PCM Installation Guideline for Shelter Applications

admin — Mon, 28 Sep 2009 14:37:31 +0000

The following steps should be taken to ensure reliable, good quality back-up, particularly for installation in Telecom Shelters:

Heat transfer rate mainly depends upon convection (major source of heat removal) and some by radiation. Q = h x A x ΔT is the formula where ‘h’ is the Convective coefficient and depends upon the mass flow rate of fluid, (i.e. air in the telecom shelter). ‘A’ is the area exposed for air to come in contact with the PCM profiles. ‘ΔT’ is the temperature difference which is of the user’s interest.
Heat transfer rate mainly depends upon convection (major source of heat removal) and some by radiation. Q = h x A x ΔT is the formula where ‘h’ is the Convective coefficient and depends upon the mass flow rate of fluid, (i.e. air in the telecom shelter). ‘A’ is the area exposed for air to come in contact with the PCM profiles. ‘ΔT’ is the temperature difference which is of the user’s interest.
Since placement of profiles in a shelter is constrained by the placement of the BTS (Base Transreceiver Station) unit, batteries, power interface units or switching equipment, the profiles containing PCM are placed only in the free area available. Hence, not all the surface area is available for heat transfer.
Generally, for good fluid flow in a shelter, 2-3 fans with the specifications of approx. 50W, 24V/48V DC, and 3000 RPM are recommended. Lower RPM fans will reduce the air circulation and may hamper necessary heat transfer.
Locations of the fans depend entirely on the position of the PCM profiles and other Electronic equipment.
Theoretically, for one hour back-up, for 1kWh, 20 kg of savE™ HS 29 is required, based on the latent heat of savE™HS 29. This translates to 240 kgs of HS 29 for four hour backup with 3kWh heat source.
For four hour back-up 3kW x 4 hrs (12kWh) an exposed (in direct contact with air) area with a minimum of 27 m2 of surface is required. The number of savE™ HS 29 profiles of 4 kgs (0.4 Sqm) mm is usually 70 profiles for this exposed area (translating it to 280 kgs of HS 29). While using the 2.8kgs profiles (0.3 Sqm), the requirement of both area and salt quantity is met by using only 86 profiles (translating it to 240kgs only).
It may be noted that it is not only the quantity of salt essential for desired backup but also a minimum of exposed surface for heat absorption. This may at times necessiate additional profiles.
In general, the position & number of profiles and fans will vary from shelter to shelter. It is strongly advised that individual testing and experimentation be done by the Shelter manufacturer/installer to determine the optimum:
- number of profiles required
- placement of profiles
- location of fans
- RPM of fans for effective heat distribution/direction towards profiles

The PCM panels are mounted on-site approximately 30° from vertical. Three to four such racks can be put on one frame, having the facility of mounting 35-60 PCM panels. The upper three sections in each rack are normally left empty for effective air circulation provided by a DC fan (24V/48V) placed on top of the frame. Two different pattern of racks are available.

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PCM Installation Guideline for Shelter Applications