Consider calculating the heat removed from the refrigerant in the condenser and comparing it to the heat absorbed by the water in the condenser (“Qout”, which is calculated automatically).
Vapour-Compression Refrigeration Unit Instruction Manual RA1-MKII ISSUE 2 August 2013 ii Table of Contents Copyright and Trademarks………………………………………………………………………….. 1 General Overview …………………………………………………………………………………………. 2 Equipment Diagrams……………………………………………………………………………………… 3 Important Safety Information…………………………………………………………………………… 6 Introduction……………………………………………………………………………………………….. 6 Electrical Safety…………………………………………………………………………………………. 6 Hot Surfaces……………………………………………………………………………………………… 6 Moving or Rotating Components………………………………………………………………….. 7 Wet Environment……………………………………………………………………………………….. 7 High Pressure……………………………………………………………………………………………. 7 Heavy Equipment ………………………………………………………………………………………. 8 Water Borne Hazards…………………………………………………………………………………. 8 Refrigerant R134a ……………………………………………………………………………………… 8 Description …………………………………………………………………………………………………. 10 Overview…………………………………………………………………………………………………. 10 Compressor…………………………………………………………………………………………….. 10 Pressure and Temperature Sensors …………………………………………………………… 10 Pressure switch ……………………………………………………………………………………….. 11 Pressure Relief Valve……………………………………………………………………………….. 11 Condenser………………………………………………………………………………………………. 11 Receiver …………………………………………………………………………………………………. 11 Filter……………………………………………………………………………………………………….. 11 Variable Area Flowmeter…………………………………………………………………………… 12 Thermostatic Expansion Valve (TXV)………………………………………………………….. 12 Evaporator………………………………………………………………………………………………. 13 Variable Speed Water Pumps ……………………………………………………………………. 13 Water Flow Sensors …………………………………………………………………………………. 13 Electrical Console…………………………………………………………………………………….. 13 Table of Contents iii Installation………………………………………………………………………………………………….. 14 Advisory………………………………………………………………………………………………….. 14 Electrical Supply………………………………………………………………………………………. 14 Installing the PC Software …………………………………………………………………………. 14 Installing the Equipment ……………………………………………………………………………. 15 Data logger / remote controller and software ……………………………………………….. 15 Electrical Wiring Diagram ………………………………………………………………………….. 16 Operation …………………………………………………………………………………………………… 17 Operating the PC Software………………………………………………………………………… 17 Operating the Equipment…………………………………………………………………………… 17 Equipment Specifications……………………………………………………………………………… 19 Overall Dimensions ………………………………………………………………………………….. 19 Refrigerant………………………………………………………………………………………………. 19 I/O Port Pin Connections and USB Channel Numbers…………………………………… 19 Motor Details …………………………………………………………………………………………… 22 Environmental Conditions………………………………………………………………………….. 22 Routine Maintenance …………………………………………………………………………………… 23 Responsibility ………………………………………………………………………………………….. 23 General…………………………………………………………………………………………………… 23 RCD Test………………………………………………………………………………………………… 23 Calibration of Temperature Sensors……………………………………………………………. 23 Calibration of Pressure Sensors…………………………………………………………………. 24 Setting of the expansion valve for normal operation ……………………………………… 24 Recharging the system with refrigerant in the event of a leak…………………………. 25 Laboratory Teaching Exercises……………………………………………………………………… 27 Index to Exercises ……………………………………………………………………………………. 27 Nomenclature ………………………………………………………………………………………….. 27 Table of Refrigerant Properties for R134A (Temperature) ……………………………… 29 Table of Refrigerant Properties for R134A (Pressure) …………………………………… 30 Armfield Instruction Manual iv Table of Pressure v Saturation Temperature for Refrigerant R134a………………… 30 Exercise A – Introduction to the Vapour-Compression Refrigeration Cycle ………….. 31 Exercise B – Varying the Water Flow Rate in the Condenser …………………………….. 35 Exercise C – Varying the Water Flow Rate in the Evaporator …………………………….. 37 Exercise D – Varying the Compressor Speed ………………………………………………….. 39 Exercise E – Varying the Expansion Valve setting …………………………………………… 41 Exercise F – Manual calculation of system performance using refrigerant properties …………………………………………………………………………………………………………………. 44 Contact Details for Further Information…………………………………………………………… 48 1 Disclaimer This document and all the information contained within it is proprietary to Armfield Limited. This document must not be used for any purpose other than that for which it is supplied and its contents must not be reproduced, modified, adapted, published, translated or disclosed to any third party, in whole or in part, without the prior written permission of Armfield Limited. Should you have any queries or comments, please contact the Armfield Customer Support helpdesk (Monday to Thursday: 0830 – 1730 and Friday: 0830 – 1300 UK time). Contact details are as follows: United Kingdom International (0) 1425 478781 (calls charged at local rate) +44 (0) 1425 478781 (international rates apply) Email: support@armfield.co.uk Fax: +44 (0) 1425 470916 Copyright and Trademarks Copyright © 2013 Armfield Limited. All rights reserved. Any technical documentation made available by Armfield Limited is the copyright work of Armfield Limited and wholly owned by Armfield Limited. Brands and product names mentioned in this manual may be trademarks or registered trademarks of their respective companies and are hereby acknowledged. 2 General Overview The vapour-compression refrigeration system is the most the most common refrigeration system used today. RA1-MKII is a computer controlled vapourcompression refrigeration unit with automatic recording of appropriate process variables using an integral USB interface device. This allows the student to gain a thorough understanding of the refrigeration process by changing the operation of different parts of the process and recording the response of the complete system. The single vane compressor is driven by a three phase DC electric motor with a speed controller that allows operation at different operating speeds. Measurement of the electrical current to the speed controller allows the speed and electrical power to the motor to be measured and logged by the controlling PC. Temperatures throughout the system and pressure on both sides of the compressor are measured and logged. The refrigerant flow rate is also measured by a variable area flowmeter. The condenser and evaporator both consist of a brazed plate heat exchanger. The water cooled condenser and water heated evaporator utilize a large reservoir of water to minimize changes in water temperature during operation. The use of a reservoir to recirculate the same water continuously eliminates the need for a permanent mains water connection or water flowing continuously to drain and isolates the system from fluctuation in mains water pressure or temperature. The flow of water through each heat exchanger is independently varied by changing the speed of a submersible centrifugal pump. The speed of both pumps is set by the operator using the PC. The unit is totally self-contained, only requiring connection to an electrical supply and a suitable PC (not supplied). The unit is supplied with the necessary software and incorporates a USB computer interface device for connection to a PC. The water reservoir is designed to stand on the floor. The process components are mounted on a metal support frame that is designed to stand on top of the reservoir. Quick release connectors and flexible hoses connect the reservoir to the refrigeration unit. RA1-MKII Refrigeration Unit 3 Equipment Diagrams Figure 1: Front View of the RA1-MKII Figure 2: Condenser end of RA1-MKII Armfield Instruction Manual 4 Figure 3: Evaporator end of RA1-MKII Figure 4: Console on RA1-MKII Equipment Diagrams 5 Figure 5: Schematic Diagram of the RA1-MKII Vapour-Compression Refrigeration Unit 6 Important Safety Information Introduction All practical work areas and laboratories should be covered by local safety regulations which must be followed at all times. It is the responsibility of the owner to ensure that all users are made aware of relevant local regulations, and that the apparatus is operated in accordance with those regulations. If requested then Armfield can supply a typical set of standard laboratory safety rules, but these are guidelines only and should be modified as required. Supervision of users should be provided whenever appropriate. Your RA1-MKII Vapour-Compression Refrigeration Unit has been designed to be safe in use when installed, operated and maintained in accordance with the instructions in this manual. As with any piece of sophisticated equipment, dangers exist if the equipment is misused, mishandled or badly maintained. Electrical Safety The equipment described in this Instruction Manual operates from a mains voltage electrical supply. It must be connected to a supply of the same frequency and voltage as marked on the equipment or the mains lead. If in doubt, consult a qualified electrician or contact Armfield. The equipment must not be operated with any of the panels removed. To give increased operator protection, the unit incorporates a Residual Current Device (RCD), alternatively called an Earth Leakage Circuit Breaker, as an integral part of this equipment. If through misuse or accident the equipment becomes electrically dangerous, the RCD will switch off the electrical supply and reduce the severity of any electric shock received by an operator to a level which, under normal circumstances, will not cause injury to that person. At least once each month, check that the RCD is operating correctly by pressing the TEST button. The circuit breaker MUST trip when the button is pressed. Failure to trip means that the operator is not protected and the equipment must be checked and repaired by a competent electrician before it is used. Hot Surfaces This apparatus is capable of producing temperatures that could cause burns / serious burns. Allow time for the equipment to cool before handling any of the components. Do not touch any surfaces with a ‘Hot Surfaces’ warning label. Do not allow the apparatus to come into contact with flammable materials or liquids. Do not cover or store the equipment until it has cooled. Any safety guards are there for operator protection- they must not be removed except as described in this manual, and nothing should be inserted through the guards. Important Safety Information 7 Always operate the apparatus according to the Operational Procedures described in this manual. The apparatus should not be left unattended while switched on. Moving or Rotating Components This apparatus has moving or rotating components. Do not remove any protective guards while the equipment is in operation. When operating the apparatus ensure that long hair is tied back out of the way, and that clothing and jewelry cannot come into contact with any moving parts. Dangling items such as necklaces or neckties must be removed or secured so that they cannot become entangled in the equipment. Do not touch any moving components while the apparatus is in use, or insert any item into any moving or rotating section of the equipment, unless specifically instructed to do so in the Operational or Experimental sections of this manual. Ensure that the apparatus is switched off and that all moving parts have come to rest before handling the equipment, except as described in the Operational Procedures section of this manual. Wet Environment The equipment requires a header tank containing water. During use it is possible that there will be some spillage and splashing. All users should be made aware that they may be splashed while operating the equipment, and should wear appropriate clothing and non-slip footwear. ‘Wet Floor’ warnings should be displayed where appropriate. Electrical devices in the vicinity of the equipment must be suitable for use in wet environments or be properly protected from wetting. High Pressure This apparatus is designed to operate with internal pressures greater than that of the surrounding atmosphere. Ensure that any safety valve on the equipment is positioned so that it discharges in a safe direction. Ensure that the apparatus is always operated within the pressure limits described in the Specifications section of the manual. Follow instructions in the Operational Procedures section to ensure that the pressure within the apparatus is raised and lowered correctly to avoid damage to the equipment. Armfield Instruction Manual 8 Heavy Equipment This apparatus is heavy. The apparatus should be placed in a location that is sufficiently strong to support its weight, as described in the Installation section of the manual. Use lifting tackle, where possible, to install the equipment. Where manual lifting is necessary, two or more people may be required for safety, and all should be made aware of safe lifting techniques to avoid strained backs, crushed toes, and similar injuries. Safety shoes and/or gloves should be worn when appropriate. Water Borne Hazards The equipment described in this instruction manual involves the use of water, which under certain conditions can create a health hazard due to infection by harmful micro-organisms. For example, the microscopic bacterium called Legionella pneumophila will feed on any scale, rust, algae or sludge in water and will breed rapidly if the temperature of water is between 20 and 45°C. Any water containing this bacterium which is sprayed or splashed creating air-borne droplets can produce a form of pneumonia called Legionnaires Disease which is potentially fatal. Legionella is not the only harmful micro-organism which can infect water, but it serves as a useful example of the need for cleanliness. Under the COSHH regulations, the following precautions must be observed: Any water contained within the product must not be allowed to stagnate, ie. the water must be changed regularly. Any rust, sludge, scale or algae on which micro-organisms can feed must be removed regularly, i.e. the equipment must be cleaned regularly. Where practicable the water should be maintained at a temperature below 20°C. If this is not practicable then the water should be disinfected if it is safe and appropriate to do so. Note that other hazards may exist in the handling of biocides used to disinfect the water. A scheme should be prepared for preventing or controlling the risk incorporating all of the actions listed above. Further details on preventing infection are contained in the publication “The Control of Legionellosis including Legionnaires Disease” – Health and Safety Series booklet HS (G) 70. Refrigerant R134a This equipment uses refrigerant R134a (Also known as: HFC-134a; 1, 1, 1-2 Tetrafluoroethane; Norflurane; Norfluran). This is a common refrigerant introduced to replace CFC (chlorofluorocarbon) refrigerants such as R-12. R134a is colourless, non-flammable and non-corrosive with a very faint odour. In the RA1-MKII the refrigerant is contained within a completely sealed circuit and is safe under normal use as described in this manual. Important Safety Information 9 It is the responsibility of the owner to check local regulations regarding R134a and ensure that these are complied with. R134a can reach temperatures capable of causing cold burns (frostbite). This may specifically constitute a hazard if R134a has been cooled and pressurised into liquid form and then escapes as a liquid through a leak, or experiences sudden expansion (as may happen if the sealed unit is pierced) forming a jet of cold vapour. R134a vapour may cause irritation of the eyes and mild irritation of the skin. It is relatively non-toxic if inhaled, but may cause asphyxiation if inhaled in sufficient concentration. In the event of exposure to flames or high temperatures (over 50°C), R134a may break down into toxic components. Do not attempt to open or pierce the sealed circuit containing the refrigerant. Always operate the equipment within the safe temperature limits described in this manual. In the event that the sealed circuit is ruptured, follow local regulations and take appropriate steps to reduce the potential hazard. As a suggestion only, the procedure may be as follows (but local requirements will vary): o Remove all personnel from the immediate area o Avoid skin and eye contact with any escaped refrigerant o Extinguish nearby flames o Increase ventilation so that vaporised refrigerant can dissipate harmlessly In the event of damage to the refrigeration unit, the unit must only be repaired or replaced by a suitably qualified engineer. Contact Armfield or your local agent for advice. 10 Description Where necessary, refer to the drawings in the Equipment Diagrams section. Overview The process components of the RA1-MKII Vapour Pressure Refrigeration Unit are mounted on a metal support frame that is designed to stand on top of a large water reservoir. The water reservoir is designed to stand on the floor. Water is drawn from the reservoir and returned to it via flexible hoses. With the exception of the compressor, the important process components are mounted on a panel at the front of the frame. The refrigerant circuit is located on the front of panel with the water circuits at the rear so that the student can clearly observe the flow path through the process. The components that create the refrigeration process are detailed below. The process is fully instrumented to allow all of the important parameters to be measured so that the performance can be monitored. Temperature sensors T1 to T9 measure the temperature at every stage of the refrigeration process, including the water entering and leaving the condenser and evaporator. Pressure sensors P1 and P2 measure the pressure of the refrigerant before and after the compressor. Water flow through the condenser and evaporator is measured with electronic flowmeters F1 and F2. The refrigerant flow rate is determined using a variable area flowmeter F3. The equipment must be connected to a suitable PC (not included) to allow remote control and data acquisition using the RA1-MKII software supplied with the equipment. Compressor The variable speed compressor with integral motor is located at the rear of the support frame. The function of the compressor is to raise the pressure of the refrigerant vapour and to circulate the refrigerant around the system. The compressor consists of an eccentric rotor with a single sliding vane that is driven directly by an electric motor. The combined compressor and drive motor are hermetically sealed inside a metal canister with inlet and outlet connections for the refrigerant and electrical connections to the motor. The three phase DC motor inside the canister is operated via a speed controller located inside the electrical console that allows the speed of the compressor to be varied by the operator by setting the required speed on the PC. A fixed 24 V DC supply to the motor and a current shunt measuring the electrical current supplied to the motor allow the electrical power to drive the compressor to be determined. Pressure and Temperature Sensors Two Bourdon pressure gauges (P1g and P2g) measure and indicate the pressure of the refrigerant on both sides of the compressor. These gauges allow the pressures in the system to be observed whether the system is operating or not but do not allow the pressures to be logged using the PC. A second scale on each of the gauges indicates the saturation temperature of the R134A refrigerant corresponding to the measured pressure. Two electronic pressure sensors P1 and P2 measure the pressure of the refrigerant on both sides of the compressor for the purpose of logging on the PC. Description 11 Nine thermistor sensors T1 to T9 measure the appropriate temperatures of the water and refrigerant throughout the process. The location of each sensor is shown in the schematic diagram Figure 5, on the mimic diagram in the software and on the front panel of the equipment. Pressure switch A mechanical pressure switch, mounted at the rear of the electrical console, monitors the pressure at the inlet and outlet from the compressor and switches off the compressor motor if the inlet pressure falls too low or the outlet pressure rises too high. This device protects the compressor from damage during operation. The operating software includes warnings about pressures that are too high or too low and switches off the compressor if these warnings are ignored. The pressure switch mechanically protects the system in the event of a failure associated with the instrumentation or PC control. Pressure Relief Valve A mechanical pressure relief valve connected to the refrigerant pipework at the outlet from the compressor provides constant protection against over pressurisation, even when the unit is switched off. If the pressure in the system rises too high e.g. if the unit becomes overheated during storage then the relief valve will bleed off some of the refrigerant to prevent damage to the system components. Topping up of the refrigerant may be necessary following operation of the relief valve but this is only likely to happen under extreme conditions. Condenser The action of compressing the refrigerant vapour by the compressor raises the temperature as well as the pressure of the refrigerant. The function of the condenser is to cool the hot refrigerant vapour and condense it back into liquid for circulation through the system. The condenser consists of a brazed plate heat exchanger that uses water at room temperature, from the large water reservoir, to condense the refrigerant. The use of water with appropriate temperature and flow sensors allows the heat transfer in the condenser to be determined. The use of a reservoir to recirculate the same water continuously eliminates the need for water flowing continuously to a drain and isolates the system from fluctuation in water pressure, flowrate and temperature to give stable operation of the system. Receiver The receiver, alternatively called an accumulator, is a reservoir in the pipework that stores excess liquid refrigerant. The receiver is located after the condenser to ensure that the refrigerant is totally liquid from this point in the process. Filter Any particles of debris in the refrigerant can damage sensitive components such as the expansion valve and compressor. For this reason a filter is incorporated in the refrigeration system to eliminate these problems. The filter consists of a metal outer container containing a strainer to remove any debris. Armfield Instruction Manual 12 Variable Area Flowmeter The variable area flowmeter F3 measures and indicates the flow of liquid refrigerant through the system and is installed upstream of the expansion valve. It is not usual for a refrigeration system to incorporate a flow meter but this is incorporated on RA1- MKII to allow complete analysis of the process for educational purposes. The flowmeter replaces the need for a sight glass and allows the operator to view the liquid refrigerant flowing through the system after it has passed through the condenser. At this point in the system no vapour should be present and any bubbles of vapour that are visible indicate that there may be a problem that requires investigation. This is especially important in a system with a thermostatic expansion valve because the flow through the valve will become unstable if vapour is present. Any bubbles seen passing through the sight glass that do not clear within several minutes of start up or after making an adjustment to the system indicate that the process is outside normal operating condition. If bubbles persist then the system must be serviced. Thermostatic Expansion Valve (TXV) The liquid refrigerant flowing through the Thermostatic Expansion Valve expands through a small orifice causing the temperature of the refrigerant to fall significantly. It is this cooling effect that is utilised in refrigeration systems, air conditioning systems etc. The flow of refrigerant through the valve is varied by a thermostat inside the valve that is connected to a temperature sensing bulb attached to the refrigerant outlet pipe on the evaporator. The bulb is connected to the expansion valve via a metal capillary tube. After the expansion valve the refrigerant is typically 90% liquid / 10% vapour. The flow of refrigerant to the evaporator is automatically adjusted by the valve to ensure that the evaporator does not become starved or overloaded with liquid refrigerant. If too much liquid enters the evaporator it may not all boil off which could result in liquid entering the compressor and possible damage to the compressor. Insufficient refrigerant in the evaporator can result in instability in the system. It is therefore important to adjust the thermostatic expansion valve to match the system load so that its range of operation matches any changes in the system load etc. The nominal setting of the valve is adjusted using a screw that is located under a protective cap on the valve body. When the valve is correctly set, the temperature of the refrigerant leaving the evaporator (T3 ) should be typically 5 to 6°C above the saturation temperature of the refrigerant when it leaves the evaporator. This is referred to as the amount of evaporator Superheat. The saturation temperature TSAT at the evaporator outlet is determined from the pressure at the evaporator and indicated on the mimic diagram in the software. Alternatively it can be determined from the measurement of pressure P1 using the Table of Pressure v Saturation Temperature for Refrigerant R134a in the Nomenclature section of the Laboratory Teaching Exercises. The Superheat is then calculated from T3 -TSAT. If the Superheat is set too low then the system may become unstable and liquid may enter the compressor. If the superheat is set too high then the effective heat transfer area of the evaporator is reduced and overheating of the compressor could occur. To increase the Superheat turn the screw on the expansion valve clockwise. Description 13 There will be additional heating of the refrigerant before it enters the compressor so the total effective Superheat is likely to be in the region of 6 to 10°C. Evaporator The function of the evaporator is to transfer heat from the process to the refrigerant and to evaporate any liquid remaining in the refrigerant after the expansion valve so that vapour only enters the compressor. The evaporator consists of a brazed plate heat exchanger that uses water at room temperature from the large water reservoir to evaporate the refrigerant. The use of water with appropriate temperature and flow sensors allows the heat transfer in the evaporator to be determined. The use of a reservoir to recirculate the same water continuously eliminates the need for water flowing continuously to a drain and isolates the system from fluctuation in water pressure, flowrate and temperature to give stable operation of the system. Variable Speed Water Pumps The flow of water through the condenser and evaporator can be independently varied using a pair of low voltage submersible centrifugal pumps located inside the water reservoir. The speed of both pumps is controlled independently via the computer – the speed is manually set by the operator on the PC to give the required flow of water through the condenser and the evaporator. Screwdriver adjustable valves are installed in the Condenser and Evaporator water circuits to throttle the flow and improve flow control to suit ambient water temperature. These valves are adjusted prior to shipping to give approximately 3 l/min maximum condenser flow and 8 l/min maximum evaporator flow to suit a typical ambient water temperature of 20°C in the reservoir. If temperatures vary significantly from this or different operating ranges are required for particular tests then the valves can be adjusted to give the required range of flowrates over the speed range of the submersible pumps. The pumps are mounted at the rear of the electrical console for shipping so that all connections remain intact. During commissioning the pumps are simply unhooked from the storage position and lowered into the water reservoir together with the two return hoses. Water Flow Sensors Electronic turbine type flowmeters F1 and F2 are used to measure the flow of water through the condenser and the evaporator. Pulses generated by the rotation of a paddle wheel are counted by the PC to determine the flow of water. Electrical Console The electrical console is located at the rear left of the assembly. Accessible from the left hand end are the mains power inlet socket, On/Off power switch for the whole unit, a combined circuit breaker / RCD with test button, and the USB socket for connection to a PC with status indicators. The electrical control box incorporates a signal conditioning PCB for the sensors, water pump motors etc, an interface PCB for the USB connection to the PC and a speed controller for the compressor drive motor together with the necessary power supplies etc. 14 Installation Advisory Before operating the equipment, it must be unpacked, assembled and installed as described in the steps that follow. Safe use of the equipment depends on following the correct installation procedure. Electrical Supply RA1-MKII-A RA1-MKII-B RA1-MKII-G Green Yellow Lead Earth (Ground) Earth (Ground) Earth (Ground) Brown Lead Live (Hot) Live (Hot) Live (Hot) Blue Lead Neutral Neutral Neutral Fuse Rating 10 Amps 15 Amps 10 Amps Voltage 220-230 V 110-130 V 220-230 V Frequency 50Hz 60Hz 60Hz Installing the PC Software Before operating RA1-MKII it will be necessary to install the software from the CDROM supplied with RA1-MKII onto an appropriate PC (PC not supplied). For instructions on how to install and run the software insert the CD-ROM into the optical drive on the PC (PC not supplied) then choose ‘Help’ from the menu. After installing and running the software on the PC, instructions on how to operate the software can be obtained by choosing the ‘Help’ tab in the top right hand corner of the screen as shown below: Note that when operating the software for the first time it will be necessary to enable the USB virtual COM port by choosing the Red telephone icon (Start COM session). Full instructions about enabling the port are included in the Help menus. Installation 15 Installing the Equipment The RA1-MKII Vapour Compression Refrigeration Unit is supplied with the refrigeration system fully assembled and ready for use with the exception of installing the unit on top of the water reservoir, lowering the submersible pumps into the reservoir and connecting it to a suitable PC. The equipment is shipped with the water reservoir inverted on top of the refrigeration system to minimise the shipping volume and to afford protection to the process components during transit. The RA1-MKII is heavy and should be carried by two people. The equipment should be installed as follows prior to operation: After removing the transit packaging, carefully lift the GRP water reservoir vertically upwards to reveal the RA1-MKII refrigeration unit underneath. Lift the RA1-MKII off the lid for the reservoir. Place the GRP water reservoir in the desired location; when full of water the reservoir will be very difficult to move. Screw the large diameter drain valve into the tapping near the base of the reservoir, on the side, ensuring that the sealing ‘O’ ring is fitted. Close the drain valve fully then fill the reservoir with water to a depth of 650mm, a volume of approximately 400 litres. Place the lid on top of the reservoir with the turned down edges located over the front and rear edges of the GRP moulding and the rectangular cut-out at the left hand end when viewed from the front of the reservoir. Temporarily locate the lid approximately 100 mm towards the right on the reservoir to increase the size of the cut-out sufficiently to allow the two submersible water pumps to be lowered into the reservoir. Place the RA1-MKII refrigeration unit on top of the lid ensuring that the feet are positively located in the machined recesses. Detach the two submersible pumps from the transit fixings at the rear of the electrical console then lower the two pumps and the two flexible return hoses into the reservoir via the cut-out in the lid of the reservoir. When the pumps are in place, slide the lid back to its normal position so that the refrigeration unit is fully supported with the four hoses entering the reservoir via the narrow rectangular slot in the lid. Connection to an electricity supply Check that the voltage specified on the equipment matches the supply voltage. Note: this unit must be earthed. Ensure that the RCD and miniature circuit breakers are in the off (down) position. The mains inlet socket is located at the end of the electrical control box below the circuit breakers. Where more than one mains lead is supplied use the appropriate lead to suit the style of mains outlet sockets. See Electrical Supply above. Data logger / remote controller and software The RA1-MKII unit is controlled using a PC via a USB port located on the end of the electrical console. The USB lead supplied should be connected from the socket on Armfield Instruction Manual 16 the electrical console to the USB port on a suitable computer running the Armfield RA1-MKII Software. The basic operation of the RA1-MKII can be confirmed by referring to the Operation Section or Laboratory Teaching Exercises for further information. Electrical Wiring Diagram Click on the relevant link to invoke the Wiring Diagram: Wiring Diagram ABM35298SHT1 & ABM35298SHT2 Printed Versions of this Instruction Manual Please note, all wiring diagrams are appended at the rear of this manual. If viewing this Instruction Manual via Help Text in Armfield Software refer to the printed version of the manual for these diagrams. 17 Operation Where necessary, refer to the drawings in the Equipment Diagrams section. Operating the PC Software Details about operating the software can be obtained by choosing the ‘Help’ tab in the top right hand corner of the screen as shown below: Operating the Equipment Powering Up Ensure that the mains switch on RA1-MKII is in the Off position then connect the electrical supply to the RA1-MKII and ensure that the RCD and breakers are switched on (levers in the Up position). Connect the USB lead from the RA1-MKII to the PC and confirm that the LED’s are illuminated adjacent to the socket on RA1-MKII. Load the RA1-MKII software on the PC and display the mimic diagram by clicking ‘View’ then ‘Diagram’ or the Diagram icon n the top menu bar. Check that the PC is communicating correctly with RA1-MKII by observing the message in the bottom right hand corner of the PC screen. If operating correctly then the message will read ‘IFD: vCOM (n) m’ where n is the number of the virtual COM port on the PC. If this message is not displayed then it will be necessary to enable the Virtual COM port. Refer to the section Installing the Software if necessary. Turn on the mains switch on RA1-MKII then check that sensible values are displayed on the PC mimic diagram e.g. temperatures indicate ambient conditions. Do not click the ‘Compressor On’ button at this stage until instructed below. The Watchdog alternating on and off is normal and indicates that the equipment will be switched off if communication with the PC fails. To achieve a smooth start-up it is sensible to set appropriate flows through the Condenser and Evaporator before starting the Compressor as follows: Set the condenser water flow F1 to 1.5 l/min (Typically 40% Pump 1% speed setting after adjusting the condenser inline valve to give 3 l/min maximum). Check that the required flow is indicated by flowmeter F1. Set the evaporator water flow F2 to 5.5 l/min (typically 60% Pump 2% speed setting after opening the inline valve fully). Check that the required flow is indicated by flowmeter F2. Set the compressor motor speed to 50% (Typically 3200 RPM). Armfield Instruction Manual 18 When both flowrates are stable set the required compressor speed (Range 2000 to 4400 RPM) then click the ‘Compressor On’ button. If not sure what compressor speed to set, adjust the speed to 50% give an initial speed of approximately 3200 RPM. When switched on and enabled via the PC, the compressor motor will run at a fixed speed of 3000 RPM for 30 seconds then assume the speed that is set by the operator on the PC (the set speed will be indicated in the software during this period). The compressor speed, evaporator water flowrate, condenser water flowrate, expansion valve setting etc can then be changed by the operator as required to test the refrigeration system. Note: Screwdriver adjustable valves are installed in the Condenser and Evaporator water circuits to throttle the flow and improve flow control to suit ambient water temperature. These valves are adjusted prior to shipping to give approximately 3 l/min maximum condenser flow and 8 l/min maximum evaporator flow to suit a typical ambient water temperature of 20°C in the reservoir. If temperatures vary significantly from this or different operating ranges are required for particular tests then the valves can be adjusted to give the required range of flowrates over the speed range of the submersible pumps. The screwdriver adjustable valves can be set without the compressor running. Set the appropriate pump speed to 100% then adjust the appropriate valve to set the required maximum flow indicated in the software. The valves can be adjusted during operation of the refrigeration unit if necessary but the minimum flow through the evaporator must not fall below 2 l/m or the compressor will be stopped by the software to protect the system. Safety The refrigeration circuit on the RA1-MKII contains a highly volatile fluid under pressure, but it is completely safe provided the instructions in this manual are followed correctly. Safety devices have been incorporated into the unit to prevent accidents. Moreover the working fluid is relatively harmless in the gas or liquid state. It is neither inflammable nor toxic, but in the event of an escape it must not be allowed to enter the eyes. Warnings in software The software incorporates limits that will switch off the compressor if various pressures, temperatures or flowrates are excessively high or low. To avoid unexpected tripping, resulting in loss of results during a test, warnings have been included in the software to advise the operator when conditions are approaching one of the limits. This will allow the operator to take appropriate action to avoid a complete shutdown by making appropriate adjustments. When the particular condition has been corrected, the warning indicator can be switched off by clicking the appropriate reset button. If the warning illuminates again then the condition has not been adequately corrected. Note: The refrigeration system includes pressure switches that will switch off the Compressor motor in the event of excessively high or low pressure in the system. If a fault occurs it will be necessary to press the reset button on the switch box to reset the switch. The reason for the fault should be investigated. 19 Equipment Specifications Overall Dimensions Dimension (mm) RA1 RA1 Tank (496 litres) Height 520 711 Width 950 1092 Depth 500 787 Refrigerant This equipment includes a sealed unit containing refrigerant R134a (Also known as: HFC-134a; 1, 1, 1-2 Tetrafluoroethane; Norflurane; Norfluran). This is a common refrigerant introduced to replace CFC (chlorofluorocarbon) refrigerants such as R-12. R134a is colourless, non-flammable and non-corrosive with a very faint odour, and is safe under normal use as described in this manual. See Important Safety Information. I/O Port Pin Connections and USB Channel Numbers To allow access to the measurement signals in applications other than when using the apparatus with an Armfield data logger interface and associated software, the connections to the 50 way connector are listed below for information: The Armfield Windows
-compatible software allows data logging of the sensor outputs [and operation of the controls]. However, users may prefer to write their own software for [control and] data logging, and for the convenience of those wishing to do so, Armfield has provided additional USB drivers allowing operation of the equipment via the USB socket on [RA1-MKII] relevant numbers are as follows: Pin No Channel No RA1-MKII Function Signal Function Eng Unit Analog Outputs (0-5 V dc exported from socket) 1 Ch 0 Temperature T1 0.55 to 4.96V -10 to 100o C 2 Ch 1 Temperature T2 0.55 to 4.96V -10 to 100o C 3 Ch 2 Temperature T3 0.55 to 4.96V -10 to 100o C 4 Ch 3 Temperature T4 0.55 to 4.96V -10 to 100o C 5 Ch 4 Temperature T5 0.55 to 4.96V -10 to 100o C 6 Ch 5 Temperature T6 0.55 to 4.96V -10 to 100o C Armfield Instruction Manual 20 7 Ch 6 Temperature T7 0.55 to 4.96V -10 to 100o C 8 Ch 7 Temperature T8 0.55 to 4.96V -10 to 100o C 9 Ch 8 Temperature T9 0.55 to 4.96V -10 to 100o C 10 Ch 9 Not used 11 Ch 10 Motor drive current 0 to 5V 0 – 20 Amps 12 Ch 11 Pressure P1 0 to 5V -0.8 to 7.0 Bar 13 Ch 12 Pressure P2 0 to 5V 0 – 30 Bar 14 Ch 13 Not used 15 Ch 14 Not used 16 Ch 15 Not used 17 Analogue Ground 0 V 18 Amp Lo 0 V 19 Analog Out 2 Compressor Speed Control 1.2 V to 3.25V 2000 RPM to 4400 RPM 20 Analog Out 3 Not used 21 Power Ground 0 V Analog Inputs (0-5V dc input from socket) 22 Analog Out 0 Condenser Pump Speed 0 to 5V 0 to100% 23 An Out 0 Ground 0 V 24 Analog Out 1 Evaporator Pump Speed 0 to 5V 0 to100% 25 An Out 1 Ground 0V Equipment Specifications 21 Digital Outputs (0-5V dc) 26-27 Digital Ground 0V 28 Digital Input 0 Evaporator OK if: T9 > 4°C T7 > -2.5°C F2 > 2.0 l/min P1 > 2.0 Barg 29 Digital Input 1 Hi side OK if: P2 < 17 Barg T4 < 80°C 30 Digital Input 2 Condenser Flowrate F1 Pulses / 0 to 80 Hz 760 Pulses/L 31 Digital Input 3 Evaporator Flowrate F2 Pulses / 0 to 80 Hz 760 Pulses/L 32 Digital Ground 0 V 33 to 36 Digital Inputs 4 to 7 Not used 37 Digital Ground 0 V Digital Inputs (0-5V dc) 38 Digital Output 0 Power on required 39 Digital Output 1 Watchdog pulse 40 Digital Output 2 Compressor Motor Drive enable 41 Digital Output 3 Aux heater control Not used Armfield Instruction Manual 22 42 Digital Ground 0 V 43 – 46 Digital Outputs 4 to 7 Not used 47 – 48 Digital ground 0 V Motor Details Compressor Motor: Three phase DC electric motor with speed controller Motor speed range: 2000 to 4400 RPM set by the operator using the PC Note: When switched on and enabled via the PC, the compressor motor will run at a fixed speed of 3000 RPM for 30 seconds then assume the speed that is set by the operator on the PC. Nominal Supply Voltage: 24 Volts DC Current measurement: 20 Amps at 5 V output Environmental Conditions This equipment has been designed for operation in the following environmental conditions. Operation outside of these conditions may result reduced performance, damage to the equipment or hazard to the operator. a. Indoor use; b. Altitude up to 2000m; c. Temperature 5°C to 40°C; d. Maximum relative humidity 80% for temperatures up to 31°C, decreasing linearly to 50% relative humidity at 40°C; e. Mains supply voltage fluctuations up to ±10% of the nominal voltage; f. Transient over-voltages typically present on the MAINS supply; Note: The normal level of transient over-voltages is impulse withstand (overvoltage) category II of IEC 60364-4-443; g. Pollution degree 2. Normally only nonconductive pollution occurs. Temporary conductivity caused by condensation is to be expected. Typical of an office or laboratory environment. 23 Routine Maintenance Responsibility To preserve the life and efficient operation of the equipment it is important that the equipment is properly maintained. Regular maintenance of the equipment is the responsibility of the end user and must be performed by qualified personnel who understand the operation of the equipment. General The equipment should be disconnected from the electrical supply when not in use. Water should be drained from the equipment before storage. RCD Test Test the RCD by pressing the TEST button at least once a month. If the RCD button does not trip when the Test button is pressed then the equipment must not be used and should be checked by a competent electrician. Calibration of Temperature Sensors The thermistor temperature sensors supplied with RA1-MKII are closely matched in characteristics and in most situations this calibration should be sufficiently accurate. However, manufacturing tolerances mean that individual sensors may differ slightly and sensor calibration may also drift over time as a result of aging of the components. To improve accuracy the temperature sensors may be individually calibrated within the RA1-MKII software if required. General calibration instructions for calibrating sensors are given in the RA1-MKII software. The thermistor has a non-linear characteristic so calibration at a series of different temperatures will be necessary. If a temperature calibration source is not available then a bath of liquid with reference thermometer can be used, however, the thermistor should NOT be submerged into a conductive liquid such as water, but can be placed inside a thin plastic bag then into the water. The suggested process is as follows: Carefully remove the thermistors from their pockets Place the ends of the thermistor wires in a plastic bag Using a reference thermometer and a kettle make a cup of hot water at no more than 60o C Place the plastic bag containing the thermistors into the hot water Choose ‘Options’ then ‘Calibrate IFD channels’ from the top menu in the software. Choose the sensor(s) to calibrate then note the voltage read out (button reads ‘Direct’) Click the button (button reads ‘Manual’) then input this voltage value and the corresponding reading from the reference thermometer into the table. Armfield Instruction Manual 24 Lower the temperature of the water and repeat process (use crushed ice, if available, to achieve a minimum temperature of 0o C). When the calibration table has been updated choose ‘Plot’ then ‘OK’. The new calibration values will take effect after the software is restarted, and will remain saved within the software on the PC used for the calibration. The original calibration supplied with the software may be recovered by re-installing the software; any modified calibration will be lost if the software is re-installed for any reason. Calibration must be performed separately for every PC that will be used with the RA1-MKII. Calibration of Pressure Sensors The electronic pressure sensors supplied with RA1-MKII are pre-calibrated and should not require recalibration in normal use. The conditioning circuit for each pressure sensor includes an offset facility that is adjusted during manufacture at Armfield. These offset potentiometers should not require further adjustment. However, if adjustment is considered necessary then the appropriate potentiometer can be adjusted as follows using the appropriate Bourdon gauge as a reference: VR5 Offset of Pressure sensor P1 on Low pressure side of compressor VR6 Offset of Pressure sensor P2 on High pressure side of compressor The equipment is supplied with the software calibrated to match the nominal calibration of the pressure sensors. If required, precise calibration may be achieved for each individual sensor by recalibrating the software. General calibration instructions for calibrating sensors are given in the RA1-MKII software. The two Bourdon gauges can be used for reference readings in this case. As the pressure sensors are linear, calibration can be carried out at two points with the system at low and high pressure. The original calibration supplied with the software may be recovered by re-installing the software; any modified calibration will be lost if the software is re-installed for any reason. Calibration must be performed separately for every PC that will be used with the RA1-MKII. Setting of the expansion valve for normal operation The system is designed for normal operation with the evaporator superheat at 6°C. If the indicated superheat is above or below this value by a few degrees when conditions have stabilised then it will be necessary to adjust the expansion valve to maintain the required 6°C. To adjust the expansion valve for normal operation when performing the teaching exercises, the following settings are recommended: Set the condenser water flow F1 to 1.5 l/min (Typically 40% Pump 1% speed setting after adjusting the condenser inline valve to give 3 l/min maximum). Set the evaporator water flow F2 to 5.5 l/min (typically 60% Pump 2% speed setting after opening the inline valve fully). Set the compressor motor speed to 50% (Typically 3200 RPM). Routine Maintenance 25 Remove the cap from the adjusting screw on the expansion valve. Start the compressor and allow the system to stabilise then confirm the average value of the superheat calculated in the software. If adjustment is necessary, slowly adjust the expansion valve by a maximum of ¼ turn then wait for the system to stabilise. Repeat ¼ turn maximum adjustments until the indicated superheat temperature (difference between T3 and TSAT ) is approximately 6°C. Note that turning the screw clockwise on the expansion valve increases the amount of superheat and turning it anticlockwise reduces the amount of superheat. The equipment can be switched off in the knowledge that the expansion valve is correctly set. Replace the cap on the expansion valve. Recharging the system with refrigerant in the event of a leak If the pressure of the refrigerant falls in the system or vapour bubbles are continuously visible in the variable area flowmeter suggesting a loss of refrigerant from the system then it should be checked by a competent refrigeration engineer. The system must be charged with 500 grams (17.6 oz) of refrigerant R134A which must be done with care. It is important that the location of a refrigerant leak is found using an electronic leak detector or by brushing soapy water around the area and looking for bubbles, this is assuming there is still pressure in the system. If all pressure has been lost then oxygen free nitrogen will have to be added to a pressure of 100 PSI and the above procedure repeated. After locating and fixing any leak, the system must be purged with oxygen free nitrogen then evacuated and checked for any further leakage before filling with R134a refrigerant. The charging points for the refrigerant system are located in the pipework, above the compressor, as shown below: Armfield Instruction Manual 26 The low pressure (suction) connection is located on the left hand side of the compressor and the high pressure (discharge) connection on the right hand side of the compressor when viewed from the rear of the equipment. Each charging point incorporates a self-sealing Schrader valve that can be accessed after unscrewing the protective cap. The protective caps must be fitted at all times except when recharging the system. 27 Laboratory Teaching Exercises Index to Exercises Exercise A – Introduction to the Vapour-Compression Refrigeration Cycle Exercise B – Varying the Water Flow Rate in the Condenser Exercise C – Varying the Water Flow Rate in the Evaporator Exercise D – Varying the Compressor Speed Exercise E – Varying the Expansion Valve setting Exercise F – Manual calculation of system performance using refrigerant properties Nomenclature Name Symbol Unit Definition Temperature 1 T1 K Temp of Water entering Condenser (Measured in °C) Temperature 2 T2 K Temp of Water leaving Condenser (Measured in °C) Temperature 3 T3 K Temp of refrigerant leaving Evaporator (Measured in °C) Temperature 4 T4 K Temp of refrigerant entering Condenser (Measured in °C) Temperature 5 T5 K Temp of refrigerant leaving Condenser (Measured in °C) Temperature 6 T6 K Temp of refrigerant entering expansion valve (Measured in °C) Temperature 7 T7 K Temp or refrigerant entering Evaporator (Measured in °C) Temperature 8 T8 K Temp of Water entering Evaporator (Measured in °C) Temperature 9 T9 K Temp of Water leaving Evaporator (Measured in °C) Pressure 1 P1 Bar (abs) Pressure at inlet to Compressor (Measured in BargG) Pressure 2 P2 Bar (abs) Pressure at outlet from Compressor (Measured in BargG) Armfield Instruction Manual 28 Condenser water flow F1 m3 /s Flow of water through Condenser (Measured in l/min) Evaporator water flow F2 m3 /s Flow of water through Evaporator (Measured in l/min) Refrigerant Flow Rate F3 m3 /s Flow of refrigerant (Manually measured on flowmeter in l/hr) Density of R134a ρ Kg/m3 1203 Kg/m3 Mass Flow Rate of R134a Kg/s Calculated from F3 and ρ Enthalpy h kJ/Kg Available from Table of Refrigerant properties (R134A) Speed of Compressor N RPM Set by operator on PC Work Done by the Compressor W Watts Boiling Point of R134a TBP K Heat Removed from R134a Heatout Watts Energy Removed from Condenser Qout Watts Water Flow Rate through condenser F1 l/min Water Flow Rate through evaporator F2 l/min Heat Absorbed by R134a Heatin Watts Energy Absorbed from Evaporator Qin Watts Specific Heat Capacity R134a Cp kJ/Kg Coefficient of Performance COP No units Measure of the performance = ratio of heat exchange in evaporator to amount of work put in by compressor (Usually > 1.0) Laboratory Teaching Exercises 29 Table of Refrigerant Properties for R134A (Temperature) Armfield Instruction Manual 30 Table of Refrigerant Properties for R134A (Pressure) Table of Pressure v Saturation Temperature for Refrigerant R134a Note: Amount of Superheat = T3 – TSAT 31 Exercise A – Introduction to the Vapour-Compression Refrigeration Cycle Objective To operate the RA1-MKII refrigeration system and understand the relation between the hardware components and the refrigeration cycle. Method Running the RA1-MKII unit at nominal settings and observing the changes in temperature and pressure around the system. Equipment Required RA1-MKII Refrigeration Unit Compatible PC with Armfield RA1-MKII software Theory Schematic Diagram of the RA1-MKII Vapour-Compression Refrigeration Unit Armfield Instruction Manual 32 Ts diagram for the Vapour-Compression Refrigeration Cycle In this cycle the refrigerant (R134a) enters the compressor as a vapour and is compressed and superheated (Points T3 to T4) i.e. it is raised above its saturation temperature. The superheated refrigerant vapour passes through the condenser which first cools and removes the superheat and then condenses the vapour into liquid by removing latent heat at constant pressure and temperature (Points T4 to T5). Heat from the refrigerant is transferred to the stream of water in the condenser. The liquid refrigerant then passes through the expansion valve (also called a throttle valve) where it expands and the pressure abruptly decreases, this results in a mixture of liquid and vapour at a lower temperature and pressure (Points T6 to T7). The cold liquid/vapour refrigerant mixture then travels through the evaporator and is heated and completely vaporized by heat transfer from the water in the evaporator (Points T7 to T3). The refrigerant vapour exiting the evaporator returns to the compressor inlet to complete the thermodynamic cycle. An important measure of the system performance is the Coefficient of Performance (COP). This is the ratio of the heat exchanged in the evaporator to the amount of work put into the system by the compressor. In a refrigeration system this is typically in the region of 3 to 6 i.e. more heat is exchanged than input by the compressor. The COP is continuously calculated from the other system variables and displayed on the mimic diagram. Exercise A 33 Equipment Set Up Ensure that the equipment has been installed in accordance with the Installation section. Check that the USB connection is made between the RA1-MKII unit and the PC, and that the RA1-MKII software is installed and running (‘IFD: vCOM (n) m’ displayed in bottom right hand corner where n is the number of the virtual COM port on the PC). Check that the combined circuit breaker / RCD on the electrical console is in the ‘On’ (up) position. Turn the unit on by pressing the ON/OFF switch on the console. Check that sensible ambient values for temperatures, pressures etc are displayed on the mimic diagram of the software. Do not click ‘Compressor On’ in the software until instructed. Procedure Set the condenser water pump (Pump 1 speed) to 40% and the evaporator water pump (Pump 2 speed) to 60%. Check that there is a flow of water through both the condenser and evaporator indicated by F1 (typically 1.5 l/min) and F2 (typically 5.5 l/min) on the mimic diagram. Set the compressor motor speed to 50% (typically 3200 RPM) then click ‘Compressor On’ (1). The compressor will run at 3000 RPM for 30 seconds then change to the set speed. Check that refrigerant flows around the system indicated by the variable area flowmeter F3 on the RA1-MKII. Configure the sample options as ‘Automatic / 10 seconds intervals’ and click the “GO” button to log the readings from the sensors. View the graphs of T1, T3 & T7 on the primary Y axis and P1 & P2 on the secondary Y axis. Let the system run until the temperatures and pressures are reasonably stable then click the ‘Stop’ button to stop data logging and Click ‘Compressor on’ (0) to stop the compressor. View the table of results and confirm that a set of readings has been logged then save the result for future reference. Results View the table of results and select a row of results when the process has stabilised. Observe the changes in pressure and temperature around the process and identify the changes that take place in the Compressor, the Condenser, the Expansion valve and the Evaporator identified on the Ts diagram shown in the theory above. Observe that the calculated Coefficient of Performance (COP) is significantly greater than unity whereby more useful heat is transferred in the evaporator than electrical energy is required to run the compressor. Conclusion These observations should provide a basic understanding of the refrigeration process. Armfield Instruction Manual 34 Describe the function of the important parts of the refrigeration process, namely the Compressor, Condenser, Expansion valve and Evaporator and explain the temperature and pressure changes associated with each. Observe the value of the Coefficient of Performance obtained and comment on the magnitude of this value being greater than unity. The exercises that follow investigate the vapour-compression refrigeration cycle in more detail and the effect of changes to individual parts of the refrigeration system. 35 Exercise B – Varying the Water Flow Rate in the Condenser Objective To investigate the effect on the refrigeration system of the flow of water through the condenser and to determine the optimum flow rate for a given load. Method Running the RA1-MKII at nominal settings then varying the flow of water through the condenser, whilst logging the results to observe the effect on the remainder of the system. Equipment Required RA1-MKII Refrigeration Unit Compatible PC with Armfield RA1-MKII software Theory The hot vapour from the compressor passes through the condenser where it is cooled and condensed into a liquid. Heat is removed from the refrigerant and carried away by the cooling water. In RA1-MKII the condenser is a plate heat exchanger, composed of multiple, thin, closely spaced plates that have a very large surface area and fluid flow passages for heat transfer. The plates are brazed together to give a permanent, leak free arrangement. The refrigerant and the cooling water streams are separated by the thin plates allowing good heat transfer. The First law of thermodynamics, about the conservation of energy states that the change in the internal energy of a closed thermodynamic system is equal to the sum of the amount of heat energy supplied to the system and the work done on the system. Therefore the energy entering equals the energy leaving. Equipment Set Up Ensure that the equipment has been installed in accordance with the Installation section. Check that the USB connection is made between the RA1-MKII unit and the PC, and that the RA1-MKII software is installed and running (‘IFD: vCOM (n) m’ displayed in bottom right hand corner where n is the number of the virtual COM port on the PC). Check that the combined circuit breaker / RCD on the electrical console is in the ‘On’ (up) position. Turn the unit on by pressing the ON/OFF switch on the console. Check that sensible ambient values for temperatures, pressures etc are displayed on the mimic diagram of the software. Do not click ‘Compressor On’ in the software until instructed. Procedure Set the condenser water pump (Pump 1 speed) to 100% and the evaporator water pump (Pump 2 speed) to 60%. Check that there is a flow of water through both the condenser and evaporator indicated by F1 (typically 3.0 l/min) and F2 (typically 5.5 l/min) on the mimic diagram. Armfield Instruction Manual 36 Set the compressor motor speed to 50% (typically 3200 RPM) then click ‘Compressor On’ (1). The compressor will run at 3000 RPM for 30 seconds then change to the set speed. Check that refrigerant flows around the system indicated by the variable area flowmeter F3 on the RA1-MKII. Configure the sample options as ‘Automatic / 10 seconds intervals’ and click the “GO” button to log the readings from the sensors. View the graphs of T1, T3 & T7 on the primary Y axis and P1 & P2 on the secondary Y axis. Let the system run until the temperatures and pressures are reasonably stable then reduce the speed of the condenser water pump by 10%, wait for the system to stabilise. Repeat the procedure reducing the condenser water pump speed in steps of 10% until temperature T4 reaches 65o C. (Note: if any warnings are indicated on the computer then the flow should be increased again or appropriate steps taken to avoid the compressor being switched off). Return the condenser water pump speed to 50% and allow the system to settle. If time permits change the flow of water through the evaporator then optimise the flow of water through the condenser to suit. Results View the table of results and compare the changes in the system as the flow through the condenser is reduced. Using a spreadsheet or plotting graphs independently using data obtained when conditions have stabilised at each setting of compressor speed: Plot the graph of Coefficient of Performance against condenser water flowrate (F1). Conclusion Discuss what happens to the system when the water flow rate in the condenser is changed. Comment on the effect of the increase in temperature at T5 as the flow of water through the condenser is reduced. Is there an optimum flow rate for greatest performance in the condenser? 37 Exercise C – Varying the Water Flow Rate in the Evaporator Objective To investigate the effect on the refrigeration system of the flow of water through the evaporator and to determine the optimum flow rate for a given system load. Method Running the RA1-MKII at nominal settings then varying the flow of water through the evaporator, whilst logging the results to observe the effect on the remainder of the system. Equipment Required RA1-MKII Refrigeration Unit Compatible PC with Armfield RA1-MKII software Theory The cold mixture of liquid/vapour refrigerant, after the expansion valve, passes through the evaporator where it is heated and evaporated into a vapour. Heat is transferred to the refrigerant and from the warmer water. In RA1-MKII the evaporator is a plate heat exchanger, composed of multiple, thin, closely spaced plates that have very large surface areas and fluid flow passages for heat transfer. The plates are brazed together to give a permanent, leak free arrangement. The refrigerant and the cooling water are separated by the thin plates allowing good heat transfer. Equipment Set Up Ensure that the equipment has been installed in accordance with the Installation section. Check that the USB connection is made between the RA1-MKII unit and the PC, and that the RA1-MKII software is installed and running (‘IFD: vCOM (n) m’ displayed in bottom right hand corner where n is the number of the virtual COM port on the PC). Check that the combined circuit breaker / RCD on the electrical console is in the ‘On’ (up) position. Turn the unit on by pressing the ON/OFF switch on the console. Check that sensible ambient values for temperatures, pressures etc are displayed on the mimic diagram of the software. Do not click ‘Compressor On’ in the software until instructed. Procedure Set the condenser water pump (Pump 1 speed) to 40% and the evaporator water pump (Pump 2 speed) to 100%. Check that there is a flow of water through both the condenser and evaporator indicated by F1 (typically 1.5 l/min) and F2 (typically 8.0 l/min) on the mimic diagram. Set the compressor motor speed to 50% (typically 3200 RPM) then click ‘Compressor On’ (1). The compressor will run at 3000 RPM for 30 seconds then change to the set speed. Check that refrigerant flows around the system indicated by the variable area flowmeter F3 on the RA1-MKII. Armfield Instruction Manual 38 Configure the sample options as ‘Automatic / 10 seconds intervals’ and click the “GO” button to log the readings from the sensors. View the graphs of T1, T3 & T7 on the primary Y axis and P1 & P2 on the secondary Y axis. Let the system run until the temperatures and pressures are reasonably stable then reduce the speed of the evaporator water pump by 10%, wait for the system to stabilise then click the “GO” button once to log the parameters. Repeat the procedure reducing the evaporator water pump speed in steps of 10% to reduce the flow through the evaporator to the minimum of 2.5 l/min. Note: If the flow drops below 2 l/min or any of the warnings appear in the low temperature alarm may operate before this depending on ambient conditions.) Return the evaporator water pump speed to 60% and allow the system to settle. If time permits change the flow of water through the condenser then optimise the flow of water through the evaporator to suit. Results View the table of results and compare the changes in the system as the flow through the evaporator is reduced. Using a spreadsheet or plotting graphs independently using data obtained when conditions have stabilised at each setting of compressor speed: Plot the graph of Coefficient of Performance against evaporator water flowrate (F2). Conclusion Discuss what happens to the system when the water flow rate in the evaporator is changed. Is there an optimum flow rate for greatest performance in the evaporator? 39 Exercise D – Varying the Compressor Speed Objective Looking into the affect of the flow of refrigerant through the refrigeration system, and whether or not there is an optimum flow rate. Method The objective will be achieved by running the RA1-MKII normally and using the software, turning the speed of the compressor down. Equipment Required RA1-MKII Refrigeration Unit Compatible PC with Armfield RA1-MKII software Theory Below is a description of how the compressor, situated at the rear of the RA1-MKII Unit, works and how the refrigerant behaves. A variable speed motor inside the casing is connected to an eccentric rotor that rotates inside a profiled housing with one inlet port and one outlet port. A sliding vane mounted inside the pump body is continuously pushed against the side of the rotor by a spring so that the refrigerant cannot escape directly from the inlet to the outlet. The combined shape of the rotor and pump body ensure that refrigerant is squeezed more and more as the rotor rotates, transferring the refrigerant from the inlet to the outlet while increasing its pressure. The flow of refrigerant increases with rotor speed so increasing the motor speed increases to the flow of refrigerant. The actual flow of refrigerant depends on the backpressure in the system which varies as the expansion valve opens and closes to maintain the correct superheat at the evaporator exit. Equipment Set Up Ensure that the equipment has been installed in accordance with the Installation section. Check that the USB connection is made between the RA1-MKII unit and the PC, and that the RA1-MKII software is installed and running (‘IFD: vCOM (n) m’ displayed in bottom right hand corner where n is the number of the virtual COM port on the PC). Check that the combined circuit breaker / RCD on the electrical console is in the ‘On’ (up) position. Turn the unit on by pressing the ON/OFF switch on the console. Check that sensible ambient values for temperatures, pressures etc are displayed on the mimic diagram of the software. Do not click ‘Compressor On’ in the software until instructed. Procedure Set the condenser water pump (Pump 1 speed) to 40% and the evaporator water pump (Pump 2 speed) to 60%. Check that there is a flow of water through both the condenser and evaporator indicated by F1 (typically 1.5 l/min) and F2 (typically 5.5 l/min) on the mimic diagram. Armfield Instruction Manual 40 Set the compressor motor speed to 1% (typically 2000 RPM) then click ‘Compressor On’ (1). The compressor will run at 3000 RPM for 30 seconds then change to the set speed. Check that refrigerant flows around the system indicated by the variable area flowmeter F3 on the RA1-MKII. Configure the sample options as ‘Automatic / 10 seconds intervals’ and click the “GO” button to log the readings from the sensors. View the graphs of T1, T3 & T7 on the primary Y axis and P1 & P2 on the secondary Y axis. Let the system run until the temperatures and pressures are reasonably stable then read the refrigerant flowrate on the variable area flowmeter F3 and enter the value on the mimic diagram. Increase the speed of the compressor to 20% (typically 2460 RPM) then let the system run until the temperatures and pressures are reasonably stable then read the refrigerant flowrate on the variable area flowmeter F3 and enter the value on the mimic diagram. increase the speed of the compressor to 40% (typically 2945 RPM) then let the system run until the temperatures and pressures are reasonably stable then read the refrigerant flowrate on the variable area flowmeter F3 and enter the value on the mimic diagram. Repeat the procedure increasing the compressor speed to 40% (typically 2945 RPM), 60% (typically 3430 RPM), 80% (typically 3915 RPM) then 100% (typically 4400 RPM). Return the compressor speed to 50% and allow the system to settle. Click the ‘Stop’ button to stop data logging then click ‘Compressor on’ (0) to stop the compressor. Results View the graphs and observe the changes in the system as the compressor speed is varied. Using a spreadsheet or plotting graphs independently using data obtained when conditions have stabilised at each setting of compressor speed: Plot the graph of Coefficient of Performance against Compressor speed. Plot the graph of Coefficient of Performance against pressure P2. Conclusion What effect does the speed of the Compressor have on the refrigerant flow rate? What does the graph of the Coefficient of Performance against the compressor speed show? What does the graph of the Coefficient of Performance against the pressure P2 show?
: Refrigeration Lab
Objective Statement
Background:
The vapor-compression refrigeration cycle is the most widely used refrigeration cycle; it is commonly used for refrigerators, air-conditioners, heat pumps, and wide variety of industrial refrigeration systems.
Objective:
Using the Armfield Vapor-Compression Refrigeration Unit, determine the effects of varying the compressor speed (you can follow the procedure in “Exercise D” in the Instruction Manual, which is posted on D2L). In addition, you should discuss/explain any trends observed and any conclusions from your study. Note: Food or drink in the lab is prohibited.
You must wear safety glasses at all times while in lab (even when sitting at tables processing data). Infractions will result in a zero grade on the safety section of this lab.
Please Note:
- You should read through the Instruction Manual (posted on D2L), inspect the equipment, and consider running a quick test to familiarize yourself with the Armfield software (on the computer connected to the refrigeration unit) prior to writing your pre-lab plan.
- Rather than having a low-temperature reservoir and a high-temperature reservoir, for practical purposes this “instructional” refrigeration system absorbs heat from and rejects heat to the same large reservoir (water tank).
- All data (temperatures, pressures, flow rates) can be recorded automatically using the software, except for the refrigerant flow rate, which must be read manually from the Refrigerant Flowmeter (F3) and can be entered manually into the software’s “Diagram” Graphical User Interface.
- You should consider viewing all temperatures, pressures and flow rates on the live graph while the unit is running. Temperature “T4” (after compressor) typically takes the longest to reach steady-state.
- If pressure “P2” (after compressor) goes above 15 bar, the unit will automatically shut down. If this happens, please notify me. You will need to hit the green “reset” switch on the mechanical pressure switch mounted near the top of the electrical box behind the refrigeration system.
- You may want to refer to your Thermodynamics textbook.
- Consider calculating the heat absorbed by the refrigerant in the evaporator and comparing it to the heat removed from the water in the evaporator (“Qin”, which is calculated automatically).
- Consider calculating the heat removed from the refrigerant in the condenser and comparing it to the heat absorbed by the water in the condenser (“Qout”, which is calculated automatically).
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The post Consider calculating the heat removed from the refrigerant in the condenser and comparing it to the heat absorbed by the water in the condenser (“Qout”, which is calculated automatically). appeared first on STUDENT HOMEWORKS .
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