IEA Solar Heating and Cooling Programm - NachhaltigWirtschaften.at

IEA SHC Task 38 Solar Air Conditioning and Refrigeration
Subtask A Report, Date:…
Simulations confirm the significant increase of the solar gain e.g. during the heating period
from October to March of about 20 %, compared to a hot water tank system with the same
specific cubic content per square meter collector surface area (in this case 40 Liters/m²).
All data of the solar fraction given above refer to the total amount of solar heat supplied to
the building. These results by far exceed the performance of conventional large-scale solar
installations. Pre-requisite for the obtained efficiency of the solar thermal system is the
operation at moderate collector temperatures stabilized by means of the low-temperature
latent heat storage. As a consequence, the major part of the solar heat supplied to the
building passes through the low-temperature (LT) heat storage and only minor parts of the
heat are generated at higher temperature levels, as given by the monthly data for the total
heat supply to the building (total) and the contribution of the latent heat storage (LT).
5 Experiences / Lessons Learned
Within the monitoring period of 3 years various efforts in increasing the energy efficiency
have been made. As a result reliable and efficient components, e.g. EC technology for
pumps and fans, have been applied. Apart from this, the system effectiveness also depends
on:
- the thermal COP has a crucial impact on the electrical COP. A poor COP results in
an increase of the secondary energy used for dissipating the reject heat to the
ambient.
- the standby electricity consumption should be reduced to a minimum. At best,
unutilized components are shut down completely.
- the knowledge of the real heat content in the latent heat storage is essential for an
optimized and efficient storage management aiming at high solar fraction and
minimized electricity consumption.
- the pressure drop in all components should be minimized, obeying economic and
thermodynamic limitations.
Further improvements will be realized in the near future:
- Replacement of the 3-phase AC fan of the dry air cooler by a 1-phase EC model.
This reduces the electric energy consumption of the cooler by about 50 % and the
parasitic energy demand in standby by about 15 %.
- Integration of an optimized latent heat storage with increased performance and
reduced setup area (-50%).
- Implementation of a 3-way mixing valve in parallel to the latent heat storage allowing
for an easy adjustment of the cooling water temperature and preventing unintended
loading of the latent heat storage.
- Test of a heat content sensor for the latent heat storage.
- Control of the flow rate of the primary solar loop depending on the current insolation
on the solar collectors.