Home heating/cooling

[SomptingGuy]

I saw this phrase in a suggestion scheme posting here today:

"Tradeoff would have to be made to ensure the amount of energy required to cool down the building in the morning does not outweigh the savings by not running it overnight."

This is equivalent to people who think that they should leave their heating on low during periods of absence to avoid having to "heat their house through" on returning.

Taken to the extreme these arguments are clearly hokey. If you are absent for a year, leaving the heating/cooling on is clearly wrong. But I wonder if there is any point where it does make sense to leave the heating/cooling running.


- Steve

 

[kchan711]

In the cooling case, the only reason I may leave it on (like when I go to work) at higher temp of course, would be to shorten the lead time in waiting for the home to cool down. In the heating case, I would simply leave the heat at a set temp to eliminate the possibility of freezing pipes and maybe my family .

In reality, Ein = Eout with some efficiency loss. So whether you run it intermitently throughout the day or you let the HVAC system attack the temperature and humidity difference in one shot, you're still using the same juice. Now, different parts of the day have different energy costs (peak hours vs off-hours) and environmental effects on the building (hot day verse cool night, sun, wind, rain). The best energy saving technique is get out of your comfort zone a bit. If all things work out well, turn it off while your not there or at least down or up (depending on if your heating or cooling).

When push comes to shove, I'm cheap. So, I let the environment take me where it takes me unless the building or home in my case is at stake. The other problem is the fact I'm married, so she is dictates the environment we live in, figures...



Kyle Chandler

http://www.KylesGuide.com

"To the Pessimist, the glass is half-empty. To the Optimist, the glass is half-full. To the Engineer, the glass is twice as large as it needs to be!"

 

[GregLocock]

This always seems to be a tragic case of ignoring Newton's law of cooling (ie dQ/dt=k*(T1-T2)) against the actual experience of walking into an ice cold house, or in Oz a very hot house, and then waiting for the thing to get comfortable. I /think/ it is physicaly impossible for it ever to be more efficient to continually heat or cool a house rather than sorting it out as required.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.

 

[SomptingGuy]

I gave up trying to explain any of this to my wife. It would always end up with the "What makes you think you are right?" question. I never had the guts to reply "An engineering degree and 20+ years of experience". So I just paid the extra heating bill for a quiet life.

- Steve

 

[IRstuff]

That's because it's not an engineering question, it's, "Do you want to be happy, or do you want to be right?"

Anyways, this question has been asked in this forum a while ago, but I can't remember if there was a consensus.

TTFN

FAQ731-376

 

[MintJulep]

I answered this a few years ago here - even used calculus - but I can't find the thread now.

Anyway, the answer is that it is always cheaper to turn heating or cooling equipment off rather than to leave it running.

This thread403-173742 is somewhat related.