Path: utzoo!news-server.csri.toronto.edu!cs.utexas.edu!usc!zaphod.mps.ohio-state.edu!ub!kitty!larry
From: larry@kitty.UUCP (Larry Lippman)
Newsgroups: sci.electronics
Subject: Re: Need to buy or build 3-phase recording kW meter
Summary: Not trivial
Keywords: 3-phase power measurement
Message-ID: <4781@kitty.UUCP>
Date: 7 Mar 91 05:26:24 GMT
References: <1991Mar5.161244.503@phri.nyu.edu>
Followup-To: sci.electronics
Organization: Recognition Research Corp., Clarence, NY
Lines: 58

In article <1991Mar5.161244.503@phri.nyu.edu> roy@alanine.phri.nyu.edu (Roy Smith) writes:
>	The building I live in (a 54 unit residential cooperative) is
>getting whomped by peak usage charges on our electric bill (last month was
>$650 in kWh charges and $350 in peak usage).  Our peak last month was 18.0
>kW (our average was about half that).

	I am assuming that this is a separate service for common building
functions, since such a low amount of usage and peak demand would be
highly improbable for all 54 tenants.

>I have been given the task of trying
>to figure out how to cut our electric bill.  A few years ago, we got timers
>for all the lobby and hallway lights (which are more than half of our power
>usage) but while that cut our total usage, it didn't lower our peak any.

>	What I'd like to do now is put a recording meter on our main power
>feeder and watch our power usage during the course of the day for a few
>weeks.  What's the cheapest way to do that?  I could go to the board and say
>"Look, if you front me $2000 for equipment, I'll find a way to save you
>$300/month in electric and you'll make back your investment in 7 months" but
>I suspect they won't go for it, so it's got to be something I can do out of
>pocket.

	There must be some motor or electric heating loads that account for
the peak demand.  I would guess elevator loads, for one.  Many older
elevator systems can create a significant demand.  All you need is to have
that demand present just ONCE for ANY 30 contiguous minutes in one month
and you are saddled with that figure!  I can envision morning go-to-work
elevator operation as readily accounting for your peak demand.  Also,
older elevator systems are not that efficient - some use a motor-generator
to provide DC power for the elevator motors.

	I have a feeling that you are NOT going to save $ 300.00 per month,
no matter what you do.  Being generous, 18.0 kw demand is no more than 20
effective horsepower by itself - not much of an elevator load!

>I can probably scrounge up an old chart recorder, but I'm stuck for
>sensors.  Any ideas?  It has to be non-invasive (I can't interrupt the wire
>to insert a series-shunt ammeter) so I'm stuck with clamp-on meters.  Are
>there clamp-on power meters that one can get cheap in these sorts of power
>ranges?  I can get some clamp-on ammeters, and volt meters for each phase,
>but that I'll only get me kVARS, which isn't very useful for my purposes.

	You can probably rent a recording system from General Electric
Rentals, EIL Instruments, etc. for probably $ 200.00 per month.  You
certainly should be able to see where you stand in one month.

	Even before doing that, I would suggest taking a serious look at
your elevator system - which could well be your most significant cause
of peak demand.  Since you may not have any options here, why even go
to the trouble of setting up a recording system?

	If you are bound and determined to assemble your own recording
system, then let me know, and I can give you more specific advice.

Larry Lippman @ Recognition Research Corp.  "Have you hugged your cat today?"
VOICE: 716/688-1231       {boulder, rutgers, watmath}!ub!kitty!larry
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