Abstract:
A water-to-air system using a modulating/proportionate control valve to regulate the amount of sensible reheat when operating in a dehumidification mode is disclosed. When in the reheat/dehumidification mode of operation, the modulating valve regulates the volume of water through a condenser coil to regulate refrigerant temperature to provide for sufficient reheating of the equipment supply air temperature within a narrow range, regardless of the inlet water temperature. The air conditioning system may be any type of water-cooled system, including a water source heat pump or water-cooled air conditioner.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    This application claims priority to U.S. Provisional Application No. 62/342,427 filed May 27, 2016, which is hereby incorporated by reference in its entirety. 
     
    
     BACKGROUND 
     A. Field 
       [0002]    This disclosure relates generally to water-to-air systems, and more particularly to a method and system of controlling a water-to-air system in dehumidification mode. 
       B. Description of Related Art 
       [0003]    A water-to-air system or geothermal heat pump is a central heating and/or cooling system that transfers heat to or from the ground. When water-to-air systems are applied to areas that have excessive humidity issues, simultaneous operation of cooling mode and a reheating mode are used as a means to mitigate the indoor humidity levels, while trying not to necessarily cool or heat the conditioned space. This is referred to as a dehumidification mode of operation, because it operates like a typical dehumidifier used in a home/basement to remove excessive moisture. 
         [0004]    One means of providing a dehumidification mode in a cooling system is referred to as a “reheat” process. In a reheat process, the supply air is reheated to a comfortable level after being cooled for adequate dehumidification. There are several known techniques to perform the reheating process, such as electric resistance heaters, de-superheating or condensing heat exchangers connected to the cooling refrigerant system, and heat exchangers connected to a boiler. The heat source in the preferred methods is some form of waste heat generated in the system as a result of the cooling process. This greatly improves the energy efficiency of the dehumidification process, as no new energy is consumed for reheat. 
         [0005]    The simultaneous operation of both a cooling and reheating mode is an issue with these systems because the subsequent compressor discharge temperatures are much lower than an air source product. In most systems, while operating in active dehumidification mode, the reheat coil and the refrigerant-to-water coil are in direct series with one another, and the lowered discharge pressure/temperature that the refrigerant-to-water coil provides, doesn&#39;t allow for adequate heat in the indoor reheat coil to keep the supply air temperature high enough to prevent over-cooling within the conditioned space. 
         [0006]    Thus, it would be desirable to provide a method of regulating the refrigerant temperature to maintain a neutral cooling effect while in dehumidification mode. 
       SUMMARY 
       [0007]    The following embodiments and aspects thereof are described and illustrated in conjunction with systems, tools and methods which are meant to be exemplary and illustrative, not limiting in scope. 
         [0008]    In one aspect, a method for controlling the dehumidification of a water-to-air system is disclosed. The water-to-air system includes water flow provided by a water source, a refrigeration circuit through which a refrigerant gas flows, and an air circuit having an inlet and an outlet. The method includes operating the water-to-air system in dehumidification mode, sensing outlet air temperature with a temperature sensor and generating a temperature signal, and reducing the water flow via a modulating valve if the temperature signal is below a predetermined set point. The refrigerant liquid changes state to a refrigerant gas after passing through an expansion device. Air passes through a reheat coil to be rewarmed prior to being exhausted through the air outlet. The reduced water flow reduces the amount of heat absorbed by water passing through the reheat coil, thereby raising the temperature of the refrigerant gas in the refrigeration circuit. Lastly, the raised temperature of the refrigerant gas passing through the reheat coil increases the amount of heat rejected into air passing through the reheat coil, thereby resulting in an increased outlet air temperature. 
         [0009]    In another aspect, a water-to-air system is disclosed. The water-to-air system includes a water source configured to provide water to the system, a condenser connected to the water source, the condenser having a water inlet and a water outlet for receiving water from the water source, a modulating valve connected to the condenser, a compressor having a refrigerant inlet and a refrigerant outlet, an evaporator being configured to convert heat from air to refrigerant, an air circuit for circulating air in a space, the air circuit having an air inlet and an air outlet, and a temperature sensor located at the air outlet, the temperature sensor being configured to sense the outlet air temperature and generate a temperature signal. When the temperature signal is below a predetermined set point, the modulating valve reduces the water flow to the condenser, thereby raising the refrigerant condensing temperature. 
         [0010]    In addition to the exemplary aspects and embodiments described above, further aspects and embodiments will become apparent by reference to the drawings and by study of the following detailed description. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]    Exemplary embodiments are illustrated in the drawings. It is intended that the embodiments and figures disclosed herein are to be considered illustrative rather than restrictive. 
           [0012]      FIG. 1  is a circuit diagram of a prior art water-to-air system circuit diagram; 
           [0013]      FIG. 2  is a circuit diagram of an example water-to-air system of the present application; and 
           [0014]      FIG. 3  is a flowchart of an example method of the operation of the water-to-air system operating in dehumidification mode according to an embodiment. 
       
    
    
     DETAILED DESCRIPTION 
       [0015]    The present application discloses a method of controlling a water-to-air system in dehumidification mode which reduces/modulates the water flow in the refrigerant-to-water coil to raise the corresponding pressure and temperature of the discharge/outlet gas, so that a consistent supply air temperature at a neutral condition can be maintained. This can be accomplished, in one embodiment, by monitoring the supply air temperature with one or more temperature sensors only when in dehumidification mode of operation, and using its signal along with a control and modulating valve to regulate the supply air temperature to a consistent set point through the reduced water flow through the coil. 
         [0016]    The water-to-air system of the present application comprises a water-cooled air conditioning system designed to condition the air in an enclosed space, such as a building or other structure. As used herein, “water-to-air system” denotes a system that uses a water source as a heat sink or heat source, and includes water-cooled air conditioners and water-source heat pumps, such as the system illustrated in the drawings. 
         [0017]    Referring to  FIG. 1 , a typical water-to-air system  100  includes a water source  102 . The water source  102  may be one of three basic types: (1) liquid circulating in a temperature-controlled piping loop with temperature control being mechanical, such as cooling towers and boilers or similar devices; (2) ground water pumped from a well, lake, river or stream; or (3) liquid circulating through a sub-surface heat exchange piping loop, which may be placed in horizontal trenches or vertical bores, or submerged within a body of surface water. 
         [0018]    The system  100  further includes a condenser  104  that comprises a refrigerant-to-water heat exchanger or condenser/coil which is adapted to conduct heat from a refrigerant to water. As used herein, “refrigerant” denotes a suitable phase-changing heat exchange fluid for use in a vapor-compression air conditioning or heat pump system. The refrigerant condenses from a high pressure gas into a high pressure liquid once adequate heat has been removed from it within the condenser coil  104  once the refrigerant has been cooled below its adiabatic state. The refrigerant within the system is in a high pressure liquid state in the last 10-18% of the condensing coil, and in the liquid line (tubing) from the condenser coil to the inlet of an expansion device (described below). The condenser  104  contains both high pressure gas and high pressure liquid. The refrigerant enters the condenser coil as a superheated high pressure gas, is cooled to just a high pressure gas, is cooled further to where the refrigerant passes through its adiabatic state and transitions to a high pressure liquid. The liquid is then further cooled below the condensing temperature (point of adiabatic change), which is then referred to as sub-cooling. The condenser  104  has a water inlet  106  and a water outlet  108 . 
         [0019]    The system further includes an evaporator  110  comprising a refrigerant-to-air heat exchanger. Refrigerant gas circulating within the evaporator  110  (being circulated by a compressor  112 ) absorbs heat from the air passing through it, moved by a circulation blower  136  (which is described in more detail below). The evaporator  110  and condenser  104  are connected via a refrigerant circuit with a compressor  112  and one or more expansion devices  114 ,  116 . The expansion devices  114 ,  116  may be valves or similar devices that control and regulate the amount of high pressure liquid refrigerant that is flashed-off (converted) into a low pressure gaseous refrigerant into the evaporator side of the system (dependent on the mode of operation). In other words, the refrigerant changes states from a liquid to a gas through the expansion devices  114 ,  116 . Refrigerant on the entering side of the expansion device  114 ,  116  is a high pressure liquid, and on the outlet side of the expansion device is a low pressure vapor. Although two expansion devices are shown (one for heating, one for cooling), a single expansion device may be used dependent upon specific system characteristics. The compressor  112  changes the state of the low pressure superheated refrigerant gas into a high pressure superheated refrigerant gas to allow the heat to be transferred from one space into another by compressing it. 
         [0020]    The refrigeration circuit within the water-to-air system  100  is a continuous loop that the refrigerant circulates through: compressor  112  to condenser  104  (through the discharge tubing); condenser  104  to expansion device(s)  114 ,  116  (through the liquid line tubing); from the expansion device(s)  114 ,  116  to the evaporator coil  110  (through a distributor); and from the evaporator coil  110  back to the compressor  112  (through the suction line tubing). When running in dehumidification mode, the refrigerant travels from the compressor  112  to the reheat coil  126  first, prior to going to the condenser coil  104 , which is described in more detail below. 
         [0021]    Still further, the system  100  includes an air circuit  130  for circulating air in the space (not shown) through the system  100 . More specifically, the air circuit  130  is adapted to receive return air from the space at an air inlet  132 , to circulate the air through the evaporator  110 , across a reheat coil  126 , and to direct the conditioned supply air leaving the system  100  through an air outlet  134  back into the space. The air circuit  130  usually will include one or more blowers  136  for moving the air. 
         [0022]    The system  100  also comprises conduits (piping/tubing) adapted to circulate refrigerant between the various components of the refrigerant circuit. A dehumidification refrigerant circuit will contain a valve(s)  118  that directs the superheated gas to the refrigerant-to-air reheat coil  126  when operating in dehumidification mode. The reheat coil  126  utilizes the hot refrigerant waste heat to warm the supply air temperature to a desirable sensible neutral temperature when the system is operating in dehumidification mode. From there, the refrigerant flows to the refrigerant-to-water condenser  104  to expel the remaining waste heat. 
         [0023]    The refrigerant circuit may further include a second valve  120  where the system comprises a heat pump. A heat pump is a reverse cycle air conditioner. Instead of extracting heat from the conditioned air space and rejecting it to the water, the refrigeration system reverses (via the reversing valve  120 ), and heat is extracted from the water, and is rejected to the conditioned air. The system  100  may further comprise check valves  122 ,  124 , to ensure the refrigerant flow direction is correct, dependent upon the mode of operation. 
         [0024]    In dehumidification mode, system  100  operates as follows: inlet air  132  from a conditioned space is drawn into the system  100 , first traveling over the evaporator coil  110  which cools the air and extracts humidity due to the coil temperature being below the dew point temperature of the humidity contained in the entering air. The air is thus cooled sensibly (temperature), and latently (moisture removal). The air then passes through the reheat coil  126  to be rewarmed (sensible-temperature) prior to being exhausted back in the conditioned space  134 . 
         [0025]    The issue with the prior art system is that there is no way to balance or control the capacity differential between the evaporator coil  110 , and the reheat coil  126 , since indoor air temperatures and water temperatures from the water source  102  differ and change due to changing conditions, such as seasonal and daily swings. There is only a singular cross-through condition that allows for a sensible-neutral condition for the air between  132  and  134 , and all other conditions with a water-to-air system typically lead to a cooling condition rather than a sensible neutral condition when operating in dehumidification mode. 
         [0026]    As mentioned above, the system of the present application differs from that of the prior art by reducing/modulating the water flow in the refrigerant-to-water coil  104  in dehumidification mode, to raise the corresponding pressure and temperature of the refrigerant discharge gas, so that a consistent supply air temperature at a neutral condition can be maintained. In an example embodiment, shown in  FIG. 2 , a water-to-air system pump circuitry  200  of the present application is shown. The system  200  operates generally in a similar manner to the system  100  shown in  FIG. 1 . 
         [0027]    The system  200  includes a water source  202 , a refrigerant-to-water condenser/coil  204  having a water inlet  206  and a water outlet  208 . The system  200  further includes an evaporator  210  comprising an air-to-refrigerant heat exchanger. The evaporator  210  is adapted to change heat from air to a refrigerant. The evaporator  210  and condenser  204  are connected via a refrigerant circuit with a compressor  212  and one or more expansion devices  214 ,  216 , which operate in a similar manner as the compressor  112  and expansion devices  114 ,  116  described above with respect to  FIG. 1 . 
         [0028]    Still further, the system  200  includes an air circuit  230  for circulating air in the space through the system  200 . More specifically, the air circuit  230  is adapted to receive return air from the space at an air inlet  232 , to circulate the air through the evaporator  210 , through reheat coil  226 , and to direct the conditioned supply air leaving the system  200  through an air outlet  234  back into the space. The air circuit  230  usually will include one or more blowers  236  for moving the air. 
         [0029]    The system  200  also comprises conduits (piping/tubing) adapted to circulate refrigerant between the various components of the refrigerant circuit. A dehumidification refrigerant circuit will contain a valve  218  that directs the superheated gas to a reheat coil  226  when operating in dehumidification mode. The refrigerant circuit may include a second valve  220  where the system comprises a heat pump. 
         [0030]    A modulating/proportionate control valve  240  is used to control the flow of water flowing through the condenser  204 . The modulating valve  240  is located at the water outlet  208 . In an alternate embodiment, the modulating valve  240  may be positioned at the water inlet  206 . In one embodiment, the modulating valve  240  may be a modulating water flow valve which accepts multiple different inputs (0-10 Vdc (Volts Direct Current), 4-20 MA (Milli-Amps), or PWM (Pulse Width Modulation)) as a means of controlling the valve&#39;s position relative to an input signal from a control device. The mechanical portion of the modulating valve  240  may be a ball type valve, a gate type valve, or a globe type valve, for example. It should be understood that any type of known modulating valve can be used, as long as the valve has an actuator that is capable of modulating the position of the valve to modulate the water flow rate through the valve. 
         [0031]    When supply air temperature in dehumidification mode is below the desired or specified set point, which may be adjustable by an end user, building architect, or building mechanical systems engineer, modulating valve  240  modulates or reduces water flow to raise the refrigerant condensing temperature, subsequently raising reheat coil temperature, since both the refrigerant-to-water condenser  204  and reheat condenser coils  226  are piped in series with one another. By rejecting less heat into the water condenser coil, an increased amount of heat is available to be rejected by the reheat coil  226 . 
         [0032]    With continued reference to  FIG. 2 , a closed loop controller or modulating valve actuator  242  is connected to the modulating valve  240 . The closed loop controller/actuator  242  accepts temperature input from a supply air temperature sensor  250  and gives proportional output to regulate the modulating valve  240 . The type of closed loop controller/actuator  242  used may vary with the specific input signal required by the modulating valve actuator requirements. For example, the closed loop controller  242  may comprise a proportional—integral—derivative (PID) Loop Controller or a Programmable Logic Controller (PLC). In some embodiments, the PLC of the water-to-air system may also be used for the closed loop controller  242 . 
         [0033]    The supply air temperature sensor  250  is located in the supply air discharge air stream and provides input to the loop controller via a wire  252 . In alternate embodiments, the supply air temperature sensor  250  and the loop controller  252  may communicate wirelessly. The supply air temperature sensor  250  may comprise a thermocouple, a thermistor, or an RTD type probe, for example. The type of supply air temperature sensor  250  chosen is dependent upon the type of input required by the loop controller  242 . The supply air temperature sensor  250  may be selected based upon specific requirements, such as, for example, the requirements of the selected loop controller  242 . 
         [0034]    A single supply air temperature sensor  250  may be used in a system having only a supply air set point, such as a system being set to modulate the valve  240  to a specific temperature, with±tolerances capabilities of all components stacked together. In another embodiment, the system  200  may include a second air temperature sensor (not shown) located at or near the air inlet  232 . The second temperature sensor may be used to measure the intake air and allow the system to operate the modulating valve to a differential temperature between the two sensors, within specific±tolerances of all the combined components. 
         [0035]    As the water flow rate through the refrigerant-to-water coil  204  is reduced, it will directly emulate a higher entering water temperature, thus raising the condensing temperature, and raising the temperature of the reheat coil, which in turn raises the discharge air temperature. This system would only be active when unit is in dehumidification mode. The modulating valve  240  would normally be driven to the full open position for standard cooling and heat pump operation. 
         [0036]    In dehumidification mode, system  200  operates as follows: inlet air  232  from a conditioned space is drawn into the system  200 , first traveling over the evaporator coil  210  which cools the air (sensible-temperature cooling), and extracts humidity (latent cooling) due to the coil temperature being below the dew point temperature of the humidity contained in the entering air. The air then passes through the reheat coil  226  to be rewarmed (sensible-temperature only) prior to being exhausted back through the air outlet  234  into the conditioned space. To regulate and control the amount of reheat supplied by the reheat coil  226 , in balance with the net sensible cooling effect of the evaporator coil  210 , the modulating valve  240  controls the refrigeration systems condensing temperature to control the capacity of the reheat coil  226  in balance with the sensible capacity of the evaporator coil  210 . 
         [0037]    With the reheat coil  226  and the refrigerant-to-water condenser  204  being in direct series with one another, modulating the amount of water through the refrigerant-to-water condenser  204  directly changes the capacity of the refrigerant-to-water condenser (reduced water flow=reduced heat rejection to the water), which subsequently raises the capacity available to the reheat coil  226  to balance the net sensible cooling capacity with the net sensible reheat capacity. The modulating valve  240  is controlled in measuring the outlet air  234  temperature by a temperature measurement from temperature sensor  250  fed into a logic controller  251 , which then regulates the modulating valve controller/actuator  242  to control a set point of the outlet air  234 . 
         [0038]    In some embodiments, the logic controller  251  and actuator  242  can be combined into a single device dependent upon component selection.  FIG. 2  shows the modulating valve  240  being located on the water outlet  208  side of the refrigerant-to-water condenser coil  204 . 
         [0039]      FIG. 3  shows a flowchart  300  detailing the method of operation of the water-to-air system of the present application. First, the system runs in dehumidification mode in step  302 . As explained above, in dehumidification mode, humidity is extracted from the air. Next, the outlet air temperature is sensed using the temperature sensor  250  at step  304 . The temperature sensor  250  generates a temperature signal based on the measured temperature which is transmitted to the valve controller/actuator  242  at step  306 . At step  308 , the water flow rate in the condenser coil  204  is reduced using the modulating valve  340  based on the temperature signal and the predetermined set point. That is, if the predetermined set point is higher than the temperature signal measured by the temperature sensor  250 , then the modulating valve  340  reduces the water flow rate in the condenser  204 . As the water flow rate is reduced, the condensing/refrigerant temperature is raised through a reduced capacity of the condenser coil  204  at step  310 . The reduction in water flow through the condenser coil  204  reduces the amount of heat the coil is capable of rejecting into the water circulating through coil  204 . Supplying additional capacity availability to the reheat coil  226  results in an increased temperature of the refrigerant gas circulating through the reheat coil  226 , which produces a greater amount of heat available to be rejected. This in turn counters the cooling effect from the evaporator coil  210  more efficiently. Finally, the temperature of the air at the air outlet  234  is raised at step  312 . The temperature sensor  250  continuously measures the air at the air outlet. 
         [0040]    While a number of exemplary aspects and embodiments have been discussed above, those of skill in the art will recognize that still further modifications, permutations, additions and sub-combinations thereof of the features of the disclosed embodiments are still possible. It is therefore intended that the following appended claims and claims hereafter introduced are interpreted to include all such modifications, permutations, additions and sub-combinations as are within their true spirit and scope.