Kitchen hot water

A while ago, I wrote about my reasons for wanting a dedicated hot water system for the kitchen. Today, the system is finally operational. It's a big day!

I decided I wanted to do all the plumbing myself, which has made things take a bit longer (I have no previous experience brazing or bending copper pipe), but it has gone reasonably smoothly (albeit slowly), and in the end I'm reasonably happy with the standard of work. I left the most visible parts until last, when I'd had most practice and they look reasonably professional.

Here is a picture of the little hot water system on the roof (with the unfinished space heater next to it). It holds 30L of water, and has 8 x 50cm evacuated tubes. It is a low pressure system, so I can't just connect it to mains pressure with a tap in the kitchen (as is the norm). This system cost me $300 on ebay. It came with the aluminium racking immediately underneath it, but all the rest of the aluminium on the roof I installed myself.

Because the unit can't run at mains pressure, I needed a system whereby the tap to it controls its supply (before that supply reaches the tank). Then the tank is just sitting there at atmospheric pressure. To do this, I used an electric solenoid valve, which cost about $20 on ebay, with a 12 V transformer that I installed in the roof. We had an existing powerpoint in the roof that is controlled by a switch in the kitchen. That switch now energises the solonoid valve, switching it from normally-closed to open and allowing more water to flow into the tank of the hot water system.

Because the tank is always basically full, this causes it to overflow. The overflowing water exits the tank via the (hard-to-see) pipe at the top-left in the first image, and that pipe leads straight down to a (tapless) faucet in the kitchen below. Here is the last bit of pipework that directs that overflow through the kitchen window and out the spout in the kitchen.

How to use it

In the kitchen, flick the power switch, and wait. That switch activates the solonoid valve, opening it. Water enters the tank and causes it to overflow, and come out of the kitchen faucet (separate to the existing tapware). A bit before we have enough water, flick the switch back off -- the rest of the water will drain from the pipe into the sink before it stops.

 Quirks

Yes, this is quite an unusual system.

The main quirk is that, because the "overflow" pipe is basically empty of water most of the time, there is quite a latency between flicking the switch and getting water out of the tap. There is also quite a latency between un-flicking the switch and the water stopping. There's more testing to go here, but I think it's about 20 seconds.

Also, because the faucet is open to the tank, it is possible that the tank will boil in summer and lead to dripping in the kitchen. This remains to be seen.

Reflection on goals

The goal was to have "instant solar hot water" available at the flick of a switch. I now think this was a bit naive, but I still think it will be handy for two main reasons:

1. Because it is a shorter run of hot water (it is basically hot immediately with no wastage), it decreases the load on the main solar HWS during winter. 
2.  For the same reason, less water is wasted in summer (when we really need it!) -- we've been catching that water in jugs and drinking it later, but it is a bit of a pain, and still results in some wastage (from the main HWS, there is just over 2 L wastage to get hot water in the kitchen)

If I was doing this again, I'd consider installing an additional full-size solar HWS down that end of the house and just run the kitchen from that. One day, I may do that (depending how we go for hot water in winter).