Home energy conservation Cliff’s notes

Some comments on an earlier post suggest this would be useful to set out.

Heating

The energy required to keep your house warm in heating season is exactly the energy lost through the exterior walls, windows, doors, roof, and up the chimney if you have one.  Period.  First lesson: cut that loss. Weatherstrip, get storm windows, close windows, close the shades at night, insulate, close the damper (or the whole fireplace; a fire in an open fireplace actually cools your house by inhaling warm air and blowing it up the flue), etc.   These losses are about proportional to the temperature difference between inside and out, so if you turn down your thermostat at night, when you’re not at home, and even when you are  (put on a sweater), you are absolutely ahead.  You already know to do those things, but most people underinvest in them. You can save a lot of money and do the planet a big favor by just keeping heat in your house better. Second lesson: live in a smaller house, or an apartment building with living units on the other side of some of the walls and the ceiling.

This lost energy is replaced in several ways.  The first way is stuff you do for other reasons, like people and pets in the house metabolizing food, lighting , and operating your various appliances.  You can pick up a fair amount of free energy from the sun through your windows if you attend to the shades and drapes. All the electricity used by all your devices turns into heat; they are 100% efficient space heaters from the plug onwards.  The light from a light bulb too; it turns into heat when it’s absorbed by whatever it hits.   All this is usually not enough, so you have the second way: a furnace or boiler to make up the difference, and a thermostat to make this happen automatically (recall first lesson: turn it down).  Every time you turn off a light bulb, you are turning on your heating system.The electricity these gadgets use delivers from 30 to 50% of the energy consumed to make it if your power is thermal (coal or gas), counting generation and transmission losses.  Your home heating system is either electric or burns fuel; if the latter, it’s between 70 and 85% efficient.  If it’s electric, you have nothing to gain by turning off the lights or the TV; you can just skip to the next section.  If you buy gas or oil to heat with, and your electricity is from gas or coal, your net energy saving is only about 30% of whatever electricity you save by managing lights and appliances. Not nothing, but nowhere near as important as managing heat loss through the envelope of the building. Perversely, if your local power is nuclear or hydro, and you don’t have electric space heating, you are accelerating climate change (though you are probably saving money) by turning out the lights or substituting CFLs for incandescent lamps, because you are burning more fossil fuel instead of using near-zero-carbon energy.  Lesson three: energy, money, and climate savings from being careful about home electricity use in the north, and in the winter, are much smaller than you would think just by looking at the wattage of your various devices. It’s neither comfortable nor safe to use your gas range as a space heater, but it’s 100% efficient, so there’s no reason to be stingy with it: go ahead and fry up those burgers soy patties.

Cooling

During the short periods when you are neither heating nor cooling your house, what you see, wattage-wise, from conserving electricity is what you get. It’s worth taking care.

When you are air conditioning, everything changes.  It takes about half a joule to pump a joule of energy out of your house into a hot day. So lesson one again: weatherstrip, insulate and all that, and also keep the sun from shining in your windows.  Awnings are much better than interior shades for this.  Make sure you have a really efficient air conditioning system.  Do the math; it may be worth upgrading sooner than you think. Turn the thermostat up; put on shorts and pad around barefoot.

Cheat the air conditioner as much as possible by taking advantage of cool outside air at night.  Most people don’t know how to do this.  What you need is a whole-house fan, installed in your roof or in the top half of a window, on an upper floor if you have one, in a room you don’t occupy at night.  Look for at least 3000 cfm, more for a large house; this is not a drugstore box fan, though a couple of these will work in a smaller house.  Don’t worry about the electricity it uses; it will be in the low hundreds of watts, and your air conditioner draws thousands.

The fan needs to blow air out, not in.  Out. Open a window in each of the rooms you want to cool and open the doors between those rooms and the fan.  With the fan running, this will generate a nice jet of cool air perpendicular to each window, right across your bed if you can arrange it. There are very few places in the US where you need air conditioning at night if you can get outdoor air to blow in at you.  Overnight, your house will fill up with nice cool air.  In the morning, shut off the fan and close everything to keep that air inside as long as possible, and keep the sun from shining in.  With good insulation and shading, you will need minimal air conditioning when you come home from work until you can use the fan again.

All the energy you use in lights, cooking, and appliances costs you and the planet almost half again as much as their wattage, so using less energy for the same light and other services  (CFLs, efficient refrigerator, etc.) starts to really pay off, especially as the air conditioner and the appliances are all on the same electric grid. Lesson four: during the summer and in the south, get down with fluorescent lighting, and turn things off when you don’t need them.  Kitchen range…well, how about a nice salad for dinner? As the summer is getting longer and hotter, and the south is moving north, these skills will be increasingly valuable.

 

Author: Michael O'Hare

Professor of Public Policy at the Goldman School of Public Policy, University of California, Berkeley, Michael O'Hare was raised in New York City and trained at Harvard as an architect and structural engineer. Diverted from an honest career designing buildings by the offer of a job in which he could think about anything he wanted to and spend his time with very smart and curious young people, he fell among economists and such like, and continues to benefit from their generosity with on-the-job social science training. He has followed the process and principles of design into "nonphysical environments" such as production processes in organizations, regulation, and information management and published a variety of research in environmental policy, government policy towards the arts, and management, with special interests in energy, facility siting, information and perceptions in public choice and work environments, and policy design. His current research is focused on transportation biofuels and their effects on global land use, food security, and international trade; regulatory policy in the face of scientific uncertainty; and, after a three-decade hiatus, on NIMBY conflicts afflicting high speed rail right-of-way and nuclear waste disposal sites. He is also a regular writer on pedagogy, especially teaching in professional education, and co-edited the "Curriculum and Case Notes" section of the Journal of Policy Analysis and Management. Between faculty appointments at the MIT Department of Urban Studies and Planning and the John F. Kennedy School of Government at Harvard, he was director of policy analysis at the Massachusetts Executive Office of Environmental Affairs. He has had visiting appointments at Università Bocconi in Milan and the National University of Singapore and teaches regularly in the Goldman School's executive (mid-career) programs. At GSPP, O'Hare has taught a studio course in Program and Policy Design, Arts and Cultural Policy, Public Management, the pedagogy course for graduate student instructors, Quantitative Methods, Environmental Policy, and the introduction to public policy for its undergraduate minor, which he supervises. Generally, he considers himself the school's resident expert in any subject in which there is no such thing as real expertise (a recent project concerned the governance and design of California county fairs), but is secure in the distinction of being the only faculty member with a metal lathe in his basement and a 4×5 Ebony view camera. At the moment, he would rather be making something with his hands than writing this blurb.

18 thoughts on “Home energy conservation Cliff’s notes”

  1. Underground it’s 56 degrees all year. Geothermal heat/cool takes advantage of this, with a deep well to pump fluid through you get a heat sink/source for which you need much less power plant electricity to extract conditioned air for your house. It’s costly to set up, but then runs at very low cost for years.

  2. Some folks have heat exchangers for heat as well: If it isn’t ridiculously cold outside, one _does_ gain something by turning out the lights or the TV, because, like the air conditioner, the heat exchanger will pump more heat into the house than the energy of the electricity it draws. But this is a minor point.

  3. The whole house fan method is great and can keep the house cool, but it doesn’t do anything to dehumdify, and that is a severe drawback in humid climates.

  4. “… like people and pets in the house metabolizing food, lighting, and operating your various appliances.”
    We want to hear more about these remarkable pets.

    1. Well, I have a panda who eats, shoots, and leaves…I can’t get him to remember to close the door on the way out, though.

  5. I asked about this on a previous thread, because I’m doubtful about the claim that all the heat added from electrical appliances will reduce the heat added by the central heating system. I have two reasons for thinking so:

    1) Most of the radiant energy from incandescent light bulbs will be absorbed by the walls (I believe) not distributed evenly to the air in the room. If that is the case then the rising temperature of the walls will radiate back into the room to some extent, but it will also go into increasing the heat flow out of the room. In short, it seems that only a part of the energy from the incandescent bulbs could reduce the heat needed from the central heating.

    2) If the house is on a system where the temperature is set to a relatively high value in the evening, when people are awake and at home and a lower value when asleep or away, then it is distinctly possible for the heat added in one room to never get to the thermostat. The additional heat from electrical appliances would then just be dissipated faster through the walls of rooms between the appliance and the thermostat. The heat from appliances could then only offset that from the central heater if the time for the heat to diffuse was short compared to the on/off cycle time.

    So it seems to me that the effect of a number of appliances being on in the den say would serve only to cause that room to be at 68.2 F rather than at the thermostat setting of 68 (for an example) and the central heater to run exactly the same whether the appliances were on or off. This difference would be too small to matter if you were in the room and certainly useless if you were not.

    Now, as I said in the previous post in the other thread, this is all based on essentially my guesses about things like how much IR is absorbed by walls rather than air and the diffusion rate of heat in a house. I know my conclusions could well be wrong. If anyone knows better please inform us all. Thanks.

    1. 1) Walls will transfer the heat to the air mostly by diffusion, not radiation, and unless the walls are really, really thin, they’ll do that much faster than diffusing it to the other side of the wall. So, this isn’t a big factor in the calculation.

      2) This is really part of the more general problem of household temperature balance: In your example, if no one spends any time in the den, then yes, the extra heat from those appliances might be more waste than anything. Not because the heat isn’t there, but because the wrong parts of the house are being heated. On the other hand, if you have some control over your temperature balance (forced air: by opening/closing individual air outlets, steam: by adjusting the flow at each radiator), then you could also turn down the heat in the den, not have the den be colder than the rest of the house, and save some bucks.

      1. Ok, I agree that my wall argument was the weaker of the two.

        I agree on the second point. For the heat dissipated by appliances to subtract from the heat needed to be supplied by the central heating system there must be a way for the heat from the appliances to get evenly distributed around the house. But I also think that in many cases you can’t adjust the heat distributed to a high enough precision for the appliance heat to matter. No user will adjust the vents in the den to be a little smaller when the TV is on so as to keep the Den at the nominal 68 F of the thermostat. Rather with the TV on the Den will be a fraction of a degree warmer. The result will be that with the appliance on the house will use more energy than with it off. If the house uses incandescent bulbs, it will use more energy than with CFLs, contra Michael O’Hare’s claim.

  6. It’s not just the south where the equation is different. Heating season where I live in the Pacific Northwest is about five months out of the year. The other seven months are almost all that “short period” where we don’t need significant heating or air conditioning. On average we probably use air conditioning for a week or a bit more a year.

    I agree with Keith’s first lesson, the most important thing is to do what you can to keep the heat/cool where it’s useful.

    For others of you who don’t live in a particularly small house or apartment, I have learned a lesson that for us has made a big difference in our energy consumption. Make sure your heating system is properly sized to your house. Ask to see the load/loss calculations before you have anyone install a new heating system. Don’t think that you should oversize your heating system “to be safe”.

    Our first ten years in our house we used the 80% efficient gas furnace that came with the house. The capacity of that furnace was too high for our house and there was no modulation of the output. It ran in short bursts and the house seldom felt comfortable during heating season at any reasonable temperature setting. We replaced it with a higher efficiency gas furnace and what we found was that with a modern, properly-sized furnace we are much more comfortable in our house at significantly lower temperature settings.

  7. “they are 100% efficient space heaters from the plug onwards.” 100% sounds good, but if you live somewhere with reasonably mild winters it’s actually a very low efficiency. For example, here in New Zealand, where (in the settled areas) temperatures much below freezing are very rare, heat pumps have about 400% efficiency in actual use. The theoretical limit is more than another factor of four away, so there’s plenty of room for improvement. A heat pump will heat your house much more efficiently than a TV or a lightbulb.

    I do understand that in places where winter is actually cold, heat pumps are much less impressive.

    1. Yes, air heat pump efficiency diminishes as temperature gets lower – obviously there is less heat that can be extracted from the air – although heat pump technology has improved in recent decades. The other important variable is the efficiency of your home in slowing heat escape. Very inefficient homes do not necessarily benefit greatly from heat pumps even in less than extreme climates. If heat loss exceeds the heat pumps ability to keep up (generally not designed to push a lot of air,fast) then the backup heat mechanism will run too much and negate the value of the heat pump.

  8. > “I’m doubtful about the claim that all the heat added from electrical appliances will reduce the heat added by the central heating system.”
    This is one of those things that’s trivially, or perhaps, uninterestingly true. Most importantly, unless you never run an air conditioner, then cutting down on your electrical use will indeed be a big benefit. Particularly as air-conditioning days are the peak electrical demand days, so all the least-efficient, most-polluting power plants are run mostly to provide power for air conditioners. So using more efficient light bulbs, etc. does matter.

    Of course, in the beautiful in-between times when you’re not running the heat or the air conditioning, then cutting electrical use is also a no-brains benefit. The waste heat doesn’t matter, but you’re still wasting electricity that you have to pay for and something has to generate.

    Then even in the winter, as the post admits, unless you’re heating your house with electric heat, the waste from appliances is less efficient that your gas or oil boiler, so cutting back on electric use is still a gain. Finally, I’ll note that unless you’re running stage lighting or an Amazon server room or something, waste heat from electrical devices isn’t going to be that much, as far as heating your house goes. So it’s not like you can get by with a smaller furnace because you’re leaving the living room light on all night.

    So, yes, if there’s electric heat on nearly the entire time you’re in your house (I suppose some winter-only ski houses might qualify? Anyone else?) then it’s true that investing in more energy efficient light bulbs for fixtures in the middle of your house might not be much of a net gain for you, or for the environment (but it won’t make things worse either). But for everyone else, it generally is a net gain. I’m not sure what the point of the post really is. Does the author think that there’s a huge population of readers who only live in winter-only houses? (Commuting between hemispheres I assume).

  9. The energy required to keep your house warm in heating season is exactly the energy lost through the exterior walls, windows, doors, roof, and up the chimney if you have one

    Had a lovely conversation with a retired structural engineer about this very thing the other day. The way we designed our buildings in the era of cheap energy is starting to cost us. We have to find a decent way to retrofit durable residential building envelopes without kicking people out of their houses for three weeks. Whoever does this will become the next Bill Gates.

    1. It’s not so hard. I retrofitted a fifty plus year old house with new argon filled double pane windows with a heat gain/loss reduction coating, put in some insulation in the uninsulated active and effectively eliminated 90% of need for AC in a very hot area. Plus, the new windows cut way down on street noise and the house stayed much cleaner due to no dirt blowing in through the very tight new windows.

      The new windows also let us sit, without being cooked, in the East facing breakfast room when the sun was blasting in.

    2. We got kicked out of our house (had a fire) for some months. What we did: revised the furring strip system on our brick and block walls to allow 3″ of insulation instead of 1″, 6″ of closed cell foam in the roof, replaced the HVAC system with geothermal, replaced the older windows with modern air-tight. HVAC replacement made much more sense because the old one had been damaged by the fire – still very expensive, 800 feet of well at $25 a foot, and then the heat pump is fairly comparable to conventional. We expect solar to be markedly cheaper in two to five years than it is today, so a conduit with #6 wire from roof to circuit breakers makes us ready for that without disturbing the walls then.

      As far as doing this sort of thing without disturbing the occupants, a friend of ours is considering EIFS system for his house (“Outsulation”) but the neighbors had the idea of the nice brick being submerged under stucco. Probably they have been visiting the Ugly Persian Houses site http://uglypersianhouses.com/ though I think you can do EIFS which does not offend the eye. EIFS had a big problem with moisture and rotting when applied to wood walls, this seems to have been resolved but people have lingering questions.

      And, banging the same drum as our gracious host: weatherstripping! foam around your electric outlets! deciduous trees shading south facing windows!

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