The Notre Dame Catholic girls' school in Southwark, Central London has been based on the same site for over 150 years. The existing building has a number of areas where overheating is a problem for various reasons, including external heat gains, changing usage and additional heat loading within the space due to computers and other equipment.

Split air conditioning (AC) systems were installed to provide cooling for a number of problem areas, but the only ventilation available was via the opening and closing of manually operated windows. Due to concerns with running costs, sustainability and the mounting of external split AC units to the outside of the building, the school was keen to consider an easily-retrofitted, environmentally- friendly solution for its future ventilation and cooling needs.

Monodraught's new Cool-Phase ventilation system was recommended by the school's consultant Tom Cairns, for "its potential to maintain classroom temperatures, and improve air quality while minimising energy usage and running costs".

A trial was run to compare Cool-Phase to the AC systems installed elsewhere in the school. To evaluate the Cool-Phase system's phase change material (PCM) technology, two systems were installed in April 2011 in an IT classroom that experienced high internal heat gains from 30 PCs and an overhead projector, and suffered solar gains created by partly shaded windows.

Two 'control' areas were chosen. The first was also an IT classroom equipped with 30 PCs and an overhead projector. It suffered similar internal heat gains to the classroom in which Cool-Phase systems were installed and, due to solar gains from south-west facing windows, slightly higher external heat loading. A wall-mounted split AC system was already providing cooling for the control IT classroom.

The second control area was a geography classroom equipped with only a single PC and overhead projector, which experienced a much lower internal and external heat loading. This room was chosen because it was located next to the Cool-Phase equipped IT classroom and would provide a baseline with which to compare performance.

Data logging equipment was installed in each classroom to monitor temperature and CO2 levels. The results show that Cool-Phase achieved a reduction in average temperatures before and after the installation.

Says Monodraught: "The percentage of hours between 8am and 4pm when temperature or CO2 levels were above a set point, confirm that the Cool-Phase system achieved better performance than both control rooms even with the air conditioning installed. The geography classroom, despite its lower heat loading, experienced temperatures above 25 deg C for 59 per cent of the time, while Cool-Phase reduced the time in its IT classroom to just 2 per cent.

"With the AC system turned on in the second control room some areas were overcooled and the AC was turned off as a result. Predictably, temperatures then rose until the AC needed to be turned on again. Also, since opening windows provided the only ventilation source, they contributed to higher temperatures because the AC's cooling effect was lost."

A similar pattern emerged with CO2 levels, where data showed that the control IT classroom fitted with AC was not as well-ventilated as the Cool-Phase IT classroom.

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