Local Experts Share Advice on Ducted Heating Setup

In the United States, the efficiency of air conditioners is often rated by the seasonal energy efficiency ratio (SEER) which is defined by the Air Conditioning, Heating, and Refrigeration Institute, a trade association, in its 2008 standard AHRI 210/240, Performance Rating of Unitary Air-Conditioning and Air-Source Heat Pump Equipment.^[1] A similar standard is the European seasonal energy efficiency ratio (ESEER).

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 U.S., the SEER is the ratio of cooling in British thermal units (BTUs) to the energy consumed in watt-hours.

For example, consider a 5000 BTU/h (1465-watt cooling capacity) air-conditioning unit, with a SEER of 10 BTU/(W·h), operating for a total of 1000 hours during an annual cooling season (e.g., 8 hours per day for 125 days).

The annual total cooling output would be:

5000 BTU/h × 8 h/day × 125 days/year = 5,000,000 BTU/year

With a SEER of 10 BTU/(W·h), the annual electrical energy usage would be about:

5,000,000 BTU/year ÷ 10 BTU/(W·h) = 500,000 W·h/year

The average power usage may also be calculated more simply by:

Average power = (BTU/h) ÷ (SEER) = 5000 ÷ 10 = 500 W = 0.5 kW

If the electricity cost is $0.20/(kW·h), then the cost per operating hour is:

0.5 kW × $0.20/(kW·h) = $0.10/h

The energy efficiency ratio (EER) of a particular cooling device is the ratio of output cooling energy (in BTUs) to input electrical energy (in watt-hours) at a given operating point. EER is generally calculated using a 95 °F (35 °C) outside temperature and an inside (actually return-air) temperature of 80 °F (27 °C) and 50% relative humidity.

The EER is related to the coefficient of performance (COP) commonly used in thermodynamics, with the primary difference being that the COP of a cooling device is unit-less, because the numerator and denominator are expressed in the same units. The EER uses mixed units, so it does not have an immediate physical sense and is obtained by multiplying the COP by the conversion factor from BTUs to watt-hours: EER = 3.41214 × COP (see British thermal unit).

The seasonal energy efficiency ratio (SEER) is also the COP (or EER) expressed in BTU/watt-hour, but instead of being evaluated at a single operating condition, it represents the expected overall performance for a typical year's weather in a given location. The SEER is thus calculated with the same indoor temperature, but over a range of outside temperatures from 65 °F (18 °C) to 104 °F (40 °C), with a certain specified percentage of time in each of 8 bins spanning 5 °F (2.8 °C). There is no allowance for different climates in this rating, which is intended to give an indication of how the EER is affected by a range of outside temperatures over the course of a cooling season.

Typical EER for residential central cooling units = 0.875 × SEER. SEER is a higher value than EER for the same equipment.^[1]

A more detailed method for converting SEER to EER uses this formula:

EER = −0.02 × SEER² + 1.12 × SEER^[2] Note that this method is used for benchmark modeling only and is not appropriate for all climate conditions.^[2]

A SEER of 13 is approximately equivalent to an EER of 11, and a COP of 3.2, which means that 3.2 units of heat are removed from indoors per unit of energy used to run the air conditioner.

The SEER and EER of an air conditioner are limited by the laws of thermodynamics. The refrigeration process with the maximum possible efficiency is the Carnot cycle. The COP of an air conditioner using the Carnot cycle is:

$\displaystyle COP_Carnot=\frac T_CT_H-T_C$

where $\displaystyle T_C$ is the indoor temperature and $\displaystyle T_H$ is the outdoor temperature. Both temperatures must be measured using a thermodynamic temperature scale based at absolute zero such as Kelvin or Rankine. The EER is calculated by multiplying the COP by 3.412 BTU/W⋅h as described above:

$\displaystyle EER_Carnot=3.412\frac T_CT_H-T_C$

Assuming an outdoor temperature of 95 °F (35 °C) and an indoor temperature of 80 °F (27 °C), the above equation gives (when temperatures are converted to the Kelvin or Rankine scales) a COP of 36, or an EER of 120. This is about 10 times more efficient than a typical home air conditioner available today.

The maximum EER decreases as the difference between the inside and outside air temperature increases, and vice versa. In a desert climate where the outdoor temperature is 120 °F (49 °C), the maximum COP drops to 13, or an EER of 46 (for an indoor temperature of 80 °F (27 °C)).

The maximum SEER can be calculated by averaging the maximum EER over the range of expected temperatures for the season.

This section contains instructions or advice. Wikipedia is not a guidebook; please help rewrite the content to make it more encyclopedic or move it to Wikiversity, Wikibooks, or Wikivoyage. (October 2011)

SEER rating reflects overall system efficiency on a seasonal basis and EER reflects the system's energy efficiency at one specific operating condition. Both ratings are useful when choosing products, but the same rating must be used for comparisons.

Substantial energy savings can be obtained from more efficient systems. For example, by upgrading from SEER 9 to SEER 13, the power consumption is reduced by 30% (equal to 1 − 9/13).

With existing units that are still functional and well-maintained, when the time value of money is considered, retaining existing units rather than proactively replacing them may be the most cost effective. However, the efficiency of air conditioners can degrade significantly over time.^[3]

But when either replacing equipment, or specifying new installations, a variety of SEERs are available. For most applications, the minimum or near-minimum SEER units are most cost effective, but the longer the cooling seasons, the higher the electricity costs, and the longer the purchasers will own the systems, the more that incrementally higher SEER units are justified. Residential split-system AC units of SEER 20 or more are now available. The higher SEER units typically have larger coils and multiple compressors, with some also having variable refrigerant flow and variable supply air flow.

In 1987 legislation taking effect in 1992 was passed requiring a minimum SEER rating of 10.^[4] It is rare to see systems rated below SEER 9 in the United States because aging, existing units are being replaced with new, higher efficiency units.

Beginning in January 2006 a minimum SEER 13 was required.^[5] The United States requires that residential systems manufactured after 2005 have a minimum SEER rating of 13. ENERGY STAR qualified Central Air Conditioners must have a SEER of at least 14.5. Window units are exempt from this law so their SEERs are still around 10.

In 2011 the US Department of Energy (DOE) revised energy conservation rules to impose elevated minimum standards and regional standards for residential HVAC systems.^[6] The regional approach recognizes the differences in cost-optimization resulting from regional climate differences. For example, there is little cost benefit in having a very high SEER air conditioning unit in Maine, a state in the northeast US.

Starting January 1, 2015, split-system central air conditioners installed in the Southeastern Region of the United States of America must be at least 14 SEER. The Southeastern Region includes Alabama, Arkansas, Delaware, Florida, Georgia, Hawaii, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, and Virginia. Similarly, split-system central air conditioners installed in the Southwestern Region must be a minimum 14 SEER and 12.2 EER beginning on January 1, 2015. The Southwestern Region consists of Arizona, California, Nevada, and New Mexico. Split-system central air conditioners installed in all other states outside the Southeastern and Southwestern regions must continue to be a minimum of 13 SEER, which is the current national requirement.^[6]

There have been many new advances in efficient technology over the past 10 years which have enabled manufacturers to increase their SEER ratings dramatically in order to stay above the required minimums set by the United States department of energy.^{[citation needed]}

Effective January 1, 2023, cooling products will be subject to regional minimum efficiencies, according to Seasonal Energy Efficiency Ratio 2 (SEER2). New M1 testing procedure^[7] is designed to better reflect current field conditions. DOE increases systems' external static pressure from current SEER (0.1 in. of water) to SEER2 (0.5 in. of water). These pressure conditions were devised to consider ducted systems that would be seen in the field. With this change, new nomenclature will be used to denote M1 ratings (including EER2 and HSPF2).^[8]

Electric power is usually measured in kilowatts (kW). Electric energy is usually measured in kilowatt-hours (kW·h). For example, if an electric load that draws 1.5 kW of electric power is operated for 8 hours, it uses 12 kW·h of electric energy. In the United States, a residential electric customer is charged based on the amount of electric energy used. On the customer bill, the electric utility states the amount of electric energy, in kilowatt-hours (kW·h), that the customer used since the last bill, and the cost of the energy per kilowatt-hour (kW·h).

Air-conditioner sizes are often given as "tons" of cooling, where 1 ton of cooling equals 12,000 BTU/h (3.5 kW). 1 ton of cooling equals the amount of power that needs to be applied continuously over a 24-hour period to melt 1 ton of ice.

The annual cost of electric energy consumed by an air conditioner may be calculated as follows:

(Cost, $/year) = (unit size, BTU/h) × (hours per year, h) × (energy cost, $/kW·h) ÷ (SEER, BTU/W·h) ÷ (1000, W/kW)

Example 1:

An air-conditioning unit rated at 72,000 BTU/h (21 kW) (6 tons), with a SEER rating of 10, operates 1000 hours per year at an electric energy cost of $0.12 per kilowatt-hour (kW·h). What is the annual cost of the electric energy it uses?

(72,000 BTU/h) × (1000 h/year) × ($0.12/kW·h) ÷ (10 BTU/W·h) ÷ (1000 W/kW) = $860/year

Example 2.

A residence near Chicago has an air conditioner with a cooling capacity of 4 tons and an SEER rating of 10. The unit is operated 120 days each year for 8 hours per day (960 hours per year), and the electric energy cost is $0.10 per kilowatt-hour. What is its annual cost of operation in terms of electric energy? First, we convert tons of cooling to BTU/h:

(4 tons) × (12,000 (BTU/h)/ton) = 48,000 BTU/h.

The annual cost of the electric energy is:

(48,000 BTU/h) × (960 h/year) × ($0.10/kW·h) ÷ (10 BTU/W·h) ÷ (1000 W/kW) = $460/year

Today there are mini-split (ductless) air conditioner units available with SEER ratings up to 42.^[10][11] During the 2014 AHR Expo, Mitsubishi unveiled a new mini-split ductless AC unit with a SEER rating of 30.5.^[12] GREE also released a 30.5 SEER rating mini split in 2015 as well.^[13] Carrier launched a 42 SEER ductless air conditioner during 2018 Consumer electronic Show (CES), held in Las Vegas.^[14] Traditional AC systems with ducts have maximum SEER ratings slightly below these levels. Also, practically, central systems will have an achieved energy efficiency ratio 10–20% lower than the nameplate rating due to the duct-related losses.

Additionally, there are ground-source residential AC units with SEER ratings up to 75.^[15] However, ground-source heat pump effective efficiency is reliant on the temperature of the ground or water source used. Hot climates have a much higher ground or surface water temperature than cold climates and therefore will not be able to achieve such efficiencies. Moreover, the ARI rating scheme for ground-source heat pumps allows them to largely ignore required pump power in their ratings, making the achievable SEER values often practically lower than the highest efficiency air-source equipment—particularly for air cooling. There are a variety of technologies that will allow SEER and EER ratings to increase further in the near future.^[16] Some of these technologies include rotary compressors, inverters, DC brushless motors, variable-speed drives, and integrated systems such as those found in solar-powered air conditioning.^[16]

A refrigeration cycle can be operated as a heat pump to move heat from outdoors into a warmer house. A heat pump with a higher SEER rating for cooling mode would also usually be more efficient in heating mode, rated using HSPF. When operated in heating mode, a heat pump is typically more efficient than an electrical resistance heater. This is because a space heater can convert only the input electrical energy directly to output heat energy, while a heat pump transfers heat from outdoors. In heating mode, the coefficient of performance is the ratio of heat provided to the energy used by the unit. An ideal resistance heater converting 100% of its input electricity to output heat would have COP = 1, equivalent to a 3.4 EER. The heat pump becomes less efficient as the outside temperature decreases, and its performance may become comparable to a resistance heater. For a heat pump with the minimum 13 SEER cooling efficiency, this is typically below −10 °F (−23 °C).^[17]

Lower temperatures may cause a heat pump to operate below the efficiency of a resistance heater, so conventional heat pumps often include heater coils or auxiliary heating from LP or natural gas to prevent low efficiency operation of the refrigeration cycle. "Cold climate" heat pumps are designed to optimize efficiency below 0 °F (−18 °C). As of 2023 heat pumps are marketed that will extract heat from outdoor temperatures as low as −40 °F (−40 °C). In the case of cold climates, water or ground-source heat pumps are often the most efficient solution. They use the relatively constant temperature of ground water or of water in a large buried loop to moderate the temperature differences in summer and winter and improve performance year round. The heat pump cycle is reversed in the summer to act as an air conditioner.

• Air conditioner
• Air conditioning
• Annual fuel use efficiency (AFUE)
• Coefficient of performance
• Energy star
• Heat pump
• HSPF
• HVAC
• Thermal efficiency

• A new measure for the energy efficiency of heating and cooling devices – Information from Daikin on seasonal efficiency
• Climate Impacts on Heating Seasonal Performance Factor (HSPF) and Seasonal Energy Efficiency Ratio (SEER) for Air Source Heat Pumps

Variable refrigerant flow (VRF), also known as variable refrigerant volume (VRV), is an HVAC technology invented by Daikin Industries, Ltd. in 1982.^[1] Similar to ductless mini-split systems, VRFs use refrigerant as the primary cooling and heating medium, and are usually less complex than conventional chiller-based systems. This refrigerant is conditioned by one or more condensing units (which may be outdoors or indoors, water or air cooled), and is circulated within the building to multiple indoor units. VRF systems, unlike conventional chiller-based systems, allow for varying degrees of cooling in more specific areas (because there are no large air handlers, only smaller indoor units), may supply hot water in a heat recovery configuration without affecting efficiency,^[2] and switch to heating mode (heat pump) during winter without additional equipment, all of which may allow for reduced energy consumption. Also, air handlers and large ducts are not used which can reduce the height above a dropped ceiling as well as structural impact as VRF uses smaller penetrations for refrigerant pipes instead of ducts.^[3]

VRFs are typically installed with an air conditioner inverter which adds a DC inverter to the compressor in order to support variable motor speed and thus variable refrigerant flow rather than simply perform on/off operation. By operating at varying speeds, VRF units work only at the needed rate allowing for substantial energy savings at load conditions. Heat recovery VRF technology allows individual indoor units to heat or cool as required, while the compressor load benefits from the internal heat recovery. Energy savings of up to 55% are predicted over comparable unitary equipment.^{[1] [4]} This also results in greater control of the building's interior temperature by the building's occupants. The lower start-up power of VRF's DC inverter compressors and their inherent DC power requirements also allow VRF solar-powered heat pumps to be run using DC-providing solar panels.

VRFs come in two system formats, two pipe and three pipe systems. In a heat pump two pipe system all of the zones must either be all in cooling or all in heating. Heat Recovery (HR) systems have the ability to simultaneously heat certain zones while cooling others; this is usually done through a three pipe design, with the exception of Mitsubishi, Carrier and LG whose systems are able to do this with a two pipe system using a branch circuit (BC) controller to the individual indoor evaporator zones. In this case the heat extracted from zones requiring cooling is put to use in the zones requiring heating. This is made possible because the heating unit is functioning as a condenser, providing sub-cooled liquid back into the line that is being used for cooling. While the heat recovery system has a greater initial cost, it allows for better zoned thermal control of a building and overall greater efficiencies.^[5] In heat recovery VRF systems, some of the indoor units may be in cooling mode while others are in heating mode, reducing energy consumption. If the coefficient of performance in cooling mode of a system is 3, and the coefficient of performance in heating mode is 4, then heat recovery performance can reach more than 7. While it is unlikely that this balance of cooling and heating demand will happen often throughout the year, energy efficiency can be greatly improved when the scenario occurs.^[6]

VRF systems may be air or water cooled. If air cooled, VRF condensing units are exposed to outside air and may be outdoors, and condensing units are the size of large refrigerators, since they need to contain a large condenser (heat exchanger) which has a large surface area to transfer heat to the surrounding air, because air doesn't have a high heat capacity^[7] and has a low density, volumetric thermal capacity and thermal conductivity thus needing to transfer heat into a large amount of air volume at once. If water cooled, the condensing units are placed indoors and are much smaller and cooled with water by a closed type or circuit cooling tower or dry cooler.

VRF systems have been used in Japan since the 1980s. By 2007, in Japan, VRFs are used in 50% of midsize office buildings (up to 70,000 ft² or 6,500 m²) and 33% of large commercial buildings (more than 70,000 ft² or 6,500 m²).^[5]

There are dedicated gateways that connect VRFs with home automation and building management systems (BMS) controllers for centralized control and monitoring. In addition, such gateway solutions are capable of providing remote control operation of all HVAC indoor units over the internet incorporating a simple and friendly user interface.^[8]

Japan:

• Daikin
• Panasonic
• Mitsubishi Heavy Industries
• Fujitsu (Fujitsu General)
• Hitachi (Now Johnson Controls-Hitachi (Air Conditioning) (Jci-Hitachi)
• Mitsubishi Electric
• Toshiba
• Yanmar (gas heat pumps)
• Sharp(former)
• Sanyo(now Panasonic)
• Toshiba Carrier(Former Air-conditioning & Heating International (AHI)(AHI-Carrier/Toshiba) (Toshiba-Carrier)^[9][10] (As of 2018, the joint venture(s) seem to have been broken up, as Carrier now manufactures VRF systems of its own and Toshiba's websites no longer show the Carrier logo in their product images (which is not the case in some of Carrier's images^[11][12]) and web pages, and the AHI-Carrier(Toshiba) website has not been updated since 2016)

Korea:

• LG
• Samsung

India:

• Blue Star Limited
• Voltas
• SB Cooling Corporation

Bangladesh:

• Walton Hi-Tech Industries Limited^[13]

Italy:

• Innova SRL

United States:

• Ephoca
• Innovair
• Carrier (Made by Toshiba)
• York International(Made by Hitachi)
• Trane (formerly made by Samsung, now made by Mitsubishi Electric)
• Lennox
• Afka Group (American Pro)
• CIAC(Carrier)

France:

• Airwell

China/Other:

• Acson
• Gree
• Tosot
• Haier
• Hisense
• Midea
• Bosch (^[14][15])^[16]

• Energy Conservation Standards for Variable Refrigerant Flow Multi-Split Air Conditioners and Heat Pumps
• VRF Systems Promise Savings in Targeted Building Types and Climates
• VRV vs VRF: Know the Differences Between Them
• Mobile Klimaanlagen / Multi-Split Air Conditioners (in German)