Armfield RA2 User manual

An ISO 9001 Company
INSTRUCTION MANUAL
RA2
ISSUE 2
September 2009
Air Conditioning Unit RA2

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IMPORTANT SAFETY INFORMATION
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 Air Conditioning Unit RA2 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 may 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.
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.

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•When lifting is required, two or more people will be required for safety. 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 as appropriate.
Hot Liquids and Steam
This apparatus contains steam and hot water at temperatures capable of causing scalds.
•Always allow time for the apparatus to cool before disassembly.
•Avoid skin contact with hot water and steam. Take particular care if refilling the
apparatus during use. Be aware that the flow of hot steam can extend for some
distance and may not be visible.
•Ensure that the outlet is directed away from anything that could be harmed by
raised temperatures or damp air.
•Always operate the apparatus according to the Operational Procedures described in
this manual.
•Use only those fluids described in this manual when setting up and operating this
equipment.
Hot Surfaces
This apparatus is capable of producing temperatures that could cause burns.
•The apparatus should not be left unattended while switched on.
•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.
•Allow enough time for the equipment to cool before handling any of the
components.
•Do not cover or store the equipment until it has cooled.
•Any safety guards or insulated covers are there for operator protection- they must
not be removed except as described in this manual,.
•Always operate the apparatus according to the Operational Procedures described in
this manual.
Moving and Rotating Components
This apparatus has a rotating fan.
•Do not remove any protective guards while the equipment is in operation.

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•Long hair should be tied back out of the way and dangling items such as necklaces,
scarves or neckties should be removed or secured so that they cannot become
entangled in the equipment.
•Do not touch or insert any object into any moving component while the apparatus is
in use.
•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.
High Pressures
A component within this apparatus (the refrigeration unit) is designed to operate with
internal pressures greater than that of the surrounding atmosphere.
•Do not attempt to pierce or open any part of the refrigeration unit.
•Ensure the unit is positioned so the pressure relief valve is pointed in a safe
direction.
•Keep the external temperature above 0°C and below 40°C.*
•Protect the unit from damage.
*Temperatures for storage only. The operational range is described in the Operation section
of this manual.
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, i.e. the
water must be changed regularly and drained if the equipment will not be in use for
some time.
•Any rust, sludge, scale or algae on which micro-organisms can feed must be
removed regularly, i.e. the equipment must be cleaned regularly.

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•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 UK publication “The Control of
Legionellosis including Legionnaires Disease” - Health and Safety Series booklet HS (G)
70.
Refrigerant R134a
This equipment incorporates 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 (chloro-fluoro-carbon) refrigerants such as R-12.
R134a is colourless, nonflammable and noncorrosive with a very faint odour. In the RA2 it
is contained within a completely sealed unit, and is safe under normal use as described in
this manual.
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 unit containing the refrigerant.
•Always operate the equipment within the safe temperature limits described in this
manual.
•In the event that the sealed unit is ruptured, follow local regulations and take
appropriate steps to reduce the potential hazard. As a suggestion only, procedure
may be as follows (local requirements will vary):
oRemove all personnel from the immediate area
oAvoid skin and eye contact with any escaped refrigerant
oExtinguish nearby flames
oIncrease ventilation so that vaporised refrigerant can dissipate harmlessly

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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.

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AIR CONDITIONING UNIT
RA2
Contents
1Introduction to the Equipment......................................................................................................................... 8
1.1 Diagram 1: Front View of Apparatus ........................................................................................................ 9
1.2 Diagram 2: Top View of Apparatus......................................................................................................... 10
2Description ....................................................................................................................................................... 11
2.1 Overview .................................................................................................................................................. 11
2.2 Control Box.............................................................................................................................................. 11
2.3 Axial Fan.................................................................................................................................................. 12
2.4 Pre-heater and Re-heater ........................................................................................................................ 12
2.5 Evaporator ............................................................................................................................................... 13
2.6 Condensing Unit ...................................................................................................................................... 14
2.7 Humidifier................................................................................................................................................ 15
2.8 Air Velocity Sensor .................................................................................................................................. 16
2.9 Temperature / Relative Humidity Sensor ................................................................................................. 17
2.10 Data Logger/Equipment Controller and Software................................................................................... 17
3Operation and Software.................................................................................................................................. 18
3.1 Safety........................................................................................................................................................ 18
3.2 Using the Software................................................................................................................................... 18
3.3 Operation of the Humidifier..................................................................................................................... 19
3.4 Operation of Remote Controller/Data Logger and Software................................................................... 19
3.5 Data Logging Facilities ........................................................................................................................... 21
3.6 USB Interface........................................................................................................................................... 22
4Specifications.................................................................................................................................................... 23
4.1 Overall Dimensions.................................................................................................................................. 23
4.2 Electrical Supply...................................................................................................................................... 23
4.3 Ventilation................................................................................................................................................ 23
4.4 Refrigerant ............................................................................................................................................... 23
4.5 USB Channel Numbers ............................................................................................................................ 24
4.6 Operating Conditions............................................................................................................................... 25
5Routine Maintenance ...................................................................................................................................... 26

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5.1 General..................................................................................................................................................... 26
5.2 RCD Test ..................................................................................................................................................26
5.3 Calibration of Relative Humidity Sensors................................................................................................26
5.4 Calibration of Temperature and Air Flow Sensors ..................................................................................27
5.5 Cleaning Procedure .................................................................................................................................27
6Background and Theory..................................................................................................................................30
6.1 Background .............................................................................................................................................. 30
6.2 Nomenclature ...........................................................................................................................................31
6.3 Psychrometric chart and Glossary ...........................................................................................................32
6.4 Using Calculations instead of the Psychrometric Chart to Determine the Air State................................34
6.5 Other Calculations Required....................................................................................................................38
7Laboratory Teaching Exercises ......................................................................................................................41
7.1 Exercise A: Psychrometric Charts ...........................................................................................................41
7.2 Exercise B: Sensible Heating ................................................................................................................... 44
7.3 Exercise C: Humidification ......................................................................................................................48
7.4 Exercise D: Cooling with Dehumidification ............................................................................................51
7.5 Exercise E: Enthalpy................................................................................................................................55
8Installation Guide................................................................................................................................................i
8.1 Connection to an electricity supply .............................................................................................................i
8.2 Data logger/remote controller and software...............................................................................................i
9Electrical Wiring Diagram................................................................................................................................ii

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1 Introduction to the Equipment
The Armfield RA2 Unit represents a model of an Air Conditioning system by
demonstrating the effects of essential Air Conditioning processes: cooling, heating,
humidifying and dehumidifying. The effect and relationships of the primary processes
involved in air handling systems can be investigated. The RA2 Unit is designed so that the
student can simulate different environments and perform measurements to allow
psychrometric data analysis.
The unit is totally self-contained and is supplied with software and a computer interface
device to allow remote control, on-line monitoring and logging of results. The software
also includes an online Help Text detailing each of the exercises defined in this manual.
RA2 Air Conditioning Unit

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1.1 Diagram 1: Front View of Apparatus
Evaporator
Pre-heaters
Fan
assembly
Boiler
outlet
Air velocity
sensor
RH/T
sensor
Louver
assembly
LH duct assembly
Re-heaters
RH duct assembly
RH/T
sensor
RH/T
sensor
RH/T
sensor

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1.2 Diagram 2: Top View of Apparatus
Evaporator
Pre
-
heaters
Fan assembly Steam lance
Air velocity
sensor
RH/T
sensor
Louver
assembly
Re-heaters
RH/T
sensor
RH/T
sensor
RH/T
sensor
LH duct assembly RH duct assembly

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2 Description
Where necessary, refer to the drawings on pages 9 and 10.
2.1 Overview
The RA2 is a bench-top unit which comprises of a square ventilation duct mounted
on a mild steel support frame. The duct is made of clear acrylic so all components
are clearly visible: air fan, air preheater, humidifier tube, chiller/dehumidifier heat
exchanger and air reheater. The duct consists of 4 main parts: Left-Hand (LH)
assembly, Right-Hand (RH) assembly, Fan assembly and Louvre assembly.
An axial fan moves the air to be conditioned through the duct. Heating elements are
used to heat the air. Humidification is provided by steam delivered through a tube
from a boiler. The refrigerating capacity is generated by an evaporator (heat
exchanger) which is connected to the refrigeration unit. The refrigeration unit and
boiler are located underneath the duct.
Temperature and humidity sensors record the temperature and relative humidity at
every stage of operation. The air flow rate is determined using an air velocity
transmitter. An acrylic louvre is located at the end of the duct.
The equipment needs to be connected to a suitable PC (not included) to allow
remote control and data acquisition with the RA2 software. Additional USB drivers
are included to allow students to create their own control software, for example
using LabView.
2.2 Control Box
The control box is located beneath the louvre assembly. Accessible from the front
of this are the On/Off power switch for the whole unit, the RCD switch and test
button, and the USB socket for connection to a PC.
The signals accessible via the USB interface include the On/Off remote compressor
switch, fan speed control, air velocity display, preheater, reheater and boiler heater
control, temperature sensor displays and Relative Humidity sensor display.
Figure 1. RA2 electrical control panel
RCD
Power On/Off
USB
Interface
Connection
USB Status
Indicator Lights

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2.3 Axial Fan
The axial fan moves the air through the duct. The speed of the fan may be
controlled to give different air flow rates. The fan must be on when both the pre-
heater and re-heater are on to avoid heat damage to the acrylic duct during
operation.
The fan is protected with a guard, which prevents objects from reaching the blades.
Figure 2. Front view of fan assembly
2.4 Pre-heater and Re-heater
The pre-heater comprises two electric elements of 200W each, for a total power of
400W. It is located downstream of the fan in order to preheat the air flowing
through the evaporator. In the second part of the duct, after the evaporator, there is a
re-heater (200W) which can be used to reheat the cooled or cooled and
dehumidified air. The elements are arranged at an angle to give efficient heat
transfer to the air stream. Air sensing thermostats are incorporated in the duct above
the heater elements to provide overheat protection.
Figure 3. Heating coils
Axial fan
Flow straightener

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2.5 Evaporator
The refrigerating capacity of approximately 500W at 20°C is generated by an
evaporator, which is part of a compact refrigeration system. The refrigeration unit is
used to cool and dehumidify the air stream. The evaporator consists of a direct-
expansion coil operated with a thermostatic expansion valve. The evaporator is
clearly visible within the ventilation duct, and the rest of the refrigeration unit- the
condensing unit- is placed just underneath the duct.
The refrigerant used is R134a.
Air passing across the evaporator fins is cooled as the refrigerant flowing through
the tubes absorbs heat and is boiled (evaporated). Refrigerant flowing through the
coil tubes is controlled by a thermostatic expansion valve mounted at the inlet to the
evaporator coil. This valve automatically feeds just enough refrigerant into the coil
for the refrigerant to be completely converted (boiled) from liquid to gas. The valve
is controlled by a temperature-sensing bulb mounted on the coil outlet (suction)
connection.
The evaporator itself is complete with an angled draining tray at the bottom. During
the dehumidification experiment, condensate can be collected and measured with a
graduated cylinder.
Figure 4. Evaporator assembly
Evaporator fins
Condensate outlet

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2.6 Condensing Unit
The Condensing Unit, located below the ventilation duct, incorporates a compressor and a
condenser. The compressor is used to compress gaseous refrigerant leaving the evaporator,
and in the fan cooled condenser the refrigerant gives away the heat gained in the
evaporator. The Condensing Unit also incorporates a refrigerant collector, filter/dryer, sight
glass and high/low pressure cut-out for safety purposes.
Figure 5. Refrigeration unit assembly
Receiver
Compressor
High pressure
line
Low pressure
line
Expansion
valve
Filter/Drier
High/Low
Pressure
Sight glass
Exp. valve
thermocouple
Condenser

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2.7 Humidifier
Humidification is provided by a water boiler of 5L total volume. Steam is generated when
the water is boiled using the electric element, (2kW). The boiler is made of plastic and
includes a tube which delivers steam to the air duct. It also includes a drain valve, and can
be refilled manually through the filler cap and refill lance. Distilled water is recommended
in order to avoid scaling of the vessel and duct.
The boiler incorporates a cut-out switch, which prevents the electrical element from
overheating if the water level falls too low. If this occurs, wait 2 minutes and refill boiler,
the cut off will self reset and steam can be produced again with 5 -12 minutes.
Power to the boiler heaters can be remotely controlled and monitored using the Armfield
RA2 Software.
Figure 6. Boiler assembly
Refill Cap
Boiler
vessel
Vapour
Lance

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2.8 Air Velocity Sensor
The air velocity in the duct is measured by the air velocity transmitter. This operates on the
hot film anemometer principle, using special thin film. It has very good accuracy at low air
velocities. The working range is 0–10m/s and the response time can be up to 4 seconds at
constant temperature. Therefore it is important to obtain steady conditions in order to have
stable velocity measurement. Steady state in the system is usually obtained after about 15
minutes.
The velocity transmitter is mounted in the duct in the best position to measure the average
air velocity. Care should be taken to ensure the correct angle between the sensor head and
the air flow.
Figure 7. Air velocity sensor
Air velocity
sensor tip
with thin film

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2.9 Temperature / Relative Humidity Sensor
Temperature and Relative Humidity (T/RH) sensors are located at every stage of operation.
There are 4 T/RH sensors in total: at the duct inlet, before the evaporator, after the
evaporator and at the duct outlet. Temperature and Relative Humidity is measured by the
sensor. The RH sensor is a water resistant type so that it can operate in the range from 10 to
100% Relative Humidity.
Figure8. Temperature/Relative Humidity (T/RH) sensor block
For improved accuracy, each RH sensor is provided with a manufacturers’ calibration
certificate. The values on this certificate should be entered into the software, see the
Routine Maintenance section.
2.10 Data Logger/Equipment Controller and Software
The Armfield RA2 Air Conditioning Unit is designed to be operated using the RA2-304
software supplied with the equipment. The RA2 Air Conditioning Unit must therefore be
connected to a suitable PC running the RA2-304 software (or an equivalent program
created by the student). The RA2 software also allows data logging of experimental results,
and performs some standard calculations on the data.
Relative
Humidity sensor
Temperature
sensor
Holding Assembly

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3 Operation and Software
Where necessary, refer to the drawings on pages 2 to 10.
3.1 Safety
The RA2 unit 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 it must be not allowed to enter the eyes.
3.2 Using the Software
The CM12-304 Software is powerful Educational and Data Logging Software with
a wide range of features. Some of the major features are highlighted below, but the
full details on the software and how to use it are provided in the presentations and
Help texts provided with the Software
Check that the USB connection is made between the RA2 unit and the PC, and that
the RA2 software is installed and running. Check that the circuit breakers and RCD
device at the rear of the unit are in the on (up) position. Turn the unit on by pressing
the ON/OFF switch on the unit, then click on the Power On switch on the RA2
software mimic diagram.
On starting the software, the user is met
by a simple presentation which gives
them an overview of the capabilities of
the software and explains in simple terms
how to navigate around the software and
summarises the major facilities complete
with direct links to detailed context
sensitive ‘help’ texts.
A toolbar is displayed at all times, so
users can jump immediately to the
facility they require. The toolbar shows a selection of icons (standard for all
Armfield Software) and pop-up text naming the icon when the cursor is placed over
it.
Example of Standard Toolbar