PASSIVE HEATING ANALYSIS

Transcription

1 PASSIVE HEATING ANALYSIS Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 1 Passive Heating System Performance Measures Efficiency (= output / input) is an applicable measure, but it is not particularly relevant since the input is free SSF (solar savings fraction) is the most commonly used performance indicator See the Passive Solar Design Handbook for full information (Los Alamos, ASES, and ASHRAE have all published this resource) or consult your textbook (MEEB) for summary information Change in annual energy consumption due to passive solar features (pretty much a trial-and-error process) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 2

2 Basis of the SSF Method The Passive Solar Design Handbook draws upon research results which are presented using a correlational approach with a few key indicators (LCR and SSF) and many sensitivity charts. The underlying research used simulations, test cells, and some full-scale validations. Amazingly, not much substantive research to support revised or enhanced design analysis methods has been conducted in the past 30 years. Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 3 Solar Savings Fraction (SSF) SSF = (reference building active heating* solar building active heating) (reference building active heating) Note 1: a solar building may use more total heating energy than a reference (non-solar) building due to envelope design decisions Note 2: the solar building active heating referred to is that provided by a backup system * heating, above, denotes annual heating requirements (Btu or kwh) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 4

3 Example of SSF SSF = (reference building active heating solar building active heating) (reference building active heating) Assuming a reference (non-solar) building would use 70 units of heat and if redesigned as a solar-heated building would use only 25 units of active heat the SSF is (70-25)/70 = 64 from an energy perspective, the higher the SSF the better Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 5 Using the SSF Method as a Rough Estimating Tool (in early design) Estimating appropriate solar glazing area as a function of nighttime treatment of glazing (standard or superior) and desired SSF (low or high) Example: in Flint, MI, a 15% solar glazing area would provide a SSF of 11 with standard glazing; while the highest reasonably obtainable SSF in this location is 62. Mechanical and Electrical Equipment for Buildings, 11 th ed. Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 6

4 Using the SSF Method as a Performance Predicting Tool (refining design) one variation of water wall, showing key properties select system description and data that are most like the system you are designing Mechanical and Electrical Equipment for Buildings, 11 th ed. Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 7 Using the SSF Method as a Performance Predicting Tool (further refining design) LCR = load to collector ratio (Btu/DD ft 2 ) find predicted system performance (SSF) as a function of site location, system type, and LCR literally, the ratio of heating load to aperture size Mechanical and Electrical Equipment for Buildings, 11 th ed. Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 8

5 SSF Method: Tweaking System Characteristics with Sensitivity Curves these charts show the sensitivity of system performance to variations in thermal mass thickness (this is one example of available sensitivity data) all else equal: the required mass/glazing ratio increases with increasing LCR Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 9 SSF Method: Sensitivity LCR = load to collector ratio these charts show sensitivity of predicted system performance (SSF) to variations in solar absorptance of thermal mass for two different cities Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 10

6 Picturing LCR, Distribution, Delivery load collector LCR = x LCR < x LCR > x delivery distribution Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 11 Direct Gain System Concept a fairly powerful, quickly changeable energy resource * occupants are in heat collection area * occupants are seeking thermal comfort, perhaps privacy, perhaps a view Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 12

7 Direct Gain Examples Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 13 Indirect Gain System Concept occupants are adjacent to heat collection area Trombe wall or water wall heat collection occupants roof pond has different view/privacy characteristics * occupants are potentially buffered from heat source and exterior environment Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 14

8 Trombe Wall Examples earth sheltered passive solar house in MO; Trombe walls are the taller dark rectangles on facade Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 15 Water Wall Examples variations on a theme the more transparency, the more daylighting and the less indirect heating Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 16

9 Water Wall with Night Insulation styrofoam beads blown between two glass layers = nighttime insulation OPEC-chic, with recycled material and LEED design innovation credits? Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 17 Roof Pond collect retain and deliver Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 18

10 Roof Pond Example Atascadero House (CA) by Harold Hay; roof open on left and closed on right Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 19 Roof Pond Example Atascadero House (CA) by Harold Hay; note exposed structure-ceiling on left and load bearing masonry (more thermal mass) walls on right and left Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 20

11 Isolated Gain System Concept sunspace thermosyphon occupants are in the vicinity of the heat collection area heat collection occupants * occupants may be quite buffered from heat source and exterior environment Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 21 Sunspace Not Greenhouse more than just semantics, it is about basic intent on a cold night will you let the plants die to pull more heat from the collection space, or will you add heat to the collection space in order to maintain the plants? Is the space a heat source or a heat sink? horizontal aperture asset or liability? Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 22

12 Sunspace Example Atlanta, GA; left is North façade (reduce heat losses); right is South façade (open up to accept solar resource) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 23 Sunspace Example direct gain to left and sunspace to right; note fixed shading over most apertures and rolled-up shade cloth above sloped glazing Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 24

13 Thermosiphon and Sunspace Santa Fe, NM; thermosiphon (isolated gain) to left; sunspace to right; thermosiphon involves a collector area placed some distance from heated space Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 25 Passive, Direct Gain Domestic Water Heating Lucite meets Pueblo Culture somewhere near Santa Fe, NM Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 26

14 Simulating Passive Heating Performance One example: HEED (Home Energy Efficient Design) developed at UCLA free software Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 27 HEED and Passive Solar Heating passive solar heating is not an explicit design strategy Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 28

15 HEED and Passive Solar Heating but, cool graphic outputs allow investigation of various design moves high-mass walls Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 29 HEED and Passive Solar Heating graphic outputs allow investigation of various design moves effects of specific elements Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 30

16 HEED and Passive Solar Heating graphic outputs allow investigation of various design moves effects of south glazing, shading, and mass Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 31 HEED and Passive Solar Heating graphic outputs allow investigation of various design moves annual cooling performance (looking ahead to passive cooling) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 32

17 Balance Point Temperature (a reminder) The outdoor air temperature at which a building needs no heating to maintain thermal balance Is a function of envelope design and internal loads Historically this was assumed to be 65 F thus the commonly encountered HDD 65 value Temperatures below the balance point constitute the underheated period where heat must be provided to maintain thermal comfort Well-insulated houses (or commercial spaces with internal loads) may have balance point temperatures of 50, 40, 30 deg Non-residential buildings tend to have lower balance point temperatures; remember this when considering the potential of a passive heating or cooling system Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 33 Building Thermal Classifications (a reminder) Envelope-load dominated building The majority of loads are the result of climate (interacting with occupants through the envelope) Design focus should be on the envelope Very good candidate for a passive heating system Internal-load dominated building The majority of loads are the result of internal gains (lighting, people, plug loads) Design focus should be on reducing manageable internal gains (lighting, plug loads) Often there is little need for a passive heating system in these buildings Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 34