Wasabii - cold house

I've been thinking of growing some Wasabii and have been following a thread on Backyard Aquaponics discussing things like the temperature it likes.

It seems it likes to grow in less than 10c water, and less than 25c air.

I'm about to get two solar panels for my epic solar boat adventure, so when they're are not powering the boat, I'll be using them to power my aquaponics system, and I've been thinking of ways to keep the system cool to extend the trout growing season, so perhaps I could use them for that as well.

I ran the problem through the invention engine, and it suggested running coils of hose through a container of water in a fridge as a heat exchange. And connecting the hose to my system. This would obviously cost a lot to run because each time the water went through the growbed, it would collect a stack of heat on a hot day.

But if I put a shade house over the top, I might be able to work something out.

Wasabii likes shade as well, so it should be easy enough to get a couple of layers of that grown up bubble wrap they use for pool covers, and make a tent. Wasabii doesn't grow very tall, so it should only need to be around half a metre high. Perhaps on hinges so it can be lifted when access is required.

I'd add a window so I wouldn't need to let all the heat in whenever I took a peek.



120 Things in 20 years is being told to finish the boat first.

Solar hot water - Poly pipe collector

It was a chilly and windy day in the hills today. But the sun was out for a while in the morning.

The ambient temperature was around 11°C as I added the rest of the T junctions to my new poly pipe collector, and I was almost confident that I'd sooner or later, be making some solar hot water. 

The water temperatere was around 10°C from my rainwater tank.

It was interesting to note the temperature of the collector was very close to the temperature of the storage tank, and the air temperature in the collector stayed low. (digital thermometer is testing water temperature and the glass one is testing air temp in the collector) 
No doubt this means that the heat exchange area of the black poly pipe is sufficient. This came as a bit of a surprise to me, although in hindsight it would appear that the transfer rate is self governing to some degree. The hotter the water gets, the faster it will flow and thus the more heat exchange will occur.




Final temp before it started raining and I went inside was only 22°C, and it didn't get any higher in the overcast, windy and rainy conditions, even when I went outside hours later. But, I think it was actually a success. I doubled the temperature of the water and it only took an hour and a half. 


Given I only used two sheets of corflute for insulation, and the insulation for the top, bottom, and sides was just tape, which isn't really insulation it's really just tape, It did about as well as I hoped.


The experiment served its purpose in that I learnt a few things and didn't cost anything as I'll be pulling it apart and using all the bits in the real thing.


Lessons learnt ...

• Air bubbles are not your friend. Don't let them collect.
• You don't need a lot of tubing to shift a lot of heat from a collector.
• Insulation is amazingly important. (tape leaks heat so that you can feel it leaking)
• A tube based solar siphon regulates itself, so there wont be any issues with the collector overheating.
• Even at the rate this poorly constructed solar collector collected heat, it would still be worth using it as a bathroom heater or something*. On a bigger scale without changing anything except scale I could heat my house by building a wall out of water tank and simply circulating the water to my collector.
• Collecting free energy is a worthwhile pastime.
• I'm not very skilled at gluing.
• there was a reason I collected all that 19mm poly pipe for all those years, even though it had holes in it every few metres, and kinks in the sections between the holes.

*Hmmm towel heater...

Solar hot water - Pre-heater

I have a perfectly good hot water service at home so I wont be throwing it away just yet. But I think I've decided on what I'll do instead. My plan is to make a pre-heater to heat the water that goes into my hot water service, so less energy is required to get my water up to temperature.

I already have a working understanding of heat exchange principles, so I'll leverage my new knowledge and attempt to apply it to pre-heating my hot water inlet. By doing so I'll avoid having to make a solar collector that is capable of taking mains (in in my house mains-like) water pressure.

Currently my hot water service takes delivery of its water at around 13 deg C and then uses fossil fuel to heat it to something like 65 deg C. If I can collect some heat and store it in an insulated container, I should be able to make a simple heat exchange device to transfer that heat to the inlet water of my hot water service. If I can spare my hot water service the trouble of even a few degrees It will have been worth it. But I'm hoping to contribute more like half the energy required to make my showers hot. If I can do that I can feel a bit more confident that I can make a replacement hot water service when my existing one gives up one day.

I guess that means my official target for my inlet water temperature is a 26 deg C increase from 13 deg C to 39 deg C.

That should be easy enough in summer but it's moving towards mid-winter here so I will be very pleased if I can get even close.

Solar hot water - Heat exchange

Some things allow heat to move from them to other things really well and some things don't.

The rate of heat exchange between one item and another makes us say words like insulation, and conductor. The reason people selling you insulation can claim that it keeps you warm in winter and cool in summer is because it does. Insulation achieves this by denying heat exchange between the sun and your house, or your house and winter. A perfectly insulated house would always be the average yearly temperature of your region.(unless you add or remove heat (Actually a perfectly insulated house would always be whatever temperature it happened to be on the day it was built.))

Heat conductors, on the other hand, love passing heat around and sharing it with anything that also conducts heat. An example of a good conductor of heat would be an aluminium cooking pot. Or in my house, copper based stainless steel cooking pots. The reason the copper is on the bottom of the pot is because it conducts heat well and the stainless steel doesn't. The reason the stainless steel is there is due to a scandalous error from within the scientific community, and some ill-informed law. A poor heat exchanger makes for a poor pot. When you heat a pure stainless steel pot the heat doesn't spread evenly and your food burns because all the heat is in just a few spots where the flame or electric element touches it.

If you want to collect heat, it turns out another thing to do is to stop reflecting it. Those silver things people put up against the inside of car windscreens work quite well at reflecting heat, as do white things. Black things on the other hand absorb heat. Matt black is even better.

For 10 years or so, from when I was about 5 years old, we had a black and white cat. Once, when it had been lying in the sun for a few hours one hot summer's day, I remember patting it. It tore strips of flesh off my arms. It was a starving stray when we took it in and it simply hated humans.

If you want to collect heat from the environment, it's best to use something that is good at heat exchange to collect heat, and then its best to use something that isn't good at heat exchange to store it and stop it escaping. If you want to collect heat from a nuclear reactor,  its best to use someone else's country.

I wont be exercising the nuclear hot water option at my house. Although at first glance it seems safe enough, I'm told it's prohibitively complicated and expensive, and could take longer than the two months I've allotted to each project to gain local council approval.