I needed a few more lights for my second greenhouse bed. I had the bright idea to use water cooling because, well, I already have a water system, why not direct the heat from the LEDs somewhere useful, like the soil bed?
You can take a look at my previous blogs on how I made the LED strips. This time, instead of using heat sinks, I used water blocks, which were about the same price.
After a long break from lights, I finally got a system put in to water cool several components at the same time from the same pump. Check it the video explaining that here:
I’ve got everything I want just about hooked up to the water system including a water cooled air intake system and the solar and CO2 generator. Only thing left is maybe another heat exchanger and maybe another strip of lights.
Initial testing is promising. After several minutes (long enough for part of the aluminum back to get very hot to the touch), the water blocks and surrounding area remained very cool.
What about cost? Well, this actually ended up being cheaper than the previous system. The water blocks where the same cost, but the savings came in the power supply. I have been using one power supply per 6 LEDs (180W per 6). Instead of a 350W power supply (that can’t really do two at full power, I’m using a 400W 24V power supply to power 12 LEDs instead of just 6. This saves me about $50 per 12 LEDs.
Stay tuned, I have something awesome in the works related to LED grow lights. I think it will take these lights to the next level.
If you are following my youtube channel, you’ve probably already seen this. If not, here it is again. This is an introduction to grow lights where I cover what are the important aspects of light relevant to plants and compare a couple different types of grow lights (T5 vs LED).
To sum things up, T5’s are cheaper out of the gate. But LEDs are more bang for the buck in the long run.
Far red (740nm) might be very beneficial to tomato production. Studies have shown that it can help produce longer “hypocotyl” (the seedling shoot that becomes the stem) by just blasting the plant with 12 minutes of light at the end of the day (16hr photoperiod with T5 lights). Other studies claim that far red can help reduce or eliminate sucker growth.
According to my research, blue light is primarily used in plants for vegetative growth. It follows, therefore that blue light is best for seedlings and clones that you want to grow in size quickly. Is this logic sound? I’ll experiment, and report back.
This video is a live build video where I make a $54 dollar blue-only grow LED floodlight. Note that at the time of posting, the floodlight price has already changed on Amazon. You can typically find these on ebay for a reasonable price.
The last few months have been trials, full of learnings and many successes. This is really only my second tomato growing experience and first experience with a greenhouse. First let’s look at the successes.
I’ve harvested several pounds of tomatoes so far. There’s several more pounds to harvest. On addition to the tomatoes, I’ve harvested lots of parsley as well.
The greenhouse is fully automated. The irrigation, the lights, the solar, heater the blower… just about every electronic component is controlled by my custom automation software. I’ve been tweaking the rules for months and its working really well.
Humidity sufficated many flowers in Sept and October. They developed mold which prevented fruiting. Adding a dehumidifier to the system solved that and fruit started to set in November.
Electricity has been my latest trial. It started getting below freezing so I added an electric heater. The load from the heater started popping my 20A breaker. On night it popped and temperatures dropped to -2C air and 9C soil. This caused serious damage to more than half of the 10 tomato plants. The planta dropped flowers and aome of the youngest fruits. To solve the issue temporarily I put the heater on a separate breaker with a long extension cord.
Between the humidity and the cold I probably lost 2 months of future harvests. After December, I may not see another harvest until March.
Avoid higher than 80% humidity. 85% is a critical threshold and mold will start to take over.
Don’t share electric breakers. I did not foresee the need for a heater. Even so, future proof yourself by putting your greenhouse on an independent breaker or two.
The door leaks heat. It needs to be rebuilt. When I start, it needs to get done *fast* because I can’t leave it unfinished at night.
CO2 generator/water heater. I found a water cooled CO2 generator. This is perfect for a geothermal water system because it heats the water AND produces CO2. I may be able to eliminate the electric heater if this thing works.
Measure electrical cost. I plan on adding a current sensor to the new breaker. I’ll be able to see what my electrical costs are and use that in my automation software. I’ll be able to create “power saving” rules when costs exceed expected production. The current sensor has been installed, now I need to get it tied into the system.
I have almost 600 Watts of grow lights that still need to be built and installed. 200 watts on bed A (the tomato bed) and 360 watts for bed B (strawberries, onions, garlic, herbs). This will help with growth especially with the onions and garlic which don’t get any direct light because of how low the sun is in the horizon and how high my fence is. It will also help produce heat at night as a fallback if the geothermal system or water heater can’t keep up.
It’s been a rough few months, but things are literally looking up as new growth is being observed in many of the damaged plants. After the door is rebuilt, I believe the heat and even the cooling and humidity problems will be solved for good. The new wall where the door will go will have vents and fans for intake and exhaust. I’m excited about the improvements in progress and seeing some real results.
Happy new year everyone and happy 2016 harvesting!
Here’s another example of a greenhouse, this time a huge commercial greenhouse, that uses water as the heating medium.
There are substantial differences between a geothermal water system and this system, namely, the temperature of water they use is very hot relative to a geothermal application and therefore they do not use the system to heat the growing medium directly.
They also use natural gas to heat the water. Natural gas is good because it burns into primarily water vapor and CO2 which they recycle by giving it to plants.
The ultimate source of heat for my greenhouse is the sun. Even if the outside temperature is less than 10C, inside, due to the energy input from the sun, I’m seeing up to 40C on sunny days and almost 30C on overcast days. However, my water reservoir, which I pump through a geothermal bank 6 feet under the ground and through my soil bed, is only seeing a maximum of 15C on those hot days. As nights have been dropping below freezing (-4C), it drops about 5C to 10C when I wake up. That’s not acceptable.
The issue is that the air in the greenhouse can only heat the water if it comes in contact with the reservoir container. Further, waiting for the air to heat up by the sun, and then the air to heat up the water isn’t ideal. Air is a poor conductor of heat and has relatively low energy storage capacity. To improve this situation, we need to increase the surface area of the water system. We could put in a bigger reservoir but space is a scarce resource inside my greenhouse. A larger reservoir will increase the surface area, but only a little bit of that will receive direct photon penetration from the sun. What we really need is a solar heater.
I have a 4 ft x 6 ft area above my components. I could mount a board of some sort up there are coil some water tubes to increase the surface area. I also have 2 old CPU radiators with fans. This will increase the effective surface area of the water’s contact with the air.
Over a couple weekends, I took the 200 ft of black poly tubing and made two spiral loops almost 2 feet in diameter on a 8 ft by 4 ft Styrofoam board I picked up at home depot. In between the two spiral loops, I placed the radiators in series. To hold down the tubes, I used automotive-grade 3M double-sided tape in an “X” pattern. On the top, I used gorilla tape, but this wasn’t effective. Right before installing, I used 10 gauge wire to lock it down in case the 3M tape fails.
I mounted the setup at a 30 degree angle near the top of my greenhouse facing south. This is not ideal. In my area, a 70 degree angle would be better, but space is limited, so this will have to do.
Before I installed it, I tested it on the ground at a 70 degree angle. Over the space of an hour or two, the water heated up from 13C to 19C. It was a sunny day. This is about the same as pouring two good size pots of boiling water inside the reservoir.
I’ll continue tracking the performance, but today I’m optimistic this will help. The running cost is pretty cheap too at only 28 Watts (12V @2.4A max). I’ve coded up an algorithm in my automation controller to only turn on the pump if the air is hotter than the reservoir. This is good for the winter time, but this rule probably won’t work will in the summer. In fact, I may have to add a rule to turn on the solar heating system to help cool the greenhouse. We’ll see.
What about the cost? Well, this addition was relatively cheap. If you want the cheapest solution, this might be it.
It was cold today. It’s been cold all week. The high for today was 7C (about 44F, yes, Tidder, I love you) and the low was 6C. This caused my soil temperature to drop to 11C (52F). This is bad. In addition, it looks like it was very dark most of the day. My artificial lighting accounted for 85% of the total light energy in my greenhouse (how my light algorithm works). The sunlight was only able to warm the greenhouse to 15C.
In a conversation on IRC, a friend, wondered if PEX tubing was very good at thermal conduction (ability to transfer heat energy to another substance). After a bit of searching, I found that PEX has very poor thermal conduction relative to, say, copper. If PEX is 0.4W/(mK), copper is like 28. Big difference. All is not terrible, however, because water is only 0.6W/(mK).
Looking at today’s data, there was a couple degree discrepancy between the reservoir temperature and the soil temperature. I would have thought it would be almost the same. Could thermal conductivity explain the difference?
I conducted an experiment. I boiled some water and poured it into the reservoir. This brought the temperature to about 21C (from about 14C). Over the space of a couple hours, I logged the temperatures from both over the space of 3 hours. Here’s a scatter plot of the reservoir and soil temperatures:
The chart shows a negative correlation between dropping reservoir temperatures falling and rising soil temperatures. We have energy transfer! It also shows about how much pumping time is required to raise the temperature of the soil by a few degrees. This could certainly explain how there could be a difference between the reservoir temperatures and the soil. If the reservoir heats up quickly during peak temperature, it could be several hours before the soil will rise.
During this test, the control soil bed (unregulated) remained around 13.11C and eventually fell to 12.9C after 3hrs. The air temperature dropped from 10.1C to 9.7C. We lost some energy to the air, but not enough to change the air temperature upward. We also likely lost a significant amount of energy to the geothermal bank which as about 4 or 5 time the contact area as the soil bed.
When I started researching about building additional garden beds for food growing I came across the idea of a geothermal air greenhouse while surfing youtube. I had heard of homes being heated/cooled with geothermal and understood it’s efficiency. I started researching the methods used. What struck me as odd is that geothermal homes use liquids, not air like the greenhouses I saw on youtube. Coming from a computer background, I understood the best way to cool a computer, was liquid, not air. Why then use air as the energy transport? I had to do more research.
I ended up watching a thermodynamics lecture series on youtube. This gave me a foundation for more work. Turns out that different substances have different heat properties. For example, to raise the temperature of water by one degree, you’d need about 4 times more energy than what you’d need to raise the temperature of air by one degree. This makes air quicker to heat up, but also quick to cool. Water on the other-hand takes much more energy to heat it up, but retains that energy longer.
I looked at how water is used in radiant heating applications. They use PEX tubing in 9″-spaced serpentine loops in the flooring. Heated water is pumped and the energy transfers bottom-up to the surrounding air. I decided to combine these principles in my greenhouse build. I would dig a hole, lay some PEX tubes through the earth and directly into my garden bed. The garden bed would then “radiant” heat the rest of the greenhouse.
That was the theory then. I was wrong.
Temperatures in my area are now getting really cold at night. Much colder than the 15C that my tomatoes need to be happy. The outside temperatures have gotten as low as 1C. What about inside my greenhouse? Inside, I’ve seen it get to as low as 6C. The radiant heating effect is minimal. So was my experiment a failure? No. Not yet at least.
What I didn’t understand then, but understand more now, is the process of transpiration. Plants move water from the soil up to through the plant to the leaves. I thought I’d be keeping the roots warm, but I’m actually keeping the entire plant warm as it moves the warmer water from the soil up through the plant and out the leaves.
This is why when you want to cool the plant on a hot summer day, you water the soil, not the leaves!
This discovery lead me to the next: greenhouses that use geo air are actually ultimately using water. The plant will store the heat energy in the water inside the plant. It will get it from the soil, which is warmed by air, and it will get it from the ambient air around the plant but ultimately air is cooling/heating water. The above image illustrates how energy is passed around in both situations. There’s not much difference except this: water holds more energy. That means less movement, less digging and lower cost.
There’s still a lot of work to be done before I call the experiment a success. So far the results are positive, but I’ve got several more months of winter to go through.