Wednesday, August 4, 2010

Everything you ever wanted to know about hot water and more

This is the story of the Jones family and our choices of hot water.  We've had a lot of people ask us about it, which means some people are thinking about keeping up with these Jonses.  The experiment is working!

In this article we'll take you through how we made our decisions, why these may or may not be the right decisions for you and what our life's like with a solar evacuated tube system on our roof.

Energy options, constraints & greenhouse gases

The Jones family lives in an area where there's no natural gas connected, so for energy here we've got several options:
  1. Use coal fired power which is relatively cheap but is a huge contributor to global warming
  2. Pay a bit extra to buy Greenpower from the grid, but also knowing that a lot of energy gets lost between where it is generated and our front gate
  3. Have natural gas delivered which is less CO2 intensive than coal, but has to be trucked to our gate in diesel trucks
  4. Generate as much as we can on site.
Naturally we liked option 4, but needed also to be realistic with living within our means.

When we first arrived at Jones Manor, there were two off-peak electric storage systems, totalling just under 200 litres.  This would have made perfect sense at the time. Off-peak is cheaper and can be delivered within existing capacity of the grid, and at the time, global warming wasn't well understood and energy saving options weren't as viable as they are today.  Great case for a retrofit.

So you can imagine our delight when our building report told us our old electric systems were nearing the end of their useful lives, were at risk of failing and would need to be replaced.  Solar water rebates were also available which was going to help a lot (these are still available, but not as generous as they were).  Considering that hot water is the largest single source of energy use and greenhouse gas emissions for most homes (around 20-25 per cent of household emissions), this seemed to be a great place to start and solar was the obvious choice.

Choosing a hot water system

We did our research - the usual places: ask your friends, ask Google, ask your Dad, talk to some providers, try and cut through their spin and bias and then try and find some authoritative sources and buyers guides.  In our case the most useful sources were the Your Home Technical Manual, the Alternative Technology Association and Mr Jones' Dad.  (Yes Jones Sr, we did ask you first and all our research proved you right, but don't get a big head about it).

We did some comparisons between solar flat panels (the types that have been an Australian icon for many years) and the new fangled evacuated tubes which hit the market in the last few years.  What we consistently heard from a number of sources was the solar evaluated tubes were nearly twice the price of flat panels, but were worth the extra money because:

  1. They are nearly twice as efficient, which means you don't have to run your coal powered electric booster as much on cloudy days
  2. The tubes handle hail better and can be replaced one tube at a time if they get damaged
  3. A stainless steel tank with the system should last for a good 25 years, which could be twice as long as normal.

Knowing that the flat panel system on Mr Jones dad's house was a disappointment because it's booster seems to be running most of the time, and also wanting something to last until the rest of Mr Jones beard turns grey, we decided to give this new fangled contraption a go.

Our phone calls and background checks seemed to indicate Apricus was the brand to go with, so we gave them a call and they introduced us to our new mate Stephen from Viabuild who was the local agent and experienced guru on the product.  Now you've got to be careful with a bloke like Stephen, because you'll quickly realise that perhaps you don't know everything about sustainability, and next thing you know Mr Jones will be doing a Permaculture Design Certificate and wanting to know how to build an earthship and live in the desert, but that's another story.

Fit for purpose
Anyway, Stephen took us through it all and looked at our limiting factors.  There were four in particular:

  1. A ridge line and huge Lilly Pilly tree to the North-East which gives us about 1 less hour of direct sun in the mornings
  2. A ridge line and large trees to the North-West which give us about 2 less hours of direct sun in the afternoon
  3. Heritage limitations which mean the tubes must be flat, and slightly sub-optimally placed
  4. Practicalities which mean the tank needed to be on the ground instead of in the roof.
Our new fangled solar tubes. mid-afternoon, winter.
As a result of this we decided to go with a 30 tube array and a 250L stainless steel tank, which is enough for a reasonably sized family with minimal boosting, even in winter. And for a couple it should require nearly no boosting at all, even on cloudy days in winter.  

The reality - what's it actually like?

We've had our system nearly 12 months now and we love it.

Our configuration means we've got a pump and a controller, which is really clever.  The controller measures the temperature in the tank, and also in the tubes on the roof.  When the tubes are 8 degrees hotter than our tank, the pump turns on and sends water from the bottom of the tank (coldest part) to the tubes on the roof and brings back hot water.  If there is only a 2 degree difference, it turns itself off, and waits for the tubes to get hot again.

There is a big display on the controller which shows these temperatures, which means most males and anyone techy / geeky will be out looking at it every few minutes for a month or so and probably keep doing this for the first year or two.  It's a bit like watching the display on a Prius and getting excited about braking... actually, now that I mention it...  {Mr Jones wanders outside to take photos as an excuse to look at the display and see what the system is doing} 

Controller 12 months on with a few cobwebs
Sorry about that, back now, but here's a two photos.  It's 2pm which means we've got another hour or two of direct sunlight to go.  As you an see, the temperature on the roof is 57 degrees, and the ambient temperature on the back verandah (below) is 15 degrees.  It's a sunny winter's day here, and the bottom of the tank was at around 15 degrees this morning because we deliberately ran the system down.  The bottom of our tank is 54 degrees, which means the whole thing is toasty warm and an ideal temperature, all free from the sun.  

Ambient temperature in the shade
So the important thing is whether we actually saved all that electricity or not.  The answer to this is yes and no.

As we indicated before, our placement is suboptimal.  The unit is laid fairly flat which means we're getting around 8-10% less input than we'd normally get.  Also because we're on the low side of a ridge, we're getting around 5-6 hours of direct sun instead of 9-10, so deduct another 40% for that.  And lastly this is a very cloudy place, so it's overcast regularly which brings most things to a slow churn, so it seems the gods are against us our little experiment and we should be doomed to failure.

But, we didn't fail, it's been a great success.  Take today for example, it's a winter's day, and our hot water for the day will be free apart from running the pump (which is negligible energy and cost). Free. No booster like Mr Jones' dad.  Free.  Woohoo.

In spring through summer and autumn, we turn the booster off entirely when there's just Mr & Ms Jones at home and only turn it back on on really cold cloudy days or when we've got guests.  The system can keep up with sort of behaviour except when we get a few cloudy days in a row.

So if every day was like today, the system would pay for itself in 5-10 years, and still keep giving for another 15 or so, so that's not bad for a system which is severely handicapped by where it's located.  It's also worth noting that electricity prices will double every 5-10 years and continue to heat the planet, so it starts becoming an obvious thing to do.

Also it's good to know that because the tank is stratified and shows the coldest part, which means even when it's really cold in the tank (say 15 degrees), you've probably still got enough for two hot showers from the top half.  And on a warm day, we've clocked 146 degrees on the roof (the pump shuts off to protect itself above 83 degrees).

So these are the tangible bits, and the stuff you need to know so that you're not kidding yourself.  But for us there was something much more important.  

The moment we installed the tank, was the moment we became the Jonses.  

We live on a street with a lot of foot traffic on it, and at least a dozen people have stopped to ask us about our disco tubes on our roof.  We also put a few pictures on Facebook and people asked us questions. We were able to tell them all about it and now some are looking into it closely, and are doing it too, or had already done it.  It was at this point we realised how much impact you can have by being the new Jonses or following some other Jonses.  One day we might even be able to spell Jonses.

Lessons and what we'd do differently

If we had our time again we'd probably consider a thermal siphon, which is basically a fancy name for having a tank on/in your roof that self-circulates without needing a pump.  Simply, hot water rises and if your tank is above your panels you don't need a pump.  If your tank is below your panels, you do need a pump, which means moving parts and a small amount of energy to run the system.

Why would we do this?  Well our pump died after 11 months, just gave up the ghost, and we wouldn't have noticed if our power bill didn't look unusually high, so it might have been dead for a while.  Having said that, we still had hot water because the off-peak booster kicked in, but we generated a few black balloons without realising it.  The Apricus team were great, replaced and installed a new pump in less than a week at no charge and it seems we're one of their only pumps to ever have failed, so hopefully this is an isolated problem.  This is all pretty impressive for new fangled technology.  

Now if we had a tank on/in the roof, there would have been no pump, and nothing to die on us, which is nice to know.  But it also might have meant reinforcing the roof to carry the extra 250 kg of weight, and there wouldn't have been a cool gadget to look at {Mr Jones leaves the room again...}.  Quick update from Mr Jones, the tank has increased in temperature by 3 degrees in the last 30 minutes.  How cool is that?

The Jonses
Be the Jonses you want to see in the world

Useful references for digging deeper

Your Home guide - what type of system should I get?
Your Home Technical Manual - Hot water
Hills fact sheet: solar tubes vs flat panels