Week 13

Week 13 unfortunately missed the only Friday the 13th (my lucky day) this year by one week.  But I digress.  This week, much external trim work was  completed except under the gables. Placement of the siding commenced.

The brackets for the entrance portico were also attached and the ceiling of the portico was covered with pine planking similar to the solarium.  (This is a portico without columns). Gable shingles yet to come.

Inside, the channels for the electrical lines carved into the ICFs were filled with expandable polyurethane foam.  Nail plates were placed at 18 in. intervals along the top and bottom of the walls to allow for easy fastening of  trim and baseboards.

The radiant floor hot water tubing was attached to the floor in preparation for the concrete pouring of the floors next week.  The 1/2 in. (inner diameter) PEX tubing is looped at intervals of 9". There are three control zones: the living room,  kitchen, entry way, and bathroom room area (900 ft), the bedroom (300 ft), and the basement (600 ft). The living room and basement have two loops/per zone.  There is also about 380 ft of tubing placed next to one of the living room loops which is to serve as a small volumetric capacity (7 gal) preheater of washing water for the instant-on water heaters.

More Realistic Solar Heat Gain
Using the US Solar Radiation Resource Maps, based on solar radiation data gathered from 1961-1990, one can compile the average solar energy impinging for a year on a flat surface here in Vermont.  The graph below shows this energy density in kWh/m2-day, Jan - Dec, under the following conditions:
Series 1 : 30 year average daily energy density falling on a vertical surface pointing south
Series 2 : minimum average daily energy density on above surface during the 30 year interval
Series 3 : 30 year average daily energy density falling on a south facing surface tilted at latitude
Series 4 : As in Series 3 with East West single axis tracking.

Since these curves are functions of cloudy days and sun position in the sky throughout the year a few observations can be made from these graphs. The summer dip in Series 1 is mainly due to the high sun angle in summer. One would expect a dip also in winter partially due to shorter days and this can be seen in Nov. and Dec. but not in Jan. and Feb. because of sunnier days than in Nov. and Dec.  The Series 2 curve shows that there can be some very cloudy months throughout the year on occasion. Series 1 and 2 are for vertical panels such as widows.  Series 3 and 4 are for panels tilted at latitude (44.3deg, which is very close to the roof angle), i.e. for roof-mounted solar thermal or photovoltaic collectors.  Series 3 is for a roof-mounted panel and shows a flattening during the summer as the sun actually rises above the latitude angle by almost 25 degrees.  Series 4 shows the advantage of east-west tracking.  No data was taken for 2-axis tracking which should further broaden the area under the Series 4 curve.

Translating these data to practical terms, we can say that except for the dark and cloudy Nov. and Dec. months we can expect to have around 30K BTU penetrate the south facing windows daily.  This is assuming full illumination which isn't quite the case as except for the western most south facing windows the others are partially shaded in the afternoon by the walls to their west protruding to the south. So let's say, for further discussion, there's only a 20K BTU gain per day.

Next time we'll look at total thermal gains and losses and estimated yearly energy cost if the only heat source other than solar is electric.  We'll also look at the influence of the thermal mass on the temperature regulation.

Please send me comments that add to the discussion and correct any errors of comprehension.