Heat from the Underground:
A new twist on an old favorite—the heat pump—is gaining
ground in the green building movement. Geothermal heat pumps (GHPs) use natural thermal energy stored just below the earth's
surface to provide space heating during the winter and cooling in the summer. They also can be configured for radiant heat
and domestic water heating.
Just a few feet underground,
the temperature remains at a relatively constant 50 to 60 degrees Fahrenheit year-round. Animals take advantage of this warmth
by burrowing into the ground to hibernate. Similarly, geothermal heating systems employ buried pipes to access the earth's
warmth for indoor heating.
Geothermal systems do not
burn fossil fuels to create heat. They cost very little to maintain and operate, and they provide homeowners with an affordable
alternative to rising fuel prices–although they are significantly more expensive in first cost.
A Dream Home
When John and Linda Cavanagh built their dream home in Rye, N.H., in 1992,
they wanted to avoid using oil or natural gas. They installed a geothermal heat pump system, but not without careful thought.
John was a little apprehensive about being a pioneer in geothermal technology.
"Geothermal was somewhat of
a leap of faith in technology because the traditional heating system up here is fossil fuel," says John. "When it's not something
your neighbor has, you greet it with a bit of skepticism. That's the New England way."
Today, though, he's happy
with his choice–a direct-exchange (DX) geothermal heat pump from ECR Technologies, Inc. A "desuperheater" takes the
heat collected during the air-conditioning cycle and transfers it to the home’s hot water storage tank for supplemental
water heating in the summer. The result is substantially lower water-heating bills for Linda and John, as the system saves
energy normally used by the hot water heater.
Direct and Efficient
DX geothermal systems offer a number of advantages
over standard water-based geothermal heat pumps, according to Joe Parsons, director of marketing for ECR Technologies. The
key difference is that copper is used for the underground heat-exchange process, which involves only one heat transfer process.
Water-based geothermal systems typically rely on plastic for underground piping, which requires two heat exchanges. As a result,
the system uses about twice the energy as a DX geothermal system, says Parsons.
Greater thermal conductivity,
flexibility and availability in small diameters make annealed or "soft" copper tubing ideal for the long underground tubing
runs required in DX geothermal heating/cooling systems, says Andy G. Kireta Jr., national program manager of building and
construction, Copper Development Association. "Heating and cooling are the biggest energy-users in the home," he says.
Energy Savings
In the past 12 months, the Cavanaghs estimate they have spent a total
of $972 or 38 cents per square foot for heating, cooling and hot water for their 2,600 sq. ft. home. If oil had been their
primary fuel source, their annual heating costs alone would have exceeded $2,000, according to ECR calculations.
The system cost about $9,000
including installation, which required drilling four bore holes about 100 feet into the ground. However, the Cavanaghs received
$8,000 in energy rebates for building their house to Energy Star specifications set by the U.S. Environmental Protection Agency. (Other energy-efficient features used in the home's construction
include structural insulated panels, energy efficient windows and compact fluorescent lighting.)
"DX geothermal gives homeowners
a way to reduce their energy bills, while helping promote a healthier environment," notes CDA's Andy Kireta. "That's technology
all of us can live with."
Making Your House Watertight:
The following steps will give you information about the types of commonly used materials and their
basic properties.
- Building Paper -- Also know as felt paper, tarpaper, roofing paper
or roofing underlayment. Building paper is an asphalt-impregnated paper that comes in different weights. For example, 15-lb.
paper is used for most roofing and wall applications. For most builders, felt appears to be the drainage plane of
choice for roofing, and many builders use it to provide a drainage plane for the walls as well.
Building paper resists air and water getting into
the home, but allows moisture to diffuse through it. Microscopic pores in the paper allow moisture through but are so small
that bulk water can't penetrate its surface.
- House Wrap -- House wrap is a thin plastic that's literally wrapped
around a home over the wood or foam sheathing, cut out around windows and doors and taped at the seams.
Like building paper, house wrap resists air and water
getting into the home, but allows moisture to diffuse through it.
- Thin Structural Sheathing -- Thin structural sheathing can provide
both a sheathing and a drainage plane for the walls. It's approximately 1/8-inch thick, is constructed from recycled wood
fibers and has a water-resistant surface that provides the drainage plane.
- Rigid Foam Sheathing -- Rigid foam sheathing provides insulation
as well as a sheathing and a drainage plane for both framed walls above grade and foundation walls below grade. The R-value
of rigid foam sheathing ranges from R-3 to R-5.
Heating Your Home: Alternative Options:
There are many ways to supplement your central heating system, but one of the most common is to use a fireplace to
gain additional heat in your home.
Fireplaces
are good as an extra heat source. Let's say it runs on gas. If you have a power outage in the winter, you can get a lot of
warm air from the fireplace. In fact, if you have the luxury to plan ahead, putting fireplaces in key places and using them
as zone heating devices is a tremendous benefit to you. The fireplace would produce an efficient heat, and the concept is
to heat the areas that you are living in rather than heating the whole house with a central heating system.
Other
Benefits to Having a Fireplace
Whether you use a wood-burning or gas unit, a fireplace is a great way to add heat to your home, but
adding heat isn't the only benefit a fireplace provides:
- Adding ambiance to your home is another key benefit to having a fireplace.
- Another big advantage to adding multiple fireplaces to your home is that they can -- if you live in mild climate --
replace the need for a centralized heating system.
Note: Like the rest of your heating
system, fireplaces should be installed by qualified, licensed technicians that specialize in this kind of installation.
Selecting
fireplaces early in the building process will enable the home builder to match the HVAC requirements. Note that fireplaces
are tested to the same standards as the central furnace system.
Which
Type of Fireplace Is Best for Your Home?
Of the
two choices -- wood burning or gas -- both provide the same qualities of additional heat to your home; however, a gas fireplace
will be more efficient in the long term. It used to be that fireplaces were started early in the morning and kept going all
day, but now homeowners aren't in the house all day, so you can walk in, flip a switch on a gas furnace and it's instant heat.
It's instant efficiency!
Rooms That Are Hard to Heat
Speaking of efficiency, how do you handle those rooms in your new home that are hard to heat because
they have an abundance of exterior doors and windows?
Localized space heating does a great job of providing an alternative heating option for just those places. A small
localized space heater can be used to heat a problem area where a person is cold -- yet the whole home doesn’t' need
to be heated. Normally for a residential application, a space heater will be a regular appliance that plugs into a regular
110-volt outlet, and it will have a thermostat usually. It will heat the room without heating the rest of the house.
Some places where you might consider using a space heater to warm things up are a den, a back patio or a bathroom.
Constructive Advice: Be careful when
using space heaters to warm your home. Although small, electric or gas space heaters operate at extremely high temperatures.
They should never be left unattended. Remember, a space heater is just that -- it heats a small amount of space. So take care
not to use it in place of a centralized heating system.
Jump Ducts Increase Energy Efficiency
Jump ducts are an increasingly
popular method for improving the energy efficiency of homes with forced-air heating and cooling systems. They address the
critical issues of equalizing air pressure in various parts of the home and of handling return air.
When managing the heating and cooling flow within any building, it is challenging to ensure that air moving into rooms
equals the air moving out of rooms and back space-conditioning system. If more air enters than exits the room, the air pressure
in the room increases and exceeds the pressure outside it. Without balanced air pressure, energy efficiency decreases as conditioned
air escapes through the building envelope, through unplanned routes such as leaky windows or around electric outlets.
Houses have traditionally used a very distributed means of handling return air, according to Duncan Prahl, an architect
and research manager with architecture and engineering consulting firm IBACOS, which conducts research for the U.S. Department
of Energy's "Building America" program.
"Historically contractors would try to take return air from every room," Duncan says. "They would use wall cavities or floor cavities
and connect them in a convoluted way to the return air system of a building. Research has found that is a very inefficient
way of handling return air. It's leaky, and it draws in outside air because cavities are typically connected to the outside."
Jump ducts are a way to avoid the highly distributed, leak-plagued traditional means of handling return air. Duncan explains that one central return in the main body of the house
reduces the cost of HVAC and provides effective air flow. Jump ducts handle return air from rooms that can be isolated by
closing doors; the jump ducts move air from the room to the hallway and ultimately to the central return air duct. "Jump ducts
are a best practice," he adds.
Keeping it simple
With comparable
initial costs, jump ducts are relatively simple and more efficient than the traditional method of using building cavities
for return air. A grille on the ceiling of the room is connected through ductwork to a grill in the hallway's ceiling. Air
exits the room through the jump duct into the hallway, and then moves through the hallway to the main return duct. The simplicity
of the system makes leaks less likely.
But what about noise and light following the same pathway in and out of a room? Duncan recommends the use of insulated
flexible duct, which muffles sound. And although a jump duct can be as short as three feet, Duncan recommends a length of six to eight feet to help prevent light pollution, as well
as to further dampen noise moving between a room and the hallway. Low-cost stamped-metal grilles are typically used to provide
a finished look on the ceiling. Duncan adds that those with
a net free area of greater than 80% may increase the ease with which air passes through the jump duct.
Duncan says that while builders should use jump ducts in any new home with a forced-air HVAC
system, retrofitting existing homes may not be cost-effective. However, if a home's occupants experience problems related
to return air, such as extreme inefficiency, dampness or other comfort problems, jump ducts are worth considering. It is relatively
straightforward to gain access to the space above the bedrooms and hall, and a central return can be accommodated in the main
space of the house.
