How does herms work?

[HopOnHops]

So I've been looking into rims and herms. Rims is pretty simple because it's direct heat contact. I'm not quite sure how herms is supposed to control the temperature. Do you just fill up the hlt with hot water and adjust that temperature to raise your mash temps?

 

[Monster Mash]

Basically yes. I use it to mash out so I set my HLT to 174 and the wort enters the mash tun @170. It takes about 35 minutes to raise my 30 gallon mash tun from 155 to 168. When I sparge I run my hot liquor through the HERMS to clean it.

 

[jasonsbeer]

You basically have it correct-

Most HERMS systems work by running wort during mash through a copper heat exchanger in your hot liquor tank. The heat exchanger is a lot like an immersion chiller mounted inside the HLT. You pump the wort through the heat exchanger - the water temp in the HLT controls the wort temperature.

There a number of RIM vs HERMS and HERMS build threads. A quick search will yield a lot of info.

https://www.homebrewtalk.com/wiki/index.php/Recirculating_mash_systems

 

[audger]

The reason people choose HERMS over RIMS is usually to get the heating element out of direct contact with the wort. instead of heating the wort directly, you pump the wort thru a coil that sits in a hot water bath. the reason HERMS is usually thought of as more 'involved' is because the hot water bath isnt as quick at transfering heat, so there is some 'finess' involved in controlling the temperature. you dont instantly see the temp of the wort rise when you turn the heater on, nor does the temperature instantly stop rising when you turn the heater off.

HERMS doesnt have to be in the HLT, most people just use the HLT as a HERMS tank because it cuts down on number of parts needed. having a HERMS with that much water in it though (usually 5-10 gallons) makes it slower to respond to temp changes than a smaller seperate tank, assuming similarly sized heating elements.