So this is a take home quiz and I'm not too sure how to do it: "James has decided to replace his 15 year old 40 gallon gas hot water heater with a new tankless electric unit. This unit will operate on a 220v circuit and can deliver up to two gallon of hot water per minute. If the incoming water temperature is 35F and the output temperature is 125F, what size circuit is required to supply this electric hot water heater" It takes 1055J to raise 1 pound of water by 1 degree. One gallon of water weights 8.33lbs. So, it flows 16.66lbs of water per minute? and then what? I need to change the temperature of the water by 90 degrees. So do i do 90 * 1055 * 16.66? Is that how much power i need to change the temperature of the water? Then I can do P = IV and solve for I?
Not going to do your homework for you, but... You need 1 BTU to raise the temperature of 1 lb of water 1 degrees F. You can convert BTU to kWh... You need to have the capacity of raising the heat of 120 gallons by 90 degrees F in an hour. You already know P=VI.
Sorry, didn't see you were dealing in Joules already. 1 joule = 1 watt second, and now I've pretty much given you the whole thing.
hmm, I ended up getting 119.956. Does that sound right? lol. what i did: 1 gallon = 8.345404 lbs. It flows 2 gallons/min so 8.345404 * 2 = 16.691 So i need to change 16.691 lbs of water 90 degrees. 16.691 * 90 = 1502.17272BTU (i ended up using kWh) 1 BTU = 0.0002928kWh so 1502.17272 * 0.0002928 = 0.43984kWh then convert that into Watts/Minute so 0.43984 * 60 * 1000 = 26390.4 So, 26390.4 = I(220) so I = 119.956A?
edit: nevermind, I misread something Here's a real world one for comparison: http://www.nextag.com/40-gallon-electric-water-heater/search-html