How do you calculate if it costs less to totally turn heat off or turn it down for a building?

Question

In order to save money, some people believe it's better to totally turn off the heat for a building over the weekend (or overnight) and then turn it back on when people come back. Others argue that it's more cost-effective to leave the thermostat on a lower temperature than typically desired (like near 60), but not let the building's temp get as far down as 50 or 55 so that it will take less energy to reheat it to comfortable. Can someone provide the equations to calculate the amount of heat used in each case so that we can do a comparison? Thanks!

Answer 1

It will always be more economical to turn off the heat, unless there is a danger of damage from the cold.

When the building is heated, you have to add heat at the same rate it is being lost to maintain a constant temperature. When you turn the heat off, it is initially losing heat at the same rate, but as it cools off, the rate of heat loss slows, because it is driven by the temperature difference with the outside. So it loses less heat if it is unheated over the weekend than it would if the heat stayed on. Monday morning, all you have to do is replace the heat that was lost over the weekend to get back to where you were.

Answer 2

It will save money to turn the heat off altogether, as long as it does not get so cold that pipes freeze -- that will cost big money to fix. The heat loss from a building is proportional to the difference between outside and inside temperature. The heat required to warm up a building once it gets cold is difficult to calculate -- it depends on the structure of the building, and the nature of its contents. A computation can be done if you obtain data: with a known outdoor temperature, read the indoor temperature every hour or two with the heat shut off. The initial rate of fall of the temperature is proportional to the average heat load, and you can determine that from the utilities bill. Some numerical integration with a calculator will give a good idea of the heat loss at various temperatures.

Answer 3

You could do a calculation if you know the heat transfer rate of the building to the environment, the heat input rate of the heater, the cost per unit time of running the heater, the average heat capacity of the building, and the period of time over which you are comparing the two options.

As you might now suspect, it's not particularly practical to do calculation wise, as the only way you're going to get accurate numbers is through days or weeks of experimentation and data recording and then analysis.

The simplest way to figure it out would be to just try one method, then try the other, and compare the heating bill to what you've been doing previously (assuming you had similar heating conditions last month).

Answer 4

For comparison, you have to set your standard points. Say, standard points is the normal operations of 60 degrees F.

Let's us denote Q as the heat

Condition 1, The lowering of thermostat to 50 degrees F when you leave for the weekend. So Q1 = Qa + Qb. Where Qa is the required heat to maintain the temp of the house to 50 F for two days, while Qb is the required heat to raise the temp. back to 60 F when you arrived.

Condition 2, The turning off of thermostat to 0 degrees F when you leave for the weekend. So, Q2 = Qc + Qd. Where Qc is the heat required to maintain your house to 0 F, which is minimal. Just for comparison, you can assumed it to be zero. Qd will be the heat required to heat your house when you get back.

Knowing these two Q's, you can now calculate for the gas consumptions on each conditions. Next, basing from the rate, $ per cubic meter, from your monthly billings, you can now compute for the amount of gas consumptions on each conditions.

Knowing both amounts, you can now compare and draw your conclusions. Good luck!!!

sorry, it's been years and years since and I'm not in practice so I totally forgot the exact formulas. In theory, I think that's your way to go.

Answer 5

We began doing the comparable in an 1100 sq. ft apt final wintry climate and it did help some. We close the two mattress room doorways and the two bathing room doorways and used oil filled electric powered radiators. an somewhat advantageous heat temperature from them. the element is that once you place the thermostat returned up the subsequent AM the gasoline furnace has to run longer to convey it returned up. yet regardless of this we did have a mark downs on the two our gasoline and electric powered charges it wasn't a good deal yet each and every greenback counts. in case you're utilising any area heater with an open element that turns orange or crimson they are not power saving. something that heats up rapid with an element like that including an electric powered range and oven, area heater, toaster makes use of greater electric powered.

Answer 6

There is not a simple formula to calculate this but it is always more efficent to turn the heat off.

Answer 7

this all depends on how long the building will be vacant...how well it is insulated...what is the desired temperature...etc....you never want to turn it off...you can end up with frozen pipes...very expensive to fix

Answer 8

It will always save money.
E1=a*T1*T1*T1*T1 (fully turn on)
E2=a*T1*T1*T1*T1
E3=a*T1*T1*T1*T1
E4=a*T2*T2*T2*T2 (partially turn on)
E1+E2> E3+E4