Gravity fed hot water as dump load

[arthurK]

Hello everyone!

I apologize if a thread like this already exists and I have missed it due to wrong wording etc.
I have searched whole web and found bits and pieces but no concrete answer or other examples like mine.

The background:
It is an off grid tiny house where I want to install a wind turbine, for which I thought off a water heater as diversion load. As far as this goes, there is plenty of information online. Unfortunately nothing specific. The easiest for me to do would be connecting a shunt resistance to the turbine. However, I want to learn something new, as well as use the excess energy for something more useful than heating air.
To cut the long story short.
I have a cold water tank one meter above the hot water cylinder and a 250W 12V heating element for which recommended max working temperature is 60 degrees Celsius. Normally, this would not be an issue, as water would be only heated on windy days and when batteries are full, so it would hardly get close to that threshold. However, when we are away and the wind won't stop blowing, temperature is likely to exceed the limit. I could install the pressure valve, but this will open way too late (I don't know what may happen to the heating element, but should it fail, the wind turbine will spin too fast and can cause much more damage than water heater).
Hence, is there a way to control the temperature other than a thermostat that will disconnect the element (which is not an option, as said above)? Something like the pressure valve but adjustable, so that it will open when water hits 60 degrees?

Secondly, when I pumped water to the tank, I realized there will be air trapped in the hot water cylinder. Would that be a problem other than very low hot water pressure in the tap? (there will be only one, right by the cylinder). On reading some posts, I realized it might even help against too much pressure building up, along with loose lid cold water tank above it, am I right?

I decided to start this topic as there seem to be a great deal of people with extensive knowledge in plumbing on this forum. Should some of you have a better idea for my design, please feel free to laugh at me but also do share your way of tackling my problem.

I look forward to seeing some responses.
Arthur

 

[John D v2.0]

Hence, is there a way to control the temperature other than a thermostat that will disconnect the element (which is not an option, as said above)? Something like the pressure valve but adjustable, so that it will open when water hits 60 degrees?

So it's not clear what you want here, the won't really be any pressure at 60c as the water won't boil.
What you would need is a cooling tower or something like they have on power stations, where you have a DT thermostat closer to the bottom of the tank and on the normally open terminals you wire a pump or valve to add cold water and purge the hot to somewhere it can cool (or the drain if you want to waste it)
I'm sure you can get a solenoid controlled valve like a washing machine and overflow it to the drain

Secondly, when I pumped water to the tank, I realized there will be air trapped in the hot water cylinder. Would that be a problem other than very low hot water pressure in the tap?

If you don't fill it completely, make sure the element is covered. If it burns out you'll lose your load.

 

[arthurK]

Thank you for your reply, John.

I have recycled one of these heaters which had corroded contacts and started to leak:
http://solucionesbizkaia.com/wp-content/uploads/2016/03/02-Termo-eléctrico.png

The element will be covered at all times, as only the top 5-10 cm of hot water can be pumped out without replacing with more cold water.

The old heater did have a thermostat and coil you are talking about (I assume) but It was a normal mains heater so could be switched on and off easily.

What you suggest sounds like a major job. It will involve drilling for overflow through insulation, won't it?
Since people suggest heating water as dump load, I thought there would be an easy way.
Perhaps the 60 degrees is only a safety measure? And the element could handle 100 degrees easily?

 

[arthurK]

John,

I looks like I've solved my own problem.
Once I settled on water heating, I didn't even think about air heating. But now, while writing the first post, I mentioned the easiest solution. I will connect a shunt resistor in parallel with a switch that can be flicked when we are going away.
I shall wait, perhaps someone has designed a better o simpler system to mine.
There is an analog thermometer on the heater. I might be able to hook it up to the switch. But that requires more research.

 

[John D v2.0]

Start simple them build from there!