HVAC Efficiency Requirements
- The National Appliance Energy Conservation Act (NAECA) supersedes the minimum efficiency requirements addressed in the IECC.
- NAECA applies to heating, cooling, and water-heating systems.
- Manufacturers must comply with NAECA, so equipment purchased by a builder should automatically comply with the provisions.
Temperature Controls
Thermostats are required for each separate HVAC system. They must be adjustable and be able to accommodate the following temperature ranges:
- Heating only, 55-75°F
- Heating and cooling, 55-85°F
- Cooling only, 65-85°F
Thermostats must be able to reduce temperatures during periods of non-use by either manually adjusting the temperature upward or downward or shutting the system off entirely.
Heat Pumps
Heat pump thermostats are required to be capable of preventing supplementary heating when the heating load can be met by the heat pump alone
- supplemental heater operation is only allowed during the outdoor coil defrost cycles and is not to exceed 15 minutes
The supplemental heater isn’t as efficient, so the less it is used, the more energy that will be saved.
Humidity Control
Humidistat’s used for comfort shall be capable of being set to prevent the use of fossil fuel or electricity to reduce relative humidity below 60 percent or increase relative humidity above 30 percent. The intent is to limit the energy used for humidification until the level in the space falls below 30 percent.
HVAC Piping Insulation
The requirements in the table apply to HVAC piping located in unconditioned space and conveying fluids > 120°F and < 55°F. Typically, this will apply to refrigerant piping and water piping for hydronic heating systems.
Minimum HVAC Piping Insulation Thickness
Summary
- Manufacturers must comply with NAECA, so HVAC equipment purchased by builders should automatically comply with code requirements.
- Thermostats are required for each separate HVAC system.
- The 2000 IECC has minimum insulation thicknesses for HVAC piping by type of piping system, pipe size, and fluid temperature range.
AFUE
Annual Fuel Utilization Efficiency. Used to express the efficiency of gas furnaces. The higher the AFUE rating, the SUITE more efficient the unit. Federal law has required that all new residential furnaces built after January 1992 operate with an AFUE of 78% or higher. All Rheem® furnaces are manufactured to exceed these requirements with a minimum AFUE of 80%.
If your furnace was built before 1992, chances are it is operating with an average efficiency of around 60%. Most of the heat is lost up the chimney or out the exhaust vent – devices used by older furnaces to expel dangerous fumes created by the furnace, such as carbon monoxide, carbon dioxide, aldehydes, and even soot.
HC.
Modern furnaces use more technologically advanced venting techniques to achieve greater energy efficiency. An important note: Be sure to ask your installing contractor if your chimney or exhaust vent is suitable for use with your new equipment.
ARI
The Air Conditioning and Refrigeration Institute is an organization created by HVAC manufacturers to ensure an acceptable level of quality within the industry. ARI is a voluntary, nonprofit organization which publishes ratings standards and benchmarks for testing cooling and heating products.
BTU
Short for British Thermal Unit. The amount of heat required to raise or lower the temperature of one pound of water by one degree Fahrenheit.
BTUH
The heat transfer rate of HVAC equipment is measured in British Thermal Units per Hour.
CAPACITY
Usually measured in BTUs or tons, capacity refers to an air conditioning or heating unit’s ability to cool or heat a space. For instance, a 20-ton air conditioning unit has twice the capacity of a 10-ton unit.
CFM
A unit to express movement of volume, including air, in Cubic Feet per Minute. A 400 CFM air handler moves 400 cubic feet in one minute.
COMPRESSOR
The compressor plays an integral role in cooling your home. It is the device responsible for pumping refrigerant through the refrigerant lines and the coil, making the transfer of heat from inside your house to the outdoors possible.
CONDENSER
The coil responsible for dissipating heat to the surrounding, outside air. Also called the condenser coil, or outdoor coil, its role is reversed when a heat pump is used in heating mode.
COP
The Coefficient of Performance rates a heat pump’s ability to efficiently use electricity in its operation. The Air Conditioning and Refrigeration Institute provides the Coefficient of Performance at 47 degrees Fahrenheit and 17 degrees Fahrenheit. This is because a heat pump is more efficient at higher, outside-air temperatures.
dB
The relative loudness of a sound is expressed in dB, short for decibel. As an example, the sound of a human voice talking is around 70 dB. (See also SRN.)
DOE
A federal agency, the Department of Energy, sets the standards for efficiency throughout the HVAC industry and monitors consumption of energy sources.
DOWNFLOW
A term used to describe the direction of airflow through a furnace. A downflow furnace takes return air from the top, heats it and then delivers the warm air from the bottom
DUCT/DUCT WORK/DUCTING
A central heating and air conditioning system uses many components to heat or cool air This warm or cool air is then transferred to different registers throughout the house via special flexible large-diameter pipes or ducts The system of ducts throughout your house is often referred to as ductwork or ducting
EER
Energy Efficiency Ratio The ratio of the cooling capacity of the air conditioner in BTUs per hour to the total electrical input in watts This measure is determined by comparing test units to the Air Conditioning and Refrigeration Institute specifications
EFFICIENCY
A general term used to describe how effectively a heat pump air conditioning system or furnace converts incoming energy to outgoing energy The higher the number the more efficient the unit and the lower the operating costs
EVAPORATOR COIL/EVAPORATOR
An integral part of the indoor unit of a heat pump or air conditioning system. So called because when warm air passes over a coil filled with liquid refrigerant, the refrigerant itself evaporates and absorbs some of the heat. This gas refrigerant is then pumped to the outdoor coil, where it releases heat into the surrounding air and returns to its liquid state.
HEAT EXCHANGER
Responsible for transferring heat from furnace burners to the blower. Rheem uses some of the finest heat exchangers in the industry with limited lifetime warranties on some models.
HOR FLOW
A term used to describe the direction of airflow through a furnace. A horizontal flow furnace takes return air from one side, heats it, arid then delivers the warm air from the other side.
HSPF
Heating Seasonal Performance Factor. It measures the efficiency of the heating portion of your heat pump. The Department of Energy minimum is 6.8. (Similar to SEER.)
HUMIDIFIER
Usually available as an optional accessory, a humidifier is used to inject water vapor into the dry, heated air expelled from a furnace/air handler. The benefits can be improved efficiency and a more comfortable living environment.
HVAC
Heating, Ventilating and Air Conditioning. Used to refer to the industry at large, particularly dealers of heating and air conditioning equipment.
INDOOR COILS
Split-system home comfort systems use two main components to deliver air for a comfortable living environment. The indoor coil is the device responsible for transferring heat from indoors to the outdoors (or the reverse in the case of a heat pump in heating mode) Most modern systems are designed to achieve maximum efficiency when the indoor unit (coils and blower) is properly matched with the outdoor unit (air conditioner or heat pump). For best results, be sure to replace both the indoor and outdoor units at the same time.
K
A unit used to express 1,000 Watts. Denoted as kW.” Note that the W in ‘kW’ is always capitalized because the Watt unit was named after a person.
KWH
If a unit uses 1,000 Watts in 1 hour, it is said to have an energy rating of lkWh.
MODULATING FURNACES
Furnaces are designed to deliver maximum heat for comfort on the coldest of days In most cases those days account for fewer than three percent of winter days. The rest of the time, your furnace is providing more heat than necessary. Because conventional furnaces are either providing no heat or at full capacity the temperature in your house goes up and down by several degrees adversely affecting your comfort and your energy bills Modulating furnaces solve this problem by varying the amount and temperature of air delivered between different capacities so that the air flowing out of the registers is always at the temperature you determine This results in lower operating costs, more comfortable temperatures throughout the house and quieter operation.
PACKAGE UNIT
Equipment in which all heating and cooling components are located in one cabinet. Installed either beside or on top of a home or business.
REFRIGERANT
The liquid used to absorb and transfer heat from one part of the home comfort system to another.
REFRIGERANT LINES
Copper lines used to transfer the refrigerant between the outdoor unit and the indoor unit.
SEER
Seasonal Energy Efficiency Rating. Used to express the efficiency of an air conditioning unit, or a heat pump in cooling mode. The higher the SEER rating, the more efficient the unit. The Department of Energy minimum is 10
SPLIT SYSTEM
A home comfort system that uses an indoor and an outdoor component to deliver comfortable air to a living environment.
SRN
The Air Conditioning and Refrigeration Institute performs tests and assigns a Sound Rating Number (SRN) to units. A lower SRN rating indicates a quieter unit with average SRNs of between 74dB and 80dB.
THERMOSTAT
A temperature-measuring device used to control the operation of home comfort systems to maintain a comfortable temperature within the house. Programmable thermostats allow you to program different temperatures for different times of the day.
TON
The ton ratings you see here have nothing to do with the weight of the unit. In fact a ton is simply 12,000 BTUs (see BTU definition on this page). A typical home cooling/heating system uses heat pumps or air conditioners with a capacity of between 1.5 and 5 tons.
UPFLOW
A term used to describe the direction of airflow through a furnace. An upflow furnace takes return air from the bottom, heats it, and then delivers the warm air from the top.
WATT/WATTS
Electrical power also expressed as ‘W’ For example a 100W globe consumes 100 Watts of electrical power The W in Watt is always uppercased, because it is named after a person.
ZONE/ZONING
A home may be divided into several different areas, or zones, to better control the temperatures throughout the house The process of dividing your home into different zones is called zoning
How do Air Conditioning Compressors Work?
| The (usually) outdoor half of a typical air conditioning system is a unit containing the refrigerant compressor and condensing coil. The air conditioning compressor motor is a pump which draws heat laden refrigerant gas from the building’s indoor components (evaporator coil and air handler), and compresses the low pressure refrigerant gas to high pressure and higher temperature.The high pressure high temperature refrigerant gas enters the condensing coil where it is cooled to a liquid state by a fan blowing outside air across the condensing coil or by immersion of the condensing coil in cooling water.
The heat produced in these steps is transferred to the outside by a fan which blows outside air across the condensing coil. The liquid refrigerant is then able to return to the indoor components for cooling and dehumidifying the building interior. The diagnosis and repair of various defects in the air conditioning compressor/condenser unit are discussed in detail using the links provided at the left of this page. Here is a little more detail about the components of the compressor/condenser unit: What are the Components of the Outdoor Portion of a Central Air Conditioning System – the Air Conditioning Compressor Unit? |
- The Air Conditioning Compressor Itself – on residential units the A/C compressor motor is most often a hermetic motor-compressor combined in a single sealed unit like the Carrier(TM) unit shown at above left. Sketch from Carson Dunlop.If a ductless split-system is installed an outside compressor unit is still required, typically looking like the Sanyo(TM) unit shown at the top of this page.
The compressor is a basically a pump which moves refrigerant gas to the compressor via the larger refrigerant “suction line” returning it from the in-building air handler and evaporator coil.
How does an air conditioning compressor motor work?
The air conditioning or heat pump compressor compresses the incoming refrigerant to a high pressure gas and moves that gas into the condensing coil described just below. Typically a piston moves up and down inside of a cylinder inside the compressor motor, drawing in refrigerant gas on the down stroke of the piston, and compressing the refrigerant gas on the up stroke of the piston. (Some refrigeration compressors such as those made by Frigidaire™ used a rotary compressor design that we found durable and powerful enough to lead us to salvage and re-use these motors for other purposes.
The refrigerant gas leaves the compressor at high pressure and at high temperature (since compressing a gas will raise its temperature). In most air conditioning or heat pump compressors, a piston moves up and down to draw in and then compress refrigerant gas, moving refrigerant vapor from the incoming low side to the outgoing high side of the compressor.
The refrigerant gas leaving the compressor (and entering the condensing coil) will contain both heat that the refrigerant absorbed at the evaporator coil (heat from air in living space of the building), and additional heat produced at the compressor by the process of compressing the gas. The refrigerant gas is thus heat laden with sensible heat from the living area and compressor heat from the compressor motor. Low side and high side refer to the low-pressure and high-pressure areas of the air conditioning equipment and are defined in more detail at SEER RATINGS & OTHER DEFINITIONS where we also explain sensible heat and other air conditioning terms.
Refrigeration and Air Conditioning Theory: In an air conditioning system, pressure is used to change (increase) the vaporization point (state change from liquid to gas) or condensation point (state change from gas to liquid) of the refrigerant. On the A/C system’s high side, the condensation point must be some temperature above ambient outdoor air temperature (if air is being used to cool the condensing coil) or condensation of the refrigerant gas back to a liquid will not occur.
Creation of high side & low side in a refrigeration system: The restriction in refrigerant flow created by the thermostatic expansion valve (TEV, discussed below) located close to the evaporator coil (cooling coil) allows the compressor to raise the pressure and increase the temperature at which the refrigerant (coolant) will change state (from liquid to gas in the cooling coil, and from gas back to liquid in the condensing coil). This restriction in refrigerant flow at the TEV is what allows the compressor a pressure difference between the high side and low sides of the system. Evaporator coil is defined at A/C COMPONENTS and discussed further at AIR HANDLER UNIT. TEVs are discussed at THERMOSTATIC EXPANSION VALVES.
State changes of refrigerant are what remove heat: Refrigeration systems rely on two state changes of the refrigerant: gas to liquid, and liquid back to a gas. It is these state changes of the refrigerant that move sensible heat from one side of the air conditioning system to the other: by absorbing BTUs of heat during evaporation (in the evaporator coil) and by releasing BTUs of heat during condensation (in the condenser coil).
R12 refrigerant has a boiling point of -21 degF (change of state from liquid to gas vapor) and R22 has a boiling point of -41 degF.
State change of refrigerant gas to liquid: The state change of the air conditioning refrigerant from a high pressure high temperature gas back to a liquid occurs inside the outdoor condensing coil. This state change (gas to liquid) releases energy in the form of heat which is blown into outdoor air (or transferred into water). Note: the compressor has to produce high enough output pressure that the gas moving through the condensing coil moves at a good velocity in order to scrub the entire condensing coil tubing surface and thus transfer its heat out through the condensing coil tubing into ambient air (or water).
State change of refrigerant liquid to gas: the state change from a liquid refrigerant to a low pressure gas occurs in the indoor evaporator or cooling coil, absorbing energy in the form of heat (the heat in indoor air being blow across the evaporator coil), thus moving heat from the indoor air into the refrigerant gas in the system.
So summing up this theory and practice of air conditioning, the job of the air conditioning compressor is to reduce pressure on the low side (cooling side) of the system and to increase pressure on the high side (warming side) of the system. These pressure differences move refrigerant through the system and enable it to change states from liquid to gas (at the TEV and in the evaporator coil) and from gas to liquid (in the condensing coil). This process moves heat (absorbed by the evaporator coil inside the cooling or refrigerated area) through the condenser coil and into outside air (or water).
Special oil used in air conditioning & refrigeration compressor motors
Air conditioning and refrigeration compressors use a special oil which does not react with the refrigerant liquid or gas in the system. The oil may mix and travel with the refrigerant however, and some cooling systems are designed for deliberate movement of the compressor oil in order to lubricate some parts such as refrigerant metering valves or compressor valves.
- Refrigerant lines:The larger diameter refrigerant suction line connects the indoor evaporator coil outlet to the compressor inlet. The larger refrigerant line (located on the low side of the system) reduces system pressure and causes vaporization of the refrigerant (so that sensible heat is absorbed and the suction line feels cool to the touch). Refrigerant returning to the compressor from the evaporator coil and through the refrigerant low pressure suction line, is in the form of a low pressure, low temperature gas.
Most air conditioning compressors are designed only to pump gas vapors, not liquid refrigerant (which could damage compressor internal parts).
The refrigerant gas entering the compressor at its inlet port is said to be heat laden, that is, it was at a low-enough temperature to have absorbed heat from the evaporator coil in the living area.
The smaller-diameter high pressure refrigerant lines connect the compressor outlet and the condensing coil inlet and also move refrigerant liquid in it’s cooled, condensed and now liquid state from the outlet of the condensing coil to the thermal expansion valve (basically a refrigerant metering device) and the evaporator coil inlet in the air handler unit in the building. This smaller (in diameter) refrigerant piping or tubing (located on the high side of the air conditioning system) reduces volume and thus increases pressure and temperature in the lines (so that sensible heat can be transferred to ambient outdoor air or water if a water-cooled air conditioner system is in use).
Service valves or ports are usually present on the refrigeration lines near the compressor. to permit testing the condition of the air conditioning system and permit removal, replacement, or additions to the refrigerant in the system.
- Condensing coil (shown at left) receives high pressure refrigerant gas from the compressor and cools this refrigerant gas back to a liquid state. Sketch from Carson Dunlop.
- Outdoor cooling fan moves outdoor air across the condensing coil to cool it and assist in condensing the high pressure, high temperature refrigerant gas back into a liquid.It is this process which completes the transfer of heat through the refrigerant from indoor air to outdoor air as the compressor/condenser unit compresses and then cools the refrigerant back to a liquid.
- Electrical shut-off switch(es) for service at the unit are provided to permit maintenance and repair of the equipment.Circuit breaker(s) at the electrical panel protect the circuit supplying power to the air conditioning system.
These components are discussed in detail throughout this website using the links at the left of these pages.
Minimum Air Conditioner Compressor Unit Observations for an Air Conditioner Report
Example home inspection report language for an air conditioning compressor:
The compressor and fan operated normally. The rated cooling capacity, estimated age and general condition of the unit are reported below.
OR … We did not operate this equipment because … so you should … [text inserted by inspector]
How to diagnose and fix an air conditioning system that is not working
If your air conditioning system won’t work, follow our diagnostic guides
See our complete list of air conditioning system diagnostic and repair guide articles just below. |
Since the failure of an air conditioner to turn on, loss of air conditioner cooling capacity, reduced air conditioning output temperatures, loss of cool air supply, or even loss of air flow entirely can be due to a variety of problems with one or more components of an air conditioner or air conditioning system, after reviewing the lost air conditioner cooling diagnosis procedures described in this article, be sure to also review the diagnostic procedures at each of the individual air conditioning diagnosis and repair major topics listed just below. To return to our air conditioning and refrigeration home page go to AIR CONDITIONING SYSTEMS.
If your air conditioning system has lost its cooling capacity or won’t start select one or more of the diagnostic articles listed below.
- CONTROLS & SWITCHES: air conditioner controls and switches – begin here if your A/C won’t start. Here’s an important tip: most refrigeration problems, in air conditioners, refrigerators, or freezers, are electrical, not mechanical. In air conditioning school, we used to drive out and collect abandoned refrigerators that people were tossing out during our community’s spring cleanup week. Taking these appliances back into the shop we found that almost always the problem that had caused the owner to dispose of their air conditioner or freezer was in an electrical connection or electrical control. So it’s worth checking out switches and controls on an air conditioner before replacing more costly components.
- OPERATING DEFECTS: major air conditioning problem symptoms and how to get the air conditioning system working again,e.g. compressor or fan noises, failure to start, and inadequate cool air volume
- LOST COOLING CAPACITY: what to do when not enough cool air comes out of the system
- What to check first if there is no cool air or not enough cool air
- Compressor failure diagnosis: basic checks of the air conditioner compressor
- Ducts & Air Handler diagnosis: basic checks of the indoor air handler (blower), air ducts, and filter systems
- COMPRESSOR CONDENSER: problems with air conditioner compressor/condenser units
- AIR HANDLER UNIT: problems with the air handler, air filters, and the cooling coil itself
- DUCT SYSTEM DEFECTS: problems with the air duct system, air filters, supply registers, return air registers
- A/C REFRIGERANT LEAK DETECTION: how to use a TIF5000 to detect air conditioning refrigerant gas leak
- A/C DIAGNOSTIC FAQs: air conditioning system diagnostic FAQs: Q&A about air conditioner repair – a detailed air conditioning system diagnostic checklist