Hello all,

Does anyone have any insight on how manufactures calculate heat loss factors for hot water cylinders? Are they comparable across different manufacturers?

eg Grant quote a heat loss factor for a 170litre, PUR insulated cylinder at .601 kw/l/24hours
Tribune quote for a similar 180litre PUR insulated cylinder 1.6 kWh/24hrs

Not quite the same units, are they?

Thanks in advance...

Brig,

I tend to agree... I called their tech this afternoon, who were adamant that they test to 'G3' whatever that is? and they stood by their figures.....?
I did what you did with regards to the maths, but then it comes out way above the others....

For the Grant one, IF the true losses are 0.601W/l, then the total power lost from that cylinder is 0.601 x 170 = 102W. The energy lost per day is power times the hours in a day so energy = 102 * 24 = 2452Wh or 2.452kWh.
For the Tribune one, power is energy / time, so power = 1600 / 24 = 66.7W

It depends if you want to work in losses as power (W) or energy (kWh).

2 kWh/day is pretty typical for normal-sized and insulated tanks.

One thing to be aware of is that the number and style of pipe connections is at least as important as the base insulation/loses of the tank. Are any of the manufacturers inculding that in their calcs? Whether pipes connect under the insulation jacket at top or bottom of tank makes an enormous difference (top of tank is hot, bottom is often cold to thermal brdges at top are _much_ more significant, often factor of several). Also dips or downward-tilted connections can again reduce by factor of 5 or so the heat loss due to internal 'waterfalling' at pipe connections (tiny little thermal loops where warm water goes into pipe, cools and then falls back into tank, bringing more hot water into pipe).

Sadly very few manufacturers of tanks take any notice of this stuff, which can make up to 30% difference to tank loses. An efficient tank woule lead every connection down to the bottom of the insulation before bringing it out (or use internal riser-pipes - (see the Rebus project paper)). Obviously compromises have to be made where thermosiphon loops are in operation and for the vent pipe of vented tanks. Thermally broken pipe connections (plastic?) and dips are next-best.