A Basic Ventilation Concept: People Cooling versus Structural Cooling

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1 PASSIVE COOLING ANALYSIS an example of CFD (computational fluid dynamics) analysis results Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 1 A Basic Ventilation Concept: People Cooling versus Structural Cooling B A airflow along path A may reduce space air temperature and remove heat from room surfaces; airflow along path B may do roughly the same PLUS make the occupant feel cooler by increasing convective and evaporative heat losses from the body understand design intent and identify design potentials Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 2 1

2 cross ventilation People Cooling versus Structural Cooling window window two inlet window locations (low and high) that will have different impacts on human thermal comfort, but roughly the same impact on building heat flows human figure from building from Islandwood Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 3 Predicting Passive Cooling System Performance Cooling capacity (both required and estimated) is generally expressed as Btu/hour (or Btu/h per sq ft) In my opinion, methodologies (for both design and analysis) are not well developed Analysis (performance prediction) methods are specific to each passive cooling system type Empirical (correlational) methods and simulations are available to predict performance Scale models (using smoke in air or dye or bubbles in water) have been used for ventilation analysis Whole-building energy simulation software may handle a range of passive cooling strategies, but such effects are usually bundled in an overall outcome Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 4 2

3 As you Design, Stay Rational is this the prevailing wind direction?? or is this the prevailing wind direction?? magic arrows analysis; physics will always trump the arrows Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 5 The Rational pos this works as a pure stack effect design scheme (see relative pressure indicators) pos pos??? pos neg neg neg neg neg this is questionable as a mixed stack/cross effect design scheme (see relative pressure indicators) pressure difference drives airflow Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 6 3

4 Ventilation Performance Visualization the figure captions provide interpretations of effects that then lead to patterns for design Olgyay: Design with Climate Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 7 Ventilation Performance Visualization Olgyay: Design with Climate Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 8 4

5 Cross Ventilation Site Analysis a site analysis does not just describe; it makes a value judgment from Climate Consultant month-by-month data plots is there a good, bad, or so-so heat sink potential? in the months when cooling matters Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 9 Cross Ventilation Site Analysis a site analysis does not just describe; it makes a value judgment from Climate Consultant annual data plots with someone s interpretation the hours within the green box are deemed OK for natural ventilation Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 10 5

6 Cross Ventilation Site Analysis The analysis resulting from this diagram suggests that in this climate, for a project with a 70 deg F balance point temperature passive cooling (stack or cross) will be of use for thermal comfort for only a very few hours in a typical year from Climate Consultant natural ventilation effectiveness zone Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 11 Cross Ventilation Site Analysis a site analysis does not just describe; it makes a value judgment from Climate Consultant one-month wind rose reasonable air temperatures, decent air speeds, no prevailing wind direction Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 12 6

7 Cross Ventilation Site Analysis a site analysis does not just describe; it makes a value judgment from Climate Consultant one-month wind rose decent wind speeds, but with high air temps prevailing winds, decent speeds, low temps Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 13 Cross Ventilation Site Analysis a site analysis does not just describe; it makes a value judgment pretty good, but inconsistent, air speeds during summer months from Climate Consultant 2-D wind speed plot Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 14 7

8 Cross Ventilation Site Analysis a site analysis does not just describe; it makes a value judgment from Climate Consultant no clear pattern for summer afternoon air speeds is evident (speeds seem random) 3-D wind speed plot Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 15 cooling capacity ( answer ) Cross Ventilation Performance Estimation wind speed (climate variable) The Green Studio Handbook this estimating tool quantifies the intuitive the larger the opening and faster the wind the greater the cooling inlet area ratio (design variable) similar to solar LCR concept based upon a 3 deg F delta t so if outdoor air is 85, indoor space will be 88 Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 16 8

9 Stack Ventilation Performance Estimation The Green Studio Handbook cooling capacity ( answer ) stack height(design variable) this estimating tool quantifies the intuitive the larger the opening and taller the stack the greater the cooling stack area ratio (design variable) based upon a 3 deg F delta t so if outdoor air is 72, indoor space will be 75 Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 17 Passive Cooling System Performance Prediction Schematic design phase performance estimating methods generally similar to those for cross ventilation and stack ventilation (presented directly above) are available for most passive cooling systems; see: Mechanical and Electrical Equipment for Buildings, 12 th edition The Green Studio Handbook, 2 nd edition Sun, Wind & Light, 3rd edition Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 18 9

10 Simulating Passive Cooling System Performance one simulation example: HEED (Home Energy Efficient Design) developed at UCLA; free software Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 19 HEED and Passive Cooling passive cooling is not an explicit design strategy Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 20 10

11 HEED and Passive Cooling but, intriguing graphic outputs allow investigation of various design moves high-mass walls Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 21 Other Passive Cooling Simulations a customized simulation analysis was developed for the earth tube system on the Aldo Leopold Center project illustration courtesy of Mike Utzinger Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 22 11

12 Some Thoughts on Passive Cooling Systems Cooling is a major energy consumer (and CO2 producer) in non-residential buildings Even high-efficiency active cooling systems consume non-renewable fuels and produce carbon emissions, so there is a clear rationale and role for passive cooling systems in high-performance buildings There are a number of passive cooling options but all suffer the same weakness, their capacity is least when the demand for cooling is greatest (there is almost always an inverse relationship between heat sink availability and cooling load magnitude) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 23 Mixed Mode Cooling The term mixed mode refers to a combination of passive and active cooling systems within the same building The mixing may be spatial (one room on passive and another room on active) The mixing may be temporal (active at one time and passive at another) The mixing should never be coincident (the two systems will fight each other) Successful operation of mixed mode systems is problematic and requires serious design team brainstorming but this approach is still worthy of consideration as a means of reducing active cooling systems use Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 24 12

13 Measured Green Roof Performance: Summer one day Seattle, WA soil mass (thermal capacitance) has a substantial effect in dampening the daily sol-air temperature excursions experienced by the roof Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 25 Measured Green Roof Performance: Winter one day Seattle, WA soil mass (thermal capacitance) has little effect on roof temperatures since there is very little solar effect and temperatures are fairly stable across time Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 26 13

14 think it through; clearly and rationally; put more science and less magic into the arrows Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 27 Cross Ventilation student project upper floor fairly easy (open plan) lower floor not so easy (no outlet Cross Ventilation library project scale makes air flow more of a challenge (the arrows become more magical) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 28 14

15 Stack Ventilation, Queen s Building, DeMontfort University, UK Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 29 Stack Ventilation BedZed, London, UK rotating stack cowls Stack Ventilation BRE, Gaston, UK stair stacks Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 30 15