Room temperature control apparatus having feedforward and feedback control and method

• US 6,095,426 A
• Filed: 11/07/1997
• Issued: 08/01/2000
• Est. Priority Date: 11/07/1997
• Status: Expired due to Term

• Current Assignee: Siemens Industry Incorporated (Siemens AG)
• Original Assignee: Siemens Building Technologies (Siemens AG)
• Inventors: Ahmed, Osman, Klein, Sanford A., Mitchell, John W.
• Primary Examiner(s): WAYNER, WILLIAM E
• Application Number:
  US08/965,961
• Time in Patent Office: 998 Days
• Field of Search: 364/165, 165/11.1, 165/217, 236/94, 236/49.3, 454/238, 454/61
• US Class Current: 236/49.3
• CPC Class Codes: F24F 11/30 for purposes related to the operation of the system, e.g. for safety or monitoring
• CPC Class Codes: F24F 11/62 characterised by the type of control or by internal processing, e.g. using fuzzy logic, adaptive control or estimation of values
• CPC Class Codes: F24F 2011/0005 to create underpressure in a room, keeping contamination inside
• CPC Class Codes: G05B 11/42 for obtaining a characteristic which is both proportional and time-dependent, e.g. P. I., P. I. D.
• CPC Class Codes: G05B 13/042 in which a parameter or coefficient is automatically adjusted to optimise the performance
• CPC Class Codes: G05B 13/048 using a predictor
• CPC Class Codes: G05B 17/02 electric
• CPC Class Codes: G05D 23/1919 characterised by the type of controller

Abstract

A controller for heating, ventilating and air-conditioning distribution systems, which includes feedforward and feedback control strategies. The controller has a feedforward control strategy that generates a control signal based on control set points and identified characteristics of the system, and which adaptively adjusts such set points based on changes that are measured with respect to the identified characteristics. The controller is particularly adapted for controlling the temperature during a heating or cooling operation in a controlled space.

Claims

1. A controller for controlling the temperature within a room in a building having at least one space adjacent to the room, the building having a heating, ventilating and air conditioning (HVAC) system with a supply duct adapted to supply air to the room and a general exhaust duct adapted to exhaust air from the room, the system having local component for controlling the supply air flow into the room, the room having at least one additional exhaust independent of the HVAC system, said apparatus comprising:

a feedforward means for generating a feedforward control signal based on a desired temperature and flow set points in the supply duct, the flow into and out of the room, the flow set point in the general exhaust duct, and based on identifying characteristics of the component and calculated system variables;

a feedback means for generating a feedback control signal based on measured system variables; and

means for combining the feedforward control signal and the feedback control signal to achieve control of the local component.

2. A controller as defined in claim 1 wherein said component comprises a supply damper/actuator, a general exhaust damper/actuator, a heating coil and a valve/actuator.

3. A controller as defined in claim 2 wherein said identifying characteristics comprise the flow rate of air entering the room, the set point of the flow rate of air entering the room, the feedforward control signal, the authority of the supply damper/actuator, the authority of the general exhaust damper/actuator the flow rate of exhaust air leaving the room and the set point of the flow rate of the exhaust air leaving the room.

4. A controller as defined in claim 1 wherein said component comprises a heating coil located in said supply duct and a valve for controlling the flow of water through said heating coil.

5. A controller as defined in claim 4 wherein said identifying characteristics comprise the desired flow rate of water through said heating coil, the flow rate of supply air entering the room, the temperature of air entering the room, the temperature of air entering the coil, the temperature of water entering the coil and the feedforward control signal.

6. A controller as defined in claim 5 wherein said identifying characteristics further comprise an authority and a percentage of water flow through said valve, said authority being the ratio of the change in water pressure across said valve to the change in pressure in the circuit in which said valve is located with said valve being fully open.

7. A controller as defined in claim 6 wherein said identifying characteristics further comprise a coil effectiveness variable, R, that is indicative of the measure of heat supplied to adjacent air by said coil, said variable being defined by the equation:

space="preserve" listing-type="equation">R=(T.sub.a,o -T.sub.a,i)/(T.sub.f,i -T.sub.a,i)

where;

T_f,i is the water inlet temperature;

T_a,i is the air inlet temperature; and

,

T_a,o is the air outlet temperature.

8. A controller as defined in claim 5 wherein said water flow rate is determined by measuring the coil outlet water temperature, T_f,o, and calculating the water flow rate utilizing the equation:

space="preserve" listing-type="equation">ν

.sub.f =k ν

.sub.s (T.sub.a,o -T.sub.a,i)/(T.sub.f,i -T.sub.f,o)

where k is a constant and a ratio of the products of the mass-capacitance of air and water.

9. A controller for controlling a component of a building heating, ventilation and air-conditioning (HVAC) fluid distribution system that affects at least one of the temperature and pressure of the air in a particular room, the room having an air supply duct and at least one general air exhaust duct, the controller being adapted to control the air temperature at a predetermined value and to control the air flow into and out of the room to maintain a predetermined differential pressure relative to an adjacent space in the building, the controller comprising:

an identification means for periodically producing identified characteristics of the component to be controlled;

a feedforward means, coupled to the identification means, for generating a feedforward control signal based on control set points and the identified characteristics of the component, said control set points being determined to be those which maintain the heat energy entering the room substantially equal to the heat energy being exhausted from the room and the mass of the air entering the room substantially equal to the mass of the air being exhausted from the room;

a feedback means for generating a feedback control signal based on measured system variables; and

means for combining the feedforward control signal and the feedback control signal to achieve control of the local component.

10. A controller as defined in claim 9 wherein said control set points comprise the supply air flow rate set point, the supply air discharge temperature set point and the general exhaust air flow rate set point.

11. A controller as defined in claim 10 wherein said control set points are adaptively changed as a function of changes in said identified characteristics.

12. A controller as defined in claim 11 wherein said component comprises a supply air damper/actuator, a general exhaust damper/actuator, a heating coil and a valve/actuator.

13. A controller as defined in claim 12 wherein said identifying characteristics comprise the flow rate of air entering the room, the authority of the supply damper/actuator and the temperature set point.

14. A controller as defined in claim 12 wherein said identifying characteristics comprise the flow rate of exhaust air leaving the room, the authority of the exhaust damper/actuator and the temperature set point.

15. A controller as defined in claim 12 wherein said component comprises a heating coil located in said supply duct and a valve/actuator for controlling the flow of water through said heating coil.

16. A controller as defined in claim 15 wherein said identifying characteristics comprise the desired flow rate of water through said heating coil, the flow rate of supply air entering the room, the temperature of air entering the room, the temperature of air entering the coil, the temperature of water entering the coil and the feedforward control signal.

17. A controller as defined in claim 16 wherein said identifying characteristics further comprise an authority and a percentage of water flow through said valve, said authority being the ratio of the change in water pressure across said valve to the change in pressure in the circuit in which said valve is located with said valve being fully open.

18. A controller as defined in claim 11 wherein said supply air flow rate set point (ν

_s|sp) and temperature set point (T_s|sp) is determined from the equations;

##EQU12## where;

P_s|sp is the supply air pressure set point;

T_s|sp is the supply air temperature set point;

ν

_s|sp is the supply air flow rate set point;

P_ad|sp is the infiltration air pressure set point;

T_ad|sp is the infiltration air temperature set point;

ν

_ad|sp is the infiltration flow rate set point;

P.sub.|sp is the room pressure set point;

ν

_e|sp is the exhaust flow rate set point;

T.sub.|sp is the room temperature set point; and

c_f is a unit conversion factor.

19. A controller as defined in claim 11 wherein said exhaust air flow rate set point (ν

_e|sp) is 0 when heating of the supply air is required and when heating of the supply air is not required said exhaust air flow rate set point (ν

_e|sp)is determined from the equation;

##EQU13## where ν

_ad|sp =K_l (Δ

P.sub.|sp)ⁿ

Δ

p.sub.|sp =P_ref|sp -P|sp

and

ν

_e|sp =ν

_fh|sp +ν

_ex|sp

where;

P_s|sp is the supply air pressure set point;

T_s|sp is the supply air temperature set point;

ν

_s|sp is the supply air flow rate set point;

P_ad|ps is the infiltration air pressure set point;

T_ad|sp is the infiltration air temperature set point;

ν

_ad|sp is the infiltration flow rate set point;

P.sub.|sp is the room pressure set point;

ν

_e|sp is the exhaust flow rate set point;

T.sub.|sp is the room temperature set point.

20. A controller as defined in claim 16 wherein said identifying characteristics of said heating coil, said valve/actuator and said dampers are determined by a General Regression Neural Network (GRNN).

21. A controller as defined in claim 20 wherein said identifying characteristics are determined by the equation:

##EQU14##

22. A method of determining the flow rate of water through a coil located in a supply air duct to a room of a building, the room also having an exhaust duct, and means for measuring the temperature of the air in the supply duct and in the exhaust duct, and means for measuring the temperature of the coil outlet water temperature, comprising the steps of:

measuring the temperature of the water (T_f,o) at the outlet of the coil;

measuring the temperature of the air (T_a,i) in the supply air duct;

measuring the temperature of the air (T_a,o) in the exhaust air duct; and

,

calculating the water flow rate (ν

_f) utilizing the equation;

space="preserve" listing-type="equation">ν

.sub.f =k ν

.sub.s (T.sub.a,o -T.sub.a,i)/(T.sub.f,i -T.sub.f,o)

where k is a constant and a ratio of the products of the mass-capacitance of air and water.

23. A method of determining the value of a control signal in a controller for controlling the outlet air temperature from an air supply duct to a room, the air supply duct being part of an HVAC system of a building, the air duct having a heating coil adapted to heat the air moving through the duct and a flow valve for controlling the flow of hot water through the heating coil, the controller being of the type which has an identification means for periodically producing identified characteristics of the heating coil and valve and means for measuring the temperature of the air at the outlet of the duct, means for measuring the air flow rate through the duct and means for measuring the water pressure across the valve and in the system in which the valve is connected, the control signal being based on control set points and the identified characteristics of the heating coil and valve, said method comprising:

activating said identification means to determine the effectiveness of the coil in transferring heat to the air flowing through the duct;

utilizing said coil characteristic to yield a desired water flow rate through the heating coil for a given measured duct outlet air temperature and air flow rate;

measuring the pressure drop across the valve to the overall pressure drop in the system when the valve is fully open and determining the ratio of the former to the latter to derive the authority value for the valve;

generating said control signal as a function of the water flow rate and the valve authority.

24. A method as defined in claim 23 further including the steps of measuring the water inlet temperature to the heating coil, the air inlet temperature of the duct upstream of the heating coil, and the air outlet temperature downstream of the heating coil and determining the coil effectiveness (R) by the following equation:

space="preserve" listing-type="equation">R=(T.sub.a,o -T.sub.a,i)/(T.sub.f,i -T.sub.a,i)

where;

T_f,i is the water inlet temperature;

T_a,i is the air inlet temperature; and

,

T_a,o is the air outlet temperature.

25. A method of determining the thermal load of a room in a building having a heating, ventilating and air conditioning system, the room having a supply air duct for supplying air to the room and at least one exhaust duct for exhausting air from the room, the amount of air being supplied to the room being approximately equal to the amount of air being exhausted from the room so that the air pressure in the room remains relatively constant, comprising

determining the room temperature using a temperature sensor;

determining the supply flow rate at a predetermined time step t-1;

determining the room exhaust flow rate at a successive time step t;

determining the infiltration air flow rate; and

solving the equation

space="preserve" listing-type="equation">q.sub.load|ss =ν

.sub.e,(t-1) ρ

c.sub.p T.sub.(t-1) -ν

.sub.s,(t-1) ρ

c.sub.p T.sub.s -ν

.sub.ad|sp ρ

c.sub.p T.sub.ad

where

space="preserve" listing-type="equation">ν

.sub.e =ν

.sub.s,(t-1) +ν

.sub.ad|sp

and ν

_ad|sp is the infiltration flow rate set point, and is determined by the equation;

space="preserve" listing-type="equation">ν

.sub.ad|sp =K.sub.l (Δ

P.sub.|sp).sup.n

where

space="preserve" listing-type="equation">Δ

p.sub.|sp =P.sub.ref|sp -P|sp.

26. A method as defined in claim 25 wherein said temperature sensor is located in the room exhaust duct.