How Solar Cooling Works

Cooling Delivery and System Integration

Many larger commercial buildings use a chiller to cool down a secondary chilled water loop.  Chilled water is then circulated to either:

           (i) Fan coil units, where it is used to cool the air being circulated around the building or

          (ii) Chilled ceilings where chilled water directly cools room air via radiant and convective cooling effects.  

Absorption and adsorption chillers are well suited to these applications and can operate in series with a conventional mechanical chiller, ideally with the absorption chiller providing lead cooling to maximise energy savings.

Where chilled ceilings are being used, the resulting elevated chilled water temperature enables lower temperature solar heat to be used. Similarly, heat rejection with a wet cooling tower is preferable to using a dry cooling circuit when attempting to use low temperature solar collectors.

Some typical integrated system design selections and resulting equipment selection/temperature requirements are illustrated below.

In other buildings, package DX units are often used and chilled water is not included in the base design.  In these buildings solar desiccant cooling configurations are likely to be more attractive.

In most cases, a backup form of cooling is required if comfort conditions in the occupied space are to be adequately controlled.  This can be achieved through installation of;

·        A backup gas burner which provides heat (in place of solar heat) when required.  In this case, no additional chiller/ cooling unit is required which makes this a low-capital cost option.  However, unless the chiller is an efficient two-stage absorption chiller, the greenhouse gas (GHG) emissions from gas firing can reduce the savings that would otherwise be attributed to the solar cooling system

·        A backup (hot or cold) thermal storage tank to defer solar cooling until later in the day when solar heat is otherwise limited.  While this can significantly increase solar fraction, it would be unusual to rely on this as the sole backup source.

·        A backup mechanical vapour compression chiller.  While generally providing better GHG emissions savings, a backup mechanical chiller leads to some duplication and additional capital cost.