General > General Technical Chat
The US electrical system
cliffyk:
--- Quote from: NiHaoMike on June 27, 2020, 03:51:11 am ---
--- Quote from: james_s on June 27, 2020, 03:32:07 am ---I think the wattage of the dryer is a rather useless metric though, what matters is the kWh required to dry a load of clothes. A lower powered dryer will consume less instantaneous power but all else being equal it will run longer. Seems like mine takes 30-40 minutes to dry a full load out of the washer, and it handles 2-3 times the load of a typical UK dryer. Bigger capacity machines are run less frequently, I doubt there is that much difference in consumption per item of clothing.
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A heat pump makes a big difference there. Or even a heat recovery exchanger, for that matter.
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Do heat pump based clothes dryers exist? Interesting concept--our "new" (2 years old) R-410a based central HVAC system with heat pump (common here in Florida) can, in heat pump mode, produce a good flow (1600+ cfm) of 85° F air with an outdoor ambient of 40° F--below that 13.2 kW of coiled nichrome kicks in for "emergency" heat. We see the latter for usually < 100 hours/year...
The neat thing about the heat pump is of course that the heat is, like fossil fuels¹, free, I just pay to "pump" it in the direction I want it to go. I wish there were a market for that I pimp out this time of year. A practical, economical heat capture/distribution technology would be a winner--
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¹ - Leaving landowner subterranean mineral rights issues aside, oil, natural gas, coal, etc, are free, we pay for them to be extracted, refined, and distributed.
Monkeh:
--- Quote from: cliffyk on June 27, 2020, 03:14:22 am ---Maybe I missed it, but it did seem that he glossed over or did not emphasize that the so-caled "neutral" wire in our silly earth return split phase system is anything but neutral. It carries the full difference of the loads applied to each phase. If you draw 200 A from 120 V phase "A", and 100 A from phase "B", the "neutral" wire will be carrying 100 A--enough to be a BIG surprise for anyone believing it to be "neutral", and mucking about with it while the full phase load is unbalanced.
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That the neutral can carry current is absolutely normal, not unique to your split-phase (which is not earth return, because you have a wire, not the earth) system. It is not neutral because it does nothing, but neutral because it is nominally at 0V.
bdunham7:
--- Quote from: cliffyk on June 27, 2020, 03:14:22 am --- If you draw 200 A from 120 V phase "A", and 100 A from phase "B", the "neutral" wire will be carrying 100 A--enough to be a BIG surprise for anyone believing it to be "neutral", and mucking about with it while the full phase load is unbalanced.
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That is exactly what a neutral is supposed to do. What big surprise would the neutral have? 3 volts?
tooki:
--- Quote from: Stray Electron on June 26, 2020, 09:02:11 pm ---
--- Quote from: themadhippy on June 24, 2020, 09:44:47 pm ---
7kw to dry yer clothes, aint you guys heard of washing lines
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Seriously, not since the 1960s. Besides with the now popular zero lot line subdivisions, there's NO room for one. I literally haven't seen a clothes line since probably 1968.
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We still had one until 1992 (when we moved from USA to Switzerland), at a house built in the late 70s. My grandma (living in Florida) used one until she passed away in 2013.
--- Quote from: cliffyk on June 27, 2020, 04:11:17 am ---Do heat pump based clothes dryers exist? Interesting concept--our "new" (2 years old) R-410a based central HVAC system with heat pump (common here in Florida) can, in heat pump mode, produce a good flow (1600+ cfm) of 85° F air with an outdoor ambient of 40° F--below that 13.2 kW of coiled nichrome kicks in for "emergency" heat. We see the latter for usually < 100 hours/year...
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Yes. They’re exceedingly rare in USA (where just a handful of models exist, e.g. Miele), but in Europe, they’ve been the only type sold for several years AFAIK, in order to comply with energy efficiency regulation. Just as window air conditioners are cheap in USA due to economies of scale, heat pump dryers are available cheaply in Europe.
My apartment came with one from Bosch-Siemens, and it’s great. It doesn’t get as hot as a traditional dryer, making it gentler on the clothes, but the dehumidifying effect of the heat pump system makes it work just as fast. It uses less than 1KW.
free_electron:
--- Quote from: NiHaoMike on June 27, 2020, 03:12:21 am ---
--- Quote from: free_electron on June 27, 2020, 01:51:30 am ---do you have any idea of the load of a 5 ton airco unit ? that thing pulls 30 to 32 ampere on a hot day ... throw in an electric water boiler, a 5 kilowatt oven (or a double one) , a 3 kilowatt cooktop , a 2 kilowatt microwave, a 2 horsepower food disposal unit , a dishwasher, washing machine and electric clothes dryer, a well pump , a 2 hp pool pump , 1kw saltwater chlorine generator, ... yup you need that 200 ampere !
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The demand can be way reduced with smart engineering, even if 5 tons of A/C really is needed. (Hint: if your insulation is decent, it's unlikely unless you truly have a huge house.) The water heater isn't going to need to run at full capacity when the A/C is needed at all, plus one based on a heat pump reduces the power usage down to a few hundred watts. The oven is only going to draw full power during preheating, same with the cooktop. The microwave is only used for short bursts and the disposal for even shorter. Heat pump dryers also use much less power. The pool equipment doesn't need to run full time so a smart controller can run it when demand is low and/or energy is cheap.
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My warm water boiler runs at night for now. The airco runs pretty much full time.. Central valley gets hot in summer. I bake bread twice a week. cooking : three times a day. The problem is that there are moments , even if only for 5 minutes where peak power is very large. if your main breakers can't handle such a load it is going to get annoying very quickly. I have a heatpump airco system , but still the load is big. And then there's two electric cars that pull 30 ampere each. The pool pump and chlorine generator run 9 to 10 hours a day. You have to, otherwise the pool turns to soup. This is a saltwater pool , so it needs circulation to do the electrolytic conversion of the salt into chlorine and sodium. Pool is solar heated so that array needs circulation as well.
Cooking indian food is very involved. they don't do simple meals and run everything on hot hot hot ( my wife is from india ) a 5 zone induction cooker pulls quite a load ...
Even the smallest homes in the us have 100 amp main breakers.
That's why i am going solar The system will give me more than 100 ampere off the panels on a bad day. Whatever is possible : dump it in the packs. Run the house at night off the packs and dump the rest in the cars. Everything else is going on smart controllers. if peak power is available on the array : use it. Run the 100 gallon water heater for the shower. run anything that can 'store energy' : water heater , pool heater , battery packs, cars. When the array becomes less productive : divert energy to large loads that are temporary : washing and drying.
As the array becomes less productive during the day : spin down the large loads and keep topping off the batteries ( if they are already full no problem. once it gets dark : shed the large loads. no running dryers ovens etc. cooking ok. Use the packs to run airco and the necessities : refrigerators and the stuff that needs to be on. keep dumping power into the cars if they require it.
the controller is self-learning and will adapt the load shift.
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