Environmental Engineering Water based heating systemszmrhavla/EE/EE_Heating_2.pdf · Environmental...

transcript

3.11.2014

Ondrej.Hojer@fs.cvut.czEnvironmental Engineering

Environmental Engineering

Water based heating systems

Ing. Ondrej Hojer, Ph.D.

Fakulta strojníÚstav techniky prost ředí

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Heat sources

Fossil fuelsGas

Coal (Charcoal)Oil

Wood (Plants)

Electricity

Nuclear

SunGround

AirWater

Heat generator (transformer)

Boiler

Boiler, Heating coil

Turbine (waste heat)

Heat pump

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TABLE OF CONTENTS

• Pressure drop (Local and Friction)• Types of distribution heating systems• The neutral point• Control of the system

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PRESSURE DROP

A flow in pipe systems is associated with pressure losses. The total pressure drop consists of local pressure drop and friction p ressure drop.

FLt ppp ∆+∆=∆

∑ ⋅⋅=∆ ρζ2

ζ = local loss coefficient [-],w = flow velocity in a characteristic cross-section S [m/s],ρ = fluid density [kg/m3],

where ρ⋅=∆2

2wpd is dynamic (velocity) pressure.

Local pressure drop

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101000

ρρ ⋅

=∆⇒⋅

∆⋅=

Local pressure drop - Valve

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where f is the friction factor ε is average absolute roughness of the pipe [m]Re is Reynolds number

Colebrook equation

where ρ is the density of the fluidV is the average velocity in the pipef is the friction factor from the Moody chartl is the length of the piped is the pipe diameter.

Friction pressure drop

ρ⋅⋅⋅=∆2

where:d = inside diameter [m],w = velocity [m/s],ν = kinematic viscosity [m2/s], (at 70°C, 0,415.10-6 m2/s)

νdw ⋅=Re

Reynolds number

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Ondrej.Hojer@fs.cvut.czEnvironmental Engineering 23

20°C 20°C 20°C 20°C20°C

-12°C

h = 3m

-106- -105- -104- -103- -102-

-101-BB

Water based Heating System – Design of a Panel radia tor

1x flow chamber

1x metal lamellas layer

TYPE 11

2x flow chamber

TYPE 21

TYPE 22

2x flow chamber

Design of a Panel Radiator

10 up 15 cm

1000 mm

Panel radiatorPanel radiator

tw1 = 50 °C tw2 = 40 °C t i = 20 °C

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Nominal thermal output Q [W]

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The bigger the t w1 – tw2 difference the smaller c value

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20°C 20°C 20°C 20°C20°C

-12°C

h = 3m

-106- -105- -104- -103- -102-

-101-BB

Water based Heating System – Design of tube diameter s

Section L [m]

m [kg/h]

dopt[mm]

wREAL[m/s]

R [Pa/m]

DpF = R . L [Pa]

Z = r . w2 / 2[Pa]

DpL =Z . z[Pa]

wopt = 0.5 m/s friction local

Q = c . m . (t1-t2)[W] = [J/kg/K] . [kg/s] . [K]

Heat output mass flow

w = m / r / (p.d2/4)[m/s] = [kg/s] / [kg/m3] / [m2]

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FRICTION PRESSURE LOSSES – IRON TUBES

kg/hkg/h

Pa/mPa/m

m/sm/s

dimensions

roughness

LOCAL PRESSURE LOSSES – IRON TUBES

Main parts z [-]

Boiler cast iron 2.50

Boiler steel 2.00

Element radiator related to pipe DN 152.50

Panel radiator – 1 flow chamber related to pipe DN 158.50

Panel radiator – 2 and more flow chambers

related to pipe DN 1519.00

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sidewalk

by-pass

T-part sharp

T-partaskew - separation

T-partaskew - conjunction

Reduction - fluent

Reduction - fluentbroadening

Flange connection

Elbow - Bend

Collector

Distributorwith edges treatment

without edges treatmentwith radius edges

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Types of distribution heating systems

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According to the circulation of heat transfer medium• gravity heating systems• pump (forced) heating systems

According to the main-horizontal feed of heat transfer medi um• two-pipe down feed system• two-pipe up feed system

According to the circulation of heat transfer medium toward s heatingappliances• vertical heating system• horizontal heating system• stellate heating system

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Gravity heating systemsThe boiler is located at the lowest point in the system. The warm water has a lower density (it is lighter) than the cooled return water. Therefore, water in the system automatically starts circulate due to buoyant pressure. There is no need for a pump. As there is only a small differential pressure, wide-diameter pipes are required.

Pump (forced) heating systemsThe location of boilers and radiators is not important. Pressure losses are largely covered by pump pressure. Wide-diameter pipes are much smaller than by gravity systems.

Two-pipe down feed systemThis is the most common type of system. The flow and return main-horizontal pipes are routed under the ceiling of the cellar or basement. The radiators are connected to the vertical risers (max. two radiators to one riser in one floor).

Two-pipe up-feed systemIn this system the main-horizontal distribution pipe is above the level of the highest radiators. If circulating pump is used, both the flow pipe and the common return pipe can be located above the highest radiators.

Vertical heating systemThere is distribution with risers (vertical distribution pipes) and there must beconnected at most two radiators to one riser in one floor. The vertical system is themost common type of system at family houses and prefabs or apartment buildings.

Horizontal heating systemThere is distribution with minimal number of risers because the radiators areconnected on floor horizontal distribution pipes. Thus each apartment or each floorcan be fitted with its own heat meter.

Stellate heating systemThe riser is placed in the centre of disposition with distributor. Circuit of eachradiator is connected at the distributor. There are used pipe systems from plastics.

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Stellate heating system

According to the circulation of heat transfer medium• gravity heating systems• pump (forced) heating systems

According to the main-horizontal feed of heat transfer medi um• two-pipe down feed system• two-pipe up feed system

According to the circulation of heat transfer medium toward s heatingappliances• vertical heating system• horizontal heating system• stellate heating system• mixed heating system

According to the layout (supply and drain of heat transfer me dium toradiators)• two-pipe heating systems with counter-flow (normal) layout• two-pipe heating systems with concurrent-flow (Tichelmann; reversed return)layout•single-pipe heating systems without bypass of radiators (with four-way valves)•single-pipe heating systems with bypass of radiators (with riding connection)

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According to the contact with atmosphere• open vent heating systems• sealed (closed) heating systems

According to the material of a pipe system• pipe system from steel• pipe system from copper• pipe system from plastics (e.g. reticulate polyethylene PEX)• pipe system from multi-layer pipes

Mixed heating systemMixed heating system represents possibilities to combine one system to eachother. As for combination, mostly it is vertical heating system and horizontalheating system or two-pipe heating system with counter-flow layout andTichelmann two-pipe heating system.

Counter-flow system (two-pipe heating systems with counte r-flow layout)The return pipes have opposite flow than feed pipes. The length of radiatorcircuits is transformed in according to the distance of radiators in the system. Thepipe net must be hydraulically balanced. Each of parallel hydraulic circuit has tohave the same pressure loss with required mass flow.

Tichelmann system (two-pipe heating systems with co ncurrent-flow layout)The pipes are routed in such a way that the overall length of the radiators circuit is the same for each radiator. Hence, the same hydraulic pressure conditions apply to every radiator. Several boilers, risers or hot water storage tanks are connected in accordance with the Tichelmann layout. This method of connection is especially important with solar panels.

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Tichelmann connection systemStandard two-pipe connectionsystem

Single-pipe heating systems without bypass of radia tors (with four-way valves)Single-pipe heating systems with four-way valves have smaller transfer ability than systems with riding connection. The radiators can be connected in one or two points according to the kind of valves.

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Single-pipe heating systems with bypass of radiator s (with riding connection)These single-pipe systems consist of master pipe to which the radiators are connected with their flow (“feed”) and return in parallel. This enables the heating water to continue through the master pipe in circuit even if individual radiators are completely shut off. As with two-pipe systems, a single-pipe heating system can be constructed as a vertical or horizontal system. The vertical system was sometimes used in high-rise building.

Pump design

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http://www.jacpumps.com/pump_school_10.html

Dr. Lev Nelik. Buying a Bigger Pump May Bring Bigger Problems. Available online: http://www.pumpsandsystems.com/topics/pumps/buying-bigger-pump-may-bring-bigger-problems

Pump design

New Old

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Dr. Lev Nelik. Buying a Bigger Pump May Bring Bigger Problems. Available online: http://www.pumpsandsystems.com/topics/pumps/buying-bigger-pump-may-bring-bigger-problems

Pump design

New Old

THE NEUTRAL POINT

The position of the expansion vessel and circulating pump in a system defines pressure conditions. Low pressure – risk of air suction into the system. High pressure – risk of construction pressure of particular parts of heating system.

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Control valve – 2 way (quantitative control)

75 °C 75 °C

Boiler

panel radiator

65 °C65 °C

Control valve – 3 way (qualitative control)

75 °C70 °C

65 °C

Boiler

panel radiator

65 °C65 °C

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Control valve – possible connection variants

Control valve – possible pressure diagram

Overpressure diagram

System

Environmental Engineering Water based heating systemszmrhavla/EE/EE_Heating_2.pdf · Environmental...

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