my inlaws have asked me to have a look at thier pond heater, semms the thermostat is not working and i can't find a replacement part.
simple answer buy a new one, but this unit is only just out of warranty, i think it is made by drall but i can't find any info on the company, anyone got any suggestions or experience of building pond heating system?
You dont tell us much about it! All I can usefully say is if its not solar, make a solar one instead. Pool heating is one of the few apps where solar energy can pay back _very_ well indeed. Hosepipe panel etc
NT
dunno if solar would be appropriate as the temp needs to be above 10 degrees c all year round, including night time.
if you think a solar system would work please let me know in more detail how to build such a system and keep in mind this is an ornamental garden and not a science museum. they like the discreet system and 'it just works' attitude(the in-laws that is not the fish!)
OK, a little info for a start, see if any of this lines up with what you want.
Pool/pond solar heaters are very efficient because they heat water to a very low temp, in contrast to DHW solar heating. Theyre also cheap to make, at under =A3100 the lot. The usual recommendation is a lot of hosepipe in a big flat coiled pancake shape, preferably with gaps between the turns and polythene on top. Plus a pump. This wont look good in an onrnamental situation though, would need something more prettified. Acid etched glass could be used to put a pretty front on such a heater.
Since you need it in winter, the power output will be a few hundred watts per square metre, rather than a good double that in summer. It can deliver this as long as you have daylight, so by knowing the power and run time of the present heater you can work out what you need to maintain 10C.
Day/night temps: the water acts as storage, its just heated in the day. If you need 10C at night, you might need 10.5 (etc) in day to keep it above 10.
Hosepipe pancakes are max output per metre of hose when the turns are spaced out a bit. But a glass cover will be the highest cost part, so to maximise return per purchase cost, pipe turns close together.
To maximise temp rise, reflective mylar sheet behind the pipes with pipes spaced out with 1 pipe dia space between each turn. Sun that misses the pipes will reflect off the mylar onto the pipe, and you get at least some concentration effect. Concentrated panels using low cost plastic pipes are best covered or hinged and swung out of the full sun in summer.
Panel is arranged so it drains at least semi-empty when the pump stops, since it will see freezing day in day out. It will freeze happily as long as it has air in as well as water.
Pipe: most colours work ok, best to avoid red or orange.
Pump: keeping pump size and rate low minimises electricity use. Use thermostat to turn pump on/off. You also need a thermostat on the panel so the pump can only come on once the panel starts to warm up. Set this to just over your target temp, so maybe 15C. It is common for people to use unnecessarily high power pumps, eg hundreds of watts. If your temp rise thru the panel is under 10C, you can use lower power pumping and save your money. 30w of pump is more the ballpark.
A low cost way to boost panel output is to use something reflective to put more sunlight onto it. Matt white paint looks nicer than mylar coated plastic film. Sun can be reflected direct into the pond as well, as probably the cheapest type of solar pond heating.
Set pond target temp to above your wanted minimum to allow for a snowy night plus a dull dark day etc.
If you wish you could keep the present heater as well as backup in case anything fails, and as 2 systems backing each other up makes a very much more reliable combination than one alone. And its there already.
alt.solar.thermal is all about this sort of thing, and often assist people work out how much panel area they need, and how much pump power.
Thermostat repair: most common fault is simply burnt switch contacts. These can be tidied up with _very_ fine sandpaper, or even go-easy use of a rats tail file. Note they may need temp setting readjustment after handling.
An open pond with snow falling in it is going to take a lot of heating. partial covering would really help.
What the solar panel does is use a little electricity to capture a lot of sunlight & skylight heat. Hosepipe panels have excellant payback figures, these things can pay their low cost back many times over. The systems are very simple, and if you calculate each number before building you can get impressive performance.
NT
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