I have a family of five. Even with a low-flow shower head, that works out to about 34000 gallons of water a year. Of course it's mixed hot and cold to create just a nice 'warm' shower of about 100F. The average year-round water supply temp for me is 55F. So that works out to about 127 Therms of NG a year. When I bought the thing, NG was $0.80/therm. The payback with that 5% interest on $270 worked out to just about three years. With NG prices running $1.30/therm, it's under 2 years. But mine has already paid for itself.
Unless there is a permanent vent at the top, it won't 'drainBACK'. Of course if there *is* a permanent vent at the top, you may need a way to catch the water that comes out the vent when the pump is running (unless you like ice on your roof). And it would be preferable that you don't have to go up on the roof to clear out the vent and catchment in the dead of winter with a foot of snow on the roof.
If single valve failure is a great concern, then two valves is a simple way of providing redundancy. Of course, depending how the system is configured, two check valves may provide quite high reliability. But then you probably will need more pumping power with vents, so it may not be worth it all.
Nice one daestrom, you obviously did your homework on payback. This company have been threatening to setup in the UK (or have an agent) for a time. Googling brings up some very encouraging feedback, and seems a better investment than solar. The US government sites speak highly of it.
Unfortunately most homes here don't have basements, as they do in the USA, so difficult to locate in a house. I see they have just brought out a batch processing unit that can be located anywhere, so clawing back bathwater is possible not just shower water. They use a controller and pump, so more complicated. As my 4 year girl likes splashing about in a bath, the payback might be a bit longer for me using the shower version.
But looks like they can be DIYed. One copper inside another, differential controller and a pump. They work by the water spiralling around the pipes and sticking to the sides as gravity pulls the water down. If a pump forced water through too fast maybe it would not do this and heat wasted. Just a thought. The pump's speed would have to be calculated.
Currently most people just would not believe they actually worked.
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And without the timer, it would have cost about the same. The heater doesn't draw 4500W when the water is already hot and no-one uses any.
Timers on HW heaters only reduce stand-by losses. Those times the heater would kick on simply because the tank cooled through ambient losses (unless you take cold showers because of the timer being set wrong ;-).
Yes this was my assumption, the water header being sufficient cross section, and within the insulated area of the house, that once the pump stopped it just filled up a bit. The only drawback I could see was that the pump would always work against the head from the header tank up to the panels. In a sealed system the pump only circulates against the friction in the system.
Most of UK is a temperate marine climate with few excursions below freezing in recent years.
Au contraire. It will, with a collector above an unpressurized tank with the ends of the supply and return pipes underwater and a small hole above the water line. This would need less pumping energy than a system with the return pipe above the water line. Neither needs a vent at the top, if plumbed with all pipes downhill.
You have to maintain the water level in the tank, otherwise no drain down. The air hole in the pipe needs to be exposed when the pump is operating. If the water level is too high then no drain down. Some sort of level maintaining mechanism needs to be installed, such as a ballcock valve and float. Then if this fails an overflow is needed. This is self regulating, but you can do it by making a level line and using a hose pipe I suppose.
At no time have I stated that there is no need to worry about freezing. Its quite obvious that a solarthermal system in Britain will need to be safe in freezing conditions.
Lots of people round the country expose hosepipes to subzero temps day in day out. Does this make them burst? No, because theyre not full of water.
by designing the system so it drains itself when the pump stops. As long as its partly drained, all is well. The expansion of water on freezing can be accomodated by a small percentage of air in the pipe. With draindowns they are almost completely empty every time the pump stops. Its how they work.
Its not because theyre not confident, but thats another story.
The piping and exchanger are at risk of leaks in a glycol loop. If a leak hapens, the glycol will be replaced by plain water, and the system will soldier on as before until it freezes and bursts. I suggest that this is as much or a greater risk than aproperly designed drainback system bursting through freezing when full of static water.
Direct systems are sometimes criticised on the grounds that dirtying of collector piping by fresh water results in reduction of efficiency over the years. With a glycol system this coating is merely moved from collector piping to heat exchanger, and the same effect occurs.
When are folks going to wake up and notice the =A320 was a solar system saving figure, not an annual HW spend figure. It was from a thread a couple of months ago talking about a study of commercial systems. I did go to get a link but wasnt willing to wade through another >100 posts to find it.
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