How to calculate psi based on gpm
mikebuild
15 years ago
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davidandkasie
15 years agolehua49
15 years agoRelated Discussions
Question on Velocity, GPM, and Water Hammer
Comments (6)I see now, they are using the 30psi for the sprinkler heads as a "loss". Anyway, I would not combine the two bigger zones, thats approx. 15 gpm through 3/4" copper service. Max we would go under right conditions is 11-12 gpm. You may get premature meter failure. You could do the 7.4 and 1.56 together. (how did you get 1.56 gpm ). 15 gpm through 3/4 K copper loses approx. 30psi/100 ft. at approx. 11 ft/sec Too high ! Stay with 2-3 zones. How long is your service line. 3 psi loss seems low for that item based on your flows....See MoreTankless Water Heater: GPM and Incoming Water Temp Questions
Comments (4)I'm a bit late to respond but I'll give you my input on how our Noritz M-084M is working in Sammamish (Seattle area), which is to say, great! The 8.4 GPM is for a 45 deg temp rise, the lower 5 or 6 GPM is for a higher temp rise needed in Winter. You can find the charts on the Noritz website. I have our unit set to 120 deg and it works well at that setting. Our kitchen is the farthest from the unit, which I installed in the garage attic, and with the temp set at 120 I run the faucet on full hot when doing hand washing of dishes and this is just fine. I find the unit actually works better with COLDER incoming water temp. In the summer the temperature at the kitchen seems to be lower for some reason. The highest load we put on the unit is running two showers at once, which we do on the weekend. It has absolutely no problem keeping up and the water temp stays nice and constant. Our unit is rated at 0.75 GPM to activate, and there is no problem at all to get it running with a bath faucet. Newer units are 0.50 or below. And once it's running it seems like you can turn it down below the 0.75 GPM rate and still get hot water. Go too low though and it will shut off and you'll get the dreaded slug of cold water. This happens very infrequently and has not been any problem. If you haven't purchased a unit and would like to see our installation, drop me an email. I have some pictures or you could come out and take a look in person. Tom...See MoreIs this calculation for an optimized Water Softener OK?
Comments (13)JAL: Good input. I have researched this, but I like to run my thoughts past people with more experience then myself. I like your numbers, but the issue is that I'm pushing the efficiency as much as I can. Right now, my calculations assume a 57 gallons per day per person. Which is pretty low, but it's the only way to hit the sweet spot with my family size, hardness and 64,000 grain capacity. So, I'm at the edge of being aggressive with my numbers and leaning towards fiction. Particularly, since I have 5 children (3 gone and moved out of the house), but come home often. Then we have lots of guests. Right now we have two young Chinese ladies from Taiwan staying with us for 5 days. So, really, I should have gotten a larger unit like the 80,000 grain capacity. But, that's another $140, also, I have real space concerns--where I've installed the unit. So, a bigger unit would just push that envelope. I agree the OPWC calculation are not optimum, but giving my needs, it's not so bad. Besides, I have bigger fish to fry; so wasteing some salt to free me up, is not so bad. My current house is my third foreclosure that I've bought. I buy them, remodel them, them move on. In my current house I've: moved interior walls around, moved the washer and dryer from the basement to the second floor, put in a 7.1 surround sound movie theater in the basement, etc, etc. Then, I have plans for a new major kitchen remodel and a center piece water fall and pond in the back yard. So, I want to move beyond tinkering with the setting on this water softener. The difference between your calculations and OPWC's would cost me about one 40 pound bag of salt every 9 weeks. I like to save money more then the next guy. But, sometimes you get to a point of diminishing returns. Anyways, thanks again for your help. I welcome any other insight that you would want to offer. Best Regards, Stan...See MoreCalculating R value of a house
Comments (7)R-value is a measure of a material's resistance to conductive heat flow - or said another way - R-value rates the thermal resistance of building materials. The formula for computing R-value is: (hr x degrees F x sqft)/Btu. It is important to note the "per sqft" part of the formula. Heat travels in three ways, conduction, convection, and radiation. R-value numbers are based on the thermal resistance to conducted heat loss in a square foot of the material to be tested and R-value "measurements" do not take into account either radiation or convection losses (or gains). Imagine an exterior wall with a couple of windows, 2x6 studs - 16" OC, electrical outlets, and fiberglass insulation. Many folks would automatically say that this wall has an insulating value of R-19 based on 6-inches thickness of fiberglass plus wall sheathing plus drywall. While it is possible to "add" R-value numbers - siding + sheathing + insulation + drywall - the final figure would be accurate only between studs and only if there were no "breaks" in any of the materials listed. If a stud, or a window, or even an electrical outlet were involved, then the R-value numbers could become meaningless. And accurate only in the sense of measuring the "ideal" of a portion of the wall with regards to resistance to conductive heat flow. In the real world, R-value is most useful because it is easy to "see" the difference between a material that is "R-10" and a material that is "R-20". But also in the real world, R-value is not really a very realistic measurement when applied to an entire structure - unless the structure was subject to an energy audit and the stated R-value was computed using U-value formulas which were then converted into R-value for easier comprehension. The formula for computing U-value is: Btu / (hr x degrees F x sqft) And as previously mentioned, the formula for computing R-value is: (hr x degrees F x sqft) / Btu To illustrate a simple example, imagine that we have one sqft of insulation (type and thickness not important for this example). We have a temp of 70º on one side of the material and 0º on the other; we can now find the U-value if we know how much energy it took to keep the 70º side at 70º for one hour. If it takes 3.68 BtuÂs to keep the 70º constant for that hour, then we have 3.68 / (1 hr x 70º x 1 sqft) = a U-value of .05257. Using the same scenario, the calculation for R-value would be (1 hr x 70º x 1 sqft) / 3.68 or an R-value of 19.02. Since 19.02 = 1/.05257 or .05257 = 1/19.02 - R-value and U-value have an inverse or reciprocal relationship - but they have entirely different meanings - and while you cannot accurately calculate the R-value of a structure using the R-value formula, you can do so using U-value formula and then converting to an R-vlaue-based number....See Moredavidandkasie
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