Integrated Assessment of Usability of Cooling Systems

Version 4 (amended and enlarged), Autumn-Winter 2006

Detailed descriptions of cooling systems, thorough analyses of their functionality and usability, test results, etc — they are certainly useful and necessary. But having read hundreds of pages of various reviews and having examined lots of images, a user may fail to find a clear answer to his/her vital question: "Which cooler should I buy after all?".

Indeed, a common drawback of the absolute majority of reviews devoted to cooling systems (including our articles, we may as well confess) is an evident lack of unified integrated assessment of functionality and quality of these systems, which would allow to organize all usability parameters and generate informative comparative characteristics of coolers to be clear even to inexperienced users. Of course, you may sometimes run across articles with some charts or ratings. But how these ratings are formed and what objective (subjective) parameters are taken into account — these details are usually a sealed book and known only to the authors. When such "charts" award dubious products, while decent models are left in the bottom of the list, inadaptability of this or that abridged approach to assessing functionality of cooling systems becomes evident.

We couldn't put up with this situation for long. We mustered all our strength and formulated our own procedure for integrated assessment of cooling systems. It is not perfect, of course. But in our opinion, it reflects the real image of a cooler rather objectively.

OK, let's proceed to the essence of our procedure.

In our opinion, any cooling system has seven key characteristics to be evaluated. They are:

1. Thermal efficiency (we actually use the inverse — thermal resistance θ_ja)
2. Noise level
3. Usability of active components (fans, centrifugal pumps in water coolers, etc) — technical characteristics, their functionality and reliability
4. Usability of a retention module — installation convenience, workability of a retention module, its reliability and compliance with standard requirements
5. Usability of passive components (heatsinks, pipes, thermal interfaces, etc) — technical parameters, technological perfection, reliability
6. Professional fitness — thermal efficiency for groups of processors a given cooling system is designed for
7. Price efficiency — price of a cooling system and its earthliness in modern economic realia

Besides, there are two bonus categories:

1. Technical level of a cooling system (thermal control circuits, fan stop alarm, adjustable power adapters, protective devices, etc)
2. Bundle (thermal interfaces, power adapters, guides and manuals, accessories)

We also introduce a system of penalties for cooling systems that reveal low quality of their components, insufficient professional fitness or insufficient ergonomics.

To objectificate all these assessments, each of them, except for a professional fitness group, gets a corresponding index, calculated (defined) in accordance with established procedure.

That's how these indices are added:

Thermal efficiency

E_t = (WF*R_ti)/TR (points), where

E_t — thermal efficiency index, WF — weight factor, R_ti — reference thermal index (reference thermal resistance θ_ja), TR — thermal resistance θ_ja of a given cooling system.

Reference thermal resistance is: 0.30°C/W for coolers for AMD Socket 754/939/AM2 and 0.25°C/W for Intel LGA775 devices (these are the best results considering modern technological capacity for mass production). Weight factor is 90.

Noise

N = (WF*R_n)/NL (points), where

N — noise index, WF — weight factor, R_n — reference noise index, NL — noise level of a cooling system.

The reference noise level is 25 dBA (a typical background noise level in a living accommodation at night). Weight factor is 180.

Usability of active components (U AC) and usability of a retention module (U RM)

Unsatisfactory — 0 points
Satisfactory — 10 points
Good — 20 points
No gripes — 30 points

There can be intermediate scores. For example, 29 points can be interpreted as "this fan is of excellent quality, but colors of its wires are too dull (the retention module is wonderful, but its mirror surface does not reflect user's face well enough)". One point — "the fan is of terrible quality, but it still can clatter along for several hours (the retention module actually damages a CPU core only during the second unsuccessful attempt to install a cooler)".

Usability of passive components (U PC)

Unsatisfactory — 0 points
Satisfactory — 10 points
Good — 20 points
No gripes — 30 points

There can be intermediate scores.

Professional fitness level

A level of professional fitness is expressed by belonging to a "professional fitness group" (PFG) that includes certain types of processors, ranked by TDP.

We define the following PFGs for AMD (Socket 754, Socket 939, Socket AM2):

Professional Fitness Group	Types of processors
"A" (TDP < 65W)	all AMD Semprons for Socket 754/939/AM2 AMD Athlon 64 3200+ Socket 754/939 AMD Athlon 64 3800+ Socket AM2 AMD Athlon 64 X2 4600+ Socket AM2
"B" (TDP < 90W)	all AMD Semprons for Socket 754/939/AM2 AMD Athlon 64 3700+ Socket 754 AMD Athlon 64 4000+ Socket 939/AM2 AMD Athlon 64 X2 4200+ Socket 939 AMD Athlon 64 X2 5000+ Socket AM2
"C" (TDP < 110W)	all AMD Semprons for Socket 754/939/AM2 all AMD Athlons 64 Socket 754/939/AM2 all Athlons 64 X2 Socket 939/AM2 AMD Athlon 64 FX-60
"D" (TDP < 130W)	all existing AMD processors for Socket 754/939/AM2

The following PFGs are defined for Intel LGA775:

Professional Fitness Group	Types of processors
"A" (TDP < 65W)	all models of Intel Core 2 Duo
"B" (TDP < 85W)	all models of Intel Core 2 Duo Intel Core 2 Extreme X6800 all models of Intel Celeron (Prescott, Cedar Mill) Intel Pentium 4 551 Intel Pentium 4 661
"C" (TDP < 115W)	all models of Intel Core 2 Duo/Extreme all Intel Celerons all models of Intel Pentium 4 Intel Pentium D 820 Intel Pentium D 930
"D" (TDP < 130W)	all existing processors from Intel, including Intel Pentium D 840 XE Intel Pentium D 965 XE

Professional fitness group of a processor is determined like this:

T_d =< 85°C, where T_d = 40+(P_h*Θ_ja), T_d — temperature of a CPU core, P_h — maximum thermal capacity of a processor, Θ_ja — full thermal resistance of a cooling system.

This condition arises from an empiric capacity of a processor to operate at a technically admissible temperature of a core (< 85°C) in hardcore thermal conditions inside a PC case (40°C and lower).

Price efficiency

E_p = (WF*R_p)/P (points), where

E_p — price efficiency index, WF — weight factor, R_p — reference price, P — average retail price of a cooling system.

Reference price of a cooling system for AMD:
5 USD — forced air cooling systems (that is usual coolers), of PFG A, 7 USD — coolers that belong to PFG B, 13 USD — coolers that belong to PFG C, 19 USD — PFG D coolers, 40 USD — water coolers. Weight factor is 100.

Reference price of a cooling system for Intel:
5 USD — PFG A coolers, 7 USD — PFG B coolers, 12 USD — PFG C coolers, 17 USD — PFG D coolers, 40 USD — water coolers. Weight factor is 100.

Bonus

Professional Fitness Group C (AMD) — 25 points
Professional Fitness Group D (AMD) — 35 points
Professional Fitness Group C (Intel) — 20 points
Professional Fitness Group D (Intel) — 30 points
Correct thermal control — 5 points
Preinstalled thermal interface — 10 points
Power adapter (adjustable) — 10 points
PWM — 10 points
Bundled thermal compound — 5 points
Bundled mounting accessories — 5 points
Localized guide — 5 points
Misc — 3 points

Penalties

Thermal efficiency below PFG A — IAF CS is reduced by 10%
50 dBA noise and higher (but still less than 60 dBA) — IAF CS is reduced by 25%
60 dBA noise and higher — IAF CS is reduced by 50%
Low quality of passive components — no bonuses, IAF CS is reduced by 25%
Low quality of active components — no bonuses, IAF CS is reduced by 15%
Low quality of a retention module — no bonuses, IAF CS is reduced by 35%

All indices and bonuses are given to cooling systems according to their test results and published in a technical-economical chart. The sum of all indices and bonuses (after penalties, if there are any) gives us the integrated assessment of usability of a cooling system (IAU CS). If we don't take price efficiency (attractiveness) into account (for example, to evaluate pure functionality of a cooler), then we should calculate the integrated assessment of functionality of a cooling system (IAF CS). Then we sort IAU CS and IAF CS results to form a table of ranks — technical-economical and usability ratings of cooling systems.

That's about all. We hope that our procedure will help our readers solve a problem of choosing a cooling system to meet their requirements to quality and functionality. In conclusion we'd like to say that your constructive comments and suggestions are welcome!