This villa in Modena is under historic preservation (figure 3). The solution was to build a masonry wall on the room side of the existing wall. The cavity between it and the old wall is insulated with coconut and cork panels, 40 and 60 mm thick, reducing the U-value from 1.75 to 0.25 W/m2K.

New insulating glass windows were installed on the room side of the old windows to preserve the character of the facade. Primary energy demand for space and water heating is reduced 81% from 367 to 70 kWh/m2. The old 104 kW boiler could be replaced by a 35 kW condensing gas boiler. 12 m2 of vacuum tube collectors on the south faqade

of the interior court space help cover this reduced energy demand [4] Fig. 3: Historic villa in Modena IT renovated with

interior insulation (V. Calderaro)

The heating costs of a 50 unit apartment building built in 1957 Linz AT were reduced by 88 %. The comprehensive renovation included an innovative solar insulation system of prefabricated panels (figure 4). Sunlight passes through a glass layer and is trapped in the air gaps of corrugated cardboard (with a fire suppressant). The resulting warm air buffer reduces heat losses by the facade. The static U-value is 0.15 but the dynamic U-value over the heating season approaches zero. To reduce thermal bridges, the balconies were glazed and at the same time enlarged. Conventional insulation was added to the roof and the ground floor (U = 0.16 and 0.20 W/m2K). New windows were installed (Uw =

0.86 W/m2K) with louvered blinds within the glazing unit for sun shading. Finally, through- wall ventilation units provide good room air quality with 70% heat recovery. As a result of this package of measures, heating demand was reduced from 150 to 20 kWh/m2a [5].

3.1. Goal, benefits and problems

If the goal is to reduce dependency on non­renewable energy, at a certain point energy delivered from a solar thermal system becomes less expensive than energy saved from conservation measures, i. e. the marginal cost of the last increment of insulation or triple verses double glazing. Installing solar collectors or a pv system as part of a renovation is not always easy, however. Panels may be forbidden because they disturb the character of an historic village. Figure 5 shows the outline of the proposed and refused location for roof solar panels. The building commission allowed that the panels could be mounted on the shed to the rear, which, however is shaded by an old, noble nut tree.

Well done renovations drastically shorten the

heating season. A solar active system can then cover the minimal space heating demand of the spring and fall as well as the hot water demand, allowing other systems to be shut down for much of the year. This saves wear and extends component life spans. Two system types are reviewed here, a water system and an air system. Each has its special advantages for a given application.

Three years after a young Swiss couple purchased a single-family house built in 1942 the oil furnace had to be replaced. This was the motivation to completely renovate the house, including a 13 m2 drain-back solar system (fig. 6) with an 800 L storage tank.

The renovation also included adding roof, wall and basement ceiling insulation (220,

200 and 80 mm). The windows were replaced with units glazed with a Ug of 0.55. The oil burner was replaced with a wood pellet stove and a ventilation system with 80% heat recovery was added. As a result, the solar system is able to cover much of the space heating in spring and fall and all the domestic water heating demand in summer. The annual primary energy demand for space and water heating was drastically cut from 230 to 47 kWh/m2, or an 80% reduction. This means instead of burning 3,500 litres of heating oil per year and they burn only 1 tons of wood pellets [6].

Solar heat from a collector can be transported by air, instead of water. No anti-freeze is needed and a possible leak causes no damage.

Over the years this technology has been used in the renovation of many houses, schools and industrial buildings [7]. An example of a very practical application, solar heating second homes, is given here.

Often after a stone rustico or wooden chalet in the Alps, log cabin in Scandinavia or masonry cottage in the Mediterranean has been purchased, it must be renovated. While vacant it becomes cold, damp and mouldy. When the owners arrive, the air and bedding smell musty and it likely takes forever to bring the mean radiant room temperature up to a comfort level. Too often the solution is an electric resistance heater set at a low temperature during the owner’s absence. Because occupancy is only for short intervals, investment in insulation or better windows is difficult to justify. Thus, the auxiliary heating, even at a low temperature setting, consumes much energy. Solar air collectors can deliver sun-warmed air by free convection thereby maintaining a minimum room temperature and dryness. Optionally, a small pv-powered fan can increase the air flow and hence collector efficiency. Figure 7 shows an application in Koroni, GR. The two 6m2 collectors each include a 50Wp pv section to power the circulation fans which can circulate up to 200m3/h. [8].