Patent Publication Number: US-11029055-B2

Title: Fan coil thermostat with fan ramping

Description:
This application is a continuation of co-pending U.S. patent application Ser. No. 15/887,887, filed Feb. 2, 2018, entitled “Fan Coil Thermostat with Fan Ramping”, which is a continuation of U.S. patent application Ser. No. 15/491,480, filed Apr. 19, 2017, entitled “Fan Coil Thermostat with Fan Ramping”, now U.S. Pat. No. 9,909,773, which is a continuation of U.S. patent application Ser. No. 14/740,789, filed Jun. 16, 2015, entitled “Fan Coil Thermostat with Fan Ramping”, now U.S. Pat. No. 9,657,959, which is a continuation of U.S. patent application Ser. No. 11/833,703, filed Aug. 3, 2007, entitled “Fan Coil Thermostat with Fan Ramping”, now U.S. Pat. No. 9,074,784, all of which are incorporated herein by reference. 
    
    
     TECHNICAL FIELD 
     The present disclosure pertains generally to thermostats and more particularly to thermostats adapted for use with fan coils. 
     BACKGROUND 
     A variety of buildings such as hotels, apartment buildings and the like are heated and cooled using fan coil systems. In a fan coil system, a heat transfer fluid such as water is pumped or otherwise forced through a fan coil. A fan is used to blow air across the fan coil. If the heat transfer fluid was heated, heated air will blow out of the fan coil system. Conversely, if the heat transfer fluid was cooled, cool air will blow out of the fan coil system. 
     Like other HVAC systems, fan coil systems often consume significant amounts of energy. A significant amount of energy may be saved, for example, by operating fan coil systems more efficiently. 
     SUMMARY 
     The present disclosure pertains to fan coil thermostats that can provide energy savings and or increased comfort by, for example, operating a fan coil system more efficiently. 
     In an illustrative but non-limiting example, a fan coil thermostat is configured for use with a fan coil system. In some cases, the fan coil system includes a fan coil that is configured for fluid communication with a source of heated fluid and/or a source of cooled fluid, a valve that controls fluid flow through the fan coil, and a fan that blows air across the fan coil. 
     The fan coil thermostat may include a user interface that is adapted to permit a user to enter a temperature set point. The fan coil thermostat may include or be in communication with a temperature sensor that is adapted to measure a current ambient temperature. The fan coil thermostat may include a controller that is adapted to implement a control algorithm for controlling the fan coil system. In some cases, the control algorithm calculates an error value relating to a temperature difference between the current sensed temperature and the current temperature set point. To operate the fan coil system more efficiently and/or with increased comfort, the control algorithm may use both a proportional term and an integral term related to the error value to regulate the fan speed of the fan coil system. 
     The above summary is not intended to describe each disclosed embodiment or every implementation of the present invention. The Figures and Detailed Description that follow more particularly exemplify these embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE FIGURES 
       The invention may be more completely understood in consideration of the following detailed description of various embodiments of the invention in connection with the accompanying drawings, in which: 
         FIG. 1  is a schematic view of an illustrative but non-limiting fan coil system; 
         FIG. 2  is a schematic view of an illustrative but non-limiting fan coil thermostat as may be used in the fan coil system of  FIG. 1 ; 
         FIG. 3  is a front view of an illustrative embodiment of the fan coil thermostat of  FIG. 2 ; 
         FIG. 4  is a block diagram showing an illustrative control algorithm that may be employed within the fan coil system of  FIG. 1 ; 
         FIG. 5  is a flow diagram showing an illustrative method that may be carried out using the fan coil system of  FIG. 1 ; and 
         FIG. 6  is a flow diagram showing an illustrative method that may be carried out using the fan coil system of  FIG. 1 . 
     
    
    
     While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular illustrative embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention. 
     DETAILED DESCRIPTION 
     The following description should be read with reference to the drawings, in which like elements in different drawings are numbered in like fashion. The drawings, which are not necessarily to scale, depict selected embodiments and are not intended to limit the scope of the invention. Although examples of construction, dimensions, and materials may be illustrated for the various elements, those skilled in the art will recognize that many of the examples provided have suitable alternatives that may be utilized. 
       FIG. 1  is a schematic view of an illustrative but non-limiting fan coil system  10 . While the illustrative fan coil system  10  is schematically shown as a two-pipe fan coil system including a single supply line and a single return line, it will be appreciated that fan coil system  10  may instead be a four-pipe fan coil system having heated water supply and return lines as well as cooled water supply and return lines. In some cases, a four-pipe system may include a single fan coil while in other cases, a four-pipe system may include two fan coils, with one dedicated to heated and one dedicated to cooling. In a two-pipe fan coil system, the single supply line may, for example, provide heated water during the heating season and may provide cooled water during the cooling season. 
     The illustrative fan coil system  10  includes a fan coil  12 . Fan coil  12  is a heat exchanger through which heated or cooled fluid flows. A fan  14  blows air across fan coil  12  as schematically shown by arrows  16 . In some cases, fan  14  pulls ambient air from within the space and/or from outside the building. The ambient air is then heated or cooled by the fan coil  12  and provided into the space. In some cases, fan coil system  10  may be disposed within a housing (not shown) having a first vent or opening upstream of fan  14  and a second vent or opening downstream of fan coil  12 . Fan  14  may pull air through the first vent or opening and then exhaust the heated or cooled air through the second vent or opening and into the space. The components may be arranged either horizontally or vertically within such a housing, as desired or perhaps as dictated by space considerations. 
     In order to accommodate fluid flow through fan coil  12 , fan coil system  10  includes a supply line  18  and a return line  20 . During the heating season, supply line  18  provides a source of heated fluid (such as water) from a suitable source such as a boiler or water heater, geothermal and/or the like. During the cooling season, supply line  18  provides a source of cooled fluid (such as water) from a suitable source such as an evaporative cooling tower or the like. 
     A valve  22  is disposed within supply line  18 , upstream of fan coil  12 , in order to control fluid flow through fan coil  12 . In some cases, valve  22  may provide binary, i.e., on/off control while in other cases it is contemplated that valve  22  may be configured to provide a plurality of flow rates into fan coil  12 . 
     Fan coil system  10  may include a fan coil thermostat  24  that controls operation of valve  22  and/or operation of fan  14  in order to achieve a desired temperature level within a space that is conditioned by fan coil system  10 . Fan coil thermostat  24  is better described with respect to  FIG. 2 .  FIG. 2  schematically shows various components of an illustrative fan coil thermostat  24 . The illustrative fan coil thermostat  24  includes a user interface  26  that may include a display  28  and a keypad  30 . Display  28  may be any suitable alphanumeric display medium that is capable of displaying visually discernible information. In some cases, display  28  may be a liquid crystal display (LCD), but this is not required. Keypad  30  may include one or more individual electromechanical buttons such as such as an on/off button, a temperature up button, a temperature down button, a fan speed up button, a fan speed down button, and the like. In some cases, it is contemplated that user interface  26  may be a touch screen LCD that encompasses the function of display  28  as well as keypad  30 . That is, the buttons of keypad  30  may include, for example, electromechanical buttons, soft buttons, and/or touch regions on a touch screen display, as desired. 
     The illustrative fan coil thermostat  24  may include a controller  32 . In some cases, controller  32  may implement a control algorithm that is adapted to at least partially control one or more components of fan coil system  10 . In some instances, the control algorithm may control and/or regulate operation of fan  14  ( FIG. 1 ). 
     In some cases, the control algorithm may determine fan speed based at least in part on if valve  22  ( FIG. 1 ) is open or closed and/or how far valve  22  is open. In some instances, the control algorithm may dictate that fan  14  ( FIG. 1 ) is off if valve  22  is closed. As valve  22  opens, the control algorithm may dictate that fan  14  is running at, for example, a low speed, a medium speed, a high speed or the like. In some cases, the control algorithm may determine a fan speed also based at least in part on a temperature differential between a current sensed temperature and a current temperature set point, and/or a current sensed humidity and a current humidity set point. 
     Controller  32  may be adapted to provide information to and/or receive information from user interface  26 . Controller  32  may, for example, display a current temperature and/or a current temperature set point on display  28 . Other examples of information that may be provided by controller  32  include a current fan speed, current fan mode, equipment status (on/off), current time, and the like. Examples of information that may be received from keypad  30  may include changes in a temperature set point, changes in fan speed and the like. 
     In some cases, the illustrative fan coil thermostat  24  may include a memory block  34 . Memory block  34  may be used, for example, to store one or more unoccupied temperature set points, a current temperature set point, and/or programming that instructs controller  32  how to regulate valve  22  ( FIG. 1 ) and/or fan  14  ( FIG. 1 ) in order to obtain and maintain a particular temperature set point. Memory block  34  may store, for example, the aforementioned control algorithm. 
     In some instances, fan coil thermostat  24  may include a sensor  36  that provides controller  32  with information pertaining to current conditions within a space conditioned by fan coil system  10  ( FIG. 1 ). Sensor  36  may be a temperature sensor, a humidity sensor and/or any other suitable sensor, as desired. In some cases, sensor  36  may be located internally to fan coil thermostat  24 , although in some instances, sensor  36  may instead be located remotely from fan coil thermostat  24 . 
       FIG. 3  is a front view of an illustrative fan coil thermostat  40 . Fan coil thermostat  40  may be considered as an embodiment or perhaps as a particular example of fan coil thermostat  24  ( FIG. 2 ). The illustrative fan coil thermostat  40  includes a housing  42  that may be formed of any suitable material such as molded plastic. The illustrative fan coil thermostat  40  also includes a display  44  that may be any suitable display such as an LCD display. 
     The illustrative fan coil thermostat  40  also includes several buttons that may be considered as examples of keypad  30  ( FIG. 2 ). The buttons illustrated are not to be considered as limiting in any way, but are merely provided to show examples of buttons that may be included. As illustrated, fan coil thermostat  40  includes a fan speed up button  46  and a fan speed down button  48 . In some cases, it is contemplated that fan coil thermostat  40  may include a single fan speed button (not shown) that can be pressed repeatedly to step through the available fan speed settings. In some instances, a slider button or even a rotary dial may be provided to select a fan speed setting. 
     As illustrated, fan coil thermostat  40  includes a temperature up button  50  and a temperature down button  52 . A user may select and/or alter a temperature setting by pressing temperature up button  50  and/or temperature down button  52 , as appropriate. A power button  54  may also be provided. It is contemplated that fan coil thermostat  40  may instead have a touch screen LCD that provides the functionality of display  44  as well as fan speed up button  46 , fan speed down button  48 , temperature up button  50 , temperature down button  52 , and power button  54 . In some cases, the various buttons may be provided as touch regions on the touch screen display. 
       FIG. 4  is a block diagram of an illustrative control algorithm for controlling the fan speed of the fan coil thermostat  24 . In general terms, the illustrative control algorithm compares the current temperature set point to the current temperature reading provided by temperature sensor  36  ( FIG. 2 ), and then calculates therefrom an error percentage  70 . The error percentage  70  is calculated using both a proportional term  66  and an integral term  64 , as shown. The resulting error percentage  70  is then used to select a suitable fan speed for operating fan  14  ( FIG. 1 ), as will be discussed subsequently. 
     For the purposes of this discussion, the error percentage  70  may be considered as representative of a temperature difference between a temperature set point and a current temperature reading relative to a throttling range (or gain). The throttling range is a parameter that may be set when programming controller  32  and may be considered as representing a temperature difference at which controller  32  would instruct fan coil system  10  ( FIG. 1 ) to operate at maximum output. 
     To illustrate, assume for a moment that the throttling range has been set equal to 5° F. If a temperature difference is 5° F., the error percentage would be 100%. If the temperature difference is 2° F., the error percentage would be 40%. It will be recognized that the throttling range is a parameter that depends at least in part upon system particulars and system performance parameters and thus the numerical examples provided herein are merely illustrative and should not be construed or interpreted as limiting in any manner. One of skill in the art will recognize that the block diagram provided in  FIG. 4  illustrates an inventive application of P-I (proportional-integral) control to a fan coil thermostat, thereby providing improved fan control and thus improved energy efficiency, consumer comfort and the like. 
     Referring specifically to  FIG. 4 , and at block  56 , controller  32  ( FIG. 2 ) receives a signal from user interface  26  ( FIG. 1 ) and/or from memory  34  ( FIG. 2 ) that represents a current temperature set point. Block  58  represents controller  32  receiving a signal representing a current temperature reading from, for example, sensor  36  ( FIG. 2 ). The signal from block  56  and the signal from block  58  are summed (or subtracted) at summation point  60  to provide a signal representing an error indicated as (Err)  62 . 
     Signal (Err)  62  is provided to block  64  as well as to block  66 . At block  64 , controller  32  ( FIG. 2 ) effectively integrates the (Err) signal  62 . In the given equation, K p  is the gain (or 100%/throttling range) and Ti is an integral time constant. At block  66 , controller  32  also calculates a proportional contribution, using a gain of K p . The resultant values are summed at summation block  68  to provide the error percentage  70 . 
     The error percentage  70  enters a fan speed driver  72 , which in some cases may be considered as manifested within the programming of controller  32 . In some cases, controller  32  may not instruct fan  14  to operate at all, if for example valve  22  ( FIG. 1 ) is closed, regardless of whether error percentage  70  would otherwise indicate a non-zero fan speed. As can be seen, if error percentage  70  is between 0 and a first threshold, controller  32  may instruct fan  14  ( FIG. 1 ) to operate at a low fan speed. 
     If error percentage  70  is above the first threshold but below a second threshold, controller  32  may instruct fan  14  to operate at a medium fan speed. If error percentage  70  is above the second threshold, controller  32  may instruct fan  14  to operate at a high fan speed. 
     While  FIG. 4  pertains to a fan  14  ( FIG. 1 ) that has a low fan speed, a medium fan speed and a high speed, it will be recognized that in some cases, fan  14  may have more than three distinct speeds, or may in some cases have fewer than three distinct speeds. In some instances, fan  14  may have an infinite number of fan speeds. In any event, fan speed driver  72  may be adjusted or altered to compensate for a different number of speeds. 
     In some cases, error percentage  70  may be exactly or almost exactly equal (within the precision of controller  32 ) to either the first threshold or the second threshold. In some cases, the low fan speed may apply if error percentage  70  is less than or equal to the first threshold while in other cases, the low fan speed may apply only if error percentage  70  is less than the first threshold. Similarly, the medium fan speed may apply if error percentage  70  is less than or equal to the second threshold, while in some cases the medium fan speed may only apply if error percentage  70  is less than the second threshold. In other words, whether a particular threshold is regarded as “equal to or less than” or only “less than” is merely a programming matter. Moreover, it is contemplated that fan speed driver  72  may provide a degree of hysteresis when switching between low, medium and high fan speeds. For example, and in some cases, when switching between the low fan speed and the medium fan speed, the error percentage  70  may need to exceed the first threshold by a certain amount, and when switching between the medium fan speed and the low fan speed, the error percentage  70  may need to drop below the first threshold by a certain amount. The same may be applied when switching between the medium fan speed and the high fan speed. Such hysteresis may help reduce short term switching of the fan speed when the error percentage  70  is at or near the first and/or second thresholds. 
     The first threshold and the second threshold may be set equal to any desired value. In an illustrative but non-limiting example, the first threshold may be set equal to about 40% and the second threshold may be set equal to about 80%. It will be appreciated that other values may be used, and thus the control algorithm may be fine-tuned for a particular application. 
       FIG. 5  shows an illustrative method that may be carried out using fan coil system  10  ( FIG. 1 ). At block  74 , controller  32  ( FIG. 2 ) obtains a current temperature value from sensor  36  ( FIG. 2 ). Control passes to block  76 , where controller  32  compares the current temperature value with a temperature set point that may be received from user interface  26  ( FIG. 2 ) and/or from memory block  34  ( FIG. 2 ) to determine a temperature difference. At block  78 , an error percentage is calculated. The error percentage includes a contribution that is made by integrating the temperature difference. In some cases, as seen at block  80 , there may also be a contribution that is proportional to the temperature difference. 
     Control passes to block  82 , where controller  32  ( FIG. 2 ) selects a fan speed based on the error percentage value. In some cases, a low fan speed may be selected if the error percentage value is below a first threshold. A medium fan speed may be selected if the error percentage value is above the first threshold but below a second threshold. A high fan speed may be selected if the error percentage value is above the second threshold. At block  84 , controller  32  operates fan  14  ( FIG. 1 ) in accordance with the selected fan speed. 
       FIG. 6  shows an illustrative method that may be carried out using fan coil system  10  ( FIG. 1 ). At block  74 , controller  32  ( FIG. 2 ) obtains a current temperature value from sensor  36  ( FIG. 2 ) and compares it to a temperature set point (at block  76 ) to determine a temperature difference. At block  78 , an error percentage is calculated. The error percentage includes a contribution that is made by integrating the temperature difference. In some cases, as seen at block  80 , there may also be a contribution that is proportional to the temperature difference. Control passes to block  86 , where controller  32  ( FIG. 2 ) controls fluid flow through fan coil  12  ( FIG. 1 ) by opening and/or closing valve  22  ( FIG. 1 ) in accordance with the temperature set point. At block  82 , controller  32  ( FIG. 2 ) selects a fan speed based on the error percentage value. In some cases, a low fan speed may be selected if the error percentage value is below a first threshold. A medium fan speed may be selected if the error percentage value is above the first threshold but below a second threshold. A high fan speed may be selected if the error percentage value is above the second threshold. At block  88 , controller  32  operates fan  14  ( FIG. 1 ) in accordance with the selected fan speed if fluid is flowing through fan coil ( 12 ). In some cases, if no fluid is flowing through fan coil ( 12 ), fan ( 14 ) will not operate, regardless of the error percentage value. 
     While the present disclosure has been described with respect to illustrative fan coil systems that include one or more pipes carrying heated water for heating and/or cooled water for cooling, it should be noted that the inventive concepts described herein are not limited to such systems. Some systems may be hybrid-type systems, with an A/C compressor for cooling and heated water for heating. Some systems may be through-the-wall systems, having one or more of a compressor for air conditioning, an electric or gas heating element for heating, and a heat pump. Fan coil thermostat  40  may, for example, be used with these systems as well as the systems described herein. 
     The present disclosure should not be considered limited to the particular examples described above, but rather should be understood to cover all aspects of the invention as fairly set out in the attached claims. Various modifications, equivalent processes, as well as numerous structures to which the present invention can be applicable will be readily apparent to those of skill in the art to which the present invention is directed upon review of the instant specification.