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Mechanical Air Conditioning

    Scope
    Scope Images
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    Proper refrigerant charging is critical to maximizing performance for compression cooling systems
    Scope

    Choose the highest performing cooling equipment that project funding will allow, to meet the cooling load of the project.

    If the design cooling load is low (below around 14,000 Btuh capacity) due to high insulation and air sealing levels or climate, consider alternative lower-load cooling sources such as ducted or ductless variable refrigerant flow heat pumps. In dry climates, consider direct/indirect evaporative coolers and ventilation cooling. Also consider passive cooling techniques such as shading with architectural and landscape features. See the Passive and Low-Energy Cooling guide for more information.

    Confirm that the selected system is a matched system, as certified according to the Air-Conditioning, Heating, & Refrigeration Institute. AHRI assigns a certification number and efficiency ratings to specific combinations of equipment (outdoor unit, indoor unit, indoor coil, fan type, etc.) that have been tested by the manufacturer according to AHRI test procedures using AHRI-specified test conditions (AHRI 2012).

    Install in accordance with the manufacturers’ instructions and relevant standards including ACCA Standard 5: HVAC Quality Installation Specification and the ACCA’s Technician's Guide for Quality Installations and ACCA Standard 9: HVAC Quality Installation Verification Protocols.

    Properly size the cooling equipment and ducts for the design cooling load of the home, following the sizing guidelines in ACCA’s Manual S: Residential Equipment Selection. When determining equipment sizing per ACCA Manual S, use the original equipment manufacturer (OEM)’s expanded performance table to obtain performance data at design conditions, rather than using the performance data on the AHRI certificate, which lists heating and cooling capacity and SEER and EER cooling efficiencies at factory conditions of 90°F outdoor, 80°F indoor, and 67°F wet bulb.

    The OEM-listed capacity at design conditions should be between 95% and 115% of the design total heating load calculated in the Manual J HVAC load calculation, or the next nominal size. The next largest nominal piece of equipment available may be used to satisfy the latent and sensible requirements. Single-speed systems generally have OEM nominal size increments of one-half ton. Multi-speed or multi-stage equipment may have OEM nominal size increments of one ton. Therefore, the use of these advanced system types can provide extra flexibility to meet the equipment sizing requirements.

    If the whole-house ventilation system uses the air conditioner air handler, then the fan motor should be a variable speed electronically commutated motor (ECM) or an integral control motor (ICM) that includes a controller (e.g., a smart cycler) that reduces the ventilation run time by accounting for hours when the HVAC system is already operating the fan for heating or cooling the home.

    Design an efficient air distribution system with a compact layout in accord with ACCA Manual D. Install ducts properly for maximum airflow and efficiency. Consider zoning for low-load homes (over 1,000 sq ft per ton of cooling) with thermostat-controlled dampers. 

    If you are participating in an energy-efficiency program, select cooling equipment that complies with the requirements for your climate zone. To determine your climate zone, see the International Energy Conservation Code (IECC) climate zone map on the Climate tab

    See the Compliance Tab for related codes and standards requirements, and criteria to meet national programs such as DOE’s Zero Energy Ready Home programENERGY STAR Single-Family New Homes, and Indoor airPLUS.

    Description
    Description

    Vapor-compression refrigeration (compression cooling) systems are the most common type of cooling equipment used to cool residential and commercial buildings. Compression cooling is often referred to as air conditioning, although technically any system used to intentionally heat, cool, or ventilate the indoor air could be referred to as an air conditioning system. Residential compression cooling systems include any system that uses the refrigeration cycle for space cooling; this includes split-system air conditioners, unitary air conditioners, air-source heat pumps, and ground-source (or geothermal) heat pumps, in system sizes up to 65,000 Btuh with forced-air distribution systems. Noncompression cooling systems include evaporative cooling and absorption systems. However, compression cooling systems hold the lion's share of the U.S. housing market. According to the latest data from the U.S. Energy Information Administration (data collected in 2009 and released in 2013), 94 million out of 113.6 million households had some kind of cooling equipment – 69.7 million of those homes had central compression-based air conditioners (19% of these were heat pumps), 25.9 million had window or wall-unit air conditioners, and 2.8 million had an evaporative or swamp cooler (EIA 2013). Other cooling options available to consumers that are worth considering because of their energy-saving potential include passive cooling techniques such as shading with architectural and landscape features, night ventilation cooling systems, and ceiling fans. See the Passive and Low-Energy Cooling guide.

    The compression cooling cycle, especially as it applies to split-system central air conditioners, is described here. Traditional split heat pumps, mini-split heat pumps, and ground-source heat pumps are described in more detail in other guides, as are evaporative cooling systems and absorption cooling.

    Central air conditioners are typically installed with central furnaces and use the same blower and duct distribution system. Residential air conditioners are typically split systems, which refers to the fact that there is an outside unit and an inside unit: the condenser and compressor are part of an outside unit and the evaporator and expansion valve are located within the air handler in the inside unit (Figure 1). Refrigerant is piped to the evaporator coil in the air handler unit where it cools the distribution air.

    Traditional split-system.
    Figure 1. A traditional split-system air source central heat pump has an outdoor unit with a condenser and compressor and an indoor air handler unit with an evaporator coil, metering device, and blower fan. (Source:  Calcs Plus.)

     

    Window- or wall-mounted room air conditioners contain all of the components in one box. Larger single-unit air conditioners called packaged-unit air conditioners also contain all of the components (the compressor, condenser, evaporator, expansion device, and blower fan) in one unit that is located outside, typically mounted on the wall or on the roof (Figure 2). The conditioned air is vented inside either directly into a room or into a duct system for distribution throughout the building. Many small commercial buildings are equipped with packaged units but they are rarely used for single-family homes.

    A packaged unit heat pump or air conditioner contains the compressor, condenser, evaporator coil, and metering device in one roof- or wall-mounted unit.
    Figure 2. A packaged unit heat pump or air conditioner contains the compressor, condenser, evaporator coil, expansion device, and blower in one roof- or wall-mounted unit. (Source: Calcs Plus.)

     

    Packaged air conditioners and heat pumps come from the factory ready to go as soon as they are connected to a duct system, thermostat, and power source. Split systems have to be plumbed, i.e., the indoor unit must be connected to the outdoor unit via refrigerant piping, and electrical wiring must be connected to both units.

    Air Conditioner Capacity and Sizing

    Air conditioners are sized by their capacity in terms of tons. One ton equals 12,000 Btu/hour of cooling capacity. The capacity is often indicated in the model number. Look at the name plate on the outdoor condensing unit and locate the model number (not the serial number). Look for two digits in the model number that match the numbers below to indicate tons or Btus/hour. For example, a model SSX160241 is a 2-ton (24,000 Btu/hr) air conditioner.

    18 = 1.5 Ton (18,000 Btu/hr)
    24 = 2 Ton (24,000 Btu/hr)
    30 = 2.5 Ton (30,000 Btu/hr)
    36 = 3 Ton (36,000 Btu/hr)
    42 = 3.5 Ton (42,000 Btu/hr)
    48 = 4 Ton (48,000 Btu/hr)
    60 = 5 Ton (60,000 Btu/hr)

    Proper sizing of air conditioners has become more important in recent decades as homes have become more air-tight and better insulated. HVAC contractors can no longer rely on rules of thumb based on a rough estimate of square footage. Where an older two-story 3,000-ft2 home might have required two 3-ton units, a new 3,000-ft2 high-performance home might be adequately served by one 3-ton unit with zone dampers.

    An overly large system will blast on quickly, bringing the air temperature below the thermostat set point and shutting off before it has had time to remove moisture from the air, which can cause moisture problems in the home, especially in humid climates. The HVAC contractor should use ACCA’s Manual J: Residential Load Calculation to calculate the home’s cooling load and ACCA’s Manual S: Residential Equipment Selection to correctly size the central air conditioning system. ACCA makes available Excel-based spreadsheets to help contractors with these calculations. Oversizing is less of an issue with cooling equipment that has variable speed motors and compressors, which can operate at lower speeds and capacities that better match low demand times, while having the ability to increase capacity when demand spikes. Even so, ACCA Manual S limits oversizing of two-speed and variable-speed units.

    The HVAC equipment that is installed must be a matched system, as certified according to the Air-Conditioning, Heating, & Refrigeration Institute (AHRI). AHRI is an industry association that assigns a certification number and efficiency ratings to specific combinations of equipment (outdoor unit, indoor unit, indoor coil, fan type, etc.), which have been tested by the manufacturer according to AHRI test procedures using AHRI-specified test conditions (AHRI 2012). See the AHRI Directory of Certified Products. Proper matching of system components according to AHRI is one of the items that will be confirmed by a Residential Energy Services Network (RESNET) rater when the home is assessed for a Home ENERGY Rating System (HERS) score.

    Many designers use the performance data listed on the AHRI certificate for selecting equipment to meet the home’s design cooling load. However, a more accurate method (and one required by ACCA Manual S) is to use the original equipment manufacturer (OEM)’s expanded performance table to obtain performance data at design conditions. AHRI uses a specific set of conditions (95°F outdoor, 80°F indoor, and 67°F wet bulb) when determining the equipment performance data, such as heating and cooling capacity and SEER and EER cooling efficiencies; these performance data are then listed on the AHRI certificate. The OEM expanded performance tables use design cooling conditions that include an indoor temperature of 75°F and 63°F wet bulb. Several manufacturers refer to this as “TVA conditions” because they were originally set by the Tennessee Valley Authority in the 1970s. Under these design conditions, equipment will usually have a lower SEER than under AHRI conditions.

    With a central air conditioning system, the cooled air will be distributed by ducts so it is important to design an efficient air distribution system with a compact layout in accord with ACCA Manual D. Good installation (with short straight runs and air-sealed and insulated ducts) is important for maximum airflow and efficiency. See the guides listed under Thermal Enclosure System 4 Air Sealing and HVAC System 6 Duct Quality Installation in the ENERGY STAR Single-Family New Homes Checklist for more information.

    For best performance, the ducts and air handler should be located within the home’s thermal boundary (this is a DOE Zero Energy Ready Home requirement).

    Some new homes are so well air sealed and insulated, they can be considered low-load homes (over 1,000 square feet of floor space per each ton of cooling). While older, less air-tight, less well air sealed homes might require two or more cooling units or one large unit, for example a 5-ton unit, with well-insulated homes, one smaller unit, perhaps 2 or 2.5 tons, might do.

    For larger homes with one unit, zone dampers are recommended. The dampers are located near the air handler unit at the base of each branch duct that will serve a zone. The dampers communicate electronically with a computer that communicates with thermostats located in each zone. Dampers are a good idea for several reasons. They save energy because different temperatures can be set for different zones, and cooling can be cut to less-used areas of the home. They also help provide more airflow where needed. For example, while a larger 5-ton unit might have 2,000 cfm of air flow, a smaller 2-ton unit would have about 800 cfm of airflow available, so dampers that close some zones make more air flow available to the zones calling for cooling. 

    The HVAC system sizing should be based on the heating or the cooling system, whichever is more in demand in your climate zone. Both the DOE Zero Energy Home Program and ENERGY STAR will allow designers to oversize furnaces by up to 150% to satisfy the airflow requirements of the cooling system. Cooling systems should not be oversized.

    The Refrigerant Cycle

    The vapor-compression refrigeration system uses a circulating liquid refrigerant as the medium that absorbs heat from the indoor air and rejects the heat outside. Figure 3 shows the path of the refrigerant as it cycles through a typical, single-stage vapor-compression air conditioner’s indoor and outdoor components. This figure depicts an air conditioner only. If this unit were part of a furnace, the furnace burner would be on the negative or return side of the blower and the cooling evaporator would be on the positive or supply side of the blower.

    Liquid refrigerant cycles.
    Figure 3. Liquid refrigerant cycles through the evaporator coil inside the air handler, pulling heat from the air that circulates through the house as the refrigerant evaporates. The vapor is transferred outside where it passes through the condenser and condenses, releasing heat to the outdoors, then the refrigerant returns to the inside unit as a liquid where it starts the cycle again. (Source: Calcs Plus.)

     

    All compression cooling systems have four main components: a compressor, a condenser, a metering device (known as a thermal expansion valve (TXV) or fixed orifice), and an evaporator coil. Circulating refrigerant moves through the suction line and enters the compressor as a saturated vapor. In the compressor, it is compressed to a higher pressure and higher temperature. The now “superheated” vapor is routed through the condenser coil where it is cooled by flowing air and condensed back into a liquid, releasing heat which is carried away by the flowing air.
    The liquid refrigerant is carried back to the indoor unit where it passes through an expansion valve. The expansion valve (or metering device) causes the liquid refrigerant to experience an abrupt drop in pressure and temperature as it enters the evaporator coil. In the coil, the liquid absorbs heat from the circulating house air, thus cooling the house air that is passing through the air handler. The heat causes the refrigerant to turn to vapor again and the vapor is again routed outside to the evaporator, beginning the cycle all over again.  

    Measuring the Efficiency of Cooling Systems

    The efficiency of compression cooling systems is measured in SEER, EER, and COP. 

    Seasonal Energy Efficiency Ratio (SEER) – the SEER rating of a unit is the cooling output during a typical cooling-season divided by the total electric energy input during the same period. The higher the unit's SEER rating the more energy efficient it is. In the United States, the SEER is the ratio of cooling in British thermal units (BTU) per hour to the energy consumed in watt-hours.

    Energy Efficiency Ratio (EER) – the EER of a particular cooling device is the ratio of output cooling (in Btu/h) to input electrical power (in watts) at a given operating point.

    Coefficient of Performance (COP) - the COP (sometimes referred to as CP) of a heat pump is the ratio of the heating or cooling provided over the electrical energy consumed. The COP provides a measure of performance for heat pumps that is analogous to thermal efficiency for power cycles.

    Technology improvements in recent years have made air conditioners much more efficient. These improvements include variable-speed fan motors, variable refrigerant flow technology, advanced compressors, and micro-channel heat exchangers. These changes enable the air conditioner to ramp up or ramp down rather than just turning on or off like a single-speed split-capacitor motor would. By better matching fluctuations in demand, the newer models can improve efficiency, lower energy consumption, and increase comfort.

    Since 2006 the federal government has required new air conditioners sold in the United States to have a SEER rating of 13 or higher. In 2011, these standards were amended to require split system heat pumps and single-package air conditioners (but not split-system central air conditioners) to meet SEER 14 if manufactured on or after January 1, 2015 (see the Code of Federal Regulations). Several states in the south are requiring split system air conditioners to also meet the minimum SEER 14 by January 2015 (DOE 2014).

    To receive an ENERGY STAR label under Version 3.2, a split system air conditioner must have a SEER of 16 or greater in hot or mixed climates, or a SEER of at least 14 in cold climates. The best available central air conditioning units can have SEER ratings of well over 20.

    Installation Concerns

    How the installation and connection of the copper tubing for the refrigerant lines is performed is critical to the life expectancy of the compressor. During new construction, the copper tubing is roughed in early on, before or during duct installation. The equipment (indoor unit and outdoor unit) is typically installed and connected to the copper tubing toward the end of construction. This means the copper lines can lay unconnected for quite some time.

    Copper tubing used for refrigerant lines is sold in 50-foot rolls. The tubing is dried out (dehydrated) and sealed at both ends before shipping. Water is the enemy of the refrigeration system. If water vapor is allowed to enter the refrigeration lines during construction, it will greatly reduce the life of the compressor and create havoc with metering devices and check valves. The oil used for lubricant in refrigeration systems is highly hygroscopic, which means that the oil wants to absorb moisture. If the lubricant mixes with water or water vapor, it creates an acidic sludge that eats away at compressor windings, causing burnouts; the sludge can also block orifices and valve openings inside the system.

    During the rough-in installation, the open ends of the copper tubing should be kept sealed at all times. When the installation is completed, the lines should be charged with dry nitrogen and soldered closed. After connecting the indoor unit and the outdoor unit, the lines should be vacuumed to 500 microns to remove air pockets, which can reduce heat transfer and cause erratic operation (Figure 4).

    Vacuum pump removes air from lines.
    Figure 4. A vacuum pump removes air from refrigerant lines in a compression cooling system prior to start up. (Source: Calcs Plus.)

     

    Proper refrigerant charging is critical for maximizing the performance of compression cooling equipment. Too much or too little refrigerant can reduce the efficiency of the equipment and lead to premature component failures. Use the charging method recommended by the manufacturer. There are three methods for refrigerant charging: the subcooling method (typically for units with a thermal expansion valve), the superheat method (typically for units with a fixed orifice), or the weigh-in method (using the refrigerant weight amount listed on the data plate on the outdoor unit). Verify that you are using the correct method for the specific air conditioning model to be installed. Refrigerant charging must be done by an EPA-certified technician.

    How to Select and Install Compression Cooling Equipment

    1. Choose the highest performing air conditioner project costs will allow, to meet the design cooling load of the project. If the design load is low (e.g., <14,000 Btu), consider alternative lower-load cooling sources such as ductless heat pumps with variable refrigerant flow technology. In dry climates, consider direct/indirect evaporative coolers and ventilation or passive cooling. If you are participating in an energy-efficiency program, select cooling equipment that complies with the requirements for your climate zone, as described in the Compliance tab.
    2. Confirm that the selected system is a matched system, as certified according to the Air-Conditioning, Heating, & Refrigeration Institute (AHRI). 
    3. Install in accordance with the manufacturers’ instructions and relevant standards including ACCA Standard 5: HVAC Quality Installation Specification, the ACCA’s Technician's Guide for Quality Installations, and ACCA Standard 9: HVAC Quality Installation Verification Protocols.
    4. Properly size the cooling equipment for the design cooling load of the home. Use ACCA Manual J to calculate your cooling load and use ACCA Manual S to correctly size your system. This is especially important if you have done significant air sealing and insulating, which will reduce your heating and cooling load.
    5. Design an efficient air distribution system with a compact layout in accord with the ACCA Manual D. Install ducts properly for maximum airflow and efficiency in accord with ACCA Manual D. See also the Building America Solution Center guides on duct installation, insulation, and air sealing in the ENERGY STAR Single-Family New Homes Checklist.
    6. Charge the copper tubing with dry nitrogen, seal the open ends with solder, and keep the tubing sealed at all times during the rough-in installation to prevent moisture from entering the lines.
    7. After connecting the indoor unit and the outdoor unit, vacuum the lines to 500 microns to remove air pockets.
    8. Follow the manufacturer’s recommendations for refrigerant charging. Verify that you are using the correct charging method for the specific air conditioning model to be installed. Refrigerant charging must be done by an EPA-certified technician.
    9. Set the time-delay relay on the unit to 30 seconds or less in humid climates to prevent moisture on the evaporator coil from evaporating back into the air stream and contributing to indoor humidity. Set the fan on the central air conditioning systems to “Auto” rather than “On” for the most efficient operation. Set the compressor to start before the blower. Make sure the drain pans are correctly installed.
    10. Test air flow and duct leakage.
    Success
    Ensuring Success

    Choose the highest efficiency SEER rating product possible.

    Verify that the air handler is correctly matched to the outdoor unit. Matched systems can be verified at the AHRI website, listed under "Air Conditioners and Air Conditioner Coils" and "Heat Pumps and Heat Pump Coils."

    Install in accordance with the manufacturers’ instructions and relevant standards including ACCA Standard 5: HVAC Quality Installation Specification and the ACCA’s Technician's Guide for Quality Installations and ACCA Standard 9: HVAC Quality Installation Verification Protocols. These standards address quality installation and commissioning requirements for vapor compression cooling systems, heat pumps, and combustion and hydronic heating systems.

    Install the air handler and ducts within the home’s thermal envelope.

    Keep the refrigerant lines sealed and dry during construction and after connecting the indoor and outdoor units vacuum the lines to 500 microns to remove air pockets.

    Follow the manufacturer’s recommendations for refrigerant charging.

    Set the time-delay relay on the unit to 30 seconds or less in humid climates to prevent moisture on the evaporator coil from evaporating back into the air stream and contributing to indoor humidity. Set the fan on the central air conditioning systems to “Auto” rather than “On” for the most efficient operation. Set the compressor to start before the blower. Make sure the drain pans are correctly installed.

    Climate
    Climate

    For ENERGY STAR and DOE Zero Energy Ready Home climate-specific guidance, see the Compliance tab.

    In mild or cold climates, consider non-compression cooling options such as trees, awnings, pergolas, and porches to shade windows and walls; ceiling fans; and timer-controlled night-time ventilation cooling (in dry climates).

    In humid and mild or cold climates, consider adding a dehumidifier for indoor humidity control in the shoulder seasons and in locations with short summers as an alternative to compression cooling.

    In humid climates, set the time-delay relay on the unit to 30 seconds or less to prevent moisture on the evaporator coil from evaporating back into the air stream and contributing to indoor humidity.

    The map in Figure 1 shows the climate zones for states that have adopted energy codes equivalent to the International Energy Conservation Code (IECC) 2009, 12, 15, and 18. The map in Figure 2 shows the climate zones for states that have adopted energy codes equivalent to the IECC 2021. Climate zone-specific requirements specified in the IECC are shown in the Compliance Tab of this guide. 

    Climate Zone Map from IECC 2009, 12, 15, and 18.
    Figure 1. Climate Zone Map from IECC 2009, 12, 15, and 18. (Source: 2012 IECC)

     

    Climate Zone Map from IECC 2021.
    Figure 2. Climate Zone Map from IECC 2021. (Source: 2021 IECC)

     

    Training
    Right and Wrong Images
    Image
    Right – Adequate space is provided near the air handler for the water lines of this ground-source heat pump.
    Right – Adequate space is provided near the air handler for the water lines of this ground-source heat pump.
    Image
    Right – The double compressor unit supplies multiple interior minisplit heat pump heads.
    Right – The double compressor unit supplies multiple interior minisplit heat pump heads.
    Compliance

    Compliance

    The Compliance tab contains both program and code information. Code language is excerpted and summarized below. For exact code language, refer to the applicable code, which may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

     

    ENERGY STAR Single-Family New Homes, Version 3/3.1 (Rev. 11)

    The ENERGY STAR Reference Design Home is the set of efficiency features modeled to determine the ENERGY STAR ERI [energy rating index] Target for each home pursuing certification. Therefore, while the features below are not mandatory, if they are not used then other measures will be needed to achieve the ENERGY STAR ERI Target. In addition, note that the Mandatory Requirements for All Certified Homes, Exhibit 2 [see list below], contain additional requirements such as total duct leakage limits, minimum allowed insulation levels, and minimum allowed fenestration performance. Therefore, EPA recommends that partners review the documents in Exhibit 2 prior to selecting measures.

    Please note that the Reference Design Home HVAC efficiencies for Version 3.1 differ from those for Version 3.0. Please see the ENERGY STAR Single-Family New Homes Implementation Timeline for the program version and revision currently applicable in in your state.

    Version 3.0 - Exhibit 1 ENERGY STAR Reference Design Home.
    Version 3.0 Exhibit 1: ENERGY STAR Reference Design Home. (Source: ENERGY STAR Single-Family New Homes, Version (Rev. 11).)

     

    Version 3.1 - Exhibit 1 ENERGY STAR Reference Design Home.
    Version 3.1 Exhibit 1: ENERGY STAR Reference Design Home. (Source: ENERGY STAR Single-Family New Homes, Version (Rev. 11).)

     

    Exhibit 2 of the National Program Requirements for ENERGY STAR Single-Family New Homes Version 3/3.1 (Rev. 11) requires that homes complete the following checklists:

    Exhibit 2: Mandatory Requirements for All Certified Homes Version 3/3.1 (Rev. 11)
    Version 3/3.1 Exhibit 2: Mandatory Requirements for All Certified Homes. (Source: ENERGY STAR Single-Family New Homes, Version (Rev. 11).)

     

    National HVAC Design Report

    National HVAC Design Report -  Cooling Equipment Selection (Version 3 / 3.1 (Rev. 11))
    Version 3/3.1 - Cooling Equipment Selection. (Source: ENERGY STAR Single-Family New Homes, Version (Rev. 11).)

     

    Footnote 15) Homes certified through the Caribbean Program Requirements, Version 3, are exempt from completing Sections 3, 4, and 5 of this report.

    Footnote 25) Equipment shall be selected using the maximum total heat gain in Item 3.12 and the total heat loss in Item 3.14 per ACCA Manual S, Second Edition, except that cooling ranges above ACCA Manual S limits are temporarily allowed, per Item 4.15.

    Footnote 26) As an alternative for low-load spaces, a system match-up including a single-speed compressor with a total capacity ≤ 20 kBtuh is permitted to be used in spaces with a total cooling load ≤ 15 kBtuh. A system match-up including a two-speed or variable-speed compressor with a total capacity ≤ 25 kBtuh is permitted to be used in spaces with a total cooling load ≤ 18 kBtuh.

    Footnote 27) If an AHRI Reference # is not available, OEM-provided documentation shall be attached with the rated efficiency of the specific combination of indoor and & outdoor components of the air conditioner or heat pump, along with confirmation that the two components are designed to be used together.

    Footnote 28) Per ACCA Manual S, Second Edition, if the load sensible heat ratio is ≥ 95% and the HDD/CDD ratio is ≥ 2.0, then the Climate is Condition B, otherwise it is Condition A.

    Please see the ENERGY STAR Single-Family New Homes Implementation Timeline for the program version and revision currently applicable in your state.

     

    DOE Zero Energy Ready Home (Revision 07)

    Exhibit 1 Mandatory Requirements.
    Exhibit 1, Item 1) Certified under the ENERGY STAR Qualified Homes Program or the ENERGY STAR Multifamily New Construction Program.

    Exhibit 2 DOE Zero Energy Ready Home Target Home.
    The U.S. Department of Energy’s Zero Energy Ready Home program allows builders to choose a prescriptive or performance path. The DOE Zero Energy Ready Home prescriptive path requires builders to meet or exceed the minimum HVAC efficiencies listed in Exhibit 2 of the National Program Requirements, as shown below. The DOE Zero Energy Ready Home performance path allows builders to select a custom combination of measures for each home that is equivalent in performance to the minimum HERS index of a modeled target home that meets the requirements of Exhibit 2 as well as the mandatory requirements of Zero Energy Ready Home Exhibit 1.
    Footnote 21) DOE recommends, but does not require, that cooling systems in hot/humid climates utilize controls for immediate blower shutoff after condenser shutoff, to prevent re-evaporation of moisture off the wet coil.
    ​Footnote 22) Air source heat pumps with electric resistance backup cannot be used in homes qualified in Climate Zones 7 & 8 using the Prescriptive Path.

    DOE ZERH Target Home HVAC Equipment Requirements.
    DOE ZERH Target Home HVAC Equipment Requirements. (Source: DOE Zero Energy Ready Home (Revision 07).)

     

    2009 International Energy Conservation Code (IECC)

    403.1 Each heating and cooling system should have its own thermostat. If the primary heating system is a forced-air furnace, at least one thermostat must be programmable and capable of controlling the heating and cooling system on a schedule to maintain different temperatures at different times of the day.

    403.2 Ducts - Insulate supply ducts in attics to at least R-8 and all other ducts to at least R-6. Duct tightness shall be verified as described in 403.2.2 Sealing.

    403.6 Heating and cooling equipment sizing shall be in accordance with Section M1401.3 of the 2009 International Residential Code.

    2012 IECC

    403.1 Each heating and cooling system should have its own thermostat. If the primary heating system is a forced-air furnace, at least one thermostat must be programmable and capable of controlling the heating and cooling system on a schedule to maintain different temperatures at different times of the day.

    403.2 Ducts - Insulate supply ducts in attics to at least R-8 and all other ducts to at least R-6. Duct tightness shall be verified as described in 403.2.2 Sealing. The air handler shall have a manufacturer’s designation showing air leakage is no more than 2% of the design air flow rate when tested in accordance with ASHRAE 193.

    403.6 Heating and cooling equipment shall be sized in accordance with ACCA Manual S based on building loads calculated in accordance with ACCA Manual J or other approved heating and cooling calculation methods.

    20152018, and 2021 IECC

    403.1 Each heating and cooling system should have its own thermostat. If the primary heating system is a forced-air furnace, at least one thermostat must be programmable and capable of controlling the heating and cooling system on a schedule to maintain different temperatures at different times of the day.

    Section 403.3.1 Insulation (Prescriptive). Supply and return ducts in attics insulated to at least R-8 if 3 inches in diameter or more or R-6 if less than 3 inches.  All other ducts insulated to at least R-6 if 3 inches in diameter or more and R-4.2 (R-6 in 2021 IECC) if less than 3 inches.

    Duct tightness verified as described in R403.3.2 (403.3.4.1 in 2021 IECC) Sealing. The air handler shall have a manufacturer’s designation showing air leakage is no more than 2% of the design air flow rate when tested in accordance with ASHRAE 193.

    403.7 Heating and cooling equipment shall be sized in accordance with ACCA Manual S based on building loads calculated in accordance with ACCA Manual J or other approved heating and cooling calculation methods.

    Retrofit:  2009, 2012, 2015, 2018,  and 2021 IECC

    Section R101.4.3 (in 2009 and 2012). Additions, alterations, renovations, or repairs shall conform to the provisions of this code, without requiring the unaltered portions of the existing building to comply with this code. (See code for additional requirements and exceptions.)

    Chapter 5 (in 2015, 2018, 2020). The provisions of this chapter shall control the alteration, repair, addition, and change of occupancy of existing buildings and structures.

     

    2009, 2012, 20152018, and 2021 International Residential Code (IRC)

    Comply with all relevant sections of the applicable International Residential Code, including Chapter 14: Heating and Cooling Equipment.

    Retrofit:  2009, 2012, 2015, 2018,  and 2021 IRC

    Section R102.7.1 Additions, alterations, or repairs. Additions, alterations, renovations, or repairs shall conform to the provisions of this code, without requiring the unaltered portions of the existing building to comply with the requirements of this code, unless otherwise stated. (See code for additional requirements and exceptions.)

    Appendix J regulates the repair, renovation, alteration, and reconstruction of existing buildings and is intended to encourage their continued safe use.

     

    Air Conditioning Contractors of America (ACCA) Standards

    ACCA Manual S. Residential Equipment Selection, ANSI/ACCA 3-Manual S-2004, provides information on how to select and size heating and cooling equipment to meet Manual J loads based on local climate and ambient conditions at the building site. Manual S covers sizing strategies for all types of cooling and heating equipment, as well as comprehensive manufacturers’ performance data on sensible, latent, or heating capacity for various operating conditions.

    ACCA Manual D: Residential Duct Systems, ANSI/ACCA 1-Manual D-2011, provides ANSI-recognized duct sizing principles and calculations that apply to all duct materials; the system operating point (supply cfm and external static pressure) and airway sizing for single-speed and multi-speed (ECM) blowers; a method for determining the impact of duct friction and fitting pressure drop on blower performance and air delivery; and equivalent length data.

    ACCA Manual J: Residential Load Calculation, ANSI/ACCA 2-Manual J-2011, provides information for calculating heating and cooling loads for equipment sizing for single-family detached homes, small multi-unit structures, condominiums, town houses, and manufactured homes.

    ACCA Standard 5: HVAC Quality Installation Specification, ANSI/ACCA 5 QI-2010, details nationally recognized criteria for the proper installation of residential and commercial HVAC systems, including forced air furnaces, boilers, air conditioners, and heat pumps. The Standard covers aspects of design, installation, and distribution systems, as well as necessary documentation. The Technician’s Guide for Quality Installation, produced by ACCA, explains the HVAC Quality Installation (QI) Specification and provides detailed procedures for the steps technicians must complete and document to show compliance with the HVAC QI Specification.

    ACCA Standard 9: HVAC Quality Installation Verification Protocols, ANSI/ACCA 9 QIVP-2009, specifies the protocols to verify the installation of HVAC systems in accordance with ACCA Standard 5. The protocols provide guidance to contractors, verifiers, and administrators who participate in verification efforts using independent objective and qualified third parties to ensure that an HVAC installation meets the requirements in Standard 5.

     

    Residential Energy Services Network (RESNET) Mortgage Industry National Home Energy Rating Systems Standards

    Procedures and technical standards by which home energy ratings are conducted including home energy audits.

    Retrofit
    Existing Homes

    SCOPE

    Assess the need for replacing or upgrading the HVAC system. See Pre-Retrofit Assessment of Existing HVAC Systems.

    For more information on compression cooling, see the U.S. Department of Energy’s Standard Work Specifications regarding compression cooling equipment.

    DESCRIPTION

    Assessment

    The typical lifespan of HVAC equipment is 15 to 20 years. New equipment has much higher efficiencies, safety, control flexibility, and performance capabilities. Existing equipment should be carefully assessed to determine if investment in repairs, upgrades, or expansion is warranted or if replacement is the better option. See the following BASC guides and resources for information to aid in making this determination. The guides provide economic guidelines to help determine if this investment is warranted, and also contain important safety and health information for dealing with older construction and equipment.

    Replacement

    Although replacement of HVAC equipment can be costly and labor-intensive, it often reaps large rewards in energy cost savings and comfort. Table 1 below gives examples of what energy cost savings can be expected when upgrading from existing HVAC equipment to equipment with higher rated efficiencies. Use your summer cooling bill and the before and after SEERs to estimate potential savings.

    Table 1. Annual Estimated Savings for Every $100 of Cooling Costs. (Source: www.energysavers.gov)
    Existing System SEER New/Upgraded System SEER
      13 14 15 16 17 18 19 20
    10 $23 $29 $33 $38 $41 $44 $47 $50
    11 $15 $21 $27 $31 $35 $39 $42 $45
    12 $8 $14 $20 $25 $29 $33 $37 $40
    13 - $7 $13 $19 $24 $28 $32 $35
    14 - - $7 $13 $18 $22 $26 $30
    15 - - - $6 $19 $17 $21 $25
    16 - - - - $6 $11 $16 $20
    *Assuming the same cooling output

    Because A/C units typically provide only space cooling and dehumidification, the demise of the current A/C system is an opportunity to re-assess the homeowner’s needs. In mild to temperate climates, if the home also has a furnace nearing the end of its expected life, an air-source heat pump could replace both pieces of equipment because a heat pump can operate the refrigeration cycle in reverse to provide heating. In warm-humid climates with moderate space heating needs, a heat pump may be a good option for comfort, control, and operating cost, since many homes in these climates focus on air conditioning, and space heating is typically provided by an electric coil that heats the airstream.

    An evaporative cooler can improve thermal comfort by adding moisture to very dry air; evaporative coolers are often much less expensive to buy and operate than A/C, but they are only effective in dry climates. The delta T of evaporative coolers is limited, so in very hot climates A/C may be the right equipment to meet peak load. Consider all options when recommending a replacement. The guide Pre-Retrofit Assessment of Existing HVAC Systems provides additional guidance.

    If a decision is made to replace your current equipment, it can be replaced in-kind or with a different type of system. See the following Building America Solution Center guides for more information on other types of HVAC systems that provide space cooling:

    For the highest efficiency and best performance with split-system central A/Cs, always replace the indoor and outdoor units at the same time. Also, replace the entire refrigerant line set when installing new cooling equipment. If any water vapor were to get into the old refrigerant line during replacement of the indoor and outdoor components, the water vapor would mix with the lubricant in the refrigerant system, causing an acidic sludge that would foul the new equipment; see the Description tab for more information. Follow the manufacturer’s directions and the suggestions in the Description tab of this guide for proper sizing, selection, and installation.

    Repair/Upgrade

    Start-up commissioning and full system maintenance are often overlooked by homeowners who do not understand the strong relationship between these precautions and actual performance. The Air Conditioning Contractors of America Association, Inc. (ACCA), is one of the best sources for guidance on the installation, commissioning, and maintenance of HVAC equipment. Their free Quality Standards can be found on the ACCA website.

    Useful documents available for download from the ACCA website include the following:

    Faulty ductwork can cause poor performance in central forced air heating and cooling systems. Duct blower testing and inspection by a certified technician may reveal leaky, uninsulated, constricted, or even disconnected ducts that prevent heated or cooled air from reaching its destination. See Ducts in the Building America Solution Center for more on improving ducted distribution systems.

    Additions

    If additional rooms will be added to the home, or if an attic, basement, or garage will be converted to living space and the home has an existing furnace, the forced-air HVAC equipment may have sufficient capacity to extend conditioning to the additional space. This should be confirmed by performing an accurate load calculation (ACCA Manual J) for the entire house including the addition. If the current system doesn’t meet the additional needed capacity (and/or for increased efficiency or for zone control) you may decide to add a new, dedicated HVAC system to serve the new space independently or you may choose to replace the existing system with a new more efficient system capable of serving the whole house.

    When installing new ducts for the addition, consider the following:

    • New ducts should be properly sized in accordance with ACCA Manual D.
    • If using the existing furnace, simply extending the nearest existing supply branch ducts into an addition is unlikely to deliver sufficient air flow to the addition because that takeoff was not designed for the new (combined) flow requirement. This will result in poor comfort for all spaces dependent on the modified branch, both existing and new.
    • Ideally, install a separate, dedicated supply air trunk duct to serve the addition. This trunk should be run back as close to the furnace/air handling unit as practical. This will ensure that air flow to the addition is removed proportionally from the total system air flow and therefore will not affect the air flow balance in the existing house. Install manual balancing dampers in the supply trunks serving the addition and existing house to allow fine-tuning of the system.
    • If there are interior doors separating the addition - or portions of the addition - from the main house, install transfer grilles, jump ducts, or ducted returns as required to ensure a return air path to the central air handling unit.

    COMPLIANCE

    Check with the Authority Having Jurisdiction to determine if upgrade or expansion to existing HVAC equipment requires compliance with current codes.

    See Compliance tab. 

    More

    More Info.

    Access to some references may require purchase from the publisher. While we continually update our database, links may have changed since posting. Please contact our webmaster if you find broken links.

    Case Studies
    Author(s)
    Building Science Corporation
    Organization(s)
    BSC
    Publication Date
    Description
    Case study describing a building project in the hot-humid climate zone.
    References and Resources*
    Author(s)
    Air Conditioning Contractors of America
    Organization(s)
    ACCA
    Publication Date
    Description
    The Technician's Guide equips practitioners with the knowledge to properly implement all of the measurement procedures required in the HVAC QI Specification.
    Author(s)
    Burdick Arlan
    Organization(s)
    IBACOS,
    National Renewable Energy Laboratory
    Publication Date
    Description
    Report describing the equipment selection of a split system air conditioner and furnace for an example house in Chicago, Illinois, as well as a heat pump system for an example house in Orlando, Florida.
    Author(s)
    Gilbride Theresa L,
    Baechler Michael C,
    Hefty Marye G,
    Hand James R,
    Love Pat M
    Organization(s)
    Pacific Northwest National Laboratory,
    PNNL,
    Oak Ridge National Laboratory,
    ORNL
    Publication Date
    Description
    Report providing information about energy-efficient heating, ventilation, and cooling (HVAC) equipment options to help homeowners cut their energy use, reduce their carbon footprint, and increase their homes comfort, health, and safety.
    Author(s)
    International Code Council
    Organization(s)
    ICC
    Publication Date
    Description
    2009 edition of code establishing minimum regulations for mechanical systems, including heating, cooling, ventilation, exhaust, ducts, fireplaces, combustion and hydronic systems, using prescriptive and performance-related provisions.
    Author(s)
    RESNET
    Organization(s)
    RESNET
    Publication Date
    Description
    RESNET standards aimed to ensure that accurate and consistent home energy ratings are performed by accredited home energy rating providers through their raters nationwide.
    Author(s)
    Air Conditioning Contractors of America
    Organization(s)
    ACCA
    Publication Date
    Description
    This Standard establishes the minimum requirements to evaluate a residence with regards to energy efficiency, water conservation, occupant comfort, and indoor air quality.
    Author(s)
    Air Conditioning Contractors of America
    Organization(s)
    ACCA
    Publication Date
    Description
    Standard providing a universally accepted definition for quality installation for residential and commercial heating, ventilating, and air conditioning applications.
    Author(s)
    Air Conditioning Contractors of America
    Organization(s)
    ACCA
    Publication Date
    Description
    Document detailing the requirements, roles, and obligations for participants in an organized effort, ensuring that HVAC installations comply with the ANSI/ACCA 5 QI – 2010 (HVAC Quality Installation Specification) QI Standard.
    Author(s)
    U.S. Department of Energy
    Organization(s)
    DOE
    Publication Date
    Description
    Website listing implementation timelines and links to various versions of the DOE Zero Energy Ready Home national program requirements.
    Author(s)
    U.S. Environmental Protection Agency
    Organization(s)
    EPA
    Publication Date
    Description
    Document outlining specifications that were developed by the U.S. Environmental Protection Agency (EPA) to recognize new homes equipped with a comprehensive set of indoor air quality (IAQ) features.
    Author(s)
    Dentz Jordan,
    Zhu Shengming
    Organization(s)
    Levy Partnership,
    USDOE Office of Energy Efficiency and Renewable Energy
    Publication Date
    Description
    Technical report describing the integration of mini split ductless heat pumps and through-wall transfer fans in small single-story homes, to achieve a 50% reduction in space conditioning energy consumption compared to the 2009 International Energy Conservation Code, while ensuring affordability and...
    *For non-dated media, such as websites, the date listed is the date accessed.
    Contributors to this Guide

    The following authors and organizations contributed to the content in this Guide.

    Sales
    Building Science Measures
    Building Science-to-Sales Translator

    High-Efficiency HVAC Equipment = High-Efficiency or Ultra-Efficient Comfort Equipment

    Image(s)
    Technical Description

    Because heating and cooling costs are the largest contributors to utility bills, inefficient comfort equipment creates significant costs for homeowners. Not installing high- or ultra-efficient comfort equipment is a missed opportunity, especially if the proper steps have been taken to insulate and air seal a home. High-efficiency comfort equipment meets ENERGY STAR requirements for efficiency. Ultra-efficient comfort equipment meets or exceeds the criteria for ENERGY STAR’s “Most Efficient” designation, indicating it is among the most efficient heating and cooling products available on the market.

    High-Efficiency or Ultra-Efficient Comfort Equipment
    Sales Message

    High-efficiency comfort equipment provides heating and cooling with less wasted energy. What this means to you is less cost to keep you and your family comfortable. Wouldn’t you agree it’s important to take advantage of proven advanced technologies in all homes?

    Last Updated

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