Energy Matters Forums

[Quokka2]

What's quality? ... For hot water, I'm referring to Siddons, Stiebel Eltron or Sanden units. Don't go near certain other "big name" brands that are notoriously unreliable. That said, I'd also seriously consider solar for your hot water but again it needs to be a good quality system.

I looked at the Siddons web site and they call their heat pump a "Solarstream" and describe it as if it were a solar HWS. If that were the case then my fridge and my air conditioner are also solar; the coal industry which supplies most of the electricity they use must also be a renewable energy industry because it was the sun which made the plants grow all those millions of years ago. Now I can say I spent 40 years working in the renewable energy industry

If they need to resort to such deceptive advertising to sell these things then I for one aren't buying!

[Smurf1976]

Given that two thirds of the heat going into the water is from the ambient air, which is ultimately heated by the sun, they're not really incorrect in their marketing. Assuming that the average person buying a solar HWS does to in order to reduce electricity usage, the Siddons does achieve that objective albeit by a different means.

I have one and it works fine. Leaves any flat plate solar system for dead in the Tassie climate that's for sure. Not sure how it really compares to evacuated tubes, but a 65% saving on hot water electricity costs over the past 4 years is pretty decent.

Back to the marketing, in many ways they're all backwards. It's not how much solar energy that matters but rather, how little fossil fuels are used. Eg in a cooler region an instant gas water heater (no solar) beats an electric boost flat plate system pretty easily so far as fossil fuel consumption is concerned.

Do a bit of research into heat pump HWS and you wont find too many horror stories with any of the brands I've mentioned whereas you'll find plenty with some of the highly promoted brands from well known manufacturers. Don't get reamed and leave the ducks in the pond (big hint as to the duds there.....).

Reason I got the Siddons was simply that it was the cheapest of the reliable means of heating water once everything is included. Solar was going to cost too much to install and LPG is expensive around here. So a heat pump became the first choice, with good old off-peak electric (no solar) running second place ahead of the others from a purely financial perspective.

[Quokka2]

Given that two thirds of the heat going into the water is from the ambient air, which is ultimately heated by the sun, they're not really incorrect in their marketing.

I agree with just about everything you say, but let's not delude ourselves. These things are no more "solar" than your fridge, air conditioner, fan, pump, or anything that uses electricity to move heat around; the only energy that is produced comes from the electricity. I have considered buying one and actually made electrical provision to install one, before deciding to "solarise" my not-so-old element HWS instead. One thing that influenced my decision was the ease with which it replaced an older unit when the tank failed - if that had been a heat pump it would have cost me a real bundle as I don't believe you can just replace the tank, and the difference buys an awful lot of electricity.

Take your point about reaming out the ducks though

[Warpspeed]

Before deciding to "solarise" my not-so-old element HWS instead. One thing that influenced my decision was the ease with which it replaced an older unit when the tank failed - if that had been a heat pump it would have cost me a real bundle as I don't believe you can just replace the tank, and the difference buys an awful lot of electricity.

This raises a few interesting points.
If your current off peak electric HWS is working fine, the lowest cost option would be to keep it.

Solar can be retro fitted to any existing storage HWS, by fitting a small hydronic circulating pump and a differential temperature controller along with some solar panels capable of running at full mains water pressure.
Solar heat is added during the day, and off peak power makes up any shortfall at night.

This works best where the storage tank is fairly large, and hot water usage is not that high.
The tank can sit at ground level and run at full mains pressure.
I did this once in Melbourne, and the payback period through energy savings was about eight years.
Payback period should be even shorter in NSW or Queensland.

For higher hot water usage, a more efficient system would be to fit a second HWS in the cold water feed to the existing main off peak electric HWS. This second HWS is used as a preheater for water going to into existing HWS, the internal heating element in this preheater is normally left switched off.
This can potentially double your hot water storage capacity at minimal cost, and because the preheater always works with lower temperature incoming water, it will be much more efficient at trapping solar heat.

Even in frigid cloudy mid winter, a solar preheater can easily gain 10C to 20C temperature rise, which is a direct energy saving no matter what else you use to heat your water up to final temperature.
In mid summer if it constantly boils, simple covers can be fitted over some of the collectors.

Its stone age technology compared to a high tech heat pump, but it can be very cost effective, and possibly a do it yourself project for the more adventurous.

[Tracker]

..... by fitting a small hydronic circulating pump and a differential temperature controller along.......

and on that comment - anyone got recommendations on the good and bad for pumps and controllers..

been looking at ebay and there are many Chinese pumps claiming to work with hot water etc...

so if one sources a solar collector.. what pump/controller could one get away with at the best price..
..
.

[Warpspeed]

You need three basic items.
A small hot water circulating pump which are in common usage in the plumbing industry typically about 15 to 25 watts depending on pipe size and flow capacity. Your local plumbing supplier should have them in stock.
I have no idea about the Chinese pumps, but the Aussie made pumps are brass. The one I had is still up in the roof along with its controller unused for a long long time. I will get up there and have a look.

The special solar "spear type" of coaxial water fitting to screw into the cold water entry at the base of your HWS. This probably has some proper commercial name, but not sure what that is.
This provides flow and return to solar, as well as the original cold water feed, and it screws into a single hole.
Its basically a tee fitting, with a long pipe extension that extends deep into the tank, so that solar flow and solar return are both located right at the bottom of the tank, but kept sufficiently apart to prevent direct mixing.
If you are clever, you could make your own fitting easily enough.

A differential temperature controller with frost protection.
This has two temperature sensors, one is installed at the base of the tank, the other at the outlet of the solar collectors.
Whenever the temperature at the collector outlet is higher than the tank temperature (by only a very few degrees), the pump starts up. If there is no temperature advantage, the pump remains off.
As clouds drift across the sky, the pump starts and stops. Its an amazing thing to watch, and a very efficient way to trap heat.

If the temperature at the collector outlet falls to just above freezing, the pump starts up, and stops when the collector temperature is warmed sufficiently to stay safely just above freezing.
In very bad frost, the pump may start up intermittently, and prevent any danger of the collectors from freezing.

Usually both the temperature differential, and freeze protection temperatures are knob adjustable from maybe zero to typically five to ten degrees.

[Quokka2]

For higher hot water usage, a more efficient system would be to fit a second HWS in the cold water feed to the existing main off peak electric HWS.

I tried something similar using a large polyethylene tank with immersed cold water coil. It worked fairly well until the tank cracked - polypropylene might be more durable with hot water, but it has a lower softening temperature. I'd planned to replace it with a high pressure tank as you've suggested, but probably won't get around to it now See the personal bit of my web site if you're interested.

[Warpspeed]

The problem with most of these systems seems to be uncontrolled boiling in mid summer.
You will have more hot water than you (or your teenage daughters) could ever possibly use !!
In winter it will save some energy but not a lot. But throughout the whole year the savings can be significant.

All the systems I have seen used mains pressure HWS steel tanks (gas and electric) and all copper pipework.
Plastic works great for low pressure low temperature swimming pool heaters, but for mains pressure domestic hot water, anything made of plastic might be a bit optimistic for very long term reliability.
There could also be chemicals and solvents leaching out of some plastics at high temperatures, I really do not know.
The whole idea of plastic in a potable hot water system has very little appeal to me.

[Quokka2]

We never had any problems with boiling because the excess heat was used for home heating in winter and pool heating in summer - we didn't waste any Use of a copper coil in the preheater enabled the preheater to be low pressure whilst the household water remained high pressure; and also avoided any issues with the plastic solvents getting into the household hot water.

[Kombinations]

Wow. There is a lot of knowledge on this site! Our problem really at the moment is a lack of hot water (80L; I haven't looked what size would be recommended or a family of (nearly) 5 yet) - so if we can get the temperature higher, or more storage that would solve our problem. At the same time, we wanted to investigate the most efficient way of doing this in terms of cost. The idea of adding solar boosting? to our existing hws is interesting. Because the existing system is off peak though, I imagine that it would just add any heat that was lost to the air between say 7am and nighttime (showers, washing up etc.?) - the actual costs of heating the water from cold if the water runs out would be the same since it would run out at night, then be heated by off peak electricity then boosted again throughout the day using solar?

I'll look at the actual costs of electricity per kWh and gas around here, but I think we'll stick with electricity I stead of gas for our needs. Particularly because heating the house is only required for a relatively short time here, so if we can make an electric type hws work for us, we save on an extra service charge. I assumed solar was out of the running due to cost, but if we can save by utilising our existing hws it might be a viable option.

Thanks for the feedback. I now just need to look into how to get our gas meter out of the way - if it could just move 300mm so it was more under the house it would be ideal. I'll get onto a plumber at some stage.

Cheers

Nick.