Heat requirement for insulated container?

[Glenmont]

I expect this is a fairly mundane question for you folks, but it is way out of my field of expertise...

Background: I'm installing a small NAS file server in a building without heat...Winter minimum temperature inside the building will likely be near 0°F. The device requires a minimum operating environment of 45°F, so I need a rise of 45°.

The little NAS device will be housed inside an insulated plastic picnic cooler with an internal volume of 0.5 cubic feet and with 300 square inches of outside surface area. Based upon physical dimensions, I'll assume the cooler is insulated on all sides and top and bottom with a 1/2" thickness of expanded polystyrene. Air infiltration into the cooler is low enough to be ignored.

OK, now for the question: how many watts of heat will be needed to yield the 45° rise over ambient?
[I'm guessing this thing will be thermally efficient given the low volume...I'm guessing it will need less than 20 watts, perhaps much less. (also, during idle mode, the NAS itself uses 7 watts of electricity which will contribute to the heating of the container).

Have I left out any details necessary for a scientific calculation? (Or, for a wild-ass guess!). Sorry for the lack of metric measurements...

BTW, the heater will be a DIY thing using power resistors and a solid-state thermostat.

Thanks-

Karl

 

[MintJulep]

Q = UA[Δ]T

Q = heat loss

U = Conductivity (or conductance - I can never remember) - the reciprocal of R-factor.

http://en.wikipedia.org/wiki/R-value_(insulation)

A = total surface area.

[Δ]T = temperature difference

Watch the units.

 

[ivymike]

my NAS would likely overheat in a box like the one you describe, even with 0F ambient... might want to run a simple experiment first (find a cold place and put your NAS in it with a thermometer, and see how high the temp gets). How hot will your unheated building get between visits (might it also get to 45F outside while you're gone, allowing the NAS to reach 150F in the box and roast itself?)

 

[chicopee]

If you know the heat generated from the NAS file server then you can figure out the [δ]T from MintJulep's second equation. The trick is to determine UA from that well insulated plastic picnic cooler.

 

[Glenmont]

The heater will be thermostatically-controlled, and there will also be a thermostatically-controlled fan, using air ducted from outside the building to prevent Summer over-heating. The interior of the building runs at least 20°F above outdoor ambient on a sunny Summer afternoon.

It sounds like perhaps the fan may cycle on even during the Winter as well...

My heater design uses power resistors (wired in parallel), with each resistor yielding 6 watts. I had planned on using three of them (18 watts, on heatsink), but one or two may be enough, from what I'm hearing. The building temperature can potentially get down to -20°F, but that is typically only for a couple of days every-other year or so.

I don't have the NAS yet (Netgear RND2150 with two drives), so empirical testing is on hold.

Any other suggestion are welcomed. It sounds like emphasis should now be on cooling rather than heating...I'm planning on using a short run of 3" PVC pipe for the duct from outdoors, using a 100cfm case fan to pull the cooler air into the cooler.

 

[IRstuff]

There seems to be a discrepancy between your stated requirement and the product data info:

http://www.netgear.com/Products/Storage/ReadyNASDuo/RND2150.aspx?detail=Specifications

which states 0°F - 95°F.

Given that, even the -20°F environment is probably a non-issue. The only thing you might need is an external container with some sort of airflow control to recirculate the fan air until the system warms up. Most electronics will start up at -20°F; they just might not meet their performance specifications, until they warm up, so a simple, brute-force solution is to power up the system and reboot when it's warmed up.

The power specification of the server is just about what's required to maintain a 45°F delta with still air convection at 2.5 W/m^2-K. Therefore, a simple air gap enclosure with the aforementioned fan flow diversion should be all that's required.

TTFN

FAQ731-376

 

[Glenmont]

Thanks. The 45° figure came from a vendor of that NAS, not from Netgear...maybe a problem with conversion...

It's looking like I can ditch the heater entirely.

 

[Glenmont]

This is interesting: that NAS ships with a Seagate ST3500320AS drive. Seagate lists minimum operating temp. to be 32°F.

Netgear must be allowing for the retained heat within the NAS case to provide the 32°F...sort of like what the present discussion has centered on, actually.

 

[rmw]

Chicopee, nice touch with the use of the 'delta' symbol.

VPL-see how far your influence reaches?

rmw

 

[MintJulep]

Hey!

I used the proper capital Delta for a discrete difference. The baby delta is for infinitesimal differences.