marine hvac system
TRANSCRIPT
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Marine Auxiliary Support System
HVACBy: Mr. Anuar Bin Bero
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How doesit work?
High Temperature Reservoir
Low Temperature Reservoir
R Work Input
Heat Absorbed
Heat Rejected
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Thermal energy moves from left to right through fiveloops of heat transfer:
How does it work?
(Bureau of Energy Efficiency, 2004)
1)Indoor airloop
2)
Chilledwater loop
3)
Refrigerantloop
4)
Condenserwater loop
5)
Coolingwater loop
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AC options / combinations:
AC Systems
Air Conditioning (for comfort / machine)
Split air conditioners
Fan coil units in a larger system
Air handling units in a larger system
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Vapour Compression
Refrigeration (VCR): usesmechanical energy
Vapour Absorption Refrigeration(VAR): uses thermal energy
Gas Refrigeration System:usedto cool aircraft and to obtain verylow temperatures after it is
modified with regeneration.
Refrigeration and Air ConditioningSystems
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Vapour Compression Refrigeration
Refrigeration cycle (Primary System)
Condenser
Evaporator
HighPressure
Side
LowPressure
Side
CompressorExpansion
Device
1 2
3
4
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Vapour Compression Refrigeration
Refrigeration cycle
Low pressure liquidrefrigerant in evaporatorabsorbs heat and changesto a gas
Condenser
Evaporator
HighPressure
Side
LowPressure
Side
CompressorExpansion
Device
1 2
3
4
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Vapour Compression Refrigeration
Refrigeration cycle
The superheated vapourenters the compressorwhere its pressure israised
Condenser
Evaporator
HighPressure
Side
LowPressure
Side
CompressorExpansion
Device
1 2
3
4
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Vapour Compression Refrigeration
Refrigeration cycle
The high pressuresuperheated gas is cooledin several stages in thecondenser
Condenser
Evaporator
HighPressure
Side
LowPressure
Side
CompressorExpansion
Device
1 2
3
4
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Type of Refrigeration
Vapour Compression Refrigeration
Refrigeration cycle
Liquid passes through expansiondevice, which reduces its pressureand controls the flow into theevaporator
Condenser
Evaporator
HighPressure
Side
LowPressure
Side
CompressorExpansion
Device
1 2
3
4
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Vapour Compression Refrigeration
Choice of compressor, design of
condenser, evaporator determined by Refrigerant
Required cooling
Load Ease of maintenance
Physical space requirements
Availability of utilities (water, power)
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Measure
Airflow Q (m3/s) at Fan Coil Units (FCU) or Air
Handling Units (AHU): anemometer Air density (kg/m3) Dry bulb and wet bulb temperature: psychrometer
Enthalpy (kCal/kg) of inlet air (hin
) and outlet air(Hout): psychrometric charts
Calculate TR 3024
hhQTR
outin
Assessment of Air Conditioning
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Indicative TR load profile
Small office cabins : 0.1 TR/m2
Medium size office (10 30 peopleoccupancy) with central A/C: 0.06
TR/m2
Large multistoried office complexeswith central A/C: 0.04 TR/m2
Assessment of Air Conditioning
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Basic HVAC Calculations
Applying Thermodynamics to HVAC Processes
Looking at a simplified (but complete) air-conditioning system.
Terminology: qsensible, mwater, qL, hw, solar gains.
First law of thermodynamics (energy) and conservation of mass.
Air is removed from the room, returned to the air-conditioning
apparatus where it is reconditioned, and then supplied again to
the room.
Many cases, it is mixed with outside air required for ventilation
Outdoor air (o) is mixed with return air (r) from the room and
enters the apparatus at condition (m).
Air flows through the conditioner & is supplied to the space (s).
The air supplied to the space absorbs heat qs and moisture mw,
and the cycle continues.
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Applying Thermodynamics to HVAC Processes
Figure 1: Working Principle of Air Conditioning System
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Outside
air
Exhaust
Mixed
air
Primary
System
Supply
air
Air Handling
Unit
Return airTo Comp.
Space
Chiller
In
Chiller
Out
Fan
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Figure 2
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Figure 3
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Absorption of Space Heat and Moisture Gains
AC usually reduces to determining the quantity of moist airthat must supplied and the condition it must have to
remove given amounts of energy and water
Sensible heat gain addition of energy only
Figure 4
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Heating or Cooling of Air without moisture gain orloss straight line on psychrometric chart sincehumidity ratio is constant
Figure 5
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Cooling and Dehumidifying Air
Moist air brought down below its dew point temperature
some of the water will condense and leaves the air stream Assume condensed water is cooled to the final air
temperature before draining from the system
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Figure 6 Cooling and Dehumidifying Air
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Cooling and Dehumidifying Air
Moist air brought down below its dew point temperature
some of the water will condense and leaves the air stream
Assume condensed water is cooled to the final air
temperature before draining from the system
Cooling and dehumidifying process involves both sensible
heat transfer and latent heat transfer where sensible heat
transfer is associated with the decrease in dry-bulb
temperature and the latent heat transfer is associated with the
decrease in humidity ratio.
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Figure 7
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Figure 8
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Figure 9 Adiabatic Mixing of Moist Air with Injected Water
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Figure 10
Approximate Equations Using Volume Flow Rates
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Approximate Equations Using Volume Flow Rates
Since volumes of air changeneed to make calculations with mass
of dry air instead of volume. But volumetric flow rates define
selection of fans, ducts, coils, etc.
Use volume while still considering mass by using volume rates
based on standard air conditions
Dry air at 20 oC and 101.325 kPa (68 oF and 14.7 psia)
Density is 1.204 kg/m3 (0.075 lb/ft3)dry air
Specific volume is 0.83 m3/kg (13.3 ft3/lb)dry air
Saturated air at 15 oC has about same density and volume
Need to convert actual volumetric flow conditions to standard
Say you need 1,000 cfm outside air rate at standard conditions Outside measured at 35 oC dry bulb and 23.8 oC wet bulb
corresponding to a specific volume of 14.3 ft3/lb.
The actual flow rate would be 1,000 (14.3/13.3) = 1,080 cfm
1,000/13.3 = 1,080/14.3 = mass rate (lb/min) of moist air
Sensible heat gain corresponding to the change of dry
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Sensible heat gain corresponding to the change of dry-bulb temperature for a given airflow (at standard ASHRAEconditions)
qs= Q(1.204)(1.00+1.872) t
Where:
qs= Sensible Heat Gain (Watt)
Q =Airflow (L/s)
1.204 = Density of standard dry air. Kg/m3
1.00 = Specific Heat of dry air kJ/(kg.K)
1.872 = Specific Heat of water vapor kJ/(kg.K)W= Humidity ratio, mass of water per mass of dry
t = Temperature difference
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Latent heat gain corresponding to the change of humidity
ratio W for a given airflow (at standard conditions).
The latent heat gain in Watts (Btu/h) as a result of adifference in humidity ratio W between the incoming
and leaving air flowing at standard conditions.
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Total heat gain corresponding to the change of dry-bulb
temperature and humidity ratio W for a given airflow (at
standard conditions). The total heat gain in Watts (Btu/h) as a result of a
difference in enthalpy h between the incoming and
leaving air flowing at standard conditions.
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Single-Path Systems
Simplest form of all-air HVAC system serving a single
temperature control zone
Responds to one set of space conditions, where conditionsvary uniformly and the load is stable.
Schematic of systemreturn fan necessary under certain
conditions ofp.
Need for reheatnecessary to control humidityindependent of the temperature requirements.
Equations for single-path systemsair supplied must be
adequate to take care of each rooms peak load conditions.
Peak loads may be governed by sensible or latent roomcooling loads, heating loads, outdoor air requirements, air
motion, and exhaust.let us look at each of these loads
and what air volume is required to satisfy these demands.
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Single-Path Systems - schematic
Figure 11
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Single-Path Systemsequations for supply air
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Single-Path Systems supply air for ventilation
1. Supply air for ventilation needed when the amountof outside air is not adequate
2. Supply air not adequate for the amount of exhaustmakeup required no return air comes from theroom and entire volume of make-up ventilation airbecomes an outside air burden to system
3. Desired air exchange rate not satisfied
supply air isdetermined
4. Desired air movement not satisfied, based on areaindex parameter, K.
Each of the above conditions are used at different times Case 1 when outside air governs, Cases 3 and 4when air movement governs, and Case 2 whenexhaust governs.
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Each state point is identified both in summer and winter
Change oft is result of sensible heat loss or gain, qS
Change in W is result of latent heat loss or gain, gL
All return air is assumed to pass from the room through a
hung-ceiling return air plenum
Supply air CFMS at the fan discharge temperature tsf(summer mode) absorbs the transmitted supply duct heat
qsd and supply air fan velocity pressure energy qsf,vp
thereby raising the temperature to ts
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Room supply air absorbs room sensible and latent heat qSR
and qLR along the room sensible heat factor (SHR) line s-
R, reaching the desired room state, tR and WR.
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Room (internal) sensible loads which determine the CFMs
consist of:
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Single-Path SystemsPsychrometric Representation
Single-Path Systems Psychrometric Representation
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Single Path Systems Psychrometric Representation
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Single-Path SystemsPsychrometric Representation
Single-Path SystemSensible Heat Factor (Ratio)
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g y ( )
Sensible heat factor (ratio), SHF or SHR=ratio of sensible heat
for a process to the total of sensible and latent heat for the
process.
The sensible and latent combined is referred to as the total heat
On psychrometric chart, the protractor provides this ratio and
may be used to establish the process line for changes in the
conditions of the air across the room or the conditioner on the
chart
The supply air to a conditioned space must have the capability
to offset both the rooms sensible and latent heat loads.
Connecting the room and supply points with a straight line
provides the sensible heat factor condition. The conditioner
provides the simultaneous cooling and dehumidifying that
occurs.
Horizontal line would be SHF = 0.0 (only sensible)
Line with SHF = 0.5 would be half sensible and half latent
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Single-Path SystemExample 2
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Single-Path SystemExample 2
Sensible and latent loads given
Room Conditions: (75o
F and 55% RH)Supply at 58o
F Outside Conditions: 96 oF DB, 77 oF WB and 20% of
total flow
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Single-Path SystemPsyc
r
o
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b.
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THANK YOU
FOR YOUR ATTENTION