Water at my house - part 2: hot water

Hot water

Please refer to this article that I wrote previously, which gives an introduction to the hot water system I've chosen.

At this point, only the main solar hot water system is connected. This supplies the whole house. It is located above the laundry and near to the bathroom, but is across the house from the kitchen (which is on the Eastern side of the house). Refer to Figure 1.

Figure 1: Schematic of the water connections at my house. Note the two hot water systems.

Having a hot water system a long way from where you want to use the hot water is a waste. This is because of two reasons:

1. the hot water cools on its way to where you want it. This can be reduced by lagging (insulating) the pipe
2. when you're finished with hot water, you're left with a pipe full of hot water. This is wasted.

This is bad for two reasons:

1. we're running rainwater, and don't want to run out in summer. Hence we catch the water that's coming out of the tap before it gets hot. This is doable, but is a hassle.
2. I want to run on pure solar hot water (without electric boosting), and anticipate that this will sometimes be marginal in winter. Any wasted hot water will make this harder.

Because of this, it is very beneficial to have hot water closer to where we actually want it. This is particularly true in the kitchen where solar heated hot water can regularly be used, if it's convenient (eg. fill the kettle with solar-heated hot water to save electricity).

For this reason, I've put a second, smaller, solar hot water heater on the roof right above the kitchen.It holds 30 L and cost AU$300 on ebay. Internally, this is different from the main heater in that there is no heat exchanger (refer to Figure 2 (b) in this article for a detail of the main solar hot water heater). The difficulty is that the unit can tolerate no more than about 5 psi, so can't be used in a normal fashion (ie. the supply fills and pressurises the tank, and a tap at the point-of-use controls the exit of water).

As far as I can see, there are two options to use this tank (which is not yet connected):

1. set up a small header-tank, and use this hot water system as gravity fed. This is not ideal because it necessitates a float valve and a tank up on the roof that is higher than the hot water system
2. use a tap that "pushes" water into the tank, causing its hot water to overflow down a pipe, and that water is what comes out of the faucet. This is not ideal because there will be quite a bit of latency between when one turns off the tap and when the water stops coming out. Also I can imagine that in summer the tap could drip if the tank boiled.

I haven't yet decided which of these arrangements to go for. At the moment I'm focusing on building a chicken house!


This article was written by Angus Wallace, and first appeared at guesstimatedapproximations.blogspot.com.au