strike water temperature with false bottom

[hennja2]

I've got a new polar ware mash tun with false bottom. I've always used a cooler before.

There is 2.5 gallons of water under the false bottom that is making my strike water temp tough to figure out. 10 gallon batch and a batch sparge technique, 20 lbs of grain, 1.5 qt/pound mash thickness. How do I account for the 2.5 gallons under the screen? I add my normal 7.5 gallons of water at 165degrees, my grain might not all get wet. If I add 10 gallons of water at 165 degrees I think I might overshoot my mash temp. Any help would be appreciated.

 

[mblanks2]

Are you using software? If so the portion of that 2.5 gallons that will not drain out of the mash tun is dead space and needs to entered into your equipment profile.

 

[hennja2]

The water will eventually reach my boil kettle, it just doesn't come into contact with the grain at the initial mash in. I'm just trying to hit my target mash in temperature.

 

[nukebrewer]

The water will eventually reach my boil kettle, it just doesn't come into contact with the grain at the initial mash in. I'm just trying to hit my target mash in temperature.

The dead space will still factor into the temperature calculation because it is part of the system. The equation calculating strike temp is:

Ts = (.2/r)(Tm-Tg)+Tm

Where: Ts = Strike temp
r = water/grain ratio (qt/lb)
Tm = Desired mash temp
Tg = temp of grain prior to mash in

 

[Grannyknot]

Try this calculator....http://www.brew365.com/mash_sparge_water_calculator.php

Just my opinion, but 2.5gallons of equipment loss is TOO much for a typical home brew set-up.
I assume its one of those flat mesh false bottoms that sits on stilts just above the valve...never was a fan.