SunRay Update 8

Following some of my previous calculations on power efficiency, carbon footprints and comments about heat/noise differences between Sunrays and PC’s; I mused we could factor in a ‘system’ we all know well – ourselves.

Heating in has become redundant in PC labs, with the computers becoming increasingly powerful and dispersing more and more heat, labs are designed with cooling as a priority.

So, as you might expect, Sunrays are changing the way we are (or should) looking at labs. If we take an average lab with two dozen PC’s, it’s easy to guess what is generating the most heat. But would you have guessed in a Sunray lab, the answer is the users!

In order to keep this as simplified as possible, various assumptions have been made; such that these figures are theoretical within a closed system, people are ‘average’ (including fitness, health and calorie intake), environment is ‘average’ and a whole flurry of other ‘ideal situations’.

Statistical assumptions:
1 watt = 3.413 Btu/h
Average person = 58.2 w/m2 (1 met)

British Thermal Unit (BTU): “A BTU is defined as the amount of heat required to raise the temperature of one pound of liquid water by one degree from 60° to 61°Fahrenheit at a constant pressure of one atmosphere.”
Initially we calculation the surface area from our person, I’ll use DuBois’ formula:

BSA = (W 0.425 x H 0.725) x 0.007184

(Weight is in kilograms and the height is in centimetres).
Thus we take our candidate standing at 60Kg and 170cm. Resulting in 1.7m2 surface area of the integumentary system – the skin.
Due to the dynamics of our ‘warmblooded’ organisms, our heat loss is dependant on our metabolic rate. Essentially the ability to generate heat is a result of our muscular activity, which could be considered as a by product of work (force x distance).
So at rest, we can assume our ‘average’ person produces per hour:
58.2 x 1.7 = 99 watts = 338 btu/h.
Each Sunray (including TFT monitor) consumes 41 W.
41 x 3.413 = 140 btu/h

Each PC (including TFT monitor) consumes 105 W.
105 x 3.413 = 358 btu/h


So if you are budgeting for cooling labs, you might consider getting over 2.5 Sunrays to every 1 PC. However, you might need to use this saving in the winter to heat the cold labs! Otherwise, fill the room full of people – the cheapest way to heat a room!

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