JCCC-HVACR_2012_SAMHUI_01

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Joint Comprehensive Certificate Course on HVAC&R System, 2012

2012

Fundamentals of HVAC&R Part 1

Presented by:Ir Dr. Sam C. M. Hui

February 28, 2012

About the Lectu rer

Dr. Sam C. M. Hui PhD, BEng(Hons), CEng, CEM, MASHRAE, MCIBSE,

MHKIE, MIESNA, LifeMAEE, AssocAIA ASHRAE Distinguished Lecturer (2009-2011) CEng = Chartered Engineer CEM = Certified Energy Manager LifeMAEE = Life Member, Associatn of Energy Engineers Worked in 1998 as a visiting researcher in the Asia Pacific

Energy Research Centre, Japan Research interests: energy efficiency in buildings and

sustainable building technologies

Joint Comprehensive Certificate Course on HVAC&R System, 2012Feb-Apr 2012

Dr. Sam C. M. HuiDepartment of Mechanical Engineering

The University of Hong KongE-mail: [email protected]

Fundamentals of HVAC&R Part 1

Contents

Introduction

Psychrometry

Thermal comfort

Load and energy calculations

Introduction

Terminology Heating, ventilating, air-conditioning and refrigerating

(HVAC&R) Heating, ventilating and air-conditioning (HVAC)

Mechanical ventilating and air-conditioning (MVAC orACMV)

Air conditioning and refrigeration (AC&R) Environmental control systems (ECS)

Misused word in HK: Air cond. (= cold air)

Introduction

Definition (from ASHRAE*) Air conditioning is the process of treating

air so as to control simultaneously itstemperature, humidity, cleanliness, anddistribution to meet the requirements of theconditioned space.

Basic processes: Cooling and Heating

Comfort air conditioning To meet comfort requirements of occupants

(*ASHRAE = American Society of Heating, Refrigerating & Air-conditioning Engineers, Inc.)


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(Source: www.howstuffworks.com/ac.htm)

See also: How Air Conditioners Work (1:07)http://youtu.be/nKZ2DPvvua8 (Source: www.howstuffworks.com/ac.htm)

(Source: www.howstuffworks.com/ac.htm)

A typical air conditioner

Air conditioning with a chilled water system

Chilledwater

system

Refrigerantcycle

What arethe major

components?

Multiple chiller variable flow chilled water system(Source: ASHRAE HVAC Systems and Equipment Handbook 2004 )

Introduction

Air Conditioning and Refrigeration No. 10 on the list of the [Greatest Engineering

Achievements of the 20th Century] http://www.greatachievements.org

These cooling technologies have altered some of ourmost fundamental patterns of living

Buildings are climate-controlled & comfortable Fresh foods & milk are kept in refrigerators/freezers Building designs are changed completely Environment for industrial processes are controlled

Introduction

The History of Air Conditioning www.air-conditioners-and-

heaters.com/air_conditioning_history.htm 1830: Dr. John Gorrie (ice for cooling hospital rooms) 1881: James Garfield (device w/ melted ice water) Late 19 th century: manufactured air (controlling

humidity in textile mills) Early 1900s: Willis Carrier (designed modern A/C

systems for offices, apartments, hotels, hospitals) 1917-1930: movie theatres were kept cool by A/C


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Introduction

Common types of air conditioning systems Centralised air systems

Constant volume (CV), variable air volume (VAV),Displacement ventilation

Partially centralised air/water systems Fan coils, chilled beams, chilled ceilings, room based

heat pumps

Local systems Split units, variable refrigerant flow (VRF) or variable

refrigerant volume (VRV) [??]

Individual room air-conditioning system

(Source: EnergyWitts newsletter, EMSD)

Primary air fan coil unit (PA-FCU) system


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Variable-air volume (VAV) package system

Psychrometry

Psychrometry The study of atmospheric air and its associated

water vapour Dry air and moist air

Daltons law of partial pressures Standard atmospheric pressure = 101.325 kPa Saturated vapour pressure

Max. pressure of water vapour that can occur at

any given temperature

Psychrometry

Psychrometric Chart: parameters Moisture content ( g), or absolute humidity ( w) Relative humidity ( rh or RH) Percentage saturation ( )

Wet-bulb temperature ( t wb) Specific volume ( v)

(See the illustration on psychrometric chart)

Psychrometric ChartCan you read them

from the chart? Wet-bulbtemperature

Enthalpy

Dew-point

temperature

Relativehumidity

Humidityratio

Specificvolume

Dry-bulbtemperature


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Psychrometry

Common processes: Sensible cooling / sensible heating Cooling and dehumidification / heating and

humidification Humidification / dehumidification Evaporative cooling / chemical dehydration

Typical devices: Cooling/heating coils

Humidifiers / dehumifiers

Basic psychrometric processes

3

5

1

84

6

2

7

Process 0-1: Sensible heatingProcess 0-2: Sensible coolingProcess 0-3: HumidifyingProcess 0-4: DehumidifyingProcess 0-5: Heating and humidifyingProcess 0-6: Cooling and dehumidifyingProcess 0-7: Cooling and humidifying

Process 0-8: Heating and dehumidifying

Psychrometric processes

Sensible cooling/heating Cooling and dehumidification

Evaporative coolingAdiabatic dehumidification

Cooling coil

Entering air

Leaving air

Cooling and dehumidificationSimple air conditioning cycle

Can you draw such a cycle for Hong Kong summer conditions?- Outdoor: DBT = 33 C; WBT = 28 C; flow = 20% of supply air - Indoor: DBT = 25 C; %RH = 50%- Air leaving cooling coil: DBT = 13 C; %RH = 95%


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Psychrometry

Further reading & learning: Air Conditioning: Psychrometrics

[www.bsenotes.com] www.arca53.dsl.pipex.com/index_files/psy1.htm

CIBSE Journal CPD Programme: The psychrometrics of air conditioning systems (Mar2010), www.cibsejournal.com/cpd/2010-03/

Daikin's Free Psychrometrics tool www.daikin.eu/binaries/Psychrometric%20diagram%2

0viewer%20V210_tcm24-133157.zip

What is Thermal Comfort?

- That condition of mindwhich expresses satisfactionwith the thermal environment.

ISO 7730

Body Temperature Normal body core temperature: 37 oC. We have separate Heat- and Cold-

sensors. Heat sensor is located in hypothalamus.

Signals when temperature is higher than37 oC.

Cold sensors are located in the skin.Send signals when skin temperature is

below 34 oC.

Heating mechanism: Reduced blood flow. Shivering.

Cooling mechanism: Increased blood flow. Sweating (Evaporation).

Hot Cold

37 oC 34 oC

Perception of Thermal Environment Heat sensor in

Hypothalamus send impulseswhen temperature exceeds37 oC.

Cold sensors sends impulseswhen skin temperature

below 34 oC. The bigger temperature

difference, the moreimpulses.

If impulses are of samemagnitude, you feelthermally neutral.

If not, you feel cold or warm.Warmimpulses

Coldimpulses Activity

The Energy Balance

Thermal Comfort can only be maintainedwhen heat produced by metabolism equalsthe heat lost from body.

HeatLost

HeatProdu-ced

Thermal comfor t

General heat balanceS = M - W - E - (R + C)

whereS = rate of heat storage of human bodyM = metabolic rateW = mechanical work done by human bodyE = rate of total evaporation lossR + C = dry heat exchange through radiation &

convection


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Conditions for Thermal Comfort Two conditions must be fulfilled

to maintain Thermal Comfort: Heat produced must equal heat lost Signals from Heat- and Cold-

sensors must neutralise each other

The sweat production is usedinstead of body core temperature,as measure of the amount ofwarm impulses.

Relation between the parametersfound empirically in experiments.

No difference between sex, age,race or geographic origin.

Metabolic Rate

Metabolic Rate

0 1 2 3 4

0 1 2 3 4

2040

60

W/m 2

S w e a

t p r o

d .

2930

323334

oC.

10080

31

The Comfort Equation

The Comfort Equation (contd)Thermal comfor t

Environmental factors: Dry-bulb temperature (also related to humidity) Relative humidity (or water vapour pressure)

Influences evap heat loss and skin wettedness

Usually RH between 30% and 70% is comfortable Air velocity (increase convective heat loss)

Preferable air velocity

Mean radiation temperature Radiation has great effect on thermal sensation

Mean Radiant Temperature

The Mean Radiant Temperature (MRT) is that uniform temperature of animaginary black enclosure resulting in same heat loss by radiation fromthe person, as the actual enclosure.

Measuring all surface temperatures and calculation of angle factors istime consuming. Therefore use of Mean Radiant Temperature is avoidedwhen possible.

Actual room Imaginary room

R Rt 1

t

2

t r

t 3

t4

Heatexchange byradiation:R=R

Energy released by metabolismdepends on muscular activity.

Metabolism is measured in Met(1 Met=58.15 W/m 2 bodysurface).

Body surface for normal adult is1.7 m 2.

A sitting person in thermalcomfort will have a heat loss of100 W.

Average activity level for thelast hour should be used whenevaluating metabolic rate, due to

bodys heat capacity.

Metabolic Rate0.8 Met

1 Met

8 Met

4 Met


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Calculation of Insulation in Clothing

1 Clo = Insulation value of 0,155 m 2 o C/W

0,15 Clo0.5 Clo

1.0 Clo

1.2 Clo

Comfort Temperature, t co (typical)

1.7 clo2.5 Met

RH=50%tco =6

oC

0.8 clo2.2 Met

RH=50%tco =18

oC

0.5 clo1.2 Met

RH=50%tco =24,5

oC

Thermal comfor t

Predicted mean vote (PMV) A complex function of six major comfort parameters Predict mean value of the subjective ratings of a group

of people in a given environment

Predicted percentage of dissatisfied (PPD) Determined from PMV as a quantitative measure of

thermal comfort Dissatisfied means not voting -1, +1 or 0 in PMV Normally, PPD < 7.5% at any location and LPPD < 6%

Predicted Mean Vote scale

- +3 Hot

- +2 Warm

- +1 Slightly warm

- +0 Neutral

- - 1 Slightly cool

- -2 Cool

- -3 Cold

The PMV index is used to q uantify the degree ofdiscomfort

PMV and PPD

PMV-index (Predicted Mean Vote) predicts the subjectiveratings of the environment in a group of people.

0 = neutral (still 5% people are dissatisfied)

PPD-index predicts the number of dissatisfied people.

Thermal comfor t

Comfort zones Defined using isotherms parallel to effective

temperature (ET) or standard ET (SET) ASHRAE comfort zones for summer and winter

(for typical indoor and seated person) Proposed comfort zones

Within 5 to 16 mm Hg water vapour pressure For summer, 22.8 oC SET 26.1 oC For winter, 20.0 oC SET 23.9 oC


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ASHRAE Comfort Zones(based on 2004 version of ASHRAE Standard 55)

Local Thermal Discomfort

Draught

RadiationAsymmetry

Vertical AirTemperatureDifferences.

Floortemperature

Acclimatisation/Adaptation!

When the air conditionsystem fails you canadapt by adjusting your CLO value

Load & energy calculations

Thermal load The amount of heat that must be added or removed

from the space to maintain the proper temperaturein the space

When thermal loads push conditions outsideof the comfort range, HVAC systems are usedto bring the thermal conditions back tocomfort conditions


Purpose of HVAC load estimation Calculate peak design loads (cooling/heating) Estimate likely plant/equipment capacity or size Specify the required airflow to individual spaces Provide info for HVAC design e.g. load profiles Form the basis for building energy analysis

Cooling load is our main target Important for warm climates & summer design Affect building performance & its first cost Cooling load profiles


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Typical HVAC load design process 1. Rough estimates of design loads & energy use

Such as by rules of thumb & floor areas See Cooling Load Check Figures See references for some examples of databooks

2. Develop & assess more info (design criteria, building info, system info)

Building layouts & plans are developed

3. Perform detailed load & energy calculations

Cooling Load Components

External 1. Heat gain through exterior walls and roofs 2. Solar heat gain through fenestrations (windows) 3. Conductive heat gain through fenestrations 4. Heat gain through partitions & interior doors

Internal 1. People 2. Electric lights

3. Equipment and appliances

Cooling Load Components

Infiltration Air leakage and moisture migration, e.g. flow of

outdoor air into a building through cracks,unintentional openings, normal use of exteriordoors for entrance

System (HVAC) Outdoor ventilation air System heat gain: duct leakage & heat gain, reheat,

fan & pump energy, energy recovery

Components of building cooling load

Externalloads

Internalloads

+ Ventilation load & system heat gains


Cooling load calculation method Example: CLTD/SCL/CLF method

It is a one-step, simple calculation procedure developed by ASHRAE

CLTD = cooling load temperature difference SCL = solar cooling load CLF = cooling load factor

See ASHRAE Handbook Fundamentals for details Tables for CLTD, SCL and CLF


External Roofs, walls, and glass conduction

q = U A (CLTD) U = U-value; A = area

Solar load through glass q = A (SC) (SCL) SC = shading coefficient

For unshaded area and shaded area

Partitions, ceilings, floors q = U A (t adjacent - t inside )


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Internal People

qsensible = N (Sensible heat gain) (CLF) qlatent = N (Latent heat gain)

Lights q = Watt x F ul x F sa (CLF)

Ful = lighting use factor; F sa = special allowance factor

Appliances qsensible = qinput x usage factors (CLF)

qlatent = qinput x load factor (CLF)


Ventilation and infiltration air qsensible = 1.23 Q (t outside - t inside ) qlatent = 3010 Q (woutside - winside ) qtotal = 1.2 Q (houtside - hinside )

System heat gain Fan heat gain Duct heat gain and leakage Ceiling return air plenum


Definitions Space heat gain : instantaneous rate of heat gain

that enters into or is generated within a space Space cooling load : the rate at which heat must be

removed from the space to maintain a constantspace air temperature

Space heat extraction rate : the actual rate of heatremoval when the space air temp. may swing

Cooling coil load : the rate at which energy isremoved at a cooling coil serving the space Conversion of heat gain into cooling load

(Source: ASHRAE Handbook Fundamentals 2005)

Block load and thermal zoning

North

South

West East

Cooling loads due to windows at different orientations

(Source: D.G. Stephenson, 1968)


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From load estimation to energy calculations Only determine peak design loads is not enough Need to evaluate HVAC and building energy consumption

To support design decisions (e.g. evaluate design options) To enhance system design and operation To compile with building energy code

Energy calculations More complicated than design load estimation Form the basis of building energy and economic analysis


Two categories Steady-state methods

Degree-day method Variable base degree-day method Bin and modified bin methods

Dynamic methods Using computer-based building energy simulation Try to capture dynamic response of the building Can be developed based on transfer function, heat

balance or other methods

Heating degree-day :

Cooling degree-day:

t bal = base temperature (or balance point temperature)(e.g. 18.3 oC or 65 oF); Q load = Q gain + Q loss = 0t o = outdoor temperature (e.g. average daily max./min.)

* Degree-hours if summing over 24-hourly intervalsDegree-day = (degree-hours) + / 24

+ Only take the positive values

Buildingdescription

Simulationoutputs

Simulation tool(computer program)

Weather data

- physical data- design parameters

- energy consumption (MWh)- energy demands (kW)- environmental conditions

Systems(air-side)

Plant(water-side &refrig.)

HVAC air systems HVAC water systems

Energy inputby HVAC plant

Energy input by HVACair/water systems

Energy storage

Energy inputby appliance

Thermal Zone

Building energy simulation process


Further reading & learning: Comfort [www.bsenotes.com]

www.arca53.dsl.pipex.com/index_files/science1.htm Thermal comfort Wikipedia

http://en.wikipedia.org/wiki/Thermal_comfort

ASHRAE Handbook Fundamentals 2009, Chps. 14-19 (onload and energy calculations)

Documents

JCCC-HVACR_2012_SAMHUI_01