Combustion Air Intake

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Friday, September 10, 2010

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Ductless, Mini-Split Heat Pumps

Ductless, mini-split-system heat pumps (mini splits) make good retrofit add-ons to houses with "non-ducted" heating systems, such as hydronic (hot water heat), radiant panels, and space heaters (wood, kerosene, propane). They can also be a good choice for room additions, where extending or installing distribution ductwork is not feasible.

Like standard air-source heat pumps, mini splits have two main components: an outdoor compressor/condenser, and an indoor air-handling unit. A conduit, which houses the power cable, refrigerant tubing, suction tubing, and a condensate drain, links the outdoor and indoor units.

Advantages

The main advantages of mini splits are their small size and flexibility for zoning or heating and cooling individual rooms. Many models can have as many as four indoor air handling units (for four zones or rooms) connected to one outdoor unit. The number depends on how much heating or cooling is required for the building or each zone (which in turn is affected by how well the building is insulated). Since each of the zones will have its own thermostat, you only need to condition that place when someone is there. This will save energy and money.

Ductless mini-split systems are also often easier to install than other types of space conditioning systems. For example, the hook-up between the outdoor and indoor units generally requires only a three-inch hole through a wall for the conduit. Also, most manufacturers of this type of system can provide a variety of lengths of connecting conduits. If necessary, you can locate the outdoor unit as far away as 50 feet from the indoor evaporator. This makes it possible to cool rooms on the front side of a building house with the compressor in a more advantageous or inconspicuous place on the outside of the building.

Since mini splits have no ducts, they avoid the energy losses associated with ductwork of central forced air systems. Duct losses can account for more than 30% of energy consumption for space conditioning, especially if the ducts are in an unconditioned space such as an attic.

In comparison to other add-on systems, mini splits offer more flexibility in interior design options. The indoor air handlers can be suspended from a ceiling, mounted flush into a drop ceiling, or hung on a wall. Floor-standing models are also available. Most indoor units have profiles of about seven inches deep and usually come with sleek, high tech-looking jackets. Many also offer a remote control to make it easier to turn the system on and off when it's positioned high on a wall or suspended from a ceiling.

Split-systems can also help to keep your home safer since there is only a small hole in the wall. Through-the-wall and window mounted room air-conditioners can provide an easy entrance for intruders.

Disadvantages

The primary disadvantage of mini splits is their cost. Such systems cost about $1,500–$2,000 per ton (12,000 Btu per hour) of cooling capacity. This is about 30% more than central systems (not including ductwork) and may cost twice as much as window units of similar capacity.

The installer must also correctly size each indoor unit and judge the best location for its installation. Oversized or incorrectly located air-handlers often result in short-cycling, which wastes energy and does not provide proper temperature or humidity control. Too large a system is also more expensive to buy and operate.

Some people may not like the appearance of the indoor part of the system. While less obtrusive than a window room air conditioner, they seldom have the built-in look of a central system. There must also be a place to drain condensate water near the outdoor unit.

Qualified installers and service people for mini splits may not be easy to find. In addition, most conventional heating and cooling contractors have large investments in tools and training for sheet metal duct systems. They need to use (and charge for) these to earn a return on their investment, so they may not recommend ductless systems except where a ducted system would be difficult for them to install.

Combustion Air Intake Installation

This chapter from the Energy Saving Edition book gives a detailed description of the Combustion Air Intake installation, which according to code must be an important element of your HVAC ductwork system. In the chapter you can find pictures of all necessary tools, materials and pictures of the Combustion Air Intake installation. There are 31 pictures. Installation is divided into six steps, which represent the entire project in the making.

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How to Use Combustion Air Intake

Homes need to breathe. Fresh air is needed for combustion in furnaces, fireplaces, wood stoves, gas water heaters and clothes dryers. As people make their homes more energy efficient by sealing cracks, adding insulation and doing other things to prevent heat loss, homes can become starved for air. This is especially true when you're using exhaust fans and vented appliances which draw more and more air from inside the house; air from the outside can be pulled into the home, possibly down the furnace vent or fireplace chimney. This is called "back drafting" and can cause carbon monoxide (CO) to form.

CO is a colorless, odorless gas produced when fuel is not burned completely. Automobiles, charcoal or wood fires and improperly vented or air-starved coal, oil and gas furnaces can produce CO.

Be aware of these CO signals:

Headaches, nausea, dizziness
Excessive humidity, heavily frosted windows
Fireplace smokes, won't draw
Furnace vents back drafts (See Fresh Air Check below)

To prevent homes from becoming starved for air, the Uniform Mechanical Code requires that all new homes be built with a special duct that brings outside air directly to the heating system. All furnace and boiler installations in existing homes are also required to have a combustion air duct.

To determine if your home is receiving sufficient fresh air:

1. Close all doors and windows.
2. If you have a fireplace(s), build a fire. Wait until the flames are burning vigorously.
3. Turn on all exhausting devices, such as:

Kitchen and bathroom exhaust fans
Dryers (gas and electric)
Attic fans

4. Turn on all exhausting devices, such as:

Heating equipment
Water heater

5. Turn on all vented gas appliances, such as:
6. Wait 10 minutes for drafts to stabilize.

7. Hold a lit match below the heating system draft hood air intake (see illustration at right).
o If the match remains lit and the match flame pulls toward the draft hood, this indicates sufficient fresh air. Check draft hoods on all other equipment also (gas space heaters, water heaters and additional heating systems). Return appliances and exhausting devices to their original condition.
o If the match goes out, it means the vent may be plugged and/or the air supply in your home may be inadequate.
o Check for plugged vent connectors and chimneys. Repair stoppage and test again.
o If the match goes out even when vent is clear, additional air must be brought into the structure from outside. Refer to the Uniform Mechanical Code or contact a qualified heating contractor or your local gas utility service department.
If your house is starving for air, a vent or fresh air intake needs to be installed directly to the furnace area; until it is installed, limit use of clothes dryers, fireplaces, furnaces, and mechanical exhaust fans. Operating more than one of these devices at a time can contribute to back drafting if your home doesn't have an adequate fresh air supply.
Materials used for ducting must meet standards described in the Uniform Mechanical Code. Flexible ducting is not recommended because ridges create turbulence which reduces air flow. Before installing a duct, check with your local Building Codes office for size and materials. Here are example of installations of fresh air ducts.

Duct Supplying Outside Air to Floor in Furnace Area

1. Be sure duct is sized in accordance with the Uniform Mechanical Code.
2. Place the outside air intake duct (A) at least one foot above grade level.
3. Cover the air intake with ¼” mesh screen and hood.
4. The duct must discharge the fresh air at a level no more than one foot off the floor.

As you understand it’s very important to have a combustion air intake also from the energy saving point of view, especially if you have a mechanical room. The idea behind this is you don’t using conditioned air as a combustion one. Also it’s important to bring a combustion air to the water heater or furnace as close as possible.