Can someone explain the BTU calculation for HID ballasts?

I know that 1000w = 3412 BTU, so theoretically the bulb itself, being fed 1000w, will put out 3412BTU.

But then you have the ballast...where I've seen quotes from as low as 1500BTU for digitals, to as high as 4000BTU for magnetic.

This is where I'm confused. When I checked my ballasts input current (quantum digital), each one was pulling about 1060w total...so 1000w was going to the bulb, and 60w was "lost" (as heat, obviously, due to inefficiency).

So, if the ballast and bulb combination as a whole is pulling in 1060w TOTAL, and we already have 3412BTU for the bulb, how is that extra 60w producing 1500-4000BTU of heat???????????

The way I see it, that extra 60w is only capable of creating 204BTU (60*3.412) of heat, nowhere near the 1500-4000 I've seen mentioned.

In order for the ballasts to create, lets say an average, of 1750BTU, that would take 512watts to make.....so 512 watts for the ballast, added to the 1000w for the bulb, gives us each ballast/bulb combo pulling 1512w....which I know mine and many others I've measured definitely don't, as that would be less than 50% efficient.

I've seen one guy say ballasts have a "heat leakage" of 2.5BTU/watt, but I have no idea what that even means....you can't make heat from nothing....and as I said, the ballasts are only using/shedding an extra 60w over the 1000w for the bulb, so I can't see where all that heat is coming from.

This all started when I tested a new sealed start-up room with 6000w of uncooled HID (20,472BTU) and also the ballasts in the room as well (supposedly another 10,500 BTU using the 1750/ballast figure), putting total BTU at 30,972.......the 24000BTU AC had no issue at all cooling the room, in fact, it only ran at about 90% (inverter unit), indicating the BTU load was actually around 21,700, which closely matches the BTU calc for 6 1060w ballast/bulb combos. If the ballasts had been putting out the rumored 1750btu, the 24k AC would not have been able to keep up at all.


Can anyone shed some light on this "heat leakage" thing, and how the ballasts are supposedly putting out so much heat, while only losing 60w from inefficiency?

Anyone?

Ive been doing further testing on a 4000 watt 8x8 room and am finding the same thing.

using the total ballast input of 1060w x 4 = 4240w and 4240w x 3.412btu= 14466 BTU total from the non air cooled lights, plus the 500w dehumidifier which is 500 x 4.412 = 1706 BTU

That gives the room total 16172 BTU. There is a 18000BTU mini split that is handling it perfectly fine.

I'm really trying to figure out why so many companies and growers tell you to use 2500BTU PER BALLAST as a figure, when the ballasts are only putting out 200BTU.

This is also backed up by Gavita saying their 1000w ballasts only put off about 60 watts of heat (205BTU)

Was the 2500-4000BTU per ballast just a myth that has been perpetuated over time into "truth"?

Whose truth is this?

Know your source, because that's malarkey, or you have misunderstood somewhere.

Mikell said:

Whose truth is this?

Know your source, because that's malarkey, or you have misunderstood somewhere.

Click to expand...

Just google it, look at all the AC companies websites (like excel air etc), all the grow store websites, and search this very forum. Everyone is saying 2500-3500 BTU per ballast, in addition to the 3500 per bulb. Doesn't add up at all, and my tests have confirmed it doesn't.

So if a magnetic uses 1100watts 1000w to the bulb the other 100w goes to heat generated from the transformer ballast . 100w for 2500btu of heat from the ballast alone ? That's cheap heat

all energy spent within a closed system MUST remain inside the system either as heat or potential energy or momentum etc.

for the purpose of an insulated grow room, you consider the system closed for purposes of conservative calculation.

so.....watts in = watts out.

1100watts/hour = 3.412 * 1100 = 3753 btu/hour.

there IS a small amount of energy that is basically "stored" inside the plant cells via photosynthesis sorta like charging a battery, but there is no way to quantify this figure accuratly so you ignore it entirely. moreover... this number is probably very very small so trying to quantify it in the first place is a waste of time.

yes of corse your room is not "perfectly insulated", and as such you will have external heat gains or losses from the environment.

to calculate this value you need to do a reasonable manual J calculation.

with the internal heat gain, + latent heat gain, + external heat gain, you can arrive at a reasonable approxiamtion of your total heat gain or loss, and can then size your ac system properly.

queequeg152 said:

all energy spent within a closed system MUST remain inside the system either as heat or potential energy or momentum etc.

for the purpose of an insulated grow room, you consider the system closed for purposes of conservative calculation.

so.....watts in = watts out.

1100watts/hour = 3.412 * 1100 = 3753 btu/hour.

there IS a small amount of energy that is basically "stored" inside the plant cells via photosynthesis sorta like charging a battery, but there is no way to quantify this figure accuratly so you ignore it entirely. moreover... this number is probably very very small so trying to quantify it in the first place is a waste of time.

yes of corse your room is not "perfectly insulated", and as such you will have external heat gains or losses from the environment.

to calculate this value you need to do a reasonable manual J calculation.

with the internal heat gain, + latent heat gain, + external heat gain, you can arrive at a reasonable approxiamtion of your total heat gain or loss, and can then size your ac system properly.

Click to expand...

This is how I've always done it...but I've noticed the 2500-4000BTU per ballast number popping up left and right lately so I wanted to see what people were saying in here.

Ideal-Air says to use 3500BTU per ballast alone when sizing their AC! I also see a lot of people saying use 6000BTU for non air cooled lights, which makes no sense, as a 1000w bulb can put out no more than 3412BTU, air cooled or not air cooled.

I get needing to slightly oversize your AC system, but using some of these numbers thrown around would double, or more, your required AC!

2500 is probably with air cooling the hoods.

6000 is probably for a small number of lights where the ratio to internal to external heat is very large.

so say you have like 4 lights inside a 20x20 room with like 8,000 btuh heat gain from windows and attic partition...

i say this all the time, but a manual J is always warranted. an over sized ac will not control humidity as well as a properly sized unit can.

It's pretty commonly accepted that a ballast puts out around 200 btu of heat. Most of the conflicting daat you're seeing is people combining the bulb and ballast heat into one figure.

The other common figures are:

Single ended 1000w light : 4000btu
Air cooled single ended 1000w light: 2000 btu

Double ended 1100w light: 5000 btu
Air cooled double ended 1000w light:4000btu

De's need heat to render their colors properly, so very little heat can be removed without adversely affecting their CRI.

Hope that helps!

these bulbs are encapsulated inside a partial vaccum... heat effects the alumina tube very little.

unless a double ended bulb is somehow different... they should not drop in output more than like... 5% when you cool the outer envelope down somewhat.

flourescents are 100% different, if you blow cold air on a PLL, you can drop the output by a shit load... more than 15%.

but again all HID's i know of are enclosed in a partial vacuum so they are more insulated.

Heat, or lack thereof, affects DE bulbs much more significantly than single ended. Ask Gavita.

Lazyman said:

Heat, or lack thereof, affects DE bulbs much more significantly than single ended. Ask Gavita.

Click to expand...

i do actually remember when that guy was on this forum alot, i think though he was simply stating that they should not be cooled if you wanted to achieve the remarkable efficiency they offered.

there should be ceramic on each side that the conductors pass through. i suppose its possible though, that the additional conductivity of having 2 such ceramic caps instead of 1 would make them more vulnerable to cooling.