EAT Training Program Building Energy Efficiency Project New Delhi, 25 July 2013

Earth Air Tunnel: Principles, case studies, guidelines

Pierre Hollmuller

EAT principle

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32°C

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20°C

Summer

-8°C

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16°C

Winter

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35 °Cextrêmes journaliers moyenne journalière

extrêmes journaliers moyenne journalièredaily min/max

daily average

• Use of soil thermal inertia

• Reduction of temperature peaks carried by ventilation

Meteo: New Delhi Airflow: 2000 m3/h Diameter: 40 cm Length: 100 m Depth: 2 m

EAT principle

Typical hourly dynamic

EAT principle

Periodic charge / discharge

Winter and Night Summer and Day

EAT principle

Interaction with surface and between pipes

Winter and Night Summer and Day

Case studies

Aymon building (Sion)

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16.08 18.08 20.08 22.08 24.08 26.08 28.08 30.08 01.09

C Météo

Bureau, vent. par cave

Bureau, vent. nocturne (10 ach)

• Additional thermal mass

• Day/night oscillation cut-off + over-ventilation = important cooling effect

• Robustness of simple solutions (reproducibility / optimization)

Case studies

Cité solaire (Plan-les-Ouates)

• Buried pipes in competition with recovery on exhaust air (but avoids freezing of heat recovery unit)

• Important cost, little preheating (mainly daily effect)

Case studies

Schwerzenbacherhof (Zurich)

• Cooling by over-ventilating !

• Water infiltration/evaporation ?

• Thermal link with building

Background

Perret building (Satigny)

terrain

local technique / bâtiment

échangeur eau/sol échangeur air/sol

récupérateur air vicié

humidificateur

chauffage

éch. air/ eau filtre • Simple solution

• Bottle neck: air- water heat exchanger

• Energetic loss due to link between building and buried pipes

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sept oct nov déc janv févr mars avr mai juin juil août

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météo éch. air/eau/sol bâtiment

Background

Geoser project (Conthey/Sion)

Rejets

solaires

(3'422)

Ensoleillement

(4'722)

serre à air

Pertes par

enveloppe

(1'601)

Pertes par

enveloppe

(1'077)

Chauffage

(1'254)

Electricité

(46)

Captage

solaire

(192)

Captage

solaire

(1'300)

Diffusion

vers serre

(45 et 46)

Rejets

solaires

(40)

Stockage

(268)

Déstockage

(93)

Pertes vers sous-sol (128)

Ensoleillement

(232)

Evaporation (20) Condensation (36)

23.6 °C

1310 K.jour

16.9 °C

2129 K.jour

• Importance of auxiliary electricity

• Importance of global energy balance

• Potential water condensation/evaporation

Periodic heat charge / discharge

Analytical approach

0r

0R

0R

aT

r0

0

0

0

Rsr

Rs

T

ou

T

stsrsrs TTr

Ta

12

arrsaat

a

axaa TThrTv

Tmc

002

1

arrsarrsrs TThT 00

sh

ah

xaa cm ,aT

sss c ,,sT

)cos(00tT

xa

00

xaT

ou

• Objective: characterization of storage/dampening

• Limitation: cylindrical symmetry, constant airflow

Periodic heat charge / discharge

Main results (without perturbation from upper surface)

• Dampening and phase-shifting of harmonic input :

tTTin sin0

mc

Skt

mc

ShTTout

sinexp0

• Phase-shifting usualy secondary

• Heat penetration depth depends on period :

c

~ 3 m in yearly mode

~ 15 cm in daily mode

• Dampening given by serial link between convective and diffusive exchange :

sa

sa

hh

hhh

0

0

0

if

1ln

R

rr

hs

hs

ha

Periodic heat charge / discharge

Comparison with charge / discharge from free upper surface

zt

zTtzT cosexp),( 00

0

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Température [C]

Pro

fon

deu

r [m

] hiver

printemps

été

automne

W/K.m2 MJ/K.m3 2c

Typical heat penetration

a

ca

Penetration depth

Design guidelines

Geometrical configurations

Dampening of annual oscillation Dampening of daily oscillation

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°Cair : 200 kg/h

soil : 0.4 m

tube : 50 m

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°Cair : 200 kg/h

soil : 2 m

tube : 50 m

daily storage: ~ 20 cm

yearly storage: ~ 3 m

yearly storage: ~3m

daily storage: ~ 20 cm

Hypothesis: no interference from upper surface !

Design guidelines

Daily oscillation reduction (15% amplitude) Soil around pipe: ~20 cm

Nomographs for daily and annual amplitude reduction

Annual oscillation reduction (15% amplitude) Soil around pipe: ~260 cm

Dry soil (conductivity: 1.1 W/K.m, specific heat: 1.6 MJ/K.m3)

Design guidelines

Daily oscillation reduction (15% amplitude) Soil around pipe: ~20 cm

Nomographs for daily and annual amplitude reduction

Annual oscillation reduction (15% amplitude) Soil around pipe: ~260 cm

Dry soil (conductivity: 1.1 W/K.m, specific heat: 1.6 MJ/K.m3)

Design guidelines

Use of nomograph with other pipe length

Pipe length relatively to value from nomograph

Res

idu

al a

mp

litu

de

𝜃

𝜃0= 𝑒𝑥𝑝 −2

𝐿

𝐿0

𝜃0

𝜃

𝐿0

𝐿

Pipe length from nomograph

Half amplitude inlet

Pipe length

Half amplitude outlet

Design tools

Two complementary tools for design of EAT:

• EasyPipes Basic: pre-design

• EasyPipes Plus: detailed design

EasyPipes Basic: pre-design

hs

ha

• Analytical solution of heat charge and discharge around a pipe

• Excel integrated • Analysis in terms of annual and

daily frequencies

EasyPipes Plus: detailed design

• Numerical simulation algorithm • Excel interface to Trnsys simulation environment • Transient aiflow • Interference with upper surface and between the pipes • Water condensation/evaporation

Model validation

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°Cair : 200 kg/h

soil : 2 m

tube : 50 m

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analytical [°C]

num

érical [

°C]

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°Cair : 200 kg/h

soil : 0.4 m

tube : 50 m

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analytical [°C]

num

érical [

°C]

Dampening of annual oscillation

Dampening of daily oscillation

Numerical versus analytical model

Model validation

Numerical simulation versus monitoring (Schwerzenbacherhof)

Hourly dynamic over one week

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kW

dis

charg

echarg

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sensible

Weekly dynamic over one year

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0.51 monitoring simulation w ith infiltration simulation w ithout infiltration

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charg

echarg

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