Thanks for the info, sounds like we agree about the btu results just not on the value.
time for me to go swimming. 
Hotspot FPH AC heat reclamation pool heater - a review!
- Thread starter Joshii
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Thanks for the info, sounds like we agree about the btu results just not on the value.
time for me to go swimming. Captain,
Back in post #48, your numbers say, 5-ton unit produces 60k btu/hr. Due to inefficiencies in heat transfer and equipment, assume a 50% capture rate. So that gives 30k btu / hr for pool heat. My understanding is that 1 btu = heat required to raise 1 gallon of water by 1 degree F. If the AC runs 40% of the day between 12:00pm and 8:00pm, that would create about (30k x 8 hrs x 0.40) = 96k btu of heat. If all is correct thus far, then that yields a 9.6 degree increase to a 10,000 gallon pool, right? The pool will likely continually lose heat (any recommended rate?) throughout the process, so maybe it’s a 6-7 degree increase. Is my math right?
For the people that have installed the system, you are really just trying to maintain a temperature, right? So you just need to add enough heat to overcome the heat lost to the environment (air and soil) throughout the day. How much does that tend to be? When you need to supplement, do you run your NG heater?
In CA, my gas costs: $2.39/therm; which seems really high to me to use this to heat my pool. We are still in design, no equipment has been ordered or built. I am trying to figure out the best way to heat the new pool.
My pool will be 620sf surface area which, per the internet, will need 430,000 btu per day to maintain the temperature. So that would be running my 400,000 btu heater for only one hour per day. That seems low to me. Am I wrong here? If right, that would cost me $10 per day or $300 per month.
My electricity is $0.08/kWh Off Peak (9pm to 10am) and $0.35/kWh Peak (12pm to 7pm). I would love to use an electric heater in the early morning to overcome the heat lost at night. Maybe run it from 7am to 10am. Then have the FPH maintain the temp throughout the day. I don’t see many electric pool heaters on the market. Why is this? Are they super inefficient? I have read that heat pumps are not good at lower temperatures, so running it when it’s 60 – 70 degrees in the morning would be a poor use of power, right? Any thoughts here?
Back in post #48, your numbers say, 5-ton unit produces 60k btu/hr. Due to inefficiencies in heat transfer and equipment, assume a 50% capture rate. So that gives 30k btu / hr for pool heat. My understanding is that 1 btu = heat required to raise 1 gallon of water by 1 degree F. If the AC runs 40% of the day between 12:00pm and 8:00pm, that would create about (30k x 8 hrs x 0.40) = 96k btu of heat. If all is correct thus far, then that yields a 9.6 degree increase to a 10,000 gallon pool, right? The pool will likely continually lose heat (any recommended rate?) throughout the process, so maybe it’s a 6-7 degree increase. Is my math right?
For the people that have installed the system, you are really just trying to maintain a temperature, right? So you just need to add enough heat to overcome the heat lost to the environment (air and soil) throughout the day. How much does that tend to be? When you need to supplement, do you run your NG heater?
In CA, my gas costs: $2.39/therm; which seems really high to me to use this to heat my pool. We are still in design, no equipment has been ordered or built. I am trying to figure out the best way to heat the new pool.
My pool will be 620sf surface area which, per the internet, will need 430,000 btu per day to maintain the temperature. So that would be running my 400,000 btu heater for only one hour per day. That seems low to me. Am I wrong here? If right, that would cost me $10 per day or $300 per month.
My electricity is $0.08/kWh Off Peak (9pm to 10am) and $0.35/kWh Peak (12pm to 7pm). I would love to use an electric heater in the early morning to overcome the heat lost at night. Maybe run it from 7am to 10am. Then have the FPH maintain the temp throughout the day. I don’t see many electric pool heaters on the market. Why is this? Are they super inefficient? I have read that heat pumps are not good at lower temperatures, so running it when it’s 60 – 70 degrees in the morning would be a poor use of power, right? Any thoughts here?
You are off by a factor of 8 because 1 BTU is the amount of heat it takes to raise 1 POUND of water 1 degree F, not 1 gallon. 8 pounds of water in a gallon.
And, yes, FPH only needs to raise the water by what is lost to the environment. This is largely dependent on surface area. Hotspot says you need 650 BTU per sq ft of pool surface. In practice, we who have the FPH run it as much as possible to get as much heat as we can in the pool
And, yes, FPH only needs to raise the water by what is lost to the environment. This is largely dependent on surface area. Hotspot says you need 650 BTU per sq ft of pool surface. In practice, we who have the FPH run it as much as possible to get as much heat as we can in the pool
wayner
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- May 31, 2012
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Your sig says your plan is to use solar - won't that be enough to keep your pool warm, at least during the summer? Heat pumps don't use much electricity so perhaps you could use it during the day when it is warmer and it won't have to run for very long?
wayner
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- May 31, 2012
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- Jandy Aquapure 1400
Yes the evac tube solar is plumbed into my pool. When these were installed some piping was run that goes from my filter up on my roof and through the tube panels. There is a valve where I can open or close the flow to the panels. One issue is that if you shut the flow to the panels during the day then you have to keep them off until after sunset. The reason for this is that the water in the tubes gets very hot when it is static in the tubes. When you start pushing coolish 85F water through the glass tubes that are very hot they will shatter.
The evac tube panels are supposed to be good to help heat when you desired temperature is well above the ambient temperature. But I think I would have been smarter to get the regular types of solar panels.
Can you use a heat exchanger off the solar panels so you don't have to put cool pool water into the panel, it would use the primary water already in the loop.
wayner
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- May 31, 2012
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What do you mean about hidden expense for solar heating? Running your pump during the day and using more kWhs at a higher rate? My differential here is about $0.09/kWh for electricity used from 1100-1700 and $.05/kWh for electricity used between 0700-1100 and 1700-1900. So assuming the same run time per day I guess solar is costing me about $0.74/day on weekdays - the differential doesn't exist on weekends so that is $3.70/wk and about $59/yr assuming a 16 wk season.
I was referring to having to run your pump faster if you have a VS to get the same flow through the solar panels as you would without going through them. Much less difference in the case of the FPH.
But I agree with you - kind of a silly argument. I was just throwing Captain a bone. I consider solar and FPH both free or nearly so for all intents and purposes.
But I agree with you - kind of a silly argument. I was just throwing Captain a bone. I consider solar and FPH both free or nearly so for all intents and purposes.
You are off by a factor of 8 because 1 BTU is the amount of heat it takes to raise 1 POUND of water 1 degree F, not 1 gallon. 8 pounds of water in a gallon.
Doh!
wayner
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So I've finally had my HotSpot FPH running for 2 weeks and the results are amazing!
I have a 2.5 Ton A/C unit that it is hooked up to which cools the upstairs of my two story home. I'm in Tampa, FL so it runs A LOT!
Before we turned it on the pool water was 74 degrees, which I would say is the average in the summer, tops out at 78 in August generally. I have super screen surrounding the entire pool and the pool is on the back of my house that faces west, so it never really gets a full day of sun.
So anyways, pool temp was 74, air temp was probably 90+ as it usually is in the summer here, 6 hours of the A/C running almost non-stop, the pool was at a nice 80 degrees. The next day it was still the same temperature but over the next few days it got up to 82 and eventually hit 86, which was too hot for us, so I actually turned it off and the temperature of the pool fell to 82 but has climbed to 84 during the day.
Anyways, amazing results for summertime! My wife and I swim everyday now.
If you have any questions, let me know. I'll try and post some pictures soon.
I have a 2.5 Ton A/C unit that it is hooked up to which cools the upstairs of my two story home. I'm in Tampa, FL so it runs A LOT!
Before we turned it on the pool water was 74 degrees, which I would say is the average in the summer, tops out at 78 in August generally. I have super screen surrounding the entire pool and the pool is on the back of my house that faces west, so it never really gets a full day of sun.
So anyways, pool temp was 74, air temp was probably 90+ as it usually is in the summer here, 6 hours of the A/C running almost non-stop, the pool was at a nice 80 degrees. The next day it was still the same temperature but over the next few days it got up to 82 and eventually hit 86, which was too hot for us, so I actually turned it off and the temperature of the pool fell to 82 but has climbed to 84 during the day.
Anyways, amazing results for summertime! My wife and I swim everyday now.
If you have any questions, let me know. I'll try and post some pictures soon.
That sounds great. How big is your pool? Would be interested to know dimensions as well as gallons, thanks!
Yeah it sounds great.
So July Tampa weather of highs in the 90's and lows in the mid 70's and pool is only 74 on average? Ok
Then 2.5ton ac = 30,000btu an hour times 6 hours nets 180,000 btus. That's enough to heat a 4,300 gallon pool 5 degrees.
So July Tampa weather of highs in the 90's and lows in the mid 70's and pool is only 74 on average? Ok
Then 2.5ton ac = 30,000btu an hour times 6 hours nets 180,000 btus. That's enough to heat a 4,300 gallon pool 5 degrees.
Those numbers are a bit suspect. We've got another member in Tampa who is actively working to cool their pool because it is close to 100 degrees. Whichnis also questionable and they probably need a new thermometer. My brother's. pool near Destin has afternoon shade and is in the upper 80s all by itself.
But, with highs in the low 90s and lows in the low 70s pool water will naturally seek the midpoint between high and low temps so it would be expected that the pool water would be in the low 80s without any solar heat gain from the sun. If the sun shines on the pool then it should be mid-80s or warmer.
But, with highs in the low 90s and lows in the low 70s pool water will naturally seek the midpoint between high and low temps so it would be expected that the pool water would be in the low 80s without any solar heat gain from the sun. If the sun shines on the pool then it should be mid-80s or warmer.
Got another question. Along with cooling or evaporation on the surface of the pool, isn't there also the surface area of the pool on the ground or in the ground that needs to be included in the calculations? I am not sure what the thermoconductivity of gunite is, but I guess you could use concrete. So I am thinking there is also a big loss of heat to the surrounding ground around the pool that would pull heat out of the water just as fast as it was being added.
Gunite is concrete. Gunite is just the delivery method for getting the concrete to the pool shell. Yes, the gunite and the ground is a big heat sink. When I start heating the pool in the spring the initial gains for the first few weeks are slow. Once the gunite and ground are heated up it begins to work in your favor by holding heat and helping to maintain the warmer temps.
Doesn't sound like it is right for you for 2 reasons. One, you don't use your AC! Two, you are trying to force a longer season. That's not something passive heating systems like solar and the FPH are great at. I wouldn't even suggest a dedicated heat pump for you, since at those temps in Dec-Jan they don't perform very well. Your best bet would probably be a traditional gas heater. And a thermal cover for sure.