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Air Conditioning World: Solar air conditioning: what contractors need to know

For a long time the hvac industry has been talking about using solar to power air conditioning systems. Unfortunately, not much headway has been made in developing a feasible solution for the marketplace, until now that is. Graham Wright of Sanyo Air Conditioners examines the technology and what it means to the hvac contractor
Air Conditioning World: Solar air conditioning: what contractors need to know
WITH global warming already appearing to affect the UK's climate, environmental issues continue to grab the headlines daily.

This has led to commercial end-users finally realising the importance of publicising their green credentials, with corporate social responsibility becoming a competitive issue.

Since energy efficient climate control equipment can make a big difference to a business' carbon footprint it is important for end-users to purchase the right selection of hvac equipment.

To answer environmental concerns the hvac industry has been working hard to improve the efficiency of traditional climate control as well as moving to alternative solutions such as heat pump systems.
These developments mean solar power has now finally emerged as a viable way of partially powering an air conditioning system.
But what is it all about, and what will it mean to hvac contractors?

Solar power

The solar cells that make all this possible are also referred to as photovoltaic cells.

Cells, either in banks or individually, use the photovoltaic (PV) effect of semiconductors to generate electricity directly from sunlight. It is the same technology which powers those little solar pocket calculators but, until recently, their use in many manufacturing sectors has been limited because of high costs. Now thanks to a recent reduction in manufacturing costs, the range of cost-effective uses for solar power is growing. And its popularity is boosted by schemes where excess generated electricity can be sold back to the national grid.

Sanyo Air Conditioners' new technology offers the first standard solar air conditioning solution available to the UK market. Sanyo has combined its expertise in high performance solar power PV cells with its heat pumps, to produce highly efficient air conditioning systems.

The key to the technology is a power inverter which allows the solar power to be harnessed to any air conditioning system, to offer high efficiencies of up to COP at 7.0 for part load, although it is theoretically possible to achieve a COP as high as 24 in some instances. This is calculated by subtracting the power input provided by a PV array from the power required by the system at a given load profile. The subsequent COP figure is derived from the power taken from the grid system divided by the system capacity - the PV array power supply.

The technology

How does it all work then? Sanyo's model sees the photons in the sunlight hitting the solar panel cells and being absorbed by the silicon, which is a semi-conducting material. Negatively charged electrons are then knocked loose from their atoms which, in turn, facilitates flow through the material to produce electricity. This electricity enters the inverter as direct current (DC) electricity. The inverter then turns this DC electricity into 240-volt AC (alternating current) electricity, which is essential for air conditioning.

The AC power enters the utility panel and is distributed to the air conditioning system. When the air conditioning is not being used, the electricity can be diverted to power other facilities, or flow into the national grid.

Along with the inverter, the other important technological elements are the PV cells themselves. Sanyo's HIT (Heterojunction with Intrinsic Thin layer) technology features a thin amorphous layer on top of high-quality monocrystalline silicon wafers.

This makes them the most advanced and energy efficient available.
They claim a cell efficiency of up to 22%, the world's highest level of conversion efficiency in mass production, as well as offering excellent performance in low light levels which makes them ideally suited to temperate climates.

End-users

Solar power, as a means for generating electricity for air conditioning should be seriously considered by hvac contractors and their clients as a way to both reduce a business' carbon output and make cost savings.

For example, table 1 shows the power required to provide cooling and heating for a small office application working office hours:
However, by installing an array of eight PV panels measuring 10.2m2 facing due south, 1.48kW will be provided throughout the year, during normal office working hours.

The maximum power output for the array would be 1.48kW but this could be achieved during summer or winter. For the end-user this means real cost and carbon savings through using a renewable energy source - the sun.

Currently the technology is available for a number of specific projects in the UK but will be widely available next year. As the technology develops further it will surely become more widespread. Quite apart from being the environmentally-responsible thing to do, it helps end-users establish their green credentials, illustrating to the general public that they are forward thinking and willing to invest in the right technology for this century's environmental challenges.

1 September 2007

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