What is a Bioshelter?

R.L. Crosby, Biorealis Systems, Inc

Design Concepts A bioshelter is an integrated house/ greenhouse/ aquaculture system designed to emulate natural living systems in which the subsystems interact with each other to collectively create a self-regulating whole. The goal is to simulate the thermodynamic efficiencies of a complex ecological food chain.

As in all living systems, each subsystem generally performs more than one function, and the end product of one process is typically the raw material for the next. Energy does not flow through the system in a straight line from source to sink, but is first modified and stored in various forms within the structure to offset fluctuations in the supply.

The design incorporates a number of innovative concepts and components, but the real innovation is in the underlying philosophy which views the overall combination of functions and processes as a highly integrated whole system.

Project Goals The project was undertaken (1) as proof of concept for a total water reuse system, and (2) to provide a live-in laboratory, allowing development and testing of various system components.

The mechanical space below the house was designed to allow easy access to separate graywater and toilet waste piping systems, and to allow easy replacement of prototype units for testing. It includes a well lit workbench, with power for tools and electronic instrumentation.

During the past 12 years, we have experimented with a variety of biological wastewater treatment systems, materials and methods. Products developed include a low flush toilet system, a composting toilet, an anaerobic digester, and a wastewater biofilter.

Awards, Recognition The original design was selected as a winner of a 1982 Home Design Competition sponsored by The Alaska Energy Center. Construction was completed in 1986. In 1987, it was selected for a National Energy Innovation Award by the US Department of Energy.

It has since been the subject of various
articles, appropriately described as a “living house”, in which the closed water system performs functions analogous to those of the circulatory system of a living organism (i.e. temperature regulation, nutrient transport, waste removal. etc.)

The Building Envelope

The building itself is a simple 42- by 42-foot square box set into a southwest-facing slope on the diagonal, so there is an uphill and a downhill corner. The simple shape was chosen to minimize heat transfer surface area. The envelope encloses a total of about 3,200 square feet of floor space, partitioned into 2,500 s.f. of living space, 500 s.f. of full height garden/ aquaculture space and about 200 s.f. of balcony overlooking the enclosed garden space.

With the exception of one skylight near the back of the house and one small bedroom window, no other windows open directly from the living space to the outside. Instead, the interior of the living space is laid out so that all of the major rooms have large glass areas looking out into the enclosed garden space. The skylight provides natural daylight to the rooms at the back of the house, including the lower level, which is below grade. Overall envelope UA (product of U-value x Surface Area) is estimated at 530 btu/hr/degree F.

The equation used to calculate steady state heat conduction through a building envelope is:

q = UA(ti - to)

where q is the rate of heat transfer, U is the heat transfer coefficient, A is the surface area, and (ti - to) is the temperature difference between inside and outside.

From the equation we can see that, if we wish to reduce heat loss, we can reduce any or all of the three terms on the right side of the equation. To reduce U, we would provide more or better insulation. To reduce A, we would make the building smaller or design a more efficient shape to decrease the surface-to-volume ratio. To reduce the temperature difference, we would either lower the thermostat setting or locate the house in a warmer climate (or promote global warming?? (:-). Of course, in the real world, economics and other design considerations dictate the practical extent to which any of these terms can be manipulated (maybe you don't really want to live in a small windowless sphere with two foot thick walls).

Building designers generally limit their focus to the first two terms, considering the third (i.e. temperature difference) to be outside of their purview. In this design, we have addressed all three terms. The building is laid out so that most of the windows (the building element with the highest U) look out into an artificial climate with 2,500 DD, rather than the ambient 11,000 DD.

The Artificial Climate The artificial climate is maintained entirely passively with heat sources normally considered economically unrecoverable, including energy used for heating domestic hot water, heat gain from the house windows, electric lights and equipment, and solar gain.

Temperature stability is maintained by the large amount of thermal storage capacity relative to rates of gain or loss. The entire growing bed area of the greenhouse was excavated down to the footings, waterproofed, and backfilled with 4 to 8 feet of clean sand and gravel, a filter fabric and 2 feet of biologically active organic topsoil. It could be visualized as an insulated swimming pool with the bottom sloping to a collection sump and cistern at the deep end, and with a heat exchanger built into it. This area functions as (1) plant growth space, (2) graywater sand filter, and (3) thermal mass.

The combined thermal capacity of the enclosed concrete, water and sand/gravel bed is over 100,000 btu/degree F. With an overall building U-value estimated at 530 btu/degree F, this provides a system time constant of 188 hours. What this means is that, at an outdoor temperature of 10 degF, and a starting indoor temperature of 70 degF, if you had a sudden and total loss of all heat input, it would take over a week for the house to freeze.

Heating System The primary heat source is a small (100 MBH input forced draft gas-fired condensing boiler, which supplies hot water to a small (1/4 hp) fancoil unit for space heat, and to a heat exchanger coil and storage tank for domestic hot water needs. The fancoil control valve is controlled by a thermostat strategically located near the back of the fireplace, so that when the fireplace is warm, the boiler doesn't fire. The 3" boiler vent is routed through the garden area to an exterior wall cap. Provision is made for installation of a motorized damper in the vent, to allow diversion of exhaust gases to the garden area, subject to control of a CO² sensor in the growing area.

Contrary to conventional design, supply air is not distributed to a peripheral duct system, but is ducted instead to a sheet rock enclosure around the back and sides of the fireplace, and distributed from the center of the space. Floor registers under the windows to the sunspace return the coolest house air directly back to the fancoil unit, reducing the temperature difference at the window surface, providing higher coil heat transfer efficiencies, and eliminating floor drafts.

Backup heat is provided by a Finnish fireplace, a custom-built wood-fired masonry heater located at the center of the relatively open floor plan. This heater is able to heat the entire house on the coldest winter day, providing gentle low-temperature radiant heat to the surrounding surfaces. Contrary to typical cast-iron "airtight" wood stoves in which temperatures are regulated by limiting the amount of combustion air, the traditional Finnish fireplace is designed for maximum firebox temperatures, depending on the large amount of mass to regulate the heat output to the surrounding space. These heaters typically operate at efficiencies equal to or higher than modern stoves with catalytic converters.

Ventilation System House ventilation is provided by both the heating system fancoil unit, and a 200 CFM heat recovery ventilator (HRV).

Supply: The fancoil unit includes a filter and mixing box with manually controlled outside and return air dampers which can be adjusted from 0 to 100% outside air. During the winter months, the outside air dampers are closed, with the HRV providing all fresh air requirements.

The HRV runs continuously on low speed, providing about 0.3 air changes/hr. A dehumidistat in the living space cycles the two-speed fan to high speed to maintain setpoint. Tempered fresh air from the HRV is ducted directly to the sunspace at about the same temperature as the sunspace air temperature. From there, it is returned to the living space. The dry tempered outside air dehumidifies the sunspace, and the moisture picked up from the sunspace in turn humidifies the house. The inherent design solves both humidity-related problems with no additional equipment or energy penalty.

Exhaust: Typical exhaust outlets (i.e. kitchen cooktop, toilet rooms, dryer exhaust etc., are ducted to the composter enclosure instead of to individual separate penetrations through the envelope. The composter enclosure is connected to a roof mounted gravity exhauster through an air-to-air heat exhanger sized to provide one complete air change per hour.

Water Systems

Fresh water supply: Fresh water is obtained from two sources: rain water from the roof, and water from a seasonal spring. Spring water is collected and stored in an external 5,000 gallon cistern at head of the driveway. The water collected from the roof is used to replenish the treated water supply stored in a 5,000 gallon cistern inside the heated envelope. This water runs from roof drains through internal piping to the greenhouse growing bed/gravity sand filter and through a UV sterilizer before use in the house.

Gray water: Household gray water undergoes four levels of mechanical and/or biological filtration before being sterilized and stored for reuse. At each level the nutrients in the water support a micro-ecology of organisms which in turn purify the water. These consist of:

  1. Primary Biofilter: Gray water first drains by gravity to a biofilter located in the utility room below the house. Most of the organic pollutants and settleable solids (>95%) are removed at this stage.

  2. Constructed Wetland: Treated effluent from the biofilter is pumped up to the greenhouse, into one end of a small semi-circular trench encircling a goldfish pond. The trench (bog) is filled with pea gravel planted with various aquatic plants, e.g. umbrella palms (Cyperus sp.), dwarf cattail (Typha minima), pickerel weed (Pontederia sp.), duckweed (Lemna sp.). Additional polishing, and nutrient removal occur here.

  3. Pond: Water overflows the bog into a small pond with water lilies and goldfish. The fish serve as sentinel species, or water quality monitors--our "canaries in the mine". A small (6 watt) air pump continuously aerates the pond, and a small circulating pump continuously recirculates pond water through the bog.

  4. Soil Filter: Water overflows the pond into a grid of perforated drain pipe buried in the garden growing bed. A microecology of soil organisms (fungi, bacteria, earthworms etc. in the biologically active topsoil further recycle the waterborne nutrients into humus.

  5. Sand filter: The water then continues to seep down through the filter fabric and the sand/gravel filter till it hits the sloping bottom. A perforated collection pipe at the lower end collects the filtered water for UV sterilization, storage and reuse in the house. This water is used for all purposes except for cooking and drinking. Drinking water is obtained from a counter-mounted reverse osmosis unit located next to the vegetable sink in the kitchen. This accounts for 2-3 gallons/day, at most.

All graywater is purified and reused in the house. It is a fully closed system.  The house is not connected to city water or sewer systems, well or septic tank, yet we are in no way deprived, having an effectively limitless supply of clean water.  In this house, there is no good reason to, for example, shut off the faucet while brushing teeth.

Additionally, since the used water remains within the heated envelope, the temperature of the water entering the water heater is higher, reducing domestic hot water heating requirements, and the heat put into the hot water contributes to space heat demand.

Toilet Wastes Toilet wastes are composted in an innovative batch feed composter served by low-flush (1.5 pints/per flush) marine toilets.

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