SOLAR & PELLET HEATING: SPECIFICATIONS FOR HIGH EFFICIENCY SYSTEM DESIGN

Abstract Combined biomass and solar heating systems provide the opportunity for a heat supply of single family houses without the use of fossil energy. Pellet fired boilers play a predominant role within these systems because their standardised combustible allows for the fully automated operation. However, the combination of biomass boilers and solar collectors places special requirements in view of a good system solution. To analyse the proper combination of both technologies three separate projects were carried out at SPF. the main instrument thereby was the Concise Cycle Test method supplemented by preliminary tests of the boiler and subsequent simulations. It was shown that a modulating boiler operation is superior in terms of both, high energetic efficiency and low emissions compared to intermitting boiler operation. But this is only the case if the following requirements are met: Low excess-air factors for the complete modulation range, low envelope losses, a fast adaption of the output power, correct dimensioning of the boiler. Beside the characteristics of the boiler the hydraulic connection and the control is important to reach a good system performance. Mostly for combined biomass and solar heating systems the best solution is a connection of the boiler to the thermal energy store instead of a direct connection to the heating circuit. The requirements that have to be fulfilled for the control of TES charging are: Temperature sensors within the store to control the boiler dependent to the demand for space heating or domestic hot water. In order to control the power modulation of the boiler, the best option is to reduce the volume flow rate of the boiler pump based on an algorithm that takes into account the temperature measured in the TES. Other options are to increase the return temperature of the boiler using a motorized mixing valve, or to reduce the set-temperature for the water leaving the boiler