How Big of a Heater for Supplemental Heating Solar + Propane

[beartoothweb]

We're in Montana, so the "season" is a bit of a Crud shoot. I'm going to be heating my new AGP (insulated and covered) with solar, for the most part, which works exceptionally well as temps rise and when the sun comes out (often). We're at high altitude (4500') so the solar radiation is high.

I'm thinking about what I should do for times like between now and July, then as September settles in. I'm really thinking just doing a supplemental propane heater is going to help take the edge off, but I'm not sure if I size it as if the solar panels didn't exist, or if I resize it lower because they do?

Can someone help? Thanks!

The pool is 15x30 oval (~12500 gallons; 360sqft surface area), it'll be below grade with side fully insulated, cover, and I'm currently running 8 2x20' (320sqft) sungrabber panels (or will be when it's fully installed.) I'm likely going to build "boxes" for the panels to increase efficiency with heavy mil plastic covering to reduce heat loss from wind, and to increase ambient air temps around the panels.

Thanks!

 

[Davegvg]

Personally Id buy the biggest thing you can plumb in- and run it in-line with the solar.

BTU/hour is king - and the longer the heat cycle the more you lose to cooler ambient temps, wind, and nightly loss.

With relatively little water to heat 200K plus your solar ought to be fine, but 400K would be awesome.

This way you can "bump" the pool with the gas for a single weekend or even an afternoon and not plan on2-3 day pump runs.


I can get well over 700K BTU/hour with my solar feeding into a 400K heater- Im never going back to a single heat source afte having what Ive got now.

Uncle Dave

 

[bk406]

A 200,000 BTU heater will burn around 2 gallons per hour. A 400,000 BTU heater will burn around 4 gallons per hour. It will take half the time to bring up the temperture with a 400,000 BTU heater, so the net effect, basically, is zero on the amount of gas burned. In other words you will not save any money with the smaller heater since you will have to run it twice as long. Supplemetal heater or not, get the biggest one you can afford.

 

[beartoothweb]

Thanks for the info.

So, really, the advantage is control and time over getting a Bigger unit, then, vs. operating cost. I'm still a bit confused, though as you can find the 100k units for sub $700, but the 400k units are $2200.

Let's say my ambient temp is 60 degrees, and I want to raise is by 25 to 85. (this assumes no solar benefit at all).

If i use this: http://www.poolinfo.com/Pool-Heaters.htm, it would indicate I would need somewhere around 105000btus/hr to get the temp up, so the 100k would right at the edge of meeting that need.

Would a 200k heater just heat up in 1/2 the time, and 400k in 1/4? Or, would the 100k one just barely get it there and have to burn a ******** of LPG to stay there?

Thanks.

 

[bk406]

Look at it this way.

You have 12500 gallons of water or 103,750 pounds of water. It takes 1 BTU to raise 1 pound of water 1 degree F.

For a 25 degree rise, as in your example, it will take 2,593,750 BTU of heat in your pool. A 100,000 BTU heater will take ~26 hours to put that much heat in the pool. At 1 gallon of propane per hour, you will burn around 25 gallons or $75 worth of gas.

For a 400,000 BTU heater, it will take ~6.5 hours. At 4 gallons per hour, that 26 gallons or $78 worth of gas (all assuming propane is ~$3 a gallon. Also, these heaters are only about 85% efficient, so YMMV).

Big heater, little heater, they cost the same. The bigger heater will heat the water faster and the initial cost of the heater is more, but the cost to heat the pool to a given temp is about the same.

As far as holding the temp, how fast the pool loses heat varies. Wind speed, humidity, ambient air temp, etc dictate that. A 100,000 BTU heater will hold the temp, but it may run more. A 400,000 BTU heater will hold the temp, but may run less. The net effect, I would guess, is the same in cost.

 

[Davegvg]

Be aware a 400K btu heater may require significant line and Meter replumbing to accomodate the massive flow of fuel.


Uncle Dave

 

[beartoothweb]

Be aware a 400K btu heater may require significant line and Meter replumbing to accomodate the massive flow of fuel.


Uncle Dave

This is perfect info, and a key to the decision. Thanks!

What's the avatar engine, btw? I'm a car guy, mostly Chevelle's, but currently building a Factory Five Roadster with a little 340hp 302ci in it.

 

[beartoothweb]

As just an aside, I was doing some calculations (from google) on using hot water itself (like from the house) to heat the pool water.

To heat 12500 gallons from 75 to 85 degrees, it appears to take 2157 gallons at 130 degrees, or 17% of the total pool volume. That's just crazy.

I found the calcs here: (you have to convert to non-metric).

http://answers.yahoo.com/question/index ... 514AAQov4G

The equation I used was: ((54000*10*5.55)/(10*(54.44-23.89))/4.54609). That's 54000 liters at 1kg per liter, 10 is the factor for water heat transfer, 5.55 is the C rise between 75 and 80 F, and then the 4.54 number is liters to gallons. The 54.44 and 23.89 are C of 75 and 85.

Interesting stuff.

 

[Davegvg]

Be aware a 400K btu heater may require significant line and Meter replumbing to accomodate the massive flow of fuel.


Uncle Dave

This is perfect info, and a key to the decision. Thanks!

What's the avatar engine, btw? I'm a car guy, mostly Chevelle's, but currently building a Factory Five Roadster with a little 340hp 302ci in it.

Its an Ilmor 710

http://www.ilmor.com/marine/gen-III.html

Basically a 700HP dodge viper engine marinized by Ilmor engineering.

Love cars! (all of em - especially old chevies) send me a pict of your project sounds awesome!

Uncle Dave

 

[beartoothweb]

Cool! My brother used to work for Mercury, and was there and worked on the original ZR1 motor project. Cool stuff!

Here's my blog. With all of the yard/pool work, it's a bit on hold right now.

kdcobrabuild.com


KD

 

[Davegvg]

Cool! My brother used to work for Mercury, and was there and worked on the original ZR1 motor project. Cool stuff!

Here's my blog. With all of the yard/pool work, it's a bit on hold right now.

kdcobrabuild.com


KD

Super cool background you have.
Thats a flat out incredible job of documentation, and an absolutely epic car there hoss......
Ill be spending some time going over that- you are a brave and talented guy.

Heres my build on the boat that used the Ilmor 710.
http://www.offshoreonly.com/forums/lave ... -away.html

Heres us hauling some coal just skip to 3:45 and watch till about 4:30 & listen to the V10 sing.
http://www.youtube.com/watch?v=CiCEK570stY


Uncle Dave