To collect energy from the sun we use 6 flat panel solar thermal collectors with a total net. area of approximately 13.6 m² installed on the south-facing part of the roof. The solar system circuit is divided into a primary and a secondary section, both connected via a water heat exchanger. The pump speed is controlled so that a water flow at an adjustable temperature level is generated at the output of the heat exchanger and fed into the buffer. The desired temperature level is calculated dynamically and depends on the automatically selected operation mode of the overall system and the currently available solar power.
The buffer containing 1500 liter of water is the central element of our system. It is implemented as a pressurized standing water tank with taps at different heights. So within the buffer layers of different temperature can form and water can directly be fed in or out of these temperature zones individually.
From a functional point of view the buffer stores hot water in its topmost zone for the on-demand heating of tap water. Water from the lower zones is used to feed the floor heating system. These lower zones also serve as buffer for excess thermal energy produced by the gas-fired furnace but not consumed by the floor heating system. The thermal energy ist stored here and may be used at a later time thus optimizing the duty cycle of the gas-fired furnace and avoiding frequent starts and stops.
Floor heating system and on-demand tap water heating act as consumers of thermal energy in our system. The thermal energy used is supplied by the wood-fired furnace and the solar thermal system. Especially on dark winter days the primary source of thermal energy is the gas-fired furnace. The hydraulic system is designed in a way to allow the controller to always select the most economic source of heat to fulfill the demand and also to use thermal energy stored in the buffer.
The power of the gas-fired furnace is controlled by the UVR1611-Controller to produce warm water at exactly the temperature level currently required.
The primary purpose of the wood-fired furnace is to increase the coziness of the living room. It is fired from time to time only and delivers most of its thermal energy by directly heating the surrounding air and by radiation. The warm air naturally spreads through the house and thereby also heats the other rooms. The active ventilation system in our house supports this natural spreading of the warm air by heating fresh air with an air heat exchanger.
In order to lose as less thermal energy as possible via the chimney we have chosen a special model of a wood-fired furnace with a built-in water heat exchanger. This heat exchanger extracts thermal energy from the smoke gas and feeds it into our heating system and the buffer. The heat exchanger is operated at a relatively high temperature by the controller to avoid soot agglomeration on its surface thus diminishing its efficiency.
Additionally the UVR1611-Controller performs some additional calculations (e.g. the optimal temperature to feed thermal energy into the buffer) and provides the results as input for other parts of the control algorithms.