Interesting. I know the heat generated (wasted energy) has become a greater concern as processing power doubles and doubles again. What sort of $$ are we talking about here? Also, under what circumstances is 250$ saved? I'm assuming if both are left on for 24 hours a day, 365.
Each component in this build is chosen for efficiency, the cost isn't that much higher than picking random hardware, but advanced planning will go a long way in building an efficient/quiet system.
I do leave my systems on all of the time, but power savings will be significant regardless of the use. Power efficiency for me is a side benefit of silencing efforts, loud computers are distracting to my work. The system described above idles with high efficiency, and is still efficient even under full load. Providing exact numbers will require a degree of assumption on my part, but compared to a system built with the least expensive components, without regard to efficiency, it's perhaps twice as efficient (or more).
Power in my area costs $0.14-$0.35 per kWh depending on monthly volume, it averages out to around $0.25 per kWh in my case. Based on this amount, a reduction of 150W will lower my energy bill by $27.75 per month. If you use your computer for only 8 hours a day, rather than 24, it's still a savings of $9 per month, in addition to the noise benefits.
The computer I built will cost about $350-400 more than a system built for cost savings, without regard to efficiency; the total system cost for this build is $1060.00 for the tower (not including keyboard, mouse, LCD, etc.)
I spent about 30 minutes providing a detailed description of the components used, and why they were chosen; if you're truely interested, there is a forum dedicated to the creation of quiet computers,
http://www.silentpcreview.com
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CPU:
The Xeon L3110 is a bit of an exotic LGA775 chip, it provides the performance of a Core2 Duo E8400, but generates a maximum heat TDP of only 45W instead of 65W (E8400); it runs 45% cooler with the same performance ratings. In addition, Xeon chips are select picked from the assembly line, and use less power. Each Xeon is different, but the power requirement on my L3110 is 0.3V (about 1/3rd) lower than an average E8400 chip, again, with the same performance. The CPU generates 45% less heat, and uses 33% less power; the cost of an L3110 is approximately double that of an E8400, about $150 more, and it isn't officially supported by Intel for use on the G41 (although it does work). Like most modern CPU's, the Xeon L3110 also features Speed Step, which allows the chip to change it's speed in real time to save on power, when it isn't fully being utilized.
Video Card:
This is one of the largest power uses in the system, the HD 5750 uses 16W at idle, and 86W under load; it's a midrange model, but while the next model up offers 8% faster performance, it also draws 20% more power. Most gaming can be handled by a modern single slot card, instead of SLI which requires two cards, doubling the performance, but also the power use, and generated heat. The HD 5750 supports directX 11, eyefinity (3 monitors), and allows the system to handle most new games. It won't offer the performance of an SLI configuration, but it will allow you to play the games with respectable levels of performance, while using a fraction of the power, and generating a fraction of the heat. The Vapor-X version of the Sapphire HD 5750 costs more, but uses a quieter and more efficient cooling system. The fan is larger than most HD 5750 cards, which means it can spin slower while pushing more air; it is modified to spin at 20% of its factory rating, but will increase in RPM if the video card gets too hot. The Vapor-X model costs about $35-50 more than a regular HD 5750, but is better built (solid capacitors), quieter, and has a better cooling system.
Motherboard:
The motherboard chosen features two Asus technologies; an EPU (Energy Processing Unit), and Q-fan; the EPU monitors system loading and automatically moderates power in real time. It controls power being supplied to the CPU, video card, hard drives, and fans. The Q-fan automatically adjusts fan speed depending on CPU core and system temperature. The hotter these components get, the more power is supplied to the fan, increasing its cooling ability (but also rpm, and therefore noise). Because only a single video card is being used, a smaller micro-ATX motherboard can be selected, reducing energy use, and allowing the use of a smaller case. The motherboard also has solid capacitors, increasing reliability over time.
Power Supply:
Power supplies have efficiency ratings, in addition to capacity ratings; the power supply being used is "80 plus bronze certified", which means it will deliver at least 82% power efficiency at 20% capacity, and 85% or more efficiency at 50% capacity. Most power supplies are less efficient at 20-50% load, which is where your computer spends most of its time. Some bargain units will produce 60% or less efficiency, on a power draw of 250w a loss of 40% efficiency (lost to heat) is significant. The M12 also features circuitry designed to clean up the power being supplied to the computer, which helps the system run more efficiently, is modular, which means you only install the cables you require, which increases airflow inside of the case, for better cooling, and is known as one of the quietest power supplies you can purchase. The cost for this power supply is around $90, versus a bargain unit at $20 (or perhaps free with a computer case). Within a few months, the power supply will pay for itself due to its increased efficiency.
Case:
The Antec mini-P180 is a case designed for quiet computing; it has layers of insulation built into the side panels, has extensive use of rubber and silicone bushings to eliminate vibrations, and features an unusual layout which places high heat components (such as the power supply), inside of a separate thermal chamber. The power supply chamber has its own air intake and exhaust areas, keeping it separate from the rest of the heat sensitive areas (video card, northbridge, and CPU). The mini P-180 also has a custom designed 200mm fan by Antec - larger fans can move more air while spinning at slower speeds, which makes them quieter.
This case has been modified to remove some internal structure that I wasn't using, to improve airflow, and some fans which weren't required were removed. I used a smoke machine to determine how to setup the airflow, and ended up blocking off some air intake ports while increasing airflow to others. The video card has its own air intake source, and exits generated heat out of the back of the case. The rest of the components are cooled by the 200mm top fan, which pulls air from the front panel of the case, and exhausts it from the top. The heatsinks were changed from the stock units, so that their blades are oriented vertically, allowing maximum cooling from the 200mm top fan. The northbridge heat sink and Scythe heatsink are rotated 90 degrees for this reason, this increases cooling efficiency by around 15% - better cooling efficiency means the fan speed can be reduced, saving power, and lowering noise.
The fan is normally speed controlled by a switch mounted to the back of the case, it has a high, medium, and low rating, and a built-in voltage control. Based on the position of this switch, the fan motor is supplied with 5V, 8V, or 12V of power, resulting in different speeds, and different levels of noise. The faster than fan spins, the louder it is, but the more cooling it can provide. I modified the voltage control on the fan motor to only supply 5V all of the time. In addition, I changed the connector from a molex 12V connector to a 3-pin connector for attachment to the motherboard header, which allows the motherboard to control the fan speed to even lower amounts. This fan is the primary cooling fan for the entire computer, it is controlled by a software program called 'Speed Fan' - this monitors the temperature of each core in the CPU, as well as the northbridge temperature, and if the levels of these components get too high, it will increase the speed of the 200mm fan automatically. With these changes the system is much quieter, and can be left unattended; also, because of the ducting, and large heatsinks, a single large fan can provide cooling for the entire system. Less fans means less noise, and lower power usage. All cabling inside of the case is also 'tucked' out of the airflow, to increase cooling. Because many of the cables are modular, only cables which are required are installed. Compared to systems from 10 years ago, there are far less cables in modern systems, and even fewer cables in systems designed with modular power supplies. In the above pictures, few cables are visible, and all cables have been tucked.
Purchasing and modifying this case will cost about $80 more than a case chosen just for being inexpensive, and will take some minor electrical familiarity (soldering and voltmeter usage), as well as time.
Hard Drives:
The Western Digital Green Edition 750GB SATA2 harddrives offer good performance, and use less power than comparable models. They are also some of the quietest drives which can be purchased. There are two versions, one slightly more expensive, but with higher cache, for increased performance. These are the higher cache 7200rpm models. They're installed in Luxurae drive cages, which have 1/2" of sound deadening foam all around the drive, as well as large aluminum finned heatsinks to pull heat away from the drives. Because of the sound deadening, the aluminum headsinks don't provide any heat advantage, but they even out the heatsoak caused by the foam. The hard drives are mounted in the lower thermal zone, seperate from the motherboard/CPU, etc., and are cooled by the fan built into the power supply, which has been designed to pull air from inside of the case, and exhaust it out of the back. Because the power supply is mounted on the bottom, it is turned upside down, to provide airflow to its 120mm fan (which changes speed based on temperature inside of this thermal zone; the hotter it gets, the faster it spins).
The hard drives are priced comparably to most other models, and offer similar performance. The Luxurae drive silencing cages are approximately $35/ea, for an increased cost of $70.
All motors are horizontal in this system, this includes the fan inside of the power supply, the 200mm exhaust fan, the Vapor-X cooling fan, and the two hard drive motors. This prolongs the bearing life, which means increased efficiency, and reduced noise, over the life of the components.
