A bit of engineering
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Post Fiend
Joined: Jun 2003
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A bit of engineering
So I’m installing a fountain in a small pond I built. I’d like to keep it operating all year long so I presume I’ll need to add some form of artificial heat to keep it from freezing up in the winter.
I’d like to be able to determine the energy loss from the pond/fountain so I can determine what size electric heater I will need. I’m ashamed to admit that I studied engineering in college but have no idea how I can go about the calculations.
Can any of you help?
I’d like to be able to determine the energy loss from the pond/fountain so I can determine what size electric heater I will need. I’m ashamed to admit that I studied engineering in college but have no idea how I can go about the calculations.
Can any of you help?
Post Fiend
Joined: Apr 2004
Posts: 6,473
Likes: 4
From: Lafayette, IN
I couldn't help you with specifics, but if you wanted it to NEVER freeze, you'd have to size the heater so that it doesn't freeze on the coldest day. Around here, that's roughly -20F. As for a straight-up calculation, I don't think you're going to find one. It would be extremely complex because of the number of factors: ground temp, water temp, ambient (air temp) and humidity. Plus, the greater the difference in temp between the air and water, the quicker the water would change.
But, there could be an HVAC dude out there who would know what you need, or some other computer guru who could model it for you.
Jason
But, there could be an HVAC dude out there who would know what you need, or some other computer guru who could model it for you.
Jason
Posting Guru
Joined: Apr 2002
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From: Back where I started...
If you keep it operating constantly, won't that keep it from freezing? When people leave their boat docks in all year, they put "bubblers" (sp?) in the water by them, to keep the water moving conatantly, so it never (theoretically) freezes. Just a thought.
Posting Guru
Joined: Dec 2003
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From: Maine
If it's a fountain, keeping it running will go a long way towards keeping it open, at least. In central MA, my friend found that just running the fountain kept some water open most of the time, and on the coldest days he would just break up the thin layer of ice that would form overnight. If it's a waterfall, though, you are more likely to wind up with a rather attractive ice sculpture than open water.
As far as a calculation, I rather doubt there is one (too many variables), but a landscape architect might have a table that relates size and geographic area to the recommended heater output.
I assume you want to keep the water open for fish. Depending on how many there are, it might be easier/cheaper to bring them inside for the winter rather than trying to keep the outside pond open.
As far as a calculation, I rather doubt there is one (too many variables), but a landscape architect might have a table that relates size and geographic area to the recommended heater output.
I assume you want to keep the water open for fish. Depending on how many there are, it might be easier/cheaper to bring them inside for the winter rather than trying to keep the outside pond open.
Post Fiend
Joined: Feb 2003
Posts: 6,940
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From: Eastern WA
How small is this pond? Is using some antifreeze in the water rather than a heater even a viable option? BTW, I'm a Mech Engr too, but sometimes I like to avoid reinventing the wheel on things like what you're talking about. It's simply not an effective use of time. Instead, call a swimming pool company or specifically one that sells heaters for pools and/or hot tubs and see if they can do a quick and dirty calc based on years and years of what really matters, proven experience. You probably know this, but if you can cover it at times when you're not running the fountain you'll probably save yourself a small fortune on energy. That alone might make antifreeze look pretty good, depending on the pond size. I'll assume the pond has no fish in it.
Last edited by CowboyBilly9Mile; Oct 31, 2005 at 08:48 PM.
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Hotshot
Joined: Oct 2002
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From: The Big, Oregon
How cold is typical? If it tends to stay on the plus side, you could probably get away with a light bulb in an enclosure heating the water as it went by, but then you'd have a rather elegant steaming waterfall as the slightly warmer water hits the cold, dry air and evaporates. The best solution- drop a sump pump in the basin, get most of the water out, and wait till next spring.
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Joined: May 2004
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From: Melbourne, Aus
Tell me how much water you are putting in it, and the surface area of the pond, the coldest temp you could see it reaching and I should be able to tell you roughly the power output required.
Post Fiend
Joined: Apr 2004
Posts: 6,473
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From: Lafayette, IN
BigF350, the coldest temp is around -20F like I said above--hkiefus lives about 15 min from me. But that is a fairly rare temp. Most winters we don't drop below about -5 or so, and that's usually just a few nights in Jan if we do get that low. I don't know anything about the size of his pond, though.
Jason
Jason
Postmaster
Joined: Aug 2004
Posts: 4,004
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From: North of Boston MA
Coldest temperature isn't the most important factor in the equation. How long the temperature stays that cold would govern. You can put water into -20°F temps for a short time and barely change it's temp. Heck, you can fry ice cream in oil and still have a frozen chunk of ice cream. Time....
Also, it takes a lot of energy to change the temp of a body of water. It takes an even greater amount of energy to change the phase state of water such as from liquid to solid or liquid to gas. The temp of water will drop relatively quickly to 32° but will stay at 32° for quite some time as a liquid before it freezes. Same thing happens when you boil water - gets to 212° quickly, stays there a while, then boils.
So, what I am getting at is that it won't take too much of a heater to keep the water from freezing - as long as you don't have to thaw it if it does freeze. Do a search for heat loss equations of water, plug in the variables (quantity, delta temp, and time) and you should have a pretty good idea what kind of heat loss you will have. You will have to play around with some unit conversions (calories to BTU's or whatever).
Also, it takes a lot of energy to change the temp of a body of water. It takes an even greater amount of energy to change the phase state of water such as from liquid to solid or liquid to gas. The temp of water will drop relatively quickly to 32° but will stay at 32° for quite some time as a liquid before it freezes. Same thing happens when you boil water - gets to 212° quickly, stays there a while, then boils.
So, what I am getting at is that it won't take too much of a heater to keep the water from freezing - as long as you don't have to thaw it if it does freeze. Do a search for heat loss equations of water, plug in the variables (quantity, delta temp, and time) and you should have a pretty good idea what kind of heat loss you will have. You will have to play around with some unit conversions (calories to BTU's or whatever).
Posting Guru
Joined: Jun 2005
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From: Location, Location.
One thing you can do is pour in a bunch of salt.
http://antoine.frostburg.edu/chem/se...elts-ice.shtml
The lowest temperature possible for liquid salt solution is -21.1°C.
http://antoine.frostburg.edu/chem/se...elts-ice.shtml
The lowest temperature possible for liquid salt solution is -21.1°C.
"Mifflin Clay"
Joined: Jul 2005
Posts: 3,177
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From: Mifflin, PA
I think I would opt for a heater that would vary the btu input in respect to inlet temp, and then adjust it for a given output temp. Example - set it for a constant 36 deg output, and adjust up or down until ice free. This would compensate for heat loss across the standing body of water. If inlet temp is above 36, then no heating takes place. As the inlet temp drops, btu input rises, compensating for cooling effect of the pond. Might give some thought to floating styrofoam ***** on the surface to retard heat loss. JMHO