Selected Passive Cooling Techniques Potentials and Constraints

Pierre Hollmuller

Energy Efficient Building Design: Experiences and Way Forward

Indo-Swiss Building Energy Efficiency Project (BEEP) New Delhi, 30 November 2016

Institut Forel / Institut des Sciences de l’Environnement

Energy Efficiency and Passive Cooling

Efficient building design / Prevention of heat loads • Microclimate and site design • Building form and layout • Solar control • Thermal insulation • Internal gain control • … Passive cooling / Heat dissipation with natural sinks • Night ventilation • Radiative cooling • Evaporative cooling • Earth coupling • Water source cooling (sea, lake, river) • … Efficient air-conditioning • Water cooling instead of air cooling • VAV air systems • Enthalpy recovery

Earth-Air Tunnels (EAT)

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35 °Cextrêmes journaliers moyenne journalière

extrêmes journaliers moyenne journalièredaily min/max

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• Use of soil thermal inertia

• Reduction of temperature peaks carried by ventilation

EAT Case Studies

Single family house (Morocco)

• Airflow: 750 – 930 m3/h • 3 pipes (length: 72 m, diameter: 15 cm, depth: 2.2 – 3.5 m) • Design factor: 1 m2 per 9 m3/h

EAT Case Studies

University building (India)

• Airflow: 30’000 m3/h (daytime) • 1 pipe (length: 100 m, diameter: 120 cm, depth: 4 m) • Design factor: 1 m2 per 80 m3/h • EAT + direct evaporative cooling (air washer within AHU)

EAT inlet

EAT outlet

Evaporative cooling

EAT Case Studies

Administrative building (Switzerland)

• Airflow: 12’000 - 18’000 m3/h (daytime) • 43 pipes (length: 23 m, diameter: 250 cm, depth: 0.75 cm

below basement) • Design factor: 1 m2 per 23 m3/h

• Pipe array below insulated basement (no interference with

solar radiation, nor with building)

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Design Guidelines

Reduction of daily oscillation • Soil : 20 - 30 cm around each pipe • Length: 10 - 20 m per 100 m3/h

Reduction of annual oscillation • Soil: 200 - 300 cm around each pipe • Length: 20 - 40 m per 100 m3/h

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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

Design Guidelines

Reduction of daily oscillation (15% amplitude) Soil around pipe: 20 - 30 cm

Nomographs for daily and annual amplitude reduction

Annual oscillation reduction (15% amplitude) Soil around pipe: 200 - 300 cm

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

Design Tools

Two complementary tools for the design of EAT:

• EasyPipes Basic: pre-design

• EasyPipes Plus: detailed design

Easypipes Basic: Pre-design

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• 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

EAT + Evaporative Cooling : Potential in New Delhi

EAT

EAT + Evaporative cooling

Evaporative cooling

GLN District Cooling Network (Geneva)

Source: Mary, SIG (2011)

Distribution network

Caractéristiques

Characteristics • Capacity: 18 MW (cooling), 13 MW (heating) • Flow rate : 2'700 m3/h • Network : 6 km • Pumping depth: 37 m

GLN District Cooling Network (Geneva)

Pumping

Resource temperature

GLN District Cooling Network (Geneva)

Demand profile (UNO building)

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Distribution (°C) Return (°C) Return – Distribution (K)

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Distribution temperatures (building)

GLN District Cooling Network (Geneva)

Conclusions

Passive cooling techniques: • diverse techniques / interesting potentials • low energy and maintenance cost • complementary with energy efficiency measures (building and AC system) Constraints: • temperature/enthalpy level of heat sink • investment cost Earth-air tunnels: • existing and validated design guidelines and tools • complement / competition with evaporative cooling (depending on location and period of the

year) • space constraints

Thank You !