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

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.
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On July 18, 2011, as reported on WI Public Radio this morning; yesterday very near me & Prairie Du Chien, WI had a Heat Index of 127-F, yes, 127-F Heat Index! My little Half-Ton first floor A/C cooled the rooms to 76-F & a bit less that 60% relative humidity; 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.

I am now using 620-sf per floor area or, 1240-sf total. My little Half-Ton, a mere 6,000-Btuh cools perfectly that old 1937 farm home's 1st floor area with 13 window areas, which is 1240-sf per/ton of cooling Btuh. Normally the humisity will be between 50 & 55% RH & 75 to 76F sensible temperature with good air circulation.

The Btuh Tons of Cooling Capacity on all Air Conditioning units is Rated at an outdoor temperature of 95°F, and 80ºF and 50% Relative Humidity in the conditioned space; we 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.
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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 Btu/hr is always better, when the reality is the opposite!

I take showers upstairs & that humidity also flows down the stairway to the AC.

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 deal 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
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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.
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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 77ºF, and not 72ºF. [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!)

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

OUTDOOR AIR Temp ºF	COOLING CURRENT 115-volt 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

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

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