# Spa (Hot tub) Renovation - Gas? Solar?

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• posted on October 24, 2004, 9:37 pm
They used to think that the earth was flat, too.
wrote:

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• posted on October 24, 2004, 10:08 pm

Pray do explain further.

Nick

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• posted on October 25, 2004, 12:42 am
Oscar_Lives wrote:

When did HVAC people used to think that the earth was flat? That's just another one of those lies you were taught in grammar school.

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• posted on October 25, 2004, 2:51 pm

On my planet, it takes about 1000 Btu to evaporate a pound of water.
At -10 F, wo = 0.0004608 max. At 68 F and 42% RH, wi = 0.006198. Raising 154 cfm of outdoor air to 42% RH for the previous 2304x8 ft^3 house with 0.5 ACH and 192 Btu/h-F requires evaporating 60x154x.075(wi-wo) = 3.976 pounds of water per hour, which requires about 3976 Btu/h of heat.
The ASHRAE 55 standard says people are equally comfy at 68.0 and 42% RH and 69.7 F and 10% RH. Turning the thermostat up from 68 to 69.7 would only add (69.7-68)192 = 326 Btu/h to the fuel bill.
Then again, you might make 42% indoor air by caulking until 60C0.075(wi-wo) = 2x8.33/24h, ie C = 27 cfm, saving 3282 Btu/h in humidification energy plus about (154-27)(68-(-10)) = 9906 Btu/h in heating energy, for a net savings of 13.2K Btu/h or 316.5K Btu (\$5 in oil or \$9 in electricity) on a -10 F day.
Nick

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• posted on October 25, 2004, 8:51 pm
snipped-for-privacy@ece.villanova.edu wrote in message wrote:

No quarrel with the rest of your analysis, but if ASHRAE 55 says that, then it is horses**t. Hardly anybody is comfortable at 10% RH under any conditions, and prolonged exposure to humidity that low, especially in the absence of adequate air exchange (as can be created by overzealous attention to insulation), is well known to encourage upper respiratory infections.
--
Chris Green

> Then again, you might make 42% indoor air by caulking until 60C0.075(wi-wo)

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• posted on October 25, 2004, 11:27 pm

...21,000 people say you are wrong. Then again, you can caulk.
Nick

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• posted on October 25, 2004, 11:39 pm
wrote:

Oh bullshit. I am most days in summer.

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• posted on October 25, 2004, 3:36 am
snipped-for-privacy@ece.villanova.edu wrote in message