Passive cooling techniques theory and practice

Passive cooling techniques theory and practice Thoughtful Cooling TOT Workshop on Cooling Interiors Efficiently and Sustainably Rachana Sansad, Mumbai 9 th January, 2015 Deepa Parekh Environmental Design Solutions Pvt. Ltd Delhi Mumbai Pune Bangalore Chennai New York

Energy efficient buildings are designed in response to sun and climate Passive cooling techniques 2

Buildings are designed to keep occupant comfortable Definition of thermal comfort parameters has an impact on energy efficiency Passive cooling techniques 3

India has a predominantly warm climate Hot dry cooling Hot humid cooling Composite cooling + heating Temperate cooling Cold heating Passive cooling techniques 4

Energy end-use in buildings in India BAU split up of Commercial end use BAU split up of Residential building energy use Others, 10% TV, 4% Others, 7% Air Conditioning, 31% Lighting, 59% Refrigerator, 13% Evap. Cooling, 4% Lighting, 30% Air Conditioning, 7% Fans, 35% Commercial buildings Residential buildings There is an estimated 30-50% energy savings potential in these buildings Passive cooling techniques 5

Patna Chennai 12% comfortable hours 2% comfortable hours Nagpur Jaipur 14% comfortable hours 15% comfortable hours Passive cooling techniques 6

Passive design might not help solve 100% of the problem, but it certainly will reduce the demand for energy consumption Passive cooling techniques 7

Key objectives in passive cooling 1Reduce demand for cooling Avoid overheating 2Reduce the energy required for cooling Integrate passive cooling techniques Passive cooling techniques 8

Room A vs Room B All Brick walls You need a 1 ton AC to cool the room COOLING LOAD = x All Glass You need a 3 ton AC to cool the room COOLING LOAD = 3x 9

Room A vs Room B Mr. A is using the AC for 5 hours a day Energy consumption = y Mr. B never shows up for work Energy consumption = 0 10

LOADS vs ENERGY Static As a result of DESIGN Loads for identical buildings in the same location will be the same Thus, it all depends on the DESIGN! Units: kw/sqm or sqft Dynamic As a result of USE Energy consumption for identical buildings in the same location can be different. Thus, it all depends on the USER! Units: kwh/sqm or sqft 11

Key objectives in passive cooling 1Reduce demand for cooling Avoid overheating 2Reduce the energy required for cooling Integrate passive cooling techniques Passive cooling techniques 12

Techniques to avoid overheating Objectives: 1Resist heat gain 2Promote heat loss Passive cooling techniques 13

Building bioclimatic chart Integrates architectural strategies with human comfort needs Passive cooling techniques 14

Building bioclimatic chart 15.7% comfortable hours Passive cooling techniques 15

Building bioclimatic chart 15.7% comfortable hours Add passive strategies shading High thermal mass Direct evaporative cooling Natural ventilation Internal heat gain 54.3% comfortable hours Passive cooling techniques 16

Techniques to avoid overheating 1Reduce heat gain 1Using thermal mass construction 2Reduce exposed surface 3Adding insulation Passive cooling techniques 17

Techniques to avoid overheating 1Reduce heat gain 4Form and orientation 5Reduce WWR 6Use shading devices 7Reduce heat gain through glazed areas 8Minimize heat gain around the building Passive cooling techniques 18

All these strategies do not cool, they reduce overheating.. they reduce cooling demand.. Passive cooling techniques 19

Passive cooling systems These transfer heat from the building to natural energy sinks, such as the air, water, earth or outer space. Implementation of these systems in buildings reduces energy needed for cooling. Passive cooling techniques 20

Bihar Museum, Patna Passive cooling techniques 21

Bihar Museum, Patna ASHRAE Std 55 Comfort Model For conditioned areas Adaptive Comfort Model For naturally ventilated areas Thus various design strategies will have to be combined within the premise of both comfort models to achieve thermal comfort with reduced systems loads in the building throughout the year. Passive cooling techniques 26

Passive cooling systems These transfer heat from the building to natural energy sinks, such as the air, water, earth or outer space. Implementation of these systems in buildings reduces energy needed for cooling. Passive cooling techniques 27

Nocturnal ventilative cooling Concept Night time cooling of the thermal mass that gets heated up in the day time Heat absorption of the thermal is more efficient during the day Passive cooling techniques 28

Stack ventilation -Natural ventilation strategy CONCEPT -Works on the principle of thermal buoyancy -Hot air rises through the stack drawing the cool air inducing the air movement Passive cooling techniques 29

Solar chimney CONCEPT Glazed or black colored surface on the stack increases solar heat gain and accelerates rise in temperature in the stack Passive cooling techniques 30

Earth tubes CONCEPT: -Ground temperatures at about 3 to 4m do not vary through the year -Earth is a very large heat sink and can be used to exchange heat Air intake Conditioned air supplied to buildings Heat exchange with earth Passive cooling techniques 31

Earth tubes Passive cooling techniques 32

French School, Damascus, Syria Climate responsive design - daylight - night cooling of thermal mass -natural ventilation -wind and solar supported chimney - ground heat exchanger Passive cooling techniques 33

French School, Damascus, Syria Passive cooling techniques 34

French School, Damascus, Syria Climate concept summer night Passive cooling techniques 35

French School, Damascus, Syria Climate concept winter day Passive cooling techniques 36

Miramar college police station, san diego, California Thermal chimney performance goals 1 Integrate with a whole building natural ventilation system (exterior windows, interior openings doors, grills, interior windows) 2 Meet minimum OA requirements during operation 3 Maintain comfort when outdoor air conditions permit 4 Don t exceed 160 fpm through openings 5 Provide mixed mode HVAC operation Passive cooling techniques 40

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Temperatures, Heat Gains and Energy Consumption - Miramar Police Station, Building 1 EnergyPlus Output 20 May - 27 May, Hourly Student Fuel (kbtu/h) 4 3 2 1 System Fans Heat Generation (Gas) 0 Air Temperature Radiant Temperature Operative Temperature Outside Dry-Bulb Temperature Temperature ( F) 70 60 50 Heat Balance (kbtu/h) System Energy (kbtu/h) 20 0-20 3 2 1 0 Glazing Walls Ceilings (int) Floors (int) Ground Floors Partitions (int) Roofs Doors and vents Internal Natural vent. External Air Occupancy Solar Gains Exterior Windows Zone/Sys Sensible Heating Zone/Sys Sensible Cooling Zone Heating Total fresh air (ac/h) 6 4 2 0 May 2002 Mech Vent + Nat Vent + Infiltration 21 Tue 22 Wed 23 Thu 24 Fri 25 Sat 26 Sun 27 Mon Time/Date Shoulder period - Whole Building Results NV maintains 1 to 6 ACH during occupied periods. Passive cooling techniques 44

Temperatures, Heat Gains and Energy Consumption - Miramar Police Station, Building 1 EnergyPlus Output 26 Aug - 2 Sep, Hourly Student System Fans Chiller (Electricity) Fuel (kbtu/h) 40 20 0 Air Temperature Radiant Temperature Operative Temperature Outside Dry-Bulb Temperature Temperature ( F) 90 80 70 60 Heat Balance (kbtu/h) 20 0-20 -40 Glazing Walls Ceilings (int) Floors (int) Ground Floors Partitions (int) Roofs Doors and vents Internal Natural vent. External Air Occupancy Solar Gains Exterior Windows Zone/Sys Sensible Heating Zone/Sys Sensible Cooling System Energy (kbtu/h) 0-20 -40-60 -80 Sensible Cooling Total Cooling Total fresh air (ac/h) 3 2 1 0 Aug 2002 Mech Vent + Nat Vent + Infiltration 27 Tue 28 Wed 29 Thu 30 Fri 31 Sat Sep 2 Mon Time/Date Summer period - Whole Building Results NV system maintains ACH above min OA requirements and typically provides 2 ACH. Passive cooling techniques 45

Airflow Results (7am to 6pm, Mon-Sat) Zone Summer Period (Aug 26 Sep 2) Winter Period (Jan 7-14) Shoulder Period (May 20 26) Max ACH Max Airspeed (fpm) Max ACH Max Airspeed (fpm) Max ACH Max Airspeed (fpm) 1.1 5.4 77 7.7 110 14.5 207 Kitchen 9.2 36 12.7 50 21.9 87 2.3 6 37 7.8 48 18.5 113 2.4 33.4 60 25 45 46.5 83 2.5 20.1 68 16.1 54 31.7 107 2.8 2.8 43 5.7 87 6.1 93 Maximum airspeeds are all acceptable (<160 fpm) for nearly all spaces so breeze is mostly imperceptible. Zone 1.1 rises slightly above this limit but should not negatively impact comfort (still < 300 fpm) Passive cooling techniques 46

Sizing the thermal chimney Passive cooling techniques 47

Wind tower/ wind catcher CONCEPT: -Aids comfort ventilation -Capture the natural breeze and direct it inside the buildings -the tower inlet is oriented towards the prevailing breezes -The air isn t necessary cooled but the circulation creates a fan-like condition Passive cooling techniques 48

Passive downdraught cooling CONCEPT: -Similar to wind catcher, but this is a cooling strategy -Water is sprinkled at the top of the tower -When air moves through the tower, the water droplets evaporate picking up the heat the air -Cool air falls down and enters the building Passive cooling techniques 49

Passive downdraught cooling Passive cooling techniques 51

Passive downdraught cooling Passive cooling techniques 52

Summary 1Focusing on reducing building loads is key to achieving energy efficiency 2This is very much a design issue! 3This should become a business as usual way of working 4Low energy cooling techniques combined with conscious usage is the key to reduce GHG emissions. Passive cooling techniques 53

Thank You Environmental Design Solutions Pvt. Ltd Delhi Mumbai Pune Bangalore Chennai New York Passive cooling techniques 54