Hot Tub Consumption Calculation - Geeks Only!

[couzin2000]

I have been working on a tool for weeks now. It's a calculator of costs for the monthly/yearly consumption of a spa/hot tub.

I want to have certain information input on one end, and the other end must produce results.

I've been looking for help within many scientific communities, and I have managed to find many formulas that will permit me to calculate a part of the consumption. But somehow, something is wrong within the calculations, and I'm looking for assistance.

Warning: this thread is not for the average run-of-the-mill discussion: I am looking for scientific data here.

Many factors come into play here: temperature of the air, of the tub (shell), of the water, and at different times of the year. I have temperature data, so this is fine.

Ozone generator, hp of the massagers, the filter's pump, and so on, all of those aspects are already calculated. However, I am looking for the data for heating the water.

Since I'm not in the US (Quebec, Canada), temperatures here are different: July is warm with an average 19.8°C. January is snowy with -12.5°C on average.

I've managed to calculate the consumption of heating water from x° to y°. In essence, here is the formula:

Q(energy, in kWh) = (1.155e-3kWh/liter-°C, the heat coefficient) x volume of water (liters) x temp.differential (end temp - start temp, in °C)

This gives me the consumption of elevating the water temp to the desired level. However, I can't figure out how to calculate the costs of maintaining the temperature constant. I've managed to calculate heat loss, but that gives me a value that is not consistent with the amount a spa should cost here in Quebec (which varies between 600$US to 1500$US per year).

If anyone can give me some help here, it would be much appreciated.

Here are some things you may wish to consider when calculating:

• the spa is always square;
• I do not calculate in-ground or above-ground;
• the cover is closed at all times when not in use;
• insulation is not a factor, and all spas have the same for this problem;
• I'm looking for kWh (kilowatthours), not joules or time to heat the tub.

Thanks in advance for everything!

Couzin2000

[couzin2000]

Really??? NO ONE can help me here???

[Tom]

It's an incredilby complex calculation. A couple of years ago I did a similar topic as a Fermi problem (google it) with an Arctic Spa, but unfortunately lost it in a hard drive crash. I had PM'd it to a few people - anybody still got a copy?

[Glid]

Really??? NO ONE can help me here???

Nope! Just a dumb guy sitting in a tub.

I don't post on forums to think...Just look at some of my replies.

Good luck on the formula. I just go and pay my electric bill. The money is just going to fly out the window anyway!

You forgot the T-I-T factor. Time in Tub will be a variable with number of people and if someone is sick he might have a tempreture!

[wylekioti]

I have been working on a tool for weeks now. It's a calculator of costs for the monthly/yearly consumption of a spa/hot tub.

I want to have certain information input on one end, and the other end must produce results.

I've been looking for help within many scientific communities, and I have managed to find many formulas that will permit me to calculate a part of the consumption. But somehow, something is wrong within the calculations, and I'm looking for assistance.

Warning: this thread is not for the average run-of-the-mill discussion: I am looking for scientific data here.

Many factors come into play here: temperature of the air, of the tub (shell), of the water, and at different times of the year. I have temperature data, so this is fine.

Ozone generator, hp of the massagers, the filter's pump, and so on, all of those aspects are already calculated. However, I am looking for the data for heating the water.

Since I'm not in the US (Quebec, Canada), temperatures here are different: July is warm with an average 19.8°C. January is snowy with -12.5°C on average.

I've managed to calculate the consumption of heating water from x° to y°. In essence, here is the formula:

Q(energy, in kWh) = (1.155e-3kWh/liter-°C, the heat coefficient) x volume of water (liters) x temp.differential (end temp - start temp, in °C)

This gives me the consumption of elevating the water temp to the desired level. However, I can't figure out how to calculate the costs of maintaining the temperature constant. I've managed to calculate heat loss, but that gives me a value that is not consistent with the amount a spa should cost here in Quebec (which varies between 600$US to 1500$US per year).

If anyone can give me some help here, it would be much appreciated.

Here are some things you may wish to consider when calculating:

• the spa is always square;
• I do not calculate in-ground or above-ground;
• the cover is closed at all times when not in use;
• insulation is not a factor, and all spas have the same for this problem;
• I'm looking for kWh (kilowatthours), not joules or time to heat the tub.

Thanks in advance for everything!

Couzin2000

I know I should not get into this. My brain is at half power after my back injury. But I did not see "time" mentioned. Assuming heat loss were constant (not) you should have a frequency as a percent of time you would have to reheat. I would avoid getting into Constant temp but rather a "how long to heat 2 degrees divided by how long it takes to lose 2 degrees" . Sorry I dont even know where my thermodynamics, physics, etc books are any more. but maybe this will start a new thought.