Posted on: 07/01/2004
e-House: Toward The Perfect Mechanical System
Michael McDonough,AIA, NCARB & Sephir Hamilton and Lloyd Hamilton
Author's Note:
Tomorrow Overnighted
The
idea for e-House occurred to me sometime in 1999. Simply put, it was
the fact that everything required to build a perfect vision of the
future was actually available now. Anything a forward-thinking
architect could imagine was invented, manufactured, packaged,
searchable on the Internet, purchasable with a credit card, and
shippable overnight.
The
green, sustainable technologies that could make for an energy-efficient
future were there: super-efficient insulations, radiant cooling systems
with geothermal hook-ups — you name it. Smart building controls were
there, too: enough software, sensors and networking capabilities to run
an entire building automatically. A house could monitor fuel efficiency
while you watched a movie.
The
problem was that all these wonderful things were unavailable in one
coherent, marketable, understandable package. It was as if you had
stumbled across a 10,000-piece jigsaw puzzle of the Mona Lisa, but the
cover of the box was missing and the pieces were all over the floor.
You could tell it meant something important, but it would be quite an
exercise to form a clear picture.
I
had seen this incoherency for decades. First, I studied and worked with
environmental artists in the 1970s and they taught me about the
lyrical, image-making power of nature and built form’s response to it.
All this while the rest of the world was dancing to disco.
I
also saw the same short-of-the-mark efforts of enlightened
businesspeople and manufacturers throughout the 1980s and 1990s. Small
companies offered amazing recycled content, energy-efficient and
nonpolluting products: soybean wall tiles, high-strength cellular
recycled paper construction panels, hemp particle board, bamboo
printing paper.
As
often as not, these products would start in someone’s garage, and be
withdrawn from the market with the company in bankruptcy, just after
the product literature was finally distributed. Some large companies
offered green products, but didn’t market them as such, often because
they believed that talking about sustainable technologies was
irrelevant, and that it would have no impact on sales.
Fast
forward to the turn of the 21st century. Amazingly, a lot of green
technologies have somehow survived, and new ones keep popping up all
the time: new concretes, recycled blue jeans insulation, sustainable
forestry lumber, healthier paints, formaldehyde-free building panels,
and so forth.
Traditional
building techniques (so-called “alternative” technologies) now are
recognized as having value in terms of energy efficiency, local
materials sourcing and cultural identity. Operable windows and
high-efficiency fireplaces have a place in the future, only now they
are “fresh air delivery systems” and “renewable-resource-fueled
equipment.”
e-House
— located in the mid-Hudson Valley north of New York City — is the
manifestation of these ideas. Stylistically, it is both contemporary
and traditional. Big, sculptural trapezoids are cantilevered off a
traditional stone-covered core.
The
roof deck has a monumental south-facing stair. Jammed with technology,
embodying craft, I like to think of e-House as a model for the future
of building — not so much the shapes, but the “adjust to nature” ideas
behind them.
Dozens
of people have contributed to the development of e-House, but a few
deserve special mention here. The internationally renowned engineer
Valentine Lehr provided early encouragement regarding the mechanical
system’s concepts. The father and son team called Verdae has taken on
the mechanical system fine-tuning, number-crunching and installation
tasks at e-House, and have joined me here as co-authors. Peter Caruso
of Monitor Products put us on a technology diet, guiding us into the
simplest iteration of a complex system. Bruce C. Duffy serves as
project manager, forever cracking his brilliant, polymath,
perfectionist whip.
This
article is an exploration of e-House’s energy-efficient heating and
cooling technologies, and its transformation from a gleam in my eye to
what we collectively like to think of as a high-performance building
leaning toward the perfect mechanical system.
Michael McDonough, AIA, NCARB
In
the e-House model, the perfect heating and cooling system would be
based principally on human comfort factors. It would always feel like a
spring day indoors, and the human skin would be the great arbiter of
things mechanical. In other words, “If it don’t feel right, it ain’t right.”
Sure,
from a technical point of view, it would be energy-efficient and
multitask wherever it could. It would make full use of all waste heat,
store energy for future use and allow for both passive and active
systems. It would ideally control itself, using high-tech controls and
building intelligence, but would be based on readily available
software, and simple temperature and humidity sensors. It would have
super-sophisticated systems where it needed them, but would also make
use of time-tested (“alternative”) technologies when they did the job
best.
Those
are our assumptions, and — bearing in mind everything has to be ordered
over the Internet, available now, shippable now and ready to go
“out-of-the box” — this is how we see it (and how we are building it)
so far.
Think
of e-House as a high performance building first and foremost. It is a
super-tight, super-insulated, “green” building. Moisture in the
building — water vapor — is controlled through carefully engineered
sequences of materials acting as vapor diffusion resisters (in industry
parlance, VDRs). This means that the interior finishes, the core
materials of the walls (SafeCrete autoclaved aerated concrete and
Winterpanel structural insulated panels), exterior finishes, the
insulation in the roofs (Applegate recycled aper cellulose), and even
the roof assembly all are designed to complement each other, and to
allow the buildng envelope to move moisture out of the core to the dry
side of the wall.
These
“passive” whole-house moisture control systems are complemented by
active mechanical ventilation: a fully balanced, whole-house system
operating on neutral building pressure, and a state-of-the-art
Nutech/Lifebreath Energy Recovery Ventilator/Heat Recovery Ventilator
(ERV/HRV) system that provides full fresh air all year long while
saving energy — superb indoor air quality at bargain operating costs.
The passive and active systems meet up at motorized windows (carefully
placed as high-up and low-down in the structure as reasonably possible)
that can fully purge the building’s air in about five minutes (about 12
air-changes an hour).
Retaining Maximum Energy
Because
energy efficiency counts for so much in e-House, the emphasis is on
retaining both maximum harvested and generated energy. An in-ground
cistern (under a summer kitchen and terrace) acts as a ground-coupled
thermal reservoir, collecting rainwater and storing warm or cool water
rejected by building systems during normal operation.
A
WaterFurnace water-to-water geo-exchange heat pump allows this energy
to be employed for domestic hot water preheat — this using Amtrol's
StorageMate[TM] in conjunction with its new BoilerMate EZ Series and
Extrol Expansion Tanks — or for snowmelt functions. And a WaterFilm
Energy Inc. drain heat recovery unit cuts the hot water cost of a
typical shower in half.
Truth
be told, initial construction costs would be higher than a typical
home, but not out of line with custom home costs. But we also are
thinking long-term here. Lower operating costs and multitasking
strategies allow the system to “fire on all cylinders” with tremendous
efficiency 24/7/365. The cistern, for example, provides irrigation for
gardens (we get an average of 30,000 to 40,000 gallons of rainwater off
the roofs and terraces each year), and a dry-plug for exterior fire
suppression. The real fire suppression system would be indoors;
however, its distribution system is no bigger than 1/2-inch diameter
coils of potable water PEX. That is because it would be an extension of
the building’s Uponor Wirsbo AquaPEX potable water system, looping
through the ceilings, connected to recessed sprinkler heads. Note that
our “good old-fashioned potable water well” multitasks, introducing
ground-temperature water, lowering cistern temperature when necessary.
(The boiler, which would use the cistern as a preheater, can raise the
cistern’s water temperature at the geo-exchange heat pump when
required.)
Back
outside, the south-facing roofs and roof decks have mechanical system
(as well as rainwater collection) functions. Roof decks are covered
with a unique nonslip exterior grade porcelain tile that sits on
PEX-grabbing insulation and uncoupling membranes by Crossville and
Schluter, respectively. These tiled and insulated view platforms double
as deer-proof potted plant herb gardens, and three-pete as snowmelt
systems, solar collectors and solar diffusers (depending on the
season).
Nonroof-deck
roofs both shed their rainwater into the cistern, and capture air and
rain water pollution by bonding it to Follansbee’s stainless-steel and
zinc roofing. The roofing doesn’t decay when exposed to pollutants; it
gets stronger.
Interior
comfort heating and cooling are provided through the floor assembly
using a constant circulation hydronic system (also by Wirsbo, with
Danfoss controls) and an LP-gas-fired sealed combustion boiler (MZ-25C
by Monitor Products with no required annual maintenance and a near-zero
failure rate). Venting is Z-Flex by Z-Vent, with selant-free, fail-safe
gasket and locking band connection. The infloor system features he-PEX
set in concrete that is, in turn, sandwiched between two layers of
oriented strand board and topped with white oak wood flooring. e-House
can feed either warm or cold water through the floors, or harvest
passive solar heat from southeast-facing windows through the same high
thermal mass radiant floor assembly.
Temperature
and humidity sensors let e-House’s building intelligence computer know
where the system is hot and where it is not, at both interior and
exterior conditions. In full-bore building intelligence mode, the
computer gathers data from the sensor, making decisions as to what goes
where, mixing and shunting energy back to the manifolds and controls
for redistribution throughout the building.
If
you think this sounds far-fetched, just remember that the e-House uses
a small fraction of the computing power needed to, say, start your car
in the morning or deliver an e-mail. We need to ask more from building
intelligence; the capabilities are there.
The
radiant industry tells us that radiant cooling works, but in humid
conditions, dew point and condensation issues make it a risky choice.
Radiant ceilings, it also notes, require condensate gutters, and you
have to construct PEX-based ceiling panels or install manufactured
radiant ceiling panels — in addition to the infloor systems for heat.
No
matter what, the dew point must be kept below the temperature of the
circulated cooling fluid. Radiant floor temperatures have to be
strictly controlled, and condensation at a floor-based system is even
more important, because the floors will get slippery fast and warp over
a period of time. (Ceilings just drip.)
Not In My Backyard
So
why infloor radiant cooling at e-House? We like installing one radiant
system rather than two (floor vs. floor and ceiling), and we like a
challenge. But we also like to hedge our bets: “Conventional”
construction can “leak” (i.e., allow thermal, air and water vapor to
move along virtually uncontrollable and undetectable pathways) so much
that it is very difficult to fully dehumidify a building.
e-House’s
high-performance, super-insulated building envelope, however, allows us
to control thermal, air and water vapor infiltration and exfiltration.
This allows us to “deep dehumidify” first (before we cool), ultimately
reducing our cooling load by as much as 70 percent, while the house
remains free of condensation.
e-House’s
deep dehumidification is achieved by a simple chilled water coil within
the ERV-HRV ducted air flow. And it is that airflow — specifically
displacement ventilation — that completes the big mechanical system
picture here. Conventional wisdom teaches us that hot air rises and
cool air sits on the floor. Fluid dynamics and displacement ventilation
principles, however, redefine the conventional wisdom model.
In
e-House, displacement ventilation encourages air temperature to
stratify like a thermal layer cake — warmest on top, coolest on the
bottom. Ducted, recirculated interior air enters the space along and
across the floors, creating subturbulence that engineers would term a
“nearly laminar” flow. This is more typical of viscous fluids than air.
As it is (barely) churned up and warmed, the air moves up into these
stratified zones, displacing the air that was there before it.
In
other words, a little bit of strategically ducted air can shake up the
air in the thermal layer cake, but not the air temperature. Relatively
low loads, low volume and low velocity ensure that the stratification
isn’t extreme enough to be perceived as uncomfortable.
Also,
we are still primarily a radiant cooling system, cooling objects in the
room. Displacement ventilation is focused on the relatively minor
convection components of the radiant system. Also, at e-House, a
return-ducted negative pressure point exists at the high point of the
building’s relatively open floor plan. Indoor air pollutants and odors
are captured here, then filtered and recirculated though the ducted
ERV/HRV system. Except for 200 CFM of bathroom exhaust and a kitchen
ventilation hood with balanced make-up and exhaust air, what goes
around in this system comes around — literally.
In
other words, a little bit of old-fashioned convection mixed with
state-of-the-art deep dehumidification can go a long way in radiant
floor cooling, making it comfortable enough for a hazy, hot and humid
day in late August. One side note: Thermal plumes from people,
equipment and sun-exposed floors will turn cold air into warm air that
(again) moves upward — like little thermal “worm holes.” (“Star Trek”
meets e-House.)
As
to e-House’s “alternative” technologies, the exterior finishes are
wide-mortared, semi-coursed, site-sourced stone and back-primed cove
siding — a tip-of-the-hat to local building traditions. (We also get
additional thermal mass, drainage planes, increased R-factors and wind
breaks from these humble technologies.)
The
roofs and roof decks move their rainwater down and into the cistern
using scuppers, leaders and simple gravity. All the windows are
operable and screened. Passive solar glazing is on the south and
southeastern sides of the building. This is countered by roof overhangs
designed as shading devices. All rooms have day lighting, all see the
first light of dawn all year long (even if it is reflected off a wall
through a monitor window), and every room has cross-ventilation.
A
great room on the main floor contains kitchen, dining and living
spaces, and is modeled on traditional farmhouses, complete with a
wood-burning fireplace and bread oven. But these have super-insulated
(Isokern and Dura-Tech) chimneys and feature a 200-year-old
Rumford-style fireplace finished in highly heat-reflective soapstone.
Most
of the time, a few logs in the Rumford along with the occupant,
lighting and equipment loads will heat the place in winter, and
cross-ventilation from open windows in summer will keep things cool
enough to be comfortable. We figure we need about 10 Btus per square
foot at minus 20 degrees F with a 20 mph wind. No matter. The cistern
spent the summer collecting heat for that chilly day, when it comes.
About the authors:
Sephir Hamilton and Lloyd Hamilton work with Verdae LLC, a sustainable
practices consultation firm located in Poughkeepsie, N.Y.Sephir holds a
Bachelor of Science, Mechanical Engineering from Clarkson University
and Master of Science, Mechanical Engineering from Massachusetts
Institute of Technology. His primary areas of expertise are
whole-building energy design and analysis, room air-flow and thermal
system design. Lloyd Hamilton has over 25 years of field experience in
plumbing, building performance, radiant hydronic and other mechanical
systems, is an IGSHPA accredited installer of geoexchange systems, and
a charter member of Building Performance Contractors Association of New
York. Visit Verdae LLC at www.verdae.com.
Michael
McDonough, AIA, NCARB was educated at the University of Massachusetts,
Massachusetts Institute of Technology, and the University of
Pennsylvania. He has specialized in sustainable practices architecture
for more than 20 years, and has designed projects internationally.
Widely published, he has won citations from the American Institute of
Architects and Industrial Design Society of America, and has written
for the New York Times, ID Magazine, Metropolis, Metropolitan Home,
Builder, Wired, and other publications. He also authored “Malaparte: A
House Like Me,” and coauthored “The Smart House” with James Grayson
Trulove. Visit him at www.michaelmcdonough.com.
e-House For Wet Heads
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e-House heat loss modeling was based on the next-generation of DOE-2 software, called EnergyPlus (www.energyplus.com).
This allowed us to get an hour-by-hour, day-by-day energy consumption
model of the building, and informed the design of all systems. We were
specifically able to understand heating and cooling loads and the
sensible heat ratio, which runs as low as 0.60.
e-House has a 30,000 Btu/hr. peak heating load, but
almost 50 percent of that is through high-performance windows
comprising less than 13 percent of the building envelope surface. In a
worst-case scenario, less than 5 percent of the heat loss is from
infiltration, 20 percent from ventilation and 25 percent wall/roof heat
loss. In other words, the high-performance building
envelope skews the relative percentage of the window heat loss upwards;
we fight back with automated window quilts.
The 4.5-ton peak cooling load is about 30 percent
solar, 20 percent window heat gain, 30 percent internal loads, 15
percent roof and walls, and 5 percent infiltration and ventilation.
Here again, the high-performance building envelope skews the relative
percentage of the window heat gain upwards; we fight back with
automated sun shades.
e-House gets dry air delivered along its floors at ~68
degrees F all year-round (cf.: displacement ventilation). It uses a
dehumidification coil and reheat coil in summer, and a heating coil in
winter. In summer, the flow rate is sized for adequate dehumidification
and fresh air; in winter, the flow rate is sized for fresh air needs
only.
e-House supply and return grills are specially
designed and fabricated to have minimum visual impact, and to keep face
velocity low to avoid turbulence noise.
e-House has a high central ducted return that takes
advantage of natural buoyant airflow to trap air pollutants near the
ceiling using (coarse) in-duct filters; this before the stale air is
recirculated though additional filters, and then returned.
e-House employs a constant circulation hydronic
radiant system with a thermostatically modulated zone control, allowing
for optimal comfort and control and maximum efficiency.
e-House mechanical control systems employ a SCADA
(Supervisory Control and Data Acquisition) model employing temperature
and humidity sensors. The sensors signal a whole-house building
intelligence computer through data acquisition cards and a
user-friendly Internet-based GUI. Based on decision tree optimization,
modulating valves open or close to allow more or less flow, keeping
individual rooms within set-point. The e-House constant circulation system will allow
the light catcher (which is also the passive solar sun catcher) to give
up its excess heat during the winter and have it distributed throughout
the house. With this system outside, reset is not needed. e-House building envelope is so tight and so
well-insulated that the fast changing peaks and valleys of building
load associated with outside temperature in a conventional house are
just not a factor. The room sensors will tell us as the load changes,
and the change will be so slow that the high-thermal mass floors will
have no problem keeping up. In fact, we expect the slow change of floor temperature will closely match the slow change of building load.
e-House understands that doors get left open,
fireplace chimneys leak and some stuff just doesn’t work. Plenty of
cured firewood is available on site, and a photovoltaic battery back-up
system is central to our idea of efficacy. We like computer technology,
but admire the work of the late Neil Postman, author of “Informing
Ourselves to Death,” an essay about the disadvantages of computer
technology.
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