We made the approximate calculation for a vacuum tube solar collector. Because of the features of the collectors, You can't choose the case where the 100% of the DHW demand is served by solar collectors in every month. We recommend an average of 60% per a year. You can find the explanation below the calculation.

The vacuum tube collectors are more beneficial than the flat plate collectors for the DHW of detached houses. Observing the efficiency diagram, we can see that the vacuum tube collector's performance for a surface unit (y-axis) is the biggest in the range of the temperature (x-axis), required for hot water making.

source: László Fülöp PTE PMMF

Because of the cylindrical shape of the vacuum tubes the sun gets to the glass surface vertically almost for the whole day and the performance values are increasing constantly from the vertical incidence, so the thermal efficiency is pretty good from morning till late afternoon. The flat plate collector only gives its full performance at noon, when the sun is peripendicular to it's surface. On the other hand, the vacuum tube prevents the losing heate from the inside, thanks to this, the wind and cold weather have a smaller affect on the vacuum tube collector.

It is worth to measure the solar collector to serve the 60% of the yearly DHW demand. If we choose a bigger surface than this, more hot water is produced in the summer than what is really needed.

Formulas and quantities used in the calculation:

V= n x V₁=number of occupants x 50 liter/day = 0,05 m³/day/person

Q_DHW = 1,2 x c x m x ?T = 1,2 x c x ?  x V (tm - th) =1,2 x 4180 J/kg K x 1000 kg/m3 x 0,05 m3/day (45K - 10K) =8 778 000 J/day = 2,438 kWh/day x 365 day= 890 kWh/year/person

where:

Q_{collector yearly} = k x N_coll x A_abs x ?Q _{collector monthly}

where:

source: http://www.energiakozpont.hu/index.php?p=212

The calculation is an estimation, the performance generated by the unit of the absorbing surface is different depending on the type of the collector. For any further question or exact calculation, call us!

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