Heat Duty Requirement

With what is the container insulated, and at what thickness?

No insulation, steel only

I would need to know in what period of time you wish to heat the container up in? and are you insulating the container.

You could put a 3kw heater in a container and it would eventually get up to 65F depending on the insulation.

Any information, please come back to me at andy@cds-concrete.com

Best Regards

Andy Hall

In steady state the resistance of the steel to heat flow is negligible, and it's limited by convection heat flow from inside air to inside of box in series with outside of box to outside air. Steel wall is at average temperature so ΔT for both is 37.5°F.

To estimate heat flow, take analogy of domestic radiator, which outputs ~ 1 kW/m² with hot water at 180°F and room 70°F ie ΔT 110°F. Heat flow by natural convection varies as ΔT^1.25, (might be something like forced convection inside, but it's near enough for an estimate).

So heat flow = (37.5/110)^1.25*1 kW/m² = 0.26 kW/m². Taking total area for a bit of safety (heat loss lower from top and bottom) = 448 ft² = 42 m² giving 10.8 kW.

You could add a margin if you want, for safety and warm-up from cold.

Cheers.......Codey

This looks very close to another sources calculation of 9.86 Kw (Ruffneck Heater Mfg.). I currently have a convective 3 Kw in there and can only get about a 25 degree F delta. The heater has 2 fin/tube radiant heater elements, each abot 3 feet long, 1.5 inch diameter, with square Al fins 4 inch square. Not sure what temp. it is at for setpoint.

Question: If I put forced air over these elements, can I improve the 25 degree delta? Right now they just sit there, purely convective.

No, presumably you have the thermostat (if it has one) turned right up so it's on continuously. In that case it's putting out 3kW and forcing air over it won't increase this.

Codey

dsdynamics,

This application saddens me, because of lousy energy efficiency. Any way you can add a second skin or add insulation will greatly improve the efficiency and utility of your cabinet. This is true, even if only to some surfaces, such as back, sides, and top.

Which is more expensive--adding insulation once or adding energy all the time? At $0.07 per kWh, with a heat loss decreased to 1/3 by insulating back sides and top, you are saving about 6-7kWh per hour or approximately $11.00 per day. How long will the payback be compared to a larger circuit, a new heater, and the daily energy bill?

Regards--JMM

Nobody asked what is stored inside? Oil - water - sand - explosive powder or???

This is good question, but perhaps not germaine? I am very restricted