Page 43 - November 2015 Green Builder Magazine

Exteriors / Roofing / Structure / Insulation / IAQ / Windows / Heating / Lighting / Appliances / Faucets & Fixtures / Finishes / Cabinets & Tops / Alternative Energy

Mini-Split Heat Pumps Air-Source Heat Pump

Virtues Flue Warm 41
gases air to
■■ Can provide Burner house
heating Cold air Circulating
and cooling return fan

■■ No need for a
chimney or
exhaust flue

■■ More fuel efficient
than a fossil fuel
furnace or boiler

Caveats

■■ Not practical in
very cold climates

■■ Does not get air as
hot as a furnace

DUCTLESS MINI-SPLIT HEAT PUMPS, or MSHPs, HIGH-EFFICIENCY BOILER www.greenbuildermag.com 11.2015
are a good heating and cooling option for homes
without duct systems. Mini-splits can supplement Hot Water Wiz
an existing wood stove or condition a new addi-
tion, and they are also ideal for super-efficient new homes. A boiler burns oil, natural gas or propane to heat water. That heated
Mini-splits have two main components: an outdoor compres- water is then pumped through a system of pipes to radiators,
sor/condenser and an indoor air-handling unit. A conduit, baseboard heaters or a radiant floor.
which houses the power cable, refrigerant tubing, suction
tubing and a condensate drain, links the outdoor and indoor A good boiler will offer efficiencies of 90 to 95 percent and
units. MSHPs are quiet, efficient and flexible, and because will include many of the same technologies as a high-efficiency
there are no ducts, they are easy to install. Here are a few furnace. These include a modulating burner that matches the heat
points to consider if you are in the market for a mini-split: output to whatever the thermostat is calling for at the moment,
■■ Choose the Right Mode. MSHPs work best when advanced heat exchangers to extract more heat from the same
allowed to modulate. Using them in “on/off” mode not only amount of fuel, and the ability to recover heat from the exhaust gas
compromises their efficiency, but will likely result in wide by condensing it. The resulting exhaust is cool enough to be vented
temperature swings and discomfort. out of a plastic pipe. In the best cases, this condensing process
■■ Know Yourself. Because MSHPs don’t rely on duct- can squeeze 10 to 12 percent more usable energy out of the fuel.
ing to distribute air, be aware that your habits may affect
temperatures in different rooms. For example, if you tend AIR-SOURCE HEAT PUMP
to leave your bedroom door closed all the time, it may be
warmer or cooler than the rest of the house. Reverse Motion
■■ Build Efficiently. The number of MSHPs required to
heat your home depends on its square footage, but also on A heat pump is basically an air conditioner that works in reverse
your home’s layout. A small, very efficient two-story house to provide heat. The heat pump captures and concentrates heat
might be served by just one MSHP, but be aware that there from one area, then releases it to another.
may be temperature differences between the two floors, even
if you use distribution fans. In heating mode, the heat pump takes heat from the outdoor air
■■ Bigger May Be Better. Oversizing MSHPs—choos- and delivers it to the home’s distribution system. In cooling mode,
ing units rated for a larger house—is okay. Oversizing can it reverses direction to work like an air conditioner, extracting
even be beneficial, since MSHPs modulate their capacity and heat from inside the house and blowing it outside. In cooling
reach their highest efficiency when running at the lower end mode, this waste heat can also be used for water heating. The
of their capacity range. most common type is the split system, which uses separate indoor
and outdoor units, but you can also get packaged systems that
place everything in a self-contained outdoor unit. While air-
source heat pumps can offer efficiencies of 200 to 300 percent,
they’re most efficient in the southern part of the country. A
backup electric or gas heater may be needed when the outside air
drops below a certain temperature. Although different versions
are made for forced-air and hydronic distribution, the forced-air
type is the most common. Heat pumps don’t get air as hot as a
furnace or boiler, so may require more airflow to maintain the
same temperature.

continued on page 43