PASSIVE HEATING ANALYSIS

Transcription

1 PASSIVE HEATING ANALYSIS Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 1 Passive Heating System Performance Measures Efficiency (= output / input): this is an applicable measure, but it is not particularly relevant since the input (solar radiation) 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 The change in annual energy consumption due to passive solar features: this is pretty much a trial-anderror process using energy simulation software Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 2 1

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 (passive+active) heating energy than a reference (non-solar) building due to envelope design decisions involving glazing Note 2: the solar building active heating referred to is that provided by a backup system Note 3: reference building refers to a design with no solar features; solar building refers to the same design with solar features (this reference comparison approach is also found in current code compliance and LEED credit analyses) * heating, above, denotes annual heating requirements (Btu or kwh) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 4 2

3 Example of SSF SSF = (reference building active heating solar building active heating) (reference building active heating) Assume a reference (non-solar) building would use 70 units of heat a year and would use only 25 units of active heat if redesigned as a solar-heated building then the SSF is (70-25)/70 = 0.64 from an energy perspective, the higher the SSF the better as long as thermal comfort expectations (OPR) are met 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 (with 31% glazing). Mechanical and Electrical Equipment for Buildings, 11 th ed. (Table G.1 in 12 th ed.) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 6 3

4 Using the SSF Method as a Performance Predicting Tool (refining design) one variation of water wall, showing key properties select the system description and data that are most like the system you are designing Mechanical and Electrical Equipment for Buildings, 11 th ed. (Table I.1 in 12th 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. (Table I.3 in 12th ed.) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 8 4

5 SSF Method: Tweaking System Characteristics with Sensitivity Curves LCR = load to collector ratio 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 necessary 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 all else equal: absorptance has a greater affect on systems with low LCR values than on systems with high LCR values Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 10 5

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 the heat collection system * occupants are seeking thermal comfort, perhaps privacy, perhaps a view Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 12 6

7 Direct Gain Examples Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 13 Indirect Gain System Concept occupants are adjacent to the heat collection system * heat collection occupants Trombe wall or water wall 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 7

8 Trombe Wall Examples earth sheltered passive solar house in MO; Trombe walls are the taller dark rectangles on façade (above the arrows) these are vented Trombe walls (see high and low rectangles in lower right photo) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 15 Water Wall Examples variations on a theme the more transparency, the more daylighting; and the more direct (less indirect) solar heating Kalwall water tubes with cloth inserts to adjust transparency Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 16 8

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

10 Roof Pond Example movable insulation water-filled bags Atascadero House (CA) by Harold Hay; roof open (collecting solar) in left photo and closed (retaining heat) in right photo Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 19 Roof Pond Example Atascadero House (CA) by Harold Hay; note exposed structure-ceiling (to facilitate heat transfer) in left photo and load bearing masonry walls (more thermal mass) in right and left photos Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 20 10

11 Isolated Gain System Concept sunspace or thermosyphon * occupants are in the vicinity of the heat collection system (as a result, heat distribution becomes a key design issue) 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 11

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

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 13

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 14

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 15

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 Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 32 16

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 dense internal loads) may have balance point temperatures of 50, 40, 30 deg F 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 Heating Degree Days (HDD) The heating degree day (HDD) is a mathematical construct that was developed to simplify energy analysis in pre-computer days. For a given 24-hour period, HDD = (base temperature daily average temperature) The most common base temperature is 65 deg F (which is a balance-point temperature). Cooling Degree Days (CDD) can also be calculated, but latent is not included Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 34 17

18 Heating Degree Days (HDD) code requirements based upon HDD talking about the weather construction has improved greatly since the HDD concept was first established (and linked to 65 deg F), yet HDD 65 still plays a useful role here and there Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 35 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 36 18