Oskar capacity

The capacity of Oskar aircollector

Oskar in Aktion

Before we come to evaluate the performance of Oskar, here are some data to the overall understanding:

The yearly sum of global radiation of the sun is located in germany 900-1200 kWh per m² per year on a horizontal surface, which corresponds to an average of about 100 to 135 W / m². In spain, the global radiation is about 2,000 kWh, which means already 230 W / m².

Global radiation informations
Download solarstrahlung_analyse_1.pdf - 5 MB

Maps of global radiation for each european country can be found here:

Global radiation by country

In germany, the following regional power values ​​of the sun are available:

Global radiation after months
Download globalstrahlung2013.pdf - 6 MB

The instantaneous value of the global irradiance in central europe on a sunny day with a cloudless sky is about 900 W / m². In light cloud (but virtually unimpeded direct radiation) they may briefly rise significantly above 1.000 W / m² due to the diffuse radiation supplied by the white clouds. For cloudy weather it consists only of the diffuse radiation fraction and decreases to values ​​around or even below 100 W / m².

The energy yield of Oskar is thus limited. Due to the global radiation, depending on location, weather and month one m² collector surface could produce in germany at full sunlight and an efficiency of 100% 1046 kWh per year, with 2.6 m² 2719 KWh. The efficiency of the collector now determines how much of the power supplied by the sun can actually be used.

Oskar 2.6 provides with a collector area of 2.6 m² at full sunlight of approximately 1046 W global radiation at noon 1800 W. This corresponds to an efficiency of 66%. The power value for an air collector is calculated from the measured temperature increase and volume flow of the fan with a defined pipe diameter.

Oskar is ideally oriented entirely to the south on the facade or roof, and can not – according to our measurements – use the possible global radiation completely. By moving sun without tracking the collector there are power losses of about 40% arise again during the day.

Oskar - capacity

Series of measurements with Oskar 2.6 and solar module

Here now follow examples of two series of measurements in which outside temperature – T1 ,temperature in the collector above (entry into the heating zone) – T2, and outlet temperature – T3 were detained (Voltcraft temperature logger PL-125-T4). With an anemometer BA15 was held the air flow at 123mm fan tube with 2,8 m / s – 119,8 m³ .

Measurements 17.03.2013
Download 17032013.pdf - 22 kB

Measurements 18.04.2013
Download 18042013.pdf - 24 kB

You can see with the series of measurements from 18.04.2013 with our Oscar 2.6 on the solar module very nice the performance drops in clouds by stoppage of the fan, which does not occur affiliated to the home network supply. Simultaneously, the temperatureT2 shows the residual heat, which is still stored in the collector.

Series of measurements with Oskar 2.0 and 2.6 in home network power supply from the current production series

What follows is an example of two series of measurements from the current production, in which the outside temperature and outlet temperature for each collector were held (Volt Craft temperature logger PL-125-T4). There is documented with an anemometer BA15 an airflow at 123mm fan tube with 2.8 m / s – 119.8 m³ for Oskar 2.6, and an air flow at 123mm fan tube with 2.3 m / s – 98.4 m³ for Oskar 2.0. We used a 338/252 m³ Papst fan, over half of the power is in each case goes lost to the flow resistance of the collector. The 07/03/2014 documents a half cloudy, the 10/03/2014 a cloudless March day.
In addition, the current global radiation is now documented.

07/03/2014 - Oskar 2.6
Download 07032014oskar26.pdf - 21 kB

07/03/2014 - Oskar 2.0
Download 07032014oskar20.pdf - 21 kB

10/03/2014 - Oskar 2.6
Download 10032014oskar26.pdf - 22 kB

10/03/2014 - Oskar 2.0
Download 10032014oskar20.pdf - 22 kB

Here is a series of measurements from 20.03.2014 – from 12:30 to 14:15 completely cloudy – with still remarkable performance:

Oskar 2.0 - 20.03.2014
Download 20032014oskar20.pdf - 24 kB

Oskar 2.6 - 20.03.2014
Download 20032014oskar26.pdf - 24 kB

Oskar needs with its 8 m² heat exchange surface a slightly longer warm-sunlight, but it offers a very high storage capacity for temporary shading.

Finally, a series of measurements from 03.29.2014 with ideal conditions – no clouds, only a little haze by haze – on this day we have blown with the test series 16.2 KWH in the air:

Oskar 2.0 - 29.03.2014
Download 29032014oskar20.pdf - 28 kB

Oskar 2.6 - 29.03.2014
Download 29032014oskar26.pdf - 28 kB

In comparison to our Oskar and our measurement series you can find the data of the test lab Delta Test Laboratory from 17.07.2013 with the hot aircollectors Scansun Model XL27, Solar Venti SV14 und Grammer Twinsolar 1,3.

Delta Test Laboratory
Download delta_test_report__solarventi-grammer-scansun_2013.pdf - 525 kB

Realistically, the promise of many manufacturers in terms of performance, efficiency and capacity are formulated “very optimistic”.

The real supply from the documented test series from 17/07/2013 at 13:00 clock with 1045 W global radiation is:

  • Scansun Model XL27, 1,14m² collector-surface – 386 W performance, 31% efficiency.
  • Solar Venti SV14 , 1,39m² collector-surface – 628 W performance, 43% efficiency.
  • Grammer Twinsolar 1,3, 1,28m² collector-surface – 521 W performance, 39% efficiency.

With this calculator, you now can track the performance values ​​at different times of the day from all documented series of measurements:

Airflow calculation and effect

Oskar 2.6 Pipe inner diameter 123mm, 338m³ Pabst fan, wind speed at full power 2,8 m/s
Oskar 2.0 Pipe inner diameter 123mm, 252m³ Pabst fan, wind speed at full power 2,3 m/s
Pipe inner diameter (mm)    mm
Wind speed (m/s)    m/s
Temperature input     °C
Temperature output     °C
Pipe surface   m2
Airflow   m3/h
Temperature increase   °C
Effect   Watt

The calculator is working with the following facts:
Heat capacity of air (at the same pressure)is cp = 1,005 kJ/(kg•K)
Density is cd = 1,293 kg/m³
Airflow cl
Temperature increase dT
Effect in Watt ist E=cl*cd*cp*dT/3,6
For one m³ to one degree warmed you need E= 1,293 kg*1,005 kJ/(kg•K) *1 = 1,299465kJ / 0.3608 Wh
Relationship : 1 Wh = 3.6 kJ

Heating requirements

A well insulated building requires about 0.0232 KW heating demand per cubic meter of room volume and a temperature increase from 0 to 20 degrees. With Oskar 2.6 thus can be heated under ideal conditions a maximum of 35m ² with a ceiling height of 2.3 m.

Heating requirements individually:

Volume of room: m3
Temperature difference: Grad Celisus (Indoor / outdoor temperature)
Heating requirements =  kW

Conclusion power calculation

The measured values ​​show that an air collector is auxiliary heating only, but can efficiently and effectively save a lot of costs.

Respect, no miracles are to expect of a hot air collector, but certainly, depending on the design and size, a very effective contribution to the reduction of energy costs!


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