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SEER
Payback needs to be Properly Represented to Consumers
The SEER ratings are too nebulous & do not translate to the specific application conditions that each consumer will normally have. EER is simpler & more reliable when the systems are correctly sized to the load.The SEER of a system is determined by multiplying the steady state energy efficiency ratio (EER) measured at conditions of 82°F outdoor temperature, 80°F dB and 67°F wB indoor entering air temperature by the Part Load Factor (PLF) of the system. (The PLF is supplied by the government.) Quoting Tescor: Psychrometric Test Rooms are used by air conditioner manufacturers to determine the thermal performance of unitary air conditioners and split systems. Tescor utilizes dual rooms (indoor and outdoor) and the air enthalpy method to determine unit capacities and provide heat balances. Code testers, which include AMCA nozzles, provide accurate determination of the test unit air flows and outlet air conditions. Tescor’s control software allows the user to perform all of the ARI standard tests including the capability to perform SEER and HSPF calculations: http://www.tescor-inc.com/datasheets/Tescor_Psychrometric_Test_Room.pdf The SEER rating is at only one set of conditions that are NOT typical of what we design for. Summer Outdoor Design varies however, we usually design for 75°F indoors NOT 80°F, also when systems' are downsized properly to achieve long runtimes the Part Load Factor becomes far less of a factor. Always go by the EER Rating NOT the SEER rating because as the SEER goes higher the EER ratio to it drops. Therefore, when the system is sized properly you have have a lot more steady-state continuous runtime cycles & the PLF will be minimized. Well, that is misleading because the PLF figures in, -the cyclical start-ups, whereby it takes 5 to 7 minutes to reach full operating capacity. In many climate areas there is an advantage to slightly Btu/hr under-sizing the A/C system, as there are very few seasonal hours that you need Btu/hr ratings that are called for by using the existing over-capacity sizing methods. "During average operating conditions in its particular environment, I want to peak-load the evaporator at near its Btu/hr Rating." First, consider EER: ARI introduced the Energy Efficiency Ratio (EER) in 1975. This was an HVAC industry instituted way to determine the relative efficiencies of one unit to another in the cooling mode. EER was determined by dividing the published steady state capacity by the published steady state power input at 80°F dB & 67°F Wb indoor and 95°F dB outdoor. Consider the criteria being used for their EER formulas. Air
conditioner EER ratings, and BTUH Tons of Cooling Capacity ratings on
Air
Conditioning units are rated at an outdoor temperature of 95°F,
and an indoor 80ºF dB 67ºF WB or, a 50% Relative Humidity.
SEER - The Seasonal Energy Efficiency Ratio is a standard method of rating air conditioners based on three tests. All three tests are run at 80°F inside and 82°F outside. The first test is run with humid indoor conditions, the second with dry indoor conditions, and the third with dry conditions cycling the air conditioner on for 6 minutes and off for 24 minutes. The published SEER will not represent the actual seasonal energy efficiency of an air conditioner in your climate and your other environmental and system factors. Add to this the Part Load Factor (PLF): The SEER of a system is determined by multiplying the steady state energy efficiency ratio (EER) measured at conditions of 82°F outdoor temperature, 80°F dB/ 67°F wb 50% RH indoor entering air temperature by the “Part Load Factor” (PLF) of the system. The PLF is a measure of the cyclic performance (CD) of a system and is calculated as follows: CD is Cyclical Data PLF = 1.00 - (CD X's 0.5) "The cyclic performance (CD) value in the above equation has been determined by the government to be 0.25." The government contends that the PLF should equal: [1.00 - (.25 x .5)] = .125 1.00 - .125 = 0.875, which yields: PLF of 0.875 A 3-ton system would be 36000 X's PLF .875 = 31500-btu/hr, or closer to 2.5-ton 30000-btu/hr system. A 4-ton system 48000-btuh X's .875 = 42000-btuh or a 3.5-ton PLF operating system ------------------------------------------------------- The critical importance of selecting the proper engineered equipment for your climate zoneIt is essential to understand why the local weather environment dictates what SEER level air conditioning equipment you should choose. In choosing equipment and its SEER level, it is important to understand the design engineering behind in its functional capabilities.First, when the engineers designed for
higher Seer levels,
they increased the volume and the BTU per hour capacity of the
condenser coils
and the evaporator coils; however, they reduced the BTU per hour
capacity of
the compressor. The volumetric capacity
of that smaller compressor depends on the absolute suction and
discharge
pressures under which the compressor is operating. The lower volumetric capacity ratio of the compressor to the higher coil capacities only works well in an 82°F laboratory weather environment with a 50% relative humidity level, which is never a stable operating condition in the real world environment. When you select the high Seer units in a climate where you have high outdoor sensible temperatures along with a high humidity, the temperature pressure ratio of the evaporator coil skyrockets as does the condenser coil pressures and temperatures, therefore the smaller capacity compressor in its relationship to the coils becomes overloaded.Here comes the engineering caveat, if you
are in a high
temperature high humidity climate zone the evaporator pressure
temperature
ratio will be so high that there will be very little condensation of
the
moisture in the air. Additionally, the volumetric capacity of the smaller compressor will not be able to handle the increased volume of vapor. Added to this the condensing pressure will be much higher with also reduces the volumetric capacity of the compressor which is rated at less than the BTU per hour of both coils. The higher SEER level you select above the 13 or 14-SEER levels the ratio between the lower BTU per hour capacity of the compressor compared to the evaporator and condenser coils becomes worse. Therefore, if you are located in a hot or, a hot and humid climate from an engineering standpoint and a performance standpoint, I do not believe it is a wise decision to go to extremely high SEER rated equipment.There maybe rare exceptions to the above statements, if a variable speed compressor and variable speed blower motors are used. When these components are used, you should make sure that the contractor proves to you, before you buy the equipment, that the combination of components will work properly in your climate zone. ---------------------------------------------------------Relationship of SEER to EER and COP SEER is related to the Energy Efficiency Ratio (EER) and also to the coefficient of performance (COP) commonly used in thermodynamics. COP is a measure of efficiency. The COP of a heat pump is determined by dividing the energy output of the heat pump by the electrical energy needed to run the heat pump. The higher the COP, the more efficient the heat pump. For example resistive heat has a COP = 1. The EER is the efficiency rating for the equipment "at a particular pair of external and internal temperatures," --- "while SEER is calculated over a range of 'expected external temperatures' (i.e., the temperature distribution for the geographical location of the SEER test). [Real tricky nebulous temp & humidity expectations or assumptions! - udarrell] Formulas for the approximate conversion between SEER and EER or COP in California are: [2] SEER = EER ÷ 0.9 SEER = COP x 3.792 EER = COP x 3.413 From equation (2) above, a SEER of 13 is approximately equivalent to a COP of 3.43, which means that 3.43 units of heat energy are removed from indoors per unit of work energy used to run the heat pump. The relationship between SEER and EER is relative depending on where you live because equipment performance is dependent of air temperatures, humidities, and pressures. The relationship stated above is typical if you live in the lower-elevation portions of California; however, if you live in the higher humidity of Georgia, it is better approximated by: SEER = EER ÷ 0.80 due to the much higher humidities. A similar relationship exists in relating SEER and COP, also depending on where you live. ------------------------------------------------------ I want a room TH (with NO cooling anticipator) that I can set within the "Human Comfort Range" to kick-in at say 78°F and off at say, 75°F - that would result in longer run-time cycles. The result would be a big improvement in dehumidification, improved efficiency plus longer equipment & component life. Combined with a 3-degree differential, there is a need for very low cost air circulation at the location of the occupants. That is a way to boost SEER, reduce utility bills & provide adequate "Human Comfort Levels Design Engineering and Installation Objectives should be focused towards achieving the most efficient and effective means toward a conditioned space that is within the "Human Comfort Zone, and within an affordable investment 'payback' period." The proper system sizing for long runtimes along with a computerized variable speed blower to keep the heatload up near the evaporator's rated capacity would reduce the EER & SEER ratio! That is why if you live in a dry climate like Dallas TX or in Arizona I would us at least 450-cfm per ton through a wet cooling coil and measure the BTU/hr output of the condenser. Condenser Gross BTU/hr = condenser temp = CFM X's Temp/split X's 1.08 Motor Btu/hr =Volts times Amps (or) Watts X's (PF) Power Factor of 0.90 X's 3.413 converting watts to Btu's (Indoor blower motor to) = Net Btu/hr Output. The condenser and compressor will both handle overloads when conditions exceed your average seasonal heatloads. High efficiency, variable speed blower motors, along with TEV refrigerant controls could help reduce those higher heatload periods. Some of the high SEER units do not look so great when you figure their EER. ----------------- Maytag and other companies now have some of the computerized engineering I have been talking about: Paired with a SignatureStat™ this control combines the functions of a humidistat and thermostat into a single device. Simple menu-driven programming helps you control your energy costs and comfort. - udarrell - Darrell ===================================== Specific condenser equipment Information such as this older graph "updated" with both the Wet Bulb (WB) and the associated Relative Humidity (RH) along with the condenser split at say 90 or 95 outdoor ambient temperature. The chart split listed below is at Condenser Design conditions: Indoor Return Air 80-F dry bulb 67-F Wet Bulb or 50% Relative Humidity as you go up to 99% RH the condenser split could increase by up to 6°F; down as much as 4°F at a very low humidity of 55°F Wet Bulb. Do your own figuring based on this formula. Motor BTU/hr additive = Watts X's PF x's 3.413 for Btu/Watts additive added to rated BTUH, divided by condenser fan CFM X's 1.08 = condenser Temp-Split. Get the Motor Power Factors (PF) of the compressor and fan motor from the manufacturers. (A 0.80 factor could be close.) Some of the 10-SEER temp-split figures need correcting, will do ASAP. Most Splits rounded off. CONDENSER TEMP-SPLITS - Comfortmaker® 12-SEER units - I used 0.80 Motor Power Factor 1.5
T 18,400 +17°F
Split Cond.
CFM
1400 WATTS 2222
2-Ton 24,800 24°F Temp-S Cond. CFM 1400 WATTS 2659 2.5-T 30,200 21°F Temp-S Cond. CFM 2000 WATTS 3404 3-Ton 35,600 18°F Temp-S Cond. CFM 2800 WATTS 4117 3.5 T 42,500 21°F Temp-S Cond. CFM 2800 WATTS 4554 4-Ton 48,500 19.5°FSplit Cond. CFM 3400 WATTS 4761 5-Ton 59,000 25°F Temp-S Cond. CFM 3400 WATTS 6969 ==================================================== http://www.udarrell.com/Return_Air_Wet_Bulb_Condenser_Split.jpg Page 618, Refrigeration & Air-Conditioning (ARI) Second Edition, C 1987 Those lower SEER units had higher condenser splits than 12-SEER and higher units. Sorry, I defiled the graph, 95°F-db outdoor, 80°F-db indoors with 67 wet bulb/50% RH represents the condenser splits shown above. Typical matched units from major manufacturers have Sensible Heat Ratios (SHR) in the 68% to 80% range (or 32% to 20% Latent) when it is 95-F outside and 75-F with 50% relative humidity inside. Proper mixing of the air and proper distribution to individual rooms is critical for comfort. All air-handler equipment should have capped ports for taking static pressures with information on how to do it along with a line graph or other information of the blower performance at various static pressures. These are added value features that can be used in all advertising and marketing, providing your company with a distinct value advantage to all potential customers.All of the above information should be easily accessed on the Internet for the convenience of techs and equipment owners. Air-conditioning contractors could make up sticker graphs showing how to check the capacity of the A/C they bought from you. It's a "Value Added Feature," you could promote to even your potential customers, they will appreciate you doing that for them. Better Cooperation by manufacturers' toward, distributors, HVAC/R Contractors, Techs, and all consumers of their equipment would make performance evaluation simple and easy to perform.The
motor vehicle techs have
the dynamometer
to evaluate the delivered
horsepower of the motor under various loads and conditions.
HVAC/R techs and consumers have NO easy way provided to evaluate the varying load BTU/hr performance of an air conditioner evaporator and condenser design combination. Let us say it is getting the design optimal-load on the evaporator and condenser however, the run-time is much too long for the A/C unit's design and the design cooling heat-load, --where do we look next? We look at the supply-air (SA) and (RA) return air-ducting system for design and installation problems. Many Return Air systems set the furnace on top of a RA chamber that is not sealed off from hot attic air —which overloads the cooling coil. This is also very dangerous, as the RA suction will put a negative pressure on the combustion-air venting and could easily result in carbon monoxide poisoning and death! In most homes there is NO Return Air ducting to the various rooms. When the system pressurizes a bedroom, this positive pressure forces the conditioned air out through any opening in the room to the outdoors. Building science research states that for every cubic foot of air forced out of a building, a cubic foot of air infiltration must be drawn in from outside to replace it. Therefore, when air is forced out of a room under pressure an equal amount of air is drawn into the main body of the home to replace the air forced-out. Depending on the number of doors that are closed, the rate at which hot or cold outside air enters the home goes up by from say, 300% to 900%. In turn, utility bills go up, comfort goes down, and health problems may ensue. In a four-bedroom home with all of the doors closed & with a large 2000-cfm airhandler, it could be drawing in almost 1,000-cfm of outdoor air! "With a high outside humidity and/or temperature difference, the air-conditioner will never catch up to the added heat-load." To allow for cooling mode Return Air, the "upper panel of a door can be removed and an upward louvered wooden or metal grille can be installed." Alternatively, make a grilled opening of the proper size through the wall near the ceiling. The Case for (TXV) Thermostatic Expansion Valve Refrigerant Controls & Higher SEER RatingsTXV's give a colder coil than (Flow-rator) pistons under the same conditions and get colder faster. I have a data logger that has two external temperature probes. I put one before the coil and one after the coil. I start the data logger, then turn the AC on. The TXV gets 18 to 22 degrees across the coil in 5 minutes and 80% of that in 1 to 1.5 minutes.The piston gets 16 to 18 degrees in 10 minutes and 80% of that in 5 minutes. Under part load conditions the TXV will dehumidify better. Most systems run most of the time under part load conditions. Guess what? I am going to install TXV's most of the time, just to cover my back side. - Stretch | 4/28/05 alt.home.repair (NG) ----------------------- Gurgling Pulsating Sounds at TXV: Low evaporator heat-loads lead to reduced liquid line mass and increased evaporator mass could be due to airflow problems. Eliminate low evaporator heat-loads before looking into adjusting the refrigerant charge. Gurgling and pulsation noises at the expansion device can be caused by low charge, and/or non-condensibles and moisture in the system. Unbalanced airflow through the various distributor circuits of the evaporator coil will cause the TXV to close down refrigerant flow starving the coil; while Piston-Flow-Rators will make it impossible to properly charge the system and cooling will be greatly compromised unless you eliminate the cause! "Cup your ear to the liquid line at the evaporator coil., & listen." You can hear some of them pulsating 10 feet away. On every Rheem condenser cover it lists "non-condensibles and or moisture" as causes for a gurgling or pulsating noise at the expansion device. The entire evaporator circuits, may not become active for various reasons, - "the entire coil must become fully active for efficient performance." The purpose of these recommendations is to provide liquid refrigerant at the expansion device and provide efficient operation. Hopefully, this will aid your research. If I can be of additional assistance, contact me. ----------------------------------------------------------- There are far too many things to evaluate in any determination of whether there will be PayBack going to a higher SEER to list on this page. There are no assurances that a higher SEER will be more efficient than a 13 or 14-SEER. When going to a higher SEER, there may be some efficiency gain or, there may not be any. A quality installation is what really counts when it comes to getting the rated BTUH performance & the EER Rating. You will have to do a lot of figuring while dealing with the SEER engineering realities based on your specific climate & many other conditions. Talk to the local contractors & pick the one that shows a genuine interest in doing what is right by you! - udarrell ========================================== http://www.udarrell.com/air_temperature_drop_evaporator.jpg Air Temperature Drop Through Evaporator Coil (1987 Period) Indoor temperature and humidity load variations graph. Refrigeration & Air-Conditioning (ARI) Second Edition, Page 624, © 1987 ====================== Getting it right makes all the difference in the world.
Darrell's Refrigeration Heating and Air
Conditioning - Retired To
Contact me: udarrell@pcii.net
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MY GLOBAL ECONOMIC Policy PEOPLE EMPOWERMENT PAGES Send your
residential air conditioning questions to Darrell
Udelhoven - udarrell
Empowerment Communications Covering The Real Political Issues Posted: 04/20/05; Last Edited: 09/29/07 |
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