RIMS tube with brew commander

[erikn68]

I am wondering for people that uses a rims tube, do you keep the valve fully open or adjust the speed. I am wondering since I don't want my element to scorch the tube by getting it to hot. With the brew commander, I can adjust the percent of the heat that will be on to heat the wort coming through the tube from my pump. I am thinking at 20%. Please let me know.

 

[Whisky River]

I do not have a RIMS system so I may be wrong, however I think most people use a valve to control the rate of flow very carefully. I believe the calculation to ensure you do not scorch your wort depends on knowing the flow rate accurately, knowing the heating element wattage and the percentage of power delivered to the element. The percentage that you mentioned does not tell the whole story unless the wattage of the element is also known.
I am certain that others who know more about operating a RIMS system will comment soon with their experience to help you out.

 

[doug293cz]

You need to balance the heat input (element power) with the heat removal from the RIMS tube. If the heat input and output are not in balance, the exiting wort will either increase or decrease in temperature until the two powers are again in balance. Some heat will be lost from the RIMS tube by heating the air around it, just like you lose heat from your mash vessel to the air around it. But most of the heat is removed by the heat transferred to the wort flowing thru the tube. The amount of heat transferred to the wort is proportional to the mass flow rate times the temperature difference between the incoming and outgoing wort. At a constant input power, doubling the flow rate will cut the temp rise of the wort going thru the tube in half, and vice-versa. Likewise doubling the power input will roughly double the temp rise of the wort flowing thru the tube, if the flow rate remains constant. Power input and flow rate are the two variables you can adjust to control the temp rise of the wort between the RIMS input and output.

The thing to focus on is the temperature of the wort at the exit end of the heating element, as this is where it will be the hottest, and you want to limit the temp at that point to avoid denaturing the enzymes too quickly during your mash. You should try to limit this temp to ~5°F above your target mash temp. To do this properly the temp probe that is used to control the element power needs to be placed as close to the exit end of the element as possible. Putting the controlling temp probe in the bulk of the mash is a recipe for disaster. You should have a way to measure the mash temp (using a separate temp probe), so you know how much higher the controller set point needs to be in order to maintain the desired mash temp - there will be a few degrees of offset between the temp of the wort exiting the RIMS and the bulk mash, and you need to know what this delta is for your system. The faster the flow rate, the lower the delta will be. For this reason most brewers run the RIMS flow as fast as they can, without compacting the grain bed and getting a stuck mash. Often this means starting at a low flow rate and increasing as the mash viscosity drops after the start of the mash.

As already mentioned, 20% is a meaningless number without knowing the maximum power available from your element.

Brew on

 

[erikn68]

My element from brewhardware.com is 1550 watts at the max, and a 18 inch tube. On my brewcommander pid, I can adjust the power percent.

 

[Bobby_M]

My strategy would be to dial the max power down a 10 percent at a time until you find that it will no longer maintain the temp set point, then go back up a bit until it does.

Also get into your advanced options menu and set the cycle time to the lowest number.. I think it's 1 second.

 

[doug293cz]

My strategy would be to dial the max power down a 10 percent at a time until you find that it will no longer maintain the temp set point, then go back up a bit until it does.

This is a good strategy for figuring how much power you need to maintain mash temps. But if you want to increase the temp for a higher temp rest or mash-out, you will need to use a higher power setting. It takes 1 BTU to raise 1 lb of water 1°F, and 1 gal of water weighs 8.33 lb, so each gal needs 8.33 BTU to increase 1°F. If you want to raise a gal 1°F in 1 minute, then you need a power input of 8.33 BTU/min. 1 BTU/min is equal to 17.584 W, so to heat 1 gal 1°F in one minute you need to supply power of 8.33 * 17.584 = 148.7 W. Let's round that up to 150 W-min/gal.

So, to determine the watts of power you need, in addition to amount of power required to maintain a constant temperature, for a desired ramp rate in °F/min, you use the following equation:

Additional power = Gal of wort * ramp rate [°F/min] * 150 W-min/°F-gal​

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You will need more power than this because you are heating more than just the wort. You are also heating the grain and the mash vessel.

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Brew on

 

[Bobby_M]

This also gets to the topic of how hot you'd allow any system to heat the wort in an effort to ramp the total mash upwards. In other words, if you want to move your mash from 150 to 158F, setting the RIMS output temp to 158F will essentially never get the mash up to 158F. At the very least you'll need to set to 160F to allow for a heat loss offset but even that will take hours.

Since the wort only stays that hot from the time it takes to get from the tube to surface of the mash, I'm relatively confident +10 to +15 is reasonable. So, say you set the RIMS output temp to 175F. **

In that case, my proposition still stands. Go ahead and set the 175F target on the controller and use whatever minimum power output you can get away with to have it consistently output 175F. In the case of a 1650 watt element that's likely going to be 100% when the delta is 25F (at least initially).


** People will often balk at heating mash wort "over mash out temps" in RIMS, etc but it's misplaced concern because all heated mash systems do this. The surface temps of a steam heated mash tun, or the bottom surface of a direct fired mash tun are WAY hotter than mashout temps. Denaturing is time x temperature.