PASSIVE COOLING STRATEGIES. Passive Cooling

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1 PASSIVE COOLING STRATEGIES fact or fiction: does saying it s so with arrows make it so? Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 1 Passive Cooling Before refrigeration technology first appeared, people kept cool using natural methods: breezes flowing through windows, water evaporating from trees and fountains as well as large amounts of stone and earth absorbing daytime heat. These ideas were developed over thousands of years as an integral part of all building designs. Today this is called passive cooling and, ironically, is considered an 'alternative technology', as if untried and untested compared with reliable and robust mechanical cooling that requires complicated refrigeration systems. Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 2 1

2 Reminder: A Passive System Uses no purchased energy Involves components that perform multiple tasks (view, daylight, airflow, ) Is highly integrated into the overall building fabric (it is not a plug-and-play device) Is most likely designed as an architectural (versus mechanical) system Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 3 While, An Active System Uses purchased energy Employs system components that are typically specialized and single-purpose Is often loosely inserted into or lightly attached to the larger building context/fabric Is most likely designed as a mechanical or electrical system by a consultant Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 4 2

3 Cooling Cooling is the process of reducing the temperature (and perhaps the moisture content) of something Sensible cooling is possible Latent cooling is possible Both are typically necessary for thermal comfort Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 5 Cooling System Components Heat sink a place to which heat from a building can flow Coolth distribution means for moving coolth around a building Coolth delivery means for moving coolth around a room or occupant Controls in order to match needs with resources these basic elements will be found in both active and passive cooling systems Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 6 3

4 A Passive Heat Sink is a place to which heat will flow naturally from the interior of a building during the overheated period in order to maintain thermally comfortable conditions air is heat sink 95 air is heat source 78 Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 7 Natural Heat Sinks Might include??? Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 8 4

5 Natural Heat Sinks outdoor air dry bulb temperature can be a heat sink or a heat source heat source period of need heat sink dry bulb temperature ranges and distribution images from Climate Consultant software Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 9 Natural Heat Sinks outdoor air wet bulb temperature can be a heat sink or a heat source (a sink for evaporative cooling) dry bulb temperature and RH images from Climate Consultant software wet bulb temperature Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 10 5

6 Natural Heat Sinks ground (soil) temperature can be a heat sink or a heat source, but is usually a sink in passive systems soil temperature image from Climate Consultant software Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 11 Natural Heat Sinks river, lake, sea, or ground water (temperature) can be a heat sink or a heat source, but usually a sink Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 12 6

7 Natural Heat Sinks night sky MRT NIGHT sky can be a heat sink (while DAYTIME sky with solar radiation is a heat source) sky cover image from Climate Consultant software Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 13 Natural Heat Sinks desiccants are always a heat sink (a latent sink) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 14 7

8 Connecting to Natural Heat Sinks Outdoor air dry bulb temperature via convection Outdoor air wet bulb temperature via evaporative cooling Ground/soil temperature via conduction/convection River, lake, sea, ground water temperature in the real world, this will be via a hybrid system Night sky MRT via radiation Desiccants via convection, for latent cooling Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 15 Passive Cooling Systems: Thermodynamic Classifications Convective loss systems Conductive loss systems Radiative loss systems Evaporative loss systems Multiple (hybrid) loss systems these classifications are a useful reminder of what is happening physically and will often be seen in textbooks, but Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 16 8

9 Passive Cooling Systems: Architectural Classifications Heat gain reduction <<< PASSIVE STARTS HERE! Direct loss Heat sink enters or is within the space Indirect loss There is a buffer between heat sink and space Isolated loss There is separation between heat sink and space these classifications are a useful reminder of what is happening relative to the building occupants (and mirror passive heating classifications) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 17 Heat Gain Reduction Systems These systems provide no coolth, but reduce the need for cooling (they reduce cooling load) Collectively, these are the first design moves in all successful passive cooling approaches Involve architectural strategies to reduce design cooling load (and all other hourly cooling loads) Examples include: insulation, air tightness, microclimate modification, shading, reflectivity, heat storage, increasing indoor air temperature and/or RH, and many others the term coolth signifies a negative flow of heat Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 18 9

10 Heat Gain Reduction Systems/Strategies vernacular house, Blue Springs, FL earth-bermed house, Ajo, AZ Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 19 Heat Gain Reduction Systems/Strategies Dune House (earth-sheltered), Atlantic Beach, FL, William Morgan Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 20 10

11 diagram by David Wright Direct Loss Systems specific system = cross ventilation; sink = outdoor air temperature A heat sink is brought into the occupied space Simplest system Cheapest system Hardest to control Privacy may be a concern Switches are often used as a means of control Distribution of coolth to all building spaces (compartmentation) is a design issue Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 21 Another Direct Loss Strategy diagram by David Wright combining evaporative cooling* with cross ventilation * see psychrometric slides later in this set of notes Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 22 11

12 A Palette of Direct Loss Strategies diagrams by David Wright Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 23 Example: Direct Loss System Logan House, Tampa Florida crossand stackventilation cross stack Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 24 12

13 POE of a Direct Loss System Logan House, Tampa Florida trying to measure cross ventilation air speed (quite hard to do) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 25 More POE Efforts Logan House, Tampa Florida still trying to map air flow Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 26 13

14 diagram by David Wright heat sink Indirect Loss Systems occupied space specific system = Trombe wall (stack induced ventilation) There are several indirect loss variants Here, a storage element acts as a buffer More complex, more expensive than direct loss systems More control options, more privacy than direct loss systems Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 27 Another Indirect Loss Strategy diagram by David Wright essentially a short-stack buffered ventilation system Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 28 14

15 A Palette of Indirect Loss Strategies diagrams by David Wright Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 29 Example: Indirect Loss System Visitor Center, Zion National Park, UT cool towers Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 30 15

16 What s this System Do? diagram by David Wright When would this act as an indirect loss system and when would it act as a heat gain reduction system? Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 31 Isolated Loss Systems Cool tube (or earth tube) is one example The heat sink is disengaged from the occupied space therefore allowing maximum control of system operation as a major attribute More complex, and more expensive, than direct or indirect loss systems Also, more control options, more privacy diagram by David Wright Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 32 16

17 Example: Isolated Loss System cool tubes residence, Alberta, Canada used to precool/preheat outdoor air Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 33 Example: Isolated Loss System cool tubes institutional building Baraboo, WI Aldo Leopold Center (image courtesy Mike Utzinger) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 34 17

18 Another Strategy: Nighttime Ventilation of Thermal Mass Emerald People s Utility District offices, Eugene, OR cool night air flows through thermally massive floor slabs and wall cavities Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 35 Vernacular Passive Cooling Strategies: Florida reflective roof overhang shading operable windows vegetative shading isolate internal loads (kitchen) external sitting space anti-cooling: ground decoupling Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 36 18

19 Vernacular Passive Cooling: South Carolina comfort??? beware of unbridled nostalgia Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 37 Passive Cooling Thoughts Viable heat sinks are usually diffuse resources (with high entropy, low potential) Broadly speaking, there is usually no one go to cooling resource (such as solar radiation provides for passive heating) Creativity and flexibility (and a strong dose of persistence) are valuable designer attributes when dealing with passive cooling Comfort (as we currently define/expect it today) may be an elusive outcome Even if passive cooling won t work at all times, every hour it can work reduces energy use Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 38 19

20 Psychrometric Processes evaporative cooling; a net-zero-energy (constant enthalpy) process Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 39 The Psychrometric Chart the evaporative cooling process enthalpy SOURCE: ASHRAE Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 40 20

21 Enthalpy Is a measure of the total energy content of air at a given condition Units = Btu per pound of air A derived property (not directly measured) Quantifies the energy cost of changing the condition of air (of undertaking a psychrometric process) evaporative cooling exchanges a Btu of sensible heat for a Btu of latent heat with no net change in enthalpy Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 41 While we re on Psychrometrics -- Dew Point Temperature The temperature of a surface or material that will cause condensation upon contact with air at some defined condition A derived property (not directly measurable) Units = deg F Critical to architectural design decisions (envelope design) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 42 21

22 Phoenix Central Library north façade shading and cool toplighting Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 43 Dilbert on DESIGN INTENT * Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 44 22