Refrigeration and Cryogenics
Bogusław Białko
Air Condition Systems
Air conditioning
•
•
•
•
•
Temperature;
Moisture in the air (humidity);
Supply of outside air for ventilation;
Filtration of airborne particles;
Air movement in the occupied space.
Air-conditioning processes
• Heating – the process of adding thermal energy to the
conditioned space for the purposes of raising or
maintaining the temperature of the space.
• Cooling – the process of removing thermal energy
from the conditioned space for the purposes of
lowering or maintaining the temperature of the space.
• Humidifying – the process of adding water vapor to
the air in the conditioned space for the purposes of
raising or maintaining the moisture content of the air.
Air-conditioning processes
• Dehumidifying – the process of removing water vapor
from the air in the conditioned space for the purposes
of lowering or maintaining the moisture content of the
air;
• Cleaning – the process of removing particulates and
biological contaminants from the air delivered to the
conditioned space for the purposes of improving or
maintaining the air quality.
Air-conditioning processes
• Ventilating – the process of exchanging air between
the outdoors and the conditioned space for the
purposes of diluting the gaseous contaminants in the
air and improving or maintaining air quality,
composition, and freshness.
• Air movement – the process of circulating and mixing
air through conditioned spaces in the building for the
purposes of achieving the proper ventilation and
facilitating the thermal energy transfer.
Thermal comfort
•
•
•
•
•
•
•
Activity level;
Clothing;
Expectation;
Air temperature;
Radiant temperature;
Humidity;
Air speed.
Thermal comfort
Air flow
p( I ,o)
0
p( I ,o)
0
p( I ,o)
0
Cooling sensation
tod
tod
13,12 0, 6215 t p 11,37 v0,16 0,3965 t p v0,16
33
0, 478 0, 237
tod – sensible temperature, oC;
tp – air temperature, oC;
v – wind velocity, km/h
v 0, 0124 v
t p 33
Thermodynamic bases
Thermodynamic bases
Thermodynamic bases
Air Conditioning Systems
Classification
• Individual room air conditioning systems
or simple individual systems;
• Evaporative cooling air conditioning
systems;
• Desiccant-based air conditioning systems
or simple desiccant systems;
• Thermal storage air conditioning systems
or simple thermal storage systems;
Air Conditioning Systems
Classification
• Clean room air conditioning systems or
simple clean room systems;
• Space conditioning air conditioning
systems or simple space systems;
• Unitary packaged air conditioning
systems or simple packaged systems;
• Central hydronic air conditioning systems
or simple central systems.
Psychrometric chart
Psychrometric chart
Psychrometric chart - heating
Psychrometric chart – cooling and
dehumidifying
Psychrometric chart – humidifying
by water
Psychrometric chart – humidifying
by water
vapor
Psychrometric chart – air mixing
m1 t1 m2 t2
m1 m2
m3 t3
m3
Psychrometric chart
• Mixture of dry air and water vapor:
– The temperature is constant, but the quantity of water vapor is
increasing;
– The temperature is dropping, but the quantity of water vapor is
constant;
• Specific amount of energy in the mixture at a specific
temperature and pressure:
–
–
–
–
The temperature of the air;
The proportion of water vapor in the air;
Sensible heat to the air;
More water vapor, which increases the latent heat of the mixture.
Indoor Air Quality
• Fatal in the short-term;
• Carcinogenic (cancer causing
substances);
• Health threatening;
• Annoying, with an impact on
productivity and sense of wellbeing.
Contaminants
Major Source
Particles
Dust (generated inside and outside), smoking, cooking
Allergens
Molds, pets, many other sources
Bacteria and Viruses
People, moisture, pets
Carbon Dioxide
Occupants breathing, combustion
Odoriferous chemicals
People, cooking, molds, chemicals, smoking
Volatile Organic Compounds
Construction materials, furnishings, cleaning products
Tobacco Smoke
Smoking
Carbon Monoxide
Incomplete and/or faulty combustion, smoking
Radon
Radioactive decay of radium in the soil
Formaldehyde
Construction materials, furniture, smoking
Oxides of Nitrogen
Combustion, smoking
Sulfur Dioxide
Combustion
Ozone
Photocopiers, electrostatic air cleaners
Indoor environment
• Human respiration which requires 0.1 – 0.9 l s−1 per person
depending on metabolic rate;
• Dilution of gaseous contaminants to achieve acceptable shortterm exposure limits for carbon dioxide, odor and vapors of
harmful chemical compounds;
• Control of aerosols inside buildings using (filtered) outdoor air
with lower aerosol concentration;
• Control of internal humidity as outside air normally has lower
moisture content;
• Promoting air movement by proper air distribution design to
provide comfort for the occupants.
Typical air leakage paths
Ventilation
•
•
•
•
Trickle ventilation;
Passive stack ventilation;
Extract fans ventilation;
Mechanical ventilation and heat
recovery;
• Ventilation in pitched roof spaces;
• Sub-floor ventilation;
• Wall cavity ventilation.
Ventilation
Ventilation
• Air-handling systems;
• Supply air systems, return air systems, recirulating air
systems and exhaust air systems;
• Single-zone or multizone systems;
• Fan combination systems;
• Single-duct or dual-duct systems;
• Constant-volume (CV) or variable-air-volume systems;
• Dedicated ventilation and space recirculating system.
Ventilation
Ventilation systems
• Natural ventilation:
– Single-sided ventilation;
– Cross-ventilation;
– Stack ventilation.
• Combined natural and mechanical (hybrid)
ventilation:
– Hybrid ventilation in domestic and small buildings;
– Hybrid ventilation in commercial and large buildings.
• Ventilation for fire control.
Ventilation systems
Air distribution
Heat exchangers
•
•
•
•
•
Plate heat exchanger;
Thermal wheels;
Heat pipe heat exchanger;
Run around coils with water circulation;
Run around coils using refrigeration.
Energy reclaim efficiency, %
Type of equipment
Parallel plate metal
Glass tube
Thermal wheel
non-hygroscopic
hygroscopic
Heat pipe
Run-around coil
water/glycol (25%) (B)
water/glycol (25%) (C)
Temperature
Winter
62
65
57
61
74
75
74
74
70
64
67
64
55
Summer
62
59
53
57
74
75
74
74
70
64
61
60
50
Enthalpy
Winter
40
41
37
40
48,5
72
52
74
70
43
35
Summer
26,5
26
20
23
30
44
37
74
70
29
30
Direct evaporative cooler
Direct evaporative coolers
Indirect evaporative cooler
Indirect evaporative coolers
Air stream and heat transfer
through the plate
Evaporative cooler and DX coil
Outdoor conditions
37.8°C dry, 21.1°C wet
Supply air
14.2°C dry, 13.6°C wet
Space temperature
25.6°C
Space relative humidity
50 percent
System pressure drop
DX coil only
2 in. WC (500 Pa)
Evaporative cooling and DX coil
2.75 in. WC (688 Pa)
Wet air
0.85 in WC (213 Pa)
Fan efficiency
0.6
Indirect cooler effectiveness
0.7
Direct cooler saturation efficiency
0.9
EER refrigeration
9 Btu /Wh (COP 2.64)
Outdoor ventilation air
15 percent
Ratio of installation cost of evaporative coolers and DX coil to DX coil only
2.25
Energy use (air and refrigeration side)
Evaporative coolers and DX coil
1.10 kW/ ton (COP 3.20)
DX coil only
1.79 kW/ ton (COP 1.96)
Basics of airflow in ducts
v2
2 gc
p
p1'
v12
2 gc
u1 J
1
'
1
p
2
1 1
v
2 gc
gz1
gc
1
'
1
p
gz1
gc
v
2 gc
g c p1'
g 1
v22
2 gc
u2 j
2
gz2
gc
2
p
v
2 gc
z1
g c p2'
g 2
v22
2g
'
2
W
2
2 2
gz1
gc
1
v12
2g
qJ
v
2 gc
p
constant
p2'
2
2 2
'
2
2
1 1
gz
gc
gz2
W
gc
J u2 u1 q
gz2
gc
2
z2
pf
gc p f
g
Types of air duct
• Supply duct. Conditioned air is supplied to the
conditioned space.
• Return duct. Space air is returned to the fan room
where the air-handling unit is installed or to the
packaged unit.
• Outdoor air duct. Outdoor air is transported to the airhandling unit, to the fan room, or to the space directly.
• Exhaust duct. Space air or contaminated air is exhausted
from the space, equipment, fan room, or localized area.
Air duct design
•
•
•
•
•
•
•
•
Stack effect;
Laminar and turbulent flow;
Velocity distribution;
System pressure loss;
Maximum pressure difference;
Material;
Temperature rise or drop due to duct heat gain or loss;
Duct insulation.
Types of air duct
Round elbows
The magnitude of the local loss coefficient of an elbow:
• Turning angle of the elbow;
• Ratio of centerline radius to diameter
• A three-gore, five-gore, or pleated seven-gore 90° elbow;
• Installation of
splitter vanes;
• Shape of crosssectional area of
the duct.
Round tees, wyes and cross
Diverging tees and wyes with elbows
Flat oval tees and wyes
Air duct design procedure
•
•
•
•
The designer should verify local customs, local codes, local union agreements, and
material availability constraints before proceeding with a duct design.
The designer proposes a preliminary duct layout to connect the supply outlets and
return inlets with the fan(s) and other system components through the main ducts and
branch takeoffs. The shape of the air duct is selected. Space available under the beam
often determines the shape of the duct and affects the layout in high-rise buildings.
The duct layout is divided into consecutive duct sections, which converge and diverge at
nodes or junctions. In a duct layout, a node or junction is represented by a crosssectional plane perpendicular to airflow. The volume flow rate of any of the cross
sections perpendicular to airflow in a duct section remains constant. A duct section may
contain one or more duct segments (including duct fittings). A duct system should be
divided at a node or junction where the airflow rate changes.
The local loss coefficients of the duct fittings along the tentative critical path should be
minimized, especially adjacent to fan inlets and outlets.
Air duct design procedure
•
•
•
•
•
•
Duct sizing methods should be selected according to the characteristics of the air duct
system. The maximum design air velocity is determined based on the space available,
noise, energy use, and initial cost of the duct system. Various duct sections along the
tentative critical path are sized.
The total pressure loss of the tentative critical path as well as the air duct system is
calculated.
The designer sizes the branch ducts and balances the total pressure at each junction of
the duct system by varying the duct and component sizes, and the configuration of the
duct fittings.
The supply volume flow rates are adjusted according to the duct heat gain at each supply
outlet.
The designer resizes the duct sections, recalculates the total pressure loss, and balances
the parallel paths from each junction.
The airborne and breakout sound level from various paths should be checked and the
necessary attenuation added to meet requirements.
Convective and radiant heat
Heat transfer between the space air and
the surroundings
•
•
•
•
•
•
•
Space heat gain represents the rate at which heat enters a conditioned space from an
external source or is released to the space from an internal source during a given time
interval.
Space cooling load is the rate at which heat must be removed from a conditioned space
so as to maintain a constant temperature and acceptable relative humidity.
Space heating load is the rate at which heat must be added to the conditioned space to
maintain a constant temperature and sometimes a specified relative humidity.
Space heat extraction rate is the rate at which heat is actually removed from the
conditioned space by the air system.
Coil load is the rate of heat transfer at the coil.
The heating coil load is the rate at which heat is added to the conditioned air from the
hot water, steam, or electric heating elements inside the coil.
Refrigerating load is the rate at which heat is absorbed by the refrigerant at the
evaporator.
Components of cooling load
• External cooling loads:
–
–
–
–
–
Heat gain entering from the exterior walls and roofs;
Solar heat gain transmitted through the fenestrations;
Conductive heat gain coming through the fenestrations;
Heat gain entering from the partition walls and interior doors;
Infiltration of outdoor air into the conditioned space.
• Internal cooling loads:
– People
– Electric lights
– Equipment and appliances
Heat balance
Qc
Qrc qss qrs Q0
k
qi ,t
hci Tr ,t Ti ,t
hij T j ,t Ti ,t
Ai
Sir ,t
Lir ,t
Eir ,t
Oir ,t
j 1
m
Qrs ,t
hci Ti ,t Tr ,t Ai 60Vif ,t c pa To,t Tr ,t
S c ,t
Lc ,t
El ,t
Ol ,t
Ec ,i O c ,t
i 1
Qrl ,t
qil ,t
60Vif
Qrc,t
wo ,t
qrs ,t
wr ,t h fg
qrl ,t
V [m3 / min]
Heat transfer calculation
• Conduction heat gain through exterior walls and roofs:
qe ,t n
qe,t
bnTsol ,t n
dn
Tr cn A
A
n 0
n 1
n 0
• Heat gain through ceilings, floors, and interior partition walls:
q p ,t
UA Tad Tr
• Solar heat gain and conductive heat gain through window glass:
qso ,t As ,t SC SHGFt Ash ,t SC SHGFsh ,t
qwin ,t
U win Awin To ,t Tr
Heat transfer calculation
• Internal heat gain:
qsp ,t
qs ,l
N p ,t SHG p
qlp ,t
3.413Wlamp Fusl Fal
3.413WA Afl
N p ,t LHG p
• Radiative and convective heat transfer from the lighting fixture
downward directly into the conditioned space:
qld
qs ,l
qlp
1 Flp qs ,l
• Heat carried away by return air from the ceiling plenum:
qret
60Vr r c pa Tp Tr
Heat transfer calculation
• Heat transfer from the plenum air to the conditioned space
through the suspended ceiling and heat transfer from the plenum
air to the conditioned space through the composite floor:
qcl
U cl Acl Tp Tr
q fl
U fl Afl Tp Tr
• Heat gain from the electric lights that enters the conditioned
space:
qes ,l
qld
qcl q fl
qlp
qret qcl q fl
Refrigerating cycle basic parameters
q0
lt
h1 h3 ,
lob
h2
h1 ,
qk
h2
h3 ,
qd
h3
h4 ,
t
q0
lob
h1 h3
;
h2 h1
t
;
C
ψ 1
t
C
;
Refrigerating cycle basic parameters
m
Qo
q0
V
Pt
mlt
m(h2
Pt
Qo
lob
q0
q
m 1,
V
h1 ),
Qo
t
q0
1
Qk
mqk
m(h2
h3 ),
Qd
mqd
m(h3
h4 ),
QWR
m(h1
h1' )
m(h3
h4 )
Qo
q0
1
Qo
q
Refrigerating cycle basic parameters
Pm
Po Pk
qo
lob
t
Pm
qo
lt1 lt 2
lt1 h2 h1
qo h7 h1 lt 2
t
t
(h2
'
Po Pk
h4 h3
h7 h1
h1 ) (h4 h3 )
h7 h1
h2' h1
t
0, 035 Tm
ToTk
Heat Recovery Systems
• The recovery of internal heat loads—such as heat energy from
lights, occupants, appliances, and equipment inside the
buildings;
• The recovery of heat from the flue gas of the boiler;
• The recovery of heat from the exhaust gas and water jacket of
the engine that drives the HVAC&R equipment, especially
engine-driven reciprocating vapor compression systems;
• The recovery of heat or cooling from the exhaust air from air
conditioning systems.
Air-to-air heat recovery
It is always beneficial if the cooling effect of the exhaust air can
be used to cool and dehumidify the incoming outdoor air
during summer, and if the heating effect can be used to heat
the cold outdoor air during winter.
• Effectiveness:
actual transfer
maximum possible transfer between airstreams
T
Ch The Thl
Cmin The Tce
Cc Tcl Tce
Cmin The Tce
Heat Exchangers
•
•
•
•
Fixed-Plate Heat Exchanger;
Runaround Coil Loop;
Rotary Heat Exchanger;
Heat Pipe Heat Exchanger;
Heat Exchangers
Benefits and drawbacks of thermal
storage systems
• Thermal storage systems are one of the few legitimate tools
which shift the higher electric demand for air-conditioning
systems fully or partially from on-peak hours to a lower
electric demand in off-peak hours, and therefore lower
operating costs;
• Thermal storage systems reduce the equipment size and save
initial cost.
• Thermal storage systems do not negatively impact the
building’s indoor environmental control operations, as the
load shedding or some load control programs have done.
Benefits and drawbacks of thermal
storage systems
• As a thermal storage system is a central system, it uses chilled
water from the central plant to cool the air.
• Real-time pricing and other rate structures are available as the
power providers maneuver to offer the most competitive
structure in the electric deregulation environment.
• Thermal storage systems have longer operating hours of
compressors and pumps, and chillers and cooling tower at
full-load operation, at lower outdoor temperatures at
nighttime, and a backup source for cooling during
emergencies.
Ice storage and chilled water
storage
•
•
•
•
•
Ice-on-coil, internal-melt ice storage system (IMISS)
Ice-on-coil, external-melt ice storage system (EMISS)
Encapsulated ice storage system (EISS)
Ice-harvesting ice storage system (IHISS)
Stratified chilled water storage system (SCWSS)
Comparison of various ice storage
systems
IMISS
EMISS
EISS
IHISS
Discharge temperature, °C
1.1 – 3.3
1.1 – 2.2
1.1 – 3.3
1.1 – 2.2
Chiller energy use, kW/ ton
0.85 – 1.2
0.85 – 1.4
0.85 – 1.2
0.95 – 1.3
Storage tank volume, m3 /ton h
0.073 –
0.082
0.08
0.073 –
0.082
0.085 –
0.093
Storage installed cost, $/ ton h
50 – 70
50 – 70
50 – 70
20 – 30
200 – 500
200 – 500
200 – 500
1000 – 1500
Chiller cost, $/ ton
Energy sources for the heatingcooling systems
The sources of waste energy for the driving of waterammonia refrigerant absorption systems should
satisfy the following conditions:
• – temperature t ≥ 90oC – for fluid, t ≥ 150oC for gas;
• – exergetic power Ex ≥ 30 kW;
• – minimal chemical and mechanical pollutants;
• – long and steady time of work τ ≥ 7000 hours/year.
Energy sources for the heatingcooling systems
• Vapor and hot water – form of flows which have the pressure
of 0.1 – 0.2 MPa and the temperature of 90 – 130oC;
• Hot air and combustion gases from gas burning –relatively low
pollutants rate. In most cases hot air occurs as a rather low
exergetic medium: t = 30 – 90oC;
• Combustion gases from the burning of solid fuels – high
exergy, even up to 8 MW and temperature up to 600oC:
– metallurgic;
– coking and pottery systems.
Energy recovery from the
technological system
Energy recovery from the
technological system
Coupled drying – cooling system
Coupled drying system
Coupled drying – cooling system
Heat recovery effectiveness
• The necessary condition for profitability of a given variation of a recovery system:
E
E ( I opt ) max
0
• Waste heat source exploitation (dimensionless parameters):
QTECH
QWF QWC
QWF
QAF
QA
A
QWF QWC
A
• Objective function E divided to a fuel cost (dimensionless form):
( , , , x1,...xn )
1
[
KF
k j ( , , , x1,...xn )
j
Pi ( , , , x1,...xn )
i
zk I k ( , , , x1,...xn )]
k
(
opt
,
opt
,
opt
, x1opt ,...xnopt ) max
Parameters of the theoretical cycle of the
absorption heating-cooling system
Quantity
Combustion gases temperature at generator outlet
Heat recovery by generator
Refrigerant flow rate
Heat of dephlegmation
Heat of condensation
Heat of absorption
Cooling efficiency
Heating efficiency
Heating-cooling efficiency
Evaporation temperature
Condensation temperature
Absorption temperature range
Water temperature at absorber-outlet
Water temperature at condenser-outlet
Symbol
t2
t0
tk
ta1 ÷ ta2
twa
twk
Value
100oC
265 kW
0.121kg/s
-40 kW
-150 kW
-220 kW
0.55
1.55
2.1
-5oC
35oC
65 ÷ 40 oC
60 oC
31 oC
The simplest form of adsorption refrigerator
Solid gas – systems possible for cold
production application
Application/temperature
level
System
possible
Adsorption
Air-conditioning/chilled
Chemical
water (+2oC to +10 oC)
reaction
Chemical
reaction
Refrigeration (–20 oC to 0 oC) Adsorption
Metal
hydrides
Chemical
reaction
o
o
Freezing (–40 C to –30 C)
Metal
hydrides
Working pair Temperature range
–24oC/90oC ~
AC/methanol
–5oC/30oC
–20oC/120oC ~
AC/methanol
–12oC/110oC
Zeolite
–12oC/165oC ~
(NaX)/water
10oC/165oC
–5oC/25oC ~
AC/methanol
25oC/110oC
Zeolite
–5oC/30oC ~
(NaX)/water
25oC/115oC
–5oC/28oC ~
CaCl2/NH3
25oC/110oC
5oC/22oC ~
AC/methanol
30oC/85oC
COP
0.11
0.16
0.10
0.12
0.32
0.10
0.36
Exploitation of heat and energy for exemplary
manufacturing process
Advantages of cogeneration
Cogeneration topping-cycle system
Fuel
P T
conv
0 conv
Fuel
P T
cogen
0 cogen
Fuel savings
Fuel
conv
Fuel
cogen
Topping and bottoming cycles
Bottoming-cycle system
Applications of cogeneration systems
Cogeneration systems may involve different
types of equipment and may be designed to
satisfy specific needs at individual sites
• Industrial sector;
• Institutional sector;
• Commercial sector.
Cogeneration systems equipment and
components
• Prime movers:
– Steam turbines;
– Gas turbines;
– Reciprocating engines;
• Electrical equipment;
• Heat recovery devices;
• Absorption chillers.
Steam generation process
Reciprocating
engines
Microturbines
Stirling
Engines
PEM Fuel Cells
Electrical power (kW)
10 – 200
25 – 250
2 – 50
2 – 200
Electrical efficiency, full load (%)
24 – 45
25 – 30
15 – 35
40
Electrical efficiency, half load (%)
23 – 40
20 – 25
35
40
Total efficiency (%)
75 – 85
75 – 85
75 – 85
75 – 85
Heat/electrical power ratio
85 – 100
85 – 100
60 – 80
60 – 80
Output temperature level (oC)
85 – 100
85 – 100
60 – 80
60 – 80
Fuel
Natural or
biogas,
diesel fuel oil
Natural or
biogas,
diesel,
gasoline,
Alcohols
Natural or
biogas,
LPG, several
liquid
or solid fuels
Hydrogen,
gases,
including
hydrogen,
Methanol
Interval between maintenance (h)
5000 – 20,000
20,000–30,000
5,000
N/A
800 – 1500
900 – 1500
1300 – 2000
2500 – 3500
1.2 – 2.0
0.5 – 1.5
1.5 – 2.5
1.0 – 3.0
Investment cost ($/kW)
Maintenance costs (¢/kW)
IC-engine-driven micro cogeneration system
Basic components of absorption system
•
•
•
•
•
•
•
Evaporator;
Absorber ;
Generator;
Condenser;
Pumps;
Heat Exchanger;
Purge Unit.
Basic components of absorption system
•
•
•
•
•
•
•
Chiller controls;
Expansion valve;
Thermostatic expansion valve;
Electronic expansion valve;
Head pressure controls;
Capacity controls;
Safety controls.
Counterflow induced draft cooling tower
Crossflow induced draft cooling tower
Counterflow forced draft cooling tower
Value
Typical Range or Description
Heat load — kW
Determined for the specific application
Condenser water flow
rate — L/s
0.06 L/s/kW of rejected load is commonly used to size the cooling
tower water
recirculation rate.
Entering condenser
water temperature
32°C to 46°C is a common range for HVAC and refrigeration
applications.
Leaving condenser water
temperature
27°C to 32°C is a common range for HVAC and refrigeration
applications. This
value depends on ambient wet-bulb temperature.
Outdoor wet-bulb
temperature
Depends upon geographical location. The designer should consult local
weather archives (use 1 or 2.5% summer value). A typical conservative
design value is 25°C.
Range
Depends on water recirculation rate and load to be rejected. Range
can be as high as 8°C. A typical value is 5.5°C.
Approach
Varies from 3°C to 7°C for HVAC applications. Approach less than 3°C is
not economical (extremely large tower required).
Theoretical cycle of the absorption air-conditioner
Absorption refrigerator with BrLi - water
Absorption refrigerator with BrLi - water
Operating characteristics of absorption airconditioning systems
• Evaporating temperature;
• Cooling water entering
temperature;
• Heat removed from absorber
and condenser;
• Condensing temperature;
• Corrosion control;
• Rated condition of absorption
chiller;
• Minimum performance.
Type
Minimum
efficiency
Efficiency
Air-cooled, single
effect
0.48 COP
0.63 COP
Water-cooled,
single effect
0.60 COP
0.76 COP
Double-effect,
indirect-fired
0.95 COP
1.00 COP
Double-effect,
direct-fired
0.95 COP
1.00 COP
Types of centrifugal chiller
• Single-stage or multistage;
• Air-cooled, water-cooled, or double-bundle
condenser;
• Open or hermetic
• Direct-drive or gear-drive
• Capacity control provided by inlet vanes or variablespeed drive.
Water-cooled centrifugal chiller
• It enters the first-stage impeller through inlet vanes;
• Hot gas from the first-stage impeller mixes with flashed vapor from the
low-pressure (second-stage) flash cooler;
• The mixture enters the second-stage impeller;
• Hot gas from the second-stage impeller mixes with flashed vapor from
the high-pressure (first-stage) flash cooler;
• The mixture enters the third-stage impeller;
• Hot gas discharged from the third-stage impeller enters the water-cooled
condenser;
• Hot gas is desuperheated, condensed and subcooled to liquid form in the
condenser;
Water-cooled centrifugal chiller
• A small portion of the liquid refrigerant is used to cool the hermetic
motor;
• Most of the liquid refrigerant enters the high-pressure flash cooler
through a multiple-orifice throttling device; and a small portion flashes
into vapor and mixes with the hot gas discharged from the second-stage
impeller;
• Most of the liquid refrigerant from the high-pressure flash cooler enters
the low-pressure flash cooler through a multiple-orifice throttling device;
and a small portion flashes into vapor and mixes with the hot gas
discharged from the first-stage impeller;
• Most of the liquid refrigerant from the low-pressure flash cooler enters
the evaporator through a multiple-orifice device;
• Liquid refrigerant vaporizes to vapor in the evaporator and produces its
refrigeration effect there.
Compressor air-conditioning systems
Compressor air-conditioning systems
Compressor air-conditioning systems
Compressor air-conditioning systems
Refrigeration plant components
• Refrigerating pipework:
– minimise oil loss from the compressor;
– ensure satisfactory refrigerant flow to the evaporator;
– prevent liquid refrigerant or oil in slugs from entering the
compressor;
– prevent oil from collecting in any part of the system;
– avoid excessive pressure loss;
– maintain the system clean and free from water;
Refrigeration plant components
• Evaporator:
• Compressor:
– Dry system;
– Flooded system;
– Direct expansion (DX);
• Condenser:
– Air-cooled;
– Water-cooled
• Evaporative coolers:
– Natural draught;
– Fan draught;
–
–
–
–
–
Reciprocating;
Centrifugal;
Rotary;
Scroll;
Screw.
Capacity ranges and efficiencies of
vapor compression system
Type of chiller
Nominal capacity
range (kW)
Refrigerants used
in new systems
Range in full load
efficiency (kW/ton)
Reciprocating
50 – 1750
R-22
0.80 – 1.00
Screw
160 – 2350
R-134a, R-22
0.60 – 0.75
Scroll
30 – 200
R-22
0.81 – 0.92
Centrifugal
500 – 18,000
R-134a, R-123
0.50 – 0.70
Carnot cycle of absorption refrigerator
Qw ' Qw
Lp
Q0 Qw Qk
Qw
QA
0
Q0
T0 S6
S5
T0 S0
QA
Tm S7
S8
Tm S A
Qk
Tm S3 S 4
Tm S k
Qw ' TZ S 2
S1
Tw S w
Carnot cycle of absorption refrigerator
Sk
SA
Sw
S0
SA
Sw
S0
Sk
S w Tw Tm
z
z
z
T0 S0
Tw Sw
S 0 Tm T0
Q0
Qw
T0 Tw Tm
Tz Tm T0
Tw Tm T0
Tw Tm T0
z
z
z s
1
Tm
1
Tz
1
T0
1
Tm
Sorption refrigeration systems
• Divariant:
– Liquid–vapor absorption;
– Solid–vapor physical adsorption;
• Monovariant:
– Solid–vapor chemical adsorption (chemisorption).
The resorption cycle efficiency:
– Increasing the cooling capacity per unit of heat input;
– operating with double, triple or even with quadruple
effects to produce multi-useful heating and cooling effects,
from a single heat input.
One-stage resorption cycle
One-stage resorption cycle
Resorption refrigerator
Resorption refrigerator with
mechanical compressor
Resorption refrigerator with
sorption compressor
The resorption system conditions
MnCl2 – 6/2
NH3
NiCl2 – 6/2
NH3
TB1, oC
-10.00
-10.00
TB2, oC
118.40
217.15
TA, oC
40.00
40.00
TR, oC
56.2
139.13
QB1, kJ
34.50
34.50
QA, kJ
-41.50
-46.90
COP
0.642
0.514
The resorption system conditions
Air conditioning system main
components
•
•
•
•
•
•
Air conditioning system level;
Air system;
Water system;
Central plant cooling system;
Central plant heating system;
Control system level.
Indoor Air Quality
• Low-efficiency air filters (dusts of size 3 to 10 mm, such as,
spores, pollens, and textile fibers);
• Medium-efficiency filters (dusts of size 1 to 3 mm, such as,
bacteria, automotive-emissions);
• High-efficiency filters (dusts of size 0.3 to 1 mm, such as,
bacteria, cooking oil fumes and tobacco smoke)
• Ultrahigh-efficiency filtration, (HEPA has a DOP efficiency of
99.97 percent, and ULPA filters have a DOP efficiency of
99.999 percent).
Zone sound control
Condition
Air conditioning system
Equipment
Estimate
Poor
Room air conditioning system
Room air conditioner
45 to 50 dBA
Acceptable
Four-pipe fan-coil system
Fan-coil unit
35 to 40 dBA
Good
VAV reheat central system
AHU, VAV-box
25 to 35 NC
Excellent
Single-zone VAV central system
AHU
15 to 20 NC
Individual air conditioning systems
• Room air conditioning (RAC) systems;
• Packaged terminal air conditioning (PTAC) systems.
Advantages
Disadvantages
There are no supply, return, or exhaust ducts.
Temperature control is usually on /off, resulting in
space temperature swing.
Individual air conditioning systems are the most
compact, flexible, and lower in initial cost than
others, except portable air conditioning units.
Air filters are limited to coarse or low-efficiency
filters.
Building space is saved for mechanical rooms and
duct shafts.
Local outdoor ventilation air intake is often
affected by wind speed and wind direction.
It is easier to match the requirements of an
individual control zone.
Noise level is not suitable for critical applications.
They are quick to install.
More regular maintenance of coils and filters is
required than for packaged and central systems.
Room air conditioning systems
• Room air conditioning (RAC) systems;
• Packaged terminal air conditioning (PTAC) systems.
Characterisics for RAC, PTAC and
their heat pumps
RAC, RHP, SAC
PTAC, PTHP
Zone thermal and sound control
Control zone
Single
Single
Control methods
Electric, two-stage thermostat
or DDC, HI-LO, or HI-MED-LO
fan speed
Electric, two-stage thermostat
or DDC
Control modes
On-off
On-off
Heating-cooling mode
changeover
Manual
Manual, automatic
Sound control
45 to 50 dBA
45 to 50 dBA
Characterisics for RAC, PTAC and
their heat pumps
RAC, RHP, SAC
PTAC, PTHP
Indoor air quality (IAQ)
Minimum ventilation
air control
Single
Control methods
Constant-volume flow, affected Constant-volume flow, affected
by wind direction and speed
by wind direction and speed
Filters
Coarse or low-efficiency filters
Single
Coarse or low-efficiency filters
Air systems
Types
Constant-volume or VAV air
mixing
Constant-volume air mixing
Characterisics for RAC, PTAC and
their heat pumps
RAC, RHP, SAC
PTAC, PTHP
Indoor fan
Forward-curved centrifugal
Forward-curved centrifugal
Indoor fan (IF) total
pressure
0.6 in. WC
0.6 in. WC
Combined IF-motor
drive efficiency
25%
25%
Volume flow control
HI-LO or HI-MED-LO fan speed
Single-speed or HI-LO speed
Outdoor fan
Propeller
Propeller
Cooling systems
Refrigeration
compressor
Rotary
Rotary and reciprocating
Characterisics for RAC, PTAC and
their heat pumps
RAC, RHP, SAC
PTAC, PTHP
Refrigerants
HCFC-22, HFC-407C, HFC-410A
HCFC-22, HFC-407C, HFC-410A
Evaporator
DX coil
DX coil
Condenser
Air-cooled
Air-cooled
Refrigerant flow
control
Capillary tube, RHP with fourway reversing valve
Capillary tube, PTHP with fourway reversing valve
Heating systems
Type
Heat pump, or electric heating
Hot water, electric heating, or
heat pump
Energy use, cooling
8.0 to 10.0 EER
8.5 to 10.0 EER
Packaged terminal air conditioner
The differences in construction and
operational characteristics between
packaged and central systems
• Central system (CS) adopts chilled water as the cooling medium
• In packaged system gas-fired furnace, electric heaters are often used to
heat the air, and DX coils, often air-cooled, or sometimes evaporative
condensers are used.
• In a packaged system, the controls of the heating and cooling system are
often a part of the discharge air temperature control in the packaged unit.
In a central system, there are separate water system controls, heating
system controls, and refrigeration system controls in the central plant.
• In general, low- , medium- , and high-efficiency filters are used in
packaged systems; and usually, medium- and high-efficiency filters are
used in central systems.
The differences in construction and
operational characteristics between
packaged and central systems
• Packaged units used in packaged systems are factory-fabricated and assembled, whereas some components in an AHU may be custom-built in
the field.
• The modulation of cooling capacity in a packaged system with scroll and
reciprocating compressors is achieved by cycling of the cylinders or step
controls.
• Both the PS and the CS can provide the minimum ventilation air to dilute
the air contaminants.
• Both the PS and CS can provide the humidity control and prevent wet
surfaces and mold growth in the ducts and conditioned space.
Types of packaged systems
• Single-zone constant-volume packaged system
(SZCVPS);
• Single-zone VAV packaged system (SZVAVPS);
• VAV cooling packaged system (VAVCPS);
• VAV reheat packaged system (VAVRPS);
• Perimeter-heating VAV packaged system (PHVAVPS);
• Fan-powered VAV packaged system (FPVAVPS).
Desiccant-based air conditioning system
Desiccant-based air conditioning system
Types of VAV central systems
•
•
•
•
•
•
Single-zone VAV central system (SZVAVCS);
VAV cooling central system (VAVCCS);
VAV reheat central system (VAVRCS);
Perimeter-heating VAV central system (PHVAVCS);
Dual-duct VAV central system (DDVAVCS);
Fan-powered VAV central system (FPVAVCS).
Clean-room systems
• Clean-room system is a custom-built central system with AHUs
and water-cooling and heating coils to condition the supply
air;
• Clean-room system is required to provide airflow of specific
velocity to reduce lateral air contamination;
• It can be either a single-zone system or a multizone system;
• It always has a separate makeup air unit (MAU) to condition
the outdoor air and a recirculating air unit (RAU) which
recirculates the space air, filters it, cools it, and pressurizes the
mixture of outdoor and recirculating air.
Ice storage and chilled water storage
systems
•
•
•
•
•
Ice-on-coil, internal-melt ice storage system (IMISS);
Ice-on-coil, external-melt ice storage system (EMISS);
Encapsulated ice storage system (EISS);
Ice-harvesting ice storage system (IHISS);
Stratified chilled water storage system (SCWSS).
Ice-on-coil external-melt ice storage
system
Electric demand and the storage cycle
Ecological house
A building that sets up and operates itself
• High-quality, personalized, and localized environmental
control, including all aspects of the environment – heat,
cooling, light, ventilation, and acoustics;
• Highly reliable, cost effective building services and
environmental control — levels of reliability that far exceed
today’s at minimal costs, as automated learning systems that
adapt to changing conditions are introduced into buildings;
Ecological house
• High speed multimode communication for voice, data,
graphics, audio and video;
• Flexible, reconfigurable workspaces and services;
• Efficient, robust, cost effective building operation
• Sustainable building practices;
Services and amenities:
• Comfortable temperatures;
• Good indoor air quality;
• High-quality building maintenance;
Ecological house
Services and amenities:
• Responsive building management;
• Building management’s ability to meet tenant needs;
• Effective noise control.
Intelligent building technologies
•
•
•
•
•
•
Advanced control system;
Automated diagnostic;
Intelligent environmental control system;
Flexible building system;
Smart windows;
Wireless Controls.
Plug and play control concept
• Reduce the manual labor in setting up control
systems and crafting control algorithms;
• Ensure compatibility of control strategies with
equipment characteristics;
• Utilize the best appropriate control strategies;
• Provide a degree of standardization for control
strategies and algorithms that assists with their
maintenance;
• Reduce callbacks by detecting errors at the time of
installation;
• Generally result in a higher quality product.
Integrating alternate generation
technologies
•
•
•
•
Fuel Cells;
Microturbines;
Solar Power;
Automated Real-Time Energy
Purchasing Capabilities;
• Optimized Dynamic Building
Systems.
Effects of tmin on the energy in heat
exchange system
The importance of energy efficiency in
buildings
•
•
•
•
•
Review historical energy use;
Perform energy audits;
Identify energy management opportunities;
Implement changes to save energy;
Monitor the energy management program, set
goals, and review progress.
Control systems for HVAC applications
•
•
•
•
•
•
•
•
•
Operate HVAC equipment only when the building is occupied or when heat is needed to
prevent freezing;
Consider the efficacy of night setback vis a` vis building mass. Massive buildings may not
benefit from night setback due to the overcapacity needed for the morning pickup load;
Do not supply heating and cooling simultaneously. Do not supply humidification and
dehumidification at the same time.
Reset heating and cooling air or water temperature to provide only the heating or cooling
needed.
Use the most economical source of energy first, the most costly last.
Minimize the use of outdoor air during the deep heating and cooling seasons, subject to
ventilation requirements.
Consider the use of “dead-band” or “zero-energy” thermostats.
Establish control settings for stable operation to avoid system wear and to achieve proper
comfort.
Commission the control system and HVAC system for optimum efficiency based on actual
building conditions and use.