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23rd Feb 2020 Login  
Low energy/High efficiency toilet flushing
by Bryan Rendall at 2009-09-26 16:00:36 (Forum::Public::Household)
Flushed with success!
OK, so you've read the title and wondered how on earth you can have anything other than low energy toilet flushing, when all it takes is a pull of a handle or a push of a button and gravity takes over?

As you maybe read in another thread, I am in the process of modernising my house - Its become known as the "never ending story" due to the time I am taking (and how much is still to do), but at the moment, I am on the bathroom....

I have always thought that a lot of energy must be wasted on a conventional cistern arrangement, whereby cold water (~5 degrees in winter?) is brought into the cistern in the bathroom, only to draw heat out of the room (causing condensation on a ceramic or porcelain cistern!), only to then be flushed down the pan after it has warmed up! My old cistern held an antique 9 litres and by reckoning, if it were flushed 5 times a day, the incoming water was 5 degree, and it attained room temperature of 20 degrees before being flushed, then about 0.75 kWh a day was going down the drain! Over a year, almost 300 kWh - Not a lot, but always something I thought could be improved upon!

OK, reducing the flush volume to 6 litres or even a dual flush low volume of 6/4 litres would greatly reduce this "lost" energy to less than 200 kWh a year, but I had a couple of other considerations to take into account before deciding how I was going to flush the loo in future....

The first was a pet hate of toilets that are "ineffective" at flushing, if you pardon the expression! - You know, the ones, (usually in someone else's house!) that seem to need about 4 flushes before the pan is clear!

The second was less space in the new bathroom than I would really have liked - This was partly due to 4" of Kingspan then half an inch of foil backed plasterboard being applied to the outside walls, but also due to the addition of a shower that took up more floor space.

The answer? Moving the existing cistern into the loft, lagging it to prevent freezing, retrofitting it with a remote, electric drop valve, and piping the flush water down behind the plasterboard and right into the pan.

The benefits?

1. The toilet pan now sits right back against the wall, with even less space being occupied had it been a close coupled toilet / cistern combination. Unlike a concealed cistern, the toilet itself can now be very close to the actual wall.

2. The toilet flushes with cold water from the loft and doesn't draw any heat from the bathroom.

3. By, does it flush! So effective is it, that it only needs 4 litres or less for an effective flush, every time. The timer on the control box can be set in 1 second increments, with 1 second allegedly being 1 litre, and 4 seconds is sufficient to clear the pan, and make sure the drain doesn't block. It will actually clear the pan most of the time with a 3 second flush, but on the odd occasion, it needs a second flush, so its been set at 4 seconds.

4. Unlike a concealed cistern, which will be better, although not perfect, at not drawing heat from the room than a convention cistern, maintenance access is up in the loft, so no panels to remove. So if my ballcock starts leaking (fnarr fnarr), I only need to nip up into the loft, undo the lagging jacket, whip off the lid and sort it.

Although the flush valve manufacturer says 1 litre per second, trials have shown that it is possible to get 3 and a bit "4 second flushes" from the old 9 litre cistern with the inlet water turned off, so actual volume at 4 seconds must be a shade under 3 litres

Makes for a tidy installation, with only a proximity sensor on the wall near the toilet that you wave your hand in front of to flush (added bonus of increased hygiene in these swine flu, e coli, paranoia ridden times! ;-)

Overflow still comes down the flush pipe and into the pan for visibility, and in actual fact is probably easier to detect than a down the pan overflow from a close coupled cistern - Reason being that the tiny bit of water I have tried overflowing to test it makes an audible trickling noise, even when the water running down the back of the pan is barely visble. So I think I should be able to spot (hear!) even a very minor leak from the ballcock or the drop valve, better than with a close coupled combination.

Flush system came from Dart Valley Systems


and OK, whilst it costs a bit (it will take a wee while for the 300 kWh saved a year to pay for it!), when all the advantages are added together, as well as the very streamlined appearance, I think its been worth it! Whether I will still be thinking that if it packs in and I cant flush the loo without climbing in the loft and manually lifting the drop valve will remain to be seen!

Downsides? Well, its a wee bit noiser, but only in the bathroom itself. The flush pipe is buried in insulation, behind plasterboard, so that bit is no noiser - But when the water arrives in the pan, it does make a bit more noise than normal, and there is a second or so of noise up the pipe before the water actually arrives which is a bit unusual!

The control system does consume a bit - 18 watts maximum during flushing to be precise. Must measure the standby consumption to see what that is, but expect it to be quite a bit less. But by having the control box (where all the losses seem to occur) within the houses insulation envelope, that 50 kWh or whatever a year contributes to the heating, which here in Orkney is an almost year round requirement!

In the meantime, I am well chuffed with now using less than 3 litres of icy cold water to flush the bog, compared to the 9 litres of nice warm stuff it used to take!


Bryan Rendall

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Low energy/High efficiency toi... Bryan Rendall - 26/09
    Re: Low energy/High efficiency... Stuart - 28/09
       Re: Low energy/High efficiency... Bryan Rendall - 28/09
          Re: Low energy/High efficiency... muymalestado - 29/09
             Re: Low energy/High efficiency... Bryan Rendall - 29/09
                Re: Low energy/High efficiency... muymalestado - 29/09
                   Re: Low energy/High efficiency... Bryan Rendall - 29/09
                      Re: Low energy/High efficiency... Bryan Rendall - 4/03
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