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From: wb8foz@mthvax.cs.miami.edu (David Lesher)
Newsgroups: sci.electronics
Subject: Re: Need to buy or build 3-phase recording kW meter
Message-ID: <1991Mar05.225113.8417@mthvax.cs.miami.edu>
Date: 5 Mar 91 22:51:13 GMT
References: <1991Mar5.161244.503@phri.nyu.edu>
Reply-To: wb8foz@mthvax.cs.miami.edu (David Lesher)
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Organization: NRK Clinic for habitual NetNews Abusers
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In <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 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?  

Wattmeters cost real money. I suggest you just assume you have a
reasonably constant power factor, and just stick to measuring
volt-amps, vice watts.

To do so, you will need appropriate current transformers. Some are
available clamp-on, but I don't know if that would include sizes suited
to your application. As I recall, 1000 to 1 is at least one ratio
available. You may wish to buy none-clamp-on models, and get an
electrician's help to cut building power, disconnect each feed cable,
ship it thru the donut, and reconnect it. (the solid model are MUCH
more likely to be available surplus, i.e much cheaper.) You MIGHT be
able to get them from the utility - push the "energy saving/cut peak
loading" angle.

As for the metering, you could get a chart recorder. I would avoid
this. Most chart recorders have pens. These are devices designed to put
ink on your hands and clothes, but NEVER on the chart. They succeed.
Some chart recorders do use non-ink (thermal paper, electro-discharge
marking, etc.) schemes.

If you could get a PeaSea with an A/D board, it could not only log
data, but plot charts, and also generate real-time alerts, etc - all a
SMOP {simple matter of programming ;-}

One question I have is: what ARE your loads? The most well-known peaks
are elevators. But at least in my experience, the utility bills them on
a separate account, with ultra-premium rates. The #2 peak is HVAC. Do
the suites have individual window units?  In general, what do you plan
to do with this data you get? The commercial systems offer
load-shedding on peaks. Will the residents go along with this?

(Have you considered using PIR sensors/timers on the hall lighting, so
it is off until someone enters the area?)
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