Top Ten Things Consumers Should Know About Air ...

HOW AN AIR CONDITIONER WORKS

The job of your home air conditioner is move heat from inside your home to the outside, thereby cooling you and your home. Air conditioners blow cool air into your home by pulling the heat out of that air. The air is cooled by blowing it over a set of cold pipes called an evaporator coil. This works just like the cooling that happens when water evaporates from your skin. The evaporator coil is filled with a special liquid called a refrigerant, which changes from a liquid to a gas as it absorbs heat from the air. The refrigerant is pumped outside the house to another coil where it gives up its heat and changes back into a liquid. This outside coil is called the condenser because the refrigerant is condensing from a gas back to a fluid just like moisture on a cold window. A pump, called a compressor, is used to move the refrigerant between the two coils and to change the pressure of the refrigerant so that all the refrigerant evaporates or condenses in the appropriate coils.

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The energy to do all of this is used by the motor that runs the compressor. The entire system will normally give about three times the cooling energy that the compressor uses. This odd fact happens because the changing of refrigerant from a liquid to a gas and back again lets the system move much more energy than the compressor uses.

WHAT A 'TON' OF COOLING IS

Before refrigeration air conditioning was invented, cooling was done by saving big blocks of ice. When cooling machines started to get used, they rated their capacity by the equivalent amount of ice melted in a day, which is where the term &#;ton&#; came from sizing air conditioning.

A ton of cooling is now defined as delivering 12,000 BTU/hour of cooling. BTU is short for British Thermal Unit (and is a unit that the British do not use) The BTU is a unit of heating - or in this case, cooling - energy. It&#;s more important, however, to keep in perspective that a window air conditioner is usually less than one ton. A small home central air conditioner would be about two tons and a large one about five tons.

WHAT GOES WRONG

Unlike most furnaces, air conditioners are complex mechanical systems that depend on a wide variety of conditions to work correctly. They are sized to meet a certain &#;load&#; on the house. They are designed to have certain amount of refrigerant, known as the &#;charge&#;. They are designed to have a certain amount of air flow across the coils. When any of these things changes, the system will have problems.

If you produce more heat indoors either from having more people or appliances or because of changes in the house, the air conditioning may not be able to keep up.

If the refrigerant charge on the system leaks out, it lowers the capacity of the system. You will simply get less cooling and system will not be able to keep up when the load gets high.

If airflow across the outdoor (condenser) coil is reduced, the ability to reject heat outdoors is reduced and the again the capacity of the system may go down, especially at higher outdoor temperatures.<

In dry climates such as the Southwest United States, the same issues happen with regard to the indoor (evaporator) coil: higher airflow helps, lower airflow hurts. In humid climates, the situation is more complex. At higher airflows, there will be less dehumidification, leading to high indoor humidities. If the airflow gets too low, however, the evaporator coil may freeze. This makes performance worse and can damage the compressor until it fails - leaving you with an expensive repair bill and no cooling!

WHAT THOSE FILTERS DO

Almost every air conditioning system has a filter upstream of the evaporator coil. This can be in the return grille or in special slots in the duct system and can be a fuzzy-looking or a folded paper filter. This filter removes particles from the air stream to both keep the air conditioning system clean and to remove particles from the air.

As the filter does its job, it gets loaded with more and more particles. This actually has the effect of making it more efficient, but it also increases resistance and reducing airflow. When this happens, it is time to change the filter. How long it will take to happen depends on how dirty the air is and how big the filter is.

If you don&#;t change the filter, the air flow will go down, and the system will not perform well. Not only that, but if the filter is too dirty, it starts to become a source or air pollution itself.

If you take the filter out completely, you would solve the low air flow problem, but this victory would be short lived. The particles that the filter would have taken out will now build up on your evaporator coil and eventually cause it to fail. A new filter is a lot cheaper.

When you do buy a new filter, ASHRAE recommends getting one with a Minimum Efficiency Rating Value of MERV 6 or higher.

MAINTAIN THE SYSTEM

Routine maintenance such as changing filters can be handled by most consumers, but others require professional service.

It&#;s a good idea to brush dirt and obstructions from the coils and the drains at the start of each cooling season. Depending on the system and the consumer, this may require a service call from a professional.

If the system is not producing as much cold air as is normal, it could also be an indication of a refrigerant charge or airflow problems. These problems may require servicing.

DUCTS MATTER - A LOT

Another reason systems may appear not to be producing enough cold air is because of duct leakage. Duct leakage can sap 20 to 40% of the energy out of even a well-operating air conditioner, if the ducts pass outside the cooled space (this includes attics, crawlspaces and garages). Ducts outside need to be well insulated. Various products exist specifically for insulating ducts that can be installed by a keen home owner or a professional contractor.

You might be able to get an extra half ton of air conditioner capacity for free, if you seal your leaky ducts. If the ducts are accessible, handy consumers can seal ducts with mastic&#;that white sticky stuff you can paint on the ducts. Otherwise you would need a professional to seal the ducts.

HOW TO INCREASE ENERGY EFFICIENCY

Sealing leaky ducts may be the biggest single thing you can do to improve efficiency, but a lot of the issues mentioned above will help as well: replace dirty filters, keep the right charge and airflow, clean the coils.

Another thing to do is to make sure the outdoor (condenser) unit is not so hidden from sight that its air flow is blocked or that leaves or other matter are not clogging it.

If you are replacing the air conditioner, look to buy high efficiency equipment. The most generally known efficiency rating is Seasonal Energy Efficiency Rating (SEER). SEER 13 is the minimum efficiency you should consider, but higher efficiencies are likely to be quite cost effective.

Depending on your climate, you may wish to consider other efficiency numbers as well. For example, in hot, dry climates you should look at the Energy Efficiency Rating (EER) which says how well the system will work at peak conditions. If you live in a hot, humid climate you need to consider how well the unit can dehumidify.<

LIGHTEN YOUR LOAD

You can make your air conditioner work better by reducing the size of the job it has to do. You can do this by improving the building or reducing the internally generated loads that your air conditioner must deal with.

Improving the building &#;envelope&#; includes things such increasing insulation levels or shading windows or reducing air leakage. Such improvements will reduce energy spent on heating and cooling, but may require substantial time or investment. When putting in a new roof or new windows, it is usually cost effective to use high-efficiency products. &#;Cool&#; roofing, for example, can save half a ton of cooling and a lot of energy over the year.

Reducing internal loads can be simpler. Shut off unneeded electrical appliances, lights and equipment. Shift appliance use (such as washers and dryers) to cooler times of the day. Use local exhaust fans to remove heat and humidity from kitchens and baths. Buying Energy Star or similarly efficiency appliances helps as well.

In some climates other techniques can be used to reduce the load on the air conditioner. In dry climates evaporative air conditions (the modern version of what used to be called &#;swamp coolers&#;) can provide substantial cooling. In climates with large temperature swings, such as the hot, dry climates, you can reduce the load by bringing in large amounts of cool outdoor air. Such systems can be called &#;night cooling&#; &#;ventilative cooling&#; or &#;residential economizers&#;.

VENTILATE

The previous points have focused on cooling, but the original definition of air conditioning contains more than that; an ideal air conditioner should heat, cool, clean, ventilate, humidify and dehumidify as needed to provide health and comfort. In fact the second most important objective of the original definition is to provide ventilation. Whether or not the piece of equipment we call an air conditioner provides it, ventilation is needed.

Without adequate ventilation, contaminants generated indoors will can lead to significant health and comfort problems. ASHRAE recommends that there be at least enough ventilation to exchange the air inside house once every four hours, depending on house design.
Older homes tend to have leakier walls and leakier ducts and mostly get sufficient ventilation through such leakage. Such leakage and infiltration may not be the most energy efficient approach to ventilation and is an opportunity for savings.

Most new homes and some existing homes are relatively tight and thus require mechanical ventilation to meet minimum ventilation requirements.

IT'S NOT THE HEAT, IT'S THE HUMIDITY

Humidity control was the problem that originally spurred the need for air conditioning. Lack of humidity control in hot, humid climates, in particular, can lead to mold growth and other moisture-related problems. High indoor humidities can lead to health and comfort problems.

Modern air conditioners dehumidify as they cool; you can see that by the water that drains away, but this dehumidification is incidental to their main job of controlling temperature. They cannot independently control both temperature and humidity.

In hot, humid climates the incidental dehumidification that occurs may not always be enough to keep the indoor humidity conditions acceptable. (ASHRAE recommends roughly a 60% relative humidity maximum at 78F.) The maximum dehumidification happens not at the hot times of the year&#;when the air conditioner is running a lot&#;but at mild times of the year when the air conditioner runs very little.

Although there are some leading edge air conditioning systems that promise to independently control humidity, conventional systems may not be able to sufficiently control the problem and can cause comfort or mold problems in certain situations. Some current high-end systems have enhanced dehumidification, but when the existing system cannot sufficiently dehumidify, it may be necessary to buy a stand-alone dehumidifier.

There are things that consumers can do to lessen the need for dehumidification:

Do not set your thermostat to the &#;fan on&#; position. In this position the fan blows air all the time whether your cooling system is running or not and one key impact is that a lot of the moisture your system just took out of the air, will be blown back into the house before it can drain way.

Use exhaust fans during moisture-producing activities. Cooking, bathing, washing, and similar activities produce a lot of moisture inside the home. Exhaust that moisture directly outdoors using a fan. Similarly, avoid drying clothes indoors except with a clothes dryer that is exhausted directly outdoors.

Do not open windows or use ventilative cooling when it is too humid outside.

10 Points to Help Consumers

These 10 points will help consumers more aware of their air-conditioning systems and better able to care for them and use them well. Should it become necessary to replace that system seek out a qualified HVAC professional, preferably, of course, a member of ASHRAE.

ASHRAE is the world&#;s foremost technical society in the fields of heating, ventilation, air conditioning and refrigeration. The Society helps keep indoor environments comfortable and productive, deliver healthy food to consumers and preserve the outdoor environment. ASHRAE&#;s technical foundation is built by some 50,000 volunteer members, including consulting engineers, contractors, manufacturers, manufacturing representatives/sales, and architects.

References:
Nagengast, B., , 'Early Twentieth Century Air-Conditioning Engineering', ASHRAE Journal, March (p.55)
ANSI/ASHRAE Standard 55, Thermal Environmental Conditions for Human Occupancy
ANSI/ASHRAE Standard 62.2, Ventilation and Acceptable Indoor Air Quality in Low-Rise Residential Buildings

1.1    Scope

Air-cooled condensing units covers products that are specifically designed to provide cooling to other equipment and systems that incorporate evaporators (and associated expansion valve control systems). Air-cooled condensing units are factory-assembled units that consist of an air-cooled condenser, one or more compressors, and interconnecing pipe work. They may include liquid receivers, filter driers, oil separators, shut off valves and related controls, and a weatherproof housing. 

1.2    Definitions

An air-cooled condensing unit is a factory-assembled, packaged unit that consists of a refrigeration compressor, an air-cooled condenser and various ancillary components. This packaged unit does not contain a complete refrigeration system, but is designed to provide a convenient method for cooling a cold room or other equipment fitted with an evaporator that is controlled by an expansion valve.  

Air-cooled condensing units are used in a variety of commercial and industrial cooling applications, including cold rooms, refrigerated display cabinets, back-bar equipment, temperature controlled food preparation areas, and for air conditioning systems.  

Air-cooled condensing units are available in a range of different designs and efficiencies. The Energy Technology List (ETL) Scheme aims to encourage the purchase of the higher efficiency products.  

If you are looking for more details, kindly visit air cooled condensing units manufacturer.

The ETL Scheme covers products in three temperature categories:  

• High temperature units.
• Medium temperature units.
• Low temperature units.  

These categories are defined in terms of the product performance at a particular temperature rating point. Products may be submitted under more than one category.  

To be eligible for inclusion on the ETL, products shall meet the requirements as set out below.

1.3    Requirements 

1.3.1    Eligibility requirements

To be eligible, products shall:  

• Be designed to operate with one or more clearly identified standard refrigerants.
• Be a factory assembled unit that incorporates at least the following components:  

a)    Air-cooled refrigerant condenser.  
b)    One or more electrically driven refrigeration compressors. 
c)    A control system that controls the product&#;s compressor(s) and cooling fan(s). 

• Conform to the requirements of The Pressure Equipment (Safety) Regulations in respect of their design, manufacture and testing procedures.

1.3.2    Performance requirements

Products shall have a coefficient of performance (COP) or Seasonal Energy Performance Ratio (SEPR) that is greater than or equal to the values shown in Table 1.1, according to the rated cooling capacity of the product.

Table 1.1    Performance thresholds for air-cooled condensing units 

    Evaporating temperature (Dew point) Rated cooling capacity, PA (kW) Performance parameter Threshold Operating temperature HT +5°C n/a COP &#; 3.4 MT -10°C 0 < PA &#; 5 COP &#; 2.0 5 < PA &#; 20 SEPR &#; 3.30 20 < PA &#; 50 SEPR &#; 3.30 PA > 50 COP &#; 2.0 LT -35°C 0 < PA &#; 2 COP &#; 1.1 2 < PA &#; 8 SEPR &#; 1.70 8 < PA &#; 20 SEPR &#; 1.80 PA > 20 COP &#; 1.1

'&#;' means 'greater than or equal to'
'&#;' means 'greater than or equal to'

The COP, where applicable, should be measured at the specified standard rating points shown in Table 1.2.

Table 1.2    Testing conditions for COP of air-cooled condensing units at the standard rating points

Temperature category Evaporating temperature (Dew point) Ambient (Condenser air-on) temperature Compressor suction gas temperature High temperature units +5°C 32°C 20°C Medium temperature units -10°C 32°C 20°C Low temperature units -35°C 32°C 20°C

 

Where: 

• COP = refrigerating capacity divided by the power absorbed. 
• SEPR = reference annual cooling demand divided by the annual electricity consumption of the product 
• Refrigerating capacity, power absorbed and reference annual cooling demand are as defined in BS EN: &#;Condensing units for refrigeration &#; Rating conditions, tolerances and presentation of manufacturer&#;s performance data&#;. 
• Any condenser sub-cooling factored into the refrigerating capacity shall be clearly declared, noting that when a liquid receiver is incorporated into the product with no subsequent sub-cooler, the liquid temperature at the unit outlet should be used to determine capacity.  

1.4    Measurement and Calculations

1.4.1    Measurement standards

The following standards, where applicable, shall be used for measuring and calculating product performance:

• BS EN : &#;Condensing units for refrigeration &#; Rating conditions, tolerances and presentation of manufacturer&#;s performance data&#;
• BS EN -2: &#;Compressor and condensing units for refrigeration. Performance testing and test methods. Part 2: Condensing units&#;
• BS EN : &#;Refrigerant compressors. Rating conditions, tolerances and presentation of manufacturer&#;s performance data&#;

Please note that performance data obtained in accordance with the test procedures set out in BS EN -2: will be accepted as an alternative to testing in accordance with BS EN -2: until further notice. 

For product categories where a COP threshold is specified, performance data obtained in accordance with BS EN : will be accepted as an alternative to BS EN : until further notice.

1.4.2    Test Requirements

Product performance can either be determined using Method A or Method B to determine COP, or Method C to determine SEPR, subject to the following reporting requirements:    

1. For COP measurement, a detailed test report shall be provided and include a statement of achieved performance at the required standard rating point.  
2. For SEPR measurement, a detailed test report shall be provided for test point condition A or condition B according to the rating conditions defined in BS EN : &#;Condensing units for refrigeration &#; Rating conditions, tolerances and presentation of manufacturer&#;s performance data&#;. In addition, a statement of performance at load conditions A, B, C and D, shall be provided. Where results are determined by calculation then this should be on the basis of design and/or extrapolation. In this case, details of such calculations and/or extrapolations, and of tests to verify the accuracy of the calculations undertaken shall be made available. 
3. The refrigerant properties used in the analysis of product / compressor performance shall be obtained from one of the following sources:  
   
   The US National Institute of Standards & Technology (NIST) Standard Reference Database 23 Thermodynamic and Transport Properties of Refrigerants and Refrigerant Mixtures Database: Version 6.0 or later. See http://fluidproperties.nist.gov/ or http://www.nist.gov/.
   
   The ASERCOM properties database as defined in the ASERCOM Compressor Certification scheme, which is based closely on the NIST database (see http://www.asercom.org/).  
4. For the high temperature category only, data for a suction gas temperature of 20°C may be obtained by the thermodynamic translation of data physically tested at 10K superheat.  
5. To enable calculations to be checked, the report shall include (or be accompanied by) the manufacturer&#;s design data for the product and its key components, including the type of refrigerant used, condenser fan motor power, and compressor make and model number.  

1.4.3    Performance metrics

1.4.3.1    Method A to determine COP 

Under method A:  

• The product&#;s coefficient of performance (COP) at relevant standard rating point (as specified in Table 1.2) shall be calculated with the method used to generate its published performance over the standard range of air temperature and evaporating temperature conditions. 
• The accuracy of these calculations shall be confirmed in the following manner:

a)    Actual product performance should be determined at two test conditions close to the relevant standard rating point specified in Table 1.2 that comply with the following limits:

i.    Evaporation temperature shall be within ±1°C of the standard rating point. 

ii.    Ambient temperature shall be within ±5°C of the standard rating point, and one point shall be above the standard rating condition, and one below it.

iii.    Suction Temperature shall be within ±1°C of the standard rating point.  

The following measurements shall be made at each test condition with the level of measurement uncertainty specified in Table 3 of BS EN -2: , whilst the product operating under stable conditions at full load:  

i.    Condensing and evaporating pressures and dew point temperatures at the compressor inlet and outlet.

ii.    Superheat and sub-cooling at the compressor&#;s inlet and the product&#;s outlet.

iii.    Condenser air inlet temperature.  

b)    The condenser&#;s UA value is determined at each test condition using the verified compressor performance data to establish the heat rejection rate. 

c)    The arithmetic mean of the UA values at the two test conditions is used to determine the condensing temperature, and the product&#;s performance at the standard rating point.

• The test report shall include (or be accompanied by):  

a)    Details of the calculation used to determine product performance. 

b)    The following information on the product&#;s compressor: 

i.    Refrigerating capacity and COP at the appropriate standard rating point specified in BS EN : , and at the relevant standard rating point specified in the eligibility criteria for &#;refrigeration compressors&#;. 

ii.    Evidence that the product&#;s compressor is listed on the Energy Technology Product List, or that its performance has been independently verified 

iii.    A copy of the manufacturer&#;s published performance data (or a print out of its key performance data from the manufacturer&#;s design/selection software).  

1.4.3.2    Method B to determine COP 

Under method B, product performance shall be demonstrated by testing the product in accordance with BS EN -2: &#;Compressor and condensing units for refrigeration. Performance testing and test methods. Part 2: Condensing units&#;. 

1.4.3.3    Method C to determine SEPR 

Under method C, product performance shall be demonstrated by testing the product in accordance with the procedures in BS EN -2: &#;Compressor and condensing units for refrigeration. Performance testing and test methods. Part 2: Condensing units&#;. The test conditions to be used, and the SEPR calculation method, should be those described in BS EN : &#;Condensing units for refrigeration &#; Rating conditions, tolerances and presentation of manufacturer&#;s performance data&#;. 

1.4.4    Rounding  

For the avoidance of doubt COP test data should be presented to 1 decimal place. SEPR test data should be provided to 2 decimal places. As an example, a product in the high temperature category with a COP of 3.3 would be deemed to not meet the performance requirements.  

1.5    Verification for ETL Listing 

Any of the following testing routes may be used to demonstrate the conformity of products against the requirements:

• In-house testing &#; Self-tested and self-certified
• In-house testing &#; Self-tested and verified or cross-checked by an independent body
• Witnessed testing
• Independent testing
• Representative testing (see clause 1.5.1)

Further information regarding the first three routes can be found in the ETL Testing Framework.

1.5.1    Representative Testing  

Where applications are being made for a range of two or more products that are variants of the same basic design, test data may be submitted for a representative selection of models, provided that all variants:  

• Use the same refrigerant as the representative model. 
• Have the same compressor type (i.e. manufacturer, method of compression (e.g.  reciprocating or scroll) and type of enclosure (e.g. hermetic or semi-hermetic)) as the representative model.
• Have the same sub cooling arrangement as the representative model.
• Fit within the same product category (e.g. are all high temperature units).  

The representative models shall be selected by dividing the range of products into groups of models with similar design characteristics, and testing a model in each group. The performance of each model in the group shall be predicted using a validated mathematical model. As a minimum, at least one model shall be tested in each range of products.  

It should be noted that:  

• If a manufacturer voluntarily removes the representative model from the ETL then other products linked with that representative model may or may not be permitted to remain on the ETL. 
• If any product submitted under these representative model rules is later found not to meet the performance criteria when independently tested, then all products based on the same representative model will be removed from the ETL.

1.6    Conformity testing

Products listed on the ETL may be subject to the scheme&#;s conformity testing programme in order to ensure listed models continue to meet the ETL requirements.

1.7    Review 

1.7.1    Indicative review date 

This specification is scheduled for review during the /22 ETL review cycle.

1.7.2    Illustrative future direction of the requirements  

As the use of new low Global Warming Potential (GWP) refrigerants becomes more widespread in the air cooled condensing units market, eligibility and performance requirements may be reviewed, to account for the range of new lower GWP refrigerants that will become more widespread due to the EU F-gas regulations. The performance parameters may also be reviewed; products could potentially be assessed on their overall environmental impact accounting for seasonal efficiency, refrigerant GWP and refrigerant leakage.