Most energy efficient methods for heating
Hotsauce1183
| Posted in Energy, Heating & Insulation on
I live at 6000 feet in heating zone 5 with early morning temps in the teens and below. I have often wondered which is the most energy efficient heating program to employ:
1. Leave the thermostat at 72 all night to keep heat in the walls and infrastructure? Heating system cycles normally according to set point demand.
2. Turn thermostat down to 68 at night then warm rooms back up to 72 in the early am? Heating system runs for an hour or two restoring set point of 72.
3. Turn thermostat down to 62 at night. Next morning thermostat returns to 72 but runs for hours on high before rooms are fully reheated.
4. Turn system off at night then turn back on around 4am in order to get rooms back up to 72 by 8am?
TYIA
Replies
4 uses the least energy. The higher the temperature inside the faster you lose energy. Heating up a house by 20 degrees is less demanding than keeping it at that higher temperature for a long time.
In practice, you probably don't want to do 4. If the temperature gets too low in parts of the structure, pipes could freeze.
I have no idea how to compare your list from experience as we are in total radiant heating in our home. Gas boiler fed floor heat and a soapstone (4000 lb) heater. Currently here in NW Ohio our floor heat is not on. The sun (passive solar built home) has been marginal but pretty good in Nov. - now. With 2 firings of about 15 lbs of wood a day the indoor temp in this 2600 sf stays about 73/74 as the wife likes it.
However, our nat gas company has a monthly report of usage according to how you list the gas using appliances in the home. How they figure how much each appliance uses beats me. But in the monthly report, they do list percentages for them. Our water is heated by the boiler but their breakdown still lists “water htr, cooking, dryer, heating”. So, when I look at the bill I can sort of figure the diff between “water” heating in the summer vs when the boiler heats the floor when it is on.
Pretty big worthless leadin to your question.
If you were to take your different cases......during a same outdoor temp week....and read your meter (assuming gas) morning to morning......you might get an answer to your particular situation.
Otherwise, I’m sure there’s an hvac site like maybe Heatinghelp.com that has a generic answer.
If you ever get a real answer make sure to post back. It’d be interesting and informative.
Since I’ve wasted all this space already, here’s what I can tell you about a radiant system. With not much sun help, when we leave floor off and go away for a few days in late fall or early spring (with no threat of “freeze”) it takes a good 2 or 3 hrs to bring the temp up to comfortable with the soapstone heater. Adding the floor heat or it alone would be about the same.
Sorry for the novella.
Don't set the thermostat above 68.
Physics and differential equations.
Heat energy flows from hot to cold proportional to the difference in temperature.
If the difference in temperature is more, the heat energy moving is more.
my favorite differential equations problem from college was about the king and queen who were served coffee. Both take cream but the king puts his in right away, while the queen likes to wait a bit. which one drinks the cooler coffee?
(you can assume other variables are controlled, and that the king is a gentleman and waits for his queen to enjoy his coffee.)
This helps as well:
Newton's law of cooling can be modeled with the general equation dT/dt=-k(T-Tₐ)
You can refer to the tutorial for energy-efficient heating, maybe this one: https://www.heathome.org/
Adding my opinion with it, you should set your indoor regulator to your objective temperature and leave it there constantly - in any event, when you're away from home for broadened periods. The thinking is that it takes more energy to warm up a virus house or chill off a hothouse than it takes to keep a consistent temperature.
"The thinking is" that programable thermostats save energy by adjusting the temperature to different periods of usage during the day rather than wasting a lot of energy when it is not needed.
There is not any easy answer to your question. Other than the standard: Turn down your thermostat at night and when your away for 4 or more hours and you will save 1% for each degree of turndown.
That altruism very seldom holds true for each and every household as it requires you to set your temp at 68* and have a set-back thermostat that is set and left alone to operate. And never touched again. As well as having a furnace that is meticulously maintained and the ductwork is sized, installed and sealed correctly. Which of course happens every time.
Of course, if you happen to have baseboard heating, or some other type of heating other than Gas Forced Air, this may not hold true for you.
Or, if your GFA is either sized improperly or if the ductwork is not sized, sealed or installed correctly.
Now, assuming your GFA heating system is reasonably well sized and the same goes for the ductwork. (sized, sealed and installed) And you have a modern GFA furnace with a multi-stage burner and continuously variable DC blower. And your house is newer with reasonable insulation, bypass sealing and so on.
Your best bet for energy savings would be to have a learning type of thermostat that can follow your lifestyle and learn your ways. It should also have a way of detecting the outside temperature as that is crucial to determining how far to lower the thermostat and when to start raising the temperature to reach the set-point.
@nomorecoffee is correct. Its Physics, it is an easy answer, and there is no "the thinking is".
I can't tell you how much you will save or whether it is worth it to you but the most efficient way is to let the temperature drop and then heat it back up when you want it warmer.
What type of heat source? If hot water heat, I have had several HVAC engineers tell me that cutting down the heat during some hours will cost more fuel to get back to full heat than is saved by the set back.
Good luck.
The mechanism for heat transfer within the conditioned space has no bearing on the energy loss of the building itself. Reducing the temperature in a building reduces heat loss because the temperature difference between conditioned space and outside environment is reduced.
The energy required to warm up the building is only replacing the energy given up by the building when cooling down to the set back temperature.
Hydronic systems will have the same energy savings as forced air when using a temperature set back.
People say all kinds of stuff that is not accurate.
Not on the internet, everything there is true.
If this was accurate, I would need a new hobby.
me too
*building performance engineer here*
Simple physics, cut and dry, as someone stated above there's no "the thinking is."
It's very simple-the lower you let the temperature get at any given time, the less energy you lose to the outside. It doesn't take any extra energy to "let the house cool then heat the house back up," when you heat it back up youre just using fuel that wasn't used when it was cooling down. The only energy you are actually *losing* is the heat that's seeping through the wall insulation, which is directly related to temperature difference between inside and outside. You might lose 300,000 BTU in a night if the heat is at 72, but only 275,000 if you let it drop to 68 and 250,000 if you let it drop to 62.
Your scenarios are listed in order from highest to lowest, 1 uses the most energy, then 2, then 3, then 4.
The ONLY caveat to this is if you have a heat pump or geothermal system (which you should 100% put in geothermal by the way, 5x higher efficiency than gas, worth every penny), then you can sometimes kick the system into inefficient emergency heat mode if you make it do a big temperature swing, but this is easily avoided by having the setpoint step back up