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Let’s Not Be Passive About Phase Change Materials (PCM)

Phase Change Materials

This is a guest post by Jeremy Sumeray of Armstrong Ceilings, looking at the benefits of using of PCMs in ceiling products.

“Greening” buildings is not a modern phenomenon. Using elements of them to conserve energy and their impact on the environment is a practice that goes back to prehistoric times when cavemen intuitively recognised the value of thermal mass in creating a comfortable indoor environment.

Hundreds of years before the adoption of the Kyoto Protocol in 1997 brought climate change to the attention of the contemporary masses, the Vikings took that most obvious of eco-friendly signs – the green roof – with them when they settled throughout the Northern Hemisphere in the 8th to 11th centuries. And it was back in Germany in the 1960s that the modern trend for green roofs really started to gain momentum.

At around that time, scientists started experimenting with PCMs (Phase Change Materials) which absorb heat when temperatures are high, typically during the day, and release it when temperatures drop, typically at night.

This technology is now incorporated in a plethora of building products ranging from wall boards through plaster and screed to ventilation systems. But one of the least intrusive solutions, especially for refurbishment purposes, is PCM ceiling tiles which are ideally suited to climates like ours in the UK that drop below 20ºC at night.

These passive LHS (Latent Heat Storage) units can be exchanged for standard ceiling tiles with minimum disruption, to delay the requirement of air conditioning by up to eight hours by reducing high-usage peaks and help use up to 50/70% less energy.

These are just two of the results of a two-year R&D programme during which more than 50 different PCM materials, configurations and conditions were tested, with fire resistance and acoustic performance tested alongside the thermal element.

A trial of PCM at a mid-rise masonry office building in central London saw a number of PCM metal cassettes replace standard mineral tiles in the centre of the ceiling of a meeting room that was suffering from overheating and heavily reliant on air-conditioning.

The 600x600mm PCM tiles, which are reversible and can be wholly recycled at the end of their life,  comprise an infill of 25% PCM material with a melt point of 23ºC, providing a total heat storage capacity of 136.2 Wh/m².

They covered 60% of the 47.5m² ceiling in the basement room that had an air circulation rate of 13l/s m² managed by a split HVAC system incorporating a ventilation fan. Occupancy, temperature, airflow and air conditioner energy use were monitored for six months.

The pilot showed that when heat could be purged at night, the room used 20% and 70% less energy compared to a similar untreated room.

In addition, three individual tests (conducted as part of BSRIA job number 55749 and reported in BSRIA report 55749/1) by BSRIA Ltd (Building Services Research and Information Association) using three types of air conditioning systems – displacement ventilation, overhead air and overhead air ducted return – in a 16m² insulated thermal test chamber at the organisation’s independent Laboratories in Bracknell, Berkshire, showed:

#1. PCM tiles provided useful energy storage with 30%-50% ceiling coverage, more coverage allowing for greater thermal storage.

In this first test, 0%, 30% and 57% PCM coverage gave 0Wh, 662Wh and 1,260Wh of thermal storage respectively. Adding 662Wh of thermal storage delayed the operation of the air conditioner by 1:20 hours with a 30 W/m² load in the displacement ventilation configuration while 1,260Wh delayed this by 4:27 hours. The PCM tiles typically reduced temperature variations on the ceiling to +/- 1ºC.

#2. It was possible to discharge the accumulated heat using airflow rates typical in HVAC systems.

This test, with 0% and 30% coverage, showed PCM can be successfully purged with airflow rates typically used in overhead air and unducted return systems. Purge times are affected by the amount of energy stored in the ceiling (662Wh), purge air temperature and purge air velocity. The key result was that lowering the purge temperature from 18ºC to 14ºC decreased the purge time by 3:07 hours.

#3. Selection and design of HVAC played a key role in ensuring optimal efficiency of PCM ceilings.

Again with 0% and 30% coverage, the test showed thermal mass is used most effectively in displacement ventilation types of systems which typically feature low airflow rates and greater amounts of stratification. Ceiling-based thermal mass also worked well in “well mixed” overhead air systems although the storage does not last as long as in displacement ventilation systems.

Tests are now also being carried out on two naturally-ventilated classrooms at schools in Bath and Nottingham where PCM coverage is 47% (for a 62m² room) and 53% (52m²) respectively.

With increasing energy costs and greater awareness of carbon emissions, so the old lessons of thermal mass, natural ventilation and low-energy cooling are becoming part of modern energy strategies.

And with most of the software packages available for the energy modelling required during a building’s design stage now including the possibility of adding PCM to the analysis, the development of more effective cooling and ventilation strategies is available from the word go.

About the Author: Jeremy Sumeray is Senior Segment Manager, Sustainability for Europe, Africa & Middle East at Armstrong Ceilings. You can check out their range of products on SpecifiedBy or follow them on Twitter @ArmstrongCeilin

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