Chiller calculations

[reno-jazz]

Anyone have the equations to deal with cooling loads on fermenters? We're getting a couple of new tanks and I want to see if our current setup can handle the load. I'm having quite a time finding that info.

Thanks,
Jazz

[gitchegumee]

Usually, the maximum cooling load comes with crashing the fermenters to conditioning temperatures. Maybe you should try an easy experiment: Simultaneously crash as many tanks (use water where you have no beer) as you would with your new setup. If your glycol does not warm up, and you get attemperation in the required time, then you have what you want. Your equipment supplier may also have a good idea. Otherwise, I can give you the calculations, but they involve many assumptions. You will need to know how many new tanks and how many existing? Sizes? Starting temp? Ending temp? Glycol temp? Glycol flow rate? How many of the fermenters will you crash at one time? And how long would you like the temperature reduction to take?

[Moonlight]

The fermentation load is approx. 1540 BTU per barrel and degrees P fermented. If you have an ale obviously this load would be spread over fewer days than if it were a lager fermentation. Crashing a tank would be a bigger load if you choose to do that. Remember that your glycol tank (or any tank of water becoming cold in your cold box) will hold quite a lot of ("negative") heat so if it has enough capacity (ie. gallons times Temp differential), you could accomplish this with a small compressor running over a long time, perhaps like how your wort cooling is accomplished...and much more cheaply.

[oppigards]

To adjust the temperature of one litre beer one degree during one hour you need 1,16 watt. That is the easy thing. The hard thing is to estimate the cold loss in tanks, cooling tubes, heat exchangers and more.

[reno-jazz]

I have all the info needed to calculate the cooling load during crashing, should be Q = mcDt, right? Using that and our current setup, I should be able to crash all our fermenters in about 15 hours (figuring one 5 hp and one 3 hp, 1 hp=12,000 BTUs/hr, chillers running at running at something like 57.7% efficiency during the hottest day in summer). Only thing I don't really know is flow rate but I can probably find that in the manual. What am I missing here?

[gitchegumee]

There are really two relevant sets of heat transfer equations; one for the compressor to glycol, and the other is glycol to unitank. Sounds like your initial calculations show your compressors able to handle the fermenter load, if your glycol circuit can deliver the cooling. Crashing ALL tanks at once in 15 hours is certainly more than adequate. You wouldn't crash more that one or two at a time, would you? Your equation Q=MCdT is right. But to use it you have to assume dozens of things that may, or may not be significant. I still think that an in-situation test using current equipment would be the most accurate indicator of future performance. If you can manage that around production. That would take into account all the real world factors. Good luck!

[Tbrew]

I would fleece this question in a slightly different manner. I would work out the cooling demand for one brew from start to finish (assuming they are consistent, if not work it out for one of each type). In each brew you will have varying energy demand so work out the load in 8 hour increments. (calcs done on 10hl of beer)

If we accept that 1217KJ of heat are produced for every kg of glucose fermented we can capture the fermenting load. So if in 8 hours you ferment from 10P to 7P you would have 1217kj/kg*10hl*3kg*(1/3603j/kwh)=10.13kwh.

Secondly, you have the sensible cooling load of crashing a fermenter for aging. You already "know" your heat transfer coefficient because you know how much temperature drop you have per hour. Let's assume your dropping the classic 1c/hr from 20C to 12C (8 hours right). This would yield 10hl*100kg *8C*4.18(sp. heat of beer/h20)*(1/3603j/kwh)=9.28kwh

Now the hard part is deciding how much energy is used to maintain the chilled fermenters and how much heat loss you have in the system. If you turn off the cooling to a fermenter for 1 day you will find the heat loss associated with the beer in the tank. Of course there is much more heat loss in the plant. Examples include loss of cold that is in the jacket out towards the room or loss in pipes or parasitic losses due to pumps etc. In this case Gitche’s idea of testing real world performance might be best. Try shutting down the fermenters and measure the amp load on the compressor units after an hour for an hour. Remember to keep your coolent temp as high as you can while still getting the job done and you will run much more efficiently.

Now that you have your cooling demand for 1 brew, work out the maximum number of brews you can do and when and lay the 8hour loads out over a month. Sum all the loads for each 8hour period and now you have the total demand and will be able to identify your peak period to design for. Good luck!