High embodied energy results in significant carbon emissions. According to the ECOsmart Foundation, one tonne of carbon is emitted for every tonne of cement produced. Trees by comparison absorb carbon during their lives, resulting in many wood products being effectively carbonneutral. Using locally harvested wood will be more responsible than importing or using many other products shipped from great distances. The type of transportation is also very important. shipping locally by truck is at least six times more intensive than shipping overland by rail and definitely more intensive by cargo ship which requires additional land transport at both ends of the delivery process.
The first step of my exploration was to ensure that the logs for this home were harvested locally in Eastern Ontario from a location that incorporated reforestation as part of the cycle of removal of this renewable resource. It turns out that we secured a location within 250 miles of the site producing the Eastern Pine species.
Once this concern was satisfied, the rest was quite simply applying the basic principles of sustainability and the knowledge I have gained after 28 years in the practice of Architecture and a life long attraction to nature and its' importance in our lives. It has been 37 years years since I was old enough to understand that each individual had a responsibility to be part of the solution. The environmental challenges and pressures facing Canada and the rest of the planet are unprecedented and the need for action has never been more compelling. Many of our demands on the environment seem to be reaching a critical point while the degree of change exceeds our ability to understand, predict or control it. We must test our limits of knowledge and understanding, and mobilize the "Forces of Technology and the Forces of Nature « necessary to respond to our environmental challenges and opportunities. We, as Canadians also have a responsibility to address the social aspects of our aging society. The social change in our society is manifested by (1) the evidence of an increasing multicultural/multiethnic population and (2) the changes and differences between age groups and their ability to contribute to the overall solution. The creation of these Urban models allow for certain flexibilities builtin to allow adaptation to future endeavours in sustainable design.
The creation of this home took us on a journey that started with the site and its' limitations/opportunities.The site affords excellent orientation for maximizing active & passive solar gain techniques. The design of this home figuratively and physically indicates the overlap between the two forces; Nature and Technology. This overlap yields the ability to employ "Trombe", "Mass wall", and "Greenhouse", technologies while maintaining a minimal surface area to floor ratio.
Basic Design Qualities integrated with this High Performance Log home.
Mechanical Design Concept
When designing the mechanical systems for the Log Home, a number of factors were considered. How to heat the house the most efficiently, if cooling was truly necessary, how to incorporate renewable energy sources, how to ensure good indoor air quality in the design? It was important to address these issues in a way that would allow them to contribute to the sustainability of the house without detracting from its unique look and beauty. Through careful planning and design, all of these elements have been tied together into an energy efficient package that will provide enhanced comfort for the occupants and result in a lower ecological footprint than current subdivision style homes.
The Log Home makes use of a mechanical ventilation system ensuring adequate ventilation is distributed throughout the home at all times. A high efficiency HRV located in the basement introduces outdoor air to all of the occupied spaces (bedrooms, and living spaces) in the home. The amount of outdoor air being introduced into the house can be increased in one of a few ways: automatic control by a centrally located humidistat, a centrally located override switch, and/or a timer located in each washroom. Each of these devices can adjust the 5speed fan in the HRV to improve the indoor air quality as required.
A specially configured TFP/HEPA filter system filters the outdoor air before it is ducted to the spaces in the home. These filters clean the air to maintain the home’s healthy indoor air quality. The TFP prefilters remove any larger particles to help reduce the maintenance requirement on the secondary HEPA filters. The TFP filters require annual replacement, and the HEPA filters are only scheduled for replacement every three years! The low maintenance requirements of this system result in improved indoor air quality, with little inconvenience to the homeowner.
The heating system used in this sustainable house is two fold. The HRV which introduces outdoor air to the house has an aluminum core that allows exhaust from the washrooms and kitchen to transfer their waste heat to the cold incoming outdoor air before being exhausted to the outdoors. This, combined with gains from the fan in the RV and the ductwork, are enough to heat the outdoor air to a reasonable temperature without supplying additional heat.
The entire Log Home is fed by a 10 ton Geothermal loop that is placed at the existing site surface before the 6 feet of overburden is placed for the thermal buffer of the lower level. The loop consists of Horizontal runs to approximately 3,000 linear feet. There is one 5 ton Heat Pump for water to air exchange and one 5 ton Heat Pump for water to water exchange. The hydronic feeds radiant coils listed above as well as the heat pumps are run with a glycol medium and a heat exchange using a 120 gallon storage tank for hot and cold applications.
Radiant heating allows the occupants on the ground floor to feel the heat as it is radiated to them from the floor they are standing on. With a traditional air based heating system, stratification of the heat would be an issue in the high spaces on ground floor resulting in reduced home owner comfort – the radiant system helps prevent this and increase the occupant’s comfort levels.
Since mechanical cooling is an inherently “unsustainable” process (it uses refrigerants which are harmful to the environment and consumes large amounts of electricity) it has not been included in the design of the Log Home. In order to try to minimize the heat in the home in the summer months, high ceilings on the ground floor have been provided to allow heat to stratify, strategically placed windows allow air to circulate through the home, trees are located on the landscape plan to provide shade in the summer months and ceiling fans in bedrooms allow the occupants to experience evaporative cooling.
The domestic hot water system takes advantage of two resources available on site: the sun and the high efficiency boiler used for space heating. Through a series of controls, the dual coil domestic hot water tank is able to be heated by the sun when it is available, and the condensing boiler is able to “top up” the heat in the domestic hot water tank as required to meet the family’s domestic hot water demands.
Reduction in potable water usage in the home has also been addressed in a number of ways. Care has been taken to include ultra low flow faucets and showers and dual flush toilets. The Log Home does not stop there however, included in the second floor washroom is a waterfree urinal which reduces the water used for liquid sewage conveyance for male occupants in the space to zero.
The mechanical systems of the Log Home have been designed to create the greatest impact with the least “shock factor” to home owners. The systems included in the home work quietly in the background to improve the home owner’s living conditions while saving energy and making use of ‘free’ solar power.
Electrical Design Concept
An essential part of sustainable living is reducing consumption. A number of measures have been included in the Log Home design to minimize the house’s electrical energy consumption. The majority of the south facing portion of the home is glazed. This allows natural light to enter the home and the open concept design allows the light to penetrate deep into the spaces. The light fixtures in the home are ENERGY STAR compliant, as are the ceiling fans with integral lighting capability. The outdoor lighting elements are solar powered and have photocells to ensure they only run when required.
The Log Home has eliminated one of the largest consumers of electrical power in homes – there is no mechanical cooling in the home. Removing the mechanical cooling reduces the peak electrical loads usually experienced during the cooling season due to air conditioning.
Finally, a photovoltaic (PV) array on the roof is sized to offset at least 30% of the estimated annual energy consumption of the home.
The Solar system is intended to offset the power consumption that is related to the ancillary areas and Domestic Hot Water supply. This total consumption is approximately 7,200 Watt hours/day and will be connected to approximately 26 photovoltaic panels designed to provide 1 day of battery storage as a backup.
There is also room of the dwelling’s rooftops to expand the system up to 19,100 Watt hours/day capacity of panel B and accommodate additional optional equipment or be fed to the provincial Microfit program. The split would be 11,900 Watt hours/day allocated to the Microfit program yielding approximately 16,500 kilowatthours (kWh) $13,000 per year over a 20 year contract period. Since the installation cost for that portion of output would be approx. $65,000 then the Return on Investment will be approximately $195,000 over the life cycle.
Progress Gallery photos during Construction
The subbase of the site was prepared with approximately 3'3" (1m) of granular fill after removal of the peat and organic material sitting above the water table. Surface compaction was not required because the layering of different grades of granulars ensured 120 kPa bearing capacity. The building size estimated at over 80 tons required extra wide footing pads and considerable amounts of reinforcing in comparison to a standard dwelling.
The lower portions of the structure are steel and concrete and designed not to shrink as it supports the entire volume of logs above. There are two full height log stacks in the home that sit along the beam lines shown. The floor system is a preengineered wood product setup for 16'0" (4.88m) spans.
Once the floor system for the main level is in place, the log shipments begin by level. The perimeter concrete foundation is fully insulated with 3 1/2" (89mm) of rigid insulation and a full drainage membrane that extends up 6'6" (2m) above the footings. The final base finish will be a cultured stone on metal lath that will be the exposed surface 3'3". (1m) above the finish grade.
Subsequent log shipments will continue as soon as the floor systems of the current levels are put in place using the same preengineered system approach. The upper level of the garage structure has been conventionally framed to save on the project costs. The cladding material will be a shiplapped pine with 3/4 cut vertical log corners and 1/4 cut horizontal log base trims. The roof structure is a preengineered truss system pending a metal reflective roof covering.
The second floor lift is now in place on the main house and the roof cathedral web is in place anticipating the two tier roof trusses and front entrance portal.
The tie-in for the front portal structure and the link between the house and garage has started pending the delivery of the trusses.
Appendices:
Background information on horizontal ground coupled systems using slinky coils:
Closed horizontal slinky loop, 4T system
Geothermal slinky coils wrapped around the widened perimeter of the house during construction of the foundation.
"Slinky" is the term commonly used rather than the imposing scientific name curtate cycloid. When used with geothermal heat pump systems, the Slinky is a flattened, overlapped plastic pipe circular coiled ground loop heat exchanger. It concentrates the heat transfer surface into a smaller volume, requiring less land area and shorter trenching.
The compact slinky at 10 inch pitch is equivalent to 12 feet of pipe per foot of trench and will reduce trench length by about twothirds compared to twopipes at 4 and 6 foot depths.
An extended slinky at 56 inch pitch is equivalent to 4 feet of pipe per foot of trench and will reduce trench length by about onethird. Specific design lengths will vary with climate, soil and the geothermal heat pump's run fraction. Slinkys can be installed horizontally at the bottom of a 3 foot wide trench or vertically in a narrow trench.
Contractors have developed other Slinky configurations specifically to meet their installation needs. The coils are fabricated flat for transportation by tying the return pipe to the base of the coil. Before the coil is placed in the trench, the return
pipe is cut free from the bottom and is installed on top of the coils. In this case, the spacing is about 20 inches between each loop and only intersect at the bottom.
In another method the coils are 30 to 32 inches in diameter making it easier to shape while the worker is standing up and the coils are tied together. Slinky assemblies can be fabricated on the job site, or preassembled in the shop on rainy days or slack periods using a simple fixture and later trucked to the job site.
In forming the slinky from a pipe roll, allow the pipe roll to remain in the same circular configuration as manufactured and shipped. A common mistake is to uncoil the pipe as if it were to be placed in a straight line. Begin with the outside coil of the pipe roll. The individual pipe coils are pulled from the roll to and through the fixture for tying, much the same way you would unroll a new garden hose.
Ties are applied with the coil in the fixture. They must be strong enough to hold the coil in position during fabrication, transportation and placement in the trench. After backfilling, the ties are of no value and can deteriorate with no adverse effect. Plastic wire tie wraps with metal catches is one alternative; rebar wire ties is another. Some contractors prefer duct tape with a sufficient number of wraps. Duct tape secures the pipe over a wider area with less pressure and requires no special tools. The pipe is less likely to crimp and the cost is typically less.
Tie spacing is about 10 inches between each loop. The pipe does overlap and is tied where the loops intersect at top and bottom. With the extended slinky, the loops are tied where they intersect. Evaluation tests conducted by Pennsylvania Power and Light Company for example indicated: No significant difference was found in the performance of a vertically versus a horizontally installed Slinky
Proper backfilling is critical for good performance
Horizontal installations seemed easier to properly backfill
Loops for one circulator should use no more than 750 to 800 feet of pipe to minimize pressure losses and maintain turbulent flow
PP&L recommends for each ton of capacity a 100 foot trench, 3 feet wide and 6 feet deep in the Slinky area, 4 feet deep in the pipe header area, using 750 to 800 feet of ¾inch pipe on a 17 inch pitch.
There are a number of new ways the "Slinky" coil concept is being applied. For example, a contractor innovated a way to install the coils vertically in shallower 20 to 30 feet deep but
larger diameter boreholes. A series of plastic strips keep the coils properly spaced when the assembly goes into the ground. The saving is in the installation time. Other such innovative improvements will no doubt be made as more installations are completed.
