Optimizing a Room - Window Air Conditioner's EER and Btu/hr Performance Output    

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with Darrell Udelhoven  - SUMMER of 2002-2012 A Half-Ton Room-AC Cools My 676-sf First Floor Farm Home 
Best ROI Investment or Lose the Investment money annually "Home Energy Efficiency Pays You." Video
MY HOME 2007
The spruce trees on the South-side, in photo, & West-side, not in photo, of My Home, have been removed. The other Maple tree is on the West side of my home, the North Cedar tree provides no shade for cooling.

The actual Total electric bill summertime with electric range, hot water heater, 2 TV's & high wattage PC average around 45 to $50.  Unbelievable! My home is ALL electric except for a new 60,000-Btuh
input 95% Propane furnace; had an old 140,000-Btuh input Oil furnace.

The 1st floor input data heat-gain calc.,  Excel Spreadsheet is 7,547-Btuh; Spreadsheet load-calc, 1/2Ton Cools Mine: Darrells-house-Heat-gain 1st Floor (1).pdf | Dons-House -Heat-gain room detailed HTMs7613.pdf
is for SALE! My little Half-Ton cools the house perfectly at all extreme conditions. I used 90F outdoor summer design & 76F indoors at 50% RH. The terrific House for SALE @90F & 75F 50% RH.
On July 18, 2011, as reported on WI Public Radio; very near me, Prairie du Chien, WI had a Heat Index of 127F, yes, 127F Heat Index! All shades pulled, etc., my little Half-Ton first floor A/C cooled the rooms to 76F or 77F & and rarely above 55% relative humidity; with good air movement, a totally comfortable all day. The same for the up-stair's less than Half-Ton window A/C, cools my bedroom, hallway & bathroom; I use a Wind Machine 3300 to move the air throughout the rooms, both on first & 2nd floors.

Record Heat Index for continental US:

I think I found the answer to the thread's question.

see: Weather Extremes : Record Dew Point Temperatures : Weather Underground

But it was during the July heat wave of 1995 that the highest dew point of all was measured in the Upper Midwest: 90 at Appleton, Wisconsin at 5 p.m. on July 13th of that summer. The air temperature stood at 101 in Appleton at that time leading to a "heat index" reading of 148, perhaps the highest such reading ever measured in the United States. Seemingly Unbelieveable, but a documented reality...

Normally my indoor humidity will be at 50%, rarely as high as 55% RH & 75 to 76F sensible temperature with good air circulation.

The 6,000-Btuh Half-Ton of Cooling Capacity on all window Air Conditioning units is Rated at an outdoor temperature of 95F, and 80F and 50% Relative Humidity in the conditioned space; however, we normally use 75F & 50% RH Indoor design conditions.

Before doing any testing for btuh ratings of a central AC unit in use, "the condenser, evaporator coils, indoor blower wheel, and filters must be clean, with NO duct air leaks." View my other page, "Air Conditioner SEER Ratings and Btuh Capacity Ratings," for the simple testing procedures.

What outdoor ambient temperature zone will the majority of the run-time fall into? Providing it is not too far below the "Design Point seasonal-peak-load-hours," (that's when the unit runs continuously to maintain the comfort zone).

However, "the 90% of run-time period temperature zone," will be the outdoor temperature zone where your central and window air-conditioner should be optimized to very near its full rated BTU/hr capacity by adjusting the CFM indoor airflow-heat-load through the evaporator coil.

Since optimum efficiency is achieved at continuous running at your unit's optimal BTUH capacity rating, it is important that the entire air conditioning system and all controlling components be design engineered to achieve the longest run times possible during the seasonal longest running hours time period, at those outdoor and indoor temperatures. A theoretical perfectly-sized air conditioner will run continuously for the 73 hours during the year when the outdoor temperature is greater than the (2.5%) Design Point.
Two major factors determine the human comfort zone: the two major comfort zone determinant factors are relative humidity levels coupled with adequate room air circulation. "When these two factors are optimized the temperature comfort zone becomes much wider." This will make possible longer, much more efficient run time cycles.

This lengthening of the temp comfort zone permits cooling thermostats to lengthen the time between run cycles as well as greatly lengthening each run cycle. On each start-up it takes 5 to 7 minutes or more for the system to achieve optimum cooling performance. This is where "the down sizing of equipment to the optimal Btu/hr level is critical to efficient and effective comfort zone design engineering."

I tried allowing my two room A/C's to cycle on their thermostats, and though they are small units cooling large areas with the use of two 20" floor type fans, they both short cycled leading to inefficient operation and less dehumidification.

I will not allow my little room A/C's to cycle on their Thermostats. Most room A/C's are also oversized & are limited due to insufficient throw of their airflow! We simply can't get away from believing that more Btuh is always better, when the reality is the opposite!

I take showers upstairs; the A/C up there takes quick care of the humidity.

After I shower in the morning I usually turn the 5,950-BTUH window AC on in the bedroom, which is aided with a couple of fans now, a small fan taken from a room humidifier directed toward the bathroom or sometimes back toward the bedroom A/C, & a 12" fan directed at the AC's Return Air Intake, it brings the humidity & temperature down in a very short period of time.

Yes, I use electric heated hot water to wash the dishes plus shower & cook my meals, no problem, the first floor little Half-Ton handles the added heat-loads without a hitch.

I simply do not hype or misrepresent anything in respect to air conditioning performance, I am a retired longtime HVAC Contractor & Tech & have nothing to sell to anyone or any reason to misrepresent or exaggerate the performance of a simple little window AC.

It is the airflow through the rooms and back through the evaporator coil that optimizes the cubic foot of air the little room units can condition to deliver conditioned comfort standards! Put the little Half-Ton in a 225-sq. ft. room which it says it is rated for, and that will be all it will cool; it will also cycle a lot... .

Optimizing the latent & sensible heat-loads in the rooms through the Evaporator Coil, is key to optimal Btuh performance and efficiency. HVAC RETIRED - udarrell
The simple conclusion is that the public must be much better educated and, the engineers' need to design the units to optimize dehumidification and length of run cycles. With the advanced technologies we have available, there are many effective ways for engineers to accomplish these objectives.

Computerization of blower speeds and compressor loading ratios, much longer thermostat and dehumidistat computer controlled run time cycles. Everything can adjust to the load and comfort zone requirements with pure automated perfection. Come on, get on the stick and beat your competitors to the punch and eat their lunch! Need some help? Get in touch with me.

On flow-rater refrigerant controlled systems, the tech can cover portions of the condenser to achieve the discharge temperature pressure relationship needed to allow the adjustment of indoor CFM airflow heat loading of the evaporator coil to achieve the normal comfort zone TH setting for the occupants. With good room air circulation along with sufficient run-times to reduce the humidity to the comfort zone levels, those normal room TH settings ought to be around 77F, and not 72F. [Slightly Undersized is better than Oversized!]

Another thing that would improve the length of the run-time cycles would be to digital room TH's programmable to allow a greater rise of temperature before cycling the system on again! Also, it should be setup so both the TH and dehumidistat settings would have to be satisfied. The control should also have a programmable run time length setting, this would provide three controls over the length of run time.  This would increase the run-time of every cycle and increase SEER much more effectively, reducing the humidity level to the comfort-zone and maintaining a wide comfort zone.

Providing there is low air infiltration, as the room temperature rises the %RH drops or stays relatively constant therefore, when you have a floor fan circulating the air, you will feel comfortable at the higher room temperature. Then with a wider comfort-zone index along with other low wattage fans circulating the air, the cycle on could be 79-F ON and 75-F OFF. These longer cycles would lower the  percent of Relative Humidity (%RH say 45 or 50% and as the temperature gradually went back to 79-F, with other air fan circulation, this would keep the occupants in a genuine "Human Comfort-Zone" during the cycles.

The lower the temperature in the conditioned area the more difficult it becomes to get the %RH down to a comfort-zone level.

Thus, the critical value of down sizing sizing the BTU/hr of the unit is to achieve adequate run-time during the less than peak run-time periods of the cooling season.

Seventy-five percent is only 4,500-btu/hr sensible, 1,500-btu/hr latent at 50% Relative Humidity. Amazing performance, huh; but time tested and true! (NO special windows or insulation,  no cooling upstairs to drift down the stair-well & a 1937 home!)

Design Engineering objectives should be focused towards achieving the most efficient and effective means for getting the conditioned space within the "Human Comfort Zone "at affordable costs." Scroll down to the "initial affordable cost marketing factors."

Summer Comfort Zone.
Relative Humidity Maximum Comfortable Temperature Minimum Comfortable Temperature
60% 78.5oF  72.5oF
50% 79o 73oF
40% 79.5oF   73.5oF
30% 80oF 74oF

The above comfort zone was found to be acceptable to 90% of test subjects drawn from a range of age groups and genders, with work and life-styles involving varying levels of activity and clothing. An air conditioning system that establishes and maintains indoor conditions within this zone will provide thermal comfort.

It will produce a neutral sensation, occupants will feel neither too hot nor too cold. Above chart and findings From: Home Energy Magazine Online September/October 1996) Sizing Air Conditioners: If Bigger Is Not Better, What Is?  by John Proctor and Peggy Albright

During summer of 2002, my New little Half-Ton 6,000-Btu/hr 9.7-EER 115-volt Whirlpool Quite Partner Series room A/C unit Air Conditioner kept the first floor humidity as low as 45% (usually 50 to 55%) and during above average outdoor temps would drop the indoor temp to as low as 74-F in around a -676-sq.ft. first floor level, with NO cooling operating on the second floor.

It says it cools up to a 225-sq.ft., room; well you can forget that nonsense, as it cools perfectly nearly 3-times that area; it cools  a 676-sq.ft., first floor area; may be a little less. That is 1352-sf per/ton of cooling!

It is rated to pull 5.4-amps @ 115-volts or  621-watts. My brother's furnace blower is rated at 5-amps @ 115 volts he has a 1.5-ton AC system with an airflow restriction between .the A-coil & the oil furnace heat exchanger so his unit runs more than my little 621-watt cooling system.

His 1.5-ton AC pulls around 9-amps @ 230-Volts is 2070-watts plus 575-watts for the blower which is 2645-watts when running compared to 621-watts, my electric bill is small compared to his! (His has problems.)

 I checked my relative Springfield humidity gauge with a wet bulb test and it was too high, so I recalibrated it today 09-01-03. You can use an ordinary pliers to recalibrate this Springfield model.

I just found the Chart below on my 'old' little Kenmore Cool 'N' Lite 5,950-btuh window or room AC unit that cooled my entire 620+-sq.ft., 8-ft ceilings first floor level in WI Temp and rather high humidity. It uses a Current/Temperature Chart to be used as a diagnostic tool procedure. It has a 7.5 amp nameplate rating at 115 volts however, the nameplate Rating is 850 watts. I'm using this Chart to make a few useful points.

My 'old' little Kenmore Cool 'N' Lite 5,950-btuh window or room AC unit's performance; as you can see as the outdoor temperature goes from 70 to 120 the Current goes from a low of 5.7 to a high of 10.7 amps or 5 amp spread, 1230 watts or a 575-watt spread due to the ambient temperature differential. It would be important to know whether the compressor discharge line temperature is within the safe 225F zone at those highest listed amperages.

Temp F
MIN.                            MAX
70  -  76
5.7                                7.9
78  -  84
6.1                                8.3
86  -  92
6.5                                8.7
94  -  100
7.0                                9.2
102  -  108
7.6                                9.8
110  -  116
 8.3                              10.4
118  - 120
 9.1                              10.7

Since 2004, I use it to cool the upstairs,-  one bedroom the hallway and bath room.
I don't have to run it much!
Here is the old Kenmore's instructions:

  1. Operate unit on high cool for ten minutes.
  2. Measure outdoor temp as close to unit as possible.
  3. Determine unit current rating from nameplate.
  4. Take a current reading and compare with those on the chart.
  5. If current is within limits the system is operating normally and should not be condemned.
  6. If current is outside the limits, the sealed system may be at fault BUT the following must be checked first.
  1. Check for cleanliness - (ha)
  1. Check for blockage with dirt, or other material.
  2. Check for corrosion
  1. Check for continuity
  2. Check for overheating, wiring connections
If my figuring is right, that is over a 30% increase in wattage, it appears to be over a 1.3 SF. The compressor discharge temperature is as critical as the amp/wattage draw.

Copeland engineers say that the compressor oil starts cooking at about 310F and breaks down at 350F. Measure the discharge line temperature 6 inches from the compressor and add 50-75F, that will give you the approximate temperature at the discharge valves. Discharge line temperature goes up with the head pressure and/or superheat.

The maximum acceptable discharge line temperature is 225F. | 250F indicates an overheated condition, and at 275F unless you catch it right away the compressor could go down!

All hot discharge lines should have temperature limit switches on them to protect the compressor.

PROPERLY SIZED, with a long automatic computer control system and proper blower CFM levels on a Central split system, a split-system could be operating at its optimal BTUH and EER level a very high percentage of its run time.

I use an elevated floor fan above the cool air discharge, with my little new 6,000-BTUH room or window unit, to effectively circulate the air through and around 620-sq.ft. of all three first level rooms and the hallway. This is an older 1937 home with a ton of windows and a lot of sun exposure to the South and SW here in SW WI.

It has a deep basement under the first floor. If your window A/C is oversized, get rid of it, and replace it with a small high efficiency unit that will permit longer cycles, --use a large fan to produce longer run cycles and better air distribution while putting a heavier load on the evaporator coil.

I bought a 3 speed 20" Wind Maker 3300 vertically adjustable airflow fan at Wal Mart for around + $20. I mounted it on a stand above the Evaporator Discharge air intake and it will really move air throughout the entire first floor area. (Get one). I also use one in the kitchen now, to move air back to the AC.

I like this 6,000-BTUH 9.7-EER Remote controlled Quiet Partner Series Whirlpool that I have been using since 2004. It has three speeds and excellent airflow through the evaporator coil. If the humidity is high I operate the fan a lot on the low speed.

I was using only one 20" Wind Machine fan at the AC, I just bought another 20" Wind Machine 3300 to put in the kitchen to circulate the air faster back to the Room AC.

Yes, it says it cools rooms up to 225-sq.ft., it is the positioning of the fans and the long to continuous runtime that make the difference.

Reassessing there are a lot of walls and a kitchen cupboard area,. so I will cut the actual area lower to 620-sq ft., that would be 1240-sq. ft. per ton in a 1937 home with a lot of windows. Eight foot ceilings or 4960-cu.ft of air to remove the latent & sensible heat from.

The fan stand should be just above the return air intake portion and use a wide cardboard pushed against the AC conditioner just below the discharge air outlet, this keeps the fan from pulling air away from the return air intake area. Angle the fan somewhat upward so it mixes the air throughout the interconnected rooms to be cooled.

Run the air conditioner's fan on low medium or high speed and use the floor fan on low and no faster than medium speed to pull more air through the cooling coil, this increases the heatload on the coil and the higher condenser pressure drives more refrigerant through the cooling coil for evaporation and increased heat absorption! [Man it Cools!]

On very hot days running the AC on low fan and also using the floor fan could be hard on the compressor so I am going to try the Turbo high fan speed  and see how it does. It does cool even better on the higher AC fan  speeds. 06/24/05. It both cools & dehumidifies better set on the Turbo high speed fan setting.
It keeps me perfectly comfortable even on a 112-F heat index day!

It held those temperatures all day and with the window unit set on low speed fan and my fan set on medium and then on low later in the day. The Condenser temp is NOT accurate on a room AC & can NOT be used even as an accurate comparison of what it is putting out due to the variability of the slinger-ring throwing water on the condenser coils! I  cool my old 1937 Lower & upper floors. A Half-Ton for the entire first floor. I cool with a 5,900Btu/hr upper floor bedroom hallway & bathroom.  
The spruce trees on the south-side of my home have been removed. The other large tree is on the West side of my home.

The actual Total electric home bill summertime with electric range, hot water heater, 2 TV's & high wattage PC average around 40 to $47 a month.  Unbelievable! - udarrell     - Darrell 
I assume NO responsibility for how anyone uses information on my web pages.
All HVAC/R work should always be done by a licensed Contractor! This information is only placed on these pages for your understanding & communication with contractors & techs.

This information is for the edification of contractors and techs.  - Darrell Udelhoven

Darrell's Refrigeration Heating and Air Conditioning - Federal Refrigerant Licensed - Retired Service Tech & Licensed Contractor

Please write me if you have anything you'd like to contribute! - Darrell 

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Please feel free to link your web pages to any of mine. 

Darrell Udelhoven - udarrell | Posted: 04/03/03
Links Added: 07/31/04 | Edited: 02/11/10

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