Hot Water

In considering options for a hot water system for our house I began with quite a few assumptions, some of which have proved false, a few wants, and just a few needs that could not be compromised. There seemed to be the following general options:

System	Pro’s	Con’s
Electric storage tank	Cheap upfront Many models Common (maintenance familiar to tradesmen)	energetically expensive to run takes up a lot of space
Gas storage tank	Cheap upfront Many models Common (maintenance familiar to tradesmen) less energy than electric storage tank	takes up lots of space energetically expensive
Electric on-demand	takes up less space than storage tanks	more energetically expensive than gas on demand can end up more energetically expensive than electric storage tank, depending on use
Gas on-demand	takes up less space than storage tanks	... requires gas?
Heat pump	less energetically expensive than regular electric elements	still requires electricity loud during operation
Solar	no additional energy source required	requires secondary booster system to maintain stable temperature

For the same reason as others before us Kyle and I rapidly came to the conclusion that the type of water heater we have in our current house (traditional electric element with storage tank) will not work in the intended ones, either the 'prototype' or the bigger house. I did a little bit of reading of some very boring comparison tables to confirm this assumption before quite happily discarding them altogether as an option.

We are very reluctant to chose any system relying on electricity, as this places greater pressure on solar panels which are expensive. It seems wise to follow a policy of minimising use of electricity altogether as part of our intended way of living. Thus, electrical on-demand systems and heat pumps will probably not be the eventual choice.

On a side note, an ex-geologist friend of mine presented a great argument a year or so ago about why he thought our area would find itself in the next 5 years rapidly short on fuel for gas appliances as nearby sources were exhausted. Whilst I didn't really follow the specifics of his claim at the time, and haven't (yet) looked into it in detail myself since, the discussion lingers in the back of my mind as I generally trust his opinion. Thus I would be reluctant to commit irreversibly to gas alone for water.

Solar collectors with 'boosting' from gas or electricity are becoming more common. After considerable reading I found several anecdotal accounts (1, 2, 3) of individuals who used unboosted solar collectors with satisfactory results, mostly in low use households. As we want to limit our external energy needs this would be ideal, and my (by no means expert) understanding of physics leads me to thinking that with a very large, well insulated storage tank you could achieve relatively stable temperatures.

However, Kyle has a quirky medical condition that means he doesn't feel pain and struggles to identify extremes of temperature (sounds weird, I know). Whilst I don't particularly mind the slight variation in temperature expected from solar collectors, this is a very real safety concern for Kyle who can't tell the difference between 'hot' and 'too hot' but will still burn if he turns it up further. Current strategies for avoiding daily injury depend on Kyle being able to memorise how far to turn the taps on - variable temperatures from the hot water system would make this unreliable.

Initially Kyle and I both assumed that this would rule out stand alone solar systems entirely, however I was reluctant to abandon them. My thinking ran along the lines that the risk isn't the days when the temperature is lower than 50°, it's on the days that the temperature is high enough to scald. In a traditional system this would be controlled by a valve that mixes the hot water with cold water as it exits the tank, and you can turn it up and down with a spanner. We already knew enough about these manually controlled valves to know our current home doesn't have one, hence why Kyle risks scalding daily.

A bit of digging, and I found variable valves which will result in a water mixture of consistent temperature regardless of the inputs. One of those "I can't believe we'd never heard of this before" moments. I have slight concerns that all models I found seek to provide temperature stability in both directions, whereas we're really just concerned with keeping it below a certain point and don't mind if it falls a little further, but this is a start!

So at this stage we're keen to explore un-boosted solar further, but may end up with a gas on demand system. A little more research yet.