Need advice about cooling my tent

[Venturi]

Thanks for the blade types link. You seem to be (at least) one of the most serious students of ventilation on this forum. I appreciate all the education you’re giving me.

Ventilation alone can get the tent close to the ambient temperature – especially after I lower the height of my lights to, say, 24" and dim them so they aren’t producing so much heat. @Isleofdogs noted earlier that 600 W of LED lighting in a 2’ x 4’ tent is overkill and I confirmed that with PPFD measurements in post #18. I’ve continued testing with the lights on full at 36" only to keep results comparable across my tests.

Unfortunately, my ambient temps are a bit too high. In post #38, I mentioned that this source shows that, during late flowering, 75° is the upper limit when the lights are on and 68° is the limit when they’re off. I can get down to those temps in winter without AC. Otherwise, an AC unit is needed, especially to get 68°.

Have you looked at my figure in post #51? I’d welcome any wisdom you can share about it.

[Isleofdogs]

@Venturi

75° is the upper limit when the lights are on and 68° is the limit when they’re off. I

You’re not reading that correctly. And I think most growers are successful at temps above that.

[Venturi]

@Isleofdogs

You’re not reading that correctly. And I think most growers are successful at temps above that.

You’re right – the limit shown for late-flowering in that table with lights off is 65°, which is 3° less than I stated.

I don’t think that table means the plants will die if its upper values are exceeded. Indeed, the limits probably vary from one strain to another. I think the table is meant to convey ranges that yield optimal results on average.

Are there tables like that one for specific strains? If not, respecting its limits seems prudent, especially since I’ve no experience yet.

[PhotoFinisH]

@Venturi

Thanks for the blade types link. You seem to be (at least) one of the most serious students of ventilation on this forum. I appreciate all the education you’re giving me.

Ventilation alone can get the tent close to the ambient temperature – especially after I lower the height of my lights to, say, 24" and dim them so they aren’t producing so much heat. @Isleofdogs noted earlier that 600 W of LED lighting in a 2’ x 4’ tent is overkill and I confirmed that with PPFD measurements in post #18. I’ve continued testing with the lights on full at 36" only to keep results comparable across my tests.

Unfortunately, my ambient temps are a bit too high. In post #38, I mentioned that this source shows that, during late flowering, 75° is the upper limit when the lights are on and 68° is the limit when they’re off. I can get down to those temps in winter without AC. Otherwise, an AC unit is needed, especially to get 68°.

Have you looked at my figure in post #51? I’d welcome any wisdom you can share about it.

I figured that I’d ask again about your thoughts on needing to add an air conditioner since I sort of lost track of your findings, & you had mentioned that something in there was inaccurate along the way.

I’m not sure how to see what number a post is. Is #51 the one that shows the linear decrease of tent temps, as you increased the fan speed? I did look up something on how a fan will chart as power is increased, & from what I read, if you increase power linearly, the fan will also plot linearly on the chart, even if it plots non-linearly at 100% power & changing restrictions from 0 thru 100%. Not sure if that covers every type of fan out there, but I was looking up info about centrifugal blowers mostly.

Yeah I’m still learning along with everybody else, & started mostly due to having a lot of the same questions you have now, when I was building my first setups years ago. Back then it was mostly learning about why fans in series won’t flow as much as fans in parallel, & then more recently learning about tuning the intake area, & also about the newer fan designs.

@Venturi

@Isleofdogs

You’re not reading that correctly. And I think most growers are successful at temps above that.

You’re right – the limit shown for late-flowering in that table with lights off is 65°, which is 3° less than I stated.

I don’t think that table means the plants will die if its upper values are exceeded. Indeed, the limits probably vary from one strain to another. I think the table is meant to convey ranges that yield optimal results on average.

Are there tables like that one for specific strains? If not, respecting its limits seems prudent, especially since I’ve no experience yet.

I also think that you might not need to sink your ambient &/or your tent air temps as low as you’re thinking. Kind of depends on how everything works together & where the leaf temps end up.
I have a chart which shows leaf temperature vs. photosynthesis rate, which you might find interesting. I think it actually shows leaf temp vs. CO2 consumption, but you can replace the CO2 consumption rate with photosynthesis rate apparently. Of course that would relate to lights-on temps, & lights-off temps are important too, & you just mentioned those, but the chart is going to be for lights-on. The lower line is ‘normal’ CO2 levels, & the upper line is ‘added’ CO2 levels…

[PhotoFinisH]

OK I see post 51 now,

You might be dumping a lot of your inside air to the outside, not sure if that would be good or bad for your overall setup once you do add the a/c, but try it & see how it does. I think it should probably help cool the tent. The ducting & bends will put some drag on the fans. I’d probably at least see if whatever additional a/c you get could handle having the tent exhaust just dumped back into the lung room. If not, then dump it outside, or maybe into another room where a house hvac thermostat is.

[Venturi]

The inaccuracy I mentioned was a misreading of my notes that made me think that opening the 2 extra ports reduced the controller temp, which was puzzling. Actually, its temp remained at 81°.

On this forum, Firefox on my Mac shows numbers on the right side of the screen, such as “21/30,” which means the post to the left is #21 out of 30 total. The posting date is shown, too.

My exhaust fan’s RPM is controlled using PWM, so I expect speed settings 0-10 map linearly onto RPM. RPM, in turn, should map linearly onto CFM if there are no air restrictions. My figure showing nonlinearity graphs tent temp as a function of speed setting, and the nonlinearity has the cause I described.

These days, ambient temp in the room before I turn the lights and fans on is 75° or so. Piping the tent exhaust out the window should allow me to maintain or, at least, approach that temp.

The ILGM table I’ve cited says the upper limit during late flowering is 65° when the lights are off. That’s what motivated my interest in adding AC. You and @Isleofdogs seem to be saying that table is wrong, though, and higher temps would be fine. Maybe I should skip adding AC for my first grow and see what happens. And maybe the ILGM table needs refinement.

Your figure shows that 81° is a good leaf temp at a normal (400 ppm) CO2 level and 100° is preferable at (what appears to be) 1000 ppm. It doesn’t specify the growth stage, though. I know that leaf temp is usually less than tent temp – sometimes by 10° or more – but the tables I know of show tent temps. Is it common to control leaf temp instead?

I don’t want to complicate things further by adding CO2 – yet. Nonetheless, I’ll share a useful figure I found here:

I don’t see how piping the exhaust outside can do anything undesirable except during winter, when I may need to retain some of that heat. Otherwise, it should reduce the load on the AC. But, as I said earlier, I’m thinking now of skipping the purchase of an AC for my first grow, and – unavoidably – running higher temps.

The bend in the hose will reduce the exhaust fan’s CFM, as you say. I can evaluate that once I’ve added an airflow meter to my ever-growing collection of instruments: PPFD, pH, and soil temp/moisture/conductivity. I’m leaning toward this one.

[PhotoFinisH]

@Venturi

The inaccuracy I mentioned was a misreading of my notes that made me think that opening the 2 extra ports reduced the controller temp, which was puzzling. Actually, its temp remained at 81°.

My exhaust fan’s RPM is controlled using PWM, so I expect speed settings 0-10 map linearly onto RPM. RPM, in turn, should map linearly onto CFM if there are no air restrictions. My figure showing nonlinearity graphs tent temp as a function of speed setting, and the nonlinearity has the cause I described.

These days, ambient temp in the room before I turn the lights and fans on is 75° or so. Piping the tent exhaust out the window should allow me to maintain or, at least, approach that temp.

The ILGM table I’ve cited says the upper limit during late flowering is 65° when the lights are off. That’s what motivated my interest in adding AC. You and @Isleofdogs seem to be saying that table is wrong, though, and higher temps would be fine. Maybe I should skip adding AC for my first grow and see what happens. And maybe the ILGM table needs refinement.

Your figure shows that 81° is a good leaf temp at a normal (400 ppm) CO2 level and 100° is preferable at (what appears to be) 1000 ppm. It doesn’t specify the growth stage, though. I know that leaf temp is usually less than tent temp – sometimes by 10° or more – but the tables I know of show tent temps. Is it common to control leaf temp instead?

I don’t want to complicate things further by adding CO2 – yet. Nonetheless, I’ll share a useful figure I found here:

I don’t see how piping the exhaust outside can do anything undesirable except during winter, when I may need to retain some of that heat. Otherwise, it should reduce the load on the AC. But, as I said earlier, I’m thinking now of skipping the purchase of an AC for my first grow, and – unavoidably – running higher temps.

The bend in the hose will reduce the exhaust fan’s CFM, as you say. I can evaluate that once I’ve added an airflow meter to my ever-growing collection of instruments: PPFD, pH, and soil temp/moisture/conductivity. I’m leaning toward this one.

Definitely would not add the complexity of CO2 until you can grow without it first for a while, was not suggesting that, but it’s how that chart is set up, that’s all.

May as well try venting the tent outside next, without additional a/c, & see what that does. Can you set that up with a short straight duct out the window? Maybe try to minimize restrictions that way. Also increasing the duct size with a step-up adapter & clamps & bigger ducting (+$) can help if the stock duct size is too restrictive.

Set it all up to get the most flow out of your fan at 100% power, but without the carbon filter first, & if it can’t get to where you want without the carbon filter, then you know you need to do something else or in addition. If it does get you where you want to, then add the carbon filter, re-tune the intake area if needed, & see if it still does. If not, then get a filter that can flow more (get you back to the same flow as it was without the filter) & still be effective at odor control, or run without it if you don’t want to run it. Not sure if you still plan on running it if venting outside or not.

Maybe just go with a pressure & vacuum combo gauge, since that seems like it might be more directly comparable to fan performance charts. Set up a block-off plate with the gauge attached, & clamp that to your fan port or ducting to seal it off wherever you want to test. Would also avoid any inconsistencies of measuring different airspeeds at different areas of the fan port, etc. Plus the conversion can get hazy if for instance you have a restriction on the intake side of the fan (carbon filter on the intake side) that you can’t exactly account the cross-sectional area of. The equation asks for intake area, well, how do I easily know what the ‘intake area’ of a restrictive carbon filter is? If I know where the pressure ends up, I can take that to the factory (pressure/vacuum vs. cfm) performance chart - or comparable performance chart if the factory doesn’t have one & plug in what they do give us, & it might be easier & more direct that way.

[Flatnut]

I use the same and tilt it up when temps get really hot in my loft to bring in that lower cold air. My tent is running 80/60 during heat of day in flower, in the summer, in muggy ass TN. I keep fans blowing and add inline.

[Venturi]

I realize you weren’t recommending CO2. But your figure brought to mind the figure I shared. I expect there are some who don’t realize that added CO2 is useless if you haven’t enough light, and it calls for higher temps.

Straight shot to the window = tent blocks window. Am I the only married guy on this forum? I think I can get away with a big hose running to the window, though.

Yes, I’ll have to experiment to see whether dimming the lights and piping the exhaust outside will lower the tent temp enough to make my 4" fan adequate. If not, it’s no big deal to size up.

And I haven’t forgotten @Bigcbud’s advice that I need a humidifier, which will have the added benefit of reducing the temp further.

Do you monitor tent temp or leaf temp? If the latter, do you know a source for recommended values?

[PhotoFinisH]

You should be able to get to a satisfactory result on one exhaust fan & ‘tuning’ the intake area(s) of the tent. If adding a fan on the intake helps, then I always wonder what were the issues in the first place. I’d want to know more about those setups though, if they have build threads or whatever.

I was looking at that leaf temp chart at the ‘regular’ CO2 levels to get an idea of some sort of an ‘ideal’ leaf temp range to try & stay within, & I’ll also sometimes check the leaf temps & the surrounding air temps & watch for changes, & I’ll sometimes watch the leaf temperature offset for changes there which could be possible signs of stress, or recovery from it. Also the leaf temperature offset is the key to calculating the Leaf VPD. But mostly I’ll probably just watch for changes in the leaf temperature offset, if I’m looking at the leaf temps.

[Venturi]

I lowered my lights (Vivosun AW200 Wings) to 24" above the floor and leveled them. Here’s the footprint for one of them alone:

The rectangle represents the AW200, which is an unusual unit. It consists of a 13" x 13" central LED board with a fan at its center, plus continuously adjustable hinged LED wings on either side. Laid flat, it measures 13" x 26", so I have the wings folded down enough to fit the 24" dimension of my tent, Thus, the wings help even out the light distribution.

Light setting and PPFD at the central hotspot vary proportionally:

Footprint for all 3 lights:

That’s a remarkably uniform footprint. Each light illuminates areas to its left and right, combining with light from its partner.

I’ve got enough PPFD to benefit from CO2, if I want to try it:

A 64% setting will produce 1000 umol/m2/s at the center and 880 in the dimmest corners. 100% yields 1380 at the center and 1214 in those corners.

[Venturi]

Much of the uniformity in the footprints I showed is probably due to the tent’s reflective walls. Here’s the footprint the manufacturer shows for the AW200 at a 12" height:

The corners are as much as 79% dimmer than the hotspot, and the hotspot is dimmer than expected: The 507 umols/m2/s I measured at 24" should become (507 * (24"/12")^2) = 2024 at 12".

I conclude the footprints lighting manufacturers show are measured in non-reflective settings rather than tents. That makes sense because, otherwise, the results would vary with tent dimensions. That’s the best way to make them comparable, but you’d need a ray-tracing program to predict what you’d get in your tent.

Bottom line: Manufacturers’ footprints are presumably accurate, but your PPFD in a tent is apt to be higher and more uniform.

I re-attached my carbon filter to the exhaust fan, closed the 2 extra ports I’d opened, and placed 2 pans of water on the floor, having a surface area that’s similar with four 10" grow bags. I set the lights to 57%, which should produce 850 umol/m2/s at the center and 748 in the dimmest corners, and turned the exhaust and circulation fans (including the ones in the AW200s) on full:

	In tmp	Out tmp	In hum	Out hum	In VPD	Out VPD
Initial	70	73	62%	55%
Light @ 57%	83	76	40%	52%	2.3kPa	1.5 kPa

Things are looking better. The temp increase at the controller is 3° now, vs. 6° or more with the lights at 100%. I’m wondering now whether piping the exhaust outside would be worth the trouble.

[Coaxer]

Yes, I’m actually doing it right now as my tent temps were getting too high during the day. Autos you can transition fairly quickly. I’d take more time with photos.

[Venturi]

I’m starting with photos. I’m in no hurry to reach harvest and I’d like to see how much of my tent’s 6’11" height I can make use of with sativas.

My main concern now is humidity. The 40% I got calls for a humidifier, but I’m unsure how to estimate how many mL/hour I need in a 76 cubic-foot tent to reach the 70% I’d like to have for veg.

Having four plants in the tent would add to the humidity produced by evaporation from the moist soil, which I’m simulating now with pans of water. Don’t know how much humidity the plants would add.

[Audiofreak]

Look at the AC Infinity humidifier. I have a similar issue and it cured it.

[Venturi]

Yes, I’d prefer a humidifier that’s designed for our purpose and automated control. Which one do you have? What’s your tent’s volume? What were your before and after humidities?

[Audiofreak]

I’m in a 4x2 tent so I use the T3

[Venturi]

My tent’s the same size, so your info is gold.

Can you tell me how much the T3 increases the humidity?

[Audiofreak]

Its fully adjustable. You can set it any % you want. it has it own sensors to maintain humidity as you wish. That’s what’s so good about it.

[Venturi]

It’s good to know I can expect it to keep up with any temperature I’m apt to throw at it. Thanks very much!