Phase-change system solves school over-heating problem
The capabilities of a phase-change system to offset heat gains and deliver good ventilation have been put to the test in a London school. Tony Cull describes the outcome.
The Notre Dame Catholic girls’ school in Southwark, central London, has been based on the same site for over 150 years. The existing building dates back to the Victorian era and 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 from 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. Owing 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 to its potential to maintain classroom temperatures and improve air quality whilst 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 innovative 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.
To ensure an accurate evaluation and provide a performance comparison with the Cool-Phase system, 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 IT classroom equipped with Cool-Phase and would provide a baseline with which to compare performance.
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| Good control of temperature in this IT room is achieved using Monodraught’s Cool-Phase system — which also provides ventilation. |
To compare the environments before the Cool-Phase trial, data-logging equipment was installed in each classroom to monitor temperature and CO2 levels every minute during the Spring term and confirmed that the rooms did indeed have similar internal heat loadings.
The results show that Cool-Phase achieved an impressive reduction in average temperatures before and after the installation. The percentage of hours between 8 am and 4 pm 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°C for 59% of the time, while Cool-Phase reduced the time in its IT classroom to just 2%.
With the AC system turned on in the second control room, some areas were overcooled and the AC was turned off. 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, explaining why so many hours above 25ºC and 28ºC were recorded — even with AC installed.
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. To some extent this was expected because the control IT classroom had windows only on one side, whereas the Cool-Phase classroom had windows on opposite sides of the room, allowing cross ventilation. An improvement in the background air quality between Spring and Summer terms can be explained by windows being opened more frequently.
However, despite the opening of windows the Cool-Phase system resulted in a marked reduction in the number of hours when high CO2 levels were recorded. In fact, the 44% of hours recorded above 1500 ppm in the control IT classroom was reduced to just 2% in the Cool-Phase IT classroom — a major improvement. CO2 levels above 1500 ppm correlate with studies indicating poor concentration levels and tiredness.
The deputy head-teacher Jocelyn Lewis, who regularly teaches in the classroom, says, ‘The installation of the Cool-Phase system has had a profound effect on the students. They settle more quickly, and there is a much more focused start to the lesson. Now the pupils can concentrate on their learning.’
The head teacher Sr Anne Marie Niblock commented, ‘I think this is a really positive story for the school and the students.’ She adds, ‘Cool-Phase has proved effective, sustainable and economically viable and ideally we would like the system fitted throughout the school.’
Tony Cull is managing director of Monodraught.
