International audienceA solar thermal and heat pump combisystem is one of many system alternatives on the market for supplying domestic hot water (DHW) and space heating (SH) in dwellings. In this study a reference solar thermal and air source heat pump combisystem was defined and modelled based on products available on the market. Based on the results of an extensive literature survey, several system variations were investigated to show the influence of heat pump cycle, thermal storage and system integration on the use of electricity for two houses in the climates of Zurich and Carcassonne. A singular economic cash flow analysis was carried out and the " additional investment limit " of each system variation was determined for a range of economic boundary conditions. This is the maximum extra investment cost for the system variant compared to the reference system that will give a break even result for a 10 year period. The results shows that variations in electricity price affects the additional investment limit far more than the other economic parameters. Several of the variants show potential for achieving a cost benefit, but the potential varies a lot depending on load and climate boundary conditions. For all variants, the biggest difference in electricity savings was found for Zurich rather than in Carcassonne, which is explained by the larger heating load. However, in three cases the largest savings were for the SFH45 house despite the fact that the annual electricity use of the system is much lower than that for the SFH100 house, 358
Within the project ImmoGap, the so-called performance gap for multifamily buildings was analysed. It contributes to a better classification and a clearer definition of the term “performance gap”. As a first step, a literature study on this topic was carried out. In principle, the “Performance Gap” is understood as an additional consumption of energy or a failure to meet energy benchmarks. The term “Performance Gap” suggests that a desired service is not provided. This is critical, because there are several reasons why a building consumes more energy than originally planned. In the project, the heating energy consumption of 65 multifamily buildings was compared with the design heating demand according to the Swiss standard SIA 380/1 (based on EN ISO 13790:2008). In contrast to other studies, the project team was able to access measurement data with a very high time resolution. On average, the heat demand calculated with standard use is exceeded by 44%. Four of the buildings show an additional consumption between 100% and 115%. Detailed investigations with simulations and measurements show that the additional consumption can largely be explained by the user behaviour regarding shading, ventilation and room temperature, which deviate from the standard. If the observed user behaviour was already used in the demand calculation, the examined buildings on average would not show any “performance gap”.
Solar combi-storages are used in many countries for storing solar heat for space heating and domestic hot water (DHW) in one device. When a combi-storage is used in combination with a heat pump, the temperature stratification efficiency of the storage is a decisive factor for the overall efficiency and thus, for the consumed end-energy of the system. In particular, fluid that is entering the storage with a high velocity may cause considerable mixing, thus, destroying stratification and leading to poor system performance. This work presents computational fluid dynamics (CFD) simulations of direct horizontal inlets at midheight of a typical solar combi-storage of about 800 L volume. Different inlet diffusor designs were simulated, and laboratory measurements were used to validate CFD experiments. For the given tank geometry, mass flow rates, and inlet position, it is found for a fluid inlet temperature of 30 °C that fluid velocities should be below 0.1 m/s and Reynolds numbers below 3000–5000 at the outlet of the diffusor in order to avoid the disturbance of a hotter 50 °C zone above the inlet. Furthermore, the fluid path within the diffusor must exceed a minimum length that corresponds to three to four times the hydraulic diameter of the diffusor.
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