I have a question concerning the tank loss coeff. of Type4.Is the tank loss coefficient in TRNSYS also the u-value of the insulation??
Using just the U-value of the insulation will under-predict the u-value of the tank. You're not accounting for the convective resistance of the water-side heat transfer, the resistance of the tank wall, and the combined radiative and convective air-side resistance. But all of that assumes the tank is ideally insulated and that's really never the case. There are quite a few "thermal shorts" that will reduce the effective u-value of a tank from that calculated by simply using the insulation. There are algorithms to calculate the u-value of a tank if you know the energy factor or have access to heat loss data.
I switched the unit of the tank loss coefficient to W/m^2K. It´s the same unit as the u-value. I knew knew the heat conductivity of my insulation (lambda = 0.04W(mK)) and its thickness (100mm), i was able to calculate the u-value by using u = 1/(0.1m/(0.04(W/mK))) = 0.4.
That formula only applies to 1-d conduction and does not hold for cylindrical tanks - you'll have to use a radial calculation for cylindrical tanks.
Jeff --- Jeff Thornton President - TESS LLC 22 N. Carroll Street, Madison WI USA 53703 Office: (608) 274-2577 Fax: (608) 278-1475 www.tess-inc.com E-Mail: thornton@tess-inc.com