Mid-Life Missions

Saturday 2 May 2015

Mission 2 - The Pool Heater

Pool Heater

My early temperature test suggested even knitted speedo's maybe a little chilly for the pool.

I considered an electric inline heater (expensive to buy, expensive to run) & extending the central heating system into the garden..... interesting but if something went wrong it may get very expensive. As the project had a distinctive redneck feel, I decided to make a multi-fuel burning pool heater.

I 'recycled' an old oil drum, some finned copper tube into a coil, and an old flue. Cut a flue hole with a holesaw and the fill hole with a slitting disc. Cut a piece of mesh grill to fit the open top (now the bottom). I slotted the copper coils in and fastened with wire ties. Fitted the flue. Stood the stove on a few bricks. Connected coils with automotive radiator hose.

I got lucky on the finned copper tube - as this is pretty expensive compared to normal plain tube which would work but would need more coils to get an equivalent surface area.

Bought a cheap small 12V submersible pump (caravan type) to move water through the heater. I did not have the space (vertical distance) to make a thermosiphon which I would have preferred.

I decided to keep the stove heater a simple heating circuit rather than adding a heat exchanger circuit which would be more efficient. A simple heat circuit like I was planning would always suffer from condensing on the coils which would reduce the efficiency - unless I dribbled water through and basically made a steam circuit which would be dangerous. Hence just accept the heater will be inefficient and through on another log/shovel of coal/junk mail.

To give you an idea of the efficiency loss the initial temperature rise inlet/outlet & flow rate equated to a heater circa 12kW output to the water. After a 15-20 minutes this had dropped substantially to circa 8kW and water was dripping out the bottom of the stove. This was the downside of getting 'lucky' with the finned copper. Normal copper tube would not have such a large area to soot up and hold condensed water. But... inefficient as it was I cost me the price of 10m of auto radiator hose, the 12V pump and few jubilee clips.

Mission 1 - The Fill.. the Drain... the Fill

The Fill, the Drain, the Fill

Luckily we live in Wales so if its not currently raining then it will be in the next 10 minutes (and we are not on a water meter). So rain on. Hose on.

I filled about 6 inches a time then left the pool to settle and inspected for any movement of the bales, stakes, etc.

I started to get nervous about 2/3rds full when the 2 long sides started to bow slightly with the water pressure. About 7/8 full, I chickened out. The pool was holding fine but the cost of replacing the neighbours prized bedding plants, my new fence panels and sweeping the neighbours dog in a tsunami flood led me to drain down and re-assess the red-neck simplicity of the wooden stake reinforcements.

I originally intended to drive metal stakes down through the bales, this then became wooden stakes (cost), these then went in outside the bales (as I wasn't sure I could drive them through).... too many compromises... So this time round I went a little more professional at it. 3 ground stakes on the 'downhill' side, 2 on the uphill side and 1 each end to prevent the side bowing. I reused the old metpost stakes from an old log store I tore down a few years earlier - so a few lengths of pressure treated timber and a little extra graft finished the job.

Mission 1 - Build Update

Build Update

I constructed the pool throughout May 2014. Got the PVC liner in early June.

First off I covered walls and base with builders damp proof membrane (cheap).

Next I laid the PVC liner over. This was just a pure flat sheet (cheaper than shaped). The idea was to lay it up and tuck fold the corners - origami with rubber, and have enough overlap to drop over the bale sides.

This worked pretty well. My only concern was how the PVC would react to being folded hard with the water pressure. Raining again when I did this so no pics.

Got some old wooden pallets from work and trimmed with circular saw to pop around the top to finish off. Gave them a quick sand down. Fastened with any old spare brackets, hinges I could find. Screwed through any posts to make secure.

.... and it was ready to fill.

Mission 1 - Liner

Liner Choices

Plastic - poly sheet

Difficulty here is getting the width in a single sheet.
Original intention was to use builders DPM which is the thick poly sheet that they use under a building. Its cheap, tough and would be fine for a temporary narrow shallow pool as it comes as standard in 4m wide. To get the required width 6.5/7m my only option would appear to be poly tunnel sheeting which is thinner than DPM hence more likely to leak. Cost circa £80.

Polythene tarp or groundsheet
These are available off the shelf in many sizes. Cheaper ones are pretty strong (laminate) but they puncture easily. By the time you have found a decent thickness you are looking at a vinyl coated tarp which is more costly than at vinyl rubber pond liner.

PVC Pond Liner
These are the cheaper pond liners available off the shelf or made to order quickly. Any seems are heat/factory made hence strong and come with a guarantee. The standard thickness is about 0.5mm. Cost circa £100.

I decided to go with a PVC Pond Liner - mainly to stop any leaking issues (punctures, rips) that would damage the rest of the pool (bales, etc).

Tuesday 3 June 2014

Mission 1 - Pool Overflow & Filter System

Syphon Overflow

One of problems with a 'drop the liner' in type pool is getting water in and out of the pool for filtration and heating. My plan for the filter side is to use a syphon overflow into a catch tank then pump from there into a filter. I am planning to reuse the old tomato greenhouse water butt for this purpose.

The overflow will act as a kind of pool skimmer and hopefully take all the larger floating debris out. If it bungs up too quickly I will look to have a bigger filter after the overflow.

Decided to use 40mm waste pipe & compression fittings for system - cheap and easy. Flow rate should work OK for the filter pump I have bought (submerged type that will sit in the overflow sump tank).

Syphon Overflow Schematic

Filter Bed

I could use an off-the-shelf filter but that seems rather lame and easy. So my idea is to use a blue plastic barrel that happened to blow past my works front door one windy day and get stuck in the hedge. No one claimed it for a day so it got redirected into my "purposeless stuff behind the shed waiting for a purpose" heap.

So thinking along the lines of rocks, gravel, sand then gravity overflow back into pool. Need a method of backwashing the filter to clear out the clag. Could I just gravity backwash with tap or rainwater?

Think I will be experimenting for a while as I have no real pond/pool filter experience. So I am expecting a couple of iterations.

Update: June/July 2014

I had several attempts to get a homemade filter bed working. I could get the siphon working fine but the filter bed proved a bridge too far for the time being. The final straw was me pumping a whole load of fine red sand into the pool. Thankfully I drained the pool down soon after so could clear up the mess.

I have ended up using an off-the-shelf pool filter (ebay) with a submersible pump slung over the side. I run this over night and pull it out before using the pool. Not ideal as its a 230V mains pump - but the kids have been well warned to ensure its off and out before jumping in.

Whenever the pump and/or filter packs in I will look at a different solution.

Monday 2 June 2014

Mission 1 - Base & Side Walls Complete

It Stopped Raining!
31st May

So I cracked on. Threw the last bales on. Laid 6mm ply on the base and the 3 remaining walls (should have not used the silvered polystyrene for the wall but alas too late).