Wednesday, May 2, 2012

"Final" Blower door test and SolarPathfinder pictures

Today we conducted the post-construction blower door test for the PHIUS certification.  We did the test using the same doorway we had used in the past and found a reasonable .57 ACH at 50Pa for pressurization and an amazing .28 ACH at 50Pa for depressurization.  Because there was a significant difference in the two measurements we moved to another door (we thought there might be leakage around the blower door at the strike-plate) and did some additional sealing of the ERV and make-up air ducts.  In the end the results were nearly identical with a .56 for pressurization and .28 for depressurization.  Averaging the two out that provides an overall .42 ACH which equates to about 352.5 CFM of leakage which when reverse calculated gives you the CFM leakage.  You do this by multiplying .42 (leakage in air changes per hour) by 50,348 (PHIUS calculated volume) and dividing by /60(min/hr)=352.436 cfm.  Our last test yielded .50 ACH or about 421 CFM of leakage.  I seem to remember some discussion about the average house in America being on the order of 20 to 50 times higher on the leakage front.  Regardless, we're happy to have the figures showing that indeed our house is very tightly built.

The SolarPathfinder photographs are used to calculate the percentage of available sunlight hitting the house as well as calculating the angle of inclination to the "horizon" created by the surrounding trees.  My understanding is this informatino is used in the calculations of heat and cooling loads that will be required for the house.  Below are a couple of the SolarPathfinder photos.  Typically this device is used to determine suitability, placement and slope of solar collection panels - it can also through some calculations be used to determine where trees may need to be pruned to increase the amount or duration of sun hitting the solar collection panels.  When doing that you use a different template that shows solar clock and different months (I've attached an example photo using this alternate template).
  One of the cautions when using the SolarPathfinder is, like all compasses, it is influenced by ferrous metal in any nearby structures.  I found that the house (reinforced concrete) had such an effect so I had to move away from the house to set the magnetic declination and align the unit properly.  For the purposes of the PHIUS, we only needed the inclination to the horizon so the compass orientation wasn't quite as crucial but we worked to get it correct for future reference.  As you can see there is quite a bit of deciduous cover around our house and with the overhangs not too much sunlight is directly entering the house - especially in the summer months when we don't want the added heat in the house.  Basement floors will clearly get a bit more since the overhangs don't cover them.

North Wall Solar Pathfinder Inclination to horizaon - reflection of the trees shows angle to the "horizon" which can be used to calculate height of the trees relative to the distance from the house.
East Wall inclination on Solar Pathfinder - on top of retaining wall at same level as main floor
West Wall inclination - decking boards at the height of the main floor.  You can see the overhang is intersecting the treetops so no direct sunlight hits this wall of the house.
South Wall inclination - note I'm on a step ladder to approximate level of main floor (at the floor).  

Though a bit hard to read - the idea here is you find where the sky intersects the treeline, add the numbers in the "opening" for a specific month and determine percent of available sun that is hitting.  For instance if you can see the "apr" line, you add 6+6+7+7+7+7+7+7 to get 55 which is the amount of available hours of sunlight that will hit that spot. I beliee if you look at the "open" areas from 9:30 until 1:30 that would indicate 4 hours of sunlight in April - but then you have to factor in the deciduous nature of the trees based on the time of year.

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