Maximum Demand Calculation

Without being rude, 1000 watts is nothing. I live in Thailand (I'm Australian) & even the poorest of Thais have a minimum 15 amp (at 220 volts) supply. Where did you get this figure of 1000 watts per unit? Has future expansion been allowed for? Where are you?

It is 1000W average power I feel is perfectly Ok (in fact for me it is quite high) - 24 Units/ day or 720 Units/month for a normal domestic is high.

Let us say (my case) -1.5T AC - 7 Hrs - 7-8 Units,+ fridge, CFL lamps(negligible), fans etc- may not add up the other 10 Units.

But the max demand is other case -

1.5KW (AC) + may be my washing M/C is On (1.5KW) + M/W Oven+ All fans+ Tv+Fridge+ Electric iron+...

max demand may be about 7 to 8KW

So it is very difficult to predict the max demand from the avge unless you have any idea of connected loads.

BTW- there are moments when most of the loads are on simultaneously (I have observed it) except of course the lesser ones (fans and lights)

Please look at this calculation from a different direction. Using an average is not the correct approach. For example, if I have an air conditioner that runs in the evening and a refrigerator that cycles on and lights and a TV or stereo then the demand in the evening could be quite high. Now if I turn everything off and while I sleep and only the refrigerator cycles on and off during the night, the demand is low. If I average the two conditions and use this calculation for feeders and branch circuits, the installation will not be adequate. A better approach is to total the loads that will operate at the same time multiplied by 100% and add 125% of the largest load (probably the air conditioner). This will provide an adequate design without any room for future expansion. Take this figure and round-up to next highest common overcurrent device rating. Better to have more than enough than not enough. A design that is not adequate will be seen as a failure. Err on the side of caution.

Peak and average are going to have very little to do with each other. Are the flats occupied during the hot hours, or are most of the occupants at work then? Furthermore, power consumption is going to vary according to the season- even in the tropics, when the only seasons are "wet" and "dry", there will be significant variation in peak demand during the different seasons. How many residents in each flat? This will have an impact. What economic level are we talking about? Rich people use more power than poor people.

Forget the average. Calculate the load from each unit for all possible equipment- AC's, water heaters, refrigerators, lights, entertainment, computers, etc. Multiply that times 800. That is your peak load. The average has nothing to do with this.

Hi Sunnylele,

How do you arrive at this figure i.e 1000watts? Mind you load demand calculation is not just suming up the total power requirements of your appliances. Other factors like demand factors, diversity factors, load characteristics, and others are considered in accordance with IEE regulations.

I suggest you get an engineer to handle that for you, He will duly consider all necessary parameters to give the right estimate.

thanks guys, your inputs helped solve my prob

Just don't forget to check local codes when using diversity factor. Some local authorities don't like using diversities.