Towards near zero energy buildings New developments in Earth …€¦ · Tin=T0sin(ωt) − = − cm Sk t Sh Tout T & 0exp sin ω •Phase-shifting usually secondary •Heat penetration

Towards near zero energy buildings

New developments in Earth Air Tunnel Systems

Pierre Hollmuller

[email protected]

Green Building Congress

New Delhi, 20 – 21 October 2011

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extrêmes journaliers

32°C

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Summer

-8°C

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16°C

Winter

Operating mode

Hollmuller, Université de Genève

Day / Night

Winter / Summer

Principle: use thermal inertia of ground (heat storage)

Objective: dampening of daily / yearly temperature oscillation carried by ventilation

Operating mode


Heat storage versus Heat exchange

Heat exchange with soil /surface (recharge + perturbation)

Heat storage (dampening of oscillation)

Winter / Night Summer / Day

Focus of this presentation:

• Heat storage

• Large systems

Operating mode

www.maison-bioclimatique.fr

D.Pahud, SUPSI

www.batirbio.org

• Vertical setup

• Depth : 5 à 200 m

• Soil temperature : stable (year ambient

average)

• Risk of long term drift (discharge)

• Horizontal setup

• Depth : 50 cm à 3 m

• Soil temperature subject to seasonal/daily

variations

• Long term operation granted (upper climate)

• Closed loop (water) + heat pump

• Summer/winter operation : strong link

• Open loop (air)

• Summer/winter operation +/- independent

(cf. dimensioning guidelines)

Air/soil heat exchangers (buried pipes) Geothermal boreholes


Aymon building (Sion)

Case studies : potentials and constraints

Lessons

• Delocalization of thermal mass

• Cut-off of day/night oscillation + over-

ventilation = important cooling effect

• Robustness of simple solutions

(reproducibility / optimization)

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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)


Cité solaire (Plan-les-Ouates / Genève)

Lessons

• Buried pipes in competition with

recovery on exhaust air

• Important cost for little preheating

(see dimensionning rules)



www.unige.ch/cuepe/html/biblio/detail.php?id=288

Schwerzenbacherhof (Zurich)



Lessons

• Cooling by overventilation

• Water infiltration/evaporation ?

• Thermal link with with building

B

E

D

C

A

Eintritt

Austritt

0 5 10 15 20 25 30m

Perret building (Satigny / Genève)

terrain

local technique / bâtiment

échangeur eau/sol échangeur air/sol

récupérateur air vicié

humidificateur

chauffage

éch. air/ eau filtre

Lessons

• Energetic loss due to link between

building and buried pipes

(non-symetric summer/winter

behaviour)

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

°C

météo éch. air/eau/sol bâtiment






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

Geoser (Conthey/Sion)

Lessons

• Importance of auxiliary electricity

• Importance of global energy balance

• Potential water condensation/evaporation


Cooling vs Preheating


Winter / summer constraints (Continental Europe)

Winter

• seasonal constraint

Summer

• daily constraint

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°C météo min/max

comfort min/max

Cooling vs Preheating

Dampening of yearly oscillation

(necessary for preheating)

Dampening of daily oscillation

(sufficient for cooling)


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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

=> dimensionning guidelines

Objective

• reduce winter heat loss (pre-

heating)

• airflow set to minimum

Objective

• produce summer cooling

• airflow: possible over-ventilation

• winter: avoid icing of heat

recovery system

System integration / Overall energy balance


Preheating

Negative synergy

• Interaction with heat recovery:

Net gain = (1- η) x Gain brut

η : efficiency of heat recovery

• Interaction with building:

increased heat diffusion

Example of " Perret “ system

Heat recov. only (η =50%) 3.1 MWh

Pipe + rec. – ∆diffusion 2.1 + 2.1 – 1.6 = 2.6 MWh

Net loss (!) -0.5 MWh

2°C

-8°C

22°C

12°C

-8°C

10°C

4°C

22°C

16°C


System integration / Overall energy balance


Cooling

• Daily dampening

=> Possibility of enhanced ventilation 24/24h

(“night ventilation all day long”)

• Enhanced ventilation:

=> Larger storage (see dim. guidelines)

=> care with electricity

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m3/hC

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m3/hC

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h

Sta

nd

ard

ve

nti

lati

on

Nig

ht

ve

nti

lati

on

Bu

rie

d P

ipe

outdoor (C) ventilation (C) building (C) airf low (m3/h)


Dimensioning guidelines

0r

0R

0R∆

πδ

aT=

r0

0

0

0

=∂

=

Rsr

Rs

T

ou

T

sh

ah

xaacm ,&aT

sss c ρλ ,,sT

)cos(00 tT xa ωθ==

00θ=

=xaT

ou

stsrsrs TTr

Ta ∂=

∂+∂12

( )arrsaata

axaa TThrTv

Tmc −=

∂+∂

= 002

1π&

( )arrsarrsrs TThT −=∂ == 00λ

Analytical model in cylindrical symmetry


• Objective: characterisation of

storage/dampening

• Limitation : perturbation from upper

surface not taken into account !




Main results (without perturbation from upper surface)

• Dampening and phase-shifting of

harmonic input :

( )tTTin ωsin0=

−

−=mc

Skt

mc

ShTTout

&&ωsinexp0

• Phase-shifting usually secondary

• Heat penetration depth depends on

period :

πτ

ρλ

δc

=~ 3 m in yearly mode

~ 15 cm in daily mode

• Dampening given by serial link between

convective and diffusive exchange :

sa

sa

hh

hhh

+≈ ( )δ

δλ

≥

+

≈ 0

0

0

if

1ln

R

rr

hs

hs

ha

δ


Dampening of yearly oscillation

(necessary for preheating)


(sufficient for cooling)


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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

Perturbation annuelle

Perturbation

journalière

Perturbation annuelle

Perturbation journalièr

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airf low [m3/h.pipe]

pipe length [m]

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airf low [m3/h.pipe]

pipe length [m]

10 cm 15 cm 20 cm 25 cm 30 cm 35 cm 40 cmdiamètre



Pre-dimensioning tool (without perturbation from upper surface)


nombre de fréquences : 2

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Input:

• Meteorological data

• Airflow

• Pipe : diameter + length

• Soil cylinder : diameter

Numerical simulation / Sensibility studies

• Influence of surface + surrounding soil

• Condensation/evaporation

• Variable airflow

• Inhomogeneous soils

• Integration in TRNSYS

Meteo Meteo

Tube Soil 1

Soil 2

z

y

Building

Plat

Psbl

Pdiff

Pdiff Pdiff

Pdiff

convm&

convm&

soil airflow

tube and water saturated air


Detailed simulation tool


Numerical simulation

Algorithm (at pipe node)

Plat

Psbl

Pdiff

Pdiff Pdiff

Pdiff

co nvm& convm&

( )

air

tub

tubairair

sblconv

c

hS

TTc

Pm

⋅=

−⋅=& ( )

( )air

tubtubair

convtubairlat

c

hSWW

mWWm

⋅⋅−=

⋅−= && P c mlat lat lat= ⋅ &

• Latent heat

( ) ( )P S k T T S k T Tdiff i i soil i t tubi soil

i i tub i t tubi tube

= ⋅ ⋅ − + ⋅ ⋅ −−∈

−∈

∑ ∑, , , ,1 1

• Heat diffusion

( ) ( )P

c V c m T T

tinttub tub tub wat wat t tub tub t

=⋅ ⋅ + ⋅ ⋅ −− −ρ , ,1 1

∆

• Heat storage

( )P P P Pint sbl lat diff− + + = 0• Energy balance

• Sensible heat

( )P S h T Tsbl tub air tub= ⋅ ⋅ −


Validation against extensive in-situ monitoring

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kW

discharge

charge

sensible

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evaporation

condensation latent

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w eek

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discharge

charge sensible

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week

kWh

evaporation

condensation latent



Validation against analytical solution



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°Cair : 200 kg/h

soil : 2 m

tube : 50 m

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analytical [°C]

numérical [°C]

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°Cair : 200 kg/h

soil : 0.4 m

tube : 50 m

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analytical [°C]

numérical [°C]

Dampening of annual oscillation




Phase-shifting !!

Lab prototypes (for daily oscillation)

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°Cair : 200 kg/h

soil : 0.6 m

tube : 400 m

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analytical [°C]

numérical [°C]


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C input

output

Conclusions

Analysis of buried pipe systems taking into account :

• daily versus yearly heat effects

• integration in building and technical system

• global energy balance

Main insights (European continental climates):

• preheating: marginal interest (competition with heat recovery)

• cooling: interesting potential (with compact geometry + over-ventilation)


Development of a new system

Dimensioning tools:

• guidelines and pre-dimensioning tool

• detailed simulation tool

Documents

Towards near zero energy buildings New developments in Earth …€¦ · Tin=T0sin(ωt) − = − cm Sk t Sh Tout T & 0exp sin ω •Phase-shifting usually secondary •Heat penetration