Electronic Air Cleaners
The most efficient air filter for improving air quality is the electronic air cleaner. Air returning to the furnace or air handler passes through a screen to trap any large dust particles or objects. Using line voltage to power circuitry, a positive electrical charge of high voltage (upwards of 12,000 volts) is sent through fine wires stretched across the air stream immediately behind the screen. The dust particles pick up a positive charge, and then pass through plates or grids that are negatively charged. Opposites attract, and the dust particles collect on the plates. Smoke is microscopic particles, and is trapped as well. Ozone is created from the charged air, which helps kill bacteria and odors.
Electronic air cleaners will usually operate at 95% efficiency, allowing little or no dust to pass through. The dirtier they get, the lower the effectiveness, so clean grids are a must. Before removing the screens and grids for cleaning, it is imperative to shut the power off and wait a few seconds to allow the grids to lose the static charge. They are dishwasher safe as long as they fit inside. If not, sloshing around in a tub of hot soapy water will loosen dirt that can be blasted off with a garden hose.
Extreme caution must be taken when handling to protect the grids and the person handling them. The plates are very sharp, and can cut like razor blades. The fine wires stretched across the grids are delicate and crucial to proper function. Proper spacing between the grids is important. Do not bend or distort them.
If the grids are not completely dry when installing them, do not turn the power back on; damage to the power pack can occur as the water will short the grids out. If in doubt about the dryness, leave the power switch off for a day or two; the air flow will take care of any residual water. Arrows one the grids will display the correct direction for air flow. Improper installation will render them useless. If the air cleaner was installed correctly in the return air duct by the original HVAC mechanic, air flow will be going from the duct toward the appliance. The arrows should do the same.
Troubleshooting falls into two categories: Grid failure or power failure. Excess dirt or a large object stuck in the grids will cause an electrical short. A loud snapping noise will sometimes indicate this problem. If cleaning does not stop the snapping and the grids are bone dry, inspect the fine wires stretched across the terminals. If they are white from oxidation, gently run an old soft toothbrush up and down them once, then rinse and dry again.
Most electronic air cleaners have a light to show operating power. If the light is not on when the system is running and the switch is on, there are two possibilities. The power pack has burned out, the power to it has been disconnected, or the unit has a pressure switch to sense air flow and charge the grids and it has failed. Either repair means opening up the power pack, exposing dangerously high voltage. This task should be left to a qualified technician.
13 SEER Air Conditioner Efficiency
As of January 2006, central air conditioning equipment installed in the U.S. must be 13 SEER. SEER stands for Seasonal Energy Efficiency Rating. It is the ratio of cooling produced in BTU, divided by the amount of electricity in watts, which is required to produce a certain amount of cooling. A 10 SEER air conditioner requires 30 percent more watts than a 13 SEER of the same tonnage or output. This does not include electricity needed to deliver the cooling to each room, so blower use is a constant and approximately 3 percent.
There are two main parts to a central air conditioner, indoor and outdoor. A thirteen SEER condenser (outdoor unit) can only be efficient if paired with a 13 SEER coiling coil (indoor unit). Many cooling coils can be upgraded by adding an expansion valve; in fact many manufacturers have done exactly that to their existing product line to meet 13 SEER standards.
A 13 SEER condenser is approximately 50 percent larger, physically; than a 10 SEER condenser. It is also more expensive. When an older air conditioner fails, replacing it will be considerably more expensive from now on. Not only because the outdoor unit simply costs more, but also because the indoor section must be addressed.
This efficiency upgrade does not directly affect warm air furnaces with central air conditioning, if the furnace was properly matched to the air conditioner to begin with. The heating mode is not affected, and the air flow should not need change. The cooling coil which sits on top of the furnace will be effected and possibly the corresponding ductwork.
Most air handlers however, are more specific to the coil and condenser and will be subject to more frequent replacements, if the coil cannot be upgraded or simply replaced. Unlike the furnace, where the cooling coil is a modified fit, the cooling coil inside of an air handler is more or less a custom fit. Replacing the cooling coil itself will depend on the age of the system, as manufacturers have altered their many coil styles over the years, and a new coil may not physically adapt to the old air handler cabinet. Replacing the air handler and coil will most likely require ductwork alterations. When the ductwork does indeed need modification, it would be a good time to upgrade the filter system and insulation values of plenums and accessible ducts.
Additions & Remodels
New construction is simple compared to an addition or remodel project. The insulation values are usually consistent in a new house, but in an older home, it may vary from room to room. It is not sufficient to merely supply the additional room(s) with the calculated amount of heat, as it may throw the existing rooms out of balance. Sometimes it is necessary to supply the new room with an incorrect amount to keep it proportional to the rest of the house. In severe situations, the newer area may need to be heated as a separate zone. In any case, a heat loss/gain should be performed on the existing rooms as well, and the existing system should be evaluated to determine how well it conforms to the calculated requirements. A new heat loss will also tell you if the existing heating system can accommodate the additional load requirements of the addition.
Also keep in mind that the rooms adjacent to the addition have lost exposure to the outside and will need less heat.
These same conditions also apply to remodeling projects, where the addition or removal of windows can seriously affect the room’s heating needs, as will adding doors or raising ceilings.
Air Filters
Removing air born dust and dirt benefits the people breathing the air and the machinery moving the air. Dirt accumulates on bearings and motor windings and gradually restricts air flow through a heating or cooling coil and settles in ductwork.
Collecting the dust from before it passes through the furnace or air helps to protect the machinery, and the filter should always be installed in the return air duct.
Mechanical or adhesive filters are the least expensive but the least efficient. Constructed of spun fibers shaped to form a mat, they are framed with cardboard to specific sizes. As air is moved across the fibers, dust is attracted and sticks to an oil film or glue sprayed on the fibers. This type of filter collects between 6% and 8% of the dust passing through when new. Efficiency will increase as the filter gets dirtier, but air flow will be restricted as well. Available at many hardware and retail stores, they are inexpensive, and should be replaced monthly if the system is in constant use.
Some manufacturers include a new filter with the equipment that is rubber coated and washable. Coarse fibers are rubberized to bind them together and make them sticky. As air passes through, dust collects on the fibers. A blast from the sink sprayer or garden hose will rinse the dirt away and ready the filter for re-use.
A better mechanical filter has been developed, called a media filter, which begins its life removing more dust (about 75%) and gets more efficient with use. It approaches 99% eventually, but also becomes too restrictive for proper air flow. This filter is made of paper or synthetic fabric, woven just loose enough to allow air to pass, but tight enough to trap particles as small as pollen.
Anywhere from one to five inches thick, the media is pleated to allow as much surface area exposure as possible. A cardboard frame keeps the filter in the proper shape and gives it enough rigidity to prevent collapse from air pressure. The one inch thick pleated filters need to be replaced as often as the spun filters, but the three to five inch thick pleated filters can last 6 months to a year. Dirt build up is visually noticeable; frequent inspection will help determine life expectancy. Replacement media filters can be found at HVAC and some plumbing supply stores. The one inch thick pleated filters are designed to replace the spun filters, and are available at retail and hardware stores.
The simplest filters are made of fiberglass and are disposable. Others are washable screens.
High performance media filters use pleated paper or spun materials to collect microscopic dust particles as the air passes through.
Electronic air cleaners put an electric charge on the dust particles as they enter the grids and collect the dust on plates that are also charged. In the process of putting an electric charge on the dust, ozone is created, which helps kill bacteria and odors.
Electrostatic filters use the motion of air across a weave of synthetic threads to create a static charge on the dust and collect it.
Electronic air cleaners lose efficiency as they get dirty, and should be washed monthly when in constant use. Loud snapping noises that continue through the entire heating or cooling cycle are signs that the grids need cleaning.
Non-electric filters will increase in efficiency as they get dirty, but also decrease in airflow. The balance between cleaning efficiency and proper airflow is difficult to define. Experience and familiarity with the system’s performance is the best guideline.
Full air flow is critical to the performance of a central air conditioning system; clean filters are a must. The wet cooling coil will collect a great amount of dust particles as the air passes through.
Air Handlers
Build a sheet metal box, put two holes in opposite ends of the box, then put a fan in the box. This is an air handler in basic form. Add a hot water coil, and it becomes a fan-coil for hydro-air application. Add an evaporator coil and it becomes the indoor unit for central air or a heat pump. Put electric heating elements, circuit breakers and controls and it becomes an electric furnace.
By today’s tradesman lingo, an air handler usually refers to a unit in use for central air conditioning or for a hydro-air system.
Without the risk of fire from combustion or high temperature heating elements an air handler offers the versatility of safe installation when in contact with combustibles, and multi-position application. Most manufactures build a machine that can be installed for vertical, horizontal, or counter flow (downflow) use.

Air Purifiers
Have you ever stepped outside after a thunderstorm rolled through and noticed that the air smelled a little fresher? Some of the responsibility can be given to the temperature drop and the rain washing the air, but as dangerous and terrifying as the lightning can be, zapping through the air it creates ozone, one of the best and safest air fresheners.
There are two simple ways to make ozone without the use of chemicals; ultra-violet light and an electrical spark discharge.
When sunshine strikes earth's atmosphere, the ultra-violet radiation converts oxygen to ozone, and in turn protects us from the harmful radiation.
Ozone kills bacteria, mold spores, and mildew. It also destroys odors, and can freshen smoke filled air under most conditions. As with most things, excessive amounts of ozone are not good; recommended guidelines call for between .01 and .05 parts per million of ozone versus air.
Excessive amounts of ozone are noticeable when a bleach smell is in the air.
Ionization of the air can produce ozone (as an electric spark does), but ionization is more useful as an air cleaner. Electronic air cleaners give dust particles a negative charge as the air passes through the front part of the grids, and then collects it on positively charged plates.
Direct ion generators flood the air with negatively charged dust particles in hopes that the dust will be attracted to the positively charged walls and furniture of a room, but excessively charged air particles are not healthy; and the dust still has to be dealt with at some time.
Air to Air Exchangers
With the emphasis on energy conservation and efficiency, new home construction can create a problem of indoor air pollution. Vapor barriers, thermal windows, weather-stripping and caulk have reduced or stopped fresh air from infiltrating and replacing stale air. Entering and exiting the house through doors isn’t always enough air changes. Cooking, aerosol sprays, cleaning agents, paints, and in some cases excess humidity if the house is sealed too tightly can create an undesirable environment. Keeping windows or doors open does not conserve energy. A device known as an air-to-air exchanger is used to recover heating or cooling and improve air quality.
There are many different designs, depending on the manufacturer, but the principle is the same. Fresh air is drawn in from a port open to the outside of the building, and passed through a chamber, also know as the exchanger that is surrounded by indoor air. Highly conductive metal or other materials removes the energy (heat) from the warmer air and gives it to the cooler air. The fresh air is then ducted into the house, and the indoor air is ducted to a port and expelled outside. Up to 80% of the energy can be exchanged. During the energy exchange, moisture (humidity) can condense into water. A drain pan inside the cabinet will allow the water to be collected for removal. If the unit is installed in the basement, a condensate pump might be used to eject the water outside.
Most air exchangers are controlled simply be on and off switches, but in applications for removal of humidity, a humidistat can be used to turn the machine on and off to achieve the desired level.
Routine maintenance involves replacing or cleaning the filters if so equipped, and keeping the outside air intake free of debris. After years of service the exchanger will become crusted with grease and dirt that collects during condensation. Removing this accumulation will probably take solvents or degreasers and require opening up the cabinet and compartments.
One method of adding fresh air to the space is to duct outside air directly into the return air plenum of the heating or air conditioning system. Usually required by code for commercial applications, it is an inexpensive way of improving air quality, but not the most efficient, since it means heating or cooling outside air, which could be very cold in winter or extremely humid on a midsummer day.
Central Air Conditioning
Residential central air conditioning systems that need to cool and dehumidify uses a condenser, evaporator coil, and refrigerant piping to operate. The means of moving the air might differ (furnace, air handler, etc.), but the principal is the same for all split systems. The term "split" refers to the physical separation of the condenser and the evaporator. This is in contrast to a window or wall air conditioner in which they are "packaged" together. The refrigerant is compressed and run through a series of tubes to remove as much heat as possible, then piped to an evaporator coil as a warm liquid. Expansion of the compressed liquid causes it to cool, and as the air passes over the coil, heat is extracted. The cool liquid becomes a cool gas as it gathers heat from the air, and is drawn back to the compressor to start the procedure again. As the air passes over the evaporator coil and cools, moisture in the air condenses and drains off as condensate.
Some hybrid and geothermal systems use cold water instead of refrigerants until the temperature gets to a certain point, but the majority of systems use refrigerants for the entire cooling cycle.
In arid climates when dehumidification is not needed, only cooling, evaporative air conditioning is practical and economical.
Evaporative systems can be as simple as a pond of water on a flat roof, or more involved with the use of air handling equipment and special fabrics. By running water down loose material that is suspended and blowing air through the wet fabric, the evaporation of water will lower the air temperature and raise the humidity. The water that does not evaporate will be cooled down enough to contain in a vessel and become a secondary source of cooling by moving air over the vessel to create air conditioning.
The conventional central air system is considered low velocity. In this type of system, the air temperature will drop some 15 to 18 degrees F when it passes through the cooling coil, and a 6 inch round duct will deliver approximately 2,500 BTU of cooling. Alternatives include the ductless mini-split, and the high velocity system. The latter operates at an approximate 30 degree F temperature drop and delivers about 2,500 BTU of cooling through a 2 inch round duct. This compact delivery system adapts well to retro fits and installations in older homes where duct space is limited.
The ductless mini-split, as the name suggests, requires no ductwork at all; and works well with open floor plans or where no ductwork at all can be installed. The fan unit is mounted on the wall or ceiling and piped to the outside condenser.
Split systems that use refrigerants are of the same design, no matter what the source of air handling equipment used (furnace, heat pump, hydro-air, etc.).

Condensers
The condenser for a heat pump and a central air conditioning system look similar and are constructed of the same basic parts. A cabinet houses the components and is strong enough to protect them during transport and installation. Inside of the cabinet will be a condenser coil, a compressor, a fan, and controls.
The coil is usually made of copper tubing with aluminum fins, but some manufactures use aluminum tubing. Its purpose is to transfer heat as rapidly as possible. Pressure inside the coil can exceed 400 psi, during extremely warm weather conditions. The cleaner it is kept, the better it transfers heat. Rinsing with a garden hose occasionally when the unit is not running will help keep it operating efficiently. After many years of use it may be necessary to put special chemicals on to clean it.
The condenser fan moves air across the coil to increase the transfer of heat. It is critical to the system. Obstructing the flow of air will not only reduce efficiency but can lead to compressor failure. Keep debris and objects away from the coil and fan to allow maximum air flow. Some condenser fan motors have sealed bearings, others need lubrication. Damage to the fan can occur if removed improperly. Have a qualified serviceman handle the lubricating if needed.
The compressor is the engine of the system. It compresses the refrigerant and pumps it to a coil as a hot gas. For air conditioning, it will be cooled at the condenser into a warm liquid and piped to the evaporator coil to expand and cool. For a heat pump, the hot gas will be pumped directly to the evaporator coil to provide heat. Compressors are of two designs; reciprocating and scroll. A reciprocating compressor is similar to an air compressor. An electric motor spins a crankshaft with pistons and connecting rods. Valves open and close to allow the flow of gas in the desired direction. Special lubricants are used.
Since the system is hermetically sealed, the lubricant is permanent and does not get changed. Reciprocating compressors have been in use since the first refrigerators. Scroll compressors use an electric motor to drive them, but the similarity ends here. Its uniqueness is difficult to explain, but it is ingenious. Using two spiral mazes recessed into each other, one attached to a motor drive and the other allowed to slide freely, compression occurs with rapid movement. After many years of testing and engineering improvements, the scroll compressor is available from some manufacturers as a standard or option in the condenser. It is both efficient and quiet, and improves with age.
If the condenser is used for air conditioning only, controls are minimal. A contactor switches the power on and off. Capacitors are used to start and run the motors. Optional controls are: a brown-out time delay, crankcase heater. Hard start kit, and low ambience control.

A brown-out time delay protects the compressor in two ways. If the voltage drops and the motors draw too much current (amperes) it shuts the contactor off. If the control voltage is interrupted momentarily, it shuts the contactor off. When the compressor is running, high pressure exists at the exhaust port. If it is shut down and restarted before the pressure equalizes with the intake port, the motor will not be able to overpower the pressure imbalance and overheat. The time delay will stall the restart for three or four minutes sufficient time for the pressures to equalize.
The compressor is deigned to compress a gas, not a liquid. A crankcase heater is used to preheat the oil and liquid refrigerant that might have settled in the compressor crankcase. By boiling off any refrigerant, risk of valve damage is avoided.
If rapid restarts are required for the system, a hard start kit can be installed. It consists of a potential relay and a capacitor. It gives the motor an added jolt or boost to help it start under stress.
Mostly used in commercial applications, a low ambience control could be used on a residential system if needed. It senses the liquid line pressure and cycles the condenser fan to keep pressure high enough for the air conditioning to function in cold weather.
If the condenser is part of a heat pump system, the controls get more complex. In addition to the controls already listed, there will be a reversing valve, defrost timer, and possibly an adjustable temperature sensor.
The reversing valve directs the flow of compressed gas to the condenser coil for air conditioning or to the evaporator coil for heating.
When extracting heat from outdoor air, the condenser coil gets very cold and frost will begin to form on it. Too much frost build-up will restrict air flow and reduce effectiveness of the coil. The defrost control switches to air conditioning mode without the condenser fan running. The hot gas running through the coil melts the ice that formed, and then shifts back to heating mode.
Some older model heat pumps have an adjustable thermostat in the outdoor control panel. It will limit the low temperature operation of the heat pump to prevent it from running when it is too cold out to extract sufficient heat from the air.
Controls
A relay is one of the most versatile controls at our disposal. It allows an electric current of one voltage to switch the current on and off to another device or appliance of a different voltage. The most common example of a relay exits right at the thermostat of a central heating or air conditioning system. Low voltage (24 volts) is sent to the thermostat from a transformer. When the thermostat calls for heating, the 24 volts operates a relay that sends 120 volts or 240 volts to the furnace, depending on the type of heating system. In air conditioning system, the 24 volt current trips a relay at the air handler to run the blower ( which can be 120 volts or 240 volts) and a relay known as a contactor on the condenser to provide 240 volts for the compressor and fan.
The device itself is simple in design. Thin copper wire is wound around a hollow sleeve. Inside the sleeve is a steel rod with electrical contacts attached to one end. When current is passed through the windings of copper wire, the sleeve becomes magnetic, and pulls the rod into it. The electrical contacts unite, and current is transferred to the intended device. Relays are used in motor vehicles, appliances in the home, and in the work place. The click heard when a computer connects to a telephone line for the internet service is a relay engaging.
The fan center relay can be found inside the cabinet of a furnace or air handler. It has a transformer to reduce the line voltage (120 or 240 volts) to low voltage and low amperage (24 volts; and usually less than 40 milliamps). This reduces the risk of fire or injury from exposure to live circuits and allows control wiring to be of smaller gauge and lesser expense to install. The relay will have a switching capability to make a connection (normally open) and disconnect a circuit (normally closed). On an oil or gas fired furnace with central air, the relay will disconnect the burner and engage the blower and condenser simultaneously if the thermostat calls for cooling. This prevents the heat from coming on by mistake.
The protect relay, also known as a burner relay on an oil fired furnace, is explained in the oil burner section.
In order to use 24 volts to control the condenser for a heat pump or central air conditioner, a relay known as a contactor is used. The contactor must be capable of switching a high voltage and high amperage load on and off. It can have many terminals on it. The crankcase heater, the condenser fan, and the compressor all tap into the current available at the contactor. It is constructed of materials that will allow it to function for years under stressed conditions, but eventually will need replacing. It is imperative that the power be disconnected at the main panel and at the service disconnect outside at the condenser before any access is made to the electrical connections at the condenser.

Cooling Coils
Evaporator coils come in a variety of shapes and sizes, depending on the type of installation, the amount of cooling capacity needed, and the manufacturer. It is the source of cooling as air passes through the furnace or air handler. They are constructed of aluminum finned copper tubing. The copper tubing runs perpendicular to the aluminum fins, making U-turns back and forth until the desired coil size is achieved. Added cooling capacity without an increase in length and width is accomplished by adding more rows of copper tubing.
Slant coils and horizontal coils have a slab appearance, similar to the radiator in an automobile. They can be installed in ductwork running horizontally or in an air handler. An A-coil is shaped like a capital A without the crossbar. It can be installed on top of a fuel burning furnace heat exchanger or in an air handler. The newest design is the multi-flex coil which is a series of A-coils linked together at the base. The multi-flex coil can be installed in any position when encased in a special cabinet. All evaporator coils must have a drain pan to collect the water that condenses as the air flowing across the coil cools. The water can drain away by gravity or be pumped away.
The cooling effect that takes place inside the coil requires a pressure drop in the refrigerant. This drop can be accomplished in a number of ways: capillary tube, piston or orifice, or thermostatic expansion valve.
A capillary tube is a thin copper tube of predetermined length into which the compressed liquid refrigerant is pumped. The length of the tubing causes the pressure drop and subsequent cooling effect of the refrigerant.
A piston or orifice blocks the flow of refrigerant and forces it through a tiny hole, creating the needed pressure drop.
A thermostatic expansion valve meters the flow of refrigerant to meet the cooling demand of the coil. It determines this demand by way of a sensing bulb attached to the outlet tube on the coil. Because it can meter the flow to meet demand, the expansion valve can keep the coil at optimum cooling potential.
Dehumidification
There is nothing in the home quite like the damp odor that engulfs a person walking into a room with an over abundance of humidity breeding mold and mildew. Not only is is offensive to the nose, it can become very unhealthy.
Fresh, dry air is the solution to the problem, but weather conditions and energy conservation don't always allow for the exchange of good air.
An easy fix is as simple as the installation of one or more de-humidifiers. By reducing the moisture in the air, mold and mildew along with other nasty things that breed in too humid an environment can be eliminated.
De-humidifiers that use a refrigeration cycle to condense moisture from the air are the most common for the home.
Desiccant units that use a moisture absorbing medium to collect water then dispose of it with heated or dry air passing across the medium are used on a commercial level or for indoor pools and very large homes.