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.

Week 12

Installation of all delivered windows and external doors was completed.  An adhesive backed tape is placed over the outside of the window bucks to the outside foam as a water guard against any rain driven penetrations. Much shimming and leveling is necessary to mount the windows and doors straight in their rough opening.  The remaining gaps are filled in with expandable foam, casting the windows in place and creating a well-sealed and insulated space surrounding the window frame.  The green water impermeable membrane was used to cover the wood portion of the window bucks that had angled internal sides.

The wallboard guys breezed in and out and within what seemed like an hour had the ceiling boards in place.  This ceiling board had a water impermeable aluminum layer on one side to prevent humidity from the living space from penetrating into the cold attic.

A visit by an energy inspector from Efficiency Vermont to inspect the house for Energy Star Rating, pointed out that one of the biggest leaks of energy out of the living space into the attic takes place at the interface of the ceiling board and internal walls.  (European readers may wonder how this could be as they may not realize that we have a tradition of building hollow walls out of 2" x 4" "studs" or more precisely by 1.5 in x 3.5 in wide lengths of lumber).  These hollow walls may have electrical wire or plumbing holes in them which allow air entering the wall from the attic to leak into the living space or vice versa.  Traditionally, these houses were said to "breathe well".  But to build to new standards, these gaps as well as all wall penetrations into the roof need to be sealed with a flexible caulk for air tight construction.

Miss Inspector took pictures of every glass penetration of the outside walls, as these contained the U-vale and SHGC numbers for heat loss/gain calculations.  She was happy with the fresh air supply for the wood stove as now required by Vermont law.  The solarium air preheat ability for the HRV supply air was also appreciated but she was concerned about possible blockage of inlet air by the solarium design.  The use of a  Heat Recovery Ventilator is a requirement for air tight houses to maintain proper humidity and oxygen levels.  These units inhale fresh outside air, exhale stale inside air, and recover most of the energy in the exhausting  air by using it to heat the inhaled air in an isolated aluminum cross-flow chamber.  This device is clearly still a source of heat loss, however with a perfectly tight house design, the air heat loss can be controlled by the HRV's frequency of operation.

Miss Inspector took issue with my plan to electrically heat my house, with wood heat backup for electrical power outages and extra cold days.  She conceded that Propane heat is nearly as expensive as electricity and is also not considered a future energy source.  She suggested more usage of the wood stove though I had to inform her of the smoke concern in the community.  She said that the electrical utility is concerned with excessive demand.  I wondered if she had the same concern about the demand placed on the utility by the mega-mansions going up around some parts here as she had about the minimal estimated demand of a small energy tight house.  She looked at her watch and had to suddenly leave for another meeting in her fancy crossover vehicle......

Speaking of wood stoves, I had a difficult time making up my mind on a suitable wood stove for backup heating in case of power failure, extreme cold, or romantic setting needs.  Initially I looked at a Danish made RAIS stove, however, the price tag for the stove itself plus the expensive stove pipe installation coupled with an inflexibility in installing the stove pipe in a timely fashion made me shop around at a much closer store overlooked before.  Bingo! They had a better stove for the same amount of money and they were very accommodating to our schedule needs.  The stove is from a German Company, Hase and it is the Bari model.



Window Heat Gain
In week 9 we looked at the heat requirement of the windowless house and found that at 32 degF 2800 BTU/hr would be required to keep it at a comfortable 68 degF.  In week 10 we looked at the solar energy or insolation (BTU/sqft-day), available in this part of Vermont. Today we will look at the many factors affecting passive heat gain from windows in the house.  We will not consider the reduced heat loss through the warmer walls on sunny days.

In week 11 we detailed four parameters for all of the "windows" or more precisely for all of the window and door penetrations of the house wall.  The rough opening (RO) defines the area of wall penetrated.  The U value is the parameter that defines the averaged heat loss through the complete window opening including the frame, sash, and any hardware (usually metal) for opening and closing the windows.  The SHGC  gives the percentage of normally incident solar energy falling on the complete window that actually manages to penetrate to the inside.  Non-glazed portions of the window and glazing losses such as reflection and solar heating of the glass will reduce this number.

To obtain the total heat loss due to the windows and doors of the first floor we just sum their UxRO products from week 11.  Doing this we arrive at 67.7BTU/hr-degF  which points out when compared to the heat loss of the walls, floor, and ceiling (72 BTU/hr-degF), that the windows are 48% of the heat loss at night.  This clearly shows that good shutters should clearly reduce night time heat loss.  Of course, the windows are also the main heat gain during the day, especially on cloudless days.

The north facing window will only see diffuse light most of the year with some north light at low incidence in summer.  The east and west windows will see nearly direct incidence light mostly in summer which is nice in the morning but may lead to too much heat later in the day.  Since there will be no active cooling (AC), inside summer temperatures will be modulated by opening windows during the cooler nights and closing them during the day when necessary.  Window shades will assist in diminishing the western sun. Having said all of the above, only the heating season needs will be addressed with only the south facing windows assumed to have solar gain.

To help us estimate the maximum amount of heat gained by the south facing window we first sum up their glazing area x SHGC products.  Doing this we arrive at 26.5 sqft.  Now, were direct sunlight to shine onto all windows at normal incidence on a clear day, we could capture around 8000 BTU/hr, considering that solar energy is optimistically around 300 BTU/hr-sqft at noon.  But as that isn't ever the case  for vertically mounted windows, we must subtract the reflected light which will vary as the sun travels on its path across the sky.  Our tax supported government offers for free a solar position and intensity calculator which shows all the factors involved in arriving at actual values of insolation for any place on earth.  Furthermore, our government provides for free, maps that show the energy incident on various types of fixed and tracking collectors for any period of the year, based on historical data. From this we can obtain, for example, monthly passive heat gains for vertical unobstructed south-facing windows. We can then compare that heat gain to the actual heating requirement for maintaining the house at 68 degF.   That is a task for the next posting.

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

Week 11

Other than Comcast canceling my email account and Gmail suddenly not recognizing me as an author of any blogs because of an association with my cancelled Comcast email account, it's been a good week.  Thus this somewhat late and new continuation blog.  Now for the real progress.

The main roof was completed this week including the roofs over the entrance portico and the shed.  A heavy downpour validated a good job was done.  Externally, corner trim boards and vertical strapping boards were attached in preparation for siding attachment.  Between the strapping a densely fibrous, yet porous material was added to prevent insects from creating habitats under the siding, yet allow air circulation to aid in moisture build-up prevention after heavy wind-driven rains. (This 1/2" air layer together with the siding adds almost another 2 to the R value of the walls making them R40).  

More strapping was also added in the ceiling to avoid the weight of the blown-in insulation from deforming the ceiling boards.  In preparation for the ceiling board installation an insulated stove pipe collar was placed in hopefully the correct position.

The windows and glass doors arrived from Inline and as expected perfection in ordering was not achieved.  Two of the windows had the wrong size entered in the quote and even though the error had been communicated it propagated through to production and two of the windows were too long vertically by a foot and unacceptable considering that they would be showing the back of furniture and potty-goers sitting on the toilet.  This experience has taught a lesson of identifying each window uniquely on the drawing and on the factory order and that the builder should verify each window specification on a copy of the production order which was not supplied.  Another lesson learned is not to use one manufacturer's standard size numbers for specifying window sizes for another manufacturer who has no standard sizes and has total flexibility in window size construction.

The windows all have fiberglass frames with a dark bronze color externally and a almond color internally.  All north windows are triple pane and fixed with the exception of one which was shipped as a casement window when it was also to be fixed, another product of communication and execution errors.  This error was somewhat reluctantly accepted.  All other windows are double pane. 

Window Data Stuff

(Remember that a part of this blog is personal documentation ).

The following locates the various windows and doors in the house and gives the data in parenthesis for each item (Uvalue, SHGC, glazed area, rough opening area).  The U value is BTU/hr-sqft and the areas are in sqft.  These data will be used later to compute the heat gain and loss due to the various components. 

The bedroom has one fixed north facing window (0.17, 0.3, 3.07, 5.51), one east facing awning window (0.30, 0.29, 3.19, 5.65) and two south facing double hung windows (0.32, 0.33, 19.7, 30.4).  The bathroom has only one fixed north facing window (0.17, 0.3 , 3.07, 5.51).  The kitchen has one east facing tilt and turn door (0.33, 0.26, 9.39, 19.3) which goes to the solarium and two south facing fixed windows (0.26, 0.33, 20.9, 28.9).  The living room has one east facing fixed window(0.26, 0.33, 5.67, 8.84), one south facing sliding glass door (0.29, 0.21, 29.5, 42.4), and two south facing fixed windows (0.26, 0.33, 20.9, 28.6).  On the west side there are two casement windows (0.30, 0.29, 15, 16.7) which have angled vertical sides to help distribute the light better through the thick wall openings.  The window on the north side is fixed (0.17, 0.3, 8.64, 10.9) and has similar angled sides.  The mudroom has one north facing casement window (0.21, 0.25, 7.5, 10.9) and one half-glazed entry door (0.18, 0.13, 5.12, 24).  The exit door from the mudroom into the living space is also an entry type door also half-glazed but it doesn't sit in the outside wall.  It provides some extra insulation between the mudroom and the living space.  These two doors, from Therma Tru) are meant to be more community friendly and less isolating.

The total wall penetration area for windows and doors is 254 sqft or 25%.  Total glazing area is 167 sqft or only around 2/3 of the wall penetration area.  The south side has 9%, the north 2.2%, the east 1.8%, and the west side 3.5% of the glazing.

Because of a personally busy week, geek moment will continue next week - maybe.