Southern Institute of Technology

The Challenge

The site itself is large, consisting of an older commercial building which has been extended and re-fitted with office space, classrooms, workshops and also staff and student café areas. The teaching areas and offices needed to be air conditioned and very well ventilated, requiring large fresh air quantities. The solutions chosen needed to not only be effective, but also energy efficient.

The Solution

The fresh air for teaching and office areas of approximately 1500m2 is provided by a MC150 air handling unit fitted with a purpose made DX coil, piped to a Mitsubishi Electric PUHY-P700YSHM-A City Multi condensing outdoor unit. The air handling unit duty is 3.6m3/s of fresh air and the DX coil / City Multi combination provides around 80kW of tempering. Compared to traditional methods such as electric element heating, this type of installation can save up to 75% on running costs and substantially reduce KVA charges, not to mention switchboard and cable size.

The interface between the condensing unit and the DX coil is three City Multi PAC-AH250M-H air handling unit (AHU) controllers. These units are specifically designed to allow connection of non-Mitsubishi Electric coils to the range of City Multi DX condensing units. These controllers are designed to be suitable for full fresh air applications due to the -10°C minimum coil air on temperature and the ability to control on leaving air temperature. Connection of these units is possible on both the standard and Zubadan ‘low ambient’ condensing unit range. As with all City Multi product, this unit offers a fully modulating capacity to accurately meet the desired set point while using the least possible amount of electricity.

The air conditioning for the teaching areas is provided using Mitsubishi Electric SLZ cassettes. These along with the Air Handling unit and City Multi condenser are controlled via a City Multi AG-150A LCD colour touch panel controller.

In the extremes of summer the City Multi PAC-AH250M-H AHU controllers with City Multi condensing units can also be used to pre-cool the incoming fresh air. This prevents additional cooling load on the space air conditioning systems, simply by changing the mode of the outdoor unit via the AG-150A central controller. Traditional methods of using electric elements in fresh air systems do not allow this functionality.

When considering energy efficient solutions for fresh air, the AHU Controller with City Multi condensing units is an ideal solution when heat recovery ventilation products are not practical due to large fresh air quantities, or building layout restrictions.