Air Conditioning Controller – AIRCOSAVER


The AIRCOSAVER is an electronic control system that can be used to retrofit air conditioning units of up to 20 tons per electric circuit or less to enable them to run more efficiently. It consists of a control module that reduces the run time of the compressor without affecting its air conditioning capabilities.

The system can achieve average energy savings of about 20%. Because air conditioning usually represents a fairly large portion of the electric bill, optimizing its throughput without compromising its cooling function just plainly makes sense. The AIRCOSAVER is a proven energy efficiency product which has been in use for over 10 years. It saves energy by eliminating the most wasteful portion of the cooling cycle operations in air conditioning units.

Laymen’s Terms

When switched on, typical air conditioning systems operate continuously until the room thermostat senses the desired temperature and turns the system off. As the room warms up, the thermostat switches the air conditioner back on and the cycle repeats. Air conditioning systems are usually dimensioned to cope with the extreme cooling demands of the few hottest days of the year, plus a safety margin. However, in most operational conditions, this maximum output is not required and the system is oversized. So running the system continuously until the room thermostat switches it off means that the system operates with excess capacity most of the time.

As a typical cooling cycle starts, the compressor pushes cooling energy into the heat exchanger which acts as an energy storage. At this stage, the system works with high efficiency because compressors operate most efficiently when fully loaded. In normal weather conditions, the energy storage is soon fully "charged up". From this point onwards, the compressor provides more cooling energy than the heat exchanger can take up. We refer to this as thermodynamic saturation. Running the compressor beyond this stage does not increase the cooling effect any more. It's just a waste of energy.

The way the AIRCOSAVER improves energy efficiency is by changing out the control system for a more efficient electronic one. The sensor-driven software in the electronic controller is designed to detect thermodynamic saturation and to optimize the compressor accordingly. When overcapacity is detected, the new control system switches the compressor off and avoids inefficient overcooling. In fact, the air conditioning unit switches into "saver mode". The fan keeps running and your system makes maximum use of the stored cooling energy in the heat exchanger. Once the stored energy is used up, the compressor can work efficiently again and is switched back on. That way, the set room temperature is reached without the inefficient portions of the cooling cycle. This results in significant energy savings without compromising cooling comfort.

Since the correct point to switch the compressor varies from unit to unit and changes with different weather conditions, the AIRCOSAVER is constantly monitoring the cooling status of your air conditioning unit and adapting its settings to ensure efficient operations at all times.

Now, the last consideration is that you do not want your air conditioning unit to start-up and stop more frequently as is goes from cooling cycle to cooling cycle. We call this protecting your unit against short cycling. Cycling the compressor too frequently in too short time intervals may harm the compressor and must be avoided. For this reason, the AIRCOSAVER features a built-in anti short cycling protection. Besides the continuous anti short cycling protection, the new electronic control system also adds a delay upon power-on to your unit. This valuable feature protects your air conditioner unit against damages from short power outages like they are common in many regions.

Making existing air conditioning systems more energy efficient is by far the quickest, most affordable and most effective way to reduce CO2 emissions and lower your energy bill. Expect an average of 20% savings on the electric load used by your air conditioning system.

Engineering Perspective


Air conditioning is one of the largest energy consumers in the residential, commercial and industrial sectors. Thousands of air conditioners put high demands on the electric grid. On a smaller scale, air conditioning probably accounts for a significant part of an energy bill.

Many existing air conditioners use old and quite inefficient technology. Although improved technology has become available in more expensive systems (e.g. inverter technology), the payback time of these systems is still very long and most of this technology is not suitable as an easy and economical aftermarket fit to existing systems.

In the light of today's energy problems, global warming and since older and not so advanced air conditioning systems will be in use for many more years in large numbers, we have analyzed various existing energy saving techniques for air conditioning systems and reviewed plenty of earlier research. The conclusion was that detecting the system's efficiency and switching the compressor accordingly is probably the only effective, pragmatic and economical measure to achieve a better energy efficiency.

Thermodynamic Model

An air conditioning system together with a room or facility can be modeled as a thermodynamic system. The system efficiency varies. During the cooling process with simple On/Off compressors (NOT Inverters) there are stages of higher efficiency and low efficiency. The three components that interact dynamically are the compressor or motor, the refrigerant cycle with evaporator and condenser, and the room of facility to be cooled. One has to understand that cooling a room is highly dynamic in thermodynamic terms and that energy transfer and efficiency changes dramatically over time.

Air conditioning systems are usually sized to handle peak load conditions and are most efficient when all potential cooling provided by the compressor can actually be transferred into the room air. This is very seldom the case because in most situations the room air can simply not take up all of this cooling energy. Electric energy is used to operate the fan and compressor to take ambient air and run it through a heat exchanger/evaporator system to transfer it in cooling energy and thereby produce a cold air supply. Because the aim is to save electric energy, we need to optimize the efficiency of the largest electrical consumer: the compressor. When it runs, the electrical power consumption of the compressor is almost constant and there are hardly any variations relating to actual heat load. In the first part of each cooling cycle, with the thermostat closed, the compressor manages to move a large quantity into the cooling cycle and into the room. The refrigerant cycle, including evaporator and condenser act as energy storage. In most situations the single-speed compressor can supply more cooling energy than the room air can take up. The energy storage slowly fills up. At one stage thermodynamic saturation is reached. The refrigerant cycle (storage) is fully charged and can only accept a small percentage of the available cooling potential.

The compressor efficiency worsens significantly at a certain stage during each cooling cycle. This stage can be detected by monitoring and analyzing the supply air behavior and extracting various parameters: Absolute and relative temperature levels over consecutive cycles, temperature behavior over time and several more. When thermodynamic saturation is sensed, the compressor is switched off. Stored energy is used up. When the compressor is switched on again later, it will operate at higher efficiency levels again. In doing so, the most inefficient stages of the cooling cycle are eliminated and overall system efficiency is improved. It is Important to note that anti short cycling measures are maintained and are implemented by AIRCOSAVER algorithms.

Depicted Operations

The following figure shows typical operating cycle of AC system controlled only by room or facility thermostat:

Graphic without aircosaver

The following figure shows typical operating cycle of AC system including AIRCOSAVER:

Graphic with aircosaver

Potential Tradeoffs

Installing an AIRCOSAVER can slightly alter the cooling characteristics of an Air conditioning system. With an AIRCOSAVER installed, inefficient overcooling is avoided. This is desired, since a lot of energy is wasted in this stage, but it may result in slightly higher average evaporator coil temperatures since the savings algorithm also provides an anti short cycling protection for the AC system.

In consequence, this may have two effects. Firstly, the set point may be reached slightly slower without the wasteful overcooling. However, overshoot of the set temperature is reduced as well. Cooling cycles become more gradual. This is often considered very beneficial in terms of cooling comfort by residents.

Secondly, the dehumidification capacity of the AC system may decrease slightly. In extremely wet climates this can potentially be a drawback. On the other hand, many customers have reported that the AIRCOSAVER has increased cooling comfort because a certain degree of humidity contributes to the subjective wellbeing in a room. There are various simple air conditioning units that by overcooling make the room air excessively dry.

In relation to the benefits, we consider these potential drawbacks as minor, for a wide range of applications. Numerous case studies and independent measurement have demonstrated that these changes, although measureable, have very little impact on the overall cooling performance.

What the AIRCOSAVER cannot achieve

The AIRCOSAVER cannot compensate for deficiencies in the original AC system. For example, if the AC system is poorly serviced and does not cool properly in the first place, then the AIRCOSAVER will not change this.

Secondly, if an air conditioning unit is clearly undersized for a given application, i.e. too small for the heat load and the compressor runs for very long periods, but the thermostat set temperature is never achieved, then the AIRCOSAVER will not remedy this.

In conclusion, we recommend checking two things before installing an AIRCOSAVER:

  • Only install an AIRCOSAVER on systems that are cooling properly in the first place. Make sure that the AC unit is in a decent service state (e.g. filters should be clean and not blocked). You could also measure the supply air temperature with a small thermometer prior to installation. If this does not fall significantly below 20 degrees Celsius, DO NOT install an AIRCOSAVER.
  • Check if the AC unit reaches the thermostat in normal operational conditions. If an AC unit is clearly undersized (i.e. the thermostat temperature is never reached and the compressor simply runs all day) then DO NOT install an AIRCOSAVER. In these instances there are physically no savings possible anyway and the AIRCOSAVER learning phase (until it has understood that the thermostat can never be reached) can result in higher room temperatures. So this situation should be excluded.



The AIRCOSAVER constantly adapts to the various cooling regimes to ensure the best possible savings at full cooling comfort. It can be installed on air conditioning systems of up to 10 tons capacity per electric circuit. Custom versions are also available for larger cooling systems. Separate versions of the AIRCOSAVER are available for all main power supplies, i.e. 230, 110 and 24 volts. These controllers have been designed for internal or external mounting and their housings are made of non-flammable, shock-proof polycarbonate that meets UL94-V0 Flammability Standards.


  1. Save an average of 20% of energy required to operate your air conditioning system.
  2. Optimize the compressor operations to ensure level of savings without compromising comfort.
  3. Significantly increase switching power and minimize in rush current.
  4. Improve anti short cycling protection and overall compressor protection.
  5. Protect your air conditioner against short and potentially damaging power outages.


Why Upgrade?

The AIRCOSAVER Upgrading Philosophy

Your satisfaction is our top priority. We would like to give you as much information as possible to enable you to make an informed choice. We would like to detail why installing an AIRCOSAVER makes sense and what can and cannot be achieved.

Air conditioning is a major consumer of electrical power

In many of the warmer countries around the world air conditioning is one of the largest energy consumers in the residential and industrial sector. On a small scale air conditioning accounts for a large part of home and business owners' energy bills. Millions of simple air conditioning units waste unbelievable amounts of energy every day. Not only is the absolute power demand for air conditioning very high, but air conditioning also contributes to extreme peak energy demand on the hottest days of the year which the energy infrastructure has to cope with.

Yesterday's air conditioning technology will be around for many years

Our advice to any owner of a low efficiency window unit or single split system is "Replace your entire old system today and buy a new ultra-high efficiency system. Make sure it is dimensioned properly, that it is HCFC free and that it uses the most advanced compressor and control technology!".

No matter how desirable this kind of change is, reality is different!

There are millions of older systems in use. In 2001 the Intergovernmental Panel on Climate Change (IPCC) estimated that worldwide a total of over 289 million window/wall mounted units and unducted single split systems were in use. In addition, an increasing number of these types of systems is installed every year. In 2001 only for the mentioned types of systems this number was estimated to be almost 38 million, many of them still being low and mid efficiency units. The most efficient new air conditioning systems are simply too expensive for many applications and payback time is still too long. Besides, many countries still have not adopted high-efficiency standards for new systems.

So these simple units will be operating on a large scale for many years to come. They will not just go away. Nor will they be replaced quickly. Average equipment lifetime is typically twelve to fifteen years and in many cases much longer. However, usually these units are not considered for retrofits. Controller manufacturers usually prefer to focus on very large system where even small improvements can be sold for high prices.

Solution: Bridging the gap with a cost effective retrofit

We think that retrofitting these smaller units makes a lot of sense in terms of overall reduced energy usage and reduced operating costs. Retrofitting with the AIRCOSAVER can bridge the gap and lower energy consumption considerably until new high efficiency system become more widespread. The AIRCOSAVER has been designed as an affordable and practical device with short payback times.

Savings mechanism of the AIRCOSAVER

Through research and development, the designers built a controller specifically for retrofit purposes. They became deeply persuaded that the most effective and practical method to create significant savings with the smallest tradeoffs in cooling comfort was to determine the AC system's current thermodynamic efficiency and switch the compressor off, when it is evidently inefficient. This is logical since the compressor typically accounts for 80% of the system's energy consumption. This, in combination with protecting the compressor against potentially harmful short cycling led to the AIRCOSAVER. Out of all retrofit solutions and out of all proposed cycling methods, we believe this is the most effective, with the smallest costs in cooling comfort.

Limitations of any retrofit

No retrofit will do miracles. With a given system there is always a limit to the possible improvements in energy efficiency. A number of factors are fixed such as the type and efficiency of the refrigerant in the system. Other factors can be optimized such as the runtime of the compressor. A retrofit will not remedy major planning mistakes or technical faults in an air conditioning system.

Instead of investing a lot of money into an expensive new air conditioning system, there is an easy and affordable way to improve the energy efficiency of your existing unit. Call 1-800-701-2963 to have our certified electricians install an AIRCOSAVER for your home, business or industrial facility.

Listings and Certifications

AIRCOSAVER air conditioning controllers meet UL and CSA standards, and CE certified requirements.

Tests & Approvals

Declaration of conformity

The Aircosaver conforms to the following standards:

  • EN55011: 1998
  • EN50082-1: 1997
  • EN61000-4
  • EN60669

and the provisions of the EMC and Low Voltage Directives:

  • 89/336/EEC (Electromagnetic Compatibility Directive)
  • 2004/108/EG amended by 91/263/EEC, 92/31/EEC, 93/68/EEC, 93/97/EEC
  • 73/23/EG Low Voltage Equipment Directive

EN / IEC Testing

EN 61000-4-4 (Burst): Prüfung der Störfestigkeit gegen schnelle transiente elektrische Störgrößen (Equivalent to IEC 61000-4-4: Electrical fast transient/burst immunity test)

EN61000-4-2 (ESD): Prüfung der Störfestigkeit gegen Entladung statischer Elektrizität (Equivalent to IEC 61000-4-2: Electrostatic discharge immunity test)

EN61000-4-11 (Dips): Prüfung der Störfestigkeit gegen Spannungseinbrüche und Kurzzeitunterbrechungen (Equivalent to IEC 61000-4-11: Voltage dips, short interruptions and voltage variations immunity tests)

EN61000-4-5 (1Surge) Prüfung der Störfestigkeit gegen Stoßspannungen (Equivalent to IEC 61000-4-5: Surge immunity test)

UL Conformity

The product has been tested on Electromagnetic Compatibility according to EMC requirements:

  • EN50082-1 (97) – Immunity partly – Radiated and Conducted Immunity
  • EN55011 cl. B (98) Emission


Frequently Asked Questions (FAQs)

1 - What is the Aircosaver?

The Aircosaver is an after-market retrofit electronic micro processor that adds state-of-the art intelligence to existing air conditioning systems to improve their efficiency and reduce operating costs by 15% to 25%.

2 - What types of air conditioning systems does the Aircosaver work on?

The Aircosaver can be installed and will reduce energy costs on Package Units, Single Split Systems, Ptacs, Wall Units, and Window Units up to 10 tons capacity per circuit. The Aircosaver does not work on chiller systems, evaporative cooling systems or variable speed compressors type systems.

3 - How does the Aircosaver work?

The Aircosaver uses sensor-driven software algorithms to detect thermodynamic saturation and optimize compressor run times. When the Aircosaver detects that a system has reached thermodynamic saturation (i.e., “overcapacity”), it switches the compressor off and, thereby, avoids inefficient overcooling. While the system is in this “saver mode,” the fan keeps running so that the system makes maximum use of the stored cooling energy in the heat exchanger. Once the stored energy is used up, the Aircosaver switches the compressor back on so that it can work efficiently again.

4 - What is thermodynamic saturation?

Thermodynamic saturation is the point at which the maximum amount of cooling energy is stored in the evaporator. Running the compressor past this point is inefficient since additional cooling energy cannot be stored and is thereby wasted.

5 - How does the Aircosaver detect thermodynamic saturation?

The Aircosaver’s sensor is installed on the evaporator. The unit determines thermodynamic saturation by sensing stable evaporator temperature.

6 - Isn’t the Aircosaver function similar to a factory-installed “economizer” cycle?

The term “economizer” can have several meanings, the most common of which is when an A/C is fitted with an outside air damper. The “economizer” turns the compressor off and pulls air from the outside when the temperature and relative humidity are at specified levels. Economizers are factory-installed and are worth the money if you need A/C year round due to the generation of inside heat. On the other hand, economizers are generally used at times when outside air temperature is low enough to use for cooling, a situation that is less and less prevalent the further south you are.

7 - Won’t shortening the compressor run time have a negative effect on humidity level?

There are many factors that contribute to lowering humidity. Oversized units typically do a bad job of lowering humidity. These units are the Aircosaver targets. When installed on such units, the Aircosaver can actually do a better job of lowering humidity, but most of the time, it is about the same. Remember, when the Aircosaver turns the compressor off, the evaporator is still cold and the blower is still running and condensing water from the air. In addition, the Aircosaver V4.1 has specific algorithms to prevent humidity from being compromised.

8 - Won’t shortening compressor run time increase the time it takes to reach the set point?

Yes, but only slightly. For example, if a system takes an hour to reach the set point without the Aircosaver installed, it might take about an hour and five minutes (i.e.+-, 5% longer) to reach the set point with the Aircosaver installed. However, the tradeoff is significant since the compressor and condenser fan account for about 90% of the cost of system operation with the blower accounting for the other 10%. For the additional 5% in time that it takes the system to reach the set point, the compressor and condenser will be off about 25% of the total time.

9 - Does the Aircosaver come with a warranty?

The manufacturer guarantees the Aircosaver to be free of defects in material and workmanship for at least two years from the date of purchase.

10 - How does the Aircosaver affect system life?

The Aircosaver can actually increase system life by reducing equipment operating temperature and preventing evaporator freeze over by properly cycling the compressor. The increased inrush of current due to additional compressor starts is minimal when compared to the savings from compressor off time. Moreover, the additional compressor starts/stops are offset by the lowering of the compressor and condenser operating temperatures (i.e., the #1 “killer” of motors is heat) and the fact that these additional starts are not “cold dead” starts.

11 - How is the Aircosaver affected by inside demand and outside weather conditions?

There is no affect on the Aircosaver due to changes in inside demand conditions or outside weather conditions since the Aircosaver automatically and continually adapts to changes in these parameters.

12 - Could the Aircosaver function be replicated with an “approach set point.”

Many manufacturers incorporate various aspects of the Aircosaver technology in newer systems. The “approach set point” is one of these concepts. However, most A/C systems made before 2008 will not have these technologies. These systems are the Aircosaver target market. Typically, A/C manufacturers will not endorse the Aircosaver because they are adding these technologies to their newer units. The bottom line is that they would rather sell you a new unit that saves 20% to 30% over the old unit instead of having you pay a fraction of the cost of that new unit to achieve the same savings.

13 - Will the Aircosaver cause system short-cycling?

The Aircosaver has anti-short-cycling protection built into its algorithms and actually provides protection for the A/C system to eliminate short-cycling problems. The Aircosaver provides for mandatory compressor off-time after it has reached thermal saturation / set point or with any power loss. Compressor manufacturers rate compressors to cycle no more than 10 times per hour. The Aircosaver will never allow the compressor to cycle more than 5 times per hour.

According to Copeland, who manufactures more compressors than anyone, a compressor has a 20 year life span. During this lifetime, it is not as critical how many times it starts and stops in 24 hours but rather how long it is OFF before it has to re-start. The more extreme the conditions are, the hotter the compressor will be along with high head pressure. The longer it is off, the more the pressure dissipates and cools down, making it less stressful to re-start.

14 - How long does it take to install the Aircosaver?

A trained HVAC technician can typically install the Aircosaver in 20 to 45 minutes.

15 - What are typical return-on-investment periods for the Aircosaver?

Typical ROI's for the Aircosaver range from 6 months to 2 years. The more you have to pay for KWh the shorter your ROI.

16 - What are the purchase options for the Aircosaver?

The Aircosaver can be purchased outright or through a lease-to-own option.

17 - What certifications and approvals apply to the Aircosaver?

The Aircosaver is UL and CE compliant. The Aircosaver is approved and listed as a qualified device for energy rebates from California (San Diego Gas & Electric, Pacific) to Canada,(OPA) to Mexico,(FIDE) with many other looking to come on board.

18 - Will installing the Aircosaver void my warranty

Officially it falls under the Magnasum-Moss Act passed by congress that states manufacturers cannot void warranties on their equipment when aftermarket product are added, provided they are approved by the governing body that approves such products. If it is electrical, it must be approved by UL or ETL, which the Aircosaver is. I personally never liked saying “the government says we can do it”, so here is the analogy I always use. A standard thermostat turns an A.C. on and off based on reaching the desired set point.

A Programmable thermostat does the same thing PLUS allows you to set a time table for on and off operation, in addition to, and/or regardless of, reaching the desired set point. The Aircosaver works much the same way as a programmable thermostat but is based on the time it takes to fill the evaporator with refrigerant. These timed amounts will vary based on the hotter it is, the longer it takes to fill up and get as cold as possible. The Aircosaver only intercepts the 24 volt signal from the thermostat to compressor and does not interfere with cooling ability, or modify the mechanics of the system in any way. When the evaporator is full, the Aircosaver shuts down the compressor and allows the fan to continue to pull cold air into the plenum that feeds the ductwork. If set point is still not reached during this time, the Aircosaver releases the compressor based on readings from the temperature sensor.