Facade integrated concrete solar collectors

Abstract

Concrete solar collectors are a type of solar thermal collector that are formed by embedding pipes within a layer of concrete that acts as the solar energy absorber. Concrete is a cheap, durable and abundant material that can replace the metal or plastic absorbers of classical solar collectors. Concrete solar collectors also offer a unique facade integrated solar thermal solution, allowing for seamless integration with precast concrete cladding systems. Past research of non-integrated, roof-attached, concrete solar collectors have largely focused on one-off experimental studies in high temperature climates. This research (1) experimentally investigates the performance of a fa?ade integrated concrete solar collector in a mid-latitude European climate (Dublin) (2) develops and validates a 3D numerical model which is used to predict the performance of other fa?ade integrated concrete solar collectors in other European climates and (3) conducts an in-depth parametric investigation of the concrete solar collector using a simplified 2D numerical model. The experimental work tests a real scenario, models are then validated by these results and used to consider other climates (in 3D) and to carry out a parametric investigation (in 2D). The experimental set-up of the concrete solar collector is designed to represent a south facing fa?ade installation. The experimental results showed that approximately one quarter of the annual hot water demand of a single occupant dwelling could be provided using 1m2 of concrete solar collectors with spring and autumn months producing the highest daily energy outputs; attributed to the vertical orientation of the concrete solar collectors. A validated 3D numerical model is developed and used to expand the study to different collectors and systems, as well as three additional, contrasting, Northern and Southern European climates (Helsinki, Sofia and Seville). Annual solar fractions (proportion of the energy required for hot water preparation that is provided by the solar collector) of approximately 20% (Helsinki), 25% (Dublin), 29% (Sofia) and 51% (Seville) are predicted for a small apartment building using a fa?ade integrated concrete solar collector. The thermal energy output of a concrete solar collector is dictated by its material (e.g. thermal conductivity of concrete and pipe), geometry (e.g. pipe spacing, pipe diameter, collector thickness, pipe embedment depth) surface finish (e.g. absorptance) and fluid flow (e.g. mass flow rate). Given the wide range of individual parameter values documented in the literature, an in-depth investigation into these parameters is evidently required. An experimentally validated 2D numerical model is subsequently developed to conduct the computationally intensive parametric investigation. Parameters are investigated individually and compared collectively within the range of values found in the literature. Concrete conductivity and solar absorptance, along with pipe embedment depth and spacing are identified as key performance parameters. These material and geometric parameters are limited by practical, economic and aesthetic constraints which are also examined and summarised. Furthermore, concrete solar collector?s efficiency (56% on a sample clear day) compare well with other unglazed collectors (metallic absorber; daily efficiency on the same day = 62%; polymer absorber; daily efficiency on the same day = 29%).