Will sunlight damage the electronics?

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.

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" :

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 see>> The goal isn't to save energy (though I think the laws of thermo

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).

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

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... :> )

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!

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]

Peel it off and find out.

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

Jonesy

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  Marvin L Jones    | jonz          | W3DHJ  | linux
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