INTRODUCTION
Active Cooling is the new concept in refrigerative cooling systems for use in the telecommunications industry. The Active Cooling System (ACS) is designed and proven to operate with maximum efficiency in extreme conditions experienced in Africa. The size of the cooling units can be easily configured to provide cooling of any size of Radio Base Station (RBS / BTS) where AC Mains Power is unreliable or non-existent.
FEATURES
• Constant temperature control
• Cooling without AC Mains Power for up to 48 hours
• Constant control of relative humidity
• Reliable with low maintenance osts
• Cost-effective replacement of standby generator power and conventional air-conditioning
CONVENTIONAL AIR-CONDITIONED EQUIPMENT SHELTERS FOR BASE STATION APPLICATION
When considering the power requirements of BTS sites, two main elements require power: namely the Base Station and transmission equipment, and the air-conditioning systems.
Both base station and transmission equipment require DC power supply. This is normally achieved by using AC power to charge a battery bank, which in turn supplies the DC power to the equipment. Depending on the capacity of the battery bank, it is not essential to have AC Mains power available at all times.
(See fig. 1)
The air-conditioning, needed to keep the equipment within operating temperatures, requires AC power constantly to avoid the ambient temperature rising in the shelter, thereby causing the base station equipment to shut down.
APPLICATIONS FOR ACTIVE COOLING
On reliable AC Mains powered sites, to reduce maintenance costs, increasing the Mean Time Between Failure (MTBF) on BTS and Tx equipment and battery bank, and reducing maintenance requirements on ACS, as opposed to conventional air conditioning systems.
On unreliable AC Mains powered sites the same benefits as above, but with additional reduction in maintenance and operating costs relating to standby generators. Dependent on the ACS design and degree of AC mains unreliability, the need for deployment of an SBG may be obviated. In the worst case, if an SBG is deployed, the actual run-time can be kept to an absolute minimum, allowing months - and sometimes even years - between services and refueling intervals.
On sites where no AC mains power is available, or is not economically feasible, this system can provide the same benefits as above, with the additional benefit of not having to run the SBG for 24 hours per day - as would be the need in the case of conventional air-conditioning systems. Under such circumstance the ACS is designed to operate with self-generated AC power from the SBG, being available for a maximum of 8 hours per 24 hour period. The SBG then does not run for the following 16 hours of that 24 hour period. The SBG operating and maintenance costs are reduced by 66% of the costs that would be incurred if using conventional air-conditioning systems.
COST ADVANTAGES OF ACS
CAPITAL EXPENDITURE (CAPEX)
(Note: The values below are indicative only as of January 2005 and are based on typical rates for a country such as South Africa.
Exact models are created per customer requirements in a particular country.)
When calculating capex, the following applies to a site where no AC mains power is available (cost of shelter, cooling system, AC/DC wiring, rectifiers, batteries and alarm systems):
| - ACS with 1x SBG |
USD 76,666.00 |
| - Air-conditioner cooled shelter with 2x SBG |
USD 71,833.00 |
| - Difference |
USD 4,833.00 |
If an overhead 400V AC mains power route to a site is built, at an average cost of USD 8,050.00 per kilometer, the following would apply:
| - ACS with no SBG |
USD 54,166.00 |
| - Air-conditioner cooled shelter with 1x SBG |
USD 49,333.00 |
| - Difference |
USD 4,833.00 |
| - Cost of ± 1km of AC power line |
USD 8,050.00 |
From the above it can be seen that the capex required to build an ACS site and air conditioner cooled site will be the same if the AC mains power line is ± 0.5km long. If the length of the AC mains power line is more than 0.5km, it would be more expensive to build an air-conditioner cooled site.
OPERATIONAL EXPENDITURE (OPEX)
At an air-conditioner cooled site where no AC mains power is available and an SBC is required to operate for 24 hours per day, the opex would be ± USD 3,716.00 per month on a typical metro site.
At an ACS site where no AC mains power is available and and SBC is required to operate for only 8 hours per day, the opex would be ± USD 1,450.00 per month on a typical metro site.
With reference to the above, it would require only in the order of 2 months to recover the additional capex of USD 4,833.00 required to build an ACS site where no AC mains power is available. Thereafter, the annual saving in opex would be ± USD 27,192.00/site/annum.
SUMMARY
ACS is cost-effective from a capex point of view if the site is more than 0.5km away from an AC mains power route.
ACS is cost-effective from an opex point of view where no AC mains power is available as the difference in capex (USD 4,833.00) is recovered within ± 2 months by savings achieved in the reduced operating costs of the SBG, which is only required to operate for 8 hours per day, instead of 24 hours per day.
ACS is cost-effective at a site where AC mains power is available but unreliable because there is no need to install a SBG - which would be required to operate as standby to power an air-conditioner cooled site.
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