5 ms·

Is that really a newer thing? My ancient high school had 45-degree windows (for theft and suicide prevention I imagine). Why lock it all down? Cost?

mlyle 5y ago
It's a LEED rating thing. If you can rely upon windows entirely for ventilation and thermal control, that's great. Otherwise, windows that open leak more air when you don't want them to. They also let in more humid air, which in turn has a higher specific heat capacity and requires more energy to dry the air later. Their usage tends to be uneven, so you often have open windows while AC is also running elsewhere or in the same room, and this can upset air handling. So, windows that open can paradoxically increase energy consumption in larger buildings.
- pstoll 5y ago
  We have a local school being built. This was the argument for no operable windows. Except … a pandemic! We are optimizing for the wrong thing IMO at the expense of simple practical, human driven comfort. Same reason we don’t have windows on the local trains anymore. Practically for people in classrooms at random times, being able to open a window should be an option. Only central control of when the ventilation / heat is on just fails in so many situations.
  - mlyle 5y ago
    It's an interesting tradeoff. I like having windows that will open in my classroom. But in the larger buildings with central, indoor hallways, the benefit of windows is smaller (much less outer surface area vs. volume of space) and the potential costs are higher. Aside from pandemic-proofing, the main benefit I get is from having more ventilation when I do things that don't need to be under a hood, but still produce fumes/smoke. E.g. soldering.
  - Sargos 5y ago
    If it's still being built then it likely won't start being used until sometime next year and at that point we're back to optimizing for energy usage. It's best to pick a long term metric over a short term win when dealing with a building that will last for decades.
    - dredmorbius 5y ago
      This presumes no further epidemics / pandemics, and discounts benefits to "normal" cold and flu season.
      - mlyle 5y ago
        Do you think in normal years we'll still keep classroom windows open in the middle of flu season? Even in temperate California, the costs to classroom comfort and running HVAC to try and overcome outdoor temperatures is ridiculous. Good modern buildings are being built with more ventilation and heat recovery built in. Taking this over windows that open can be a reasonable trade. Yes, on the pandemic axis, many of these buildings may be a little worse than a classroom with a whole long wall of opening windows.
        deleted 5y ago
        [deleted]
        dredmorbius 5y ago
        I don't know, though I'd suspect that plans for increased air exchange are being considered. For much of the state, through much of the year, open windows are a reasonably minor consideration. Heat-recovery air-exchange would be more efficient, and again, though I don't know what's being considered, I'd suspect that this is part of current discussions. The chief challenge is that of retrofits vs. new construction. Much of California's school infrastructure is 50--100 years old.
        mlyle 5y ago
        > I don't know, though I'd suspect that plans for increased air exchange are being considered. In general, newer buildings with sealed windows have pretty good air exchange (with heat recovery) and filtration. > For much of the state, through much of the year, open windows are a reasonably minor consideration. Yah, tell that to me languishing masked a 95 degree classroom between building heat gain and a temperature in the 90s, and now ending up with a 60 degree room. It's workable, but it sucks, and we're wasting a lot of energy just to maintain a few degree delta T from outside with open windows. We've had a few weeks where the open windows have been great, but a lot more crummy weeks. I'm a little jealous of those upstairs in the high school building that don't need to open windows.... and have nice temperatures in their classrooms... and have also had 0 secondary COVID cases. It's also really hard to conduct class when there's music, PE, etc, activities outside. > The chief challenge is that of retrofits vs. new construction. I thought we were talking in the context of a new school building being built without windows that open. That said, windows are nice. If you have a class full of kids that are restless, sometimes opening windows and getting some outside noise or a breeze through the room changes the entire mood. It would be sad to lose that.
- chrismorgan 5y ago
  More humid air with higher specific heat capacity: I’d expect the difference to be utterly negligible. Even at 40°C, the isobaric heat capacity of saturated air is only about 5% higher than that of perfectly dry air (~1.05 J/g·K, compared to ~1), and your slightly leaky window is hardly going to be resaturating the entire room. As for the energy to dry the air, I’m inexpert in this area¹ but under the impression dehumidification is essentially just a byproduct of how compressors work (the evaporator’s low temperature causes water vapour to condense) rather than something that takes deliberate effort—that, if anything, air conditioners are commonly now deliberately revapourising water to avoid dehumidification beyond the desired level. —⁂— ¹ But I am trying to learn for part of a project of my own, a velomobile and trailer to be able to live out of indefinitely, where in the ideal case that I haven’t determined is feasible I’d really like it if I could have one compressor to drive food refrigeration, cabin cooling, heating a low-temperature slow-cooker-style oven, and providing my water supply.
  - mlyle 5y ago
    > More humid air with higher specific heat capacity OK, so I should add a little more nuance: * With more water vapor in the air, the air has a little more heat capacity * With more water vapor in the air, the temperature band for comfort is a little narrower * With more water vapor in the air, air conditioners need to work extra hard to provide the same cooling. That is, the more water there is in the air to begin with, the more will condense and return its heat of vaporization to the room.
    - chrismorgan 5y ago
      Certainly the comfort band is the key to it. Everything else is rounding error under even the most pessimistic estimates. On phase change energies: I don’t know enough to quantify things definitely there, but https://en.wikipedia.org/wiki/Latent_heat#Specific_latent_heat_for_condensation_of_water_in_clouds https://en.wikipedia.org/wiki/Latent_heat#Specific_latent_he... looks like the right thing, and suggests around 2.4kJ/g, which with water being as much as 5% of the air (100% humidity at 40°C) would be as much as cooling the air down by about another 0.12°C for removing all of it.
Gigachad 5y ago
When I worked in an office, they had all of the windows screwed in to prevent opening to comply with new building codes. I imagine for suicide and accident prevention. It looks like these days you can only have windows that wind out a little. My apartment has these, but it also has an option on the AC controls to bring outside air in which can force ventilation if it isn't windy outside. This is mostly for tall buildings though. For a school, it could be that they want to be able to control the airflow and AC. Having a window open could be letting out the heat causing the heating to work harder for no reason.

mlyle 5y ago

It's a LEED rating thing. If you can rely upon windows entirely for ventilation and thermal control, that's great. Otherwise, windows that open leak more air when you don't want them to. They also let in more humid air, which in turn has a higher specific heat capacity and requires more energy to dry the air later. Their usage tends to be uneven, so you often have open windows while AC is also running elsewhere or in the same room, and this can upset air handling. So, windows that open can paradoxically increase energy consumption in larger buildings.

pstoll 5y ago
We have a local school being built. This was the argument for no operable windows. Except … a pandemic! We are optimizing for the wrong thing IMO at the expense of simple practical, human driven comfort. Same reason we don’t have windows on the local trains anymore. Practically for people in classrooms at random times, being able to open a window should be an option. Only central control of when the ventilation / heat is on just fails in so many situations.
- mlyle 5y ago
  It's an interesting tradeoff. I like having windows that will open in my classroom. But in the larger buildings with central, indoor hallways, the benefit of windows is smaller (much less outer surface area vs. volume of space) and the potential costs are higher. Aside from pandemic-proofing, the main benefit I get is from having more ventilation when I do things that don't need to be under a hood, but still produce fumes/smoke. E.g. soldering.
- Sargos 5y ago
  If it's still being built then it likely won't start being used until sometime next year and at that point we're back to optimizing for energy usage. It's best to pick a long term metric over a short term win when dealing with a building that will last for decades.
  - dredmorbius 5y ago
    This presumes no further epidemics / pandemics, and discounts benefits to "normal" cold and flu season.
    - mlyle 5y ago
      Do you think in normal years we'll still keep classroom windows open in the middle of flu season? Even in temperate California, the costs to classroom comfort and running HVAC to try and overcome outdoor temperatures is ridiculous. Good modern buildings are being built with more ventilation and heat recovery built in. Taking this over windows that open can be a reasonable trade. Yes, on the pandemic axis, many of these buildings may be a little worse than a classroom with a whole long wall of opening windows.
      - deleted 5y ago
        [deleted]
      - dredmorbius 5y ago
        I don't know, though I'd suspect that plans for increased air exchange are being considered. For much of the state, through much of the year, open windows are a reasonably minor consideration. Heat-recovery air-exchange would be more efficient, and again, though I don't know what's being considered, I'd suspect that this is part of current discussions. The chief challenge is that of retrofits vs. new construction. Much of California's school infrastructure is 50--100 years old.
        mlyle 5y ago
        > I don't know, though I'd suspect that plans for increased air exchange are being considered. In general, newer buildings with sealed windows have pretty good air exchange (with heat recovery) and filtration. > For much of the state, through much of the year, open windows are a reasonably minor consideration. Yah, tell that to me languishing masked a 95 degree classroom between building heat gain and a temperature in the 90s, and now ending up with a 60 degree room. It's workable, but it sucks, and we're wasting a lot of energy just to maintain a few degree delta T from outside with open windows. We've had a few weeks where the open windows have been great, but a lot more crummy weeks. I'm a little jealous of those upstairs in the high school building that don't need to open windows.... and have nice temperatures in their classrooms... and have also had 0 secondary COVID cases. It's also really hard to conduct class when there's music, PE, etc, activities outside. > The chief challenge is that of retrofits vs. new construction. I thought we were talking in the context of a new school building being built without windows that open. That said, windows are nice. If you have a class full of kids that are restless, sometimes opening windows and getting some outside noise or a breeze through the room changes the entire mood. It would be sad to lose that.
chrismorgan 5y ago
More humid air with higher specific heat capacity: I’d expect the difference to be utterly negligible. Even at 40°C, the isobaric heat capacity of saturated air is only about 5% higher than that of perfectly dry air (~1.05 J/g·K, compared to ~1), and your slightly leaky window is hardly going to be resaturating the entire room. As for the energy to dry the air, I’m inexpert in this area¹ but under the impression dehumidification is essentially just a byproduct of how compressors work (the evaporator’s low temperature causes water vapour to condense) rather than something that takes deliberate effort—that, if anything, air conditioners are commonly now deliberately revapourising water to avoid dehumidification beyond the desired level. —⁂— ¹ But I am trying to learn for part of a project of my own, a velomobile and trailer to be able to live out of indefinitely, where in the ideal case that I haven’t determined is feasible I’d really like it if I could have one compressor to drive food refrigeration, cabin cooling, heating a low-temperature slow-cooker-style oven, and providing my water supply.
- mlyle 5y ago
  > More humid air with higher specific heat capacity OK, so I should add a little more nuance: * With more water vapor in the air, the air has a little more heat capacity * With more water vapor in the air, the temperature band for comfort is a little narrower * With more water vapor in the air, air conditioners need to work extra hard to provide the same cooling. That is, the more water there is in the air to begin with, the more will condense and return its heat of vaporization to the room.
  - chrismorgan 5y ago
    Certainly the comfort band is the key to it. Everything else is rounding error under even the most pessimistic estimates. On phase change energies: I don’t know enough to quantify things definitely there, but https://en.wikipedia.org/wiki/Latent_heat#Specific_latent_heat_for_condensation_of_water_in_clouds https://en.wikipedia.org/wiki/Latent_heat#Specific_latent_he... looks like the right thing, and suggests around 2.4kJ/g, which with water being as much as 5% of the air (100% humidity at 40°C) would be as much as cooling the air down by about another 0.12°C for removing all of it.

Gigachad 5y ago

When I worked in an office, they had all of the windows screwed in to prevent opening to comply with new building codes. I imagine for suicide and accident prevention. It looks like these days you can only have windows that wind out a little. My apartment has these, but it also has an option on the AC controls to bring outside air in which can force ventilation if it isn't windy outside. This is mostly for tall buildings though. For a school, it could be that they want to be able to control the airflow and AC. Having a window open could be letting out the heat causing the heating to work harder for no reason.