Concerns about the hole in the ozone layer have impacted many products we use, and air conditioners are no exception. Many air conditioning systems use a HCFC (hydrochlorofluorocarbon) refrigerant, a substance known to cause of depletion of the ozone layer. The EPA currently limits the amount of HCFC that may be produced, and intends to prohibit use of HCFCs by 2030. The refrigerant R-410A is one of the substitutes currently accepted as a replacement for the commonly used HCFC-22 (also known as R-22). The new material is marketed under the trade names AZ-20, Suva 9100 and Puron.

Air conditioners use a system of compressors, coils, fans, pipes and controls to remove heat from the home. A refrigerant is the medium used to transfer heat through this closed loop system. In the past, refrigerants like HCFCs containing chlorine were widely used because of their excellent heat transfer properties with respect to the refrigeration cycle. While air conditioners don't normally release chlorine gas, it can often escape into the atmosphere through a leak or during service of the unit. Because of the potential damage to the ozone layer, several countries have agreed to reduce and eventually eliminate the production of HCFCs.

An air conditioner using R-410A has slightly different specifications than traditional cooling systems. Higher pressures are needed for the refrigerant to have the same cooling effect. This increased pressure requires design changes in the compressor and piping. An unfortunate consequence is that R-410A may not be substituted into existing systems. Efficiency of the new refrigerant is comparable with the older product. There are models currently available that have a SEER (Seasonal Energy Efficiency Ratio) of 18.

(LEAF): R-410A refrigerant does not pose a threat to the ozone layer.

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A heat recovery ventilator (HRV) can help make mechanical ventilation more cost effective by reclaiming energy from exhaust airflows. HRVs use heat exchangers to heat or cool incoming fresh air, recapturing 60 to 80 percent of the conditioned temperatures that would otherwise be lost. Models that exchange moisture between the two air streams are referred to as Energy Recovery Ventilators (ERVs). ERVs are especially recommended in climates where cooling loads place strong demands on HVAC systems. However, keep in mind that ERVs are not dehumidifiers. They transfer moisture from the humid air stream (incoming outdoor air in the summer) to the exhaust air stream. But, the desiccant wheels used in many ERVs become saturated fairly quickly and the moisture transfer mechanism becomes less effective with successive hot, humid periods. In some cases, ERVs may be suitable in climates with very cold winters. If indoor relative humidity tends to be too low, what available moisture there is in the indoor exhaust air stream is transferred to incoming outdoor air.

Although some window or wall mounted units are available, HRVs and ERVs are most often designed as ducted whole-house systems. The heat exchanger is the heart of an HRV, usually consisting of a cube-shaped transfer unit made from special conductive materials. Incoming and outgoing airflows pass through different sides of the cube (but are not mixed), allowing conditioned exhaust air to raise or lower the temperature of incoming fresh air. ERVs also allow the exchange of moisture to control humidity. This can be especially valuable in situations where problems may be created by extreme differences in interior and exterior moisture levels. For instance in cold, heating-dominated climates, better air flow and the introduction of humidity to the indoor environment can help control wintertime window condensation. In humid summer climates which are cooling dominated, it can be critical to dry out incoming air so that mildew or mold do not develop in ductwork.

After passing through the heat exchanger, the warmed or cooled fresh air goes through the HVAC air handler, or may be sent directly to various rooms. Stale air from return ducts pre-conditions the incoming flow before exiting. Systems in various sizes and configurations are available to automatically maintain 0.35 air changes per hour, the rate usually recommended to maintain good air quality. Many systems include filters to further control contaminants that would otherwise re-circulate through the home. Conventional fan and vent assemblies for bathrooms and kitchens, often required by code, may allow significant energy losses. An HRV system can incorporate small, separately switched booster fans in these rooms to control moisture or heat generated by activities like showering or cooking. Odors and pollutants can quickly removed, but energy used to condition the air is recycled in the heat exchanger. Some codes or applications may still require stoves to be separately vented for removal of grease or gas fumes.

(Lightning): By transferring energy from exhaust air to incoming air, less energy has to be put into conditioning the supply air, reducing consumption.

(Leaf): Because indoor air quality is generally lower than it is outdoors, ventilation is sometimes vital. This equipment help improve those conditions.

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Have you ever noticed how cool it feels near a waterfall on a hot summer day? That's evaporative cooling: the reduction in air temperature that occurs when water evaporates. Evaporative coolers, commonly called "swamp coolers," use this effect to cool homes. Evaporative coolers have a low first cost, use a lot less electricity than conventional air conditioners, and do not use refrigerants, such as chlorofluorcarbons (CFCs) and hydrochlorofluorocarbons (HCFCs), that can harm the ozone layer.

There are two types of evaporative coolers: direct and indirect (all called two-stage). In a direct evaporative cooler, a blower forces air through a permeable, water-soaked pad. As the air passes through the pad, it is filtered, cooled, and humidified. An indirect evaporative cooler has a secondary heat exchanger, which prevents humidity from being added to the airstream which enters the home. Evaporative coolers can be used as a sole cooling system in a home, as an alternative cooling system to a conventional refrigerant air conditioner, or in combination with a refrigeration system. However, conventional air conditioners should not be operated simultaneously with direct evaporative coolers, because air conditioners dehumidify while evaporative coolers humidify, and the two systems will work in opposition.

Evaporative coolers are sized based on cubic feet per minute (cfm) of airflow. Airflow for evaporative coolers is typically higher than conventional air conditioning systems. Two to three cfm per square foot or three to four cfm per square foot in hot desert climates is typical. Improperly sized evaporative coolers will waste water and energy and may cause excess humidity or other comfort problems. Two-speed coolers are available that can handle varying cooling loads. Unlike air conditioned rooms, windows or ceiling vents need to be open when an evaporative cooling system is operating. The large volume of fresh air added to the home replaces a significant amount of air that exits from the home.

Many systems incorporate bleed-off valve that purges water about every six hours. This leads to an additional five gallons of water used per hour, but may be necessary to avoid mineral build-up. Bleed-off valves are generally recommended.

Indirect, or two-stage, evaporative coolers do not add humidity to the air, but cost more than direct coolers and operate at a lower efficiency. Two stage evaporative coolers combine indirect with direct evaporative cooling. This is accomplished by passing air inside a heat exchanger that is cooled by evaporation on the outside. In the second stage, the pre-cooled air passes through a water-soaked pad and picks up humidity as it cools. Because the air supply to the second stage evaporator is pre-cooled, less humidity is added to the air, whose affinity for moisture is directly related to temperature. The result, according to one manufacturer, is cool air with a relative humidity between 50 and 70 percent, dependent on the regional climate. A traditional system would produce about 80 percent relative humidity air.

(Dollar): Direct evaporative coolers cost about $700 to $1000, installed, compared with several thousand dollars for conventional air conditioner and ductwork. In addition, operating costs are about 1/3 that of conventional air conditioning (including the cost of water, depending on electric and water costs). Indirect evaporative coolers cost are much higher.

(Lightning): Evaporative coolers use about ¼ the electricity of conventional air conditioners.

(Leaf): Evaporative coolers can improve the indoor air quality inside a home by drawing a large supply of fresh outdoor air through the home. However, they consume between 3.5 and 10.5 gallons of water per hour of operation.

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Geothermal heat pumps (GHPs) are a relatively new technology that can save homeowners money. These ground-source heat pumps use the natural heat storage capacity of the earth or ground water to provide energy efficient heating and cooling. GHPs should not be confused with air-source heat pumps that rely on heated air.

Geothermal heat pumps use the relatively constant temperature of the ground or water several feet below the earth's surface as source of heating and cooling. Geothermal heat pumps are appropriate for retrofit or new homes, where both heating and cooling are desired. In addition to heating and cooling, geothermal heat pumps can provide domestic hot water. They can be used for virtually any size home or lot in any region of the U.S. A geothermal heat pump system consists of indoor heat pump equipment, a ground loop, and a flow center to connect the indoor and outdoor equipment. The heat pump equipment works like a reversible refrigerator by removing heat from one location and depositing it in another location. The ground loop, which is invisible after installation, allows the exchange of heat between the earth and the heat pump.

Geothermal heat pumps can be open- or closed-loop. Open-loop systems draw well water for use as the heat source or heat sink, and after use, return the well water to a drainage field or another well. Closed-loop or earth-coupled systems use a water and antifreeze solution, circulated in a ground loop of pipe to extract heat from the earth.

Ground loops can be installed in a vertical well or a horizontal loop. Vertical wells are usually more expensive and used where space is limited. The length of loop pipe required will vary with soil type, loop configuration, and system capacity. Loop length can range from 250 to 1,000 feet per ton of capacity.

Special heat pump features can include variable speed blowers and multiple-speed compressors. These features can improve comfort and efficiency in areas where heating and cooling loads are quite different. Add-on features include the capability to produce hot water.

Desuperheaters can be added to supplement the production of domestic hot water when there is a demand for space heating or cooling. These devices make use of excess heat during the cooling cycle and use some of the heat during the heating cycle to supplement hot water production. Dedicated water heaters can be added which operate whenever there is a demand for hot water. Geothermal heating can be more efficient than electric resistance heating. These systems are also typically more efficient than gas or oil-fired heating systems. They are more energy efficient than air-source heat pumps because they draw heat from, or release heat to, the earth, which has moderate temperatures year round, rather than to the air (which is generally colder in winter and warmer in summer than the earth, resulting in less effective heat transfer).

(Lightning): Geothermal heat pumps have demonstrated energy savings over air heat pumps because they extract energy from the constant temperature of the earth (via a water pipe buried in the earth) to condition the air in a home. In a sense, geothermal is a partially renewable form of energy.

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In cold climates, well-insulated, tight exterior envelopes are used to achieve energy efficiency. In such cases, bringing in make-up air to meet ventilation requirements can be problematic, as it should be preheated to avoid uncomfortable drafts or excessive heat loss. The passive solar ventilation air pre-heater has exterior corrugated steel cladding perforated with tiny holes that allow fresh air to penetrate. An air space (between the cladding and the exterior wall finish) under negative pressure draws air in through the holes, and is collected in a canopy plenum (which has a by-pass damper for summer). A fan and distribution ducting direct the air through the house.

The system effectively creates a thicker wall that circulates not only solar heated air but also outwardly-conducted heat back inside, creating a higher effective R-value (the manufacturer claims R-55). The fan helps to destratify warm air at the ceiling. Shading the south wall with the cladding reduces cooling load. Indoor air quality and occupant comfort are improved. Ventilation actually increases on colder days. The manufacturer also makes a similar wall system with integrated photovoltaics. (Lightning): By reducing the cooling and heating loads on the home, less energy is used to effectively keep the home at a comfortable temperature.

(Leaf): In addition to helping save on energy consumption, indoor air wuality is improved through the ventilation and fresh air supply.

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Air-source heat pumps provide efficient heating when outdoor conditions are moderately cool, but lose capacity in very cold weather when auxiliary heat is required, typically supplied by less efficient electric resistance strips. The hydronic "Reverse Cycle Chiller™ (RCC)" heat pump uses hot water as the source for auxiliary heating demands. The manufacturer claims that the RCC will supply residential heating with greater comfort and improved cost-efficiency, even when exterior temperatures are below zero.

Heat pumps work by circulating a working fluid, or refrigerant, which vaporizes at a low temperature (in the evaporator), producing additional energy in the process.

A compressor further concentrates the warmed vapor, raising it to a temperature where it can be circulated through an air handler and used for heating. When the cycle reverses, heat is pumped from indoors to out, as with standard air conditioners (in Canada heat pumps are known as "reverse cycle air conditioners") Traditionally, heat pumps have been sized to cooling loads and used where outdoor temperatures rarely fall below freezing. As outdoor temperatures drop, there is less heat available for efficient extraction by the evaporator, and supplemental heat may need to be provided by electric resistance strips. To protect the evaporator from freeze damage, it must occasionally run in a defrost cycle where the flow of refrigerant is reversed, so that heat from the interior of the house will melt accumulated ice deposits in the outdoor coil. This results in uncomfortably cold air being circulated throughout the home during the cycle, a common source of frustration and complaint among heat pump owners.

The Reverse Cycle Chiller, produced by Aqua Products Company, Inc. uses a highly efficient heat exchanger to transfer energy to a water line, achieving temperatures up to 120 degrees in the heating mode, and down to 50 degrees in cooling mode. The water line can then supply a central air handler, a radiant floor heating system or multiple zoned air handlers. This configuration allows the system to be sized for heating loads rather than typically smaller cooling loads. On its return trip towards the evaporator, the water replenishes a super-insulated tank that serves as a "thermal flywheel," replacing resistance strips as the auxiliary heat source, and supplying heat for the defrost cycle. The system is said to supply a more consistent, comfortable level of heating, that operates efficiently, even at temperatures below 0 degrees Fahrenheit.

The technology applied in the Reverse Cycle Chiller is not new. Similar larger scale systems have been in operation for decades in commercial, institutional, and industrial applications, but this hydronic heat pump configuration has not typically been used for single-family residential units.

(Lightning): Reverse cycle chillers can supply higher temperature heating energy than air-source heat pumps, resulting in less use of back-up resistance heating.

(Star): Reverse cycle chillers can supply higher temperature heating energy than air-source heat pumps, resulting in higher comfort levels for homeowners.

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