HEATING, VENTILATION AND AIR CONDITIONING (HVAC) SYSTEM

Abstract

The present invention relates to a heating, ventilation and air conditioning (HVAC) system for conditioning the air of a room (2) comprising: a cooling stage (12) configured to provide a supply of cold air to the room (2) through an air supply duct (4); a heating stage (13) configured to provide a supply of hot air to the room (2) through the air supply duct (4); a control device (R) configured to adjust the amount of cooling provided by the cooling stage (12) or the amount of heating provided by the heating stage (13) in order to control the temperature of the air supply and to keep the temperature in the room (2) stable; and an electronic controller (15) configured to act on the control device (R) by means of a pilot signal (R). Figure 1

Description

Title of the invention: HEATING, VENTILATION AND AIR CONDITIONING (HVAC) SYSTEM Technical field

[0001] The present invention relates to a heating, ventilation and air conditioning (HVAC) system. Background of the invention

[0002] Heating, ventilation, and air conditioning (HVAC) systems are used in hot and cold climates to control the air temperature in a room inside a building.

[0003] An HVAC system generally and essentially comprises a fan, a heating unit and a cooling unit. The HVAC system can operate in one of three modes: a heating mode to warm the air in the room, a cooling mode to cool the air in the room, or a ventilation mode to ventilate the room.

[0004] The operation of an HVAC system is governed by measuring, by means of a sensor, the instantaneous temperature inside the room and comparing the measured instantaneous temperature with a set target temperature (corresponding to a desired temperature set by a user) in order to calculate a temperature error which is sent to a controller (normally a proportional integral derivative, PID, controller) which outputs a control signal to various control components of the HVAC system.

[0005] The control signal is used to drive a control device that adjusts the level of a heating or cooling action to maintain a stable desired temperature in the room.

[0006] More specifically, during the cooling operation, if the temperature in a room is higher than the target temperature, the controller activates a fan and one or more compressors of a cooling unit to move cold air into the room to decrease the temperature therein.

[0007] The level of a cooling action is adjusted by regulating the position of a water valve and / or the number of compressors.

[0008] When the controller detects that the room temperature has dropped below the target temperature, the cooling unit is turned off and the controller continues to operate in ventilation mode.

[0009] The level of a cooling action is adjusted by regulating the position of a water valve and / or the demand of the compressors.

[0010] Conversely, during the heating operation, if the temperature in a room is lower than the target temperature, the controller activates a fan and one or more compressors or electric heating units of a heating unit to move the hot air into the room to increase the temperature therein.

[0011] The level of a heating action is adjusted by regulating the position of a water valve and / or the number of compressors / [electric heating units].

[0012] When the controller detects that the room temperature has exceeded the target temperature, the heating unit is turned off and the controller continues to operate in ventilation mode.

[0013] The above control is not effective for controlling the room temperature in some specific cases, for example in case of variable cooling demand.

[0014] Thus, in the event of disturbance of environmental demands, the state-of-the-art controller cannot maintain the room temperature close to the target temperature, and fluctuations-overshoots of the room temperature occur.

[0015] In other words, at the start of a cooling operation, the temperature may drop well below the target temperature, causing discomfort before reaching the target value.

[0016] A similar problem occurs at the start of heating operations. It is necessary to provide a controller to overcome the aforementioned drawback by eliminating the overshoot of state-of-the-art control systems. Summary of the invention

[0017] The need set out above is obtained and at least partially fulfilled by the present invention which relates to a heating, ventilation and air conditioning (HVAC) system for conditioning the air of a room comprising: a cooling stage configured to provide a supply of cold air to the room through an air supply duct; and a heating stage configured to provide a supply of hot air to the room through the air supply duct; a control device configured to adjust the amount of cooling provided by the cooling stage or the amount of heating provided by the heating stage in order to control the temperature of the air supply and maintain a stable temperature in the room; an electronic controller configured to act on the control device by means of a pilot signal, the electronic controller comprising an external control loop having a first subtraction node for comparing an air temperature instantaneous Tair room measured with a target air temperature Ttarget which is chosen by a user; in which the first subtraction node is configured to produce a first error signal èl = ABS (Ttarget - T,, which is sent to a first input of a proportional integral derivative unit which is configured to produce at its output a PID return output signal PIDreturn_out(s);

[0018] a converter is configured to receive at its input the feedback PID output signal PIDretuni_out(S) and is configured to apply a conversion to the input in order to produce a converted feedback PID output signal PIDreturn_out(s)_converted;

[0019] the electronic controller further comprises a nested internal control loop having a second subtraction node for comparing the instantaneous value of the air temperature Tairduct measured by a sensor placed on said air supply duct and the converted feedback PID output signal PIDr e tum_out(S)-converted the second subtraction node is configured to produce a second error signal è2 = (Tairduct - PIDreturn_out(s) converted) which is sent to a second PID controller which produces the driving signal for the control device.

[0020] According to a second aspect of the present invention, the first sensor is configured to measure the instantaneous air temperature Tair room inside the room or in said air supply duct providing the air supply to the room or in a return air duct drawing air from the room.

[0021] According to a third aspect of the present invention, the converter is configured to produce an output according to a ramp function Rf when the first error èl is between a first value èa and a second value èb, i.e.: èa < èl < èb; And a fixed saturated output when the error is greater than the second value èa or greater than the first value èb, i.e.: èl > èa or èb, i.e.: èl > èb.

[0022] According to a fourth aspect of the present invention, said ramp function Rf a a slope a = (target return air temperature from room (2) - maximum / minimum air supply temperature) / (band of second PID controller (26)). Brief description of the drawings

[0023] For a better understanding of the present invention, a preferred embodiment is described below, by way of non-limiting example, with reference to the accompanying drawings in which:

[0024] [Fig.l] schematically represents a heating, ventilation and air conditioning (HVAC) system;

[0025] [Fig.2] shows the structure of an HVAC system controller; and

[0026] [Fig.3] schematically represents the operation of a part of the controller of [Fig.2]. Detailed description of the invention

[0027] In [Fig.l], the reference sign 1 indicates a heating, ventilation and air conditioning (HVAC) system for conditioning the air of a room 2 (shown schematically).

[0028] The HVAC system 1 is connected to the room 2 by an air supply duct 4.

[0029] A return air duct 5 connects room 2 to the HVAC system 1 and returns the air from room 2. For ease of understanding, room 2 is shown with a single space. However, the invention can be applied to rooms with several spaces, each space being connected to the supply duct by separate ducts, as well as to the return duct by separate ducts. Furthermore, the number of air supply ducts 4 and air return ducts 5 may be different.

[0030] The HVAC system 1 comprises a fan 8 which may be a blower or any other air moving device easily identifiable by a person skilled in the art. Actuation of the fan 8 moves air from the HVAC system 1 into the air supply duct 4 (see the direction indicated by the "inlet" arrow). The air is returned to the HVAC system 1 through the air return duct 5 (see the direction indicated by the "outlet" arrow). For the purposes of this disclosure, the air entering the room 2 from the air supply duct 4 will be referred to as "air supply" and the air returning to the HVAC system 1 from the room 2 through the air return duct 5 will be referred to as "air return".

[0031] As shown in [Fig.l], the HVAC system 1 also includes an air damper 9. The air damper 9 may be modulated to allow a predetermined amount or selectively variable amounts of outside air to enter the HVAC system 1. When the air damper 9 is at least partially open, operation of the fan causes the outside air to pass through the air damper 9 and mix with the return air.

[0032] The system of the invention preferably comprises two temperature sensors: a sensor 10 positioned in the room 2 to detect the temperature of the air contained in the room 2, and another sensor 11 positioned in the air supply duct 4 to detect the air supply. The sensor 10 may also be positioned in the air return duct 5 (shown in dotted lines) or in the room 2 as disclosed above, to measure the temperature of the air supplied to the room 2 or of the air drawn from the room 2.

[0033] As schematically illustrated in [Fig.l], the HVAC system 1 comprises both: a cooling stage 12 which, in the illustration, is positioned between the fan 8 and the air supply duct 4; and a heating stage 13 which, in the illustration, is positioned between the fan 8 and the air supply duct 4.

[0034] The fan 8 moves air into the cooling stage 12 to cool the air supply or moves air into the heating stage 13 to heat the air supply.

[0035] Preferably, the cooling stage 12 comprises in known manner a series of compressors or water valves (not shown) associated with one or more refrigerant loops (not shown) having air-fluid exchanges, so that one or more of the compressors can be operated at a given time to control the quantity of cooling supplied to the air supply.

[0036] A regulating device R (of known type) is provided to regulate the amount of cooling provided by the cooling stage 12 in order to control the temperature of the air supply and to keep the temperature in the room 2 stable.

[0037] The regulation device R may comprise a physical device for controlling the supply of a cooling fluid (for example a valve) into the refrigerant loop, or a device for regulating the power and / or the number of compressors.

[0038] Preferably, the heating stage 13 comprises, in a known manner, a series of heat pumps (not shown) associated with one or more hot fluid loops (not shown) having fluid-air exchanges, so that one or more of the heat pumps can be actuated at a given time to control the quantity of heating provided to the air supply.

[0039] The heating stage 13 may also comprise one or more electrical heating elements, such as for example heating resistors (not shown).

[0040] The regulating device R is also configured to adjust the amount of heating provided by the heating stage 13 in order to control the temperature of the air supply and to keep the temperature in the room 2 stable.

[0041] The regulation device R may comprise a physical device for controlling the supply of heating fluid (for example a valve) of the hot fluid loop or a device for adjusting the power of the number of heat pumps / electrical resistors.

[0042] An electronic controller 15 establishes a pilot signal P for the regulating device R to control the operation of the cooling stage 12 / heating stage 13 as indicated below with reference to [Fig.2].

[0043] The electronic controller 15 according to the present invention comprises an external control loop 20 having a first subtraction node 21 for comparing the instantaneous air temperature measured by the sensor 10 inside the room 2 / in the return air duct 5 with a target air temperature Ttarget which is chosen by a user.

[0044] The first subtraction node 21 is configured to produce a first error signal èl = ABS (Ttarget - Tair room) which is sent to an input of a proportional integral derivative unit 22 of known type which produces at its output a feedback PID output signal PIDretUm_out(S)-

[0045] A converter 23 receives at its input the PID feedback output signal PIDr e tUm_out(S) and applies a conversion to produce a converted PID feedback output signal PTD -1- JL-,return_out(s)-converted*

[0046] The controller 15 according to the present invention comprises a nested internal control loop 24 having a second subtraction node 25 for comparing the instantaneous temperature Tairduct of the air supply duct 4 measured by a sensor 11 in the air supply duct 4 and the converted return PID output signal PID return_out(s)-converted*

[0047] The second subtraction node 25 is configured to produce a second error signal è2 = (PIDreturn out(s) converted - Tairduct) which is sent to a PID controller 26 (of known type) which produces the control signal for the regulation device R.

[0048] The conversion unit 23 produces: an output according to a ramp function Rf when the first error èl is between a first value èa and a second value èb, that is to say: èa < èl < èb; and a fixed saturated output when the error is less than the second value èa or greater than the first value èb, that is to say: èl < èa or èb, that is to say: èl > èb.

[0049] The ramp Rf has a slope a which is defined as follows:

[0050] a = (target return air temperature - maximum / minimum supply air temperature) / (return PID controller band 22).

[0051] The main advantage of the above controller having two nested loops 20 and 24 is that the temperature Tairduct of the air supply duct 4 is located close to the room air inlet and the feedback loop 24 associated with it can react quickly, thus improving the overall closed loop response.

[0052] The above control allows for energy savings because the self-adaptive logic of the return temperature loop 24 generates a dynamic set point for the supply loop.

[0053] In other words, the controller is more predisposed to reject disturbances.

[0054] Early feedback control can equally effectively compensate for feedback and feed disturbances.

[0055] In fact, with conventional control, the system can only compensate for its control variable. For example, if the control variable is the return air temperature and the disturbance affects the supply air temperature, then the compensation is not effective.

[0056] In addition, the feed process must react to the feedback loop three to four times faster. This ensures that the feed loop has sufficient time to compensate for its disturbances. It also ensures that disturbances in the feed loop do not affect the feedback processes.

Claims

Claims

1. Heating, ventilation and air conditioning (HVAC) system for conditioning the air in a room (2) comprising: a cooling stage (12) configured to provide a supply of cold air to the room (2) through an air supply duct (4); and a heating stage (13) configured to provide a supply of hot air to the room (2) through the air supply duct (4); a control device (R) configured to adjust the amount of cooling provided by the cooling stage (12) or the amount of heating provided by the heating stage (13) in order to control the temperature of the air supply and to keep the temperature in the room (2) stable; an electronic controller (15) configured to act on the regulating device (R) by means of a pilot signal (R), characterized in that the electronic controller (15) comprises an external control loop (20) having a first subtraction node (21) for comparing a measured instantaneous air temperature Tair room with a target air temperature Ttarget which is chosen by a user; the first subtraction node (21) is configured to produce a first error signal èl = ABS (Ttarget - Tair room) which is sent to a first input of a proportional integral derivative unit (22) which is configured to produce at its output a PID return output signal PIDreturn out(s); a converter (23) is configured to receive at its input the PID return output signal PIDreturn out(s) and is configured to apply a conversion to the input in order to produce a converted PID return output signal PIDreturn_out(s)_converted; the electronic controller (15) further comprises a nested internal control loop (24) having a second subtraction node (25) for comparing the instantaneous value of the air temperature Tairduct measured by a sensor (11) placed on said air supply duct (4) and the converted return PID output signal PIDreturn_ou^s^_converted, the second subtraction node (25) is configured to produce a second error signal è2 = (Tairduct - PIDreturn_out(s)_converted) which is sent to a second PID controller (26) which produces the control signal (P) for the control device (R).

2. A heating, ventilation and air conditioning (HVAC) system according to claim 1, wherein the first sensor (10) is configured to measure the instantaneous air temperature inside the room (2) or in said air supply duct (4) providing air supply to the room (2) or in a return air duct (5) drawing air from the room (2).

3. A heating, ventilation and air conditioning (HVAC) system according to claim 1 or 2, wherein the converter (23) is configured to produce an output according to a ramp function Rf when the first error èl is between a first value èa and a second value èb, i.e.: èa < èl < èb; and a fixed saturated output when the error is greater than the second value èa or greater than the first value èb, i.e.: èl > èa or èb, i.e.: èl > èb.

4. A heating, ventilation and air conditioning (HVAC) system according to claim 3, wherein said ramp function Rf has a slope a = (target return air intake temperature of the room (2) - maximum / minimum air intake temperature) / (band of the second PID controller (26)).

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