From: amirza@bronze.ucs.indiana.edu (Anmar Caves)
Subject: Re: Why not 120 VDC ?  Why invert?
Organization: Indiana University
Date: Wed, 27 Jan 1993 15:18:04 GMT

In article <1k0635INNrkq@gap.caltech.edu> carl@SOL1.GPS.CALTECH.EDU writes:
>In article <1993Jan25.014943.1904@michael.apple.com>, ems@michael.apple.com (E. Michael Smith) writes:
>>>True.  However, if you care anything at all about energy efficiency, you don't
>>>use resistive heat sources.
>>
>>Blanket statements don't always hold ...  speaking of which, what 
>>non-resistive electric blankets are you aware of? ;-)
>>
>>There ARE places where resistive heat continues to make sense...
>
>Electric blankets (except, perhaps, in hospitals) don't fall into one of those
>places.  Maybe an electric blanket is useful when treating someone for
>hypothermia.  For any application where the person using the blanket is capable
>of generating heat, other alternatives work equally well.  For moderate (i.e.,
>above -20 degrees F) conditions, simple wool blankets are quite useful (you
>might need to use a few of them, but they work).  For lower temperatures, a
>blanket with an aluminum core works quite well.

Maybe for you Carl, but this doesn't extrapolate well.  Specific
examples are elderly people, IE people who are prone to developing
chronic hypothermia, you know, those people who keep their houses at
80F.  Many of these people *don't* generate enough heat at basal
metabolism to keep warm unless they're in a very warm environment.
Other examples are people with poor peripheral circulation.  These
people will have cold legs and feet no matter how many blankets they
have.  This includes a large percentage of the female population.

Personally, I like it cold, and generally don't like electric
blankets, but that's just my prference.

>Jus how is it that you, known, unless I'm confusing you with someone else, for
>favoring energy conservation, are now advocating electric blankets in
>situations where they're not required?

I can see it quite easily.  Someone can have an electric blanket which
may use 500-600 watts over the night (most blankets are between
100-150 watts and may have a duty cycle of 50-70%), and be able to
keep the house cooler during the night, or keep a lower overall temp
in the house, or avoid heating at all in warmer climes.  In that case
such an item would be appropriate to conservation.

Please note that I'm not saying that it's appropriate in all cases,
merely that it's not as innappropriate as you seem to think.

>
>So you're going to run TWO sets of wires throughout your home, one for AC and
>one for DC?  Once you've committed to the expense of having an inverter in the
>first place, the cost of increasing the capacity of the unit under
>consideration is relatively small.

Running both makes a lot of sense from the efficiency standpoint.  Low
demand items such as doorbells, DC clocks, answering machines, some
lighting such as closets or marker lights, etc, can be run a lot more
efficiently on low voltage because they were designed that way from
the start.  I've only done one all-120VAC design, I've done dozens of
mixed designs and a couple of small low voltage only designs.
As far as inverters go, I'd rather my inverter set be able to go into
sleep mode when there is no draw than to have it constantly running
supplying all those low draw appliances.  The best designs have a
dedicated inverter for the lighting circuit, and another for the high
demand items like the fridge or microwave or the like.  
This stuff is fun to play with because it can be mixed and matched to
suit an individuals needs and wants, in other words, no absolutes.

-- 
Anmar Mirza   # Chief of Tranquility  #My Opinions! NotIU's!#Purveyor of
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