3. ACTIVE STORAGE VERSUS BUILDING M

3. ACTIVE STORAGE VERSUS BUILDING MASS

Using the mass of a building to store cooling is being applied in some new construction (pipes embedded in concrete floor slabs) and even some retrofit applications (controls to pre-cooling the building). Successful applications need to take great care in assuring comfort conditions do not swing out of acceptable levels, since yearly salaries per square meter are over 100 times the cost of energy to condition that some space. Therefore a 10% savings in yearly energy use is lost with just 2 hours per year of non-productive time, keeping people comfortable and productive is the highest priority of most employers.

Active cool storage systems are undetectable by the occupants of the building and now are very similar to a standard central chilled water system (Figure 2). The systems are chiller based, closed and pressurized, with only three main differences: The chiller is controlled differently since it is not operated in direct response to building load; you need a secondary coolant (usually 25 % glycol/75% water solution) so you can run the chiller below freezing point of water, and of course the thermal storage device.

The most popular[5, 6] ice storage devices sold around the world are known as Internal Melt Ice-On Coil which have a heat exchanger coil submerged in an insulated tank (Figure 2a). The water in the tank never goes

anywhere and depending on the mode of operation is frozen and thawed by the secondary coolant that circulates between the chiller, the storage device and the load. During off-peak hours, the chiller runs and creates a -4 C solution which gets circulated to the submerged ice coil, thereby slowly causing the water in the tank to freeze. The ice expansion simply increases the water level in the tank. This change in water level can be measured to give an accurate inventory of your storage.