Solar Energy Harvesting Systems

Commercial Systems

SolarWall® Heating Systems

By John Hollick, SolarWall, Canada

Product Description

Brief Concept Description

SolarWall heating systems heat air used for ventilation and heating of buildings. SolarWall consists of a perforated metal panel absorber that is integrated into sun facing walls of large buildings and connected to the heating ventilation fans. The system has been available since the 1990's, with particularly positive results in climates where space heating represents a large share of the building´s total consumption.

Architectural and Technological Integration into the Envelope

SolarWall is a building integrated solution and, once installed, resembles other typical metal wall facades. The metal panels are spaced out several centimetres to create an air cavity with the main wall. This air cavity is then connected to the building’s ventilation fans or HVAC units. The solar panel components are assembled on site to suit the existing wall dimensions and openings such as windows and doors.

The air collectors are unglazed or partially glazed depending on the desired temperature rise. The unglazed wall sections offer architects the ability to select from a range of dark colours, with black and dark brown being the most popular. Experience gained from thousands of installations over two decades shows that the durability and aesthetics of the wall are key factors in deciding whether to proceed with a solar heating technology. The ability to work with colours and shapes appeals to the design community for many higher profile buildings. Building integration allows the solar heating system to blend in and not become an eye sore. Some clients have resorted to including logos or sun images on their walls to identify it as being a solar heating wall rather than just another wall. The air collectors have virtually no maintenance, which is especially relevant considering the long-term operation of such systems, typically several decades.

Integration into the Building: System and Comfort

All projects require coordination with the designers and installers for the panels, mechanical equipment and controls to achieve complete integration into the building and its heating and ventilation and controls systems. The SolarWall systems are daytime heaters using the solar energy when available. Heat storage is not generally an option due to higher costs and the fact that most commercial, industrial, school and government buildings have minimal occupancy at night. It is necessary to have auxiliary heat in buildings. The solar heat is programmed to be the first choice followed by the auxiliary heat when solar is insufficient to meet demand. Typical overall energy savings with SolarWall are designed to be in excess of 20%. However, some buildings have reported savings over 50% without heat storage.

Figure 02. SolarWall installation on a warehouse in Latvia.

Figure 03. Roof-mounted SolarWall on a hospital in Spain (left) and Jaguar/Land Rover training centre in England with grey collectors to match the colour of the main wall (right).

Figure 04. Dark green SolarWall collectors on three walls of a bus garage, New York City.

Figure 05. SolarWall installation on the Greater Toronto airport authority building, Canada.

SWOT Analysis

Strengths

The system harvests solar heat with high solar collection efficiencies when the sun is shining and offers some solar preheating on cloudy days
The solar collectors are architecturally integrated into facades and are available in various dark colours. The appearance resembles conventional metal walls
The system utilises the existing wall for structural support and as the back side of the air cavity, achieving cost savings
The air collectors are easily erected on site by metal wall and roof installers
There are no snow accumulation issues
No maintenance on the wall system is needed
It is a proven technology installed on thousands of buildings since 1990
The integration with the building automation controls is easy
The upfront investment (cost per square meter) is lower with respect to solar liquid or PV collectors

Weaknesses

Climates with a short heating season are less suited for solar heating applications
It requires buildings with sufficient day time heating or ventilation needs, and is generally not suitable for residential homes
It requires a sun facing wall with access to the ventilation heating system
It requires custom design drawings for the integration into walls and the coupling with the ventilation system
The installation of a glazing on the upper portions of the wall (2-stage system) is needed for high temperature applications
There is no heat storage to cope with time-shifts between solar radiation availability and heating demand
A bypass ducting is required to access to fresh air at ambient temperature when solar heat is not required

Opportunity

Awareness is growing in the building and design community about the topic of solar air heating
The payback time is particularly favourable if the existing heat source is expensive
Solar air heating can be easily included in energy simulation programs to be considered as a solution for meeting renewable targets for buildings
Governments could include solar air systems in their incentive programs

Threats

Competitors might try to copy the panel construction without understanding the science behind the precision perforations in the panels
Ventilation systems with heat recovery are competitors of solar air heating
The cost of fossil fuels (e.g. natural gas) may remain low in the next years reducing the savings achieved with solar air heating
Governments might abandon climate change concerns

Lessons Learned

Building-integrated solar technologies must be aesthetically appealing to be accepted by the architectural community.
The initial approval or specifying person is normally the architect in new construction and the energy engineer in retrofit sales.
Solar space heating is not included in many solar thermal programs which usually focus only on domestic hot water and not space heating.
Heating buildings with air is not as common in Europe as it is in North America.
Building integration requires more approvals in many countries than conventional solar panels which are not integrated into the wall or roof.
Clients tend to prefer building integrated designs when offered a choice: architects want an aesthically appealing facade and have concerns with appearance of non integrated items such as solar panels.

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