Led Btu Calculations (hvac)

[MediNice]

Hi all, so I am trying to get to the bottom of of this.

Scenario: If a SpydrX Plus covers 16' square and runs at 685 watts, that is 42.8 watts/sqft. In comparison, for similar ppfd, a DE HPS runs 1060 watts and covers 25 sqft with overlap in a large room. Calculations for this layout are 42.4 watts/sqft. The PPFD levels are provided by both Fluence and Gavita in their modeling software.

Question: Will the LED require the same amount of cooling?

My reasoning that they require the same AC load: 42.4 watts/sqft x 3.41 BTU/watt = 144.5 BTU per sqft.

I have heard people talk about how HPS is only a small amount of light compared to heat while LED is the opposite. HOWEVER, a watt is a watt. It may go out as light, but it is eventually turned into heat. Afterall, a watt is a measure of heat. So, can someone please tell me why an LED would require less AC? I would love to save on cooling costs, but I don't believe the hype.

Thanks in advance,

 

[AvidLerner]

you have to consider efficiency when calculating heat loads. HPs is much less efficient than an led light. The led develops more lumens per watt than an hps. lumens are heat as well. leds are determined by the lumens/watt efficiency. to get a good comparison you would have to take that into account.

HPS makes fewer lumens per watt, while led make more lumens per watt. this is the core difference between the two in regards to heat.

 

[sixstring]

Hi all, so I am trying to get to the bottom of of this.

Scenario: If a SpydrX Plus covers 16' square and runs at 685 watts, that is 42.8 watts/sqft. In comparison, for similar ppfd, a DE HPS runs 1060 watts and covers 25 sqft with overlap in a large room. Calculations for this layout are 42.4 watts/sqft. The PPFD levels are provided by both Fluence and Gavita in their modeling software.

Question: Will the LED require the same amount of cooling?

My reasoning that they require the same AC load: 42.4 watts/sqft x 3.41 BTU/watt = 144.5 BTU per sqft.

I have heard people talk about how HPS is only a small amount of light compared to heat while LED is the opposite. HOWEVER, a watt is a watt. It may go out as light, but it is eventually turned into heat. Afterall, a watt is a measure of heat. So, can someone please tell me why an LED would require less AC? I would love to save on cooling costs, but I don't believe the hype.

Thanks in advance,

well ya lost me at 16 sq ft for spydrx and 25 sq ft for gavita lol but,,,,on average you can figure to need 15 to 20% less cooling for top quality leds because of 2 things.1st is most white light led do not have much if any IR light which hps has and is the reason things within the room like plants and walls heat up just from the light shining on them.2nd is that you need 25 to 35% less wall watts to produce the same ppf/ppfd over an area with good leds.so you wil need less a/c to cool a room if you drop your power use from say 10,000w down to 7500w.gotta toss this in there to,,,,oooooooooomoles :)

 

[Icemud]

Equal wattage = equal heat load... thats physics...

What a lot of people fail to remember is that light (photons) when they hit a surface become heat, which adds to your heat load of the grow environment...

Therefore the only difference would be the light absorbed by the plant that becomes "stored energy" would be slightly different on the light sources so if you have a 600w HPS and a 600w LED (actual draw) the heat load would be the same. Irregardless of efficiency. This difference of absorbed and stored energy is very minimal as plants only use a very small fraction of the light that hits their leaves.

So the reason that the LED grow light industry makes claims like "leds run cooler" is that the efficiency matters in terms of PPFD/watt used... generally an LED is more efficient than a HPS in terms of putting out more photons at the same wattage, therefore with LED, typically you can reduce the "actual wattage draw" by about 20% which means that LED's would be a cooler solution, but its not because of some magical efficiency, its just because they can be used at a lower wattage and produce the same light.

600w total draw = waste heat + heat generated by photon absorbed.

HPS can actually be cooler than LED (at equal wattage). when HPS is using a air cooled hood, due to the fact LED's vent all heat into the grow area, and HPS can actually remove a large portion of heat with air cooled hoods, before it hits your grow environment.

The whole "leds are cooler" concept comes from the building industry where LED replacements can put out the same amount of light, at a lower wattage than CFL or incandescent lights. In this case to reach "X" amount of lumens or light intensity, a LED may require 10w, CFL 26w and incandescent 60w... so with all putting out equal light, but at different draw wattage, then the LED would be cooler, because it is using 6x less watts... in this case efficiency would matter.

 

[MediNice]

Equal wattage = equal heat load... thats physics...

What a lot of people fail to remember is that light (photons) when they hit a surface become heat, which adds to your heat load of the grow environment...

Therefore the only difference would be the light absorbed by the plant that becomes "stored energy" would be slightly different on the light sources so if you have a 600w HPS and a 600w LED (actual draw) the heat load would be the same. Irregardless of efficiency. This difference of absorbed and stored energy is very minimal as plants only use a very small fraction of the light that hits their leaves.

So the reason that the LED grow light industry makes claims like "leds run cooler" is that the efficiency matters in terms of PPFD/watt used... generally an LED is more efficient than a HPS in terms of putting out more photons at the same wattage, therefore with LED, typically you can reduce the "actual wattage draw" by about 20% which means that LED's would be a cooler solution, but its not because of some magical efficiency, its just because they can be used at a lower wattage and produce the same light.

600w total draw = waste heat + heat generated by photon absorbed.

HPS can actually be cooler than LED (at equal wattage). when HPS is using a air cooled hood, due to the fact LED's vent all heat into the grow area, and HPS can actually remove a large portion of heat with air cooled hoods, before it hits your grow environment.

The whole "leds are cooler" concept comes from the building industry where LED replacements can put out the same amount of light, at a lower wattage than CFL or incandescent lights. In this case to reach "X" amount of lumens or light intensity, a LED may require 10w, CFL 26w and incandescent 60w... so with all putting out equal light, but at different draw wattage, then the LED would be cooler, because it is using 6x less watts... in this case efficiency would matter.

Thank you Icemud, this has been my thinking all along. As long as HVAC is distributed well and good air circulation between lights and canopy is on point, I cant theorize any differences in needed cooling assuming wattage is equal.

It's sad how even HVAC and electrical professionals will tell you these things, but when you show them the math, they try to explain apples to oranges.

The formulas that many of these LED companies use are skewed and in my opinion intentionally misleading.

I get it, it CAN produce a better product with certain strains and some small savings in watts, but often at 3-5X the cost.

I'm awaiting the calculations on an exact same PPFD comparison. The last one I received was within 10% of each other in PPFD. If anyone is interested, I'll share the results.

I do not pretend to be an authority on this matter and welcome someone to show me otherwise. Afterall, I will be purchasing LED at some point in the future for flowering purposes. Im sold on veg.