Heating systems mk tisk - cvut.cz

Czech Technical University in PragueFaculty of Civil Engineering

Department of Microenvironmental and Building Services Engineering

Michal Kabrhel 12008/2009

Heating systemsApllied thermodynamics

Indoor environment

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Heating

n The function n Heat supply to guarantee required indoor

temperaturen Heat supply for technology n Heat supply for hot water generation

n The principle

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Heating - History 700 BC - 0

Hypocausta

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Heating - History – Middle Ages

n Fireplace, stove

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Heating - History 18th-19th

century - steam system

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Heating - History 20thcentury

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History 20th century warm water systems

Steam systems are replaced by warm water ones - use of electricity, pumps, control

Warm water boiler Strebl 1927

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1900-1945

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Heating nowadaysn Warm water systemsn Gas boilers operated by

electronics n Heating surface inside

floor, wall, ceilingn Computer models

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Heating nowadays

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Applied thermodynamicsn Heat, heat energy

n Heat is the energy transferred between a system and its surroundings due solely to a temperaturedifference between the system and some parts of itssurroundings.

n Temperaturen State variable describing kinetics energy of the

particles of the systemn Thermodynamic /Kelvin/ T [K]n Celsius t [°C] t= T-273,15n Fahrenheit [°F] 1°F=5/9°C (°F-32).5/9=°C


Basic laws of thermodynamics

n Zeroth lawn There is a state variable TEMPERATURE. Two

systems at the same temperature are in thermodynamics equilibrium.

n The zeroth law of thermodynamics states that if forexample you have a Body (A) and a Body (B), both atthe same temperature; and then you have a Body (C) which is at the same temperature as Body (B); Therefore the temperature of Body (C) is equal to thetemperature of Body (A).


Basic laws of thermodynamics

n 1.lawn The total energy of the system plus the surroundings

is constant. (internal energy of system)n 2.law

n The second law is concerned with entropy (S), whichis a measure of disorder. The entropy of the universeincreases.

n 3.lawn It is impossible to cool a body to absolute zero

by any finite process


Heat transfer modesn Heat Conductionn Heat is transferred between two systems

through a connecting medium, Biot-Fourier

n Heat Convection n Macroscopic movement of the matter in the

forms of convection currents. n Newton-Richman, Fourier-Kirchhof


Heat transfer

n Transmissionconvection+conduction+convection

n Radiation nElectromagnetic waves


Indoor environmentn Theory of the indoor environment

n Hygrothermal microclimaten Acoustic microclimaten Psychical microclimaten Light microclimaten Electrostatic microclimate

n Hygrothermal microclimaten Indoor environment state from the viewpoint of

thermal and moisture flows between the human body and surroundings


Heat Exchange between the Human Body and the Enviroment

n Metabolic Rate Mn degree of muscular activities,n environmental conditions n body size.

n Heat loss Qn Respirationn Convectionn Radiationn Conductionn Evaporation

n Body thermal balance equationM=Q comfortM>Q hotM<Q cold

Ta

Tp

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n Humann Metabolic Raten Clothing Insulation

n Spacen Air Temperature (Dry-Bulb)n Relative Humidityn Air Velocityn Radiation (Mean Radiant Temperature)

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Factors Influencing Thermal Comfort

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n Operative Temperature

n where tg = operative temperaturen ta = ambient air temperaturen tr = mean radiant temperaturen hc = convective heat transfer coefficientn hr = mean radiative heat transfer coefficient

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Environmental indices


Environmental indicesn Mean Radiant Temperature

n wheren tr = mean radiant temperaturen Ti = temperature of the surrounding surface i,

i=1,2,....,nn φrn = shape factor which indicates the fraction of

total radiant energy leaving the clothing surface 0 and arriving directly on surface i, i=1,2,...n


Thermal comfort evaluation

n PMV index (Predicted mean vote)

n PPD index (Predictedpercentage ofdissatisfied)



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HeatingPrinciples of heating equipment

Heat emmitters

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Hot water heating

n Principlen Heating system

n Heat sourcen Distribution

networkn Heat emitter

n Heat transfer mediumn watern steamn air

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Convectors

NaturalFan-convectorsFloorWall

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Radiators

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Off-peak storage

n Staticn Dynamicn Hybrid

n Convectorn Radiator


Air flow patterns


Heat emittersn Design principlesn Heating outputn Locationn Covering - furnituren Connection to the pipe systemn Type


Heater emitters design

n Covering = changes in the output


Low - temperature radiant heating

n floor, wall and/or ceiling with embedded pipes or el.wires in concrete slabn Temperature distribution


Underfloor heating

n History

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n Floor structure


Underfloor heating - structure

TYP ATYP B

TYP C



n Technical solutionn Pipe layout



n Output n Limited surface temperature á limited output cca

100 W.m-2

n Energy savings n Lower air temperature á lower heat losses

n Controln Low temperature difference á autocontrol effect


Underfloor heating - examples


Radiant panels

n Low temperaturen heaters max 110 °C (water, steam, el. power)

n High temperaturen dark - about 350°C - radiant tube heating

system (gas)n light - about 800 °C - flameless surface gas

combustion


Heat emitters



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HeatingHot water heating systems


Hot-water heatingn Terminology

Boiler

Emitter

Main supply/return pipe

Branch supply/return pipe

Radiator valve

Ventcock

Drain/feed cock

Shutoff valves

Expansion vessel

Manual Control valve

Emitter


Heating system designInitial information about the

buildingn Type

n industrial, office, dwelling

n Operationn continuous, intermittentn single, multiple

n Structuren heavy, light n new, reconstruction


Heating system design Functional requirements

n Connection of the heat emitters with the heat source

n Deaerationn Drainingn Integration into the building


Design parameters of hot water heating systems

n (1) Water circulationn (2) Geometry of the systemn (3) Water temperaturen (4) Expansion vessel n (5) Materials


Water circulation

n Natural – without pumpP1=h.ρ1 .g

P2=h.ρ2.g

ΔPF=ΔPn + ΔPP

n Forced – with pump

ΔPn=P2-P1=h.(ρ2- ρ1 ).g

P1 P2

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Geometry of the system

n Relative connection of the heat emittersn One-pipe, two-pipe

n Main pipe lay-outn Upper, lower, combined

n Branch pipes lay-out n vertical, horizontal , microbore


Geometry of the system Relative connection of the heat emitters

n Two-pipe systemn One-pipe system


Two-pipe systems

n Contraflow, parallel flow

Tichelmann


One-pipe systemsBasic schemes of the connection

•With mixing valve•Two-point•One-point

• With By-Pass–“Horse Rider“ – Controlled by-pass

•Serial


One-pipe systemsMixing valves

Two-point valves

One-point valves

Ventil compact


Relative connection of the heat emitters

Conclusion

Two-pipe X one-pipe system

n Length of the pipesn Water circulationn Measuring and controln Pressures in the system


Geometry of the systemMain-pipe layout

Upper

Lower

Combined


Branch pipes layout

Vertical

Horizontal

Microbore


Temperature Operational temperature

n Design temperature

t2

t1

tw1

tw2

tTp,max

tw

Temperature difference - emitter = tw1 - tw2

Temperature difference system = t1 - t2

System supply t1

System return t2

Emitter supply tw1

Emitter return tw2

Maximal emitter surface temperature tTp max

Mean emitter temperature tw


Temperature in the system

n Heat transferred by the system

n Heat transferred by the emitter

t2

t1

tw1

tw2

tp1,max

tw


Temperatures Design Criterions

• Economical criterions

• Physical properties of the medium

• Hygiene requirements

• Technical properties of the heat source


TemperatureParameters design

n Heating system supply temperature• Low- temperature t1 <=65°C• Medium - temperature 65°C< t1 <= 115°C• High temperature t1 > 115°C

n Temperature difference n 10K - 25K, high temperature 40K - 50K. n 90/70 °C, 80/60°C, 75/55°C, 55/45°C


Temperature Parameters Design

n Emitter n Maximal surface temperature (85 - 90°C)

n Temperature differencen Two-pipe = system temperature difference (15 - 25

K) n one-pipe < system temperature difference OS (5 -

10 K)


Piping materials

n The material should be selected at the beginning of the design process

n Used materialsn steeln coppern plastic


Piping materialsSteel

n Traditional materialn Welding, flanges


Piping materialCopper

n Lower material usagen Chemical reaction with water pH min7n Electrochemical corrosion (Al)n soldering , torch brazing


Piping materialPlastic

• Materials• Netted polyethylene (PEX, VPE),• polybuten (polybutylen, polybuten-1,PB),• polypropylen (PP-R, PP-RC,PP-3),• Chlorided PVC (C-PVC, PVC-C)• Multilayer pipes with metal

n Life-cycle !!!n Oxygen barierre ?

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Heating systemhydraulic calculation

Heating systemhydraulic calculation

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Calculation

n Temp difference setupn Transferred outputn Circulation moden Hydraulic scheme,

sections, circuitsn Water flow rate

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Design of the pipe diameter

n Forced circulationn method economical specific pressure loss

60 - 200 Pa.m-1

n method optimal velocityn 0,05 - 1,0 m.s-1 (!!! Noise)

– method given pressure differencen buoyancy + pump headn 10-70 kPa

n Natural circulation– method given pressure difference

n buoyancy

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Pressure loss calculationn Pressure lossn frictionn local resistance

n Pressure loss of the circuit compare with the pump head

nPressure excess is reduced by the control valves

nPressure lack – must be changed the pump or redesigned the system

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n boiler plantsn combustion process in the

boilers

n heat-exchanger plantsn district heating

n renewable sourcesn utilization of solar, wind,

geothermal energy, co-generation, heat pumps

Heat sources


Boiler plants classificationn Fuel

n solid, gas, liquid

n Burnern atmosphericn pressurized

n Operating temperature

n steam n hot watern low temperature -

condensing boilers



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District heating


Boiler plants classificationn Output

n I.category n >3500 kW

n II.categoryn >500 <3500 kW

n III.categoryn >50 <500 kW


Boiler rooms function

n Fuel supplyn solid, liquid, gas (natural x propane)

n Heat distributionn heatingn hot water generationn air-condition heatern technology


n Safety devicesn Expansion vessel, pressure relief valves

n Control of the boiler outputn Electronic control

n Requirements to the building constructionn Supports of the piping, foundation below heavy

elements (hw tanks, boiler)

n Operation




n Air supplyn combustionn ventilationn heat gains removal

n Air outletn ventilationn heat gains removal

n Waste gases removaln atmosphericn pressurizedn “turbo” boilers


District heating

n Heat sourcen Distribution networkn Transfer plantn Heating system

Heat source

DistributionPrimary network

DistributionSecondary network

Transfer plant


Distribution network

n ductn ductlessn collectorn surface

a) b) c) d)


Heat exchangersn Tubular n U-tubesn Kit

n Platen sealed and screwedn soldered


Heat transfer plantn Pressure dependent, water-water


Heat transfer plantn Pressure independent - water - water

Consumer network

Heat exchager

Secondary network

manifold

Safety and expansion device


Heat transfer plantn Pressure dependent - steam - steam

Condensate meter

Secondary network manifold

Reduction valve

Condensate tank

Repumping of the condensate

Steam trap

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Example of heat transfer plant water-water

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Example of transfer plant


Electric energy - utilisation

n Direct heatingn Infra red heatersn radiatorsn Convectors, warm air

heatingn Radiant heating

n panelsn curtainsn sheetsn cables

n Warm water (electric boiler)

n Storage heatingn Off-peak storage

n staticn dynamicn hybrid

n warmwater (boiler)n Resistant cables

Appliances



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HeatingRenewable heat sources


Electric energy – productionSituation in CZ•70% coal 7,5 GW tj cca 51 000 ton of coal daily, •18% water 1,8 GW•17% nuclear 1,7 (2,7) GW 47,6 ton uranium anually (130 kg daily)•0,5 % other (wind, solar)


Biomass

² wood² wood residue² straw


Biomass sources

v Cultivation

v Waste product


Manufactured biomass

ØBriquettes

ØPellets

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Fuel value

vWood 16 MJ/kg

v Briquettes, Pelets 19 MJ/kg

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Biomassv Renewable sourcev Local source – not related to

global politicsv Balanced production CO2 – no

greenhouse effect

• Water content – fuel value• Fuel storage• Ash• Lower operation comfort


Biomass combustion boiler - gasification


Scheme of gasification boiler connection


Pellets boiler

n = gasification boiler + fuel storage + screw conveyor


Pellets transport - pneumatic


Pellets delivery


Pellets transport

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Solar energyn SUN – sky move

n Difusse and direct radiation

n Solar constant 1360 W/m2

n Clouds

n Real radiation max 1000 W/m2

Global radiation ČR [MJ . m-2 .a]


Renewable heat sourcesn Solar Energyn Passive Systems

n solar windown greenhousen accumulation wall


Renewable heat sourcesn Solar architecturen location in the countryn building plann thermal insulationn balanced accumulation of the structuren additional heating systemn minimizing of heat gains in summer by

shading


Renewable heat sourcesn Active solar systemsn Thermal solar systemn water, air collectors

Water solar system

• Direct• Undirect

• Natural • Forced close

Water solar system

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Renewable heat sourcesn Active solar systemsn Photovoltaics cells

Cell Panel Field


Renewable heat sources

n Grid-onn Grid-off

Inverter Appliance

Appliance


Renewable heat sourcesGeothermal energy - Heat pumpsn Evaporator, compressor,

condenser, reducing valven Evaporator

n air, water, soil

n Condensatorn low temperature heating, hot

water, swimming pool

n Efficiency -n Output/Input= avg.2,4

http://www.geoexchange.org/frames/case_studies.htm

Energy ofenvironment

Utilisation: heating, hot water

Compressor

Medium vapour

Compressed hot vapour

Liquid mediumCooled medium

Evaporator

Condenser

Reducing

valve


Heat pumps - alternatives of heat sources


Combined heat and power generation (CHP)

n gas engine with el.powergenerator

n cooling of the engine is the heat source

n output e.g. 42 kW heat 25 kW electric

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Fuel CellsIn principle, a fuel cell operates

like a battery. Unlike a battery, a fuel cell does not run down or require recharging. It will produce energy in the form of electricity and heat as long as fuel is supplied.

A fuel cell consists of two electrodes sandwiched around an electrolyte. Oxygen passes over one electrode and hydrogen over the other, generating electricity, water and heat.

n http://www.esru.strath.ac.uk/EandE/Web_sites/00-01/fuel_cells/

Michal Kabrhel

Wind energy

Wind energyn Wind+building

Geothermal energy

Documents

Heating systems mk tisk - cvut.cz