Temperature affects from outside skimmer line in hot environments

[ScottF]

Hello reefers!

My tank is right next to an exterior wall. It would be simple to replace my CO2 scrubber with a line running outside. My big concern is that I live in south Florida where it is super hot most of the year. I don't have a heater or chiller on my 250gal tank. It just naturally stays steady at 80 degrees with my air conditioning keeping the house comfortable.

I'm afraid that if I start pumping 100 degree air into my skimmer, the temp of my tank is going to shoot up. Does anyone have experience with this? Do outside temps affect your water temps when you are drawing outside air into your skimmer?

 

[Randy Holmes-Farley]

you have any idea how much air you are drawing? If you did, we could convert that to effective watts of heating or a simple temp rise.

 

[DCR]

The amount of heat that would be drawn in through that air flow is trivial in the overall heat balance. The mass air flow is low and the heat capacity of air is very low. You could do the actual calculation if you know the air draw but it is nothing to worry about. The pump is adding far more heat.

 

[Randy Holmes-Farley]

The amount of heat that would be drawn in through that air flow is trivial in the overall heat balance. The mass air flow is low and the heat capacity of air is very low. You could do the actual calculation if you know the air draw but it is nothing to worry about. The pump is adding far more heat.

I’m not sure how you can be so sure. The same words would basically apply to a tank in a room full of 100 degree air.

 

[Aaron Stone]

He's right. The heat capacity of air is crap.

Btu/hr = cfm*1.08*(deltaT)

At 10 CFM and 30 dT it's like 324 btu/hr

 

[Ryan Souza]

I live in south florida, line from skimmer to outside, tank stays between 81 and 85 depending on time of year. That's with 8 t5s and a uv sterilizer. Wouldn't worry about it. Huge ph boost and was well worth it.

 

[Randy Holmes-Farley]

He's right. The heat capacity of air is crap.

Btu/hr = cfm*1.08*(deltaT)

At 10 CFM and 30 dT it's like 324 btu/hr

I know what the heat capacity of air is. The volume is also far higher. A typical skimmer might take in 50 tank volumes in a day. At 20 degrees above tank temp, the contribution may well be small, but I was just surprised one could discount it without deeper consideration.

 

[Aaron Stone]

I know what the heat capacity of air is. The volume is also far higher. A typical skimmer might take in 50 tank volumes in a day. At 20 degrees above tank temp, the contribution may well be small, but I was just surprised one could discount it without deeper consideration.

Why do you think I didn't give it deeper consideration?

 

[Randy Holmes-Farley]

I was talking about the person I responded about, DCR.

Let’s calculate…

1 liter of air weighs 1.3 grams.
1 l of seawater weighs 1,024 g.
The mass based heat capacity of air is about 1/4 of liquid water.


If a tank pulls in 50 tank volumes of air per day, that amounts to about 0.063 times as much mass in air as water.

With a heat capacity 1/4 as much, that’s equivalent to mixing with 0.016 times as much water.

If the air is 20 deg F higher, that will raise the tank temp by 20 x 0.016 =0.32 deg F.

Small, and perhaps insignificant, but I’m very impressed with anyone who could know that sort of value without working through it.

 

[Aaron Stone]

It comes with experience. I deal with fluid and air heat transfer everyday, and other may as well. Never hurts to run the numbers though.

 

[Randy Holmes-Farley]

It comes with experience. I deal with fluid and air heat transfer everyday, and other may as well. Never hurts to run the numbers though.

Again, I was not referring to you.

 

[Aaron Stone]

Again, I was not referring to you.

Your reply saying such was to my comment.

Hence the confusion apparently.

 

[Randy Holmes-Farley]

Your reply saying such was to my comment.

Hence the confusion

You led with “he’s right”. That led to my post, but I certainly see why you might have thought it meant you and not the he in your statement. Sorry for not writing that more clearly.

In any case, we have arrived at a number and whether one considers that number trivial or not, folks can decide for themselves with their own tank volumes and skimmer and gauge if there’s anything to worry about for themselves

 

[Aaron Stone]

I agree. I think it's a worthwhile question and hopefully others will find it useful.

OP's awfully quiet. Lol

 

[ScottF]

Follow up question, do you run the outside air through any media? Would running it through GAC do any good?

 

[Aaron Stone]

I see no reason to turn it through any type of scrubber unless you have a local environmental concern (astoundingly close to airport or something similar).

 

[DCR]

I was talking about the person I responded about, DCR.

Let’s calculate…

1 liter of air weighs 1.3 grams.
1 l of seawater weighs 1,024 g.
The mass based heat capacity of air is about 1/4 of liquid water.


If a tank pulls in 50 tank volumes of air per day, that amounts to about 0.063 times as much mass in air as
With a heat capacity 1/4 as much, that’s equivalent to mixing with 0.016 times as much water.

If the air is 20 deg F higher, that will raise the tank temp by 20 x 0.016 =0.32 deg F.

Small, and perhaps insignificant, but I’m very impressed with anyone who could know that sort of value without working through it.

I completely respect your knowledge of chemistry, but your engineering is not correct. This is not a valid calculation for an energy balance. You really cannot determine how much the tank temperature will increase without knowing how the rate of heat rejection from the tank will change with increasing temperature, which is very complicated, but you can determine how much heat is being added relative to the inside air. Assume the skimmer has the equivalent of a PSK1000 pump which draws 264 gal/hr of air according to Sicce. That is 2.5 lb/hr of air (0.07 lb/ft3 and 7.48 gal/ft3) with a heat capacity of 0.24 Btu/lb/Deg F. If there is a 20 deg F delta between the inside and the outside air, then the added heat to the tank is 2.5 lb/hr x 0.24 Btu/lb/Deg F x 20 deg F or 12 Btu/hr or 3.5 watts - which is trivial compared to the pumps, powerheads and lights.

 

[Reefering1]

Follow up question, do you run the outside air through any media? Would running it through GAC do any good?

Yes, gac would provide protection from contamination. Pesticides/fumes/smells, for example.

 

[PapaFishRocks]

Texas Gulf Coast reefer here. Skimmer line outside, haven’t noticed any difference.

I was also curious with the cold snap we had recently. Heater didn’t cycle anymore than usual. (Apex data)

 

[Randy Holmes-Farley]

I completely respect your knowledge of chemistry, but your engineering is not correct. This is not a valid calculation for an energy balance. You really cannot determine how much the tank temperature will increase without knowing how the rate of heat rejection from the tank will change with increasing temperature, which is very complicated, but you can determine how much heat is being added relative to the inside air. Assume the skimmer has the equivalent of a PSK1000 pump which draws 264 gal/hr of air according to Sicce. That is 2.5 lb/hr of air (0.07 lb/ft3 and 7.48 gal/ft3) with a heat capacity of 0.24 Btu/lb/Deg F. If there is a 20 deg F delta between the inside and the outside air, then the added heat to the tank is 2.5 lb/hr x 0.24 Btu/lb/Deg F x 20 deg F or 12 Btu/hr or 3.5 watts - which is trivial compared to the pumps, powerheads and lights.

We seem to agree basically on the number, but not, perhaps, on the triviality.

I do not agree that my calculated 0.32 deg F temp boost is off, and your assertion that this small temp rise will cause increased heat release from the tank is true, but the uncorrected is close enough for a ball park calculation that involves big assumptions of tank volume and skimmer air.

You did not convert the watts to a tank heat, nor assume anything about tank volume. 3.5 watts for 24 h gives 84 watt hours.

That’s enough to boost 300 L of water by 0.24 deg C = 0.43 deg F.

Regardless of what we think is significant or not, folks can see the numbers and decide.