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Power Density - Single or Three Phase?

Simon87
Hello all,


Quick question regarding initial load assessments using power densities.


Keeping my numbers simple, lets say we take a small power density of 20W/m2, over a GIA of 1000m2, this gives a max demand of 20kW. Now i have always taken this to be a single phase load, and so if the space is being served via a three phase power supply, would it be correct to split this 20kW across the three phases (assuming perfect balance across phases). i.e. the small power maximum demand for the space would be 6.7kW.


Any help would be appreciated.


Thanks in advance,


Simon.


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  • 0
    Hello Andy, and thanks for your response.


    The problem is they dont total up to th same. If we are looking to size the incoming supply there is a big difference if the max demand is single or three phase. If we take the outcome of the earlier example and assume the small power load is all three phase, we would need to apply for a 21 kVA TP&N supply (assuming .95 PF), whereas if we assume the load is all single phase (and will be split across all three phases) this would mean we only need a 7 kVA TP&N supply. Depending on the building type there may be some three phase equipment that would fall into the banner of small power, but the majorty of small power is likely to be single phase (in hindsight the example would have worked better with lighting!)


    The figures ive used are only hyperthetical, but if we consider the same method for load analysis on a 5,000m2 office building, this would have a huge difference in the size of supply required.
Reply
  • 0
    Hello Andy, and thanks for your response.


    The problem is they dont total up to th same. If we are looking to size the incoming supply there is a big difference if the max demand is single or three phase. If we take the outcome of the earlier example and assume the small power load is all three phase, we would need to apply for a 21 kVA TP&N supply (assuming .95 PF), whereas if we assume the load is all single phase (and will be split across all three phases) this would mean we only need a 7 kVA TP&N supply. Depending on the building type there may be some three phase equipment that would fall into the banner of small power, but the majorty of small power is likely to be single phase (in hindsight the example would have worked better with lighting!)


    The figures ive used are only hyperthetical, but if we consider the same method for load analysis on a 5,000m2 office building, this would have a huge difference in the size of supply required.
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