There are definitely AC motors (and DC motors) that are built (even designed)
so
badly that they are inefficient. As I stated in my last post, the automotive
industry is noted for these.
Even when we start with a good motor, there are situations where it is
misapplied,
and that affects efficiency. You have pointed out one, where the motor cycles
on
and off frequently, which forces the motor into its inefficient operation
region
frequently (e.g. capacitor start mode). Another cause is a commercial decision
to
use a single type of motor across a line of different sized products to get a
longer production run of motors (hoping for economies of scale in manufacture
of
the motors and the goods in process inventory for manufacture of the units that
use
the motor). In the case of refrigerators, this means that there may be a
mid-line
unit that uses the motor efficiently, a small unit for which the motor is too
big
(so it runs often for short periods, so spends a higher ratio of its time in an
inefficient mode), and a larger unit where the motor is too small, so the load
may
force the motor to work too hard, saturating the field, producing excess heat,
thus
lowering efficiency.
It is hard for the consumer to know what design work and decisions went into
the
creation of a specific appliance or machine they are purchasing. However, the
EnerGuide and EnergyStar (and similar in other jurisdictions) systems give some
idea of relative efficiencies (not absolute efficiencies, and the consumer also
needs to know to keep as many other variables constant as possible).
For heat pumps and air conditioners, there are also standards related to the
CoP
(Co-efficient of Performance). Provided this data is available from a reliable
source, it should be possible to compare across machines to establish relative
efficiency.
Picking the right size AC or heat pump unit for a house is difficult (based on
correct scientific and mathematical formulae), which is why those in the trade
rely
on rules of thumb. And the rules of thumb almost always are based on the worst
case (slightly overestimate the area of the building, assume worst orientation
to
the sun, no shade, no thermal mass, maximum human occupancy... ) Because it is
cheaper for the installer to put in too large a unit (the home owner pays for
the
extra size, and the inefficiency of the unit) than to have to come back, remove
the
unit that has turned out to be too small (perhaps only once and in a completely
unusual situation) and replace it with a larger one. So long as energy prices
remain cheap and hidden (one hydro bill for 60 days at a time, provided to the
customer a full month after that period is over, for the entire building)
instead
of realistic and up front (appliance-based readouts, instantaneous and with
logs),
given my experience with human nature, I don't see much hope for change with
the
mass of consumers. To borrow a phrase from my business consulting days, "you
can't
manage what you can't measure". It certainly applies to our energy consumption.
It seems almost innate, we try to maximize what we can measure or sense. Put
somebody in a conventional gasoline-powered car today, equipped with a
speedometer
and little else in the way of instrumentation, they will drive to maximize
speed.
Put in instrumentation that displays fuel economy (e.g. the Prius "hybrid" or a
Chryser New Yorker I owned a long time ago), and people start to drive to
maximize
fuel economy.
For appliances, this is probably a ways off. I have built a set-up with
batteries,
DC ammeter and an inverter that permits me to get a good sense of what any
specific
machine (12 volts DC or 120 volts AC, with alllowance for inverter losses) is
using
in the way of energy. No automated logging. There are such units available
commerically as well. However, until these are in widespread use, and possibly
built into large devices (e.g. household-scale heat pumps), I think mass
concern
over the efficiency of such devices will not happen.
Darryl McMahon
To: biofuel@yahoogroups.com
From: Hakan Falk <[EMAIL PROTECTED]>
Date sent: Fri, 19 Mar 2004 06:56:22 +0100
Subject: Re: [biofuel] AC vs. DC electricity, was: Electricity
storage
solutions.
Send reply to: biofuel@yahoogroups.com
>
> Thanks Darryl,
>
> I appreciate your explanation and your support. Because of several factors,
> the common equipment for compressors are very in inefficient, especially
> AC/Heat pump units. The way they have been designed and then dimensioned,
> are a great robbery and rip off. The customers know nothing and the common
> HVAC engineer is trained by the suppliers. It must be someone in the design
> and development of them, that know much more than me. The large majority of
> people involved, are probably quite ignorant and belive what they learn in
> school and information from suppliers. Older and experienced professionals,
> often know that something is wrong, but not exactly why. There are no
> specially develop dimensioning rules and therefore it has been used linear
> dimensioning formulas, that traditionally are used for heating systems.
> This despite that those formulas are already faulty for heating systems, or
> any heat transfer calculations.
>
> I posted earlier,
> http://energy.saving.nu/hvac/acunits.shtml
> on this issue, and as a part of my "first aid" advices
>
> With this, I probably got away easier and with less losses, by have them
> running longer periods. My savings from switching to "new" technology are
> probably around 20%, instead of the more common 30 to 35%.
>
> I am getting older and have to think about health risks. As a young man, I
> was upset bout those "rip offs", but have now developed a more humorous
> attitude. In Sweden the most common cause for triggering heart attack, is
> shoveling snow. In Spain it is probably trying talking to the infamous PTT
> company Telefonica and I am not going to add the HVAC engineers to this. It
> is better to laugh about it and slowly change it to the better. LOL
>
> Hakan
>
>
> At 03:28 19/03/2004, you wrote:
> >Actually Hakan, I thought you pretty much covered the topic for electric
> >motors at
> >a high level. For me, the AC vs. DC decision comes down to what each one
> >is good
> >at. I have some experience with the subject (and the electric vehicles and
> >appliances from antique to modern to back that up).
> >
> >AC motors strengths.
> >No brushes, for reduced maintenance, and reduced drag.
> >Best in low torque, fixed-speed, relatively constant load
> >operation. Work-around
> >for demands with high start torque is to use a capacitor start. So, with
> >some good
> >design work around sizing, they should be good for things like refrigerator
> >compressors and furnace fans (with the capacitor start), and also cooling
> >fans,
> >pumps, rotisseries, clocks, etc.
> >AC motors weaknesses.
> >Providing efficient operation at varying speeds and loads requires modifying
> >frequency in conjunction with voltage and current in non-linear fashion, a
> >complex
> >control issue. Therefore, varying loads and speeds are a headache for AC
> >control.
> >Certainly can't just hook it up to the mains and expect reasonable
> >operation and
> >efficiency.
> >
> >DC motors strengths.
> >Several configurations available, series, shunt, compound, separately
> >excited,
> >which can be tailored to meet specific load and speed
> >requirements. Typically can
> >handle heavy starting torque demands quite easily. Varying speed and load
> >fairly
> >easy by simply controlling voltage.
> >DC motors weaknesses.
> >Brushes reduce efficiency, increase maintenance.
> >
> >I know there are motors called brushless DC, but for my purposes these are
> >effectively AC motors. There are also universal motors, which can run on
> >AC or DC,
> >but in effect, these are AC motors with brushes, and seldom are found in
> >sizes
> >above 1/2 hp.
> >
> >So, if you want your electric motor to operate efficiently, the most
> >important
> >things are to pick the right type of motor for the job to be done, then
> >pick the
> >right size for the expected load, then focus on getting a quality unit
> >that will
> >reduce operational losses.
> >
> >In my opinion, in most commercial appliances, the motor and control are
> >usually not
> >the main focus for efficiency gains. Outside of mass-produced automotive
> >units,
> >motor efficiencies will exceed 85% in their specified operational
> >range. Better
> >than 90% is not unusual. Especially in household applications, where lack of
> >efficiency is expressed as objectionable noise and heat, there is an
> >incentive for
> >manufacturers to keep those losses to a minimum. (In automobiles, there
> >is already
> >so much heat and noise being produced that the amounts coming from
> >electric motors
> >simply is not noticed, so the standards are lower.)
> >
> >For example, in the case of a refrigerator or freezer, it would probably
> >make more
> >sense (energy saved per dollar invested) to improve/increase the
> >insulation in the
> >refrigerator to reduce heat infiltration, and improve the seal of the
> >door(s) to
> >reduce air exchange.
> >
> >Where DC motors in refrigerators were deemed to be more efficient than AC
> >motors,
> >my analysis concluded that the gains actually came from operating the unit
> >from
> >batteries rather than mains (AC) power, or the refrigerator was smaller
> >(because
> >battery power, usually off-grid, is more precious than mains power), or
> >the unit
> >was better insulated and sealed (again to meet the different needs and
> >values of
> >off-grid customers). In areas that get more insolation than we do, it
> >usually
> >turned out to be cheaper to buy an additional solar panel, an extra
> >battery and an
> >efficient, relatively small, mass-market refrigerator (one that would
> >qualify for
> >an Energy Star rating now) than to buy one of the specialty,
> >"hyper-efficient" DC-
> >powered refrigerators developed for the off-grid market. (The analysis
> >assumed
> >there would already be an inverter in the household that could be used.)
> >
> >Now, you probably wished you had killed the thread. <grin>
> >
> >Darryl McMahon
> >(off to do some sewing on an antique Pfaff sewing machine - the kind where
> >the foot-
> >powered treadle was replaced by a small electric motor with a pulley to
> >the same
> >pulley driven by the treadle)
> >
> >To: biofuel@yahoogroups.com
> >From: Hakan Falk <[EMAIL PROTECTED]>
> >Date sent: Thu, 18 Mar 2004 22:31:38 +0100
> >Subject: Re: [biofuel] AC vs. DC electricity, was:
> >Electricity storage
> > solutions.
> >Send reply to: biofuel@yahoogroups.com
> >
> > >
> > > MM,
> > >
> > > I seams to have done it again! Killed off a very interesting discussion.
> > >
> > > I do not know if I maybe am to abusive or what is wrong? Not good for me
> > > and the goals that I thought that I was championed. If I offended you or
> > > anyone else, I must apologize to both you and the list, but I hoped that
> > > this could lead to an important energy saving discussion.
> > >
> > > My belief is that variable output DC engines in appliances, AC units and
> > > heat pumps, are very important. These (up to 30% savings), together with
> > > CFL lamps (more than 60% savings), are probably the closest we can come to
> > > simple "silver bullet" and "ready for use" saving technologies, in
> > > domestic electricity use.
> > >
> > > Hakan
> > >
> > >
> > > At 02:44 17/03/2004, you wrote:
> > >
> > > >MM,
> > > >
> > > >Before we get too exited about savings by using DC instead of AC, we
> > > >might look
> > > >at where and why we have this large differences in the energy use by
> > > >appliances. Let us first establish the fact that a conversion as such,
> > will
> > > >cost us between 3 to 10%, depending on method, size and application.
> > > >
> > > >When you talk about appliances, we should also include the AC/Heat pump
> > > >unit in this and very large savings can be done. The losses are more
> > > >created by the use of electrical engines/compressors, than by the use of
> > > >alternate current or direct current. The large differences in energy use
> > > >does not come from the type of current, but from the way the capacity
> > > >control is done. The revelation control in AC engine used in the
> > appliances
> > > >is governed by the fixed AC frequency and the capacity control is done by
> > > >starting and stopping the compressor. The revelation control in the DC
> > > >engine is governed by voltage/current and the capacity control is done by
> > > >varying the speed/force of the engine. Since you already are very
> > familiar
> > > >with electrical engines, you are probably ahead of me now, about the
> > > >consequences of the different methods. I will anyway mention that the
> > > >consequences can be somewhere between 30 to 45% more energy use by the
> > > >capacity control of the AC engine. After the conversation losses, we
> > end up
> > > >with around 25-30% difference in energy use for appliances.
> > > >
> > > >In the past it was very large differences cost and durability between the
> > > >AC and DC engines, in favor to the AC engines. By new development, these
> > > >differences are no longer an critical issue and the energy use have
> > started
> > > >to be the absolute critical issue for certain engine applications.
> > > >
> > > >If you look at losses in distribution of DC, we must agree with the much
> > > >higher efficiency of AC. One very important issue is also the security
> > > >aspects, which more or less totally disqualifies high voltage DC in homes
> > > >and for general use in appliances. It is better and more manageable of
> > > >security design, if the conversion is done in the appliance and close to
> > > >the engine. The large loss of lives, that a general high voltage DC
> > > >distribution would cause, is not worth it.
> > > >
> > > >Hakan
> > > >
> > > >
> > > >At 22:13 16/03/2004, you wrote:
> > > > >On Mon, 15 Mar 2004 23:48:36 -0800 (PST), you wrote:
> > > > >
> > > > > >
> > > > > >Monday, March 15/04
> > > > > >murdoch <[EMAIL PROTECTED]> wrote:
> > > > > >
> > > > > >>What about the issue of efficiency in converting from AC >to DC and
> > > > > >>then back to AC?
> > > > > >
> > > > > >>Each of these conversion actions may have
> > > > > >>consequences in terms of lost energy, but I haven't yet >figured out
> > > > > >>the losses. This has come up for me recently, so it's >on my mind.
> > > > > >
> > > > > >According to an "Inverter comparison chart," supplied by West Marine
> > > > > Co. Maximum efficiency of the inverters they list range from 88% to
> > > > > 94%. All of the products that they list appear to be made by Xantrex,
> > > > > (Heart Interface, Trace Engineering and Statpower are all now owned by
> > > > > Xantrex making them probably the biggest manufacture of
> > > > > inverters). Many of these products have built in battery chargers.
> > > > > I
> > > > > don't know if the efficiency of the charging circuit is equal to
> > that of
> > > > > the inverting circuit. I don't have efficiency data on chargers.
> > > > > >
> > > > > >If we assume that a good charger will deliver about 90% efficiency on
> > > > > the conversion from 120 VAC to DC, and a good inverter will deliver
> > about
> > > > > 90% back to AC, you can expect to lose about 20% in conversion.
> > > > > >
> > > > > >I hope this helps put you in the ballpark regarding efficiency.
> > > > >
> > > > >Yes, it does help, thank you. I was looking into a converter, to go
> > > > >from AC to DC, because there is a DC refrigerator out there
> > > > >(Sundanzer) that appears to be so efficient that I thought it might be
> > > > >worthwhile to consider.
> > > > >
> > > > >The price for an AC-to-DC converter was reasonable, but the salesman
> > > > >wasn't 100% sure about efficiency losses. We made sort of a little
> > > > >side-project about this, because nobody had really asked these
> > > > >questions before, and they're just starting to sell Sundanzer,
> > > > >alongside Equator and Sun Frost.
> > > > >
> > > > >He got a figure of 5% that we used as a sort of stop-gap. But I think
> > > > >to be safe, I'd add a bit more on to that 5%, and that "bit-more"
> > > > >jibes with your research.
> > > > >
> > > > >In the end, I think I'm going to get a Sun Frost RF-12, and eschew the
> > > > >separate Fridge-separate-freezer idea. I had that thought because
> > > > >there are times when I want a fridge but don't use a Freezer that
> > > > >often, and the savings of unplugging the freezer could be substantial?
> > > > >
> > > > >The Sun Frost is super-expensive compared to a decent small Energy
> > > > >Star Conventional Fridge I could buy at Home Depot, but it's still
> > > > >about twice-or-more efficient, and might in the end save me enough
> > > > >energy to save me money. And since it's AC, I'll be able to avoid
> > > > >this inconvenience of changing over my whole house to this or that.
> > > > >
> > > > >Sundanzer does have this one wild product... a fridge that is designed
> > > > >to operate solely on a modest (90-120 watts?) solar array in certain
> > > > >types of regions without any batteries at all:
> > > > >
> > > > ><<<http://www.sundanzer.com/PDF/SunDanzer_Batt_Free_Tech_Sh.pdf>http:
> > //www.sundanzer.com/PDF/SunDanzer_Batt_Free_Tech_Sh.pdf>http://www
> > > >
> > .sundanzer.com/PDF/SunDanzer_Batt_Free_Tech_Sh.pdf><http://www.sundanzer.com/PDF/S
> > u>http://www.sundanzer.com/PDF/Su
> > > > nDanzer_Batt_Free_Tech_Sh.pdf
> > > > >
> > > > >MM
------------------------ Yahoo! Groups Sponsor ---------------------~-->
Buy Ink Cartridges or Refill Kits for your HP, Epson, Canon or Lexmark
Printer at MyInks.com. Free s/h on orders $50 or more to the US & Canada.
http://www.c1tracking.com/l.asp?cid=5511
http://us.click.yahoo.com/mOAaAA/3exGAA/qnsNAA/FGYolB/TM
---------------------------------------------------------------------~->
Biofuel at Journey to Forever:
http://journeytoforever.org/biofuel.html
Biofuels list archives:
http://infoarchive.net/sgroup/biofuel/
Please do NOT send Unsubscribe messages to the list address.
To unsubscribe, send an email to:
[EMAIL PROTECTED]
Yahoo! Groups Links
<*> To visit your group on the web, go to:
http://groups.yahoo.com/group/biofuel/
<*> To unsubscribe from this group, send an email to:
[EMAIL PROTECTED]
<*> Your use of Yahoo! Groups is subject to:
http://docs.yahoo.com/info/terms/
