Hi-Tech Wardian Case Temp Problems

[Ocelaris]

Hello, first time poster, few years experience.

I've got a problem with my new Orchid Case, it's too hot. The problem is that it's small enough that keeping humidity up and the temp down are sometimes counter productive... I'm seeking a way to balance temp and humidity and outside air...

The tank is about 2 foot square, by 5 feet tall, seperated into two chambers. The upper is lit by a 150watt HQI Metal Halide ~4000k 80CRI bulb. The bulb is totally encased in an acrylic tube and fan, so the direct heat of the bulb is not in the case it's self. However obviously the light creates heat. Bottom section is lit by 2x36w Compact Florescents.

So It's about ~3 feet tall and 2 foot square, and at the moment I have the mini fogger IN that space... which adds to the heat...

I'm wondering if anyone has any idea of the efficiency of the Peltier coolers... I know people have had limited success with them because they have such a small capacity, but seeing as how it's only a 2x2x3 foot area... hoping I could get by...

I bought a humidistat, and thermostat to pump in air, but ideally I would vent air infrequently, and keep the temp and humidity in range with their respective meters...

I will take pictures, as I'm quite proud of it, right now have 2 paphs, a BLC, a Phal, a masdavelia, and a ascoscenda... Would like to do more Asc, but seeing how space is a constraint, the shorter plants would probably be a better fit, small paphs, phals etc...

[Ross]

I think there are several issues you need to address. First, the HD metal light is the source of most of the heat (self explainatory) thus most folks here use t5 florescent lights of various styles which run way cooler.

I have a peltier cooling unit in my cigar humidor which is approx 30"x30"x40"H. Wood is a better insulator than acrylic or glass so your unit will probably run overtime trying to maintain coolness. It's operation is based on reducing temps a fixed amount of degrees below the outside temps. So when you select a certain temperature, it operates by running more or less time in order to achieve the temp desired. Refrigeration units run based on the operation of the compressor. This explaination is over simplified but serves to illustrate my main concern - insulation.

[Ocelaris]

Maybe some of these pictures will serve to illustrate a little bit more...

I've enclosed the MH light in a tube, so the direct heat from the bulb is sufficiently removed, it never enters the case... the lack of ventilation is my concern... I have a thermostat on the way which I will vent when it reaches say 75* or so...

I've used peltiers before for computers, and used a refrigerator also for a computer (long story), so I'm fairly familiar with the operation, but when it comes to how much heat the peltier will remove versus say the actual heat being created, I don't have a good way to measure...

I plan on moving the humidifier section outside the "tank" and possibly chilling the water for venting...? Would be easier than sawing through acrylic to mount an ugly heatsink inside/outside the tank... but I'm just looking for ideas to bring the temps down, I've pretty much settled on the Metal Halide since I had it already... It's a lot prettier color, but the digital camera adjusts wierdly when taking pics of such bright light. Thanks for the help. -Bill

[Magnus A]

Hi

First I have to agree with Ross that tha HD metal light is the source of most of the heat . Not by convection but by radiation!

Second I just have had a look on the peltier elements for cooling. I have done some simple calculations on an orchid case.

This is the assumptions:
Case dimentions 1*1*0.6 meter (3.5*3.5*2 foot?)
Perfect isolation!
no heat from light!
temperature from 25 to 15 degree Celsius
Case filled with water vapor (Heat capacity higher then air!)
Temperature different between cool and hot side on peltier element 10 degree Celsius.
No condensation of water on the cool side (inside of the case)!

The cooling unit:
The commercial air-air (heatsink with fan) mounted peltier-element rated at 33W work at 70 % under this condition.

Result:
Under this assumption my calculation shows that lowering the temperature 10 degree Celsius should take approximate 25 minuts.

BUT
Heat radiation from light, energy loss through walls and condensation of water vapor on the cool side will be a reality, and will make this unit useless!


This calculation was done to see the rate of heat transfer over the peltier element.

I hope it could explain some of the limitation in cooling.

/Magnus

[Ocelaris]

Thanks, that is helpful... "Radiation" is exactly what I need to figure out the heat capacity needed... I can figure out some rough estimates later for my heat requirements.

i am shooting for a <100$ budget for a ~200 watt cooling capacity... I'll have to figure out whether my 150-200 watt is reasonable though...

I came up with a couple ideas last night... Trying to keep the actual growing area as clean as possible lead me to the idea of removing all extraneous equipment to the outside. The idea of removing equipment from the growth space is seperate from the methods of cooling... I want to reclaim the humidifier area which is a large 40cm (~15") water dish. So I had planned on using a 20 liter (5 gallon) bucket or so with a lid, to blow humid air into the chamber, and obviously it would have to vent out... To be brief, the ultrasonic humdifier disk would float in the bucket, and a DC fan would blow air into the bucket, and out through a hose would the now moisture laden air travel up to the growth chamber. Condensation would have been removed by the length of the hose, and turbidity inside the hose should assure I'm getting near 100% humidity coming out of the hose... I think... Now if I can actually pump enough air into the enclosure to replace the humidity which is leaving due to heat etc... will be seen.

Regardless of whether that humidity contraption will be successful, it gives the chance for cooling also externally... If I cool instead the air, but the water, it would then be blowing cool moist air into the growth chamber...

On to the methodology... I've found peltier units in the 150 watt range, which should be around 500 BTU... Another method is a water cooler, the type they have in offices... they're a ~1/10 hp cooler which is about 1200 BTU... I can run 2 150w Peltiers in series which is approximately 300watts of power consumption.... for roughly 200 watts of cooling...

The Water cooler can be found for about 50-60$ and has a nice compact evaporator, it could sit in the tub... Ugly... but probably the cheaper of the two... and more reliable...

The question is whether If I cool the water down, I will be able to pump enough into the chamber... I could always mount the peltier units inside the growth chamber, but I wanted to move the humidification part outside anyways, so might as well take advantage of that and cool directly the water... thoughts?

[Magnus A]

Hi Ocelaris

As you have figured out there is alot to think about. I have not have time to go through your thoughts in detail but I have one important point on the peltier element.

The rated power is the maximum under ideal condition, the same temperature on both the cool and worm side of the peltier element. One big problem is the rate of heat transfer to the cold side and the heat transfer from the hot side. This mean that as fast the peltier element gets current it will lose power due to temperature difference it create.

You need to now the loss in power due to temperature difference over the element to be able to evaluate the usfullness.

There is one problem with condensation that will also eat power. When water condensate on the cool surface it gives away alot of energy. This dehumidfies the air. You then need to rehumidify the air and for this you need to put in some sort of energy. If you are unlucky you will end with a fast transport of energy from your humidifier through your cooling device without lowering the temperature in the case.

/Magnus

[Ross]

I think I am agreeing with Magnus on the Peltier. Mine works as desired in my cigar humidor for a couple reasons -

1) the heat source is mearly ambient room temps which are modest.

2) the cabinet is solid wood with a 1" layer of foam insulation.

3) I am creating a 70 degree F environment in a 70-90 degree F ambient temp environment.

My peltier doesn't run at all in winter. It runs maybe 50% during hottest summer months.

I suspect if you connect one to your uninsulated tank, with the temperatures you have and the cooling you desire, you will (at best) run it constantly, at least during day. At worst, you will burn it out.

The principle is simple - get rid of heat before it gets into tank. Ventilation of the tank will dry out the tank if it is sufficient to exhaust all the heat. Try running t5 florescents inside that tube and see the difference in the heat!

[Ocelaris]

Well, I already had the Metal Halide bulb, and it's vented directly so it's only radiant heat... the bulb it's self produces no heat felt by the orchids, totally enclosed in a tube which sucks air from outside, passes by the bulb, and exits stage left, the acrylic tube is cool to the touch. I will say that the ultrasonic disk gets hot to the touch, and rated at 25 watts, definetly not cooling...

MHs being about 100-120 lumens per watt, this one is starting 12000 lumens at 150 watts = 80 lumens/watt, the T5s which might fit are 2000 lumens @ 21 watts, so I would need 6 of those to equal the same intensity, and even so I couldn't get the same amount of light down on the plants.

I could scale it back to a 100w MH, but down below, I have 2x36w long compact fluorescents, which for all practical purposes are T5 fixtures... from ahsupply.com they're 36w @ 2900 lumens = 80.5 lumens/watt see this page for specs:
http://www.ushio.com/files/specs/UltraL.pdf

The T5s and long Compact fluorescents ( really just a T5 bent back on it's self) are harder to keep cool because they take up more space. With the small MH bulb, I can easily cool it where only radiant heat prevails. My Compact Fluorescent section is actually are hotter than the metal halide section...

I know it's against your reccomendations, but I think I am going to give the peltiers a shot... Worst comes to worse, I'll have to lower the lighting, move down to the 100w MH. I'll keep an update how things turn out.

[Magnus A]

Hi again

I am very interested to know the performance of the peltier elements! I have my doubts but real life test is always good. As you state the high power peltiers could work. I would have tested myself but I can not afford the high powered peltier elements (as long I am in doubt).

Keep us updated!

/Magnus

[Ocelaris]

I am in doubt too But it's worth a shot, and to me, building the environment is half the fun of having orchids.