Mining University Technical University of Ostrava Faculty of Civil Engineering Department of Building Environment and Building Services

Transcription

1 Mining University Technical University of Ostrava Faculty of Civil Engineering Department of Building Environment and Building Services Testing, measurement and regulation Subject number: STUDY SUPPORT FOR COMBINED STUDIES FOLLOWING UP ON THE MASTER S PROGRAM CIVIL ENGINEERING - BUILDING ENVIRONMENTS COURSE SUPERVISOR: doc. Ing. Iveta Skotnicová, Ph.D.

2 Types of controlling activities Control - is an action directly or indirectly affecting a regulated building Controlling - is a type of management during which the actual effect is not compared with the expected effect - there is no back-check. Regulation - compares the actual effect with the expected and the difference determines the size of the control intervention. This is so-called NEGATIVE FEEDBACK (BALANCING FEEDBACK)

3 Controlling Manual - performed by a person Automatic no human involvement (runs according a program) W u y Controller building Controlled W control variable u manipulated variable y process variable

4 Regulation Manual this can be, for example, regulation of the temperature on a gas cooker Automatic this can be. temperature regulation in a room (spatial thermostat shuts off heat supply once set temperature is exceeded). W u y controller Feedback Controlled building W control variable u manipulated variab y process variable

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6 Classification of regulated systems - Static regulated systems The process variables will establish themselves (selfregulation) at a new value - Astatic regulated systems - systems with int. behavior after a change of the manipulated variable, Y, the system fails to reach a new steady state, the regulation deviation continues to increase

7 Static regulated systems Static zero order system - Reacts immediately to a change in input value - A steady state is achieved immediately X process variable Y manipulated variable

8 Static regulated systems Static first order system Reacts immediately to a change in input value Achieves a steady state after some time

9 Static regulated systems Static system of a second or higher order Delayed reaction to a change in input value - A steady state is achieved after a longer period of regulation - The order of the system is given by the number of first order systems consecutively connected

10 Astatic regulated systems - During a change in the manipulated variable, the system fails to achieve a steady state the deviation continues to increase - Regulation is sometimes not possible

11 Classification of Controllers Discontinuous controllers The manipulated variable changes in abrupt jumps to two or more values Continuous controllers The manipulated variable is changed continuously, with the exception of reaction to immediate change of deviation in regulation The regulated variable can take on any value in the range

12 Discontinuous controllers - Two-position controller

13 Discontinuous controllers - Three-position controller

14 Continuous controllers - overview - P-controller (proportional) - I-controller (integral) - D-controller (derivative) - PI-controller - PD-controller - PID-controller

15 Continuous controllers - P controller The proportional controller is the most-used continuous controller Used in systems without inertia, unsuitable for systems with traffic delays. Problem in overshoot of process variable Ideal characteristics Real characteristics

16 Continuous controllers - I-controller The integral controller is able to entirely remove a deviation in regulation Suitable for static systems without inertia and system with traffic delay. Not suitable for higher-order systems Ideal characteristics Real characteristics

17 Continuous controllers - D-controller The D-controller accelerates the regulation intervention It cannot be used alone, only in conjunction with the above because it only responds to the dynamic transition portion of the deviation, and does not react to the steady state. Ideal characteristics Real characteristics

18 Continuous controllers - PD-controller Used where a P-controller is used, provides greater speed of regulation. (component D). By selecting the appropriate parameters of the D-part of the controller, it is possible to increase the stability of the control circuit. In the course of regulation, the D-component intervenes first followed by the P component (stability).

19 Continuous controllers - PD-controller The most widespread controller in HVAC applications completely eliminates the regulation deviation (component I)., and it is able to eliminate the faults entering the regulated system. In the course of regulation, the P-component intervenes first, only then followed by the I component.

20 Continuous controllers - PD-controller The most perfect controller It can be used to achieve not only short intervals of regulation (component D), but also a high level of precision of regulation operates without permanent regulation deviation (component I). In the course of regulation, the D-component intervenes first, only then followed by the P component, and finally by the I component.

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22 Regulation of heat input

23 - Outlet water temperature from heat source - Interior air temperature - direct regulated heat source - indirect regulated water temperature - local regulated output of individual heating elements - combined combination of all of the abovementioned - Outdoor air temperatures equithermally - direct regulated heat source - indirect regulated system inlet water temperature - combined combination of all of the abovementioned - Loads direct control using fuzzy controller in combination with equithermal mode or according to the air temperature.

24 Zone control Quantitative regulation for multiple radiators in one room, or in multiple rooms with the same heating properties, respectively. A controller based on temperature sensors controls a zone with a two-way or three-way valve.

25 Decentralized regulation of individual rooms Each room has a controller and regulating valve Simpler installation and cabling than for central regulation

26 Centralized regulation of individual rooms A central controller, temperature sensor and actuator (most commonly an electromotor valve) are used in each room. The advantage is the central management of regulation, both in terms of time and temperature, and fewer controllers. Used in schools, office buildings, hotels

27 Regulation of inlet water temperature - according to set temperature - according to outside air temperature - according to interior air temperature

28 Regulation according to a set temperature The simplest form of regulating water temperature Sensor with controller is place on the inlet tube Not used today, with the exception of use when the boiler or boilers deliver to a distributor

29 Regulation according to interior air temperature The temperature of the inlet water is regulated depending on the interior temperature The temperature sensor is installed in a reference room, based on which the other rooms are also controlled. Due to the constant travel delays, controllers with P and PI characteristics must be used to avoid system wobbling.

30 Regulation according to outside air temperature The temperature of inlet water is directly dependent upon the outside temperature The shape of the curve is given by the properties of the system the thermal coefficient of the heating surfaces. This corresponds to a power function with an exponent, e.g. of n = 1.3. The curve can be set for the system by changing the inclination or potentially by shifting the curve. Equithermal regulation is fast, with a small travel delay. The temperature is controlled either on the heat source (burner) or by a three-way or three- four-way valve.

31 Heating curve Regulation according to the outside temperature is called equithermal regulation. The temperature for the controller is measured on the north facade of the building. The controller works with the specified characteristics, which are selected according to the heating system of the building. In the heated rooms, installation of thermostatic control valves is necessary.

32 Control of Supply Temperature Using A Mixer The temperature of inlet water is directly dependent upon the outside temperature, according to the selected temperature curve. In this connection, the boiler works at a constant temperature. Regulation is dependent upon the selection of the heating curve, and does not include interior gains.

33 Control of Hot Water Temperature The most frequently-used method is regulation by switching on the circulation pump, or potentially, the burner. In this case, the pumps for the heating circuits shut down simultaneously, or the mixers are reset.

34 Boiler Control - Single-stage operation with switching differential - Multi-stage operation - Dual-stage - Multi-stage operation of two boilers - Modulated boiler operation

35 Single-stage operation with variable switching differential A classically controlled boiler with burner switching, the switching differential value affects burner starts. At lower outdoor temperatures (t e =-15 o C) assuming high heat consumption, the switching difference is usually less, typically 4 K, at outdoor temperatures of t e =14 o C to 10K. Thereby it is possible to achieve approximately 40% fewer starts

36 Two-stage operation Boilers are equipped with two-stage controlled burners for reduced and rated power. In view of the course of outdoor temperatures, the boiler is used to 85% of capacity, only for the first stage - this guarantees a high annual efficiency standard (annual boiler utilization). By using this design, the boiler startup frequency in the heating season decreases by up to 70%

37 Multi-stage operation of two boilers If the circulating water temperature drops, the next stage of the boiler switches on. Switching on the next stage will occur after the set delay time has elapsed to prevent boiler cycling.

38 Modulated boiler operation The burner on this type of boiler requires a special design to deliver the optimal amount of fuel and combustion air. The burner requires a minimum starting power Control is by PI Controller Temperature of the heating water is changed using the heating curve dependent on the outside temperature. Modulation of output can achieve very low temperatures of flue gases, and thereby high efficiency

39 Sensors of Non-electric Variables Sensors Sensors are the basic element providing information on the status and operation of the device and further convert the measured variable into an otherwise processable signal. The measured variable may be measured Directly, for example, measurement of volume, pressure... Indirectly, using its dependence on other variables, such as measurement of flow rate using pressure difference. Note: The design of the sensors is determined by the type and size of the measured quantity, the measurement method and the desired output signal. Requirements of exchanger construction include precision and transfer speed. Block-diagram of sensor

40 Sensor requirements Clear dependence on output on inlet Precision and reproducibility of measurement results Linearity Optimum dynamic parameters Freedom from parasitic influences Simple construction and easy maintenance Low price Structurally, they may be: Active => They behave like a source of energy, e.g. thermocouple photoelectric, piezoelectric... Passive => Change some of their parameters, for example, position, pressure, induction, resistance, capacity, etc. We differentiate sensors by: Position, angle of rotation, rotation speeds, acceleration, forces,pressure, flow, levels, temperatures, humidity, conductivity, ph sensors, properties of gases, optical variables or magnetic variables, etc.

41 Principles of sensors of non-electric variables Resistance sensors The measured value causes the sensor to change its electrical resistance. Changing the resistance in the circuit causes a change in electrical voltage or current. Two principles are used: - a change in one of the parameters length, cross section of the conductor, - a change in the electrical resistance of the metal conductor dependent upon temperature R t = R 0 (1 + t)

42 Tensometer Measured physical variable: force F (N), pressure p (Pa), error or torque M (Nm) machine parts or building parts Use: pressure gauges, force meters, scales Functions: the resistance of a conductor increases with its extension and simultaneous narrowing The nominal resistance of the tensometer is usually R = 120 Ω, R = 350 Ω, R = 600 Ω R material resistance (Ω) ρ resistivity (Ω.m) S the cross-sectional area of the material (m2) l length of material (m) R = ρ (l / S)

43 Thermocouple Measured physical value: - temperature T ( C), Application: - measurement of radiator surface temperature, Function: - At the welding point of two metallic conductors with varying free electron concentration, a source of electrical voltage that can be measured between the free ends of the conductors arises when the temperature (as opposed to the free ends temperature) changes, e.g, when heated. Properties: Pairs of metals (alloys): Fe (+) CuNi (-) is used for measuring temperatures 200 C to 700 C, NiCr (+), Ni (-) for 200 C to 1200 C, NiCrSI (+) NiSi (-) up to 1300 C PtRh (+), Pt (-) up to 1600 C Function: - the so-called Seebeck Effect is used. Two conductors of different metals are conductively connected on a single measuring end If the measuring end of the thermocouple is heated to a temperature different from the other, comparative end, a thermoelectric charge occurs on the thermocouple.

44 Thermoelectric sensors Thermoelectric sensors are based on the so-called Seebeck Effect. From the theory of free electron movement in metals it is known that the contact of two metals (but also other materials) may create a difference in electrical potential when the output of the two metals is different. For temperature differences that are commonly used in technical applications, dependence can be used with sufficient precision, according to which the thermoelectric voltage of the Ut sensor is directly proportional to the difference between the temperature of the cold (comparative) and the hot (measuring) end of the sensor. Thermoelectric temperature sensors are widely used for their properties (large range of measured temperatures, linearity, small dimensions). The opposite phenomenon to Seebeck's phenomenon is the so-called Peltier effect, when the DC current flows from the external source of the Seebeck circuit, then a temperature difference between the two connections arises. If the current flows from the external source by the junction in the same direction as the current during the heating of this connection in the Seebeck effect, then the given junction cools If the current flows in the opposite direction, the junction warms Peltier's effect depends on the kind of metals and their temperature Peltier cells are used for controlled cooling of, e.g. electronic components, etc.

45 Thermistor Measured physical value: - temperature T ( C), Application: - Measurement of oil and water temperature, indirect measurement of flow velocity of liquids, indication of liquid level - overfill monitoring of fuel tanks with heating oil, thermometer for microwave ovens... Function: - The thermistor is a semiconductor component (semiconductor piece) that is used as a temperature sensitive component. We differentiate thermistors by type, either NTC or PTC. NTC is a thermistor with a negative temperature coefficient, meaning its resistance decreases as it heats up With a PTC thermistor, resistance increases with temperature. Metal resistance sensor Measured physical value: - temperature T ( C), Use: - in air-conditioning units and freezers Function: - passive resistance temperature sensor, using the temperaturedependent resistance of metal. The sensor itself is in the form of a wire or layer resistor. Typically, nickel (Ni) or platinum (Pt) thermometers are used, with a resistance of 100 W (Ni 100, Pt 100) at 0 C

46 Inductive and inductance sensors: This category includes sensors utilizing both coil inductance changes and output voltage variations depending on the measured value. For inductance sensors formed by a coil, the total impedance is Z=R+jωL, whereas the inductance itself depends on the number of coil threads and the magnetic resistance of the coil according to the following relationship: where the magnetic resistance Rm depends on the geometrical dimensions of the coil and the core material. Geometrical dimensions of the coil usually cannot be changed, and for the measurement, the insertion of the coil core or its approximation or the change of position of the two coils in the transformer sensors is mostly used. With inductive sensors, the non-electrical quantity measured can affect either the speed of the change in magnetic flow passing through the thread of the fixed coil, or at the constant magnetic flow, the output voltage is induced in the conductor moving in that magnetic field. This then involves electromagnetic or

47 Capacity Sensors Capacity sensors convert measured values to a change in capacity. The sensor consists of one or more condensers with variable parameters. The following relationship applies to the capacity of the condenser: Non-variable quantity vacuum permitivity ε0. The effect of a non-electric quantity on the sensor can change the surface and distance of the electrodes and the variable permitivity of the dielectric εr and thus the capacity of the sensor. From this it follows that even the division of capacity sensors with a change in: - distance measured between the plates - surface areas of the plates dielectrics In the case of sensors with a change in the distance between the plates, the non-electric quantity acts on one or both plates so that their displacement changes their distance, and with other types, the interacting surface of the plates changes. In the last type, a dielectric of other permitivity is inserted between the capacitor plates.

48 Magnetic sensors: Magnetic sensors consist of a closed magnetic circuit made of ferromagnetic material and use changes in its relative permeability when the measured quantity is applied. This change either changes the induction of the coil or the mutual inductivity of the coils. These sensors use the properties of magnetic materials (e.g Permalloy) for their deformation and are used to measure mechanical stress, compressive and tensile forces, twist torque, temperature, etc. Piezoelectric sensors: These sensors use the piezoelectric effect in that, the effects of mechanical deformation cause, electrical polarization to occur within some crystalline dielectrics, causing the apparent electrical charges to form on the surface, which bind or release the actual charges in the attached electrodes. After termination of the deformation, the current on the sensors electrodes also disappears. Quartz is the most commonly used in measuring technology, but some ceramic and polycrystalline materials are also used. The familiar crystal gramophone recorders work on this principle. The advantages of piezoelectric sensors are their small dimensions, design simplicity and linear characteristics. They are suitable for dynamic measurement, for example, of pressure, increases in speed, or mechanical

49 Piezoelectric pressure sensors: Measured physical variable: - force F (N), pressure p(pa) Application: - measuring quickly changing pressure Function: - crystal deformation (by pressure, pulling or slippage) causes a movement of charges and thereby creates electrical stress.

50 Piezo-pressure sensor Measured physical variable: - measuring pressure p (Pa), Application: - Level monitoring in tanks and wells, oil level monitoring, remote monitoring of gas or hot water pressure in lines. Function: - The pressure gauge diaphragm bends the S-shaped silicon beam to deform the built-in resistors (some lengthen and some shorten). Řachanda

51 Potentiometric Sensor (position, stroke,...) A driver moves along a resistance track Application: Sensing positions of action components (servo-motors) Levels: using floaters + conversion to potential (for example gasoline in a car) Measuring pressure: ring (bellows) converts to stroke

52 Flow sensors Basic classification of flow sensors Speed sensors - turbine - induction - ultrasound - vortex

53 Cross section speed sensors - with aperture

54 Turbine speed sensors It utilizes the kinetic energy of liquid or gas to rotate the rotor. The speed of this rotation in the given turbine is determined by the velocity of the flowing medium. The rotations are mechanically transferred to the counter by a gear mechanism or recorded electronically by an induction sensor.

55 Induction flow sensors work on the principle of Faraday s law of electromagnetic induction. That is, the velocity of fluid flow, which represents the motion of the conductor, induces electrical voltage in the homogeneous magnetic field. Induction speed sensors

56 Ultrasound speed sensors Ultrasonic flowmeters, i.e. those generating a signal over a frequency of more than 20 khz, are preferably used in the measurement of aggressive (acids,...) and explosive liquids as they are measured in a non-contact manner. The time needed for the signal to get from the generator (shown in the figure as G) to the receiver is measured (indicated as S-sensor on the illustration) or the Doppler effect (only, however, for liquids containing solid particles or bubbles - that is, not for distilled water, etc.). Measurement can be influenced by temperature, pressure, etc., which, however, can be sublimated by differential connection. That is, a generator and a sensor are placed on both sides

57 Vortex speed sensors These are used in forming vortexes beyond a obstacle placed in a pipeline Thereby, vortexes are created in different numbers and frequencies - these parameters depend on the velocity, the size and the shape of the obstacle. The sensor evaluates the vibrations generated using a piezoelectric sensor, ultrasonic sensor or, pressure sensor, etc.

58 Level meters Continuous guided wave Discontinuous Radar level meters with a Ultrasound level meters Capacity level meters Hydrostatic level meters Floater Conducting

59 Radar level meters with a guided wave The principle of the function of the so-called pulsed radar (microwave) level meter is a reflectometry method in the time domain consisting in measuring the time of the reflection of the electrical signal from the actual level of the surface. The time necessary from the issue of a pulse to the receiving of the pulse is then directly proportional to the level of the surface Specifically, the level meter electronics will emit a very short electrical impulse that is coupled to a single conductor (measuring electrode). This is in the form of a rod, a rod with a reference tube or a rope, along which the generated pulse propagates in the form of an electromagnetic wave towards the surface. In this case, it is partially reflected, and the reflected component returns to the receiving module of the level meter s electronics. The electronics measure the flight time of electromagnetic waves, recalculate the level of the surface, and output in the form of a signal by an analogue output or as a numerical value on the fieldbus.

60 Ultrasound level meters Ultrasonic level meters function on the principle of measuring the lag time of reflection of the generated acoustic wave off the surface. Specifically, the transducer performs acoustic wave transmission in the form of a series of ultrasonic pulses that extend from the sensor face towards the surface. These waves are reflected from it and subsequently spread back towards the face of the level meter. Here the ultrasound pulses are received and again converted to an electronic signal. The main advantage of the ultrasound principle of measuring is the fact the sensor is not in direct contact with the measured medium

61 Capacitive level meters The principle of capacitive level meters is based on the measurement of the change of the electrical capacity caused by changing the level of the media surface. In particular, the sensor portion of the level gauge consists of an electrode that is inserted into the measured material. Increasing the level will increase the flooding of the electrodes and thus change their capacity. The measured capacity value is then converted by the inner electronics of the level meter to the level of the surface and subsequently displayed on the sensor display and sent in the the form of an analog current or voltage value, or in the form of a numerical value through a transmission bus to the superior system.

62 Hydrostatic level meters In hydrostatic level meters the entire sensing part must be permanently submerged beneath the surface. This is because the principle uses the direct dependencies of hydrostatic pressure (p) on the height of the surface column (h) of the fluid. In the event of a change in the level of the surface, h the measured value of the pressure p also changes, which is then again converted in the electronic sensor to the level of the surface.

63 Floater The basic component of the floating sensor is a floater that floats on the surface. The floater is carried on the surface of the fluid by lifting force of the fluid and the density of the floater must therefore by markedly smaller than that of the measured medium. Floaters are usually available in various shapes and sizes and made of various materials

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65 Conductivity The conductivity principle of measuring surface levels is used in tanks with conductive fluids to detect limit levels. Depending on the probe design, various measurement tasks can be performed, such as overfill protection, dry run protection, two-point pump control, or multi-point surface level detection. Using alternating current prevent corrosion of the probe rod and the electrolytic breakdown of the media. The container wall material is insignificant for measurement because it is a closed voltage circuit between the probe rods and the electronics.

66 Optocoupler This is an electronic component for galvanic separation of two circuits. It consists of an (infrared) LED and a photosensitive semiconductor component, such as a phototransistor. When we bring a small current to the input of the optocoupler to light up the LED, the phototransistor will be opened by the current through the LED (LED) - the larger the current, the more light and the more the transistor will open. For galvanic separation. It is used as an optical barrier if the case is modified to allow interruption of the beam. When using optical fiber between the LED and the phototransistor, it can be used to transmit data over long distances. Rotation sensing

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68 PIR detector "Passive infrared detector" - passive infrared sensor. The meter works on the principle of pyroelectric effect The pyroelement is the basic functional element of the PIR sensor. It is a semiconductor component (based on lithium and tantalum compounds). Pyroelectric detectors are sensitive to infrared light irradiation, generating an electrical surface charge Q. If the value of incident infrared radiation changes on the surface of the pyroelectric material, the electrical surface charge will also change.

69 CO 2 Sensors NDIR - These sensors work on the principle of measuring the dimming of infrared radiation (by specific wavelength) in the air. They consist of an infrared light source, a light conducting tube and an infrared detector with the appropriate filter. The signal from the infrared detector is further amplified and then the radiation is attenuated by additional electronics and on this basis the current CO2 concentration in the air is calculated. NDIR Sensors NDIR Sensors are generally more precise more stable over the long term measure concentration starting at zero value and can also handle high concentrations of CO2. Their drawback is, however their slightly higher cost

70 CO 2 Sensors Electrochemical - These sensors usually consist of an electrochemical cell with a solid electrolyte that will be heated to the operating temperature by additional heat. Then, chemical reactions similar to those in a fuel cell during burning of oxygen take place on its electrodes, and electromotive force is generated on the electrodes of the cell. By measuring this, the concentration of CO2 in the air is determined. The main advantage of these sensors is high sensitivity and excellent selectiveness for carbon dioxide. They are usually cheaper than NDIR sensors, but with somewhat shorter lifetimes and less accuracy, but still sufficient for use in ventilation technology.

71 CO 2 Sensors Electroacoustic - Electroacoustic sensors work on the principle of evaluating changes in the frequency of ultrasound in mechanical resonance Using electronics, the frequency change of the ultrasonic waves is evaluated, and based on the CO2 concentration-dependent change in the frequency, the actual concentration of CO2 in the air is determined. The main advantage of these sensors is long-term stability without need for recalibration. Sensors of all types typically have a continuous voltage output (0-10 V) or a current output (0-20/4-20 ma) using which they transmit information about the CO2 concentration in the air to the superior ventilation system

72 Literature: BAŠTA, Jiří. Regulace v technice prostředí staveb. Praha: České vysoké učení technické v Praze, 2014 DOUBRAVA, Jiří. Regulace ve vytápění. 2. přeprac. vyd. Praha: Společnost pro techniku prostředí, 2007 BAŠTA, Jiří a Karel KABELE. Otopné soustavy teplovodní. 2. přeprac. vyd. Praha: Společnost pro techniku prostředí, 2007 CHADDERTON, David Vincent. Building services engineering. 5th ed. London: Taylor & Francis, ISBN VILIMEC, Ladislav. Řízení a regulace energetických zařízení. Ostrava: VŠB - Technická univerzita Ostrava, ROUBAL, Jiří a Petr HUŠEK. Regulační technika v příkladech. Praha: BEN - technická literatura, 2011