TechPractices are outstanding housing projects throughout the U.S. where innovative technologies are implemented. Builders and remodelers can use these examples as models for projects of their own.
|Healing House Snapshot
||BBH Enterprises, Inc.
||Affordable single-family house
||Geo-thermal heat pump, ductless air distribution, OVE framing, purified interior air, heat recovery ventilation
While guaranteeing a "dollar a day" heating and cooling
costs, this super tight, energy and resource efficient house also
provides a healthy, indoor environment for a severely asthmatic
client. Located in a moderate income Dallas neighborhood, this
house achieves its health and energy goals on a moderate ($65/SF)
budget by pairing an innovative mechanical and ventilation system
with a novel floor plenum design.
The Healing House is the latest version of a line of energy
and resource efficient homes built by BBH Enterprises. This one
offers energy conservation and near pollution-free indoor air
quality. The new owner, who suffers from chronic asthma and multiple
chemical allergy conditions, has found relief in her new house
and has given it the name, Healing House.
There are a few strategies here for energy efficiency worth
looking into. Air infiltration (.3 ACH) is minimized by carefully
sealing all gaps in the exterior skin, there are extra levels
of insulation, and the house is sited to admit winter sun and
reduce overheating from summer sun. Most of the windows are on
the south elevation, few are to the north and east elevations,
and there are none to the west. Overhangs and thermal mass at
south walls modulate and store solar gain.
This house has a hot air system but no ducts. An electric heat
pump uses a loop of circulated water buried deep in the ground,
teamed with a novel air distribution system. 16" open-web
floor joists create a hollow floor plenum for distributing air
throughout the house with no ductwork. Conditioned air is pumped
into the plenum from a centrally located air handler. This system
works well because the house envelope is very tight and well insulated.
Infiltration loss is low, and air temperature stratification is
minimized. Conditioned air is not forced through at high velocity,
but seeps out at a comfortable, barely perceptible flow.
Return air is collected on the second floor through a dropped
corridor ceiling and at the first floor through the air handler
closet louver door. Air is supplied by an air-to-air heat exchanger
that modulates the incoming air with temperate exhaust air from
bathrooms and kitchen.
The one-and-a-half ton, geo-thermal heat pump made by WaterFurnace
operates at an impressive 16.2 EER cooling capacity rating. Two
250 feet deep wells (drilled by the local utility company) circulate
water to assist in heat pump operation. During heating or cooling,
the constant 65°F ground water exchanges its heat to the refrigerant
at the refrigeration coil. In winter the ground water helps the
refrigerant absorb heat as it is compressed into a gas; in summer
the ground water helps dispel heat from the refrigerant gas as
it reverts back into a liquid. The ground loop's tempering effect
is what gives the system its efficiency. An added plus with this
heat pump installation is the free hot water that is produced
as a by-product of both heating and cooling cycles.
Working in tandem with the heat pump is the Life Breath heat
exchanger by NuTech Energy Systems. Before it provides makeup
air to the air handler, the heat exchanger mixes with the outgoing
exhaust air and transfers 70% of its heat to incoming air. The
heat exchanger works continuously throughout the year, providing
a constant rate of 0.3 air changes per hour. The heat exchanger
works during the cooling season but not as efficiently as it does
This is a modified stick-built house with a few new twists.
Exterior walls are framed with 2 by 6s 24 inches on center. Double top plates
are not needed because joists and rafters, align so that they
never land mid span on a wall plate. Exterior corners are fastened
with metal cleats nailing plates like those used in trusses and
this saves redundant studs. Insulated headers prevent heat loss.
This Optimum Value Engineering (OVE) method saves lumber without
sacrificing structural integrity. Floor trusses support the second
floor deck and exterior walls bear on a thickened edge, post tensioned,
concrete slab-on-grade. Diagonal bracing is of metal strapping
and the exterior is sheathed in 2-foot by 8-foot sheets of 1-inch expanded
polystyrene insulation board. Joints between the polystyrene are
taped with 3M Y808 sealing tape to improve the air tightness of
the shell. The exterior is covered with building paper, metal
lath, and 3/8-inch thick conventional stucco.
Part of the efficiency of this solution is the simplicity of
the framing. The building footprint is nearly square. There are
few framing headers and no dropped beams to complicate loading.
This simplifies air flow for heating and cooling and is an efficient
way to create space with the least amount of material.
Building this house involves a few extra steps. To ensure non-toxicity
of materials, the builder had the client place samples of the
construction materials in her bedroom for a few days to monitor
her exposure to them before giving the go ahead to install. This
provided reasonable assurance that the client would be able to
live with these new materials. Materials that could not be excluded
from the building finishes (such as OSB, composite lumber, plywoods
etc.) are sprayed with Crystal Aire I by Pace Industries. This
paint-like coating of polyvinyl solution effectively seals wood
surfaces from out-gassing. The material cost for interior sealing
was about $500.00. Standard paints and construction adhesives
were replaced with non-VOC substitutes. In addition, recycled products were used wherever
Sealing the exterior envelope is critical to the air tightness
of this house. In addition to 3M tape, GE Silicone caulk and Foam
Plus expanding foam sealant were used. Taping joints and caulking
and sealing the skin is time consuming and adds expense to the
job. But the exceptional performance of the Healthy House is largely
due to its tight envelope. However, there is no vapor barrier
in the wall cavity because heating and cooling are relatively
balanced in importance. Because water vapor is generated inside
during the winter and outside during summer, trapping it on either
side would invite condensation to form somewhere in the wall.
Instead, the walls are built to breathe. The paint specified for
the wallboard is "permeable" to ensure that the painter
does not apply an unintended vapor barrier.
This 1,470 sf home cost about $65/sf for a completed price
of $95,000 including land. The selling cost is about 25% below
the median price for homes selling in Dallas and would, of course,
be lower without the need for multiple chemical allergy mitigation.
But the benefit to the owner is clear. Lower utility bills are
an ongoing benefit both to the homeowner and to the utility.
Because the builder, BBH Inc. is not non-profit, permit fees
could not be waived or reduced. Nor could a requirement to provide
20'-wide alleys be negotiated down despite the lack of need. The
health department did not approve a greywater system for the Healthy
House despite licensed engineering design. The building department
did not understand the HVAC system but permitted its installation.
The homeowner is happy with her new house and wrote a testimonial
to the builder praising the excellence and quality of the home
and describing how she was healed of her asthma and chemical reactions
because the house air is so pure. She also wondered why more houses
aren't built this way. The project mechanical engineer, Ken Muse
of Total Air HVAC of Dallas admitted that he was "pretty
skeptical" using the floor plenum design. After installation
the system performance eased his concerns -- it worked exactly
as it was intended. The house has received the Edison Institute's
E Seal Award and will receive Energy Star recognition in the coming
year. The builder, Barbara Harwood, has produced nine variations
on the house, geared to the affordable market. Her new focus will
be on the up-scale custom market with its healthier profit margins.
The lack of municipal support for lower income development is
also a factor in her new approach.
Do you have a specific question? Try the contacts listed below:
NuTech Energy Systems Inc.
511 McCormick Blvd.
London, Ontario N5W 4C8
9000 Conservation Way
Fort Wayne, IN 46809
2718 Wagonwheel Drive
Carrollton, Texas 75006
Total Air Mechanical Systems