Memoirs of an Engineering Student | Stirling Engines

The Stirling Engine was first conceived in the early 1800’s

I met our new engineering intern for the first time last week. Continue reading

Optimal Electrical Distribution Design Reduces Energy Costs

A properly planned electrical distribution design can reduce energy cost in the medium to long term while allowing for future development and growth.  St. George’s College, located in Kingston Jamaica is an example of a high school campus which has expanded over the last three decades without the electrical distribution system being optimised. One of the strategies that should be first employed is the optimisation of the electrical distribution system prior to the implementation of any alternative energy solutions.

The 8.1 hectare (22 acres) campus of St. George’s College in 1975 when I was a first former, consisted of the following buildings:

  1. The newly constructed Adrian Chaplin Industrial Arts Building,STG
  2. Dinand & Collins Lower School Blocks,
  3. Jesuit Residence (later renamed the Quinlan Building)
  4. The Faculty Building,
  5. Biology Lab,
  6. Chemistry Lab,
  7. Physics Lab,
  8. Fourth Form Block & the Headmaster’s Office,
  9. O’Hare Building,
  10. Emmet Park and Club House,
  11. Winchester Park,

After my departure in 1982, the following buildings were added or building use modified over several years:

  1. Abe Issa Auditorium & Canteen/Computer Lab Building,
  2. The Samuel Carter Library,
  3. Archbishop Lawrence Burke Building,
  4. The rebuilding of the Fourth Form Block damaged during Hurricane Gilbert which now houses the Student Development Centre,
  5. The converting of the Jesuit Residence (two floors) into an expanded Faculty and Administration (Quinlan) Building.

Furthermore, the school population grew from approximately 600 boys in 1975 to over 1400 students (since girls are now admitted to sixth form) presently.

The moot question is, was the existing (1975) electrical distribution system upgraded over the last thirty-nine (39) years to accommodate the growth in the size of the school plant? With each new building added, except for maybe the rebuilding of the original Fourth Form Block, more than likely, new electrical meters were added.  As the school evolved, the electrical distribution system evolved without proper planning which has contributed to rising operating electricity costs.  With expansion St. George’s College has ended up with multiple electricity supply meters instead of one single point of entry for its electricity supply.  It is a contributing factor to a monthly unsustainable energy bill totalling close to J$1M per month.

In order to mitigate the effects of the high monthly energy bill school administrators are looking towards the implementation of alternative energy solutions.  Steps have been taken where the some of the traditional street lights on the school campus are solar powered lights.  Although this is a laudable green alternative, it still does not solve the bigger problem the school is facing.  What if the school’s electrical distribution system instead of just evolving was planned as each expansion in the school plant took place? Would the monthly energy cost be at the current level?  Probably not, as the school’s energy rate category would have been either a Rate 40 or 50, depending on the designed Kilo-Volt Ampere (KVA) Demand. This would have attracted a lower energy rate, with a time of day option, instead of the current energy Rate 20 category that each meter in the school is now access.

Since the electricity provider’s responsibly ends at the line side (input) of the meter, it is then the responsibility of the customer to ensure that the downstream system (i.e. beyond the meter) is capable of carrying the demand load.  The Government Electrical Inspector does not provide design services. They only inspect the installed system to ensure that it is safe to be connected to the electricity provider and thereafter issue an inspection certificate.  Therefore, the efficiency of the design is not taken into consideration by either the electricity provider or the Government Electrical Inspector.  The efficiency of the design is the sole responsibly of the end user, that is, the customer.

For example, a school  plant which has three individual electricity meters, with an average Kilo-Volt Amperes (KVA) demand of 18 KVA each, at three phase, 220 volts supply, would have a total demand of 54 KVA.  Since the total demand for each individual meter is less PVthan 25 KVA, the rate category for each meter would be assigned Rate 20 service, which is the small commercial category that attracts a non-fuel charge of J$12.42 per kilowatt hour. There is no demand charge and the customer is billed solely on the amount of kilowatt hours consumed during the billing cycle. However, if the school was to combine the three electrical meters into one meter, with a single point entry, and a properly designed power distribution system, then the rate category would now be Rate 40 that attracts a non-fuel charge of J$3.54 per kilowatt hour; a saving of J$8.88 per kilowatt hour or 72%!  Although the rate 40 would attract a demand charge of J$1,332.84 per Kilo-Volt Amperes (KVA), the customer would be able to manage the KVA demand of the school plant with the implementation of demand reduction strategies, such as power factor correction, once they are enjoying a lower non-fuel energy rate.

Secondary schools do not have the required resources, financial and otherwise to undertake the necessary planning needed for an expansion in the school plant, unless it is being undertaken by the Ministry of Education.  In this case, the Ministry would ensure that POVthe necessary required resources are allocated to the expansion project.  However, in most cases the Scope of Work is limited to just the expansion for all the building consultants involved and excludes the existing buildings on the campus.  Whereas this limited Scope of Work (SOW) will be adequate for the engagement of the architects, civil/structural engineer, this is not the case with the electrical engineer.  As in the case with the expansion of the Annotto Bay High in St. Mary under the ROSE II project, the Scope of Work was limited to only the expansion for all the consultants, which resulted in a second electricity meters being installed instead of a consolidation into one cost effective electricity meter for the entire school plant.

An expansion in the school plant will always result in an increase in the KVA demand, which would necessitate an analysis of the existing electrical distribution system.  This by its very nature, even when engaged directly by the Ministry of Education is very expensive and as such is not included in the Scope of Work (SOW).  Where the schools themselves undertake the expansion, it is normally done at reduced fees by the building consultants and with the same limited Scope of Work.

If the Scope of Work include an evaluation of the existing electrical distribution system, then a comprehensive electrical distribution design, modular in nature, that will take care of the current and future expansion needs of the school can be executed.  This design at its core would be to optimise the power distribution to ensure the following:

  1. Efficiency – distribution transformers and cables are sized correctly for current and future  load growth requirements,
  2. Reliability – distribution system is 99.999% reliable with nuisance tripping of circuit breakers almost non-existent and current flow to load is properly balanced,
  3. Modular – Power take-off points are consistent with any developed school plant master plan.  This would mean that future expansion would only necessitate marginal spending on the electrical distribution system,
  4. Robust – The designed system would grow in tandem with any expansion of the school plant
  5. Adaptable – Alternative energy solutions would be easily implemented and at minimal modification cost,
  6. Manageable – Energy uses at the various load take-off points could be monitored and demand reduction strategy easily implemented.

Therefore, the first step that is necessary in reducing the monthly energy bill is to evaluate the electrical distribution system to ensure it is optimised for the current and intended uses.  This would make the implementation of the recommendations of any energy audit undertaken easier and more beneficial.  Furthermore, the implementation of any alternative energy solutions would be less expensive, since the electrical distribution backbone would have been properly designed.

It is time we forego short term gains and replace them with those that have long term well thought through benefits.

Courtney O. Currie P.E has over the past twenty-two years undertaken electrical distribution design projects for educational facilities in Jamaica and Barbados.  He also served on the Board of Governors for St. George’s College, his alma mater, between 2006 – 2009 and specialises in the design of power distribution systems and the integration of alternative energy solutions in existing facilities.