Tutorial Ventilation 101

[gdbud]

You can hold a fluorescent lamp in your hand - better not try that with even a low wattage HID lamp.[/quote]

Yes you can hold a 20 watt compact florescent in your hand, But try to hold 20 - 20 watt bulbs in your hands it will get hot.

I would bet that if you put a 20 - 20 watt compact florescent (400 watts total) in a box the heat out put would be close to the same heat out put of a single 400 watt HPS.

With compact florescent don't confuse light output with watts.
A 20 watt compact florescent will have the heat output of 20 watts, But it will have the light output of 70 watts.

A few posts back I gave the ASHRA numbers for different bulbs wattage. These are the numbers I would use to generate the heat load from lighting of office buildings in order to calculate the amount of cooling that is required to cool that space. Basically 100 used watts from a light generates the same heat whether from compact florescent, incandescent or HID light.

 

[rives]

Basically 100 used watts from a light generates the same heat whether from compact florescent, incandescent or HID light.[/QUOTE]

I believe that we are going to have to agree to disagree! Heat is a waste product of the energy conversion process. A more efficient conversion will yield more light with less heat being generated for a given wattage. Take a look at the link that I posted above, and check the 2nd law of thermodynamics and energy efficiency. Yes, you can use a lower wattage cfl to create the same light that a higher wattage incandescent makes. However, if you find equivalent wattage lamps of both types, the cfl is going to operate at a lower temperature because it is more efficient at converting watts to light (less waste product). I think that the cfm vs wattage chart is a great place to start - I just think it will overestimate the necessary flow because the PL-L's function at a much lower temperature than HID's. At this point, I am more concerned with correctly sizing the ducts in and out of my fixture. Slowing an oversized fan down is easy - trying to allow for height adjustment of the fixture in a tight cab with oversized ducting is more problematic. I want to use a scrog with DWC, so fixing the light in place doesn't work well.

 

[touchofgrey]

I believe that we are going to have to agree to disagree! Heat is a waste product of the energy conversion process. A more efficient conversion will yield more light with less heat being generated for a given wattage. Take a look at the link that I posted above, and check the 2nd law of thermodynamics and energy efficiency. Yes, you can use a lower wattage cfl to create the same light that a higher wattage incandescent makes. However, if you find equivalent wattage lamps of both types, the cfl is going to operate at a lower temperature because it is more efficient at converting watts to light (less waste product).[\quote]

OK, we can disagree but don't confuse light efficiency with energy consumption. I highlighted your statement with the operative phrase. Yes, you get more lumens per watt with more efficient light sources, but you still get the same BTU's per watt. So 250 watts of HID will generate the same amount of heat as 250 watts of LED's, but the LED's are equivalent to, let's say 400 watts of HID.

 

[bounty29]

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[rives]

I think that you are getting confused about the components of the conversion. Yes, there are 3415 BTU's per 1000 watts, if you are making heat.
There is also 1 horsepower (mechanical) per 746 watts, if you are making horsepower. There can be 146,000 lumens of HPS light per 1000 watts. The waste product of the last two processes is heat (measured in BTU's, if you like). You don't get to make 3415 BTU's and 1.34 hp and 146,000 HPS lumens out of the same 1000 watts. Each of these is a conversion of energy (watts) and depending on the efficiency of the conversion, the waste product is heat.

 

[jump117]

What % of energy consumption goes to waste heat in HPS/ CFL?

 

[rives]

What % of energy consumption goes to waste heat in HPS/ CFL?

This would be a good way of arriving at a factor for comparing the two types, but I haven't been able to find any research where the they use the same methodology for the analysis of the two. Some researchers use bare lamps, others use lumen output from fixtures, etc. Also, all of the data that I have found for the CFL is based on the self-ballasted type of lamp, where the PL-L is remote ballasted. It is an interesting problem. I think I will probably just mock up the fixture and start with the air flow projected by the chart, and work it from there.

 

[gdbud]

Rives, I hope that this info will settle all parties.
This information is out of the ASHRAE (American Society of Heating, Refrigerating and Air-Conditioning Engineers) handbook 2001 Fundamentals Book.

Instantaneous Heat Gain from Lighting
The primary source of heat form lighting comes form light-emitting elements, or lamps, although significant heat may be generated from associated appurtenance in the fixtures that house such lamps. Generally, the instantaneous rate of heat gain from electric lighting may be calculated from.

Qel = 3.14*W*Ful*Fsa

Qel = Heat gain, Btu/h
W = Total light wattage
Ful = Lighting use factor
Fsa = Lighting special allowance factor

The Total Light Wattage is obtained from the ratings of all lamps.
The Lighting use factor is the ratio of the wattage in use for the conditions under which the load estimate is being made, to the total installed wattage.
The Special allowance factor is for Florescent fixtures and/or fixtures that are either ventilated or installed so that only part of the heat goes into the conditioned space.
This special allowance factor adds the ballasts wattage to the lamp wattage.

This same formula is used for Compact Fluorescent, Fluorescent, HID.

Rives for your situation by placing the ballasts out side of your space then you will just need to use actual wattage of your bulbs with out the ballasts.

 

[rives]

Gdbud - That is certainly a good place to start, as I have agreed several times before. I am trying to nail this down as tightly as possible to keep the light fixture easily moveable over the widest range possible. What ASHRAE is doing in the handbook is erring to the conservative side by taking gross wattage irrespective of the type of lighting so that no matter what type of light is used, the sizing is adequate. The NEC (National Electrical Code) does the same type of thing in sizing out components. However, an engineered solution can supercede the code in the eyes of the inspecting authority because it is recognized that the code is based on worst-case scenarios across a broad spectrum of installations. The engineers’ stamp absolves the inspecting authority of liability and moves it to the engineer because he has calculated that the sizing is adequate.

My argument throughout is with the statement that “all lights of a given wattage generate the same BTU’s”. If this were true, it would be the first step toward perpetual motion. If you think of a gallon of diesel rather than 1 kw, it might be easier to grasp. A gallon of diesel has the potential to create 128,000 BTU’s. However, if you burn that energy in your pickup instead of your furnace, it will move you 15 miles down the road and generate some heat. The heat is a waste product of the conversion of the latent energy into motion. There is a lot of heat because internal combustion engines are grossly inefficient, but it will be significantly less that the original 128,000 BTU’s. The BTU rating of these is one measure of the potential work that the energy contains, but if you do other work, the BTU’s generated is less.

It’s been a fun discussion!

 

[scurred]

See I got a problem with passive intake. The way my area is setup, using passive intake would be very difficult. It is kind of 'remote' from the area I would be intaking from, 8-10 feet away. So, instead of passive intake I think I could do this instead... get 2 fans, same manufacturer, same model, for example 2 CANFAN 4" HO 178CFM, then get 2 of the same carbon filters like CANFilter 33. Use 1 fan for intake, 1 fan for exhaust and use a scrubber with each fan. I will be intaking and exhausting from the same area which is a room with air conditioning and supplied with fresh air.

Now I think this would be ok, it would maintain equal intake and exhaust so no odors would be leaking from the grow room, and the 178CFM fans would drop to around 135CFM with the scrubbers attached, which will still cool the grow room.

Am I wrong? I am just thinking logically that this would work for both heat and odor. Thanks!

Edit... I guess some grow room specs may help. Size = 48"W, 72"L, 48"H (not filling entire area with plants) -- Light = 400w CMH, I calculated I'd need 126.4CFM to cool the light and around 30CFM to cool the grow area. So if that CANFAN does 135CFM with the scrubber attached, I think it would work. But you guys are the experts, so you tell me!

 

[SDGUY]

Design Questions

Design Questions

Red I am going to quote a couple of things from earlier in this thread. I am going over some ideas in my head trying to come up with the best way to make the cabinet I want. I really want to get it right the first time.

First quote:
"To take the heat out of the room, you need roughly 3CFM per watt. If you use vented hoods or cooltubes and pass outside air through the tubes and exhaust it outside, you will need 0.3 CFM per watt.

A 5x5x6 room is 150 cubic feet. At an air exchange rate of once every 5 minutes you would need a scrubber that would pass 150cuft/5min = 30 cubic feet per minute"

Second quote:

"A bare 400W HPS needs about 120 CFM with a 10*F temperature rise. With a cooltube the airflow can be cut by about 1/3 so 40 CFM is all that's needed."

Wouldn't cutting 120 cfm by 1/3 be 80 cfm and not 40?

Here is what I want to build. One cabinet, 7 ft tall, 3 ft wide and 3ft deep. I want to build a flower chamber up top that is 4 ft high x 3ft deep x 3ft wide. I have a 400 watt cool tube with 6" vents on each end. On the bottom I want a nursery/veg/drying area. This is to be 3 ft x 3 ft x 3ft. I have a hydrofarm CFL reflector with glass but it is not ventilated. I have a 200 watt CFL bulb for this reflector. Stealth is of the utmost importance. I want as little noise as possible and no smell to leak out. I would prefer to pull air to the cool tube from inside the cab, through a scrubber first. I know you recommend doing the cool tube seperately but I really don't want a lot of holes in the cabinet. What do you think I would need for a one fan/scrubber combo and what would you recommend if I vented the cool tube seperately and then scrubbed/vented the cabinet. I also have a lumatek digital ballast for the 400 watt light. I would prefer to put the ballast in the cab, but not sure if this is a good idea or not. The less I have outside of the cabinet the less noticeable it will be. I am also concerned with fire hazards too though so perhaps that is not such a good idea. I am also entertaining the idea of two seperate cabinets but would prefer to do it all in one. One more thing, I am planning on venting the cabinet directly into the room it is in, so I won't be pushing the air over any long duct runs. Thanks in advance.

 

[Carl Carlson]

This has probably been answered a million times over, but my question is about odor control only, not about heat from the lamps.

Is there a hard guideline for air exchanges per minute or per hour for using passive intake, sucking through a carbon filter and exhausting with a fan?

strictly for odor control, not heat

 

[Carl Carlson]

bump

 

[Norkali]

Thank-you very much Redgreenry, this has helped me a ton while I am putting my stuff together.

 

[Dignan]

I also wanted to just say thanks to Red and the others who keep this thread alive. I'm running a 400W HPS in a 6 sq ft cabinet and thanks to Red actually 'splaining how a correctly designed 2-stage system works, I've got ambient temps of 70 and interior temps of 74-76, running just 2 small axial fans. Solid!

 

[real ting]

What would the quietest way to push 300 cfm through a carbon filter at 1 inch sp?

 

[guest 77721]

Hey Guys,

It's been a while since I checked in on my thread, like page 20 or so. I'd like to thank
all the guys that have been helping everyone one out.

It looks like there's been a few engineers drawn into the thread recently. Welcome aboard!

I think I accomplished my goal in this thread of presenting the basic ventilation calculations. All I wanted to do is find a good method of designing a grow cab and to keep people from making mistakes that would waste money buy buying the wrong stuff or give up on growing.

Keep up the good work guys!!!

Red

 

[gdbud]

I know that I'm speaking for a lot of people on this site.

Thank You Redgreenry for starting this thread and my it never die.

 

[real ting]

I have a couple questions, and I've drawn up 2 diagrams to explain.
I need about 150 cfms in 2 side by side equal sized tents. After the fan is a run of ducting that runs to an exhaust vent. So if the carbon filter is outside the tents it needs to be an inline filter. I would make a box around the filter that has ducting on end to accomplish this, or buy an inline 66 can filter.

1. Which of these two scenarios would be a better choice?

2. Would having the fan pulling through 2 filters decrease the pressure it's having to pull or increase it vs the same fan pulling through 1 filter?

The filters would be 4-6" filters. The "Y" would be 2 6" in one 8" out with the fan mounted on the 8" side. I thought that having two carbon filters hooked to the same fan would actually decrease the pressure the fan has to pull vs having one, as it gives the fan twice the surface area to pull from. Is this right? Similar to having 2 equal sized intakes decreasing pressure vs 1 intake (1/2 the total intake size vs 2).

 

[Ghostwolf]

This is very interesting.