Will sunlight damage the electronics?

[mm]

Will sunlight damage the electronics of a circuit board?

The power company installed a radio-controlled switch on my air
conditioner, and mounted it on the side of my house. It has an ugly
label which clashes with the natural look of my little yard.

I was peeling it off when I noticed that it covered a fairly darkly
tinted plastic window, and inside the window was the circuit board
that included the receiver and the control that turns the AC off when
the Power Company Central Command wants it to.

There is a much window below the label through which one can see a
green LED. In the late afternoon shaedI only knew I could see the
circuit board because I could see the glowing LED. (Does anyone know
if that means there is power to the AC, or only that there is power to
the controller device itself?)

I stopped unpeeling at that point. I don't want to cause their
product to wear out sooner than normal. I Would the sunlight harm
anything inside?


BTW, after I signed up up for this, a man showed up at my door, handed
me a brochure and then went about mounting the thing to my brick wall.
I watched. He drilled two holes and then two holes for a cable clamp,
all in the mortar, but when it's gone, I'll have to replace the mortar
and the replacement won't match in color. After he was gone I read the
brochure and it said he could mount it to the air-conditioning
condensor if I wanted. I much would have preferred that, so I
wouldn't have to look at the ugly thing at all, label or no label.
But the guy, affable and pleasant as he was, didn't say a thing about
that. The previous device had been mounted to the AC, and didn't have
a label either, but it was a little narrower, and didn't come with
such a long cable.

Thanks.

 

[Sylvia Else]

Starting about 25 years ago, the local power company started a program
whereby they installed these boxes to home AC units and electric water
heaters, supposedly to reduce peak demand on the grid in times of high
demand.

Wonderful idea. If the AC units are creating an excessive load, just
turn them off remotely. Beats investing in grid infrastructure.

Sylvia.

 

[D Yuniskis]

Wonderful idea. If the AC units are creating an excessive load, just
turn them off remotely. Beats investing in grid infrastructure.

The problem is getting people to buy into this idea. It
usually is under a different tariff than "normal service".
And, utilities often don't price those tariffs rationally.
People are hesitant to let someone else turn off a "comfort
feature" if they aren't getting something "significant" for
their potential inconvenience [1]

The same is true of ToU tariffs. Its as if the utility
*wants* the benefits that these tariffs offer *and* wants
to figure out how to get more money from the subscriber at
the same time!

[1] Though often load shedding can be implemented as load
*shifting* so you don't really feel any significant "loss".
E.g., most hotels/motels have their HVAC systems arranged
on a staggered schedule. So, even if you turn the "heat"
(ACbrrr) on in your room *now*, you might not actually
*get* that until your "timeslice" comes along.

 

[mm]

Wonderful idea. If the AC units are creating an excessive load, just
turn them off remotely. Beats investing in grid infrastructure.

SDWOTN.

(Sarcasm does not work on the net.) You might be serious. If so, I
think you're right. The infrastrucutre would be generators. Very
expensive.

Most homeowners don't really need air conditioning anyhow. They
should open the windows and buy some fans. My greatgrandparents
didn't even have electric fans.

In a way, I shouldn't take this money for putting a switch on my AC.
I only use it for 2 or 3 weeks most summers anyhow, so they probably
don't cut down the load when they radio me. Last summer was the
least hot of my life, and I didn't use the AC at all.

Sylvia.

D, it was pretty easy to get me to sign on. They pay 10 or 15 dollars
(I forget which) dollars a month during the summer for the AC and
since I almost never use the AC, it's defitely a bargain. But I think
a substantial percentage of people have signed up, 10, 20, 30 percent
or more. I have one friend who uses it all summer who did.

They also pay maybe 5 dollars a month during the summer for the water
heater. I don't know why, but I didn't like the idea of them
fiddling with that. I think I thought it woudl come out ugly looking,
even though it is in the basement, sort of like the AC did the second
time (I had signed up 10 years ago during the previous round. I don't
know if BG&E had the first round that Dave mentioned.)

I get the impression they only turn off the power for short periods
two or three days a summer. Maybe 20 days at the most in a hot
summer.

 

[Sylvia Else]

SDWOTN.

(Sarcasm does not work on the net.) You might be serious. If so, I
think you're right. The infrastrucutre would be generators. Very
expensive.

It was intended as sarcasm, but of course it's also a true statement
from the perpective of power suppliers.

Most homeowners don't really need air conditioning anyhow. They
should open the windows and buy some fans. My greatgrandparents
didn't even have electric fans.

I have AC installed. It only gets used for a dozen days a year (and a
few nights) at most. But at those times, it wouldn't be much fun without
it. The problem with comparing the present situation with that in the
past is that people in the past didn't have a choice, just as they
didn't have a choice about dying from diseases that are now either
easily treatable, or easily preventable.

Even fans are not so effective when the air is so warm that sitting in
front of a fan feels like sitting in front of a fan heater.

Would I survive if I didn't have AC? Probably. Would I like it? No.

In a way, I shouldn't take this money for putting a switch on my AC.
I only use it for 2 or 3 weeks most summers anyhow, so they probably
don't cut down the load when they radio me. Last summer was the
least hot of my life, and I didn't use the AC at all.

It's fair to take the money. The infrastructure required to support
extreme peak loads (which is not just generators, but transmission gear
as well - lines, switches, transformers, the works) is only used
infrequently. If the need for it can be obviated by persuading people
not to use it, then there is a substantial cost saving. Although you may
only use AC for two or three weeks in the summer, it's likely to be the
same two or three weeks that other people are using it.

D, it was pretty easy to get me to sign on. They pay 10 or 15 dollars
(I forget which) dollars a month during the summer for the AC and
since I almost never use the AC, it's defitely a bargain. But I think
a substantial percentage of people have signed up, 10, 20, 30 percent
or more. I have one friend who uses it all summer who did.

They also pay maybe 5 dollars a month during the summer for the water
heater. I don't know why, but I didn't like the idea of them
fiddling with that.

That actually makes more sense. It encourages people to have tanks with
a decent capacity so that turning them off at times of high load has no
impact. My own hot water is heated overnight at a lower tarif anyway.

I think I thought it woudl come out ugly looking,

even though it is in the basement, sort of like the AC did the second
time (I had signed up 10 years ago during the previous round. I don't
know if BG&E had the first round that Dave mentioned.)

I get the impression they only turn off the power for short periods
two or three days a summer. Maybe 20 days at the most in a hot
summer.

I can't even see how that would help them. ACs run on thermostats. Turn
them off for a while, and they'll simply run for longer when they're
turned back on. So unless they're left off until the peak load drops
(ie, because the outside temperature has, or at least the sun goes
down), there'll be little or no net saving.

The real problem power suppliers face is that consumers are not subject
to the true costs of supplying the power. Indeed, those consumers who
cannot afford things that create high peaks, like airconditioning, are
subsidising those who can. In Sydney, where I live, time of day metering
is being introduced, which at least charges more during period where
demand tends to be higher, but even they don't ramp up the cost during
heat waves. As an AC owner, I'm not complaining, but it doesn't seem at
all equitable.

Sylvia.

 

[Sylvia Else]

Wonderful idea. If the AC units are creating an excessive load, just
turn them off remotely. Beats investing in grid infrastructure.

The problem is getting people to buy into this idea. It
usually is under a different tariff than "normal service".
And, utilities often don't price those tariffs rationally.
People are hesitant to let someone else turn off a "comfort
feature" if they aren't getting something "significant" for
their potential inconvenience [1]

There's not much point in having a comfort feature if it's likely to get
turned off at the time of greatest need.

I'd only go with it if the saving were enough to finance a petrol
generator to supply the power instead.

The same is true of ToU tariffs. Its as if the utility
*wants* the benefits that these tariffs offer *and* wants
to figure out how to get more money from the subscriber at
the same time!

Well, they probably do.

Sylvia.

 

[D Yuniskis]

Dave M wrote:

Starting about 25 years ago, the local power company started a
program whereby they installed these boxes to home AC units and
electric water heaters, supposedly to reduce peak demand on the grid
in times of high demand.

Wonderful idea. If the AC units are creating an excessive load, just
turn them off remotely. Beats investing in grid infrastructure.

The problem is getting people to buy into this idea. It
usually is under a different tariff than "normal service".
And, utilities often don't price those tariffs rationally.
People are hesitant to let someone else turn off a "comfort
feature" if they aren't getting something "significant" for
their potential inconvenience [1]

There's not much point in having a comfort feature if it's likely to get
turned off at the time of greatest need.

It's not "turned off", per se. Rather, it is *deferred*.
I.e., maybe 10 minutes later your ACbrrr will kick in
instead of at the (slightly) earlier time when the
thermostat called for cooling.

Chances are, a normal user wouldn't really perceive the fact
that the ACbrrr kicked in "late" -- the house may rise some
fraction of a degree beyond the thermostat's set point?
But, the *idea* of this is unnerving to many people:
"Oh, I am going to be *so* uncomfortable!"

OTOH, if they were to raise their thermostat's setpoint
that degree (or two?) all the time, they would probably not
notice the difference.

I'd only go with it if the saving were enough to finance a petrol
generator to supply the power instead.

<frown> Defeats the purpose. The utility can produce electricity
far cheaper/cleaner than you can.

The point of ToU and load shedding is to let the utility
cut back on peak loads. This lets them use things like
nuclear energy (good for big, steady loads) instead of
having to fire up coal/gas generators to respond to short
term fluctuations in the load.

Well, they probably do.

The (new?) tariff here borders on ridiculous. You'd have to
shift 2/3 of your load to off-peak to break even.

 

[D Yuniskis]

SDWOTN.

(Sarcasm does not work on the net.) You might be serious. If so, I
think you're right. The infrastrucutre would be generators. Very
expensive.

It's generators plus distribution facilities. Like most utilities
(e.g., phone, gas, etc.) the systems are not designed for
"everyONE to use everyTHING" at the same time. There is some
probablistic/statistical analysis that goes into determining
what sort of "typical" loads will be experienced as well as "bad
cases" (not *worst* case) that are "likely".

Power plants, distribution systems and even the number of
"work crews" are determined by these magic numbers. Once
you start moving beyond a few standard deviations from the
norm, things get brittle. E.g., the ability of the power
plants to respond to changes in demand, the ability of the
*lines* and substations to handle those loads, the availability
of crews to respond to faults, etc.

Additional generating capacity can be brought on line by
burning more fossil fuels. This is expensive and also
bad for the environment.

Most utilities are like diesel engines: they have a sweet spot
where they like to run. Push them much beyond this and they
get cantankerous.

Most homeowners don't really need air conditioning anyhow. They

Shirley you jest? We break 100F in May and that usually
persists through mid October. July and August see this
a *slight* reduction in temperature -- as the humidity
then climbs to over 90 percent (90F at 90RH is quite
uncomfortable -- I don't care how many fans you have!).
And 110+ is *hot* even when the RH is only 10% (should we
give up swamp coolers as well as AC?)

Your comment is akin to telling folks in Chicago that they
don't really need *heat* in February -- just put on another
sweater! I've been outside in -26F with windchills below
-80; a sweatre just ain't gonna cut it! :>

should open the windows and buy some fans. My greatgrandparents
didn't even have electric fans.

And *their* greatgrandparents didn't even have *horses*! ;-)

In a way, I shouldn't take this money for putting a switch on my AC.
I only use it for 2 or 3 weeks most summers anyhow, so they probably

Sure seems like *you* are one of those who "don't really need
air conditioners". Can't you live without it for those two
weeks? :>

 

[JW]

We used to program EPROMS with UV light.

I've never been able to do THAT!

 

[D Yuniskis]

I have AC installed. It only gets used for a dozen days a year (and a
few nights) at most. But at those times, it wouldn't be much fun without
it. The problem with comparing the present situation with that in the
past is that people in the past didn't have a choice, just as they
didn't have a choice about dying from diseases that are now either
easily treatable, or easily preventable.

Even fans are not so effective when the air is so warm that sitting in
front of a fan feels like sitting in front of a fan heater.

Exactly. Every year there are deaths attributed to "lack of
adequate cooling". But, its usually "not anyone *you* know"
so it tends to get ignored. Just like folks freezing to death.

Would I survive if I didn't have AC? Probably. Would I like it? No.

The problem with "excess heat" is there aren't many ways of
"shedding it". And, once your body starts to overheat,
*you* usually aren't qualified to think about how to fix the
problem (it muddies your thinking).

It's fair to take the money. The infrastructure required to support
extreme peak loads (which is not just generators, but transmission gear
as well - lines, switches, transformers, the works) is only used
infrequently. If the need for it can be obviated by persuading people
not to use it, then there is a substantial cost saving. Although you may
only use AC for two or three weeks in the summer, it's likely to be the
same two or three weeks that other people are using it.
Exactly.


That actually makes more sense. It encourages people to have tanks with
a decent capacity so that turning them off at times of high load has no
impact. My own hot water is heated overnight at a lower tarif anyway.

A smarter solution is to have "on demand" water heaters. Silly to
keep 40 - 80 gallons of hot water available 24/7 just in case
you *might* need it. This solution is a throwback to days when
heating water was a slow process and you didn't want to
"inconvenience" the user. :-/

I think I thought it woudl come out ugly looking,

I can't even see how that would help them. ACs run on thermostats. Turn
them off for a while, and they'll simply run for longer when they're
turned back on. So unless they're left off until the peak load drops
(ie, because the outside temperature has, or at least the sun goes
down), there'll be little or no net saving.

Hotels use the same approach with their in-room HVAC units:
they aren't all "enabled" at the same time. In years past,
a simple time sharing scheme was used: some portion of the
units were enabled for N minutes; then, another portion for
the next N minutes; etc. The point being that the units could
bring the room to "the desired temerature" (on average) when
used for only a fraction of the time (i.e., they didn't need
to run at 100% duty cycle to work properly).

Nowadays, technologies like ZigBee are being deployed to
allow for smarter management. E.g., instead of blindly
enabling some portion "now" and another group "later", just
let each unit that *wants* power *request* power. And,
force it to wait until that request is granted (by some
centralized smarts that is tracking who it has "granted"
power to at the present time). So, if you get lucky,
only X% of units will *want* power at any given time.
If more than X% do, then you have to decide how to
limit the actual number of units to that percentage
(i.e., you are back to the original solution) knowing that
*eventually* each room will achieve its desired temperature.

The real problem power suppliers face is that consumers are not subject
to the true costs of supplying the power. Indeed, those consumers who
cannot afford things that create high peaks, like airconditioning, are
subsidising those who can. In Sydney, where I live, time of day metering
is being introduced, which at least charges more during period where
demand tends to be higher, but even they don't ramp up the cost during
heat waves. As an AC owner, I'm not complaining, but it doesn't seem at
all equitable.

Some (US) businesses are charged based on peak demand.
Stated simplisticly, if you use electricity at an X KWHr rate
for 10 minutes and don't use *any* thereafter, you are
charged a rate proportional to X *regardless* of your
TOTAL energy consumption during that billing period (month)!

Things like ToU and Peak tariffs lead to some incredibly
inefficient solutions that waste energy -- but, "save money".
E.g., businesses "make ice" overnight to run their air
conditioning systems during the following day. The cost
of making the ice is artificially cheaper than creating
the same "cooling" during the day (when it is actually
*needed*)

<shrug>

 

[GregS]

Sylvia Else wrote:
Dave M wrote:

Starting about 25 years ago, the local power company started a
program whereby they installed these boxes to home AC units and
electric water heaters, supposedly to reduce peak demand on the grid
in times of high demand.

Wonderful idea. If the AC units are creating an excessive load, just
turn them off remotely. Beats investing in grid infrastructure.

The problem is getting people to buy into this idea. It
usually is under a different tariff than "normal service".
And, utilities often don't price those tariffs rationally.
People are hesitant to let someone else turn off a "comfort
feature" if they aren't getting something "significant" for
their potential inconvenience [1]

There's not much point in having a comfort feature if it's likely to get
turned off at the time of greatest need.

It's not "turned off", per se. Rather, it is *deferred*.
I.e., maybe 10 minutes later your ACbrrr will kick in
instead of at the (slightly) earlier time when the
thermostat called for cooling.

I don't know how the things work, but it could be possible in the event of complete
power failure, to do progressive start ups. Starting all the refridgerators
is bad enough. You might even try to control whose air is on and
whos is off, so all on is not a possibility.

Heat will damage electronics. UV protection will be providd by
any material preferably tinted.

greg

 

[D Yuniskis]

I've never been able to do THAT!

Sure! As long as you want them "programmed" to their
erased values! :>

Actually, I think EPROMS under normal sunlight will
erase in a very short period of time (like a day?).
This is not the same as "under fluorescent light"...

 

[Charlie]

would be damaged by sumlight intrusion. There could be a UV EPROM inside
that could possibly be erased if sunlight got to it on a continual basis,
however, most EPROMS have a label covering the window that protects the
contents. Constant UV exposure from sunlight could possibly damage the
markings on components, but they will likely be OK. Most plastics and
glasses are fairly good blockers of UV. If you're concerned about the
esthetics of the label on the box, paint it or cover it with a piece of
tape. That will not harm the box.

Let me give a real world perspective on the use of EPROM's.
I was involved in a product that needed a ROM to hold some basic logic. To
be sure that the code was right, EPROM's were used because of the neat
ability to quickly update the device by UV erasure and reprogramming. We
probably had about 100 of these for testing and debugging the product.

Now we want to go into production and the required volumes ranged into the
multiple thousands of pieces.
Two factors come into the decision making. First, those ceramic packages
with a window are not cheap. Second, EPROM's and their programming are also
not inexpensive. The best economy is a mask made ROM in a plastic package.
Here the problem was the start of cost of mask making and the delay in
getting real chips of the line.

We settled on a stopgap compromise and started production with EPROM's that
were in plastic packages. The design was frozen and we knew that erasing
would not be an issue. Then when hard programmed devices became available
the transition was easy.
You have to look at the economics of this scenario to see if the savings
are there. If you want 50 to 100 thousand of these it worked well.

As they always say "YMMV".

Charlie

 

[D Yuniskis]

Sylvia Else wrote:

[attributions elided :> ]

But, as I've commented elsewhere, as soon as the AC is powered up it
will stay on for longer to bring the temperature down again.

Yes, but not *much* longer. All you are doing is shifting (in time)
when the house will be "as comfortable" again. E.g., if you
had opened the front door (to carry a large piece of furniture
in/out) you would similarly have disrupted the comfort level
in the house for a short period of time. (if you've ever
"moved" in the summer time, you'd understand :> ) But, that
comfort level is once again restored, ultimately -- *later*.

The big (psychological) problem with load shedding is that
folks don't feel like they have any control over it so
they assume it will be uncomfortable, etc.

OTOH, if the technology was implemented as an *auction*
(I am merely trying to make a point) in which the utility
could alert participants:

"Hi, we need folks to shed some load. We are currently offering
$X for you to shed Y load for Z minutes"

and then respond to folks who have accepted this offer by
adjusting their *new* "bid price" (up or down):

"Due to the overwhelming acceptance of our previous offer, we
are now only willing to offer $x (i.e., x < X) for you to shed
Y load for Z minutes"

or:

"Hmmm... we haven't had many takers of are offer at $X so we are
now sweetiening our offer to $XX for Y load for Z minutes"

Then I suspect most folks would probably complain that watching
for these "offers" is too tedious: "Can't you give me a
SWITCH that I can throw that says "I am willing to accept
ALL offers of $X or more?" (which, in effect, is what the
tariffs do -- except you have to make this commitment up
front!

There is an energy saving, but it's very much a second order effect,
arising form the slightly higher average temperature.

The goal isn't to save energy (though I think the laws of thermo
say you *do* save in this case). Rather, the goal is to
get you to *shift* your energy consumption (in time).

I'm not so sure that's necessarily true for extreme peak loads. They not
only have to generate the power, which is likely to be done using diesel
or some such, but they also have to deliver it to me, which involves
transmission infrastructure which is only used during these extreme peak
loads, but which is there all the time.

The infrastructure is sized for some percentage above nominal.
Of course, going too far *beyond* that causes things to *break*
(hence the blackouts that become newsworthy).

But, things like diesel/coal/gas fired plants that are there
*deliberately* to respond to these short term fluctuations in
demand could, theoretically, be eliminiated if the demand could
be "leveled".

Nuclear power plants, for example, like to put out a steady amount
of power (can we *please* not let this discussion digress into
the pros and cons of nuclear power? :< ) which doesn't lend
itself to rapid response. If you had <fill-in-the-blank> power
source that was ecnomical to operate and had this characteristic,
then you would have a big incentive to coerce users into
adapting their usage patterns to match.

Also, it is important to define what crteria you actually want to
optimize. E.g. "efficiency" can be defined in a lot of different
ways -- many of which are inconsistent with each other :-/

 

[Sylvia Else]

Sylvia Else wrote:

[attributions elided :> ]

But, as I've commented elsewhere, as soon as the AC is powered up it
will stay on for longer to bring the temperature down again.

Yes, but not *much* longer.

The AC has to run long enough to pump out the heat that's flowed in
during the time it was turned off. Heat is ariving in the building at a
rate that's largely a linear function of the difference between inside
and outside temperature, and the energy required to pump it back out is
a slimilarly linear function. So to calculate the average energy
consumption - ie power - you just look at the rate at which heat is
flowing in. That rate is minimally altered by deferring the turn on of
the AC. As I've observed, the rate is slightly lower because the average
difference between the inside and outside temperatures is slight lower.
On a very hot day, which is when this load shedding mechanism is likely
to be most used, the saving will be modest, because the change in
average temperature will be a small fraction of the total temperature
difference.

All you are doing is shifting (in time)

when the house will be "as comfortable" again. E.g., if you
had opened the front door (to carry a large piece of furniture
in/out) you would similarly have disrupted the comfort level
in the house for a short period of time. (if you've ever
"moved" in the summer time, you'd understand :> ) But, that
comfort level is once again restored, ultimately -- *later*.

The big (psychological) problem with load shedding is that
folks don't feel like they have any control over it so
they assume it will be uncomfortable, etc.

OTOH, if the technology was implemented as an *auction*
(I am merely trying to make a point) in which the utility
could alert participants:

"Hi, we need folks to shed some load. We are currently offering
$X for you to shed Y load for Z minutes"

and then respond to folks who have accepted this offer by
adjusting their *new* "bid price" (up or down):

"Due to the overwhelming acceptance of our previous offer, we
are now only willing to offer $x (i.e., x < X) for you to shed
Y load for Z minutes"

or:

"Hmmm... we haven't had many takers of are offer at $X so we are
now sweetiening our offer to $XX for Y load for Z minutes"

Then I suspect most folks would probably complain that watching
for these "offers" is too tedious: "Can't you give me a
SWITCH that I can throw that says "I am willing to accept
ALL offers of $X or more?" (which, in effect, is what the
tariffs do -- except you have to make this commitment up
front!


The goal isn't to save energy (though I think the laws of thermo
say you *do* save in this case). Rather, the goal is to
get you to *shift* your energy consumption (in time).


The infrastructure is sized for some percentage above nominal.
Of course, going too far *beyond* that causes things to *break*
(hence the blackouts that become newsworthy).

But, things like diesel/coal/gas fired plants that are there
*deliberately* to respond to these short term fluctuations in
demand could, theoretically, be eliminiated if the demand could
be "leveled".

But the demand cannot be levelled by short term adjustments to things
like airconditioner demand. The overall demand is higher on hot days.
Deferring an airconditioner load by ten minutes won't alter that.
Getting people to defer their airconditioner loads until night time
would be better, but of course that's not going to happen, at least not
until and unless airconditioners based on a large cold sink become the
norm. That might be a bit of an own goal anyway, environmentally,
because the cold sink would have to be kept cool against the possibility
that the day following would be hot. There would always be some leakage,
so the overall energy consumption of such systems would be higher, even
if they were running on cheaper power.

I suppose it could be argued that some transient peaks arise from a
disproportionate number of AC thermostats switching to on at the same
time, but given the number of ACs around, I'd be surprised if that were
really an issue - the probability of a significant deviation from the
short term average due to such an effect would have to be very low.

Nuclear power plants, for example, like to put out a steady amount
of power (can we *please* not let this discussion digress into
the pros and cons of nuclear power? :< ) which doesn't lend
itself to rapid response. If you had <fill-in-the-blank> power
source that was ecnomical to operate and had this characteristic,
then you would have a big incentive to coerce users into
adapting their usage patterns to match.

Also, it is important to define what crteria you actually want to
optimize. E.g. "efficiency" can be defined in a lot of different
ways -- many of which are inconsistent with each other :-/

While nuclear, and indeed coal, plants cannot respond rapidly to changes
in demand, that is not the reason they are not used to handle peak
loads. It's purely a question of economics. It is not cost-effective to
have such plants lying idle - if that's going to happen, you don't build
them, because they're too expensive to be used that way. You build less
capital intensive plant for that purpose - typically gas or oil powered
(though what we do when the gas/oil runs out isn't clear).

Sylvia.

 

[mm]

But, as I've commented elsewhere, as soon as the AC is powered up it
will stay on for longer to bring the temperature down again.

There is an energy saving,

Radio-controlled AC turn-offs are not meant to be energy saving.
They're meant to be peak-load lessening. It's meant to prevent
brown-outs because of too much load at one time.

 

[Sylvia Else]

Radio-controlled AC turn-offs are not meant to be energy saving.
They're meant to be peak-load lessening. It's meant to prevent
brown-outs because of too much load at one time.

And I'm arguing that they do not achieve that goal.

Sylvia

 

[D Yuniskis]

[bits elided to trim this to manageable size]

The AC has to run long enough to pump out the heat that's flowed in
during the time it was turned off. Heat is ariving in the building at a
rate that's largely a linear function of the difference between inside
and outside temperature, and the energy required to pump it back out is
a slimilarly linear function. So to calculate the average energy

Yes. But, the ACbrr is typically sized such that it can remove
heat much faster than heat infiltrates the home. E.g., in the
hottest portions of the summer, our ACbrrr rarely hits a 30%(?)
duty cycle.

Coonsider that the amount of hysteresis on many (most?) thermostats
is only a few degrees, at most, so we are essentially calling on
the HVAC system to maintain a comfort region of 2 or 3 degrees.
(some thermostats allow this to be adjusted but I suspect
you will find most users don't know this nor do they even know
why they might *want* to adjust it!). Deferring the onset of
the ACbrrr just increases the hysteresis temporarily. The
overall duty cycle remains largely unaffected.

consumption - ie power - you just look at the rate at which heat is
flowing in. That rate is minimally altered by deferring the turn on of
the AC. As I've observed, the rate is slightly lower because the average
difference between the inside and outside temperatures is slight lower.
On a very hot day, which is when this load shedding mechanism is likely
to be most used, the saving will be modest, because the change in
average temperature will be a small fraction of the total temperature
difference.

Again, you're not trying to *save* anything. You *do* save by
increasing the hysteresis that is acceptable to you (assuming you
don't, at the same time, alter the setpoint lower). You save
*more* by increasing the setpoint. What the utilities want is
for you to shift *when* you use that electricity.

I.e., if you shift your usage by 10 minutes, the utility still gets
the same amount of money from you -- because you are still
purchasing the same amount of electricity (essentially). *But*,
they have saved money by not having to overload their distribution
or production system in that 10 minute window!

A "thought experiment" <grin> :

Imagine all ACbrrrs require a 30% duty cycle to maintain their
respective residences at the "right temperature" (whatever
*that* is -- it may be different from one residence to the
next). Now, imagine that all of these were synchronized such
that they ALL turned on their compressors at the exact
same instant EACH TIME. The ACbrrr is the largest single
load in most homes -- it can account for up to 30% (?) of the
peak power capabilities of most homes. Most homes typically
don't use anywhere near their *capacity* ON AVERAGE.

Yet, this pathological behavior would have the utility seeing
a *huge* demand... followed by negligible demand (the load that
the rest of your house represents)... followed by that same
huge demand, etc.

And, this would happen while businesses were (elsewhere)
placing *their* huge demands on the system.
As I said:

But the demand cannot be levelled by short term adjustments to things
like airconditioner demand. The overall demand is higher on hot days.

Sure it can! Yes, the overall demand is higher on hot days.
But, letting each *huge* load (ACbrrr) operate independantly
of each other (as they do currently) means that there is a high
probability (certainty?) that several of them will engage
concurrently. If all of them coincide, then you get a big peak!
Even if that load is only present for a *minute*, the system
has to handle it -- or, "shed it" (by blowing fuses).

Deferring an airconditioner load by ten minutes won't alter that.
Getting people to defer their airconditioner loads until night time
would be better, but of course that's not going to happen, at least not

As I said, that is how some businesses operate, in a perverse
distortion brought about by economics.

until and unless airconditioners based on a large cold sink become the
norm. That might be a bit of an own goal anyway, environmentally,
because the cold sink would have to be kept cool against the possibility
that the day following would be hot. There would always be some leakage,
so the overall energy consumption of such systems would be higher, even
if they were running on cheaper power.

I suppose it could be argued that some transient peaks arise from a
disproportionate number of AC thermostats switching to on at the same
time, but given the number of ACs around, I'd be surprised if that were
really an issue - the probability of a significant deviation from the
short term average due to such an effect would have to be very low.

It isn't. Hence the motivation for these tariffs.
See if EPRI (Electric Power Research Institute) has any
publications on the subject (I know they have, I am just
not sure if they are available to the public -- I'm not
sufficiently motivated to go dig through my files... :> )

While nuclear, and indeed coal, plants cannot respond rapidly to changes
in demand, that is not the reason they are not used to handle peak
loads. It's purely a question of economics. It is not cost-effective to
have such plants lying idle - if that's going to happen, you don't build
them, because they're too expensive to be used that way. You build less
capital intensive plant for that purpose - typically gas or oil powered
(though what we do when the gas/oil runs out isn't clear).

Exactly! You want to size your load to (ideally) fit your capacity.
(sort of like matching source impedance to load). You don't want
excess capacity (if it will never be needed) so you want to get
your capacity to exactly fit your load and then you want that load to
*behave* (i.e., if it is likely to increase, then you will need
excess capacity -- which you don't *want*).

Note that the utilities aren't doing this for *your* benefit
(at least not directly). If they were, they could elect to
automatically set your thermostat higher when you are away
at work, etc. They want to sell you power. They just want
to sell it when it costs them the least!

 

[D Yuniskis]

And I'm arguing that they do not achieve that goal.

How effective they are at doing this currently is something that
you would have to investigate in each particular locality
where such tariffs exist. Note that the extent to which the
tariff is adopted (by customers) will directly impact how
effective this technology can be (i.e., if very few folks
"subscribe", then the utility doesn't have much of a tool
at its disposal).

Air conditioners are very reactive loads. As the power system
is stressed, you get voltage sag. For a resistive load, this
is fine -- the decrease in voltage creates a propportional decrease
in *load*.

But, AC compressor motors are essentially "constant power"
devices -- as the voltage decreases, the amount of current
that they require goes up. And, the relationship (phase)
of that current requirement is not coincident with the
supplied *voltage* (i.e. reactive).

Motors *starting* are even worse. (e.g., preventing
ACbrrs from *starting* is more effective than turning *off*
existing ACbrrs, all else being equal).

Note that, to avoid a "catastrophic event", it may only be
necessary to shift a load by a small time interval --just
long enough for alternate supplies to come on-line. E.g.,
imagine a high tension line tripping and effectively
resulting in a reduction of supply -- sag -- so existing
load has to be carried by other -- redundant -- lines.
Until additional lines can be brought into service, the
system is stressed. If you can shed loads at the consumer
you can avoid shedding *all* the consumers (i.e., a major
outage).

The system can *always* break. You are just trying to reduce
the number of scenarios/criteria under which it is brittle.

I think much of this is the basis for the move (in the US) to
upgrade the power distribution infrastructure (aka "Smart
Grid"). No idea how things are done elsewherein the world
but, here, the infrastructure is really pretty outdated.

[N.B. I don't know enough about the "Smart Grid" issue
to comment one way or the other -- I'm just hypothesizing
as to its intent]

 

[Allodoxaphobia]

Will sunlight damage the electronics of a circuit board?

The power company installed a radio-controlled switch on my air
conditioner, and mounted it on the side of my house. It has an ugly
label which clashes with the natural look of my little yard.

I was peeling it off when I noticed that it covered a fairly darkly
tinted plastic window, and inside the window was the circuit board
that included the receiver and the control that turns the AC off when
the Power Company Central Command wants it to.

There is a much window below the label through which one can see a
green LED. In the late afternoon shaedI only knew I could see the
circuit board because I could see the glowing LED. (Does anyone know
if that means there is power to the AC, or only that there is power to
the controller device itself?)

I stopped unpeeling at that point. I don't want to cause their
product to wear out sooner than normal. I Would the sunlight harm
anything inside?

Just paint the $#%^$ thing to match the side of the house.

Jonesy