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Can We Save The World ?Comparison of whole house fan and air conditioning (AC) systemIn the USA Air Conditioning uses 6% of residential energy and 16% of residential electricity. 
Click for a larger image Where night time temperatures drop significantly, cooling your home to a relatively low temperature with a whole house fan system can be very effective at energy saving and save many $10’s in electricity costs. A whole house fan is sometimes called an attic fan. This article is based on comparisons of a whole house fan effectiveness, and operating cost, with a residential AC system. The tests were carried out in Ohio in the summers of 2006 and 2007 and shows that cost reductions of 96% are possible. When operating the air conditioning system uses 6.5Kwhr. When operating at low speed the whole house fan uses 0.450 Kwhr, and 0.650 Kwhr at high speed. The chart shows temperatures and relative humidities from inside and outside the home on June 16 and 17, 2007. 
Click for a larger image The monitoring system used to compare the residential AC system and whole house fan system was a La Crosse WS 8610 data logger. This battery powered unit logs temperature and humidity data every 5 minutes from itself and from up to three remote wireless temperature and humidity detectors. Data files were uploaded and charted using Microsoft Excel. The whole house fan and shutter is controlled by a whole house fan control system comprised a two channel programmable timer thermostat, and a custom whole house fan control system which monitors outside and top floor temperatures and includes switch selectable manual and automatic modes for both the fan and shutter. Whole house fan effectiveness On June 16th the timer turned on the whole house fan at 0315. It turned off at 0640 and was running for 3hrs 25mins. During this time the Great Room temperature fell by 10.1 degrees. On June 17th the air conditioning system was on from 1700 to 2030, i.e. 3hrs 30mins, during this time the Great Room temperature fell by 5.8 degrees. From these figures the whole house fan effectiveness is twice that of as an AC system at cooling the home. A further factor to be considered is the energy used by both systems. The whole house fan consumed 450 watts when operating. The air conditioning system consumed 6500 watts when operating. From these figures the whole house fan uses 1/14th the electricity used by the AC system. Taking both the effectiveness and electricity usage comparisons together, the whole house fan system was more than 25 times more energy efficient than the air conditioning system. During June 16th the home temperature rose to 78 degrees, this temperature could have been lower if the whole house timer had been set to turn the cooling on earlier than 0315. Additionally a whole house fan generates a far greater air flow through the home than an air conditioning system so feels cooler, unless the humidity level is too high. If outside air characteristics permit, a whole house fan can also be used to rapidly replace inside air with outside air changing humidity levels, removing odors, or increasing temperatures. If a whole house fan is to be used an air path should be provided to allow outside air into and through your home, preferably at a low level, e.g. basement or 1st floor level, internal doors should also be opened. When the outside air is hotter than the inside air a whole house fan cannot be used for cooling you home. One way this can at least partially be overcome is to use the cool outside night time temperatures to cool the home to a relatively low temperature during nighttime hours. As the day passes close light colored shades to minimize heating, or better still use external sun blocking awnings over south and west facing windows. The chart above shows the benefits on June 16th, when the home was cooled to 64 degrees. Motorized shutter The motorized shutter consumes very little electrical energy, just a few watts. An open shutter permits hot air to be convected, flowing out through attic vents cooling your home naturally. Outside air should be permitted to enter at the coolest side and at the lowest level of your home. Caveats The whole house fan effectiveness is dependent on the difference between the inside and outside temperatures, the larger the difference the more rapid the cooling. In contrast, an AC system's efficiency is not impacted greatly by the inside - outside temperature difference. 
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