Payback needs to be Properly Represented to Consumers
If you over pay for over capacity equipment, -- you will be paying more every month and will not be as comfortable as you would sizing it right to also achieve the appropriate humidity levels!
therefore, dehumidification could become more difficult at the highest EER levels. The EER & SEER levels widen, as SEER sky rockets.
When a typical HVAC contractor quotes the efficiency of the Air Conditioning equipment's SEER & Btu/hr, and leads you to believe the new equipment will automatically deliver that SEER efficiency & Btu/hr rating, think again. Typically, --installed equipment only operates at 55% to 70% of rated capacity. Oversized equipment is the worst combination there is because the duct system airflow and heatload on the cooling coil are often way off what is required!
Equipment Ratings are only the 'potential efficiency' of that component of the system under perfect conditions." Over half of the system's efficiency depends on correct equipment sizing toward adequate run-time, on the duct system sizing, i.e., on the quality of the complete field-installation!
What you want & need is right sized equipment operating at its optimal ratings within varying conditions, for your optimal comfort and savings.If all contractor's would do the above, coupled with installing equipment sized according Manual J loads (with no safety factor), along with Manual S selection procedures, comfort would go up, humidity control would improve, and installation and operating costs would be much lower.
Utility demand loads could be cut by at least a third, or even up to a half. Energy loads would be significantly reduced, reducing our nation's energy usage. The return on the time and effort invested on this higher quality level of work would be tremendous - for customers, the community and the nation.
Unfortunately, most HVAC contractors don't use these procedures to size equipment and design duct systems. It's estimated that only 10% of heating and cooling equipment sizing decisions are based on some type of Manual J calculation and that less than 1% of the jobs are based on an aggressive accurate implementation of these recommended design procedures.
Many if not most contractors are designing new and replacement systems that feature oversized equipment, "improperly sized supply outlets" and duct runs that are too small, too leaky and inadequately insulated.
The Manual J gives appropriate answers if you use an “aggressive” set of assumptions. However, most HVAC contractors tend to skew input data to make the calculations match their favorite rules of thumb. Follow the manual J rules and you will get a reasonable margin of safety. However, after skewing the numbers, many contractors throw in an extra half ton or more of A/C to feel safe. No wonder a large percentage of equipment is considerably oversized. Also, the airflow is usually so compromised on the oversized units that it isn't putting out many more btuh than properly sized equipment would be, but it's an energy waster and is costing and arm and leg to operate.
Especially if your system is oversized or there are a lot of low AC load days use an adjustable differential room TH.
TH Differential: Differential is defined as the difference between the cut-in and cut-out points as measured at the thermostat under specified operating conditions. For example, if the thermostat turns the COOLING EQUIPMENT ON AT 78-F & OFF at 76-F that is a 2 degree differential setting; heating equipment on at 70 degrees F and turns the heating equipment off at 74 degrees F, then the differential is 4 degrees F. Some have half degree increment settings over several degrees of differential spread.
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.
However, when selecting A/C equipment between EER Verses SEER:
"How many hours (yes hours) your area spends close (or above a 60% duty cycle) to OD design temp, determines which rating method you should use." - Beenthere
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 Ton 18,400 21°F Split Cond. CFM 1400 WATTS 2222 1.5-Ton is from actual published DATA - ARI Rating Conditions
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
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.
Too many do not properly purge & evacuate contaminated central air conditioning systems.The Triple Evacuation Method is normally done on central air conditioning systems:
First, remove any valve cores with a special valve core remover this will speed up the evacuation time. Back service valves two turns off their back seat.
1) Re-claim unit charge (Recover all the refrigerant)
2) Charge system to 150 PSIG with dry nitrogen and leak test
3) On contaminated systems replace the filter dryers. Then Repair all leak(s)
4) Evacuate system to 500 microns valve off & see if it holds 500 microns for ten minutes, if it holds, break the vacuum with dry nitrogen
5) Evacuate system to a deeper 300 microns, valve off vac pump, & again break the vacuum with dry nitrogen
6) Evacuate system to 300 microns and charge unit (Recharge with fresh clean refrigerant)
7) Check to see if the Supply and Return air ducts were correctly sized & sealed by the original installer.
Many HVAC contractors will consider this excessive time & effort for contaminated residential air conditioning systems, however it is a must for low temp applications.
The “micron” is a metric unit of measure for distance. The micron is a unit of linear measure; one micron equals 1/25,400ths of an inch. Modern high capacity vacuum pumps help speed up the evacuation process.
Deeper evacuations are very important for Refrigeration Systems, Air Conditioner's are somewhat less critical.
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
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The Testo 416 Airflow Test Checking airflow must be performed before charging a system
Udelhoven - udarrell
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Posted: 04/20/05; Last Edited: 07/28/08