Thermal Mass of 10 gal Rubbermaid Cooler

Does anyone know the thermal mass of a 10 gallon Rubbermaid cooler that i can plug into my brewing software. I have always preheated and used a 0 value, but I'd like to cut out that step. Based on some searching, I've found 1.55 lb, but I didn't see how that was calculated. Anyone have a more proven number?

bump... wow... 45 views and nothin' huh...

Does anyone know how to calculate this?

I don't know that value. I just know that in any weather from 30F up to 100F the temperature loss during a one hour mash is less that one degree F. I even did a 75 minute mash once and it just dropped one degree. Sorry to not help more, but I don't know how to calculate thermal mass.

From the Promash message board...

"You can calculate this yourself using ProMash.

1. Go into ProMash and open the Strike Temp calculator.

2. For Mash Tun Thermal Mass, Enter 0.

3. For Total Grain enter 0.00001 pounds. (It won't let you go any smaller - entering 0 will give you a division error.) This should make your water:grain ratio 120000:1.

4. For Total Water, enter 16.00 quarts.

5. For Desired Strike Temp, enter 170. (You can use any temperature but this will more accurately reflect actual mash temperatures.)

6. For Grain Temp, enter the current room temperature.

7. Heat 16 quarts (4 gallons) of water to 170 degrees and pour it quickly into the mash tun. Close the lid and seal it up, and let it sit for about 5 minutes.

8. Measure the temperature of the water in the mash tun.

9. Enter the temperature of the water in the mash tun in the "Desired Strike Temp" field in ProMash.

10. Now look at the "Initial Strike Water Temp Should Be" window. You will note that, with Thermal Mass set to 0, this number will be the same as the "Desired Strike Temp" field.

11. Now, in small (say 0.1 or smaller) increments, increase the Thermal Mass field until the "Initial Strike Water" field reads 170 (or whatever temperature you started with, if you didn't use 170 for some reason.).

12. Ta-da! Whatever the Thermal Mass field says is your mash tun's thermal mass!

The values that come default in Beersmith for a 10 gallon Igloo/Gott cooler are:

Weight: 9 lbs
Specific heat: 0.300

Thanks folks... I'll have to try the ProMash approach... I think BeerAlchemy has something similar...

Beer Alchemy does... I ran through this exercise tonight. After a quick wash/rinse with hot tap water, I added 5gal of 164 deg water to my tun (with the screen and tubing, also rinsed) it dropped the water temperature to 157 which came out to a thermal mass of 3.5lbs.
I think that the thing to remember is that this needs to be dialed into your rig and process. Its not just enough to take somebodies word for it, you should follow a consistent routine and take your own measurements.

Thanks for doing this, I have the same mash tun.

The units on thermal mass are energy/degree so in this case it would be 3.55 Btu/degree F

The heat lost by the water :

Qwloss=41.7lbswater*1 Btu/lbm/degree F*(164-157)degreeF=292 Btu

The heat gained by the mash tun is equal to the heat lost by the water (assuming no heat loss to the air) :

Qmlt=[m*Cp]mlt*(temp change of the mlt)=292 Btu

where [m*Cp]mlt is the thermal mass of the mash tun, which represents the mass of the mash tun [m] involved multiplied by the heat capacity of the mash tun involved [Cp]. Involved implies that only a fraction of the total mass of the mash tun actually absorbs heat in the short term.

To get 3.55 your mlt was assumed to be at 75F

[m*CP]mlt=292 Btu/(157-75)=3.55 Btu/degree F

I find this number helpful in predicting my sparge water temperature to hit a 168F batch sparge temp in the mash tun.