Weeks 17 & 18

This may be the last posting before the final one, upon completion, now estimated to be in two and a half weeks.  Not much has been happening outside except for the start of some entry stair construction and the sealing of the natural pine ceilings of the solarium and the entry way.  Inside, however there has been much activity related to door installation and door and window trimming.  A first coat of paint has been applied by spray gun and the cabinets have started to be hung.  The cabinet appearance is funky because there was no attempt made to match adjacent pieces as to shade and structure.  It looks like a Cubist work of art - the glass is half full.

The electricity has been turned on and the electrical heat is working, currently being used to help dry out the concrete floor.  The picture shows electrician Steve, plumber, Randy and electrician Nick.  In the background you can see.......the 10 kW heater, expansion tank, and pump.  Not visible are the manifolds for the three zones (bedroom, main, and half of basement), the zone valves, the low water detector to protect the heater and many ball valves and faucets for maintenance.

The Yurt Hunt

Last week I participated in a Yurt hunt, that is to say, we went to Red Hook, NY and disassembled a 5 year old, 24 ft. diameter Pacific Yurt and hauled it back to our community to serve as an interim "Common House".  Although it was tricky disassembling the yurt, most of the work was disassembling the deck supporting it.  Yurts are great for milder climates and not too easily adaptable to colder, windy climates so we may have a few weeks where it just won't be worth trying to heat it.  With walls that are leaky and only have maybe an R5 insulation, the pellet stove will have to work hard on those windy below zero evenings.

The Solar Energy Collector Choices

In the last post it was estimated that without wood heat that I would use at minimum 6700 kWh of energy per year after subtracting the passive solar contribution.  So how can we capture that much energy with active solar?  

Many say that solar thermal is the best way to capture solar energy in the form of heated water.  But what is the complexity of a solar hot water system and how well does it perform?  Many also say that solar photovoltaic is inefficient and too expensive.  Let's look at the numbers for residential systems.

For both types of collectors, it should be noted that they are rated for the sun at full intensity shining at normal incidence, i.e. perpendicular to the collector surface.  Any deviation in angle from normal will lead to a greater proportion of the sun's energy being reflected from the transparent/translucent glass surface which protects the collector.  Thus fixed collectors cannot be as efficient as single or double axis sun tracking collectors.  Up to around 40% of potential sun energy is lost due to reflection experienced by fixed collectors.

A solar thermal system usually consists of one or more black body collectors which heat water.  When the water reaches a temperature greater than the destination temperature, a pump transfers the heated water, in most cases through a heat exchanger at the bottom of a large water tank.  A heat exchanger at the top of the tank can be used to supply heat from a backup source, be it electric or gas.  The heated water in the tank can be used for either washing or heating a floor.  A simple system consisting of one collector, tank, pump, differential temperature control and plumbing can cost in excess of $6K, I was told by one supplier.  Long periods of cold and overcast skies will require a backup heat source, yet possibly an extra expense.  Panel efficiencies are usually around  70% at normal incidence for either flat panel or solar tube collectors.   Considering that they are not pointing toward the sun at all times during the day, they are only receiving around 60% of the potential energy they could receive thus giving them in reality around 45% efficiency.

A solar photovoltaic system usually consists of one or more PV panels mounted either fixed on a roof   at an optimal angle or on a sun tracker.  The direct current (DC) produced can then be stored in costly batteries for off-grid usage or be changed to alternating current (AC) by an inverter for connecting to the grid and thus using the grid as a bank account.  This assumes that one is allowed to tie in by the local utility and assumes that the utility pays a reasonable rate for electricity received.  Installation of fixed panels on properly oriented roofs requires penetration of the roof's surface for the panel mounts and the wiring.  Other considerations for roof mounted systems are leaf debris and snow accumulation on either side of the panels and the beneficial heating of the roof in the winter months.  Trackers are complete systems that can be easily inserted into rigid soils with a small front loader.  Trackers are more complex mechanical and electrical systems with some using GPS for tracking and cell phone connections for monitoring and on-line reporting of performance.  A 4 kW tracker will have 20 solar panels, each capable now of operating at its maximum efficiency which may be around 17%.

Purchasing alternative energy equipment is currently supported by rebates and tax credits, not unlike the estimated over $500 billion support of fossil fuels worldwide (Where is this free market?).  For example, a 4000 W system, capable of generating around 5640 kWh annually in Vermont would cost $31,000.  After a $4000 rebate from the Vermont Renewable Energy Resource Center and a 30% federal tax credit, the final cost is $17,700 installed.

In the co-housing community in which I am building there is the opportunity to place the collector in the lower more wind-protected, yet wide open meadows rather than in the tight residential area.  This my plan and it will be appreciated by the sheep grazing there as they are always seeking shade in summer.  Now where is that pot of gold the rainbow last week was pointing to?

And finally a whazzit puzzle found around the construction site:

Weeks 15&16

Since there wasn't that much to report or document on the house in pictures, I thought I would start off with an evening at Charlotte Beach, the picture symbolizing the near completion of this building adventure.

The errant windows arrived and were quickly installed enabling the completion of the siding attachment.  Inside the wall board or dry wall hanging was finished one week and the plastering was finished the following week, being executed by a real artist.  The stove pipe was also installed with the help of Balky, the lift, that had been behaving since it obtained a new joystick.  The "parging" of the part of the basement wall protruding the soil was started.  This process consists of adhering multiple layers of various materials to the insulating foam surface to result in a weather resistant cover.





 The Habitat for Humanity House

I had mentioned some posts back that Habitat for Humanity has been building two houses down the road that are designed to meet the Passive House energy standard.  The first house is a conventionally constructed one whereas the second one is prefabricated.  As with all their houses, much donated material and labor goes toward their completion.  These houses are being built under the guidance of Project Directors Peter Schneider from Efficiency Vermont and Architect John Clancy.

This design does not have much thermal mass but relies on much insulation to stem heat flow.  Observed under the basement slab was 10" of "blue board" foam insulation .  The walls are conventional 2" x 6" construction with 6" of foil-faced TUFF-R isocyanurate foam boards on the outside and cellulose insulation on the inside.  The roof has a truss construction that will allow around 30 in. of cellulose insulation. The goal is to have R100 in the roof and the basement with around R80 in the walls - if I remember correctly.  The windows are triple pane from Thermotech.  There is no website yet detailing this project even though the designs are being evaluated as standard future designs for colder climates.  The recipient of one of the houses, however,  is keeping a blog.

The house will be more conventional in appearance than my house and definitely more livable for a family of four.

More Energy Discussion
Did I mention last time that my low ball estimated energy consumption of 6700 kWh is only 84 kWh/m2-hr which is 30% better than that vaunted German Passiv Haus standard.  Of course, I've not accounted for some of the heat losses yet, so for now this is only numbers in cyberspace not real life living in my Haus.  Tune in on the real story next year.

This week we will see how the total heat cost will be "covered'.  By covered I mean how will the estimated annual need of 6700 kWh heat be produced?  Options around here are propane gas, electricity, wood, coal, or oil.  I've already said that I'd like to use as little fossil fuel as possible which eliminates propane, oil, and coal, leaving wood and electricity.  Of course we all realize that wood needs to be cut, transported, chopped, and delivered which right now is done with oil powered equipment.  Electricity in our area of Vermont comes largely from two sources, 47% hydroelectric, mostly  from Quebec Hydro, Canada, and 42% nuclear from Vermont Yankee which may be or maybe not be shut down soon depending on which way this political football bounces.  My intention is to try to minimize electric use by producing much of it myself with solar PV arrays and use wood as backup heat for the colder periods of the year and for power outages, though they have been rare.

Wood heat isn't cheap if you add the cost of a chimney and a nice stove to the cost of the fuel.  My Bari stove can generate from 12K-30K BTU/hr. which is much more than my hourly needs of 9520 BTU/hr on a zero degF (-18 degC) day.  Because the stove has a soapstone liner which gives it around 50 BTU/degF thermal mass, it should be able to moderate its heat output a little and hopefully the thermal mass of the inside of the house estimated to be greater than 15000 BTU/degF should be able to further moderate the emitted heat from the stove for short burns as it will take about an hour of burning to raise the temperature 1 degF... approximately.  After the stove no longer emits heat it should take about two hours to see a 1 degF temperature decrease .... approximately.

So how much energy can one get from a pound of wood?  In the laboratory one can get about 8600 BTU/lb.  After subtracting the energy required to vaporize the water content (20%)and taking the burning efficiency of the stove into account, maybe half that amount of energy can be recovered.

All wood, regardless of species, has about the same energy per pound.  The different species vary only in density.  A cord (128 sqft) of white oak wood  for example has about 30 MBTU (approximately 8800 kWh) which would more than cover my annual expected usage of 6700 kWh. Thus as a backup heat source, a half cord/yr may be enough.

Next time we'll look at the solar energy options for fossil free energy.

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

Week 14

This was the week of the last concrete pour and the last concrete patty of about 8 left by the pumper and concrete delivery trucks for later disposal. 

The water supply rough plumbing on the first floor was also completed.  The first floor is now ready for the wall board installation next week to cover everything except the windows and doors. 

We even received the stairs to the basement which came in two sections that were quickly installed and had walls framed around them. 

Outside, the trim, siding, shingles,  gable vent,  and attic entry door were completed on the west side.  This was achieved with the help of Balky, a Genie Boom rental lift that had to be pampered just right to do any lifting.








The Cost of Heating

In week 4 we stated the basic energy need equation, En = EL - EG.  The energy needed, EN, to heat the house to a desired temperature T is the total energy lost, EL, to the outside minus the total energy gained, EG, by internal activity and solar heat gain. We defined the desired temperature at 68 degF.

In week 13 we estimated the solar gain contribution of the windows which on an annual basis is 2370 kwh, not counting June, July, and August contributions as they are too much to meet the heating need and need to be blocked.  One other gain previously discussed is the occupant generated heat, around 2.4 kWh/day-person which for one person is 876 kWh/yr.

Several weeks back we determined that the house is estimated to use around 140 BTU/degF. Using this number and combining it with the Vermont average monthly weather data we arrive at an annual need of 6500 kWh after a 2370 kWh passive solar contribution. Other heat losses are from the heat recovery ventilator, uncontrolled air leakage, ingress and egress activities, and water usage losses. 

Heat Recovery Ventilators are needed for air tight houses during heating days to avoid humidity and CO2 build up.  These units will draw in fresh outside air and heat it from the heat of the stale inside air which is expelled to the outside.  This occurs in a two chambered non-mixing polypropylene heat exchanger.  There are various ventilation standards with the Minnesota standard requiring .05 CFM/sqft + 15 CFM/person which would be 55 cubic feet/min for this house with one occupant. 
The chosen ventilator is a Venmar Constructo 1.0  which is rated at 45-96 CFM with an efficiency of 76%  at a 70 degF difference between the inside and outside air and 50 CFM.  According to the data sheet, which is not very specific, at 32 degF external and 50 CFM, 44 W of electricity are consumed.  If this ventilator were to run all the time it would annually consume almost 400 kWh just to move the air.  Judging from the two motor design layout, about half the motor heat will be exhausted to the outside, the other half will go to heat the incoming air .  It is unclear how much energy is consumed by the defrost cycling which occurs below 23 degF.

The ventilator would most likely not be used during the warmer months as the windows would then be used for ventilation and temperature control instead.  For the 264 days of usage (Sept.-May), the average outside air temperature is 38 deg. Assuming this air to be at 50% humidity, heating it to 68 degF would take 15 KBTU/day as can be determined from a psychometric chart and assuming that 2/3 of that heat can be recovered from the exhaust air.  For the heating season this would compute to an annual consumption of  1160 kWh.  Using it at less than 50% would half this to say 580 kWh/yr. Adjusting the motor heat consumption for the heating days and the 50% duty cycle of operation, would subtract 74 kWh/yr for a final 500 kWh/yr heat need.  (Disclosure: I am not a thermodynamicist just an electrical engineer who had to take thermodynamics almost a half century ago)

All water entering the house enters estimated at 50 degF.  It will most likely exit at the house temperature of 68 degF.  Thus for an estimated daily usage of around 100 l (25 gal) this represents a heat loss of around 600 kWh annually.

Uncontrolled air leakage losses are a function of the tightness of the house construction, the temperature difference of the inside and outside air, and the external wind pressure.  I will assume this to be zero currently and will wait until it can be measured with a blower door test to be performed by Efficiency Vermont.

Ingress and egress losses are a function of the life style and habits of the house occupants.  Every time a door is opened during the heating season a certain amount of heat is lost in the air escaping and a certain amount of heat is needed to heat the person's belongings and clothing from the outside temperature to the inside temperature.  This is assumed to be zero for now and will be measured later.

We thus have optimistically, the following heat needs in kWh:
En = conductive losses + HRV losses + water losses + uncontrolled heat losses + ingress/egress losses - solar gain - occupant heat
En = 8855 + 500 + 600 + 0 + 0 - 2372 - 876 = 6700 kWh
Thus at the 0.15cents /kWh expected later this year, the heat need would cost 1000 $/yr.  The only other electricity costs not covered by this would be external lights (1) and the HRV motor heat loss of 74 kWh/yr.

Next time we'll see whether this is good and how this cost is covered - or not.

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