All change or just a phase?

VENTILATION company Monodraught has introduced an air conditioning system which avoids conventional dx technology in favour of a phase-change material (PCM).

A PCM is a substance which is capable of storing and releasing energy. Heat is absorbed or released when the material changes from solid to liquid and vice versa.

Called Cool-phase, the system uses fresh and recirculated air, and has an inbuilt CO2 control to maintain air quality at all times. Running costs are said to be as little as 10p per day.

Cool-phase employs a wax as the PCM. This is micro-encapsulated - a process in which tiny particles of a substance are separately encapsulated for controlled release. Each PCM capsule is roughly 2-5 microns in diameter, and is suspended in an aqueous solution (PCM slurry).

When required, the slurry is pumped to and from the insulated tank through the heat exchangers.
Unlike conventional air conditioning, Cool-phase cannot maintain a specific temperature, but rather air quality within a designated temperature range.

When under automatic control, Cool-phase will seek to maintain a comfortable temperature range, however the integrated CO2 sensor will always override the temperature control if the level exceeds 1200ppm, allowing for the ingress of fresh air.

Cool-phase in its current configuration uses an average power consumption of approximately 40W.

The floor standing unit is mounted indoors against an exterior wall. Fresh air is drawn into the system via a series of circular louvres and recirculated air via a concealed floor level opening positioned at the front of the unit.

Both the incoming and recirculated air is controlled by insulated motorised volume control dampers. Once air has entered the system, it is drawn through a particle filter before passing through the heat exchangers and into the space.

Night time cooling

In order to provide the cooling effect, the system requires the PCM to be charged overnight. During this period, the tangential fans are set to full, providing conventional night-time cooling and as well as charging the PCM.

During the daytime, the system draws fresh air into the space. As long as the outside air temperature is below approximately 23°C, the system will simply provide fresh air without using the PCM.

If however the temperature exceeds 23°C, the system will close off the insulated exterior damper and open the interior damper and re-circulate the air within the space. The PCM is then pumped through the heat exchangers, allowing heat absorption to take place.

The inverse is true for the heat recovery mode. During late afternoon when the interior space has been heated through associated gains, the system will re-circulate a proportion of the air through the system capturing heat within the PCM. The following day, the energy can then be released, tempering the incoming fresh air.

Each system will provide a volume flow rate of around 300m3/h. In addition, the system is capable of providing 1kW of cooling, and will provide a temperature differential in the region of 5°C.

The only maintenance required is to periodically clean the filter. The PCM will require replacing at the end of its 10 year life span.