Charging mode
Overnight the chiller is used to store cooling energy in the TES tank . The heat transfer fluid is cooled by the chiller to temperatures below the phase change temperature of the PCM. Circulating this fluid through the tank causes the crystallisation of the PCM contained in the container within the TES tank. The energy is stored at constant temperature as latent heat during the liquid-solid transition at the pre-determined scheme capacity.
Discharging mode
When the system demand is greater than the on-line chiller capacity the cooling energy is provided by combining the capacity of the chiller and the TES tank. The chiller works at full capacity with the TES providing the balance or the TES can be set to discharge at the set value with the chiller providing the balance capacity.
PCM Thermal Energy Storage Benefits
The benefits of a TES scheme are as follows:
Reduce
Reduce Chiller size by 30 to 70%
Cooling towers/ Dry Coolersby 40 to 80%
Electrical supply & distribution (transformer size)
Chiller short cycling
Maintenance cost
Running cost by up to 40%
Noise level
Electricity charges: demand (kW) and energy cost (kWh
Enhancement
Cooling capacity from existing plant
Electrical and plant utilisation
Equipment life
Efficiency and reliability
System control
Over and above the benefits of the incorporation of a Thermal Energy Storage ( TES) within a Chilled Water Installation as described above the use of PCM`s as the storage media provides the following additional scheme enhancements.
Bespoke Media: The PCM media within the TES is specifically selected for the scheme operating design temperature and thus removes the requirement for interface barriers and any associated inefficiencies.
Free Cooling: Free cooling can be availed of to charge the TES with the Crystal Air PCM when external ambient conditions are at 5 deg C or lower . .
Maintenance: The PCM TES has no requirement for a regular maintenance programme .
Non- toxic Phase Change Media: The inorganic salt based media is non-toxic and disposal of the material at the end of its life in 20 years is not subject to a EPA license .
Site Installation.- GRP Sectional Insulated Tanks
The TES installation shall consist of a Tricel insulated GRP sectional tank which shall be fabricated on site on a pre-prepared level concrete base or RSJ support beams . The tank shall be complete with internal inlet and outlet sparge pipes designed to achieve a uniform flow velocity of 0.3 m/s with a resistance of 50 kPa across the tank. The tank will be complete with internal diffuser screens on both the intake and discharge ends. The tank on-site fabrication shall be completed by the tank manufacturers fabrication crew.
Once the GRP tank has completed and tested for water tightness over 48 hours the Crystal Container shall be placed in position within the tank in battery format by Crystal Air operatives.
The tank shall be complete with 2 No 25mm sockets for thermos probes ,1 No 25mm socket for a conductivity probe, 1 No 50mm drain, 1 No 50mm air siphon/alarm and 1 No 50mm water level probe per tank division. The thermos probes , conductivity probe , alarm and water level probes shall be provided under the Controls contract works. The thermos probes are for determining the available capacity of the TES in conjunction with the run time and discharge rate of the variable speed pump on the discharge side of the TES and linked back to the BMS. The conductivity probe is to monitor the water condition and should be linked back to the BMS.
The nett effects of the controls to include the following:
Control over Cooling discharge arrangements and all the associated equipment
Pumps and control valves
Storage System
Charging and discharging times
Equipment status/alarm.
Commissioning
When all the containers are placed inside the tank and available to charge the system the following protocol to be adhered to for commissioning.
1) Take a sample of the water going to the tank with system determined anti-freeze solution, measure and record the electrical conductivity.
2) Fill the tank with the system chilled water and apply the design static pressure without circulating throughout the system and ensure that no leakage especially from man holes, tank joints etc. After circulating the water within the tank take another sample for comparison with the original value and ensure that the conductivity has not changed.
Any increases may signify that some of the PCM cassettes might have been damaged during their installation. Drain the system and replace the damaged cassettes. Recheck conductivity reading.
3) After a few days operation i.e. complete freezing and melting cycles , take another fluid sample from the system circulation and compare with the original electrical conductivity readings and record the data as part of the commissioning records.
Water Treatment
Should the TES be inactive for long periods it is advisable to treat the water with biocides to avoid the effects of stagnant water.
Crystal Air can recommend or supply this solution.