Not only do you only consume off-peak kWh, you also cool your home more efficiently because the AC coil temperature is lower and the AC doesn’t have to move heat across as large of a temperature difference.
During the rainy season, humidity in (mainland and southern) japan gets above 95%, for 6-7 weeks.
And then of course, there's the local building habits, like the cardboard houses of the US.
That has been talked about quite a bit actually. Technology Connections made a nice YouTube video (https://www.youtube.com/watch?v=MFEHFsO-XSI) about it.
I'm a bit surprised though that off-peak pre-cooling isn't more common or even widely incentivised, especially with the rise of smart home and IoT stuff. All I've seen is reduction (so less cooling) during peak, if I'm not remembering wrong, people were quite annoyed with that.
1. Ice thermal storage. You freeze ice at night and melt it during the day to cool your building. Only used for large buildings - check out Chicago's district cooling for an awesome example.
2. Adiabatic and hybrid cooling towers. These are HVAC equipment that can switch between regular and a "wet mode" where they evaporate water to cool the AC coil and reduce electricity usage.
3. Better automation tools. Building automation systems are fully programmable (e.g., switch schedules when outdoor temperature is past a certain threshold), unlike most programmable thermostats which can run a fixed schedule but not much else.
From Wikipedia:
> The building was designed to be a 'green' building consuming less than half the power of a standard office tower. Utilizing natural light to illuminate 80 percent of the building helped it achieve worldwide recognition as the first Federal Building to be certified under the USGBC's Leadership in Energy and Environmental Design (LEED) criteria. Its southern wall is draped with translucent panels of perforated stainless steel (3 by 8 feet in size), intended to accumulate solar heat and thereby create an upward air flow, which in turn causes cooler air to enter the building through sensor-controlled windows, achieving an air conditioning effect. The result has been criticized as unsatisfactory by employees working in the building, which has received low workplace satisfaction ratings.
And an article on it - https://www.govexec.com/pdfs/green/080108gsa.pdf
There are some neat things they tried there.
Interesting article from the Crimson (student newspaper) from 1978 about their recent-at-the-time move to computerize the heating and cooling systems: https://www.thecrimson.com/article/1978/1/12/the-great-chill...
Edit: fixed unintentionally humorous typo, whoops
I mentioned that this one struggles to hold 75 when it's much over 100 degrees outside and was told it doesn't matter what system I buy, that will always be true. The systems can only pull down the temperature around 25 degrees Fahrenheit. Is that true? If so, how do stores hold their temperature so low?
When sized correctly that is true. If you install an oversized system it can cool down even more (which answers your store question: they have an oversized system). An oversized system will cool the air too fast and not deal with the humidity correctly. There are other problems with an oversized system as well that someone who knows HVAC better than me can talk about..
(Not an expert but I've dealt with HVAC enough) Short cycling is another problem. The system cools the room air faster than the air can absorb heat from the objects in the room and the structure itself. This causes the thermostat to cut out prematurely. The air then quickly warms from absorbing heat causing the thermostat to cycle on. The room again cools too fast and thermostat cuts off. That constant on-off cycling can damage the refrigeration compressor. Plus like you said, the humidity is not controlled so the room is cool and humid which is much less comfortable (to me at least.)
It seems like this is something that automation could help. A variable speed system could learn what the neutral setting is for different indoor-outdoor temperature gradients and cool the space slowly enough to avoid short cycling. But then I dropped out of thermodynamics when I was in school, so I really have no idea what I'm talking about.
Edit: After looking, I think everything is already in place. Our thermostat also measures humidity, so there's no reason it would run the A/C at a level that would make condensation a problem.
There might a reason for that though. There are dampers in the basement air ducting I can use to redirect airflow, so I'm running a system designed for 1,300 sqft to cool an area that's half that. My office window unit is overkill for the room I'm in.
I've optimized this using data from home assistant, which continuously monitors the outside weather and temperatures (plus occupancy, light level (lux), light bulbs, etc) for every room.
Ask This Old House (https://www.youtube.com/watch?v=-33wjzNxgSw)
Thanks for posting this video. It's pretty good, but it raises some questions for me as well (like was the 4 ton system in the video a variable speed system?).
It’s actually a problem if you have an overpowered system.
I can see it being a problem if I come back from vacation and change the thermostat from 85 to 73 and ask the A/C to get there ASAP, but even then the controller could know how much moisture is in the air and make sure the temperature drop is slow enough to deal with condensation.
If you have well insulated house it doesnt matter whether you keep ac on or off, it works way more effectively in insulated space.
https://forecast.weather.gov/MapClick.php?lat=40.751&lon=-73...
IME, temperature increases much more quickly outside than inside, and your home will stay cool. Add fans - much more energy efficient than AC - as needed. When I need AC, it's usually not until around 4pm or 5pm, even on hotter days. I cut my energy bills by ~70% using this and other measures.
I prefer them to ceiling fans plus no installation and you can keep them when you move.
Presumably the target temperature will swing less than the outside temperature making it always more efficient when it’s cooler outside.
There is the added complication of how good your insulation is, if it’s bad it might use less energy cooling when it’s hot outside.
However the driving issue isn’t really efficiency but peak power going beyond capacity. Peak usage is in the middle of the day, any off peak usage is better than near peak usage.
However, you do increase the rate of heat loss because there will be a larger temperature difference between the inside and the outside, so it does depend on how well insulated you are.