4 ms·

Heat is low-density and it's difficult to work with. And fossil fuels are extremely high-density and easy to work with. So when heat is needed, the general ap

by retrac 3y ago

Heat is low-density and it's difficult to work with. And fossil fuels are extremely high-density and easy to work with. So when heat is needed, the general approach has been to burn fossil fuels locally and just dump the waste heat. This has not properly accounted for the cost of fossil fuels. Low-intensity waste heat is valuable. And it is something that can be captured and used. But that is a different kind of mentality, and a different kind of engineering, one that hasn't been much-developed. For example, here in Canada, like in many countries, we like to take hot showers. We take hot showers even in winter, and there can be an 80 °C difference between the water flowing down the drain and the air outside. Is there no further useful work that heat could do?

48864w6ui 3y ago
Vernacular architecture here was for people to live directly over the barn, as a side effect giving them residual heating.
theluketaylor 3y ago
In BC and Ontario (and I believe other places too) the building code includes passive heat capture for drains for new builds. You can recover quite a bit of the heat for very little money.
- ip26 3y ago
  Drain water heat recovery. See: power pipe.
- hedora 3y ago
  These sorts of technologies tend to be very region and building dependent. They add complexity for some amount of energy recapture, but often the energy recapture isn’t worth it, or some other optimization would have a better pay off. (If we were talking about software, the law would be similar to “all floating point must be done in unrolled assembly loops”, which sounds reasonable but breaks GPUs, instruction cache, interpreters, etc). For example, we didn’t insulate our concrete slab floor because our windows provide too much passive heat 10 months out of the year. We’re on the edge of the region where such insulation is recommended (thankfully, it is not required here - in the fall, we have to run the air conditioning when it is in the mid sixties outside! In the summer, we don’t need A/C until the upper seventies because of the angle of the sun and passive cooling from the slab). Anyway, our hybrid hot water heat pump has a COP of two or three, and was a much cheaper upgrade than passive heat reclamation would have been. Because we bought an efficient unit, it uses hardly any power (800kwh per year, so an average of 91 watts, or about $100/year, or charging my car from empty to full 24 times), so we’d be better off with some other upgrade on a thing that hasn’t hit diminishing returns. For instance, we should have used bigger air ducts on our hvac system to improve the air handler’s efficiency.
  - mistrial9 3y ago
    this is such a telling story .. I am immediately on the side of the owner-builder, but then > in the fall, we have to run the air conditioning when it is in the mid sixties outside! what? building design has a lot of parts to it.. "big cement slab" and "some insulation" are not the only parts.. But good quality design and the parts to build it are expensive. There is an underlying theme of saving money to accomplish something otherwise not possible. I am sympathetic to that of course.. Something is not right about the design, but what bad manners to point it out first! Someone put a lot of effort into some upgrade and they likely cannot change the decisions they made, due to time and costs, etc. good to hear the details and mostly supportive here -- green building has got to get better, starting yesterday IMHO
    - hedora 3y ago
      The problem is that it is sunny in that month. Historically around here, we’d have more cloud cover, and it would be tuned right. The plan was to open the windows if this was a problem, but we’re also getting more flies / biting flies than before during those months. Of course, the excess sun means excess solar production when most people aren’t running heaters or A/C. The expensive fix is to increase the amount the roof sticks out by a foot or so to block the sun for an additional month in fall and spring. The cheap fix (what we are going for) is to put up curtains or blinds that let us manually tune the amount of passive heating we get from the sun. Either fix would also reduce glare, but only the curtains let us tune the pre/post solstice passive heating. It is colder post-solstice for a given angle of sun, so extending the roof enough for November probably implies paying more for heat in Jan/Feb.
      - BenjiWiebe 3y ago
        Do your windows not have screens? That would allow you to have the windows open even when there's flies. Now if you have bad air pollution/smells (smoke, livestock, city) then screens won't help.
        hedora 3y ago
jeffalyanak 3y ago
In the winter I always leave my tub full and the bathroom door open after taking a hot bath to allow more of the heat to warm my home. I paid to heat that water up, so I damn well want to get as much out of it as I can.
- shawabawa3 3y ago
  Sounds like a great way to encourage mould growth
  - kasey_junk 3y ago
    In winter climates it’s extremely common to run humidifiers to add water to the air. Using a bathtub for the same purpose is pretty common and I’ve never heard of either causing mold in normal operations.
    - jeffalyanak 3y ago
      Yeah, given how dry our place gets in winter the added humidity is not a problem. If I took baths every day then it might become a problem but once a week or so had had no negative effects.
  - infamia 3y ago
    Humidity is usually too low during cold months, so leaving the door open is fine and helps everyone feel warmer (humidity + a bit of extra heat).
Doxin 3y ago
These days there's heat recovery drains. The idea is generally to first make sure you use a thermostatic tap for the shower and then use the drain water to heat the cold water line going to the tap. The thermostatic tap will adjust to keep water temperature steady as the incoming "cold" water gets warmer over time. The marketing material claims energy savings of up to 50%, but presumably you'll only reach that amount of savings if you take hour long showers at ridiculous temperatures.

by retrac 3y ago

48864w6ui 3y ago

Vernacular architecture here was for people to live directly over the barn, as a side effect giving them residual heating.

theluketaylor 3y ago

In BC and Ontario (and I believe other places too) the building code includes passive heat capture for drains for new builds. You can recover quite a bit of the heat for very little money.

ip26 3y ago
Drain water heat recovery. See: power pipe.
hedora 3y ago
These sorts of technologies tend to be very region and building dependent. They add complexity for some amount of energy recapture, but often the energy recapture isn’t worth it, or some other optimization would have a better pay off. (If we were talking about software, the law would be similar to “all floating point must be done in unrolled assembly loops”, which sounds reasonable but breaks GPUs, instruction cache, interpreters, etc). For example, we didn’t insulate our concrete slab floor because our windows provide too much passive heat 10 months out of the year. We’re on the edge of the region where such insulation is recommended (thankfully, it is not required here - in the fall, we have to run the air conditioning when it is in the mid sixties outside! In the summer, we don’t need A/C until the upper seventies because of the angle of the sun and passive cooling from the slab). Anyway, our hybrid hot water heat pump has a COP of two or three, and was a much cheaper upgrade than passive heat reclamation would have been. Because we bought an efficient unit, it uses hardly any power (800kwh per year, so an average of 91 watts, or about $100/year, or charging my car from empty to full 24 times), so we’d be better off with some other upgrade on a thing that hasn’t hit diminishing returns. For instance, we should have used bigger air ducts on our hvac system to improve the air handler’s efficiency.
- mistrial9 3y ago
  this is such a telling story .. I am immediately on the side of the owner-builder, but then > in the fall, we have to run the air conditioning when it is in the mid sixties outside! what? building design has a lot of parts to it.. "big cement slab" and "some insulation" are not the only parts.. But good quality design and the parts to build it are expensive. There is an underlying theme of saving money to accomplish something otherwise not possible. I am sympathetic to that of course.. Something is not right about the design, but what bad manners to point it out first! Someone put a lot of effort into some upgrade and they likely cannot change the decisions they made, due to time and costs, etc. good to hear the details and mostly supportive here -- green building has got to get better, starting yesterday IMHO
  - hedora 3y ago
    The problem is that it is sunny in that month. Historically around here, we’d have more cloud cover, and it would be tuned right. The plan was to open the windows if this was a problem, but we’re also getting more flies / biting flies than before during those months. Of course, the excess sun means excess solar production when most people aren’t running heaters or A/C. The expensive fix is to increase the amount the roof sticks out by a foot or so to block the sun for an additional month in fall and spring. The cheap fix (what we are going for) is to put up curtains or blinds that let us manually tune the amount of passive heating we get from the sun. Either fix would also reduce glare, but only the curtains let us tune the pre/post solstice passive heating. It is colder post-solstice for a given angle of sun, so extending the roof enough for November probably implies paying more for heat in Jan/Feb.
    - BenjiWiebe 3y ago
      Do your windows not have screens? That would allow you to have the windows open even when there's flies. Now if you have bad air pollution/smells (smoke, livestock, city) then screens won't help.
      - hedora 3y ago

jeffalyanak 3y ago

In the winter I always leave my tub full and the bathroom door open after taking a hot bath to allow more of the heat to warm my home. I paid to heat that water up, so I damn well want to get as much out of it as I can.

shawabawa3 3y ago
Sounds like a great way to encourage mould growth
- kasey_junk 3y ago
  In winter climates it’s extremely common to run humidifiers to add water to the air. Using a bathtub for the same purpose is pretty common and I’ve never heard of either causing mold in normal operations.
  - jeffalyanak 3y ago
    Yeah, given how dry our place gets in winter the added humidity is not a problem. If I took baths every day then it might become a problem but once a week or so had had no negative effects.
- infamia 3y ago
  Humidity is usually too low during cold months, so leaving the door open is fine and helps everyone feel warmer (humidity + a bit of extra heat).

Doxin 3y ago

These days there's heat recovery drains. The idea is generally to first make sure you use a thermostatic tap for the shower and then use the drain water to heat the cold water line going to the tap. The thermostatic tap will adjust to keep water temperature steady as the incoming "cold" water gets warmer over time. The marketing material claims energy savings of up to 50%, but presumably you'll only reach that amount of savings if you take hour long showers at ridiculous temperatures.