Residential Air-Conditioning Systems

Less Common Ducts include Perimeter Loop and Central Plenum Systems

1. the perimeter loop uses radial feeder ducts from the blower that attach to one trunk thats installed around the outer edge of the foundation 2. the central plenum ducts use structural cavities as a pathway for supply or return air plenums

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4. Verifying the metering device is correctly sized and installed on the indoor unit 5. Installing the ACR tubing for the refrigerant lines to connect the indoor coil to the outdoor condensing unit 6. Performing a leak test on the refrigerant lines after they are connected. Evacuating the system to a 500-micron or another manufacturer-recommended level.

Last Steps

7. Connecting the 208/240 V service to the outside unit 8. Installing one low-voltage electrical circuit using 18-gauge wire between the inside unit and the condensing unit, and another from the thermostat to the air handler or furnace. The wire from the thermostat to the inside unit is 18-gauge unless longer than 100 ft, then use 16-gauge wire. 9. Installing the thermostat 10. Installing the condensate drain pipe, pitched in the direction of flow and supported every 10 feet

Multisplit System

A multisplit system connects several indoor units to one outdoor unit, preventing the need to have four completely separate mini-split systems for each room that needs a unit. This type of system saves on equipment and installation costs.

Square and Rectangular Ducts

All square and rectangular ducts must be supported properly to minimize noise and be able to withstand the weight of moving air. To minimize noise transmission, sheet metal ducts should use flexible connectors between the ducts and the air handler. Sealing sheet metal ducts can be accomplished using mastic and/or sealing tape.

Split Systems

Another popular form of residential air-conditioning systems is the split system. A split system is an air-conditioning installation that places the condensing unit remote from the evaporator. Commonly, this system employs a gas or electric furnace that serves as the indoor air handler (into which the indoor coil is positioned) for both the heating and cooling modes of the equipment.

Console Through the Wall Unit

Another type of room air conditioner is the console through-the-wall unit. These units are also known as PTACs (package terminal air conditioners). PTACs can be found in residences, hotel rooms, and nursing homes. Console through-the-wall AC units require that you create an opening in the outside wall for condenser air and ventilation.

Duct Installation

As you'll recall, metal ductwork should be insulated if the difference in temperature between the air inside the duct and outside the duct varies by 15°F or more. Square or rectangular ducts can be insulated on either the inside or outside; round ducts will be insulated on the outside only.

Ductboard Systems

Ductboard is a rigid, fiberglass, insulating board with an outer vapor barrier used to construct plenums and ductwork. Ductboard systems don't require highly skilled tradespersons. They can be fabricated on-site using special knives. Individual sections are taped or stapled together. Ductboard has the advantage of being lightweight and naturally suppresses noise transmission. Like other duct systems, ductboard ducts must be properly supported.

Duct Material

Ducts are available in sheet metal (square, rectangular, or round), ductboard (fiberglass), and flexible materials. Square or rectangular sheet metal ducts are fabricated by sheet metal tradespersons and then assembled on site. Sheet metal ducts require extra precision during manufacture and installation since they don't allow for much adjustment. Individual sections of square or rectangular sheet metal duct are held together with "S" fasteners and drive clips.

Each duct system type must be properly designed and installed to achieve the maximum conditioned airflow possible. Ducts are most commonly located inside the building's insulated environment in the attic, between ceiling or floor joists, and in the basement or crawlspace, laid out in a radial, reducing radial, extended plenum, reducing extended plenum, perimeter loop, or central configuration.

Either state or local codes will dictate minimum design criteria and installation requirements for air conditioning and heat supply duct systems. Due to geographical mandates, it's important for you to keep up to date on the latest building codes for your particular location. Different types of duct systems can be used together to achieve the best overall system performance. To ensure that proper airflow is maintained, you should pay particular attention to the method and location of the branching from the main trunk.

Extended Plenum

Extended plenum duct systems use a large trunk duct that travels the length of the building from the air handler

Flexible Duct Systems

Flexible duct is designed to allow for some movement and bending to accommodate installation. These ducts offer the installer a method to easily connect the main distribution trunk to a room diffuser. Flexible ducts are available as uninsulated or insulated units with a moisture-resistant covering. To ensure proper airflow, flexible duct runs should be kept to a minimum, the duct must be properly supported, and tight bends should be avoided if at all possible. These ducts are also lightweight and suppress noise transmission.

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If the insulation is located inside the duct, you should ensure that the insulation is permanently attached so that it can't dislodge and cause an airflow blockage. Also, insulation mounted internally should have a smooth surface to minimize slowing down the airflow.

Air Distrubution

Maintaining a comfort level within an enclosed space requires some type of air movement or air distribution system. The methods available to move air are natural draft and forced air. (Natural Draft and Forced-Air Systems)

Mini Splits

Mini-split systems, also commonly referred to as ductless systems, have steadily gained popularity. These units consist of an indoor unit mounted on the wall and connected via a run of tubing to an outdoor unit. When installed in individual rooms, mini-split systems allow homeowners the option of cooling only occupied areas rather than operating a whole-house central air-conditioning system. As with split systems, these units must be properly installed. If proper installation procedures aren't followed, system performance will be affected.

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R-410A split systems require a nitrogen purge during the brazing of the tubing joints, as cupric oxide forms inside the tubing and solidifies into flakes. Since R-410A systems use a synthetic oil that has more of a solvent tendency than the mineral oil used in R-22 systems, small chunks of the flakes are dislodged and travel through the system to the metering device, causing a restriction.

Radial

Radial systems are designed so that all or almost all ducts run originate at the central plenum

Reducing Extended Plenum

Reducing extended plenum systems have trunk ducts that reduce in size, typically after three to four takeoffs

Reducing Radial

Reducing radial systems are several larger ducts leaving the main plenum that branch into smaller ducts

Room Air Conditioners

Residential air conditioning systems are often made up of unitary air conditioning components. This means all the components are in one unit, which includes the refrigeration, airflow, and electrical systems. A unitary residential air conditioning system is factory-built and tested and typically requires service connections and perhaps ductwork. The room air conditioners are semi-portable and plug into a wall outlet.

Room Air Conditioners (More)

Room air conditioners commonly employ a single capillary tube as the metering device. They also contain a fractional horsepower compressor, more often a rotary type rather than a reciprocating (piston) type, especially in newer equipment.

Round Ducts

Round sheet metal ducts have similar characteristics and installation requirements to square and rectangular designs. The only major difference is the method used to fasten individual sections together, which is to use self-tapping sheet metal screws.

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Since an indoor coil is field installed along with the outdoor unit and the connecting tubing, split systems can be affected by improper installation procedures. Problems such as insufficient evacuation of the tubing system and overcharging at the time of installation will result in customer complaints about the performance of the equipment.

What can a technician determine about the airflow by measuring the fan motor's current?

Since the blower motor full-load amperage is known, a technician can determine if the airflow is correct by measuring the fan motor's current: If the motor's current draw is low, the airflow is reduced (inlet side is blocked). If the current is higher than it should be, a blockage in the supply duct probably exists.

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Stand-alone AC units are located inside and connected to their own duct system. They include an air handler that has an evaporator coil, metering device, drain pan, transformer, blower assembly and housing. Most have water-cooled condensers that are connected to a cooling water source or cooling water loop.

Residential Split System Installation

Steps are as follow 1. Planning the installation, which includes choosing the correct equipment size 2. Installing the indoor equipment: evaporator coils (cased coils, uncased coils, add-on coils) and air handler 3. Installing the outdoor condensing unit, which includes proper placement

A common issue with room air conditioners is that they trip the circuit breaker. How is this issue resolved?

The AC unit can be placed on its own circuit (which requires electrical rewiring). Or, you can get a smaller unit with less electrical draw.

Window Mounted Unit

The best-selling unitary system is the window-mounted room air conditioner. Window units commonly range in size from 5,000 to 12,000 BTU/hr, however; some window units have a capacity up to 20,000 BTU/hr. In cases of these larger systems, the units also have a heating mode in which heat is provided via electric heating elements. In some cases, unitary equipment provides heat via electric heating elements, or some may be designed as heat pumps.

Blower

The blower moves air within a duct system by creating a pressure imbalance (higher pressure on the supply side and lower pressure on the inlet side). Since air occupies space, has weight, and resists movement, the blower must consume electrical energy to turn the fan motor so that air moves within the duct system.

Stand Alone Units

The final type of room air conditioner is the stand-alone air conditioning unit. These are commonly referred to as package units. Package units mounted on rooftops or near the building with return and supply ducting connected are also a form of unitary equipment. These units may be heat pumps or cooling only with gas or electric attached heating systems to provide heat in the winter.

Purpose of Forced-Air Systems

The purpose of any forced-air system is to distribute a known amount of conditioned air to different areas of a structure. The rate and quantity of air delivered will depend on the size and usage of the space being conditioned. A properly sized and installed forced-air system will be apparent to the occupants or users of the space. Components that typically compose a forced-air system include blowers, air supply systems, return air systems, grilles, and registers.

More VRF

The smallest capacity VRF outdoor units are equal to or exceed the largest multisplits—multisplit units can typically handle a maximum of four to eight indoor units, while VRF systems can handle up to sixty-four. They use a refrigeration network to connect all the components of the system and have their own metering devices located in them.

Supply Duct

The supply duct system receives the conditioned air and distributes it throughout the structure.

Variable Refrigerant Flow (VRF)

Variable refrigerant flow (VRF) systems distribute variable amounts of refrigerant to multiple indoor units according to the needs of each zone. VRF systems use both ducted and non-ducted indoor units, but the refrigeration capacity is distributed throughout the building using refrigeration lines.

More Duct Installation

Various methods are used to attach the insulation to the metal duct. Metal ductwork should be wrapped tightly in insulation called duct or bubble wrap and secured using clinch staples. Then the exposed outer edge should be taped with UL 181A duct tape so that no fiberglass is showing. You can also line regular duct, plenums, and return-air boxes with duct liner or bubble wrap.

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When installing a window-mounted room air conditioner, have a drop-cloth to catch drilling and mounting debris, wear gloves to prevent cuts from sharp edges, and get help lifting a heavy unit to prevent dropping. Install the supporting bracket before placing the unit and don't grab onto the tubing when lifting. When servicing window air conditioner sealed systems, you'll find R-22 refrigerant in older units and R-410A in newer equipment.

Forward Curved Centrifugal Fan

also known as a squirrel cage fan that can be driven directly by an electric motor or by a fan belt. This type of fan has blades parallel to the fan axis and moves air at a right angle to the fan axis.

Natural Draft

relies on the principle that warm air expands and rises. Hot-water baseboard heat is an example of natural-draft air movement.

Boot

used at the end of a round duct to allow connection of a rectangular register or grill

Elbow

used for turns in the ductwork

Reducer

used to change round duct from one size to another

Transition

used to changer rectangular duct from one size to another

Wye

used to split one large duct into two smaller ducts

Forced-Air Systems

which repeatedly reuse the same indoor air, rely on mechanical devices such as fans or blowers to move the air.