Multiplying Zero Buildings: A survey of the issues
What is net zero building?

Promoting Use of Solar Air-conditioning in Net Zero Energy Buildings

Dr Jyotirmay Mathur | Faculty, MNIT

While net zero energy buildings are making their space in the building sector in India, the next logical step in this direction is to improve their financial viability. Since air conditioning accounts for more than 50% of the energy demand in buildings, use of solar air-conditioning can pave the way for achieving net zero status. The biggest advantage with solar air-conditioning systems is that their requirement is usually in sync with availability of their input i.e. solar radiation. However, with use of net metering and energy storage, their utility can further be enhanced.

There are two major technological options in solar air-conditioning: solar PV route and the solar thermal route. In both the routes, some technological solutions are available in the market. However, some of these are still struggling to find a firm footing in the air-conditioning market.

In PV-based solar air-conditioners, electricity produced by PV panels is used for running the compressor of air-conditioner. It therefore becomes somewhat problematic to work using a conventional fixed speed AC compressor, due to its AC-DC conversion losses and high starting torque requirements. Either a DC compressor or an inverter based AC compressor (often used in VRF systems) addresses these issues to some extent.

The other route, i.e. solar thermal air-conditioning, is based upon the vapour absorption/adsorption cycle has been successfully tried and tested for large scale systems. However, for small applications, these still need to address design and operational challenges. Even with large scale systems, low COP remains an issue.

Some solutions that have hit the market have attempted to make use of solar heat as well as condenser heat to replace some amount of compressor work. Such units are also found to reduce the power consumption by as much as 40% when compared to conventional systems. The biggest advantage of such systems is that even when solar radiation is not available, superheating of refrigerant is achieved through using waste heat of condenser. This effect enhances the system efficiency thereby helps in reducing the energy consumption.

There is a need to enhance focus on development of solar air-conditioning products. If the air-conditioning load is fully/partially taken by the on-site harnessed solar energy, the remaining task of meeting the lighting and equipment energy would not be very difficult.

This would definitely make the path of net zero energy buildings much easier along with helping in controlling the load on utility.

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