HOMEBREW Digest #5092 Mon 13 November 2006

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  Calculating BTU ("Mike Sharp")
  BTU ("A.J deLange")
  SG and CO2 ("A.J deLange")
  Hot side aeration (jbryant)
  Changing brew system from propane to natural gas ("Chad Stevens")

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---------------------------------------------------------------------- Date: Sun, 12 Nov 2006 23:09:37 -0800 From: "Mike Sharp" <rdcpro at hotmail.com> Subject: Calculating BTU Jon Judson is considering changing brew system from propane to natural gas, and asks: "How do I calculate how many BTUs are required to heat x number gallons of water from y temperature to z temperature in w amount of time using natural gas as the fuel?" A BTU (British Thermal Unit) is the amount of heat needed to raise the temperature of one pound of water by one degree Fahrenheit. So, a 200,000 BTU/hr burner should be able to raise 10 gallons of water from 70 to 170 degrees in 2.4 minutes, right? Wrong. You should know that a rating for a burner in BTU is talking about the BTUs of fuel consumed, not the heat applied. A lot of the fuel is not completely burned, and a lot of the heat is lost. Many burners, especially the cheap ones, are very inefficient. As a result, it's very hard to figure out how fast a burner of a given BTU will heat water. The real problem is that many burners don't have a good "turn down ratio", meaning you can't turn them down real low, so you do want to match your burner to your kettle fairly well. For highly efficient Natual Gas burners, check out morebeer's natural gas burners. http://morebeer.com/browse.html?category_id=1168&keyword=&x=1&y=1 These are of the impingement type, and they work really well. If you look to see what size burner they sell with a given size system, you'll get a good idea of how big to go. You can buy this style of burner in a wide variety of sizes and configurations, though I don't know if B3 can get them all. Regards, Mike Sharp Kent, WA [1891.3, 294deg] AR Return to table of contents
Date: Mon, 13 Nov 2006 12:29:02 +0000 From: "A.J deLange" <ajdel at cox.net> Subject: BTU Temperature shifts in water are very easily calculated from heat inputs because 1 BTU is the amount of heat required to raise 1 pound of water 1 degree Fahrenheit. Note that this is an approximation, though a very good one, as there are several definitions of a BTU and the specific heat of water does change slightly with temperature. The other piece of essential information is that a gallon of water weighs about 8.3 pounds at room temperature (but only about 8 pounds near boiling). Thus the amount of time (hours) to raise a given volume of water from x to y degrees is 8.3 times the number of gallons times (y-x) divided by the heat input in BTU per hour. The tricky part is getting the heat input. With a pot over a burner a lot of the heat is lost. The best way to get useful data is to put a measured amount of water into the vessel, measure the temperature, turn on the heat for a specific length of time, say 1/4 hour, and measure the temperature rise. The temperature rise multiplied by the mass of the water (8.3 times the number of gallons) is the number of BTU the burner transferred to the water in the vessel in 1/4 hour. Four times that is the BTU per hour value which should be used in future calculations. A.J. Return to table of contents
Date: Mon, 13 Nov 2006 13:10:26 +0000 From: "A.J deLange" <ajdel at cox.net> Subject: SG and CO2 RE: My M.O. when bottling/kegging my beer is to take a S.G. measurement when the beer goes into the keg or bottling bucket WITHOUT taking a sample out in a hydrometer jar. How are you able to do this? If you just drop a hydrometer into the fermenter or bottling bucket in addition to the frightening risk of infection the reading would likely be off because of gas bubbles adhering to the side of the hydrometer in addition to the dissolved CO2 having an effect on the reading. All the published procedures for measurement of specific gravity go into great detail concerning the importance of thoroughly degassing the sample for these reasons. Getting a good hydrometer reading from beer which has been degassed is tough enough because you never get all the gas out. If doing this in a bucket how do you get your eye down the the level of the liquid surface for proper observation of the meniscus? If in a carboy, how do you get the hydrometer out? The reason you won't find anything in the literature about this is that nobody does it. With any amount of gas present hydrometer readings get thrown off because of CO2 bubbles, pycnometer readings are no good because gas forms in the pycnometer forcing out beer and as soon as the ultrasonics hit the beer in a oscillating U-tube density meter gas comes out throwing their readings off. Furthermore, the density shift would depend on the amount of dissolved CO2 which would mean an extensive set of measurements using special pycnometers for many combinations of temperature and pressure would have to be made in order to construct tables. To use these tables you would have to know the amount of CO2 dissolved. I suppose you could assume saturation level at whatever temperature and try spinning the hydrometer to free it from the bubbles but I still wouldn't know where to send you for. I suppose we could do a gedenken experiment: Fill a corny keg absolutely full of water, hold it at 45F and put 9 psi CO2 on it. The tables say that evenutally it will come to equilibrium at 2 volumes. That means 38 litres of CO2, approximately a mole and a third, have dissolved. This is 59 grams. Thus there are 19L in the keg consisting of 19KG of water and 59 grams of CO2 for a density of (19000 + 59)/19000 = 1.00311 or specific gravity of 1.00491. That's the amount of increase in density assuming the volume does not change and is a rough indicator of the magnitude of the error. Saturated at ambient the dissolved volume would be about half of this and the resulting SG about 1.0025. The "proper" way to take an SG reading is to withdraw a sample, thoroughly degass it, bring it to the hydrometer's working temperature and lower the hydrometer into the sample. If you are doing this to save the 50 - 100 mL of beer in the sample, drink the sample or take the lees from the hydrometer/bottling bucket. A.J. Return to table of contents
Date: Mon, 13 Nov 2006 08:42:47 -0500 From: <jbryant at wrsystems.com> Subject: Hot side aeration I was wondering if HSA is a problem when mashing and sparging with water heated only to around 150 F. I know that when you boil water you effectively deoxygenate it. When I fill my pot with cold water from the sink there is plenty of splashing going on, and then I heat that water to less than boiling. Is this water oxygenated? It seems like brewers only worry about splashing hot wort, isn't adding oxygenated water to the grain doing the same thing? Does anyone boil water for mashing and then let it cool to the right temp? Jason in Norfolk, VA Return to table of contents
Date: Mon, 13 Nov 2006 18:20:21 -0800 From: "Chad Stevens" <zuvaruvi at cox.net> Subject: Changing brew system from propane to natural gas >How do I calculate how many BTUs are required to heat x number gallons of water from y temperature to z temperature in w amount of time using natural gas as the fuel?.... Coming from a long line of engineers who adhere to the motto, "When in doubt, build it stout..." I just bought the biggest f'n burner I could find and ran really big pipe over a very short run from the meter, thus ensuring I could melt stainless if left unattended. Unfortunately, this approach has lead to vast underutilization of the 200,000 BTU burner I purchased, and the flame tends to carbon the bottom of my brew kettle (indicating incomplete combustion). Next time around, I think I'd go with a 100,000 BTU burner for 5 to 15 gallon batches. This doesn't answer your question, but I'm verbose, self righteous, and always happy to throw in my $0.02 even when the resultant dialog is tangential to the point at hand. :o) Chad Stevens QUAFF San Diego Return to table of contents
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