DIY Solar Heated Hot Tub in Crossgar

[cye]

Here is Colin's excellent solar heated hot tub project.

He uses a 2 m square factory-made flat panel, a closed solar loop pressurised by a small expansion vessel, a 12v 6w pump to circulate the water around the solar loop, and a SS/inox heat exchanger inside the hot tub.

The heat exchanger is SS to avoid corrosion problems associated with the chlorinated tub water.

The panel will be drained down in winter so no need to use antifreeze, so the loop is charged simply from a mains pressure hose via an isolation valve.


Absolutely brilliant Colin, well done. please tell us more!

(Dave pictured with Colin talking us through the relevant components)


(Plumbing outside the tub)

(Plumbing inside the tub. The stainless heat exchanger is from a beer chiller I believe! )

from what i gather, in very good weather, this works almost too well!

[colin]

Hi all,
Just to confirm the background as to why I attempted this, when i first purchased the hot tub quite a few years ago electricity was relatively cheap. This model had the heavy insulation and used a 1.5KW water heater which is half the less expensive units use which obviously cost a lot more to run. However even with that it was costly and even with increasing the insulation around the circulation pipes and closing the unit down at the end of September, it still irked me. I relected on my own home water heating with the evacuated tube system and how it could raise the immersion tank to 80 oC and wondered if I could install a similar system on the hot tub. Of course I was dealing with a much greater quantity of water but at a lower temp. (34 oC to a max of 38 oC) and the water was being permanently stored and not used. A search of the internet was not promising as there was little evidence of others having attempted it and if it wasn't happening in USA and Australia where these hot tubs are nearly mandatory then what chance would I have in "Norn Iron". I had most of the bits that would put it together except for a panel and with help and encouragement fron Cye I decided to take a chance and if all failed then the panel could go to someone else for more legitimate use. I mucked up the control panel that Cye built and replaced it with a standard thermostat off a boiler which had normally open and closed contacts. I sourced a stainless steel heat exchanger(the chlorine added to the water for purification purposes would eat through copper one in no time) from a beer chilling unit and mounted it in the filter compartment on the tub, keeping it out of harm's way and as a small circulation pump drew from this compartment it was the ideal place. I didn't install a bypass for if the water became too hot, based on the thought that that would be a lovely posistion to be in that my system was overheating the tub. As it turns out that is exactly what has happened on a few occassions so far and I have had to get out and cool off before Hanibal Lecter comes round and starts slicing up carrots, onions and fava beans to go along with me. I will install a differential controller for the start of next year and see what it will do from cold starting in March. I used the tub's own heater to bring it up to temp this year and then turned its own thermostat down to 33 oC so that it will only come on if falling below that. It doesn't keep it up to temp. every day but it proves that it will work and every time the solar panel kicks in that is saving on electricity and restoring my "Green conscience" again. Thanks for your onterest, Colin Lloyd

[dave]

I was well impressed with that and also the contents of your garage,a morning well spent and as a result i,m well into getting my panel up and running. All being well i hope to be mostly done this time next week.