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Comment by rnosov | Hacker News Reader

Is it that hot in your area that you have to run air conditioner for 3-4 hours after sunset? Typically solar output correlates really nicely with the need for air conditioning. Washing and drying could be done say on a weekend ( during daylight hours ).

Many water heaters come with an integrated storage tank for hot water so they can actually be used as a form of energy storage. That leaves lights in your example and yes battery like powerwall will be more than enough to power modern energy efficient lighting and electronics overnight.

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It's not uncommon for outside temperatures in Texas to stay above 80F (27C) until midnight during the summer months. The modern homes there are designed to stay sealed, rather than open windows for ventilation at night. Running AC every ~45 minutes until morning is considered the norm.

Hmm, here in Europe were I live 27C would be considered a rather pleasant temperature. Anyway, sealed houses are not only good for keeping the heat in but also to keep the heat out. If you cool your house sufficiently during the daylight hours that should prevent it from heating up too much even after you stop cooling it (after sunset).

But if you absolutely must use active cooling after sunset you might want to get something like Ice bear 20 ( https://www.ice-energy.com/technology/ - i'm not affiliated with them just an example) hopefully it should solve it once and for all.

> Hmm, here in Europe were I live 27C would be considered a rather pleasant temperature.

There are many factors that influence how tolerable the heat is - low humidity and the presence of a breeze can make a huge difference on how tolerable 27C is.

Bear in mind that 80F is a typical overnight low in most parts of TX during the summer, particularly in most of the heavily populated areas. Typical high temps during the summer months are mid to upper 90's or higher. Most of these same areas also have relatively high humidity, so it feels even hotter and can take quite a while for the temperature to drop even after the sun sets.

I've never been to Texas but a Wikipedia article ( https://en.wikipedia.org/wiki/Climate_of_Texas ) suggests that 80F low occurs only in Galveston in July and it's more like 60s and 70s elsewhere. If a humidity is such a problem then you could run dehumidifier during the day and that would lower humidity ( in a sealed house ) overnight.

I mean these temperatures don't strike me as particularly intolerable. I wonder if it's the case of keeping up with Joneses as in "my house is cooler than yours". There are some reports ( https://www.theatlantic.com/magazine/archive/2015/07/saudis-... ) that rich Arabs in Saudi Arabia are running air conditioners at temperatures that require sweaters — even when they go on vacation. Which is really amusing for these of us who come from colder climates.

Dallas native here... and a runner and weather nerd constantly monitoring for the best running conditions...

In July and August it will often stay above 90F until midnight. There’s usually a few evenings in August where it will still be 100F at 2200.

The overnight lows in the upper 70s won’t be reached until dawn, and it will be back into the upper 80s before 10.

And the breeze is a hot wind, that feels like it makes it worse rather than helping.

Interesting, I wonder how people survived before the advent of modern air conditioning. 35C/95F should be fatal at 100% humidity (as your body can no longer shed heat).

Well, something like IceBear20 ( https://www.ice-energy.com/wp-content/uploads/2016/03/ICE-BE... ) seems to be the way to go. It can run for up to 4 hours off the stored ice so it should be able to cover you from sunset to midnight.

> Interesting, I wonder how people survived before the advent of modern air conditioning.

I believe that there used to be many fewer people (absolutely and relatively) living in the southern US. Then air conditioning was invented and people realized they could get away from the sometimes brutal winters in the north without having to be miserable in the summers.

Without solar gain you still need less solar power even if the temperature is 80+. Further, you use exponentially more energy to cool as the temperature rises. So, 80f is significantly cheaper than 90f.

Probably quadratically, or even linear, but to the difference.

Heat gain is linear, but efficiency drops with larger temperate differences. Further, you have to worry about lower relative humidity percentage as you increase temperate differences.

The hottest time of day is 3:00 PM and, due to heat-lag, the hottest time of day _inside_ a house is a little bit after that. Since I set the thermostat higher while I'm gone during the day, this means the house can be roasting by the time I return and require 3-4 hours of AC for it to get more manageable.

And no, our washing and drying can not be done on a weekend. We have 3 kids and if we waited for a weekend to do our laundry then that is the only thing we'd be doing all Saturday long.

In such case you might want to use this thermal lag to your advantage. Set AC to cool your house as much as possible during the midday and you'll come back to hopefully much cooler house in the evening ( so no need to run air conditioner ). Here essentially you would be using the thermal mass of your entire house as an energy storage medium.

With washing, if you have to do it every day you might want to start it right after the sunrise when you're likely to to leave for work. If your kids are old enough you can instruct them to take the washing out and put into a dryer as soon as they get home.

The point is you'll need to make some changes to your lifestyle and habits but these changes are not as severe and problematic as some people claim.

"Since I set the thermostat higher while I'm gone during the day"

Aren't you looking for a way to store excess solar power generated during the day? Use it to cool your house! If your house is at 68 when the sun goes down and power generation stops, you may very well be fine without AC until the morning.

Use the power when its generated and you don't need as big of a battery to store it for later use.

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