Help with Thermostar Controller

I just got a new thermostar digital controller from Midwest. I have it running through my freezer that I am going to use as a fermentation chamber. I have the set point at 66°. The ambient temperature is fluctuating from 68.1 to 63. This is unacceptable. Can anybody offer any advice? Would like to keep it within 1 or 2 degrees of set temp.

With a two degree margin of error, a setting of 66F will vary from 64-68. My understanding is that 2FZ is the normal margin. The idea is that smaller margins will lead to excessive cycling of the compressor.

You can trust me to know all about this, as I've my controller for more than a week now!

Check out the settings in the controller for the differential. I have one as well, and it came from the factory with the hysteresis preset at 3.7 degrees (If I remember correctly). You can turn it down to 1 or 2 to solve that problem. Since I reset the hysteresis I have had nothing but success with the Thermostar. It should be in the manual for how to adjust the differential/hysteresis.

I forgot to also mention that there is a setting on the Thermostar which you can manipulate to keep the freezer compressor from cycling too much, I have mine set at 4 minutes. So everytime the controller turns off the freezer, this setting dictates how soon the Thermostar can turn on again. This will help the longevity of your freezer. Hope this helps.

My short take:

Air temperature will fluctuate much more than wort temperature, and the air in your freezer will continue to cool once the compressor turns off (walls are still much colder than air for a whiles after compressor shuts off), hence the fluctuations you see in an empty freezer. This swing will be mitigated with a bunch of wort in the freezer, but you will still get the impression of overshooting.

Measuring ambient air temperature has its issues that I do not have time to get into detail about, but I suggest taping the probe to the actively fermenting carboy to get a closer representation of wort temperature, and to let the freezer better react to rapid heat generation during vigorous fermentation. Here are a couple threads that may have some info on placement of probe, if you are interested:

Taping Probe to Carboy Discussion

Probe Placement Discussion

Taping to Carboy vs. Thermowell Experiment

In terms of what you can do with your controller. I have one of these units and no longer use it (I use STC-1000+ controllers), but am familiar with them. I believe you set the temp setpoint (SP) and hysteresis (HY), the freezer is kicked on at SP+HY, kicks off at SP. So you must have a 66 SP and 2 HY. You can reduce the HY to 0.5-1.0F and see if that helps.

Here is my suggested use of the controller. Let's assume you have an ale and want to control around 66F. I would tape the probe to the carboy with a small piece of insulation over it and set the controller to 64F with a 1F hysteresis. Your freezer will kick on once the probe reads 65F, kick off at 64F. A lot of empirical evidence from folks online seems to indicate that the probe taped to the side of the carboy tracks the internal wort temperature within a carboy to 1F. My experience is similar, which is why I always set my controllers to kick the freezer on 1F below my goal. I err on the side of coolness.

Maybe my rambling helps. Hopefully, but if not, cheers anyways.

Once I change the HY, do I need to lock the advanced settings or leave them unlocked. I have my probe taped to the side of a milk jug full of water. When I went out to check it, it read 62. I have it set on 66 with a HY of 1. Want to get the temp fairly steady before I put and wort in there.

Thanks to everyone for the replies.

Wardens355,
Thanks for the links to the discussions of probe placement. Having read them, I am convinced that probe in the air is the best way to go, as it will produce the least wide swings of ambient air temps. The less the air swings, the less the wort swings, and I think that is the important goal.

Monitoring the air won't detect swings in wort temp caused by fermentation. The solution to that is to set your ambient temp lower for the active portion of the fermentation cycle, and then to slowly ramp the ambient temps up as fermentation activity declines.

I can see advantages and disadvantages to the various monitoring methods, but I think if wort stability is the goal, then ambient stability is the answer. If those temps go up and down in, say, a four degree range, they are not going to alter wort temps much at all, and you'll never see as much as a two degree swing in wort temp caused by those ambient changes.

whovous said:

I can see advantages and disadvantages to the various monitoring methods, but I think if wort stability is the goal, then ambient stability is the answer. If those temps go up and down in, say, a four degree range, they are not going to alter wort temps much at all, and you'll never see as much as a two degree swing in wort temp caused by those ambient changes.

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I would disagree that ambient air is the way to go. Before and after fermentation, that would work OK. However, during vigorous fermentation, the temperature will rise rapidly in the wort. The freezer will turn on and cool the AIR to your setpoint. However, the mass of air that has cooled to the setpoint (and caused the controller to shutoff the freezer) will not be sufficient for actually controlling the actual wort temperature. It takes a lot less energy to heat air than water. You will likely get either the freezer kicking on and off frequently (if you have a shorter ASD), or the wort will be anywhere from 3-10 degrees higher than the ambient air if you have a longer ASD. You could set the controller low, but you may then (1) cool the wort significantly lower during the lag phase, so fermentation will have a longer delay, (2) have the chance of differing levels of fermentation vigor batch-to-batch (lager --> saison, also different strains in same temp regimen), resulting in different heat production and different offsets required to maintain your setpoint (3-10F I would say is a realistic range, so picking 4F may not be sufficient for the most vigorous fermentations), and (3) once fermentation dies down, temperature will drop back to that point. You could babysit the beer and adjust as it goes, but most don't have the time for that.

Also, taping to a glass of water is not ideal either. The water will take much longer to warm from the heat given off from the fermenting carboy than air will, and your actual wort temperature will be higher than setpoint during active fermentation.

You should go back and reread the posts authored by jbaysurfer, BigFloyd, and CryoEng (thermal physicist apparently) in the second link. They cut to the heart of the matter. Cooling the air by 10F will not significantly affect the wort temperature unless the temperature differential is held for a considerable time. I would argue that while you may control the ambient air temperature better, during active fermentation you would be allowing your wort to heat up (maybe significantly) over the setpoint and have your freezer turning on/off continuously to try and 'catch up'.

Graphs from Reddit Link

The graphs shown in the link above give a good idea of how effective the probe taped to the side can be. Wort was around 1-1.5F higher in the fermenter compared to on the side. This lines up with other folks claims that the probe taped to the side is within 1-2F of the actual bulk wort temperature. Unfortunately, the homebrewer did not also measure ambient air.

Here a homebrewer has measured the thermowell and ambient air temperature:

Thermowell vs Ambient

You can see that to maintain the wort at 64F, the air in the freezer was actually 56-60F to maintain the setpoint. This shows how little the wort temperature actually changes with short-term air temperature fluctuations. Of course, this brewer used a more intricate control scheme than just the thermowell, but there is a good point to be had anyhow. I would imagine the fluctuations in wort temperature would be around the 1-2F range, rather than 0.5F or less when using a more complex controller. This brewer notes that controlling using air temperature can result in better control, but only if you babysit the fermentation. Most of us work and don't have time to do that.

Slade7077 said:

Once I change the HY, do I need to lock the advanced settings or leave them unlocked. I have my probe taped to the side of a milk jug full of water. When I went out to check it, it read 62. I have it set on 66 with a HY of 1. Want to get the temp fairly steady before I put and wort in there.

Click to expand...

I don't think you need to lock the advanced settings, but don't quote me on that... Once you have 5-6 gallons of wort in your freezer, the wort will not drop that low, as it will have 5-6 times the thermal mass of the tap water and will also be producing heat. My not-so-educated guess would be rather than 4F lower than the setpoint, the wort would be closer to 1F lower/higher depending on where you are. I think in terms of homebrewing, staying within 2-3F of your setpoint is perfectly acceptable.

I thought it interesting that jbaysurfer uses the tape method and then steps his controller anyway.

It occurs to me that there are enough differences in equipment and methods that we cannot avoid comparing apples to oranges. I was working on the assumption that the controller would allow a two degree swing up or down from the set temp because attempting narrower swings would turn the compressor on and off often enough to fry it in short order. As I read the descriptions, I am now doubtful that is the case for everyone.

This is my first attempt at controlling wort temps beyond putting the FV in a cool dark space. My controller is set to allow a 2F swing. If it allowed that swing in the wort, rather than the air, it would be on and cooling for an extremely long time, and then shutting down for long periods as well. I think that would mean some pretty major shifts in ambient air temps. I begin to wonder if these swings are unimportant, then why is controlling temps important at all.

OK, that is a silly question, but I wonder if we have complete agreement on what our goals are. For example, are we trying to prevent fermentation from changing the temp of the wort?

whovous said:

My controller is set to allow a 2F swing. If it allowed that swing in the wort, rather than the air, it would be on and cooling for an extremely long time, and then shutting down for long periods as well. I think that would mean some pretty major shifts in ambient air temps. I begin to wonder if these swings are unimportant, then why is controlling temps important at all.

OK, that is a silly question, but I wonder if we have complete agreement on what our goals are. For example, are we trying to prevent fermentation from changing the temp of the wort?

Click to expand...

I think everyone's goal is to control wort temperature as well as possible. Many would like to do so within an acceptable range with the least effort possible. Swings in ambient air temperature are not critical, but significant swings in wort temperature are. I am not worried about wort swings of up to 3-4F, but don't think I see them anyhow. At the end of the day, it's personal preference. My best experience is taping to the carboy, assigning a setpoint a degree below my ideal wort temp, and using a hysteresis of 0.5-1.0F. I protect my freezer by changing the anti-short cycle delay to 15 minutes. If I notice that the temperature is rising more rapidly and requires the compressor to kick on more often (observed by the AsD indicator flashing), I will increase my hysteresis a half degree or so. Other than that adjustment, it is really a set it and forget it method, which I appreciate because I have other things to do related to my homebrewing hobby (growing yeast starters, making recipes and planning mineral additions, racking beer, drinking beer, filling bottles for friends), and limited time to get them all done.

So, we want fermentation with as little wort temperature change as possible?

Is there a way to know in advance how much heat will be produced by a particular yeast in a particular recipe? I guess I am really just getting theoretical here and wondering if one could devise temp settings in advance based on that knowledge. As a practical matter, as a newish brewer, I mostly just want my next brew to be better than the last one.

whovous said:

So, we want fermentation with as little wort temperature change as possible?

Is there a way to know in advance how much heat will be produced by a particular yeast in a particular recipe? I guess I am really just getting theoretical here and wondering if one could devise temp settings in advance based on that knowledge. As a practical matter, as a newish brewer, I mostly just want my next brew to be better than the last one.

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Wort temperature is what drives yeast behavior, so that's what we want to control. Now the metric you use to control that is variable. Taping to the side more 'directly' tracks the actual temperature increase of the wort, while the ambient air temperature will change due to increase in wort temperature, but the freezer will cool the air down more rapidly than the wort will heat it up, so the measured ambient air temperature would shut off the freezer before the wort actually reaches that set point. (There is lag between wort heating up and air heating up, and there is also lag between the freezer air cooling and the actual wort cooling. So your wort may move over the setpoint before the air warms to trigger your freezer on, and then your freezer may shutoff once your air cools to the setpoint+hysteresis, but the air will rapidly warm back up to match wort temperature - wort may only cool minimally each freezer cycle.) You can offset the air temperature based on experience, but the rate of heat production will vary from start to finish, so would have to have a more complex approach to monitoring temperatures (multiple probes, more-complex algorithms, etc) to keep the wort temperature in a tight range. I am not the best at explaining this concept...

Thanks, I think I get the concept. The details are another thing, but aren't they always? I think the program I created for my Fermostat was in keeping with the concept, or at least it was before it crashed in very strange fashion. I cooled the wort to about 3-5F cooler than my target temp (itself a somewhat arbitrary and invented number, but hey...) before pitching. The idea was that heat from fermentation would take me to my target temp and the ambient air temp would hold at that "too low" level for 3-4 days, and then it would be stepped up by two degrees every 24 hours.

Now, I realize that all my numbers were pretty much made up numbers, but I am confident that my made up process produced temps that were quite a bit more consistent than those in a dark corner of the closet; i.e., my previous fermentation chamber. I will try to incorporate something closer to your system for my next batch, and I appreciate you taking the time to discuss this.

whovous said:

Thanks, I think I get the concept. The details are another thing, but aren't they always? I think the program I created for my Fermostat was in keeping with the concept, or at least it was before it crashed in very strange fashion. I cooled the wort to about 3-5F cooler than my target temp (itself a somewhat arbitrary and invented number, but hey...) before pitching. The idea was that heat from fermentation would take me to my target temp and the ambient air temp would hold at that "too low" level for 3-4 days, and then it would be stepped up by two degrees every 24 hours.

Now, I realize that all my numbers were pretty much made up numbers, but I am confident that my made up process produced temps that were quite a bit more consistent than those in a dark corner of the closet; i.e., my previous fermentation chamber. I will try to incorporate something closer to your system for my next batch, and I appreciate you taking the time to discuss this.

Click to expand...

If you get a cheap thermometer at a pet store (something you'd use in a reptile tank), you could tape it to the carboy during fermentation to compare what it reads out vs what your ambient air reads. Record some periodic temperature differentials to see how they compare.

Update. My freezer is maintaining within 1° of set temperature. Thanks to everyone that responded to my questions.