15 ms·

Simple trick to reduce your peak electricity usage if you’re working from home and want it cool all day: set your AC low until it starts to get hot out and then

by elil17 4y ago

Simple trick to reduce your peak electricity usage if you’re working from home and want it cool all day: set your AC low until it starts to get hot out and then turn it off. Works great if your insulation is good enough. 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.

Avamander 4y ago
So off-peak pre-cooling, did I read your comment right? That has been talked about quite a bit actually. Technology Connections made a nice YouTube video (https://www.youtube.com/watch?v=MFEHFsO-XSI 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.
- lisper 4y ago
  It only works on well-insulated buildings. There are a lot of older legacy structures where the temperature equalizes very quickly once you turn off the climate controls.
- elil17 4y ago
  I work in HVAC and it is very common for larger buildings. They get huge incentives for shedding load during peak hours. Larger buildings also have more tools at their disposal beyond simply the "thermal inertia" of the building itself: 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.
  - shagie 4y ago
    I recall watching a program on green construction on KQED and the Federal Building in SF and how it was built. 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 https://www.govexec.com/pdfs/green/080108gsa.pdf There are some neat things they tried there.
  - a3camero 4y ago
    In Toronto there's a giant cooling system for downtown buildings that uses cold lake water pumped downtown from 83m underwater:https://en.wikipedia.org/wiki/Deep_Lake_Water_Cooling_System https://en.wikipedia.org/wiki/Deep_Lake_Water_Cooling_System. It's being expanded to offer even more cooling with a low carbon footprint.
    - elil17 4y ago
      Very cool! Sort of reminds me of seasonal thermal energy storage: https://en.wikipedia.org/wiki/Seasonal_thermal_energy_storage https://en.wikipedia.org/wiki/Seasonal_thermal_energy_storag...
  - hermitdev 4y ago
    I spent nearly a decade working across the street from plant #1 without knowing what it was, it just seemed to be an out of place (for the comparatively tiny building it was on) massive cooling setup. When I needed to think, I'd often stare out the window and watch the cooling towers in the summer. It was kind of hypnotic, specifically all the running water. From the angle I was at, I could see pretty well into the cooling towers from above.
- criddell 4y ago
  My home's HVAC system is getting old and when I had the HVAC technician out for the summer inspection I asked about a new system (mine was installed in 2008). He said a new one will be a lot more energy efficient and (depending on the system we choose) would have more settings than off and blast cold. 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?
  - bluGill 4y ago
    > The systems can only pull down the temperature around 25 degrees Fahrenheit. Is that true? 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..
    - MisterTea 4y ago
      > There are other problems with an oversized system as well (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.)
      - criddell 4y ago
        Wouldn't variable speed systems alleviate some of the issues with short cycling? 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.
laurieg 4y ago
Unfortunately Japanese buildings tend to be optimized for airflow (people want buildings that don't get mouldy). Also many of them are not well insulated (double pane windows are still a rare luxury) so buildings don't retain the cold air well.
- ParksNet 4y ago
  You can build housing that doesn't get mouldy and is well insulated by having proper insulation and a modern ERV. It seems like Japan's policy of 'disposable housing' doesn't stand up to expensive electricity.
  - masklinn 4y ago
    > You can build housing that doesn't get mouldy and is well insulated by having proper insulation and a modern ERV. 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.
- oldsecondhand 4y ago
  Thermal insualation decreases mold in the winter, as the walls don't cool down enough for vapor to condense. Single pane windows also gather a lot of condensation.
  - wizofaus 4y ago
    I'd assume mould was a bigger problem in warmer months in Japan though - it's often very humid. Winters are relatively dry.
- fomine3 4y ago
  Optimized for airflow is true for traditional Japanese buildings, but recent decades buildings are just poorly made for insulating and also not optimized for airflow, because builders and regulations were lazy. It was really stupid poor regulation because Japan imports all energy source.
causi 4y ago
Only problem is you're losing a bit of efficiency because you're cooling cold air instead of warm air. If the house insulation is poor enough this strategy could waste more power than it saves.
- colechristensen 4y ago
  The efficiency will be driven by the difference in temperatures between the hot and cold side. 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.
- elil17 4y ago
  In terms of heat rejection efficiency, unless the difference between your cold/off-peak temperature and your normal AC temperature is greater than the difference between the morning temperature and the mid-day temperature, this will not be the case. It's the difference between the indoor temperature and the outdoor temperature that drives efficiency, so you want to run the AC when these temperatures are as close together as possible. 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.
- Faaak 4y ago
  In the same time the heat pump efficiency is higher because of lower delta-T, so I'm not sure about your assumption
Cloudef 4y ago
Yeah japan has no insulation unless you live in hokkaido or in some specially built house. If you have well insulated house it doesnt matter whether you keep ac on or off, it works way more effectively in insulated space.
mrfusion 4y ago
I found tower fans are a game changer. They are fairly quiet and move a lot of air. I prefer them to ceiling fans plus no installation and you can keep them when you move.
wolverine876 4y ago
Also: Open your windows at night (assuming it's cool enough) and shut them as soon after sunrise as you can. Usually the temperature starts rising at sunrise, not surprisingly. See this graph, for example: https://forecast.weather.gov/MapClick.php?lat=40.751&lon=-73.9981&unit=0&lg=english&FcstType=graphical 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.

by elil17 4y ago

Avamander 4y ago

So off-peak pre-cooling, did I read your comment right? That has been talked about quite a bit actually. Technology Connections made a nice YouTube video (https://www.youtube.com/watch?v=MFEHFsO-XSI 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.

lisper 4y ago
It only works on well-insulated buildings. There are a lot of older legacy structures where the temperature equalizes very quickly once you turn off the climate controls.
elil17 4y ago
I work in HVAC and it is very common for larger buildings. They get huge incentives for shedding load during peak hours. Larger buildings also have more tools at their disposal beyond simply the "thermal inertia" of the building itself: 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.
- shagie 4y ago
  I recall watching a program on green construction on KQED and the Federal Building in SF and how it was built. 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 https://www.govexec.com/pdfs/green/080108gsa.pdf There are some neat things they tried there.
- a3camero 4y ago
  In Toronto there's a giant cooling system for downtown buildings that uses cold lake water pumped downtown from 83m underwater:https://en.wikipedia.org/wiki/Deep_Lake_Water_Cooling_System https://en.wikipedia.org/wiki/Deep_Lake_Water_Cooling_System. It's being expanded to offer even more cooling with a low carbon footprint.
  - elil17 4y ago
    Very cool! Sort of reminds me of seasonal thermal energy storage: https://en.wikipedia.org/wiki/Seasonal_thermal_energy_storage https://en.wikipedia.org/wiki/Seasonal_thermal_energy_storag...
- hermitdev 4y ago
  I spent nearly a decade working across the street from plant #1 without knowing what it was, it just seemed to be an out of place (for the comparatively tiny building it was on) massive cooling setup. When I needed to think, I'd often stare out the window and watch the cooling towers in the summer. It was kind of hypnotic, specifically all the running water. From the angle I was at, I could see pretty well into the cooling towers from above.
criddell 4y ago
My home's HVAC system is getting old and when I had the HVAC technician out for the summer inspection I asked about a new system (mine was installed in 2008). He said a new one will be a lot more energy efficient and (depending on the system we choose) would have more settings than off and blast cold. 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?
- bluGill 4y ago
  > The systems can only pull down the temperature around 25 degrees Fahrenheit. Is that true? 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..
  - MisterTea 4y ago
    > There are other problems with an oversized system as well (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.)
    - criddell 4y ago
      Wouldn't variable speed systems alleviate some of the issues with short cycling? 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.

laurieg 4y ago

Unfortunately Japanese buildings tend to be optimized for airflow (people want buildings that don't get mouldy). Also many of them are not well insulated (double pane windows are still a rare luxury) so buildings don't retain the cold air well.

ParksNet 4y ago
You can build housing that doesn't get mouldy and is well insulated by having proper insulation and a modern ERV. It seems like Japan's policy of 'disposable housing' doesn't stand up to expensive electricity.
- masklinn 4y ago
  > You can build housing that doesn't get mouldy and is well insulated by having proper insulation and a modern ERV. 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.
oldsecondhand 4y ago
Thermal insualation decreases mold in the winter, as the walls don't cool down enough for vapor to condense. Single pane windows also gather a lot of condensation.
- wizofaus 4y ago
  I'd assume mould was a bigger problem in warmer months in Japan though - it's often very humid. Winters are relatively dry.
fomine3 4y ago
Optimized for airflow is true for traditional Japanese buildings, but recent decades buildings are just poorly made for insulating and also not optimized for airflow, because builders and regulations were lazy. It was really stupid poor regulation because Japan imports all energy source.

causi 4y ago

Only problem is you're losing a bit of efficiency because you're cooling cold air instead of warm air. If the house insulation is poor enough this strategy could waste more power than it saves.

colechristensen 4y ago
The efficiency will be driven by the difference in temperatures between the hot and cold side. 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.
elil17 4y ago
In terms of heat rejection efficiency, unless the difference between your cold/off-peak temperature and your normal AC temperature is greater than the difference between the morning temperature and the mid-day temperature, this will not be the case. It's the difference between the indoor temperature and the outdoor temperature that drives efficiency, so you want to run the AC when these temperatures are as close together as possible. 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.
Faaak 4y ago
In the same time the heat pump efficiency is higher because of lower delta-T, so I'm not sure about your assumption

Cloudef 4y ago

Yeah japan has no insulation unless you live in hokkaido or in some specially built house. If you have well insulated house it doesnt matter whether you keep ac on or off, it works way more effectively in insulated space.

mrfusion 4y ago

I found tower fans are a game changer. They are fairly quiet and move a lot of air. I prefer them to ceiling fans plus no installation and you can keep them when you move.

wolverine876 4y ago

Also: Open your windows at night (assuming it's cool enough) and shut them as soon after sunrise as you can. Usually the temperature starts rising at sunrise, not surprisingly. See this graph, for example: https://forecast.weather.gov/MapClick.php?lat=40.751&lon=-73.9981&unit=0&lg=english&FcstType=graphical 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.