Lennox UNICO User manual

TECHNICAL MANUAL

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INDEX
Page
1 Presentation 3
2 Fundamental concepts 3
2.1 Heat and temperature 3
2.1.1 Heat 4
2.1.2 Temperature 4
2.2 Transmission of heat 5
2.3 Pressure 6
3 Rapid calculation of building load factors 6
3.1 Calculation of summer re-entry 7
3.2 Calculation of winter dispersion 8
4 Principles of refrigeration 9
4.1 The refrigeration cycle 9
4.2 The components of the refrigeration circuit 10
4.3 Refrigeration circuits of devices 11
4.3.1 Refrigeration circuit diagram of UNICO
models for cooling only 11
4.3.2 Refrigeration circuit diagram of UNICO
models with heat pump 11
5 Operations on refrigeration circuits 13
6 Execution of joints in refrigeration circuit 13
6.1 Welding 13
7 Replacement of refrigeration compressor 13
8 Creation of a vacuum in the refrigeration
circuit 14
9 Filling with coolant 14
10 Operating logic 15
10.1 Power supply to unit 15
10.2 Switching on and control of unit 15
10.3 Cooling program 15
10.4 Air recycling program (fan) 16
10.5 Dehumidifying program 16
10.6 Program for night operation 16
10.7 Program of “air change” 16
10.8 General automatic program 16
10.9 Heating with heat pump 16
10.10 Programming timer and schedule 17
10.11 Operation of the system for disposal
of condensate in cooling mode 17
11 Alarm signals 18
11.1 Tests of operation and diagnosis
of possible malfunctions 18
12 Analysis of possible solutions
to prevent alarm situations 19
13 Wiring diagrams 23
14 Measurements 24
15 Assembly template 25
1 Presentation
Thismanualhasbeenwrittenforthedualpurposeofproviding
an easy, comprehensive text for people who are interested
in knowing more about our “UNICO” air conditioning system,
andausefulguidetomaintenanceandrepairoftheequipment
for professional installers and service centers.
We therefore recommend careful reading both for those
interested in undertaking an activity of installation or after
sales service of our air-conditioners and those who just want
to know more about the technology of this sector.
Any suggestions will be welcome and we will certainly take
them into serious consideration in drawing up future editions
of this manual.
2 Fundamental concepts
This chapter will illustrate the basic concepts which must be
thoroughly clear to anyone operating in this sector.
For reasons of simplicity we have not gone into concepts
that are not strictly concerned with the purposes of this
manual.Theyarecoveredinanytextbookofphysics, for those
who are interested.
Since in the sector of air conditioning the new system of
measurement called SI is still not commonly used, as the old
technical system and even the anglosaxon system still
survive, we have defined all the units of measurements in all
three systems, indicating the equivalence between one and
the others.
Reading this chapter will be rather interesting for beginners,
whilethosewho already have a solid background in the sector
may find explanations, that we hope are clear, for concepts
they have tended to take for granted.
2.1 Heat and temperature
People generally tend to confuse these two concepts that
serve to quantify, or better to measure thermal energy.
In other words, when we speak of heat we mean the amount
of thermal energy, and when we speak of temperature we
mean the potential of that thermal energy. All this has close
analogies with electrical phenomena. Effectively, heat is like
the electrical charge, while temperature is like the difference
of potential that we also call voltage.
The same way, heat flow (that is, the units of thermal energy
that enter and leave a body, a wall, etc., in a specific period
of time) has the same meaning as the electric current which
measures the amount of electric charge that passes in a
specific time period (one second) through a conductor.

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2.1.1 Heat
Like electrical energy, heat cannot be seen but produces
effects that we perceive with our senses.
In fact, when we heat a body (for example a pot full of water)
we can feel the increase in the temperature of the body. This
form of heat is called perceptible heat.
Heatcan also have other effectsona body. If we keep heating
the pot the temperature of the water in it will continue to rise
until it reaches a saturation temperature that depends on the
pressure applied to the pot.At normal atmospheric pressure,
the saturation temperature of water is 100°C, but if the
pressure on the pot is higher this value rises, as for example
in a pressure cooker where foods cook more rapidly because
the water in them boils at a much higher temperature than
100°C. The opposite occurs at low pressure as, for example,
at high altitudes where water boils at a much lower
temperature than 100°C.
The different in the saturation temperature depends on the
pressure and is common to all liquids.
Once it has reached the saturation temperature the liquid
starts to boil and its temperature remains constant. The heat
that causes the evaporation of a liquid is called latent heat.
After all the liquid has boiled, if we continue to apply heat,
the temperature of the steam increases and is superheated
absorbing more perceptible heat.
The same way, if we cool superheated steam (characterized,
therefore, by a temperature higher than that of saturation) it
releases perceptible heat until it reaches the saturation
temperature. When it reaches that temperature it starts to
condense, releasing latent heat to the medium cooling it until
it has all condensed. After the process of condensation, if
cooling continues, the temperature of the liquid falls below
the saturation value and the liquid releases perceptible heat
and is supercooled as a consequence.
The same thing happens if we heat a solid. Gradually, it
reaches a temperature at which it melts. After melting the
temperature of the liquid starts to rise. In this case too, the
phenomenonisreversible, as we can see from freezing water.
Figure 1 diagrams this process for water at atmospheric
pressure.
There are many units of measurement for measuring heat,
but the ones that can interest us in our discussion are:
- kilocalorie(kcal) that is the amount of heat needed to raise
the temperature of 1 kg of water from 15 to 16°C.;
- kilojoule (kJ) that is the amount of heat needed to raise the
temperature of 0.239 kg of water from 15 to 16°C. The kJ
is the unit of measurement of heat used by the SI system
whichis now also compulsory in Italy. One kcal corresponds
to4.187 kJ and therefore onekJ correspondsto 0,239kcal;
- the btu (still used today in anglosaxon countries) that
corresponds to 0,254 kcal (1 kcal therefore corresponds to
3,937btu) or 1,063 kJ (1 kJtherefore correspondsto 0,941
btu).
Heat flow is the amount of heat that transits in a unit of time
through a wall and can be measured in:
- kilocalories per hours (kcal/h);
- Watts(W) thatare simply J per second. OneW corresponds
to 0,86 kcal/h and therefore one kcal/h corresponds to 1,16
W;
- inbtu/h which corresponds to 0,254/h kcal (1 kcal/ therefore
correspond to 3,937 btu) or 0,29 W (1 W therefore
corresponds to 3,5 btu/h).
The last concept that concerns heat measurement is
enthalpy. Enthalpy serves to measure the amount of heat in
a kilogram of a specific substance starting from an arbitrary
zero point. The zero position of reference is unimportant
because more than enthalpy, what interests our calculations
for conditioning and cooling is always the difference of
enthalpy between an initial and a final state.
Enthalpy can be measured in:
-kcal/kg, that are the kilocalories contained in a kilogram of
a specific substance;
-kJ/kg, that are the kilojoules contained in a kilogram of a
specific substance. One kcal/kg corresponds to 4.187 kJ/
kg and therefore one kJ/kg corresponds to 0,239 kcal/kg;
-btu/pound, that are the btu contained in a pound of a
specific substance. One btu/pound corresponds to 0,559
kcal/kgand therefore one kcal/kg corresponds to1,788 btu/
pound. One btu/pound also corresponds to 2,34 kJ/kg and
therefore one kJ/kg corresponds to 0,427 btu/pound.
Measurement of the quantity of heat totally contained in a
body can be obtained by multiplying its enthalpy by its mass
(in kg or in pounds, according to cases).
2.1.2 Temperature
Temperature stands for the potential of heat. In other words,
the higher the temperature of a body, the higher the potential
of the heat that it contains.
A fundamental law of nature (and one that is confirmed to
experience every day by each of us) is that heat passes,
except in case of specific human action, only from bodies
at a higher temperature to bodies at a lower temperature.
To use a mechanical analogy, we can view the transfer of
heatlike the motion of aheavy bodythat, unlesswe intervene
by applying energy, will always move downward.
Both in the technical system in use until a short time ago and
inthenew SI system, temperature is measured on the Celsius
scale (also known as centigrade scale).
The Celsius temperature scale sets an arbitrary zero value
(0°C) at the temperature at which ice melts at atmospheric
pressure and the value of 100 degrees (100°C) at the boiling
point of water at the same pressure. One Celsius degree (°C)
therefore corresponds to one hundredth of the interval
between solidification and boiling of water at atmospheric
pressure.
In anglosaxon countries the temperature scale in use is the
Fig. 1
0
100
t
Somministrazione o
sottrazione di
calore sensibile
Somministrazione o
sottrazione di
calore latente
Somministrazione o
sottrazione di
calore sensibile
Riscaldamento
Sottoraffreddamento
Surriscaldamento
Desurriscaldamento
Ebollizione
Condensazione
Liquido
sottoraffreddato
Cambiamento
di stato
Vapore
surriscaldato
Undercooled
liquid Boiling
Addition or subtraction
of sensitive heat Addition or subtraction of sensitive heat
Addition or subtraction
of latent heat
Condensation
State
change
Superheated
steam
Heating
Undercooling
Superheating
Desuperheating

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Fahrenheit scale, that gives the melting point of ice at
atmosphericpressurethe arbitrary value of 32 degrees (32°F)
and assigns a value of 212 degrees (212°F) to the
temperature at which water boils at the same pressure. One
Fahrenheit degree (°F) therefore corresponds to 180th of the
interval between solidification and boiling of water at
atmospheric pressure.
To convert a temperature in °C to the equivalent in °F we
have to use the following formula:
°F = °C x 1,8 + 32
for example, a temperature of 7°C can thus be converted
into a temperature of 7 x 1,8 + 32 = 44,6 °F.
To convert a temperature in °F to the equivalent in °C we
have to use the following formula:
°C = (°F - 32) : 1,8.
In this case, a temperature of 70°F can thus be converted
into a temperature of 70 :1,8 + 32 = 21,11 °C.
Finally, to pass between a difference in °F to a difference in
°C it is sufficient to divide the value in °F by 1,8. The inverse
operation consists of multiplying the value in °F by 1,8.
For greater clarity figure 2 shows the synoptic
correspondence between the Celsius scale and Fahrenheit.
2.2 Heat transmission
As we have already seen, in nature heat passes from a hot
body to a colder one.
There are four ways in which heat is transmitted through
bodies:
-Conduction, that is what happens when we heat one of
the surfaces of the body. The heat that penetrates in the
body is transmitted through it with an ease that varies from
one material to another. In general a good conductor of
electricity is also a good conductor of heat and vice versa.
The thermal conductivity of bodies thus varies depending
on the nature of the bodies and in inverse proportion to
their thickness. Their insulating power (that is the opposite
of conductivity) varies according to the nature of the bodies
and their thickness.
-Convection, that is what happens when, for example, a
wall releases heat into the air at a lower temperature than
the air touching it. The intensity of this phenomenon
depends on the material with which the releasing (or
receiving) wall is made, the roughness of its surface and
the speed of the fluid touching it.
-Radiation, that is what happens when a radiator releases
thepartofheat it receives from a body near but not touching
it (figure 3).
The intensity of radiation varies depending on the nature
of the two bodies exchanging heat, their distance from one
another, their temperature and their heat. In air-conditioning,
the re-entries of heat due to solar radiation have a very
important role as much of the cooling load in a room is due
to solar radiation through windows and to the heating of
the walls due to it. In a glass wall, the radiation that passes
through it can be reduced by the reflecting power of the
glass itself and/or by the presence of screens or curtains.
Radiant heat is measured in W/m2or kcal/(h m2). One W/
m2corresponds to 0,86 kcal/(h m2) and therefore one kcal/
(h m2) corresponds to 1,16 W/m2.
-Adduction isa term that defines heat transmissionthrough
any opaque body (typically, through the walls of a building)
and that consists in part of transmission, in part of radiation
and in part of conduction.
The most important variables regulating adduction are:
- the speed of the fluid (air, in case of a wall) that touches
the inner and outer surface;
- the presence or absence of solar radiation on the outside
and thus the heat of the surface of the wall;
- the temperatures of the air touching the two surfaces of
the wall;
- the nature of the wall, that is, its insulating power.
Adduction is measured in terms of global coefficient of heat
exchange ÒKÓ, which is in kcal/(h m2°C) or in W/(m2°C).
Sometimes the global coefficient of exchange is expressed
in W/(m2K), that have the same physical meaning and same
amplitudeasW/(m2°C).Usually, one W/(m2°C) corresponds
to 0,86 kcal/(h m2°C) and therefore one kcal/(h m2°C)
corresponds to 1,16 W/(m2°C).
2.3 Pressure
As we have said, pressure regulates the level of the boiling
point and condensing temperature. It is therefore important
to have the relative concepts clear since, as we shall see, a
cooling cycle is achieved by boiling a liquid at a low
Fig. 2
100
0
-17,77
°C
212
32
0
°F
Fig. 3

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temperature and at low pressure and then condensing it at a
higher pressure and temperature.
From a general point of view pressure is the force that is
applied to a unit of surface.
Therefore:
- In the unit of measurement of the old technical system
pressure was measured in atmospheres or kg/cm2.
- In the SI system now in use it is measured in bar
(equivalent to atmospheres or kg/cm2), or in Pa, where
one Pa is a force of one Newton (N) applied to 1 m2(1 kg/
cm2= 1 bar = 100.000 Pa), or also in kilopascal (kPa),
where 1 kPa = 1.000 Pa;
- In the unit of the anglosaxon system the measurement is
in pounds per square inch (PSI). One PSI corresponds to
0,07 bar or atmospheres, while one bar or one atmosphere
corresponds to 14,28 PSI.
There are also two methods for expressing pressure,
regardless of the unit of measurement in which it is measured
(figure 4).
Pressure can also be expressed in:
-absolute terms, considering an absolute vacuum as zero,
-relative terms, considering the atmospheric pressure as
zero,
Thus, to pass from a pressure value expressed in relative
terms (relative pressure) to its equivalent in absolute terms
(absolute pressure) you must:
- increase the value by one if expressed in kg/cm2,
atmospheres or bar;
- increase the value by 100.000 if expressed in Pa;
- increase the value by 100 if expressed in kPa;
- increase the value by 14,7 if expressed in PSI.
Obviously the opposite conversion (that is passage from
absolute to relative pressure) is made by subtracting the
above values rather than adding them.
The reader should also know that in the anglosaxon system
absolute pressure is indicated by the suffix “A” (PSIA) and
relative by the suffix “G” (PSIG).
3 Rapid calculation of loads of buildings
The diagram for calculation of loads that we propose is
necessarilysimplified,but serves to make a rapid identification
with sufficient accuracy of the size of our air conditioners
necessary for an air conditioning installation.
As a general rule for application of cooling only, it will be
sufficientto calculate the summerre-entries, while inthe case
of applications with heat pump, for which we want to ensure
that the unit is able to overcome also winter dispersion, the
approach is slightly different.
In these cases we must:
a) Perform the calculation of summer re-entries and identify
as a consequence the size of the unit necessary;
b) Perform the calculation of winter dispersion and identify
as a consequence the size of the unit necessary;
c) Select the larger of the two.
We would also recommend making an inspection before
deciding the size as it is only in this way that it is possible to
discover the contingent situations that could lead to the
decision for one size unit rather than another.
It is only by determining the size on the basis of effective
measurement that we can submit an offer to the client that is
well centred and thereby increase our chances of being given
the business. By performing careful calculation, it is possible
to avoid uselessly oversized installations that, in addition to
increasing costs without any corresponding benefit, may give
rise to other problems.
Effectively, a more powerful device always implies higher
current absorption and sometimes the increase of power with
all its economic consequences may discourage the client.
IMPORTANT: A preliminary inspection will make it possible
to immediately identify the ideal position for the equipment,
the best route of the refrigeration lines and the best solution
for the problem of drainage of condensate.
Fig. 4

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3.1 Calculation of summer re-entries
For calculation of summer re-entries, we propose a form on
which the values to be considered for any possible situation
have already been indicated.
As you can see, this form does not take into consideration
any differentiation in the nature of the walls much less their
insulating power. In effect, the values on which the table is
based refer to average walls constructed according to the
terms of law 10/91.
Furthermore, our experience tells us that the variations that
can be found in different types of walls do not affect global
dispersion values by more than ±5%.
This table does, however, distinguish among geographical
zones (north, center and south (+ islands) in Italy), as they
are characterized by different external temperatures and
different levels of sunlight in the summer.
Inadditiontothefeaturesof the room, the table also considers
the number of people using it (people are, after all, heat
sources) and the type of illumination. The latter should,
however, be considered withgood judgement: in most homes,
it is unlikely that all the lights will be on in the summer in the
hottest part of the day (normally early afternoon).An office is
a completely different situation, where the lights are almost
always on all day.
For calculation of summer re-entries
Client_______________________________________________
Street_______________________________no.__________
ZIP______City____________________________________
Roomexamined___________________________________
Re-entry______W_________________________________
Model proposed___________________________________
Calculationmade by____________________on__________
Note 1 Consider only the window with the greatest total
sunlight.
2 Consider only the wall on which the above
window is located.
MULTIPLIERS Totals
No. Unit North Center South+Islands
1 Flooring on ground m277 7
2 Air renewal m367 8
3 Window exposed S or E m2140 145 160
to sun (Note 1) a: SW m2250 265 280
Wm
2345 360 380
NW or SE m2185 200 210
4 Windows not considered in item 3 m236 48 66
5 Wall exposed to sun (Note 2) m236 42 54
6 External walls not considered
in item 5 m220 30 45
7 partitions in rooms without
air-conditioning m210 15 20
8 Slabs
under rooms without air-conditioning m210 15 15
(also applies to floors over
rooms without air-conditioning m210 15 15
under uninsulated roofing m227 33 42
under insulated roofing m210 14 18
under flat roof m255 65 72
9 Occupants 150 150 150
10 Light fixtures W ———
Total re-entries for environment W
To have a better idea let us consider the real case illustrated
in figure 5, regarding a room on a middle floor with rooms
above and below it without air conditioning.
Fig. 5
1,5 2
45
3
1

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Client_Dr. Rossi__________________________________
via_____Bianchi________________ n°7
ZIP_00000 City Brescia
Name of room inspected_ Living room_________________
Re-entries______ W
Model proposed___9000 (2.755 W potential)____________
Calculationmade by____________________on__________
Note 1 Consider only the window with the greatest total
sunlight.
2 Consider only the wall on which the above
window is located.
This room has a wall that is not external but that opens onto
a room without air conditioning. Only one person uses the
room, while the heat added by illumination is negligible as
the room is in a private home.
3.2 Calculation of winter dispersion
In recent buildings, an exact assessment of winter dispersion
can be drawn from the project for thermal insulation of the
buildingaccordingtolaw373(nowlaw 10/91), a copy of which
should be in the possession of the owner of the property.
Unfortunately,this document is actually almost never available
and dispersion has to be calculated for every room.
For this purpose we propose a table that, depending on the
volume of the room and its characteristics, simplifies an
approximatecalculationof dispersion that is sufficientlyexact.
Alsointhiscase, the values indicated differas togeographical
zoneand refer to walls insulated according to law10 (formerly
373) for each zone. If the building does not comply with this
law, it is a good rule to increase the result obtained by 20%.
After identifying the pertinent case for the room considered,
tocalculatethedispersionsjustmultiplythevolume coefficient
by the cubic meters of the room.
If we consider the example in figure 5 that is pertinent to a
room:
- in northern Italy;
- with a volume of 5 x 4 x 3 = 60 m3;
- with a single wall communicating with a heated room;
- on a middle floor of a building with several floors.
From the above table we can see that the coefficient for
volume of dispersion is 27 W/m3and therefore, if the building
complies with the law, the dispersion should be 60 x 27 =
1620 W.
If the building is not insulated according to law, we could
prudentially assume that dispersion amounts to 1620 x 1,2 =
1944 W.
In both cases, the version with the heat pump selected for
cooling (size 9000), will also be suitable for heating in the
winter. Obviously, to ascertain this, based on an external
temperature of –5°C, it is necessary to see the tables in
paragraph 9.1.
MULTIPLIERS Totals
No. Unit North Center South+Islands
m2777
60 m3678360
2m2140 145 160 280
m2250 265 280
m2345 360 380
m2185 200 210
1,5 m236 48 66 54
13 m236 42 54 478
22,5 m220 30 45 450
15 m210 15 20 150
20 m210 15 15 200
20 m2200
m227 33 42
m210 14 18
m255 65 72
1150 150 150 150
W-------
2322 W
1 Flooring on ground
2 Air renewal
3 Window exposed S or E
to sun (Note 1) a: SW
W
NW or SE
4 Windows not considered in item 3
5 Wall exposed to sun (Note 2)
6 External walls not considered
in item 5
7 partitions in rooms without
air-conditioning
8 Slabs
under rooms without air-conditioning
(also applies to floors over
rooms without air-conditioning)
under uninsulated roofing
under insulated roofing
under flat roof
9 Occupants
10 Lights
Total re-entries for environment

9
4 Principles of cooling
As we said in paragraph 2.1.2, heat tends to pass only from
a warmer body into a colder one.
It would therefore seem impossible, in the summer, to cool
an environment (that is, take heat out of it) and dissipate it in
the atmosphere (that has a higher temperature), which is
exactly what happens with the refrigerator in the kitchen or
an air conditioner.
But our more attentive readers will recall that we compared
the transfer of heat to the movement of a weight that, by
nature, moves downward but that, with human intervention
and the expenditure of energy, can also be made to move
upward.
In refrigeration the same thing happens: heat is taken from a
cooler place (a room) and released in a warmer one (the
atmosphere) by expending energy.
To obtain this result, however, it is necessary to apply a
stratagem (figure 6).
In other words, we have to create a sort of “thermal
depression”at a temperature even lower than that ofthe room
so that the heat to be removed is naturally “drawn” out of it
and transferred into an intermediate fluid; then we have to
create a “thermal peak” by raising the temperature of the
intermediatefluid to a level higher than that ofthe atmosphere
so that it is discharged by “natural motion”. Finally, it is
necessary to transfer the fluid that has discharged its heat
into the atmosphere back to the thermal depression so that it
canagain absorb the heat from theenvironment andcontinue
the cycle.
All this is what is called a cooling cycle and it is how most
home refrigerators, car and room air conditioners work.
4.1 The cooling cycle
As we said in paragraph 2.1, the boiling temperature and
thatofcondensationofafluidvarydependingonthepressure.
This characteristic is common to all fluids, but there are some
that are more suitable than others for use in a cooling cycle.
Experiencehas shown that to cool an environment it is enough
for a coolant to boil at a temperature of 7°C which
corresponds to a relative pressure of about 5 bar. This
transformationoccurs in a heat exchanger that takes the name
of evaporator.
To dissipate in the air at a temperature for example of 35°C
the heat that the coolant has absorbed from the environment
byboiling at 7°C,it is sufficientto remove heat from the coolant
by having it condense at a temperature for example of 50°C
which corresponds to a relative saturation pressure of about
19 bar. This transformation occurs in a heat exchanger that
takes the name of condenser.
Therefore, our coolant cools the environment by boiling at
low pressure and changing into steam at low pressure.
To condense it, dissipating the heat into the atmosphere, it is
necessary to raise its pressure and to do this the steam from
the evaporator has to pass through a compressor that, by
expending energy, causes the necessary increase.
The energy expended by the compressor is transferred,
however, into the gas that, when it reaches the condenser, is
therefore superheated (see § 2.1.1) with respect to the
saturation temperature that would be normal for the pressure
reached.
Thus,thefirstpartofthecondenser, actually works as a cooler
in which the gas loses the perceptible heat imposed by the
compressor before starting to condense.
Also, for reasons too complicated to explain here but that
concern the safety of the device and the efficiency of the
cycle, the last part of the condenser acts as a supercooler
that absorbs perceptible heat from the liquid condensed that
therefore leaves this heat exchanger at a lower temperature
than its saturation level.
At this point, to enable the liquid to boil at at low temperature,
all that is needed is to lower the pressure, making it transit
through an organ of lamination. Due to the load loss this
Type of construction North Center South+islands
Building on 1 floor with flat roof, rooms with:
all walls exposed 50 40 30
one wall in common with a heated room 45 35 25
two walls in common with a heated room 40 30 20
Rooms on the ground floor of a multiple-story building:
all walls exposed 36 27 19
one wall in common with a heated room 30 25 18
two walls in common with a heated room 26 21 16
Middle rooms of a multiple-story building with upper and
lower floors heated:
all walls exposed 31 22 15
one wall in common with a heated room 27 20 14
two walls in common with a heated room 24 17 13
three walls in common with a heated room 18 15 12
Coefficients of volumetric dispersion (W/m3)
Fig. 6
50 °C
35 °C
25 °C
7 °C
CALORE
CALORE
CALORE
Temperatura
ambiente
Temperatura
esterna
Picco
termico
Depressione
termica
Apporto d'energia
HEAT
HEAT
HEAT
Outdoor
temperature
Ambient
temperature
Energy contribution
Thermal
depression
Thermal peak

10
can create, the pressure of the liquid drops abruptly, and part
of it boils, cooling the rest to the evaporation temperature
(7°C in the example).
There are other parts that are called:
-hot gas line, that is the pipeline that carries the gas
discharged by the compressor;
-liquid line, that is the pipeline that carries the liquid from
the condenser to the organ of lamination;
-vacuum line, carries the gas from the evaporator to the
compressor;
-two-phase fluid line, carries the mixture of gas and liquid
created in the organ of lamination to the evaporator.
In addition, in the jargon of refrigeration experts, the cooling
cycle (and thus also the refrigeration circuit that performs it)
is divided into two “sides”, that is:
- the low pressure side (or low side as they call it), that
goes from the organ of lamination to the compressor, in
the direction of flow of the coolant;
- the high pressure side (or high side as they call it), that
goes from the compressor to the organ of lamination, in
the direction of flow of the coolant.
The concept of the heat pump
Sinceacoolingcycletransfersheatfrom a cooler environment
to a warmer one, there is no reason why it cannot also be
used to cool the outside air even more to transfer the heat
taken from it into a closed room in order to heat it.
In the early days of air conditioning, certain domestic air
conditioner blocks could be installed in a window and were
movable in such a way that in the winter they could be turned
aroundtoheat the indoors by facing the (evaporator) outward,
while in the summer it faced inward to cool the room.
Obviously this is not possible for split units that have a fixed
installation.
The cooling cycle in the versions also designed for heating in
the winter (heating pump), is therefore equipped with an
inversion valve.
In the winter, this valve directs the gas from the compressor
to the heat exchanger that, in the summer functions as
evaporator, so that it functions as a condenser and heats the
environment in which it is installed.
Theliquidthat comes out flows towards what is the condenser
in summer (located in the external section) that in this case
functions as an evaporator and cools the atmosphere by
absorbing heat.
As occurs in the case of elevating a weight, in any cooling
circuit the energy expended will be greater and the output of
the system lesser depending on the “incline” (thermal in this
case) between the thermal peak and depression. So, in
practicalterms, we could say that theoutput of acooling cycle
(and thus of the equipment that produces it) reduces and its
energy consumption increases:
- the lower the temperature we want in the room we are
cooling, or the higher in case of heating (devices with
heating pump);
- the higher the outside temperature (in cooling), or the lower
(in heating with heating pump).
4.2 The components of the refrigeration circuit
Arefrigerating circuit consists of a series of basiccomponents
assembled in such a way as to produce a cooling cycle that
can be enhanced by various accessories.
The compressor
Compressors suitable for air conditioners are usually
hermetically sealed, meaning that they are constructed as a
sealed and welded package with only the connectors and
terminal board protruding.
On the inside, they contain an electric motor that is cooled by
the gas drawn in, and all the mechanical parts. These may
be driven by pistons, but compressors of this type are very
noisy and cause vibrations. The compressors installed on
our machines have a mechanical part consisting of rotating
vanes (figure 7), that, as they do not have any parts running
inalternatingmotion, make it possible to obtain a much quieter
unit almost totally lacking in vibration.
Compressors with orbiting spiral (Scroll) used by other
manufacturers, are also classifiable as rotary and have
characteristics similar to those with vanes.
The condenser
The condenser is the part that treats the external air in the air
conditioner. It is a battery with copper pipes that are
mechanicallyexpandedinafinnedaluminium pack with which
they constitute a complete assembly.
The circulation of air through the condenser is forced, by
means of an electric fan that, on our models has a rotor with
a special noise abating profile (figure 8).
The fan is directly coupled to an electric mtor with safety cut-
off.
Fig. 7
Fig. 8