Calculating Load from Meter Readings

<So if I divide this by 2,400 (total hours in 100 days) I get 5.6Kw? is this 5.6 Kw per hour?>

No. It's 5.6kW, or 5.6kWh per hour. This is the average consumption over 100 days and it is still useful information. The server peak load is required to size the generator correctly and it's going to be bigger than this. Try adding up the installed ratings of all the appliances needing generator support assuming they are all on at the same time, adding a bit on for power-up and expansion, dividing the whole by some suitable power factor, and selecting a generator from there.

Send your e-mail ID i would be glad to send you all the information you need on this subject.

crm

Invitation declined.

The utility company bills you for the energy (kWh) you use, not the power (kW). Power is the rate of energy usage, not the energy itself.

By way of analogy, think of energy as distance, and power as speed, or, distance/time. You can go ten miles, but ten miles (energy) is ten miles no matter how fast (power) you get there. Your speed can vary (as you turn on and off appliances), but eventually you'll cover the ten miles. The utility company bills you for this "distance." How fast (or slowly) you cover this distance is up to you.

PWSlack is correct. Size your generator according to peak load, plus some. You don't want your generator to labor under a peak load. If the peak load will be high, buy a Ferrari.

Some of the newer electric meters have the capability to provide information about peak loads, average loads, total kWhrs, etc. See if your local utility company can provide one, if you're not in a great hurry to purchase a generator.

Otherwise, PWSlack and europium are spot on (as the Brits (and a few others) say).

I agree with this logic Generators are sized and sold based on your peak demand your Generator manafacturer should be in a postion to help you in selection of right generator.electrical demand is expressed in Kva(Kva x.8pf=Kw)if you dont have a demand meater you need one to check.

crm

Hi Bill,

Do these meters display this info directly, or do they transmit this info to the utility company who then sends it to the customer? This would be great info to have on hand for certain applications.

-e

The ones I have seen and consulted on were made by Schlumberger. The meters (under development at the time) had a data port to connect to a computer and were primarily designed to measure the peak loads and power factors of large industrial plants. The power companies funding the R&D were losing money because they couldn't convince large users to modify their operations so that both the user and producer could benefit. The power companies started charging for peak demands and power factors, and the industries started listening.

This technology eventually led to residential meters which not only had the capability to record all the information above but also transmit it to receivers in electric company (or subcontractors') trucks, effectively replacing the meter reader who used to walk through yards of residential areas driving the dogs mad.

I don't know of a meter which displays the information at the meter, but that doesn't mean there aren't any. The ones I worked on were developed about 10 - 15 years ago.

Most service meters today have an LCD screen which scrolls through the various register values. However, customer service for your local utility should be able to provide you with a printout of your demand (peak) and average values over at least the last year.

You could also install your own meter, either on your entire service or on just the panels you want to monitor. I prefer Electro Industries, but there are several manufacturers with reasonably priced versions available.

The math is a good start , however, it assumes your site is working around the clock at the same rate.

(5.6 kw/hour is equivalent to about 94 X 60 watt bulbs on at the same time or 375 X 15 watt fluorescent bulbs.)

How much does the power change with the season with air conditioning, or heat requirements? You should be prepared for all situations. It is best practice to look at the consumption for the whole year. (even a few years to see a trend)

Assuming it stays about the same here are a few calculations to consider. Adjust as required.

If the site only works say a 8 hour day where most of the consumption is in the 8 hours, then you will have to triple the load requirement to manage peak requirements. say about 16.875 kw

Since most generators operate best at 75% of maximum power you should also add another 25% say 21 KW

Also, is the building full? Will there be any growth in the next 5 to 10 years?

If the building is at maximum now and will not change (doubtful) a 20kw generator may suffice. If growth and increased use of computers and other equipment is likely, you may consider going for a 50 kw generator, so it won't have to be replaced in a few years.

The other possibility is to get a 20 kw generator now, and when the growth happens get a second generator. It is sometimes better to have two generators in case one does not work.

You may also want to consider if you want to power everything when the generator is running. There is always the choice of only operating emergency lighting and critical systems when the generator is operating.

Good advice. As A/C units have reactances (motors), be sure to accommodate power factor in sizing the generator(s).

A local electrical supply house may be able to loan or rent a clamp on amp probe w/a paper tape

a few days or weeks of data should get you the rest on the info you need

Here's a simple formula that I believe will provide real time electrical load (power factor corrected) on a service using a conventional (rotating disk) meter:

load (watts) = (3600 X Kh)/disk revolution time in seconds

kH indicated on my meter is 7.2

Just checked my residential load with the 3T A/C operating and came up with 4470. The disk was spinning so quickly, I timed 10 revolutions and averaged the time @5.8 seconds.

Here's my source:

http://jidanni.org/geo/taipower/meter_en.html

I trust there are others :-).

With the advent of high technology meters, standing around with a stop watch will become a thing of the past as we become able to check real time usage on line.