Cooling - chiller AND window AC balance

[karimwassef]

My tank is 380 gal DT + 180 gal sump + 100 gal surge. I have a 1hp chiller and an 8000btu window AC in my 500sqft garage. The chiller is plumbed outside with water in and out through the wall.

Chiller power use is about 1000W. AC power use is about 1200W.

With both on and MH off, I can take about 11F from the outside to the tank.

The chiller does about 4F and the AC does another 7F.

Garage door is sealed and insulated as are the walls.

It seems that the AC is more efficient. So in determining the right balance between AC and chiller, I'm inclined to run the AC to a lower set point and only run the chiller as an emergency excursion when the MHs kick on in the summer?

Thoughts on how to balance for lowest power use??

 

[Poseidon]

I've always heard it is cheaper to heat/cool the room than it is to heat a tank in a cold room, or especially cool a tank in a hot room.

Based on what you show, that seems to be the case here too.

I would cool the garage.

 

[Ontheway]

Isnt it a good idea to run AC at normal level and use a blower-fan towards the DT ?

 

[karimwassef]

I always thought that removing the heat from the water to the outside air is the most efficient.

 

[Ontheway]

Well, the tank heats up due to increased room temps, so cooling the room will handle the source of issue. Of course, if the room is larger then average, it will be expensive and chiller will then become logical.

 

[karimwassef]

I see. You see the air heat as the starting chain of the heat.
The tank generates the heat though. Pumps and MH generate a lot.

 

[Poseidon]

Yes pumps and lights do. Cooler air on 3 sides, plus the added evap gain from the cooler dryer air, I still think room cooling is better.

Running the hat from the tank outside is all sorts of WIN as well.

 

[Spiffy]

I've always heard it is cheaper to heat/cool the room than it is to heat a tank in a cold room, or especially cool a tank in a hot room.

Based on what you show, that seems to be the case here too.

I would cool the garage.

+1
And you can stay cool too.

Well, the tank heats up due to increased room temps, so cooling the room will handle the source of issue. Of course, if the room is larger then average, it will be expensive and chiller will then become logical.

I have found that it is way cheaper to cool the room that I have my DT in than it is to use a chiller. The price of a chiller is about the same for the size A/C that I have in the window. Maybe the chiller would use less power, but then I would be sweating buckets.

But on the flip-side, I have more of a problem keeping my tank warm than I do keeping it cool. Except during the really hot summer days, then I have to kick the A/C on for a while.

 

[ca1ore]

It's really pretty simple. If the ambient room temperature is what is causing the tank to become over-heated, then cooling the room will be the most effective. If the tank runs inherently hot (i.e. tank overheats even when the room is at a comfortable temperature), then a chiller will be the most effective.

For example, my tank runs about 5 to 6 degrees above room ambient. So, if I keep the house AC at 75 degrees, the the tank is 80 or 81. If I'd don't run the AC, the room gets to about 80, which is too high. In the winter, when I run the heat at 67, heaters have to add about 12 degrees.

 

[karimwassef]

Ok. So as an extreme, if I only run the chiller and my garage is baking at 100F, then I'm not JUST trying to cool the tank, but by extension, the whole garage using my little chiller.

That is not a very efficient use of a chiller. Got it.

 

[Ontheway]

It's really pretty simple. If the ambient room temperature is what is causing the tank to become over-heated, then cooling the room will be the most effective. If the tank runs inherently hot (i.e. tank overheats even when the room is at a comfortable temperature), then a chiller will be the most effective.

Summarized best way. If you run chiller in a room whichs already at the limit, you just transfer heat from tank to ambient air surrounding the tank, then chiller becomes useless. Then you will need A/C for the room. If there arent anything unusually forcing tank heat upwards (like strong MH lamps maybe), AC remains best solution.

Keep in mind, especially lower kelvin lamps (hot temp) radiate heat as rays, which directly heats the water "and" sand-rock etc, think like miniature and very inefficient version of infrared heaters.

 

[planedoc]

With your chiller outside you are doing it the most efficient way possible. I would set AC at 75 and have your chiller set to come on at 80 or 82, or what ever temp you don't want your tank to go above. Another solution I have seen it to vent you light hood. Some vent ducts and a small fan can make a big difference but can look ugly

 

[karimwassef]

I don't have a hood. It's open with pendants and a fan blowing over the water constantly (unless under 72F).

It's in my garage so I have a lot if freedom. The DT face is viewable from inside the house.

 

[Ontheway]

If you can aspire the hot air out of garage, then use a chiller, since cooling garage with AC is a bit waste.

 

[Spiffy]

Why not just move the DT inside the house? I thought cars and vagrant family members/friends live in garages...?

 

[karimwassef]

The wife likes the house warmer (78F+). Add a couple (or 3) 400W MHs, 400W of LED and 3 pumps and the temperature goes to 86F. The chiller would likely keep me at 82F best case.

In the garage, I can temperature control the air and water. It's sealed and insulated so low leakage. Not as good as the house, but it's ok. I can keep the garage at 75F. That would allow me to maintain it below 79F with the chiller.

I think venting the garage roof (half has a roof) could reduce my costs but I would need an air inlet (no soffits in the garage roof). If I take it from the house, the noise would propagate into the house. If I inlet from outside, I'd be fighting the AC.

 

[ca1ore]

One thing you could consider given that the tank displays through the garage wall, is to put thick insulation on all the side that face into the garage so that the chiller would work as needed. You could also box out the top of the tank to keep it away from the really hot garage air.

 

[karimwassef]

I can "igloo" it in but here's my concern:

The heat generated inside the tank is considerable. If I insulate it from the garage air, the chiller would have to work all the heat out. With the open top, the fans circulate cool garage air.

 

[ca1ore]

Reason I suggested it was that I ran a tank in a similar way and did 'igloo' it but installed an exhaust fan in the insulation I such a way that I could vent the hood to the garage when needed (i.e. When the garage was cooler than the tank). Obviates the need for a garage AC unit.

 

[BeanAnimal]

It's really pretty simple.

Actually it is not that simple... There are a lot of variables.

How insulated is the room? How much of the "cooling" is being used to cool the outside environment (heat leaking back in from OTHER than the tank).

What is the overall efficiency of the AC unit?
What is the overall efficiency of the Chiller?


Energy (heat) flows from higher energy to lower energy (hot to cold).

The only way the room "heats" the tank is if it is hotter than the tank. Otherwise, the tank is shedding heat to the room.

So lets take the scenario where the room is cooler than the tank. The ONLY heat input to the tank is then from the equipment that imparts heat to the tank and any radiation (Sun, IR, room lights, whatever) that finds its way into the tank. The larger the Delta T between the room and the tank, the faster the tank sheds heat to the room. The smaller the Delta T, the slower the transfer.

An highly efficient AC and a well sealed room with an inefficient chiller may give the advantage to the AC but this is truly a long shot. Cooling the tank directly with a chiller and moving that heat away from the room (the condenser is outside) is likely much more efficient than trying to cool the room so that the room then pulls heat from the tank.

It would appear that many of the comments regarding "efficiency" are misting half of the equation. Chilling the tank is ALSO chilling the room. So 100% of the energy used to chill the tank also chills the room.... So given OPs example with a total Delta T of 11F, you have to consider the that every BTU of heat removed from the tank to the outside is also being removed from the room, meaning that the room AC does not have to deal with it. Moreover, the rate is 100% efficient with regard to the work being done by the chiller. On the other hand every BTU of heat removed by the window AC DOES NOT equate to a BTU of heat removed from the aquarium. That efficiency depends on the insulation of the room, but in all but the most extreme cases will be far less than the overall efficiency of the chiller itself.

Hope that helps some...