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Is solar heating and cooling the next big thing?

Dr Stephen White
Dr Stephen White

New solar heating and cooling technologies promise to deliver major reductions in energy costs and emissions, a recent HVAC industry workshop has heard.

Breakthroughs in technology were discussed at the Australian Institute of Refrigeration, Air Conditioning and Heating’s 2016 Solar Heating and Cooling Workshop at the University of Melbourne last month.

“There was a great sense of enthusiasm and engagement in the room during the workshop,” AIRAH chief executive Tony Gleeson said.

“The workshop underscored the relevance of solar cooling and heating technology in relation to the built environment.”

Hybrid solar/HVAC

One of the speakers, Dr Stephen White, who leads energy for buildings research at CSIRO, told The Fifth Estate there were many opportunities for hybridisation of building energy systems and HVAC systems.

A number of small to medium size Australian firms have solar PVT (combined photovoltaics and thermal) products that are either at or near commercialisation in as well as new products on the market that integrate solar PV systems to run conventional airconditioners.

Dr White said that while passive solar heating and cooling has been incorporated into building design for hundreds of years, active solar heating and cooling has received “very little attention”.

He said a report by the International Energy Agency in 2014 estimated that around four per cent of the worldwide installed capacity of water-based solar thermal systems supplied heat for both domestic hot water and space heating.

“This is less common in Australia, as we don’t tend to use hydronic heating systems. Instead Australia has a number of SME manufacturers producing solar air-heating products,” Dr White said.

Members of the Australian Solar Thermal Air Heating and Cooling Association have installed more than 10,000 units in homes around Australia. The technologies include systems that harvest solar heat from the roof cavity to warm the home and provide fresh air.

“This is cost effective and provides improved indoor air quality. During summer these devices can assist with night time cooling.”

There are also technologies that use solar heat for driving cooling via absorption chillers or desiccant cooling systems.

Dr White said the economics of these systems are good where there is a constraint either on the supply or price of electricity in a new development.

Thermal storage for solar energy is another emerging technology that has a promising business case.

Phase change storage cheaper than batteries

University of South Australia associate research professor Frank Bruno told workshop attendees that phase change material thermal storage was a much cheaper form of solar storage than batteries, coming in at around $200 a kilowatt-hour of storage capacity compared to around $1500/kWh for batteries.

Xiaolin (Shannon) Wang gave a presentation on her current research into warm-ice technology for cold-storage airconditioning. Ms Wang said that using a warm-ice hydrate tank provided significantly better energy efficiency over using multiple standard chilled-water tanks.

AIRAH’s executive manager – government relations and technical services Phil Wilkinson said events such as the workshop brought new technologies to the fore.

“The technology in the solar cooling and heating space is having a commercial and environmental impact right now,” Mr Wilkinson said.

The interim standard for solar heating and cooling, AS 5389:2013, is now being updated and expanded to include the new and emerging energy-efficient airconditioning technologies, Dr White said.

The draft of the revised standard is expected to be out for public comment in the middle of 2016. It will include a revised calculation of energy consumption for high-efficiency space conditioning systems, a section on solar-based desiccant cooling systems and on solar heating systems.

Start with good design and think integrated

Dr Alistair Sproule

Dr Alistair Sproule

Dr Alistair Sproul, University of Sydney associate professor in the School of Photovoltaic and Renewable Energy Engineering, gave a presentation to the workshop on integrated design. He stressed the importance of architects and engineers working together to deliver better buildings.

Speaking to The Fifth Estate afterwards, Dr Sproul said the importance of integrated design was to ensure a building itself was well-insulated and not leaky, and utilised passive solar design principles to bring the need for heating or cooling to an absolute minimum.

“Often how we build is very unintegrated,” Dr Sproul said. The architect is focused on the look of the building, then the architect gets an engineer to say how it works in terms of mechanical, civil engineering, lighting and electrical systems.

“The opportunity for integrated design is coming from a position of how we make buildings work from an energy perspective.

“Then you are not having to tack on a big HVAC and solar system.”

Any integrated solar PVT system needs to be right-sized for the building’s performance, and also storage, for example in the form of a solar hot water storage system, which needs to be sized for winter conditions, he said.

“Solar thermal is easy to store,” Dr Sproul said.

He said the property sector was “not quite there yet” in terms of integrated design being business as usual. The challenge in the commercial world was the need for big developers to take it up. Often they are under financial pressures that curb enthusiasm for an integrated, sustainability-focused approach.

Some sectors, such as universities and other education institutions take the approach because they want to make a statement about where they are heading with sustainability, Dr Sproul said.

“But there is still a challenge there because of the perception of there being extra costs involved.”

He said that designing smaller and better, with smaller and better laid out HVAC and electrical systems required there to be someone taking on the role of integrating all those technologies together. Where previously it might have been the architect or project manager that undertook the integration task, with new technologies added into the building mix, it is a role suited to the ESD consultants on a project.

“In a sense they take an overview of all these building systems, for example, the facade, the shading, the glazing, thermal performance, lighting and so on. In doing that they are taking up a broad over-arching view of the building.”

Dr Sproul said the challenge for all the new technologies such as PVT and solar thermal storage was that “buildings are a wicked problem”.

“There are lots of ways you can solve the problem. My plea would be for good design.”

He said there were currently no clear winners in the changing energy landscape, except the incumbent big power companies.

At the same time, innovation in the PV and the HVAC space continues. Compression airconditioners are becoming more energy-efficient, enabling them to harness solar PV effectively and reduce reliance on grid power.

Solar thermal HVAC and geothermal both have a challenge in terms of costs to compete, he said.

Using waste heat from solar PV

Other areas of innovation include developing ways to extract the heat from solar PV systems and utilise it. He said he is undertaking research into this with the CSIRO, specifically around using the waste heat from a solar PV system to drive a desiccant cooling system.

“I like this approach. It is one of the lowest energy pathways. But of course in the end [we] have to prove it can be scaled up.”

Another new approach being investigated is using water to cool PV panels, which increases their ability to generate electricity, while at the same time capturing the water afterwards and using the heat.

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