Marine Hvac System

8/4/2019 Marine Hvac System

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Marine Auxiliary Support System

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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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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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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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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


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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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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THANK YOU

FOR YOUR ATTENTION

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Marine Hvac System