Is the Exponential Curve Stealing from your Purse?

Sometimes we need to stop and realize just how much of our heating and cooling bill directly relates to our personal habits and our personal attitudes about that ideal temperature.

Do you know anybody who likes to walk around in sweaters or pull a blanket over themself in the middle of summer to stay cozy in the conditioned cool air of the house? Yes, you heard that right. Like to overcool the house out of habit and dress up warmer to keep warm. And you know someone who does this, too.

Maybe there is a conflict about he ideal temperature in the house? Sometimes, there is conflict in the house, on what the ideal temperature is?  This can be by personal preference, it can be caused by someone upstairs who is hotter and who also controls the thermostat, or whose complaints cannot be ignored, Or it can be issues with the construction of the house.

We have several resources to help with each of these issues.

Make sure you solve all the above issues first before going down the road towards zoning.

Whoever is the culprit here, but the household is buying a lot of extra energy, and so we come to the story of the exponential curve.

Exponential curves can be your friend or they can work against you. When you are over cooling your home, when you feel uncomfortable and turn that thermostat down another couple of degrees, the exponential curve works against you.

The exponential curve explains why the energy needed to add the next degree of cooling is so much more energy intensive that the previous degree added. Minute changes in the thermostat to get a bit more cool can be a commitment to a much larger energy bill. There are issues you need to deal with here. See the list. Something is stealing your money.

The exponential curve explains why the energy needed to add the next degree of cooling is so much more energy intensive that the previous degree added. Minute changes in the thermostat to get a bit more cool can be a commitment to a much larger energy bill. There are issues you need to deal with here. See the list. Something is stealing your money.

A is the energy used to produce the first degree of cooling. b is the energy needed to produce the second degree of cooling. The second degree is much more than energy intensive that the first and the next much more energy intensive. You home has a unique exponential curve defined by how much your home leaks air, how well your home is insulated and how effective your cooling system is.

You can impact this equation with a reasoned and coordinated effort to improve energy efficiency. Make sure you see the critical factors which determine how energy efficient your home is. That is here. More  details – even bits of math!  are offered below to better understand your home’s exponential equation.

Sometimes we need to stop and realize just how much of our heating and cooling bill directly relates to our personal habits and our personal attitudes about that ideal temperature.

Who wants more details of why changing the temp a bit takes so much extra energy?

Not much math to see because it quickly gets very complex and we would have to model it on a computer. We will start with conduction and explore the relationship between change in temperature and change in energy gain. Then we will just in general mention factors that increase in impact with changes in temperature.

The transfer of energy in a space like your home by conduction is  simple and straightforward math. Q= U x delta T. \big. \dot{Q} = U \, \Delta T \quad

Q is the quantify of energy which you buy, U is the transmittance of your house to energy transfer – [it probably makes more sense that U is the inverse of R value- how we buy insulation. U = 1/R]  and delta T is the temperature difference between your conditioned air inside and ambient. The size of the house is set- the insulation properties of the house are not changing; just the differential in temperature between ambient air and conditioned air. This would first appear to be just a linear- proportional energy transfer them.

BUT, BUT, BUT, BUT BUT things are not that simple. All these other factors rear their heads.

Change in Delta T impact the convection currents in your house. They get more active with change in Delta T. Therefore, the energy transfer rate goes up.

Energy transfer by  radiation goes up as the Delta T between the radiating bodies becomes greater. Therefore your the energy transfer rate between inside and outside goes up.

We talk about natural forces which transfer energy here around inside your home here..

Air leaks are a big factor in energy loss as your conditioned air is invaded by and , in turn invades the great outdoors. Air  exchanges get more numerous- more air leaks in and out of your house as the pressure differential between the inside of your home and the ambient air increase.

The differential temperature increase changes the pressures inside your house. As you further increase the cooling inside the air gets dryer and cooler making it heavier. More air leaks out of the bottom of the house, under the sills- into the crawl space- etc.  and more hot attic air wafts down through the ceiling to back fill against this cool air leaking out. The taller your house, the greater the effect. We cover pressure systems and energy exchange in your home here.

And mechanical issues cannot be discounted. Your HVAC system has an efficiency curve. It has defects and these defects impact your home as you require more effort from it. HVAC issues intensify as you put pressure on your HVAC system to cool, or heat.

So these are just a few of the factors that make the energy use go way up much faster than you might think, when you just want a little more cooling to be comfy.

All these natural forces when accumulated together create the unique differential equation for your home.

The leakier your home is, the bigger the defects in the mechanical systems, the more problems with insulation you have,  the greater the impact on your wallet as you step up the amount of cooling.

And, all these factors impact your home the exact same way as you are heating your home too. Like a really warm, cozy house? Energy efficiency improvements will really pay off for you, because the exponential curve is working against you now… all the time.

Small adjustments in the level of cooling you desire can greatly affect your cooling bill. Ditto for the heating bill. Now who in your house is impacting the cool? Maybe it is time to do something about it? It might be easier to address the energy efficiency than they human behavior but maybe you are better at modifying the behavior of other people than my friend.

I have a friend who has a lady friend who likes to sit around under a blanket because she has a belief of how cool the room temp should be. He hasn’t had the heart to tell her the story of the exponential curve. I think he likes to cuddle under the blankets anyway and I also don’t think he wants her to know he is a nerd. Life is very complex for my friend. Let’s just drop that story…

Any questions about how much you are paying to cool or heat the homestead? You have lots of options to save money and be comfortable and not put on extra layers this Winter. And sweating does not have to be a money saving solution in Summer. Doesn’t it make sense to know your options?

Who has a thought here? Who is defying the power of th exponential curve? What are you going to do about it?

Stu Langley

meet the author at StuLangley.com

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