Spa temp and energy usage

[Chas]

I'm still working on a simple equation to show the rate of heat loss off still water with a different delta t. But in the meantime, a thought struck me. Don't worry, it happens several times a year and I wasn't hurt this time....

A practical way of looking at this would be to do a simple calc of the cost of running the heater. For the sake of this flimsy example, let's use a one-hour soak.

If you have a 5000 watt heater, it will cost you a little over 5KWH (kilowatthours) to run for one hour. If you are paying $.25 per KWH, then your heater will cost $1.25 to run for an hour. I think a Quarter is a high rate, most non-California residents pay less.

Just for fun, imagine a spa with very low temp difference between water and ambient air. The heater may run for as little as ten minutes out of the hour.

That would be 1.25 / 6 or $.21 to run the heater for that one-hour soak.

So, the higher the temp differential between water and air, the longer the heater will run. Keep in mind that in extremely low air temp situations, the heater may run for more than an hour for a one-hour soak - taking a few minutes AFTER the lid is closed to get back to the heat setting - but I think that would only happen in extremely cold climates, and nobody with any sense would live there.  

[HotTubMan]

I'm still working on a simple equation to show the rate of heat loss off still water with a different delta t. But in the meantime, a thought struck me. Don't worry, it happens several times a year and I wasn't hurt this time....

A practical way of looking at this would be to do a simple calc of the cost of running the heater. For the sake of this flimsy example, let's use a one-hour soak.

If you have a 5000 watt heater, it will cost you a little over 5KWH (kilowatthours) to run for one hour. If you are paying $.25 per KWH, then your heater will cost $1.25 to run for an hour. I think a Quarter is a high rate, most non-California residents pay less.

Just for fun, imagine a spa with very low temp difference between water and ambient air. The heater may run for as little as ten minutes out of the hour.

That would be 1.25 / 6 or $.21 to run the heater for that one-hour soak.

So, the higher the temp differential between water and air, the longer the heater will run. Keep in mind that in extremely low air temp situations, the heater may run for more than an hour for a one-hour soak - taking a few minutes AFTER the lid is closed to get back to the heat setting - but I think that would only happen in extremely cold climates, and nobody with any sense would live there.  

A cheap shot at your Canadian friends, eh!?

At $.25/KW hour USD, you'd have to be crazy to live where you do! I pay $.085 CDN

[windsurfdog]

A huge thanks from both the goddess and myself for squeezing your brains and wringing out such knowledge.  I agree with Vinny--I certainly don't want to add "Engineering Techno Geek" to my other claims of geekdom but I just wanted to very loosely quantify my thoughts re: all parameters involved in explaining to someone, especially those who are exploring their first tub purchase, what factors are involved when considering tub energy usage.  It sounds as if the concensus is that keeping one's tub at a higher temp does indeed use more energy but not at a great differential from lower tub temps.  I would guess most keep their tubs anywhere from 95-104 degrees.  Using the thoughts we've discussed, would it be fair to guess that keeping one's tub at 104 would be < $10/month more than keeping it at 97 or $10-$20 more or even more?  From the consensus, it sounds like the first option to me.

Certainly, the other 2 main factors (are there more?) of tub design/construction and usage trends would have a much greater effect but I believe temp setting would have some effect, allbeit to a lesser degree.

Thanks again for the gray matter!

[Chas]

At $.25/KW hour USD, you'd have to be crazy to live where you do! I pay $.085 CDN

The day my power bill arrives each month, I would agree!

[salesdvl]

I still say there should have been a moving train in the formula to make it more challenging.

[Brewman]

I suppose we could vacate all of those who have the misfortune of living where electricity is expensive up to your area so they may take advantage of your low electric rates.  Of course, that would increase the demand for power in your area, driving up it's cost to maybe $0.25/kwh.
 OOPS.....Sounded like a good idea for a minute.  

How much per litre is gasoline in your area?  we're paying about $0.50 USD right now.

Brewman

[stuart]

Saturday morning I too was having an early morning soak in 103-degree water, feeling the fall chill in the air, when a bug of some kind landed in the spa. As I watched closely, he struggled between life and death in the hot water and I wondered if he was more frightened by the hot water or the fact that he was drowning.... Suddenly I had what most of you would call an "epiphany" and I knew clearly what I had to do........

STOP DRINKING BEFORE NOON!

I was halfway through this topic and my head started hurting so much I had to retract that vow!

[windsurfdog]

I was halfway through this topic and my head started hurting so much I had to retract that vow!
 

Thank goodness!  A sober bubba stu is a scaaaarrry thought!

[salesdvl]

Ok so at any point does the body temperature of the soakers enter as a variable?  For example: if you have 6 soakers with body temps of 98.6 and we are trying to keep the water at 102, do the soakers actually have a downward influence on temp?  Conversely, If you put 6 slightly feverish people with a temp of 100, and you trying to keep the water temp 95, would they raise the temp... and.... at what ambient air temp could you drop to where the 6 bodies would maintain the temp. of the water at 95?

[windsurfdog]

Ok so at any point does the body temperature of the soakers enter as a variable?  For example: if you have 6 soakers with body temps of 98.6 and we are trying to keep the water at 102, do the soakers actually have a downward influence on temp?  Conversely, If you put 6 slightly feverish people with a temp of 100, and you trying to keep the water temp 95, would they raise the temp... and.... at what ambient air temp could you drop to where the 6 bodies would maintain the temp. of the water at 95?

YEOW!!!  I'm joining bubba stu for a REAL stiff drink after this one!

[rocket]

salesdvl, you have really gotten the hang of this forum.  You're doing great and I'm enjoying your posts.

[salesdvl]

You're gonna make me blush.
thanks        ( this smiley doesnt really apply but I like watching its eyes bug out. )

[rocket]

You've become a full member is record time.  Sales must be slow which gives you the opportunity to stay on the net and post>

[salesdvl]

Well, I check at home in the morning as I am checking my regular mail ( and trying to decide whether or not to order viagra or some "extensions" ) then I check at night when I get home ( assuming I can get computer time from my 14 y/o son.  And periodically I stop by at work and check in.  If something is cookin, I chime in.

As I look back and read this posting I feel the need to put my thumb and fore finger up to my forehead in the shape of an "L".    Oh my gosh, my wife's right, I am a dork.    

[rocket]

yada, yada, yada.....