An outdoor test facility (Fig. 1) has been developed for research on double fagades with integrated photovoltaic modules. The test facility has two test-sections on the south-facing fagade so that two different systems may be tested under the same conditions.

A double fagade — airflow window with integrated photovoltaic (PV) panels is the concept tested in the new facility. In this fagade air flows from the outdoors through inlets and across a cavity behind the PV panels, cooling them, and then enters the heated space or HVAC system as preheated fresh air (in summer the air flows out). The airflow window also includes a motorized blind to control daylight transmission. The project involves both experiments in an outdoor test-room as well as formulation of a numerical model and simulations to optimize the system. The project is focused on optimization of the heat and fluid flow processes, as well as of the resulting electricity generation. The simulation model developed as a result of the project will serve as a design tool for optimization of the system and for identification of potential problems such as local overheating.

Spheral solar panels

iwatt pam

Inlet damper

irash. air intake

Figure 1. Photograph of Concordia building-integrated PV test facility.

The fagade concept developed consists of two sections, the PV and vision sections, as shown above. An indoor exhaust fan is operated to draw air through the fresh air intakes into the room. Winter operation for fresh air preheating is studied in this paper with focus on the PV section. The above facility is currently utilized to study the performance of two test sections — one with photowatt panels (PWX 500 — 47.5 W typical output) exposed to the outside and another section with spheral solar panels in the middle of a glazed cavity with air flowing on both sides. This paper reports results mainly for the cavity with the photowatt panels.

Three models are being developed to optimize the system as follows:

1. A one-dimensional model that assumes isothermal surfaces but determines the exponential rise of the air temperature with height [4].

2. A two-dimensional transient model that divides the cavity into control volumes and also models the radiation exchange between all control volume surfaces.

3. A CFD model that includes also radiation and which is intended to study and optimize the airflows.

This paper presents some predictions from a 1D analytical model and compares them with experimental results.