Air Conditioner Costs
Air Conditioning Operating Cost Guide InspectAPedia® -
This website answers most questions about air conditioning systems:
How do we calculate the seasonal cost to operate an air conditioner?
How do we calculate the air conditioning cost per hour? What are Watt hours? What's a Kilowatt?
Questions & Answers about the Operating Cost & Energy Consumption of Air Conditioners & Heat Pumps
This article explains how to calculate the actual cost of operating an air conditioning
system in easy to understand language.
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Separately at SEER RATINGS & OTHER DEFINITIONS we discuss operating cost efficiency ratings or SEER and EER ratings for air conditioners and heat pumps.This website answers most questions about air conditioning systems.
We continue to add to and update this text as new details are provided. Contact us to suggest text changes and additions and, if you wish, to receive online listing and credit for that contribution.
At SEER RATINGS & OTHER DEFINITIONS we explained SEER ratings that measure air conditioning
system efficiency, and we explained how we can determine how much energy an air conditioner
uses either by the hour of by the season of use. At the end of that section we knew how much
energy our air conditioner used, either on an hourly basis or for use during the whole
cooling season. We were able to express the total air conditioning energy
used in BTUs or in Kilowatts per hour or per season. Here we complete
the process of translating air conditioner use into actual dollar costs.
How Much Will It Cost Per Year to Run An Air Conditioner?
In the United States for December 2007 the average retail price of electricity
paid by residential consumers ranged from about $0.063 per kWh (Idaho) to $0.287 per kWh (Hawaii).
Your electrical bill will indicate the current charge per kilowatt hour
kWh of electricity you use.
How to use the air conditioning cost formula:
Plug in your actual Air Conditioner's Wh: Where we used 500,
plug into the equation below the actual Watt Hours Wh your air conditioner uses,
by following the procedure at SEER RATINGS & OTHER DEFINITIONS.
Plug in your electric bill kWh rate:
Just plug in to the equation example below the cost per kWh of electricity from
your electric bill where we've used $0.25.
Multiply these two numbers. Just below, we use an example of $0.25 or 25 cents per kWh cost from an electric utility company. [Electrical costs provided by the U.S. Department of
Energy at eia.doe.gov/cneaf/electricity/epm/table5_6_a.html]
500 kWh used per season x $0.25 = $125.00 - that's your electricity cost
to run the air conditioner for a season.
How Much Does It Cost Per Hour to Run An Air Conditioning System
This is an even simpler calculation. Using as an example information from our example air conditioner's
data tag,
((5000 BTUh) / (10 SEER)) = 500 Wh
500 Wh x $0.25 = $0.12 per hour to run our air conditioner.
Other Equations Using SEER Ratings
We can also write the SEER equation shown above as:
SEER = BTUs / Watt-hours
where "watt-hours" = (number of hours of system operation) x (watts used per hour)
Answer: List of Air Conditioning & Heat Pump System Steps or Installation Details that Save on Operating Cost
According to SoCalEdison's "Comprehensive Packaged Air Conditioning Systems", Residential and
commercial air
conditioning is
responsible for the
largest share of peak
demand in California,
contributing
approximately 33% of
peak demand. [3][4]
Saving money on central or even portable air conditioners and heat pumps starts by buying equipment with a high SEER (Seasonal Energy Efficiency Ratio (SEER)) rating. But as SoCalEd points out [4], the purchase of high efficiency (high SEER) HVAC equipment captures only a small part of the total savings in air conditioning or heat pump costs that could be saved by other installation and maintenance steps that we outline here [quoted, paraphrased, and expanded from [4]]:
Proper Sizing of the Air Conditioner. Supporting proper
sizing in residential and
commercial units can yield
savings. Contractors frequently
install oversized systems to avoid
potential comfort and call back
risks. See COOLING CAPACITY, RATED, and also, because an oversized air conditioner is likely to fail to adequately dehumidify building air, also see A/C Not Dehumidifying.
[Air Conditioner & Heat Pump] Refrigerant Charge and [compressor/condenser] Airflow. Between half and three-quarters of all packaged air
conditioning units suffer from incorrect charge and low airflow. For both new and
existing equipment, ensuring the proper refrigerant charge and airflow can increase
efficiency. [5] See REFRIGERANTS and see REFRIGERANT LEAK DETECTION where we describe types of A/C refrigeration system leaks, where they occur, and how they damage the system. Also see REFRIGERANT LEAK REPAIR. [We {DF] speculate that this problem may be more severe for residential air conditioners and heat pumps than for those commercial units whose design includes a refrigerant receiver.]
[HVAC Air] Duct Sealing. Ensuring tight ducts in residential and commercial installations yields 10-
18% energy savings.6 The peak load reduction can be higher, yielding a demand savings
of 25%.[4 and citations therein]
In our [DF] OPINION in addition to sealing duct leaks, better attention to balancing the quantity of return air available to the air handler with the supply duct and register system is needed at many buildings. See INCREASING RETURN AIR
In our [DF] OPINION, the most basic homeowner maintenance task that can reduce air conditioning and heat pump operating tasks is to be sure that air filters are in place, properly selected, sized, installed, not leaky, and that the filters are changed on a regular schedule. See Dirty Air Filter Problems and see AIR FILTERS for HVAC SYSTEMS for details. Also see our suggestions at AIR FILTERING STRATEGIES.
HVAC Economizers. Research shows that the majority of [HVAC] economizers do not function as
intended. Use of the Whole Building Diagnostician tool in new and existing buildings in
California has confirmed that problems with outside air economizers are endemic. The
potential savings from fixing a malfunctioning economizer are approximately 10 – 15%
of total packaged air conditioning load. In addition, enabling damper function is a prerequisite
for further savings from demand controlled ventilation. [4 and accompanying citation]
Definition of Economizer for HVAC systems: economizers are devices designed to reduce the operating cost (and energy used) in mechanical systems, principally by re-using heat (or cooling) already produced within the system. Examples of economizer designs in HVAC systems include details that may be found both at the ductwork / air handling system (this is the common use of "economizers on HVAC systems) and also right inside of the compressor/condenser unit (a technical use of HVAC economizer heat exchange theory):
Air-to-air heat exchangers that heat incoming fresh air (makeup air) being introduced into the duct system during the heating season by using the heat from combustion exhaust or other sources.
Refrigerant tubing co-soldering of the high pressure (high temperature or "high side") refrigerant piping alongside of low pressure (low temperature or "low side") tubing at certain locations in the air conditioning or heat pump system to improve system efficiency.
We explain this A/C or heat pump refrigerant line soldering/brazing detail at REFRIGERANT PIPING & DISTANCES - at the subtopic: Technical Note on Refrigerant Piping: HVAC economizer detail
HVAC Controls. Appropriate controls which enable variable heating and cooling conditions
based on occupancy are also critical. With a comprehensive program to address all of
these opportunities, the savings per packaged air conditioning unit easily approach 20
percent.[4]
Critique, contributions wanted: Contact Us to suggest corrections or additions to articles at this website, and if you wish, to receive online listing and credit as a contributor. Particular thanks are due to the many experts and also consumers who read and critique technical articles at InspectAPedia.com.
Additional technical contributors & reference sources for this article are listed below.
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[1] U.S. Government EnergyStar Program, ENERGY STAR Program Requirements for ASHPs and Central Air Conditioners – FINAL DRAFT, found at http://www.energystar.gov/ia/partners/prod_development/revisions
/downloads/ac_ashp/Final_Draft_CAC_ASHP_Eligibility_Criteria.pdf
Air-Conditioning and Refrigeration Institute. Standard 210/240 “2003 Standard for Unitary Air-Conditioning and Air-Source Heat Pump Equipment.”
[2] SoCalEdison Comments for ASHP/CAC Options Paper, Web search 07/22/2011 - SoCalEdison.pdf, note that by its name this article contains comments by a representative from SoCalEdison in response to a request for input to help EnergyStar develop an HVAC standard for 2006, but neither addressee nor writer are fully identified. SoCalEdison is an acronym for Southern California Edison, an Edison International Company and one of the largest electric utilities in the United States. According to SoCalEdison, "Residential and commercial air conditioning is responsible for the largest share of peak [electrical energy] demand in California,contributing approximately 33% of peak demand." [citation:
http://asset.sce.com/Regulatory/Energy%20Efficiency%
20Filings/SCE2507COMPREHENSIVEHVAC.pdf ] - also see the Kema -Xenergy energy use citation just below.
[3]Kema -Xenergy, “California Statewide Residential Sector Energy Efficiency Potential Study,” April 2003,
and Kema-Xenergy, “California Commercial Sector Energy Efficiency Potential Study,” July 2002. Base
information is factored by 0.367 to get SCE portion of savings.
[4]Comprehensive Packaged Air Conditioning Systems, SoCalEdison, web search 7/23/2011, original source: http://asset.sce.com/Regulatory/Energy%20Efficiency%20Filings
/SCE2507COMPREHENSIVEHVAC.pdf
[5] Chris Neme, National Energy Savings Potential from Addressing HVAC Installation Problems, prepared
for US Environmental Protection Agency, March 1998
Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair
Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 2010, $69.00 U.S., is available from Carson Dunlop. The Home Reference Book is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. InspectAPedia.com ® author/editor Daniel Friedman is a contributing author. Field inspection worksheets are included at the back of the volume.
"Air Conditioning & Refrigeration I & II", BOCES Education, Warren Hilliard (instructor), Poughkeepsie, New York, May - July 1982, [classroom notes from air conditioning and refrigeration maintenance and repair course attended by the website author]
Carson Dunlop, Associates, Toronto, have provided us with (and we recommend)
Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment ($69.00 U.S.).
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