclosure is not to be limited to the specific implementations disclosed and that modifications and other implementations are intended to be included within the scope of the appended claims. Moreover, although the foregoing description and the associated figures describe example implementations in the context of certain example combinations of elements and/or functions, it should be appreciated that different combinations of elements and/or functions may be provided by alternative implementations without departing from the scope of the appended claims. In this regard, for example, different combinations of elements and/or functions than those explicitly described above are also contemplated as may be set forth in some of the appended claims. Although specific terms are employed herein, they are used in a generic and descriptive sense only and not for purposes of limitation.

Claims

1. A method for controlling a heating, ventilation, and air conditioning (HVAC) system, comprising: measuring a temperature, wherein the temperature is measured by a temperature sensor located between a metering device of the HVAC system and an evaporator coil of the HVAC system,the temperature is representative of a refrigerant temperature, andthe refrigerant temperature is a temperature of a refrigerant fluid flowing from the metering device to the evaporator coil; andcontrolling a compressor of the HVAC system, wherein the HVAC system further comprises a reheat coil and a condenser coil,the compressor, the metering device, the evaporator coil, the reheat coil, and the condenser coil are in fluid communication with one another, with respect to the refrigerant fluid,the compressor is controlled by control circuitry,the control circuitry is configured to perform the controlling in a dehumidify mode based, at least in part, on a value of a humidity parameter of air of an airflow through the evaporator coil and the reheat coil, andthe value is determined using the temperature.

2. The method of claim 1, wherein the humidity parameter is a dew point of the air.

3. The method of claim 1, wherein the metering device is a thermostatic expansion valve.

4. The method of claim 1, wherein the temperature sensor is a thermistor.

5. The method of claim 1, wherein the controlling comprises: determining whether the temperature is sufficient to perform a staging operation by comparing the temperature to a first temperature threshold; andin response to a determination that the temperature is not sufficient to perform the staging operation, causing the compressor to shut down.

6. The method of claim 5, wherein the controlling further comprises: in response to a determination that the temperature is sufficient to perform a staging operation, comparing the temperature to a second temperature threshold, andin response to a determination that the temperature exceeds the second temperature threshold, performing the staging operation.

7. The method of claim 6, wherein the humidity parameter is a dew point of the air,the staging operation comprises setting the dew point of the air by increasing a compressor load of the compressor using a proportional integral control process, andan input to the proportional integral control process is the temperature.

8. The method of claim 7, wherein another input to the proportional integral control is a temperature offset.

9. The method of claim 6, wherein the controlling further comprises: in response to a determination that the temperature does not exceed the second temperature threshold, performing another staging operation, wherein the another staging operation causes the compressor to increase operation to full load.

10. The method of claim 9, wherein the HVAC system further comprises a fan,the fan causes to air to flow through the evaporator coil and the reheat coil, andthe another staging operation causes the fan to increase a velocity of the air through the evaporator coil and the reheat coil.

11. A non-transitory computer-readable storage medium, comprising program instructions for controlling a heating, ventilation, and air conditioning (HVAC) system, which, when executed by one or more processors, perform a method comprising: measuring a temperature, wherein the temperature is measured by a temperature sensor located between a metering device of the HVAC system and an evaporator coil of the HVAC system,the temperature is representative of a refrigerant temperature, andthe refrigerant temperature is a temperature of a refrigerant fluid flowing from the metering device to the evaporator coil; andcontrolling a compressor of the HVAC system, wherein the HVAC system further comprises a reheat coil and a condenser coil,the compressor, the metering device, the evaporator coil, the reheat coil, and the condenser coil are in fluid communication with one another, with respect to the refrigerant fluid,the compressor is controlled by control circuitry comprising the one or more processors,the control circuitry is configured to perform the controlling in a dehumidify mode based, at least in part, on a value of a humidity parameter of air of an airflow through the evaporator coil and the reheat coil, andthe value is determined using the temperature.

12. The non-transitory computer-readable storage medium of claim 11, wherein the humidity parameter is a dew point of the air,the metering device is a thermostatic expansion valve, andthe temperature sensor is a thermistor.

13. The non-transitory computer-readable storage medium of claim 11, wherein the method further comprises: determining whether the temperature is sufficient to perform a staging operation by comparing the temperature to a first temperature threshold;in response to a determination that the temperature is not sufficient to perform the staging operation, causing the compressor to shut down; andin response to a determination that the temperature is sufficient to perform a staging operation, comparing the temperature to a second temperature threshold, andin response to a determination that the temperature exceeds the second temperature threshold, performing the staging operation.

14. The non-transitory computer-readable storage medium of claim 13, wherein the humidity parameter is a dew point of the air,the staging operation comprises setting the dew point of the air by increasing a compressor load of the compressor using a proportional integral control process,an input to the proportional integral control process is the temperature, andanother input to the proportional integral control is a temperature offset.

15. The non-transitory computer-readable storage medium of claim 13, wherein the method further comprises: in response to a determination that the temperature does not exceed the second temperature threshold, performing another staging operation, wherein the another staging operation causes the compressor to increase operation to full load,the HVAC system further comprises a fan,the fan causes to air to flow through the evaporator coil and the reheat coil,the another staging operation causes the fan to increase a velocity of the air through the evaporator coil and the reheat coil.

16. A heating, ventilation, and air conditioning (HVAC) system, comprising: a hot-gas reheat dehumidification circuit, wherein the hot-gas reheat dehumidification circuit comprises an evaporator coil, a compressor, a reheat coil, and a metering device,the evaporator coil, the compressor, the reheat coil, and the metering device are in fluid communication with one another, with respect to a refrigerant fluid, andthe metering device is in fluid communication with the evaporator coil via a refrigerant fluid line;a sensor, wherein the sensor is positioned between the metering device and the evaporator coil such that the sensor is positioned to measure a parameter representative of a refrigerant fluid parameter of a portion of the refrigerant fluid flowing through the refrigerant fluid line; anda system control unit, wherein the system control unit is configure to measure the parameter, wherein the parameter is measured by the sensor, and control the compressor in a dehumidify mode based, at least inpart, on a value of a humidity parameter of air of an airflow through the evaporator coil and the reheat coil, wherein the value is determined using the parameter.

17. The HVAC system of claim 16, wherein the humidity parameter is a dew point of the air,the metering device is a thermostatic expansion valve, andthe sensor is a thermistor.

18. The HVAC system of claim 16, wherein the parameter is a temperature,measurement of the temperature provides a temperature value,the temperature value is representative of a refrigerant fluid temperature, andthe refrigerant fluid temperature is a temperature of the portion of the refrigerant fluid flowing through the refrigerant fluid line.

19. The HVAC system of claim 18, wherein the system control unit is further configure to: determine whether the temperature is sufficient to perform a staging operation by comparing the temperature to a first temperature threshold;in response to a determination that the temperature is not sufficient to perform the staging operation, cause the compressor to shut down; andin response to a determination that the temperature is sufficient to perform a staging operation, compare the temperature to a second temperature threshold, andin response to a determination that the temperature exceeds the second temperature threshold, perform the staging operation.

20. The HVAC system of claim 19, wherein the humidity parameter is a dew point of the air,the staging operation comprises setting the dew point of the air by increasing a compressor load of the compressor using a proportional integral control process,an input to the proportional integral control process is the temperature, and another input to the proportional integral control is a temperature offset.

21. The HVAC system of claim 19, wherein the system control unit is further configure to: in response to a determination that the temperature does not exceed the second temperature threshold, perform another staging operation, wherein the another staging operation causes the compressor to increase operation to full load,the HVAC system further comprises a fan,the fan causes to air to flow through the evaporator coil and the reheat coil, andthe another staging operation causes the fan to increase a velocity of the air through the evaporator coil and the reheat coil.