Solar water heating

[meow2222]

What exactly is the risk you refer to in a system designed to be riskless?

NT

[Steve Spence]

key word being "estimated". There really no way of knowing for sure, since it isn't metered, and they didn't do a 100% sampling. Our water usage is less than half that, even when we were on grid.

[David Hansen]

On Wed, 08 Mar 2006 10:24:15 -0400 someone who may be Derek Broughton wrote this:-

Do you have evidence for this claim?

Does your house have windows that are broken regularly by the wind? If so how does the glass in the windows survive but evacuated tubes would not?

If there are no reflectors between the tubes then it presumably mostly lands on the roof below the tubes. If there are reflectors then, unless there are lips on the bottom, it will slide off as easily as it will slide off anything. I imagine it will slide off the tubes before anything else.

Provided that there is not a lip on the bottom of the panel that will restrain the snow. If there is then it will presumably need to be brushed off, like an evacuated tube system, unless one waits for sunshine to melt the snow.

[Tony Wesley]

The risk that the system will not work exactly as designed.

[David Turner, Island Computers]

For what it costs I see no talk of timers/solar/cost comparisons etc

I installed a hot water heater timer in our house 3 months ago

It is on from 7-9:30am then 5:30 to 10pm.

That means it is only actually running (actual power availability that is) about 7.5 hours The insulation is good enough that it is not drawing power than for maybe half of that

At 13C/KW in Savannah GA that ain't much (heater is 4500W 50 Gallon) Ergo = $4.38/day which is at most $131.63 per month

In reality it is running about 1/2 of that, so it is costing about $65/month to heat water !!!!!!!!!!!!!!!!!!!!

FYI That is almost $800 per year (minimum) to have hot water

Now does anyone see the value to having a Solar Hot Water heater?!?!?!?!?!?!

[SJC]

These guys show a draindown system as one of their options. I don't think that they would recommend something unproven.

[Ed Sirett]

I thought the 20 GBP/year was a bit conservative.

A realistic saving of around 60-90 per year depending on usage patterns and cost of alternative methods of heating.

However your maintenance estimates are probably a bit optimistic.

Circulations pumps can and do fail. Some can go the 20 years other don't

I see no reason why this would not be broadly similar to CH pump reliability. So let's say 50% of system will need one new pump within the

20 years. The comparator electronics, I imagine these would be similar to the reliability of say a an electronic time switch?

Anyway: It looks like the answer to my original question is A few hundred quid system should pay for itself. Differing systems and differing usage patterns and requirements make a BIG difference in the decision. Being prepared to wait for the HW is a big help whereas always wanting instant HW works against the solar methods.

[Derek Broughton]

Sure, and you can figure out how much total water the townies use from municipal records, but you still don't know how much the well-users pump, and you don't know how much of any of that is heated, but everything points to that being pretty well normal. I would think my use is lower than most

- if for no better reason than I have to quit showering when the 10gal tank goes cold - but that still means we use well over 20gal of hot water daily, for only two people.

At a guess, we could probably do a 100% sampling of this newsgroup, and get a significantly lower usage than 50gal/day for a family of four. But then, we're the people who care about such things...

[Derek Broughton]

There is no such thing as zero risk. It's OK for you to not worry about freezing. We just had two weeks at -10C and lower. I'm not risking exposing water pipes to that. The idea of a draindown system is to _not_ permit that - but how do you guarantee that it's always sufficiently drained?

I could install a drain-down system, but (a) I'm not confident I won't have a flood, (b) nobody in this area will sell or service them (because _they_ aren't confident, either), and (c) I'm _definitely_ not confident that _I_ could build, or even install one, that would be low-risk. otoh, I can get a glycol-loop system, built locally, installed professionally, with proven reliability - and still save money over heating water with propane.

[Derek Broughton]

Handling them... Maybe they're tougher than they look, but something so like a 4' fluorescent tube doesn't inspire confidence.

My house hasn't had a broken window yet. However, neighbors have had two broken windows, and I've had a light on my car broken. So, yes, it's a risk. An engineer friend tells me that they also frequently suffer from seal failure.

The one I was looking at has very little room between the tubes (less than .5cm). That's small enough to collect.

Since the tubes aren't supposed to get warm, not nearly as fast as with a flat panel collector.

Why would you put a lip there?

[David Hansen]

On Wed, 08 Mar 2006 19:28:00 +0000 someone who may be Ed Sirett wrote this:-

Possibly. However, one would also have to allow for a reduction of maintenance of the gas boiler and associated bits and pieces if it is hardly used for at least the summer. Of course if the circulation pump on this stuck due to under-use then the reduction would be negative:-)

I assume so. It probably depends on the make to some extent.

That would pay for itself in a few years, assuming no price increases. A couple of thousand quid system would appear to pay for itself in the long term, assuming no price increases. However, as I have said, money is not the only reason for doing something.

[Mary Fisher]

How many domestic hot water systems ALWAYS want instant hot water?

And even if they want it, do they NEED it?

It's nice to have but not essential.

Mary

>

[David Hansen]

On Wed, 08 Mar 2006 15:58:30 -0400 someone who may be Derek Broughton wrote this:-

The glass is rather stronger than that found in fluorescent tubes.

That certainly was a problem with some designs.

Why personalise the discussion by asking what I would do? The fact is that there is likely to be a small lip, if only to retain things. I have no idea how much attention manufacturers pay to detailing in terms of shedding snow, but I imagine UK manufacturers pay it no attention.

[daestrom]

I cut my DHW heating by somewhere between 1/3 and 1/2 by installing a waste-water heat-exchanger. Running hot water for a shower and letting all the energy go down the drain (literally), just doesn't make sense. Of course, this system only recovers heat from *running* water, so baths and dish washing doesn't affect it.

I have one of the largest units and it is a two-pass type so is not the most efficient model they have. Mine cost only about $270, did the installation myself.

[daestrom]

His '100' number is 5% annual return on a '2000' investment (or, the interest on a 2000 loan). While one may quibble about the exact interest rate, 5% isn't all that far off from current reality.

As far as how much one saves, that is open to debate. After all, how much a household uses can vary quite a bit with the particular residents. And system performance as well.

daestrom

[Ron Purvis]

My quibble was with the made up number of only saving 20 British pounds a year. I was not referring to the 5% annual return.

[Doctor Drivel]

[meow2222]

system but not another?

NT

[meow2222]

Your hot water spend is mind boggling. Suggest you sort your system out asap.

NT

[Doctor Drivel]

Or keep out the bath.