Free heat from the sun

It might look a bit (well, more than a bit) ramshackle, but the little shed we’ve made to house the hot tub pump, filter and heat exchange unit safely against freezing and rain, is robust and cheap.

Nor are we the only family in the East Allen valley to enjoy a hot tub; we followed a new unit down the road in Sparty Lea a few weeks ago, heading for its new home!

Anyway, on with my story. Recycling two uPVC french doors to make a lean-to shed was the first inspiration; the second was to attach the top slanted door to the porch sill by its hinges, so that it can be raised to allow more convenient access. The little house is well insulated on the gable ends too. But still I fretted about depending too much on our central heating oil supply for such a luxury as heating the big tub.

Flexible, but passive solar panels for heating the water looked like a simple and convenient answer, to integrate into the filtration system. They come in 1 square meter packs with a valve for separating them out of the loop (we don’t want to circulate residual heat from the hot tub back out to the atmosphere at night!), which will be especially appropriate when we do need an hour or so of top-up heat late in the cold evenings to forestall freezing. The flexible solar panels lie at about a 30º angle facing south into the sun, and yesterday morning during intermittent cloud cover, the temperature in the 2500 litre tub rose by 0.5ºC in an hour. We rarely, of course, get uninterrupted sunshine, so that’s probably a reasonable rule of thumb for future reference.

But that’s the same sort of temperature boost I achieved after an hour of running the hot tub pump through the central heating heat exchanger. The difference, of course, is that the sun’s energy is free and green. Before someone asks, yes we could take the lid off and let the sun warm the water inside, directly; there are a few reasons why that’s not a great idea. First, the tub would quickly become contaminated with debris from the air, including leaves and bird droppings; secondly, the water would likely release its heat directly to the ambient atmosphere when the temperature drops, whereas the wooden lid should help to keep the heat intact for longer. Thirdly, the black solar panels should acquire more heat than the reflective water surface which would otherwise refract and dissipate the sun’s rays. So I think the solar panel strategy looks like a reasonable approach.

And, for that kind of free heating assistance, we’ll live with the quasi-ramshackle look of the panels. We’d be so delighted if this coming Saturday, when a family visit is scheduled, the sun were to shine all day during our adventure at the Charity Auction, the hot tub were to heat up gently, and by the close of play only a couple more hours of wood fire would be required to provide a super soaking experience at 40ºC under the stars! I reckon my aching muscles could use a soothing soak after all the lifting and shifting!

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