Sharing a solar geyser between main house and freestanding cottage

[Ockie]

Howzit guys. Just out of interest, would it be possible to instead of installing two expensive solar geysers to just install one that is a bit bigger on the house roof and then run hot water from there to the cottage? Would putting down a new hot water pipe make it prohibitively expensive to do this?

 

[Sinbad]

Howzit guys. Just out of interest, would it be possible to instead of installing two expensive solar geysers to just install one that is a bit bigger on the house roof and then run hot water from there to the cottage? Would putting down a new hot water pipe make it prohibitively expensive to do this?

The bigger problem is going to be the very long time it's gonna take hot water to reach the cottage, and heat losses along the way.

 

[agentrfr]

You can do so easily as long as the pipe is well insulated. It might take a minute or two for the hot water to get that side though - not a problem usually.

It's just a copper pipe which you'll probably run down some PVC pipe shielding with insulation around that. It shouldn't be expensive.

 

[Ockie]

The bigger problem is going to be the very long time it's gonna take hot water to reach the cottage, and heat losses along the way.

You can do so easily as long as the pipe is well insulated. It might take a minute or two for the hot water to get that side though - not a problem usually.

It's just a copper pipe which you'll probably run down some PVC pipe shielding with insulation around that. It shouldn't be expensive.

The cottage is pretty close to the house so that is why I thought about this solution. Only one person in the house and 1 in the cottage, so seems a bit silly to put two solar geysers if you can share one?

 

[BuckRogers]

Pex pipe will be cheaper and better insulated. You'll have to run both a cold and hot water pipe to the cottage for pressure balance.

 

[desiganp]

The cottage is pretty close to the house so that is why I thought about this solution. Only one person in the house and 1 in the cottage, so seems a bit silly to put two solar geysers if you can share one?

A gas geyser might work out better. Solar prices are exorbitant, and if it breaks down before cost of investment is recovered it will be an expensive exercise which will take even longer to recover the COI.

Alternatively you could go 1 x solar in the main house and 1 x gas geyser in the cottage instead of 2 x solar.

 

[The_Unbeliever]

1x solar in main house, and 1x gas in cottage

Otherwise you can look at a low-pressure solar geyser, and downgrade cottage water pressure to suit the cheaper low-pressure solar geyser.

 

[Ockie]

Do insurance cover solar geysers the same as normal geysers if it bursts?

 

[Ockie]

R850 (monthly electricity) – 60% (TWO GEYSERS TAKEN OFFLINE) – R340. Difference is R510.00 savings per month.

R20 000.00 (cost for new solar geyser) / R510.00 = 39.2 MONTHS = 3.25 and then the geyser paid for itself.

This is if the house and the cottage share 1 solar geyser and both old geysers are switched off.

This is just a rough calculation.

Did I work this out right? This is assuming that each geyser is 30% of electric bill so two will be 60%?

 

[ToxicBunny]

Do insurance cover solar geysers the same as normal geysers if it bursts?

Yup.

 

[mmacleod]

It might take a minute or two for the hot water to get that side though - not a problem usually.

You can actually solve this part with a 'hot water loop' http://www.elkeplumbing.com/wp-content/uploads/2012/03/hot-water-recirculation-system.jpg though you may have to use a diagram to explain it to your plumber as most seem to unaware of such things.

 

[Ockie]

You can actually solve this part with a 'hot water loop' http://www.elkeplumbing.com/wp-content/uploads/2012/03/hot-water-recirculation-system.jpg though you may have to use a diagram to explain it to your plumber as most seem to unaware of such things.

Erm. Can you explain it to me also? What does this do?

 

[mmacleod]

Did I work this out right? This is assuming that each geyser is 30% of electric bill so two will be 60%?

Probably not quite accurate unless both are used to full capacity.

To use an example an insulated Kwikot 150L geyser uses roughly:
2.3 kWh/day 'standing loss' (Energy used to maintain heat lost if no hot water is used)
7.8 kWh/day to heat tank from completely empty (if you were to use up all the hot water.

So lets say you have 1 150L geyser and you use the entire tank once a day, thats 10.1 kWh/day.
Now lets say you install a second geyser and split the usage in half between the two geysers.
4.6 kWh/day 'standing lost'
Still 7.8 kWh/day to heat tank as each tank now has less to heat.


So you've gone from 10.1 kWh/day to 12.4 kWh/day, which is nowhere near 30% -> 60%, if of course your usage also doubled when you install the second geyser then that is a different story.


The above assumes of course that the standing loss is identical.
If you have 1 geyser that has to run really long pipes to reach a second building, and/or those pipes are not very well insulated your standing loss could increase, it is theoretically possible in such a situation that 2 geysers could use less electricity than 1 geyser (if usage remains the same) though it would have to be a lot of heat loss for that to happen.

 

[mmacleod]

Erm. Can you explain it to me also? What does this do?

With a heat loop instead of running a single pipe from geyser to taps in which water just sits when the taps are off, you have the pipe return in a loop to the geyser (return pipe must connect lower than the exit pipe)
This creates a thermo-syphon through the pipes (basically the water naturally circulates in the pipe at a slow rate due to the heat differences), meaning that the pipes will always have hot water in them - some use a pump as well for faster circulation.
So when you open your hot tap on you won't have that period of cold water coming out before the hot water comes...

This of course comes at a trade off - you have to pay (roughly) double for piping, there may be a bit more heat loss (though if you situate the pipes close together you can minimise this), but it is convenient and you waste less water.

There are some other systems apparently that use some trickery with a pump and the cold water line instead, which avoid the extra piping, but I don't know much about those.

 

[Ockie]

With a heat loop instead of running a single pipe from geyser to taps in which water just sits when the taps are off, you have the pipe return in a loop to the geyser (return pipe must connect lower than the exit pipe)
This creates a thermosyphon through the pipes (basically the water naturally circulates in the pipe at a slow rate due to the heat differences), meaning that the pipes will always have hot water in them.
So when you open your hot tap on you won't have that period of cold water coming out before the hot water comes...

This of course comes at a trade off - you have to pay (roughly) double for piping, but it is convenient and you waste less water.

mmmm perhaps a gas geyser for the cottage would be better? But that is another R8000.00 or so for the geyser and installation I think. Just thought it would be better to then rather share a slightly larger solar geyser? What would you guys do? Share the solar geyser or have the solar geyser for the house and put in a gas geyser at the cottage?

 

[Ockie]

With a heat loop instead of running a single pipe from geyser to taps in which water just sits when the taps are off, you have the pipe return in a loop to the geyser (return pipe must connect lower than the exit pipe)
This creates a thermosyphon through the pipes (basically the water naturally circulates in the pipe at a slow rate due to the heat differences), meaning that the pipes will always have hot water in them.
So when you open your hot tap on you won't have that period of cold water coming out before the hot water comes...

This of course comes at a trade off - you have to pay (roughly) double for piping, but it is convenient and you waste less water.

mmmm perhaps a gas geyser for the cottage would be better? But that is another R8000.00 or so for the geyser and installation I think. Just thought it would be better to then rather share a slightly larger solar geyser? What would you guys do? Share the solar geyser or have the solar geyser for the house and put in a gas geyser at the cottage?

 

[mmacleod]

Another reason 1 geyser may be better is that multiple geysers tends to push insurance premiums up. How far apart are the two buildings? I'd get a quote for both options and then see

 

[Ockie]

Another reason 1 geyser may be better is that multiple geysers tends to push insurance premiums up. How far apart are the two buildings? I'd get a quote for both options and then see

Very close together. The closest walls are maybe 5 away from each other.

 

[desiganp]

mmmm perhaps a gas geyser for the cottage would be better? But that is another R8000.00 or so for the geyser and installation I think.

A good quality 12L gas geyser which is enough for shower/bath is about R2500 online including delivery. Installation cost will vary depending who is installing and you can save a alot by doing most of the install yourself, if you have some plumbing/gas knowledge.

 

[Sinbad]

mmmm perhaps a gas geyser for the cottage would be better? But that is another R8000.00 or so for the geyser and installation I think. Just thought it would be better to then rather share a slightly larger solar geyser? What would you guys do? Share the solar geyser or have the solar geyser for the house and put in a gas geyser at the cottage?

No ways.
I had a kexin 16lpm geyser put in, for R4718.

The piping was there already, granted, but that's definitely not 3k worth.